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VUTVaal University of Technology

PROCESS INSTRUMENTATION I

Module Code: EIPIN1

PREVIOUS EVALUATION AND ASSESSMENT

Process Instrumentation I EIPIN1 Unit 1 First assessment

March 2005

Question 1

Define measurement of a process variable. (2)

Question 2

State the elements that may be identified in an instrument. (5)

Question 3

Define the accuracy of a measurement. (2)

Question 4

Define an error of non linearity in an instrument. (2)

Question 5

Identify the instrument function and mounting

method, from the instrument symbol in Figure 1. (2) LRC Figure 1

Question 6

Define pressure and give the SI unit for pressure. (2)

Question 7

The container in Figure 2 has a cross sectional

area of A meter2 and is partially filled with a

liquid of density � kilogram/meter3, to a height of

h meter. Starting with the expressions for the

volume and mass of the liquid, show that the

pressure exerted by the liquid on the bottom of

the container, is given by P = �hg, where g is the

gravitational acceleration in meter/second2. (4)

P h Figure 2

A

Question 8

With the aid of a sketch, derive the expression that is used to determine

pressure with a well type manometer. All symbols used, must be shown very

clearly on the sketch. (4)

Question 9

Draw a labelled sketch to show how a bellows element may be used to

measure gauge pressure. (2)

Question 10

A dead weight tester has a primary piston with a diameter of 1 cm. The mass

of the platform and primary piston together, is 500 gram. Calculate the mass

m, of the mass pieces, that must be placed on the platform to check a gauge

at 100 kPa. (3)

..................../2


March 2005

Question 11

In Figure 3, a pneumatic

flapper and nozzle arrangement

is shown, with associated pilot

relay. Draw a labelled sketch of

the pilot relay, to show its

internal components and

construction. (3) Feedback

bellows Output

Pivot

Flapper and nozzleRestriction

Figure 3

Vent

Pilot Relay

Air supply

Question 12

Define viscosity of a liquid and give the SI unit for viscosity. (2)

Question 13

State Bernoulli’s law (in words). (3)

Question 14

A flow rate meter uses a restriction in the flow stream, to measure the flow

rate of a liquid in a horizontal pipe. When the pressure difference across the

restriction is 400 pascal, the flow rate is 2�10-3

m3/second. Calculate the

flow rate when the pressure difference across the restriction is 900 pascal. (2)

Question 15

Draw a labelled sketch of a venturi tube flow meter. Show the dimensions

and relative sizes of the instrument, clearly on your sketch. (4)

Question 16

Sketch the configuration, including dimensions and labels, when radius taps

are used for flow rate measurement with an orifice plate. (3)

Question 17

a) Describe the operation of a magnetic flow meter (magmeter). (3)

b) Give the operational equation that is used to calculate the flow rate q

from the measurements made with a magnetic flow meter. Define each

symbol that appears in the equation. (2)

Total: 50

---ooo000ooo---

Process Instrumentation I EIPIN1 Unit 1 First Assessment Memorandum

March 2005

Process Instrumentation I EIPIN1 Unit 1 First Assessment Memorandum March 2005

1. Measurement is defined as the determination of the existence [1]

or magnitude [1]

of a variable for

[2] monitoring and controlling purposes.

2. Primary element [1]

Data transmission element [1]

Secondary element [1]

Manipulation element [1]

[5] and Functioning element [1]

3. The accuracy of a measurement is the closeness [1]

with which the reading approaches the

[2] true value [1]

of a variable.

4. Non-linearity is the maximum deviation [1]

from a straight line connecting the zero and full-scale

[2] calibration points. [1]

5. Level recorder controller, [1]

mounted behind board. [1]

[2]

6. Pressure is defined as the force exerted over a unit area [1]

. The SI unit is newton per square meter

[2] (N/m2) or pascal (Pa).

[1]

P h

7. Volume of the liquid = V = Ah.[1]

Mass of the liquid = m = Ah�. [1]

Weight of the liquid = w = mg = (Ah�)�g. [1]

Pressure on the bottom of container due to weight of the liquid

= w�A = Ah�g/A = �hg [1]

A

[4] �P = �hg

ZL

P2

d

h Sketch: 1 mark

P1

�

8. P1 = P2 + �(h+d)g [1]

…………….……… (1)

A1d = A2h � d =

1A

2Ah

[1] …..………….. (2)

(2) in (1): P1 = P2 + � ��

�

�� h

1A

2Ah g

[1]

[4] �P1–P2 = �hg ��

�

��

1A

2A1 A1 A2

Pressure = � �pistonprimary of Area

pistonprimary and

platform ofweight masspieces ofWeight ��

��

� �

�100�103=

��

��

� �

��

��

4

2)2-10(1�

9.81)3-10(500 9.81m

[1]

�(100�103)�(78.54�10

-6) = 9.81m + 4.905

Atmospheric pressure [½]

9. 10.

P1 (Gauge

pressure) [½]

Bellows [½]

�9.81m = 7.854 – 4.905

[2] �9.81m = 2.949

Pressure indication [½]

�m = 0.3006 kg. [2]

[3] = 300.6 gm


March 2005

11.

Supply valve

(ball) [½]

Spring [½]

Exhaust valve

(cone) [½]

Diaphragm [1]

Valve

stem [½]

[3]

12. Viscosity is a measure of a fluid's resistance to flow. [1]

[2] The SI unit is poiseuille (PI) or pascal-second (Pa-s). [1]

.

13. If an (incompressible fluid is in a streamlined flow with no friction,) [½]

the sum [½]

of the

[3] pressure energy, [½]

the kinetic energy [½]

and potential energy [½]

per unit volume, is constant [½]

.

14. q1 = k 1h � 2�10-3

= k 400 � k = 0.0001 [1]

[2] �q2 = k 2h = 0.0001� 900 = 0.0001�30 = 3�10-3

m3/s

[1]

15. 16.

[3]

D [½] Inlet cone

(19º-23º) [½]

d/2[½]

D/2 [½]

High pressure tap

(upstream tap) [½]

Low pressure tap

(downstream tap) [½]

Flow [½]

d[½]

Throat [½]

Outlet cone

(5º-15º) [½]

d

[½]

High

pressure

tap [½]

Flow [½]

Low

pressure

tap [½]

D [½]

½D[½] D [½]

[4] /5

17. a) A magnetic flow meter generates an emf e, proportional to the flow rate, based on

Faraday’s law of electromagnetic induction (e = B�v). [1]

Current carrying coils on the outside of the meter provides the magnetic field

strength B tesla [1]

The flow plays the role of the conductor moving through the magnetic field lines with

speed v (proportional to q) [1]

. (3)

b) q = k eBD

[1]

D = distance between electrodes (meter) [½]

, B = magnetic field strength (tesla) [½]

,

[5] e = measured emf (volt) [½]

, k = calibration constant [½]

(2) /3


May 2005

Question 1

Draw a labelled sketch of a flexure tube (torque tube) displacer level meter. (4)

Question 2

The level of a liquid in an open

container, is to be measured with

the aid of a U-tube manometer, as

shown in Figure 1. The relative

density�of the liquid in the

container is 3. The manometer

fluid is mercury with a relative

density of 13,6. The zero line of

the manometer, is 0.6 meter below

the bottom of the container.

Calculate the level H, of the liquid

in the container, if the manometer

reading h, is 0.8 meter. (4)

h=0.8m Zero level

0.6 m

� = 3 H

� = 13.6

Figure 1

Question 3

Define the top fixed point on the temperature scale and give this temperature

value in degrees Fahrenheit. (2)

Question 4

Draw a labelled sketch of a liquid in glass thermometer. (4)

Question 5

The relationship between the resistance Rt (ohm),

of a certain resistance thermometer (RTD), and

the temperature t (°C), is shown in

Figure 2, and may be assumed

to be linear (a straight line).

Rt (�)

0

t (°C)

100

Figure 2

150

a) Calculate the temperature

coefficient of resistance

(TCR) of this thermometer. (2)

b) Calculate the resistance of

the thermometer when the

temperature is 40 °C. (2)

100

c) Calculate the temperature

when the resistance of the

thermometer is 110 �. (2)

..................../2


May 2005

Question 6

Draw a labelled circuit diagram to illustrate the three wire method that is

used to compensate for ambient temperatures when measuring temperature

with a resistance thermometer. (4)

Question 7

State the thermocouple law of intermediate temperatures. (2)

Question 8

Give the positive element material, the negative element material and the

temperature range of a type J thermocouple. (3)

Question 9

Define the following concepts with respect to control systems:

a) Controlled variable. (1)

b) Manipulated variable. (1)

c) Disturbance variable. (1)

d) Measured value. (1)

e) Desired value. (1)

f) Error value. (1)

Question 10

Distinguish between direct acting and reverse acting control. (2)

Question 11

A process is controlled by a proportional controller. The controller has a

positive gain and proportional band (PB) of 50 %, a set point (S) of 50 %

and a bias (R) of 50 %. The system error is given by E = S – M.

a) Calculate the proportional gain KP of the controller. (1)

b) If the measured value (M) of the process is indicated as 42 %,

calculate the output of the controller at that instant. (2)

Question 12

Draw a labelled sketch of a pneumatic proportional controller. (4)

Question 13

Draw a labelled sketch of a reverse acting pneumatic control valve. (6)

Total: 50

---ooo000ooo---


May 2005

Process Instrumentation I EIPIN1 Unit 2 First Assessment Memorandum May 2005

1. 2.

H

0.8 0.6

Y X

Patm + 3000�(H+0.6+0.4)�9.81

= Patm + 13600�0.8�9.81 [1]

�29430�(H+1) = 106733

�H + 1 = 3.627

[4] �H = 2.627 meter.[3]

3. Top fixed point: The temperature

of (distilled water that boils) [½1]

at (standard atmospheric pressure

of 760 mm. mercury.) [½]

Value of top fixed point on the

[4] /5 [2] Fahrenheit scale is 212 °F [1]

Displacer [1]

Chain [½]

Torque arm [1]

Torque tube [1]

Torque tube

flange [½]

Torque rod [½]

Level indicator [½]

4. 5. a) �o = 1000R

0R100R

�

�

= 100100

100

�150 �

= 0.005 /°C (2)

b) Rt = Ro(1 + �ot)

�R40 = 100(1 + 0.005�40)

= 100(1 + 0.2)

= 120 � (2)

c) Rt = Ro(1 + �ot)

�110 = 100(1 + .005t)

�1 + 0.005t = 1.1

�0.005t = 0.1

[6] �t = 20 °C (2)

Bulb [1]

Lens front capillary

tube (stem) [1]

Liquid column [1]

Bore [1]

Scale

(etched) [1]

[4] /5

6.

[4]

Rlead

Rlead

RT

Wheatstone bridge (R1, R2, R3 and E) – 1 mark

R2

R1

E V

R3 RTD – 1 mark

Voltmeter connected to middle Rlead – 1 mark

Rlead

3 lead wires – 1 mark

7. The law of intermediate temperatures states that the sum [½]

of the emf developed by a thermocouple

with its junctions at temperatures T1 and T2, [½]

and with its junctions at temperatures T2 and T3, [½]

[2] will be the same as the emf developed if the thermocouple junctions are at temperatures T1 and T3. [½]


May 2005

8 Type Positive element Negative element Temperature range (°C)

[3] J Iron [1]

Constantan [1]

-200 to 750 [1]

9. a) Controlled Variable: Process output variable that is maintained between specified limits. (1)

b) Manipulated Variable: Process input variable that is adjusted, to steer the controlled

variable towards the desired value. (1)

c) Disturbance Variable: Process input variable that can cause the controlled variable to

deviate from the desired value. (1)

d) Measured value: Actual value of the controlled variable, as determined by the instrumentation. (1)

e) Desired value: Required value of the controlled variable (set point). (1)

[6] f) Error value: The difference between the desired value and the measured value. (1)

10. Direct acting control: A control arrangement in which the controller output increases if the

measured value rises above the set point. [1]

Reverse acting control: A control arrangement in which the controller output increases if the

[2] measured value drops below the set point. [1]

11. a) KP = PB100 = 100/50 = 2. (1)

[3] b) C = KP�(S – M) + R = 2�(50 – 42) + 50 = 66 %. (2)

Set point S [½]

12. Controller

output C [½]

Reset

bellows [½]

Beam[½]

Bias value R [½]

Air

supply [½]

Flapper and

nozzle [½]

Measured value M [½]

Proportional

(feedback)

bellows[½]

Pilot

relay[½]

[4] /5

13.

[6] /8

Spring nut [½]

Spring [½]

Diaphragm plate [½]

Gland and packing [½]

Plug [½]

Bonnet nut [½]

Bonnet [½]

Gasket [½]

Stem connector [½]

Diaphragm [½]

Seat [½]

Travel indicator [½]

Stem [½]

Yoke [½]

Actuator

(Motor) [½]

Valve

body [½]

Process Instrumentation I EIPIN1 Unit 1 Final Assessment

June 2005

Question 1

Define the international standards of measurement. (2)

Question 2

State the functions an instrument may perform.. (3)

Question 3

Define the precision of a measurement. (2)

Question 4

Define an error of hysteresis in an instrument. (3)

Question 5

Identify the instrument

signal in Figure 1. (1)

Question 6

Define the density of a substance and give the SI unit for density. (2)

Question 7

Convert a pressure of 33 centimetre water (cm. H2O), to a pressure

expressed in millimetre mercury (mm. Hg). (3)

Question 8

A u-tube manometer, shown

in Figure 2, is filled with

two liquids, one liquid with

a relative density of 3 and

the other with a relative

density of 13.6. Calculate

the pressure difference,

P1 - P2, applied across the

manometer. (2)

P1 P2

Figure 1

�=13.6

� = 3

0.9 m

0.3 m

Figure 2

Question 9

With the aid of a sketch, derive an expression that can be used to determine

pressure with an inclined limb manometer. All symbols used, must be shown

very clearly on the sketch. (4)

Question 10

a) Draw a labelled sketch of a pneumatic differential pressure transmitter. (6)

b) Give an expression for the output pressure P0 (kPa), of a calibrated

pneumatic differential pressure transmitter in terms of the range wheel

adjustment ratio m, and the differential input pressure P1-P2. (1)

..................../2


June 2005

Question 11

Identify the forms of energy, involved in a liquid in motion. (3)

Question 12

In Figure 3, a restricted horizontal

flow line is shown. The pressure

difference p1 - p2 is measured by

taking the reading h, as shown in

Figure 3. Use Bernoulli’s theorem

and the principle of mass flow

continuity, to derive the flow

equation, q = k h . (7)

v2 v1

p1 p2 q

h

� � A1 A2

Figure 3

Question 13

State the advantages and disadvantages of a venturi tube flow meter. (2)

Question 14

Sketch a segmental orifice plate flow meter and explain its use. (2)

Question 15

a) Draw a labelled sketch of an electronic target flow meter. (3)

b) State the principles on which the operation of this flow meter is based. (2)

b) Give the operational equation that is used to calculate the flow rate q

from the measurements made with a target flow meter. Define each


Total: 50

---ooo000ooo---

Process Instrumentation I EIPIN1 Unit 1 Final Assessment Memorandum

June 2005

Process Instrumentation I EIPIN1 Unit 1 Final Assessment June 2005 Memorandum

1. International standards are defined by international agreement, [1]

representing units of

[2] measurements to the best possible accuracy [1]

allowed by measurement technology.

2. Indicating function [1]

Recording function [1]

Controlling function [1]

[3]

3. Precision is the (closeness with which repeated measurements) [1]

of the (same quantity

[2] agree with each other.) [1]

4. Hysteresis is the difference [1]

between the readings obtained when a (given value of the measured

[3] variable is approached from below) [1]

and when the (same value is approached from above.) [1]

5. Electromagnetic, sonic or radioactive signal

[1]

6. Density of a substance is defined as the mass of a unit volume [1]

of a substance.

[2] The SI unit is kilogram per cubic meter (kg/m3).

[1]

7. P = �hg = 1000�(33�10-2

)�9.81 = 3237 Pa [1]

en P = �hg � 3237 = 13600�h�9.81 � h = 0.02426 m. [1]

[3] �33 cm H2O = 24.26 mm Hg [1]

[of 33 cm H2O = (�H2O/�Hg)�(330 mm H2O) = (1/13.6)�330 = 24.26 mm Hg.]

8. P1 + 3000�0.9�9.81 = P2 + 3000�0.3�9.81+13600�0.6�9.81

�P1 + 26487 = P2 + 8829 + 80050

�P1-P2 = 8829+80050-26487

[2] = 62392 Pa [2]

(=62.39 kPa)

9. 10. a)

0.6

0.3 m

�=13.6

P1

0.9�=3

P2

Equating pressures in the XY plane:

P1 = P2 + �(h+d)g [1]

…….…..……… (1)

and with mercury incompressible:

A1d = A2L � d =

1A

2AL

[½] …….….... (2)

Also in triangle abc:

sin� = h/L � h = Lsin� [½]

…….….... (3)

(2) en (3) in (1): P1=P2+� ��

�

�� L

1A

2ALsin g

[4] �P1 – P2 = �Lg ��

�

��

1A

2Asin

[1]

High pressure (P1)

input [½]

c b

a

A1

L

A2

ZL

d

�

P1

P2

�

Sketch

1 mark

h

X Y

Low pressure (P2)

input [½]

Capsule

flexure [¼] Diaphragm

capsule [½]

Nozzle [½]

Flapper [½]

Pivot point

(range wheel

adjust) [½]

Range bar [½]

Output Po [½]

Feedback

bellows [½]

Zero adjust [½]

Pivot and seal [½]

Force bar [½]

Air supply [½]

Pilot relay [½]

Restriction [½]

Cross

flexure [¼]

(6) /8

[7] b) P0 = m�(P1 – P2) + 20 kilopascal (1)


June 2005

11. Potential energy [1]

Kinetic energy [1]

Pressure energy [1]

[3]

12. From Bernoulli’s law:

½�v12+p1=½�v2

2+ p2

[1] ………..……….…. (a)

v2 v1

p1 p2 q

h

� � A1 A2

Flow continuity demands: q = A1v1 = A2v2

�v1 = (A2/A1)v2 [1]

…….…..………….......… (b)

(b) in (a): ½�(A2/A1)v22+p1=½�v1

2+p1

�v22 = 2(p1-p2)/�[1-(A2/A1)

2]

�v2 = ]2)1

/A2

-(A[1)/2

p1

2(p �� [1]

…………..… (c)

But p1 – p2 = �hg [1]

…………………………....…... (d)

(d) in (c): v2 = ]2)1

/A2

-(A2gh/[1 [1]

……....….… (e)

Also q=A2v2 [1]

……………………………….…..… (f)

From (f) and (e): q = A2 ]2)1

/A2

-(A2gh/[1 ......… (g) [note: 1 mark for either simplified v2

in Eq (e) or for simplified q in Eq (g)]

Defining k=A2 ]2)1

/A2

(A2g/[1� [1]

in Equation (g):

[7] q = k h .

13. Advantages: Pressure loss is small [½]

Operation is simple and reliable [½]

[2] Disadvantages: Highly expensive [½]

Occupies considerable space [½]

[1]

14. The segmental orrifice plate is used in systems where solid particles [½]

[2] are present in the liquid medium or if the medium is in pulpy form. [½]

15. a)

(3) /4

Target [1]

Force bar [1]

Pivot and seal [½]

Flow [½]

Strain gauge[½]

Electronics

housing [½]

b) The target is positioned at right angles to the fluid flow and the approaching stream

exerts a drag force [1]

on the target. This force is transmitted via a force bar [1]

to a

bonded strain gauge bridge for electrical output (or flapper and nozzle arrangement for

pneumatic output). (2)

c) q = 2

d

8F4

)2

d2

(D

��

�� [1]

D = pipe diameter (m) [½]

, d = target diameter (m) [½]

, F = drag force (N) [½]

[7] � = fluid density (kg/m3)

[½] (2) /3


June 2005

Question 1

Draw a labelled sketch of a chain float level meter. (3)

Question 2

State the essential advantage that the flexure tube displacer (torque tube)

level meter, has over other float type level meters. (1)

Question 3

The level of a volatile liquid in a closed

container, is measured with the aid of a U tube

manometer, as shown in Figure 1. The

maximum level of the liquid in the container

is 5 meter. The relative density of the liquid

in the container is 0,9. The manometer liquid

is mercury with a relative density of 13,6.

The zero level of the manometer, is 0.5 meter

below the bottom of the container. Calculate

the level H, of the liquid in the container, if

the manometer reading is 0.25 meter. (4)

0.25 m

5 m

�=13.6

�=0.9 H

Zero line

0.5 m

Figure 1

Question 4

Define temperature and give the SI unit for temperature. (2)

Question 5

Convert 40 °C to degrees Fahrenheit, Kelvin and Rankine. (3)

Question 6

Draw a labelled sketch of a mercury in steel thermometer. (3)

Question 7

A Wheatstone bridge is used to measure

temperature with a resistance thermometer

RT, as shown in Figure 2. When the

temperature around the thermometer is 0 °C,

the resistance of RT is 100 � and the bridge

voltage reading is V=0 volt. The temperature

of RT is increased to 80 °C. Calculate the

reading V on the voltmeter when the

– +

V

100� 100�

100� RT

10V

Figure 2

temperature of RT is 80 °C. Assume that the temperature coefficient of

resistance of RT is 0.00391 /°C and that the resistance change of RT with

temperature, is described by the equation: Rt = Ro(1 + �ot). (5)

Question 8

Define the Seebeck effect. (2)

..................../2


June 2005

Question 9

The relationship between emf and temperature for a certain thermocouple, is

described by the relation: v = ½t2, where v is the generated thermocouple

emf in microvolt (�V), and t the temperature difference in °C, between the

hot junction and 0 °C. If the thermocouple emf reading is 2000 microvolt

and the temperature of the cold junction is 20 °C, use the law of intermediate

temperatures to calculate the temperature of the hot junction. (3)

Question 10

State the principal advantage of thermistor thermometers over resistance

thermometers. (1)

Question 11

Draw a fully labelled block diagram of a feedback control system. (5)

Question 12

Define the on-off control strategy. (1)

Question 13

The output C, of a proportional only

controller, changes with the system error

E, as shown in Figure 3. Calculate the

proportional band of the controller. (3)

100

C (%)

50

-40

Figure 3

E (%)

0 40

Question 14

A proportional and integral (PI) controller is adjusted for a proportional gain

(KP) of 2 and a reset time (TR) of 5 minutes. Calculate the integral gain (KI)

of the controller. (2)

Question 15

Give the equation that describes the output C, of a proportional, integral and

derivative (PID) controller, in terms of the error signal E and controller gains. (3)

Question 16

Draw a labelled sketch of a pneumatic proportional and integral controller. (4)

Question 17

Draw a circuit diagram of the integral (I) block of an electronic proportional,

integral and derivative (PID) controller. Give the expression of the output of

the I block, in terms of the error input signal E. (3)

Question 18

Calculate the required characteristic flow coefficient Cvc, for a control valve

that must control a maximum flow rate of 100 gallons per minute for a liquid

with specific gravity of 0.8 (G = 0.8). Assume that the pressure drop across

the valve is 10 pound per square inch at maximum flow. (2)

Total: 50

---ooo000ooo---


June 2005

Process Instrumentation I EIPIN1 Unit 2 Final Assessment Memorandum June 2005

1. 3.

PX = PY

[3] �900(H+0.5-0.125)g+13600�0.25g = 900�5.625g

�900(H+0.375) + 3400 = 5062.5

Level

indicator [½]

Float [1]

Drum [½]

Chain [½]

Weight [½]

0.25m

5 m

�=13.6

�=0.9 H

Zero line

0.5 m

Y X

2. Minimum movement �900H + 337.5 + 3400 = 5062.5

[1] [4] �H = 1.472 m

4. Temperature is defined as the degree of heat [1]

of a body. The SI unit for temperature is Kelvin (K). [1]

[2]

5. F=5

9C+32=

5

9�40+32=72+32=104 °F

[1] R=F+460=104+460=564 R

[1] K=C+273=40+273=313 K

[1]

[3]

6. 7. Rt = Ro(1 + �ot)

�RT = 100(1+0.00391�80)

= 131.28 � [1]

I = 10/(100+131.28)

= 43.24�10-3

A

�VAC = RT�I

= 131.28�43.24�10-3

= 5.677 V [1]

�VBC = (100/200)�10 = 5 V

�V = VAC – VBC = 5.677 – 5

[5] = 0.677 V [3]

[3] /3½

Steel bulb [½]

Mercury [1]

Steel tube [½]

Pointer

and scale[½]

Bourdon

tube [1]

VAB = 1 V

VAC VBC

B – +

100�100� I

100� RT C

A

10V

8. Seebeck effect: If two dissimilar metals [½]

are joined together to form a closed loop, [½]

and if one

junction is kept at a different temperature from the other, [½]

an electromotive force is generated [½]

[2] and electric current will flow in the closed loop.

T 20°C 20°C 0°C

2000�V200�V

9. Emf corresponding to (25 – 0) °C = ½�202 = 200 �V

[1]

Total emf (T - 0) = 2000 + 200 = 2200 �V [1]

According to the law of intermediate temperatures:

Hot junction temperature T = �2v = �4400 0°C

2200�V

T

[3] = 66.33 °C [1]

10. Higher sensitivity.

[1]


June 2005

11.

Measured

value [½]

Output [½]

Controlled

variable [½}

Sensor [1]

Manipulated

variable [½]

Control

unit [1]

Error

value [½]

Desired

value [½]

Process [1]

Disturbance

variables [½]

Comparator [1]

[5] /7½

12. On-off control: A control strategy in which the controller output switches the final control element

[1] fully on or off [1]

to keep the controlled variable near set point.

13. KP = �C/�E = 100/80 14. TR = 5 min = 300 sec [1]

= 1.25 [1]

�KI = KP/TR = 2/300

�PB = 100/KP = 100/1.25 [2] = 0.006667 [1]

= 80% [2]

Or by inspection: PB is the 15.

range of E that results in [3]

100% change in C

100C (%)

50

0

E (%)

40 -40

C=KPE [1]

+KI �Edt[1]

+KDdt

dE [1]

[3] = 80%

16.

Restriction [½]

Set point S [½]

Reset

bellows [½]

Beam[½]

Automatic reset R [½]

Air

supply [½]

Flapper and

nozzle [½]


Proportional

(feedback)

bellows[½]

Pilot

relay[½]

Controller

output C [½]

Needle valve [½]

Reset time adjust

[4] /6

CVC =

G

Full�P

RatedQ [1]

=

0.8

10

100

= 28.28 [1]

[2]

[3]

E

CI [1]

VI=- �Edt

IC

IR

1 [1]

RI [1]

17.

18.

VI

Process Instrumentation I EIPIN1 Unit 1 First Assessment

September 2005

Question 1

State the SI units for electric current and luminous intensity. (2)

Question 2 B

A

Figure 1C

A liquid filled thermometer

is shown in Figure 1. Identify

parts A, B and C and state for

each of parts A, B and C, the

fundamental instrument element,

represented by that part. (3)

Question 3

Define the repeatability of an instrument. (2)

Question 4

0Input displacement (cm)

40

0 5

Output voltage (mV)

The input output relationship for a

displacement measuring instrument,

is shown in Figure 2. Calculate the

sensitivity of the instrument. (2)

Figure 2 Question 5

Draw the instrument symbol for a flow indicator transmitter, mounted on board. (2)

Question 6

Define the relative density of a substance. (2)

Question 7

Both legs of a mercury

(relative density � = 13.6)

U tube manometer, are

open to an atmospheric

pressure of 100 kPa, with

the zero line, 1 meter

below the top of the

manometer, as shown in

Figure 3(a). The right hand

leg is now sealed off,

airtight, and the air inside

the sealed chamber, is

trapped at a pressure of

100 kPa, as shown in

�=13.6

100 kPa 100 kPa

1 m

Zero

line h = 1 m

100 kPa 100 kPa P

1 m

(a) (b) (c)

Figure 3

Figure 3(b). The pressure applied to the left hand tube is increased to a new

higher value of P pascal, that results in a manometer reading h, of 1 meter, as

shown in Figure 3(c). Calculate the applied pressure P. (4)

..................../2

Process Instrumentation I EIPIN1 Unit 1 First Assessment

September 2005

Question 8

The reading h on a well type mercury (� = 13.6) manometer is 1 meter, when

measuring a pressure of 135 kPa.

a) Calculate the ratio (A2/A1) of the tube area (A2) to the well area (A1). (3)

b) Determine the change in level (d) that the well mercury experiences. (2)

Question 9

Discuss mercury as a manometer liquid, with respect to its relative density,

applications, advantages and disadvantages. (4)

Question 10

a) Draw a labelled sketch of a foil type strain gauge. (3)

b) State the purpose of a strain gauge. (1)

Question 11

Define flow rate of a fluid and give the SI unit for flow rate. (2)

Question 12

With reference to the energy content of a liquid in motion, define the following

quantities and give an expression for the energy per unit volume, in each case:

a) Pressure energy. (2)

b) Kinetic energy. (2)

Question 13

a) Make a labelled sketch of a Pitot tube flow meter. (2)

b) Give a formula from which the velocity v of a liquid may be calculated,

when measuring flow rate with a Pitot tube. (1)

Question 14

State the various methods of positioning the high pressure and low pressure

tap-points, that may be used when measuring flow rate with orifice plates. (5)

Question 15

a) Draw a labelled sketch of a Doppler flow rate meter. (3)

b) Give a formula with which the flow speed v may be calculated, when a

Doppler flow meter is used to determine the flow rate of a stream.

Define the variables in the equation. (3)

Total: 50

---ooo000ooo---


September 2005

Process Instrumentation I EIPIN1 Unit 1 First Assessment Memorandum September 2005

1. Current-Ampere [1]

[2] Luminous intensity – Candela [1]

2. A – Tube [½]

Transmission element [½]

B – Bourdon tube [½]

Secondary element [½]

[3] C – Link and gears [½]

Variable manipulation element [½]

3. Repeatability is the closeness [½]

of the instrument readings when the (same input is applied

[2] repetitively) [½]

over a short period of time [½]

with the same conditions. [½]

4. Sensitivity = �output/�input [1]

= 40/5 = 8 mV/cm. [1]

[2]

5.

[2]

6. Relative density of a substance is defined as the ratio of the density of the substance [1]

to the

[2] density of water. [1]

7. According to Boyle’s law:

(100�103)�(1�A) = PX�(0.5�A)

�PX= 200�103 Pa

[2]

Equating pressures on the XY line:

P = PX + 13600�1�9.81

�P = 200�103 + 133.42�10

3

Y

Zero line

�=13.6

0.5m

P PX

Symbol [1]

FIT [1]

1m

100kPa 100kPa

1m

X

FIT

Tube cross sectional area is A meter2 [4] �P = 333.42 kPa

[2]

8. a) P1 – P2 = �hg(1 + A2/A1) [1]

�135�103 = 13600�1�9.81�[1 + (A2/A1)]

= 133416[1 + (A2/A1)]

�1+(A2/A1) = 135�103/133416 = 1.0119

�(A2/A1) = 0.0119 [2]

(3)

Zero line

d

135kPa

1m

b) d = (A2/A1)h [1]

A1 A2 �d = 0.0119�1

[5] = 0.0119 m = 11.9 mm. [1]

(2)

9. Relative density: 13.6 [1]

Applications: Pressure measurements in compressed gas, and in water and steam applications. [1]

Advantages: High density. Can be easily seen. Mercury does not: i) evaporate,

ii) mix with other liquids, iii) wet sides of tubes. [1]

[4] Disadvantages: Expensive. Mobility and density are affected by contamination. [1]

10. a) b) Convert pressure

or force to an

electrical signal. (1)

[4] (3) /4 Alignment marks[1]

Backing material [1]

Solder tabs [1]

Grid [1]


September 2005

11. Flowrate is the volume of a liquid or gas passing a given point per unit time, [1]

and is measured

[2] in cubic meter per second (m3/s).

[1]

12. a) Pressure energy is the energy which a liquid has by virtue of its internal pressure.[1]

A liquid

under pressure p pascal, possesses pressure energy per unit volume equal to p joule.[1]

(2)

b) Kinetic energy is the energy a liquid has by virtue of its motion.[1]

A liquid with density

� kilogram/meter3 and moving at velocity v meter/second, possesses kinetic energy per

[4] unit volume equal to ½�v2 joule.

[1] (2)

13. a) Stagnation (impact) pressure pstag [½]

Static pressure pstat [½]

(2)

Impact hole [½]

v [½]

[3] b) v = �

)statpstag2(p � (1)

14. Corner taps [1]

Flange taps [1]

Radius taps (D&D/2 or throat taps) [1]

Vena-contracta taps [1]

Pipe taps [1]

[5]

15. a) Piezoelectric crystals [½]

(3)

Receiver [½]

[½]

Bubbles or solid particles [½]

v [½]

or flow

Transmitter [½]

b) v = c�cosT2f

TfRf � [1]

fR = received frequency [½]

fT = transmitted frequency [½]

[6] c = speed of sound in medium [½]

= incidence angle [½]

(3)

Process Instrumentation I EIPIN1 Unit 2 First assessment October 2005 Page 1

Question 1

Draw a labelled sketch of a magnetic float level meter (magnetic coupled

float and follower). (4)

Question 2

The level of a liquid in an open container,

is measured with the aid of a well type

manometer, as shown in Figure 1. The ratio

of the tube area to the well area is 0.01

(A2/A1 = 0.01). The relative density�of the

liquid in the container is 1 (�=1) and the

manometer liquid is mercury with a relative

density of 13.6 (�=13.6). The zero level of

the manometer liquid, is 1 meter below the

bottom of the container. Calculate the

level H, of the liquid in the container, if

the manometer reading h, is 0.3 meter. (4)

Figure 1

h=0.3m

H � = 1

1 m

Zero line

� = 13.6

Question 3

Define the following fixed points on the international temperature scale:

a) The oxygen point. (2) b) The silver point. (2)

Question 4

a) Make a labelled sketch of a gas filled thermometer. (4)

b) State which gas is normally used in a gas filled thermometer. (1)

c) Give the equation that describes the gas law for ideal gasses. (1)

d) With reference to the gas law, state the basic principle underlying the

operation of the gas filled thermometer. (1)

Question 5

A Wheatstone bridge is used to measure temperature with

a resistance thermometer RT, as shown in Figure 2. The

three fixed resistors have a resistance of 100 � each,

and the bridge is powered by a 10 V battery. When

the temperature around the thermometer is 0 °C, the

resistance of RT is 100 � and the bridge voltage reading

is V = 0 volt. When the temperature of RT is increased, the

10V

– +

V

100�100�

100� RT

Figure 2 voltmeter reading V, increases to 1 volt. Assume that the

temperature coefficient of resistance of RT is 0.00391 /°C and that the resistance

change of RT with temperature, is described by the equation Rt = Ro(1 + �ot).

Calculate the temperature of RT when the voltmeter reading is 1 V. (5)

Question 6

a) State the thermocouple law of intermediate metals. (2)

b) State the practical benefit derived from the law of intermediate metals. (1)

..................../2

Process Instrumentation I EIPIN1 Unit 2 First assessment October 2005 Page 2

Question 7


temperature range of a type T thermocouple. (3)

Question 8

A simple float and lever, water level control

system with proportional controlled valve

regulated inflow, is illustrated in Figure 3.

a) Identify the quantities in Figure 3

that represent the following:

i) Controlled variable. (1)

ii) Manipulated variable. (1)

iii) Disturbance variable. (1)

b) Identify the components in Figure 3

that evaluate/determine the following:

i) Measured value. (1)

ii) Desired value. (1)

iii) Error value. (1)

Water

inflow

Float

Float

arm

Valve

Lever

Q

H

Water

outflow

Pivot

Figure 3 L

Question 9

Define the following concepts with respect to proportional only control systems:

a) Proportional control law. (1) b) Proportional gain. (1)

c) Proportional band. (1) d) Offset. (1)

Question 10

The set point of a proportional only control system

is 50%. The behaviour of the measured value M,

after a disturbance, is shown in Figure 4. Sketch a

graph of the possible behaviour of the measured

value, if the disturbance occurred while the

controller’s integral control function, was also active. (2)

Time 40%

50%

M Disturbance

Figure 4

Question 11

Draw a circuit diagram of the derivative (D) block of an electronic

proportional, integral and derivative controller. Give the expression of the

output of the D block, in terms of the error input signal E. (3)

Question 12

Explain the difference between direct and reverse acting valve actuators. (3)

Question 13

Explain the term ‘valve throttling’. (2)

Question 14

Draw a labelled sketch of a valve positioner that helps the actuator of a

pneumatic valve, to position its valve stem in the required position, as

dictated by the value of the instrument signal. (6)

---ooo000ooo--- Total: 56

Process Instrumentation I EIPIN1 Unit 2 First Assessment October 2005 Memorandum Page 1

Process Instrumentation I EIPIN1 Unit 2 First Assessment October 2005 Memorandum

1. 2.

P1

� = 13.6

h=0.3m

H � = 1

1 m

PA

P2

ZL

Ignore d and equate pressures on the zero line:

PA + 1000×(H+1)×g = PA + 13600×0.3×g [1]

�H = 3.08 m [3]

Ignore d, calculate P1 on zero line and use well

type manometer equation:

P1 = Patm + 1000�(H + 1)�g and P2 = Patm

�P1–P2=1000(H+1)g & P1–P2=�hg(1+A2/A1):

1000×(H+1)×g = 13600�0.3�g�(1+0.01) [1]

�H= 3.121 m [3]

Include d and equate pressures in line with mercury meniscus in well:

PA+1000(H+1+0.003)g = PA+13600�(0.3+0.003)g[1]

� H = 3.118 m [3]

Non-magnetic

dip tube [1]

Doughnut float

with

outer magnet [1]

Level indicator [1]

Indicator rod [1]

Follower with

inner magnet [1]

PA

d=(A2/A1)h=0.003m

Include d and use well type manometer equation:

[4] /5 [4] P1-P2=1000(H+1.003)g=13600(0.3)g(1+0.01)[1]

� H = 3.118 m [3]

3. a) The oxygen point:

The boiling point of liquid oxygen [1]

: 4. a)

–182.97 °C. [1]

(2)

b) The silver point:

The melting point of silver [1]

:

[4] 961.78 °C. [1]

(2)

4. b) Nitrogen gas. (1)

c) PV = nRT. (1)

d) V is constant, therefore P ! T [½]

P is detected by the Bourdon tube [½]

(1)

[7] (4) /5

Steel bulb [1]

Gas [1]

(Nitrogen)

Steel tube [1]

Pointer

and scale[1]

Bourdon

tube [1]

VAB = 1 V

VAC VBC

B – +

100� 100� I

100� RT

A

10V

C

5. VBC = (100/200)�10 = 5 V and VAB = 1 V

�VAC = 6 V [1]

�100RT

RT

��10 = 6 � 10RT = 6(RT+100)

�RT = 150 � [2]

�150 = 100(1 + 0.00391t) � 1 + 0.00391t = 1.5

[5] �0.00391t = 0.5 � t = 127.9 °C [2]

6. a) The law of intermediate metals states that a (third metal may be inserted into a

thermocouple system without affecting the emf generated,) [1]

(if, and only if, the

junctions with the third metal are kept at the same temperature.) [1]

(2)

[3] b) A measuring instrument may be inserted into the thermocouple circuit. (1)

Process Instrumentation I EIPIN1 Unit 2 First Assessment October 2005 Memorandum Page 2

7. Type Positive element Negative element Temperature range (°C)

[3] T Copper [1]

Constantan [1]

-200 to 350 [1]

8. a) i) Controlled Variable: Water level H. (1)

ii) Manipulated Variable: Water inflow Q. (1)

iii) Disturbance Variable: Water outflow L. (1)

b) i) Measured value: Float vertical position. (1)

ii) Desired value: Length of float arm (or vertical position of pivot). (1)

[6] iii) Error value: Lever rotation. (1)

9. Proportional control: A control strategy in which the controller output is proportional to

the magnitude of the error (C = KPE + R). (1)

Proportional gain: Ratio of controller output change to error value change (KP = �C/�E). (1)

Proportional band: The error range that causes 100 % change in controller output

(PB = 100/KP). (1)

[4] Offset: The steady state difference between the set point and the measured value. (1)

10.

Restriction [½]

Cam [1]

Air

supply [½]

Valve stem [½]

Valve actuator [½]

Pilot

relay [½]

Actuator

Output [½]

Elastic

force-

balance

beam [1]

Pivot [½]

Instrument bellows [1]

Flapper and nozzle [1]

Instrument signal [½]

or

Time 40%

50%

M Disturbance

Time 40%

50%

M Disturbance

[2]

11. 12. Direct acting actuator:

In a direct-acting actuator, an increase in the

pneumatic pressure applied to the diaphragm

extends the valve stem (for a normally seated

valve this will close the valve and is called

‘air to close’) [1½]

Reverse acting actuator:

In a reverse acting actuator an increase in the

pneumatic pressure applied to the diaphragm lifts

the valve stem (in a normally seated valve this

[3] [3] will open the valve and is called ‘air to open’) [1½]

VD=-RDCDdt

dE [1]

CD [1]

RD [1]

Op-amp

E

VD

13. Throttling occurs 14.

when the valve stem

position is between

closed and open

(0 > " > 1) and

the valve is busy

regulating the

[2] flow stream.

[6] /8


November 2005

Question 1

Discuss the significance of working standards in the hierarchy of instrument

standards. (2)

Question 2

Explain the recording function of an instrument. (2)

Question 3

Define the precision of an instrument. (2)

Question 4

0

0

100

Output pressure reading (kPa) A static calibration test was performed on

10090

a gauge pressure meter. An error of 10 % Figure 1 was recorded for each test input, as shown

in Figure 1 where the results obtained, were Applied input

pressure (kPa) plotted on a graph. State the type of error that

the instrument is suffering from and suggest

a possible remedy to cure the problem. (2)

Question 5

Figure 2 shows one section of a larger

instrumentation schematic drawing. Identify

items 1 and 2 and comment on the function

performed by this segment of the system. (3)

FIC

Figure 2

1 2

Question 6

Define atmospheric pressure and give the assigned standard value. (2)

Question 7

Convert a pressure of 50 kPa to a pressure expressed as millimeter mercury. (2)

Question 8 P 0 Pa

�=0.8

�=13.6

1 m

0.5 m

Figure 3

The left hand tube of a u-tube mercury

(� = 13.6) manometer, shown in Figure 3,

is filled up with a liquid with relative

density of 0.8 (�=0.8). The right hand

tube is sealed and forms a chamber with

a perfect vacuum (0 Pa). Calculate the

pressure P, applied to the left hand tube

of the manometer. (2)

Question 9

With the aid of a sketch, derive the expression that is used to determine pressure with

a well type manometer. All symbols used, must be shown very clearly on the sketch.

(4)

..................../2


November 2005

Question 10

The inclined limb of an inclined limb manometer, forms an angle of 30 degrees

with the horizontal plane. The relative density of the manometer fluid is 0.8

(�=0.8). The internal diameter of the well is 3 cm and the internal diameter of

the inclined limb is 12 mm.

a) Calculate the maximum applied pressure for a maximum scale reading L,

of 100 cm on the scale attached to the inclined limb. (3)

b) The range of the above inclined manometer must be extended so that the

maximum pressure that can be applied to the manometer, is increased by

1000 pascal. Calculate the relative density of the manometer fluid that is

required. (2)

Question 11

Make a labelled sketch of a C-type Bourdon tube pressure gauge. (4)

Question 12

Define a streamlined flow and a turbulent flow of a stream. (4)

Question 13

A venturi tube, shown in Figure 4, is

used to measure the flow rate of

water (�=1). The cross sectional

area of the throat is 0.001 m2

and the cross sectional area

of the pipe is 0.002 m2. The

pressure difference measured

across the high and low pressure

taps, is 375 pascal. Calculate the flow

rate q, of the water, using the flow equation, q = A2 ]2)/A(A�[1)p2(p1221

�� . (3)

p1 - p2 = 375 pascal

p2

p1

Throat area=0.001 m2 Pipe area=0.002 m

2

Figure 4

q

Question 14

a) Draw a sketch of a concentric orifice plate and indicate on the sketch

where a vent hole and drain hole may be inserted. (2)

b) Explain the purpose of a vent hole. (2)

c) Explain the purpose of a drain hole. (2)

Question 15

State the main disadvantage of an orifice plate flow meter. (1)

Question 16

a) Draw a labelled sketch of a vortex flow meter. (3)

b) Give the operational equation that is used to calculate the flow rate q,

from the measurements made with a vortex flow meter. Define each


Total: 50

---ooo000ooo---


November 2005

Process Instrumentation I EIPIN1 Unit 1 Final Assessment Memorandum November 2005

1. Workplace standards are used to calibrate instruments used in industrial applications and

instruments used in the field, [1]

for accuracy and performance. Working standards are

[2] checked against secondary standards [1]

for accuracy.

2. An instrument may provide the information of the value of a quantity under measurement

[2] against time [1]

or some other variable, in the form of a written record, [1]

usually on paper.

3. Precision is the closeness [1]

with which (repeated measurements of the same quantity) [1]

[2] agree with each other.

4. Range error [1]

(systematic error because of drift, miscalibration, mishandling, etc.).

[2] Possible cure: recalibration. [1]

5. 1: Pneumatic valve [1]

2: Venturi tube [1]

[3] Function: regulating the flow rate (FIC) of the stream by means of a pneumatic control valve [1]

6. Atmospheric pressure is the absolute pressure caused by the weight of the earth’s atmosphere. [1]

[2] Standard atmospheric pressure at sea level is 101.326 kPa. or 760 mm. mercury. [1]

7. P = �hg � 50000 = 13600�h�9.81 � h = 0.3748 meter [1]

1 0.5

0.5

P 0

�=0.8

�=13.6

[2] 50 kPa # 374.8 mm Hg. [1]

8. P+800�1�9.81 = 13600�0.5�9.81

[2] �P = 58860 Pa.

9. P1 = P2 + �(h+d)g [1]

…………….……… (1)

ZL

P2

d

h Sketch: 1 mark

P1

�

A1d = A2h � d =

1A

2Ah

[1] …..………….. (2)

(2) in (1): P1 = P2 + � ��

�

�� h

1A

2Ah g

[1]

[4] �P1–P2 = �hg ��

�

��

1A

2A1

A1 A2

10. a) P1 – P2 = �Lg(sin�+A2/A1) [1]

11.

= 800�1�9.81�[sin30° + (12/30)2]

= 7848�(0.5 + 0.16) = 7848�0.66

= 5180 Pa [2]

(3)

b) (P1 – P2)new = 5180 + 1000

= 6180 Pa [1]

P1 – P2 = �Lg(sin�+A1/A2)

�6180 = ��1�9.81�0.66

�� = 6180/6.475 = 954.4 kg/m3

[5] ��new = 0.9544 [1]

(2)

[4] /5 Pressure connection[½]

Pointer and scale [½]

Pivot point[½]

Bourdon tube [1]

Pinion gear [½]

Sector gear[½]

Hairspring [½]

Adjustable link[½]

Range adjust[½]


November 2005

12. Streamlined flow: In a streamlined flow, all the particles in the liquid, flow in the same direction and

parallel to the walls of the pipe, and the streamlines are smooth. [2]

Turbulent flow: In a turbulent flow, the particles in the stream, flow axially as well as

[4] radially, and the streamlines are in a chaotic pattern of ever changing swirls and eddies. [2]

13. q = A2�[2(p1-p2)/{�[1-(A2/A1)2]}] = 1�10

-3�[2�375/{1000�[1-(1/2)2]}]

[3] = 1�10-3�(750/750) = 0.001 m

3/sec.

14. a) b) Vent holes are provided to prevent

(gasses when transporting liquids) [1]

to

accumulate at the top [1]

the pipe on the

upstream side of the orifice plate. (2)

c) Drain holes are provided to prevent

(solid particles in liquids) [½]

and

(condensate in gasses) [1]

to accumulate

at the bottom [½]

of the pipe on the

upstream side of the orifice plate. (2)

Vent hole

(top [1]

)

Drain hole

(bottom [1]

)

[6] (2)

15. High pressure loss.

[1]

16. a)

(3) /4

Heat sensors in

bluff body

or ultrasonic sensors [1]

d

Eddies

(vortices, whirls, swirls

or Von Karman vortex street) [1]

Bluff body

(vortex generator

or shredder bar) [1]

v [1]

b) q = A�tS

fd [1]

A = unblocked flow area [½]

f = measured vortex frequency [½]

d = width of bluff body [½]

[6] St = Strouhal factor [½]

$ constant (3)


November 2005

Question 1

Draw a labelled sketch of a magnetic float switch. (3)

Question 2

The level of a liquid in a closed

container, is measured with the aid of

a well type manometer, as shown in

Figure 1. The ratio of the tube area to

the well area is 0.01 (A2/A1 = 0.01).

The relative density�of the liquid in

the container is 1 (�=1) and the

manometer liquid is mercury with a

relative density of 13.6 (�=13.6). The

zero level of the manometer liquid, is

1 meter below the bottom of the

container. Calculate the level H, of the

liquid in the container, if the

manometer reading h, is 0.15 meter. (5)

Zero line

1 m

5 m H � = 1

h=0.15m

� = 13.6 Figure 1

Question 3

Define the bottom fixed point on a temperature scale and give this temperature

value on the Fahrenheit scale. (2)

Question 4

Convert 50 °F to degrees Celsius, Kelvin and Rankine. (3)

Question 5

a) Draw a labelled sketch of a bi-metal thermometer. (3)

b) State the principle on which the operation of the bi-metal thermometer is

based. (1)

Question 6

A platinum resistance thermometer has a resistance of 100 � at 0 °C and

a resistance of 139.1 � at 100 °C. Using the linear approximation

Rt = Ro(1 + �ot), calculate the resistance of the thermometer at 140 °C. (3)

Question 7

Draw a labelled circuit diagram to illustrate the four wire method that is used

to compensate for ambient temperatures when measuring temperature with a

resistance thermometer. (3)

Question 8


temperature range of a type E thermocouple. (3)

..................../2


November 2005

Question 9 Table 1

°C 0 1 2 3 4 5 6 7 8 9

0 0 59 118 176 235 294 354 413 472 532

10 591 651 711 770 830 890 950 1010 1071 1131

20 1192 1252 1313 1373 1434 1495 1556 1617 1678 1740

30 1801 1862 1924 1986 2047 2109 2171 2233 2295 2357

40 2420 2482 2545 2607 2670 2733 2795 2858 2921 2984

50 3048 3111 3174 3238 3301 3365 3429 3492 3556 3620

60 3685 3749 3813 3877 3942 4006 4071 4136 4200 4265

70 4330 4395 4460 4526 4591 4656 4722 4788 4853 4919

80 4985 5051 5117 5183 5249 5315 5382 5448 5514 5581

90 5648 5714 5781 5848 5915 5982 6049 6117 6184 6251

100 6319 6386 6454 6522 6590 6658 6725 6794 6862 6930

A type E thermocouple is

used to measure the

temperature of a medium. An

excerpt from the type E

thermoelectric voltage table

(in microvolt) for

temperatures in degrees

Celsius, is given in Table 1.

The emf reading obtained

from the thermocouple, is

4656 microvolt (�V). If the

temperature of the reference

junction (cold junction) is 20 °C, use Table 1 to calculate the temperature of the

hot junction. (3)

Question 10

a) Distinguish between feedback control and feedforward control. (2)

b) What essential control strategy, feedback or feedforward control, is used

by a person trying to catch a ball. (1)

Question 11

Name the two kinds of delays (lags) that may be identified when a system is

subjected to a step input. (2)

Question 12

Sketch a graph of the typical behaviour of a controlled variable, when controlled

by an on-off controller, between 60% upper limit and 40% lower limit. (2)

Question 13

The output of a proportional only controller, changes by 15% when the error

changes by 10%. Calculate the proportional band setting of the controller. (2)

Question 14

Define reset time with reference to integral control action. (2)

Question 15

Draw a circuit diagram of the proportional (P) block of an electronic

proportional, integral and derivative (PID) controller. Give the expression of

the output of the P block, in terms of the error input signal E. (3)

Question 16

Name the linear movement valve types. (5)

Question 17

Sketch a graph of the inherent valve characteristic for an equal percentage

valve. (2)

Total: 50

---ooo000ooo---


November 2005

Process Instrumentation I EIPIN1 Unit 2 Final Assessment Memorandum November 2005

1. 2.

P1=Pt+1000�6�9.81 = Pt + 58860

[3]/4½ and P2=Pt+1000�(H+0.85)�9.81

Swivel pin [½]

Float magnet [1]

Non-magnetic

housing [1]

Magnetic reed

switch [1]

Float [1]

P1 1 m

5 m

Pt

� = 1

Pt

P2

h=0.15

�=13.6ZL

H

=Pt+9810(H+0.85)

3. Bottom fixed point: The temperature of ice (prepared �P1 – P2 = 58860 – 9810(H+0.85) [1]

from distilled water) mixed with distilled water [½]

, at But P1-P2=�hg(1+A2/A1)

standard atmospheric pressure of 760 mm. mercury.[½]

=13600�0.15�9.81(1+0.01)

[2] Temperature value on the Fahrenheit scale is 32°F [1]

=20213 [1]

�58860 - 9810(H+0.85) = 20213

4. C=9

5(F–32)=

9

5(50-32)=

9

5�18 = 10 °C

[1] [5] �H = 3.09 m

[3]

R=F+460=50+460=510 R [1]

{ or including d=(A2/A1)h=0.01×0.15=0.0015

[3] K=C+273=10+273=283 K [1]

P1-P2=1000�6.0015�9.81–1000×9.81×(H+0.85)

�20213=58875–9810H–8337 � H = 3.091 m }

6. �0 = 1000R

0R100R

�

� =

100100

100139.1

��

= 0.00391 [1]

Rt = Ro(1 + �ot)

[3] �R140°C = 100(1+0.00391�140) = 154.74 � [2]

7.

[3]

(3) /5

5. a) Pointer and scale [1]

Socket [½]

Bearing [½]

Shaft [1]

Guide [½]

Helical

bi-metal

element [1]

Stem [½]

Voltmeter return

across RT - 1 mark

Current source I

1 mark

Rlead

Rlead

Rlead

Rlead

I

a

c

RT

d

b

4 leadwires plus

RTD – 1 mark M

[4] b) Different temperature coefficients of expansion of two metals bondedtogether in a helix. (1)


November 2005

8.

Type Positive

element

Negative

element

Temperature

range (°C)

E Chromel[1]

Constantan[1]

-200 to 800 [1]

[3]

0°C

20°C 20°C

5848�V

4656�V1192�V

T

0°C

T 9. Emf corresponding to (25 – 0) °C = 1192 �V

[1]

Total emf (T - 0) = 4656 + 1192 = 5848 �V [1]

[3] From table, hot junction temperature T = 93 °C [1]

10. a) Feedback control: Measure the controlled variable to determine the control strategy. [1]

Feedforward control: Measure disturbance variables to determine the control strategy. [1]

(2)

[3] b) Feedforward control. (1)

11. Dead time [1]

and first order lag. [1]

[2]

Measured value

40%

60%

12.

Time [2]

13. KP = �C/�E = 15/10 = 1.5 [1]

[2] �PB = 100/KP = 100/1.5 = 66.67 % [1]

14. Time taken for integral action to equal [1]

proportional action under the influence of a constant error. [1]

[2]

15. 16. i) Globe valve [1]

ii) Gate valve [1]

iii) Needle valve [1]

iv) Pinch valve [1]

[5] v) Diaphragm valve [1]

E

RPI [1]

RPF [1]

VP = -

PIR

PFRE

[1]

Op-amp VP

[3]

17. Inherent =% characteristic

x

=%

f(x)

0

1

Valve travel

[2] 0 1

Process Instrumentation I EIPIN1 Unit 1 First Assessment 10 March 2006 Page 1

Question 1 Define the primary standard of measurement. (2)

Question 2 Define the span of an instrument. (2)

Question 3 Define the sensitivity of an instrument. (2)

Question 4 Define the error of drift that may occur in an instrument. (2)

Question 5 Identify the instrument function and mounting

method, from the instrument symbol in Figure 1. (2) TIR

Figure 1

Question 6 An electronic transmitter with an output of 4 - 20 mA, is calibrated for

a pressure range of 70 - 150 kPa. What pressure is represented by a 16 mA signal? (2)

Question 7 Define relative density. (2)

Question 8 Convert a pressure of 100 centimeter water to a pressure expressed

in millimetre mercury. (2)

Question 9 With the aid of a labelled sketch, derive the expression that is used to

determine pressure with a well type manometer. (4)

Question 10 Discuss Bromoform as a manometer liquid, with respect to its

relative density, applications, advantages and disadvantages. (4)

Question 11 Draw a labeled sketch of a force-balance gauge calibrator (‘dead

weight tester’). (6)

Question 12 Define volumetric flow and give the SI unit for volumetric flow. (2)

Question 13

a) Define a streamlined flow of a stream. (2)

b) The Reynolds number for a flow condition is determined as 4000.

Is the flow streamlined or turbulent? (1)

c) Explain the function of a flow straightener (straightening vane) in a pipe. (1)

Question 14 In Figure 2, a restricted

horizontal flow line is shown. The pressure

difference p1 - p2 is measured by taking the

reading h, as shown in Figure 2.

Use Bernoulli’s theorem and the principle

of mass flow continuity, to derive the flow

equation, q = k h . (7)

v2 v1

p1 p2 q

h

� � A2 A1

Figure 2

Question 15 Sketch the configuration, including dimensions and labels, when

flange taps are used for flow rate measurement with an orifice plate. (2)

Question 16

a) Draw a labelled sketch of a rotameter (variable area flowmeter). (4)

b) Why does the displacer in a rotameter move upwards with increasing flow rate? (1)


Process Instrumentation I EIPIN1 Unit 1 First Assessment 10 March 2006 Memorandum Page 1

Process Instrumentation I EIPIN1 Unit 1 First Assessment 10 March 2006 Memorandum

1. Primary standards are maintained at institutions in various countries. [1]

The main function

[2] is to check the accuracy of secondary standards. [1]

2. The span of an instrument is the arithmetic difference [1]

between the minimum and maximum

[2] range [1]

values, used to describe both the input and the output.

3. Sensitivity is the rate of change [1]

of the output [½]

of a system with respect to input [½]

changes.

[2]

4. Drift is the change in instrument indication over time [1]

while the input and ambient conditions

[2] are constant. [1]

x 80 130kPa

16mA 20mA 4mA

150kPa

70kPa

80/16=x/12

�5=x/12

�x=60

12

16

5. Temperature indicator recorder, [1]

mounted on board. [1]

[2]

6. P = 70 + (12/16)×(150 – 70) = 130 kPa

[2]

7. Relative density of a substance is defined as the ratio of the density of the substance [1]

to the

[2] density of water. [1]

8. PH2O = PHg � �H2OhH2Og = �HghHgg

�1000×(100×10-2

)×9.81 = 13600×hHg×9.81

[2] �1000×1 = 13600×hHg � hHg = 0.07353 m = 73.53 mm.

P1

ZL

P2

d

hSketch: 1 mark

�

9. P1 = P2 + �(h+d)g [1]

…………….……… (1)

A1d = A2h � d =

1A

2Ah

[1] …..………….. (2)

(2) in (1): P1 = P2 + � ��

�

�� h

1A

2Ah g

[1]

A1 A2 [4] �P1–P2 = �hg(1 + A2/A1)

10. Relative density: 2.9 [1]

Applications: Useful where pressure measurement demands manometer liquid with density

between water and mercury. [1]

Advantages: Density that falls between water and mercury. [1]

[4] Disadvantages: Density uncertain. Poisonous. Freezes easily. Subject to attack. Attacks rubber. [1]

11. 12. Volumetric flow is the total volume

of a liquid or gas passing a given point

over a certain period of time [1]

, and is

[2] measured in cubic meter (m3).

[1]

13. a) Streamlined flow: In a streamlined

flow, all the particles in the liquid,

flow in the same direction and

parallel to the walls of the pipe,

and the streamlines are smooth. (2)

[6] / 7 b) Turbulent. (1)

Gauge under

test [1]

Screw [1]

Oil

[1]

Primary piston [1]

Secondary

piston [1]

Platform [1]

Mass pieces [1]

[4] c) To streamline a flow. (1)


v2 v1

p1 p2 q

h

� � A1 A2

14. From Bernoulli’s law:

½�v12+p1=½�v2

2+ p2

[1] ………..……….…. (a)

Flow continuity demands: q = A1v1 = A2v2

�v1 = (A2/A1)v2 [1]

…….…..………….......… (b)

(b) in (a): ½�(A2/A1)v22+p1=½�v2

2+p2

�v22 = 2(p1-p2)/�[1-(A2/A1)

2]

�v2 = ]2)1

/A2

-(A[1)/2

p1

2(p �� [1]

…………..… (c)

But p1 – p2 = �hg [1]

…………………………....…... (d)

(d) in (c): v2 = ]2)1

/A2

-(A2gh/[1 [1]

……....….… (e)

Also q=A2v2 [1]

……………………………….…..… (f)

From (f) and (e): q = A2 ]2)1

/A2

-(A2gh/[1 ......… (g) [note: 1 mark for either simplified v2


Defining k=A2 ]2)1

/A2

(A2g/[1� [1]

in Equation (g):

[7] q = k h .

15. 16. a) 25mm [½] 25mm [½]

[2] / 2½

16 b) When the flow rate increases, the pressure

difference across the float will increase, [½]

which will tend to push the float upwards.

As the float moves upwards, the restricted flow

area will increase [½]

due to the tapered tube.

This will allow the pressure difference to

decrease to its original value where the float

[5] will remain suspended in its new position. (1) (4) Flow [1]

Tapered

tube [1]

High

pressure

tap [½]

Flow [½]

Low

pressure

tap [½]

Scale [1]

Float

(displacer) [1]

Process Instrumentation I EIPIN1 Unit 2 First Assessment 5 May 2006 Page 1

Question 1 Distinguish between point level and continuous level metering. (2)

Question 2 Draw a labelled sketch of a magnetic float sight glass level meter with

isolation (shut off) capability. (3)

h=0.5m

Figure 1

Zero level

� = 13.6

� = 1.5

0.4 m

H

Question 3 The level of a liquid in an open container

container, is to be measured with the aid of a U-tube

manometer, as shown in Figure 1. The relative density

of the liquid in the container is 1,5. The manometer

fluid is mercury with a relative density of 13,6.

The zero line of the manometer, is 0.4 meter below

the bottom of the container. Calculate the level H,

of the liquid in the container, if the manometer

reading h, is 0.5 meter. (4)

Question 4 Convert -40 °C to degrees Fahrenheit, Kelvin and Rankine. (3)

Question 5 Draw a labelled sketch of a vapour pressure thermometer. (4)

Question 6 Name three common metals used in resistance thermometers. (3)

Question 7 A Wheatstone bridge is used to measure

temperature with a resistance thermometer RT, as

shown in Figure 2. When the thermometer temperature

is 0 °C, the resistance of RT is 100 � and the bridge

voltage reading is V = 0 volt. Calculate the reading on

the voltmeter when the temperature of RT is: Figure 2

– +

V

100�100�

100� RT

10V

a) 20 °C and b) 50 °C.

Assume that the temperature coefficient of resistance of RT is 0.00391 /°C and that

the relationship between RT and temperature t, is given by: RT = Ro(1 + �ot).

Question 8 State the essential difference between the principle of operation of a

resistance thermometer and a thermocouple thermometer. (1)

(6)

Question 9 Give the positive element material, the negative element material and the

temperature range of a type K thermocouple. (3)

Question 10 Define the following concepts with respect to control systems:

a) Controlled variable. (1) b) Manipulated variable. (1)

c) Disturbance variable. (1) d) Measured value. (1)

e) Desired value. (1) f) Error value. (1)

Question 11 Define dead time (transportation lag) in a control system. (2)

Question 12 A process is controlled by a proportional controller. The controller

is programmed for a positive gain and proportional band of 80 %, a set point

of 50 % and a bias of 50 %. If the measured value of the process is indicated

as 65 %, calculate the output of the controller at that instant. (4)

Question 13 State the fundamental advantage offered by integral control. (1)

Question 14 Draw a labelled sketch of a pneumatic proportional plus integral

plus derivative controller. (5)

Question 14 Draw the graphs for the inherent valve characteristics for a

quick opening valve, a linear valve and an equal percentage valve. (3)


Process Instrumentation I EIPIN1 Unit 2 First Assessment 5 May 2006 Memorandum Page 1

Process Instrumentation I EIPIN1 Unit 2 First Assessment 5 May 2006 Memorandum

1. Continuous level metering devices measure level on a constant basis, displaying or transmitting

the actual level of the liquid as it changes. [1]

Point-level devices measure liquid at specific points

[2] within the tank. [1]

2. 3.

H

0.5 0.4

Y

1.5

X

Patm + 1500�(H+0.4+0.25)�9.81

= Patm + 13600�0.5�9.81 [1]

�14715�(H+0.65) = 66708

�H + 0.65 = 4.533

[3] /4 [4] �H = 3.883 meter.[3]

4. F = 5

9C + 32 =

5

9�(-40)+32 = -72 + 32 = -40 °F

[1] R = F + 460 = -40 + 460 = 420 R

[1]

[3] K = C + 273 = -40 + 273 = 233 K[1]

5. 6. Platinum, [1]

Copper [1]

and Nickel [1]

[3]

7. a) 20 °C: RT = Ro(1 + �ot)

= 100(1+0.00391�20)

= 107.82 � [1]

I = 10/(100+107.82)

= 48.119 mA

�VAC = RT�I

= 107.82�48.119�10-3

= 5.1882 V [1]

and VBC = (100/200)�10 = 5V

�V = VAC – VBC = 5.1882 – 5 = 0.1882 V [1]

(3)

b) 50 °C: RT = Ro(1 + �ot) = 100(1+0.00391�50) = 119.55 � [1]

I = 10/(100+119.55) = 45.548 mA

[4] �VAC = RT�I = 119.55�45.548�10-3

= 5.4453 V [1]

Isolation

valve [1]

Magnetic

float [1]

Metallic

flaps [1]

Vapour [1]

Steel bulb [½]

Volatile

liquid [1]

Steel tube [½]

Pointer

and scale[½]

Bourdon

tube [1]

Sight glass [1]

VAB = 1 V

VAC VBC

B – +

100� I

100� RT C

A

10V

and VBC = (100/200)�10 = 5V

[6] �V = VAC – VBC = 5.4453 – 5 = 0.4453 V [1]

(3)

8. A resistance thermometer produces a changing resistance with changing temperature [½]

while a

[1] thermocouple generates a changing emf with changing temperature. [½]

9. Type Positive element Negative element Temperature range (°C)

[3] K Chromel [1]

Alumel [1]

-200 to 1200 [1]

10. a) Controlled Variable: Process output variable that is maintained between specified limits. (1)

b) Manipulated Variable: Process input variable that is adjusted, to steer the controlled

variable towards the desired value. (1)

c) Disturbance Variable: Process input variable that can cause the controlled variable to

deviate from the desired value. (1)

d) Measured value: Actual value of the controlled variable, as determined by the instrumentation. (1)

e) Desired value: Required value of the controlled variable (set point). (1)

[6] f) Error value: The difference between the desired value and the measured value. (1)


11. Delay due to the time it takes information or material to be transported [1]

from one point to another. [1]

[2]

12. KP = 100/PB = 100/80 = 1.25 [1]

E = 50 – 65 = -15 % [1]

� C = KPE+R = 1.25×(-14) + 50 = 31.25% [2]

[4]

13. Offset is eliminated.

[1]

Needle valve rate

time adjustment [½]

Restriction [½]

Set point S [½]

Reset

bellows [½]

Beam[½]


Air

supply [½]

Flapper and

nozzle [½]


Proportional

(feedback)

bellows[½]

Pilot

relay[½]

Controller

output C [½]

Needle valve [½]

Reset time adjust

14.

[5] /6½

15.

=%[1] x

Quick[1]

Linear[1]

0 1

f(x)

1

0

[3]

Process Instrumentation I EIPIN1 Unit 1 Final Assessment 21 April 2006 Page 1

Question 1 Give the SI units for time and amount of substance. (2)

Question 2 A liquid filled thermometer is

shown in Figure 1. Identify parts A, B and

C, and state for each of parts A, B and C,

the fundamental instrument element,

represented by that part. (3)

Question 3 Define the precision of an instrument. (2)

A

B

Figure 1C

Question 4 Define an error of hysteresis in an instrument. (3)

Question 5 An item appears on an industrial schematic drawing that is labelled

with the letters LCV. Identify this element. (2)

Question 6 Define pressure and give the SI unit for pressure. (2)

Question 7 Assuming that the density of the atmosphere is a constant value

of 1.2 kg/m3 and that the atmospheric pressure at sea level is 760 mm. mercury,

calculate the height of the atmosphere above sea level. (3)

Question 8 You are requested to design a scale plate for a U-tube manometer that

uses mercury, with relative density of 13.6, as manometer liquid. You are told that

the maximum differential pressure to be measured, will be 100 kPa. From the zero

line upward, the following values must be marked off on the scale plate: 25 kPa,

50 kPa, 75 kPa and 100 kPa. Calculate the distances from the zero line to each

marking on the scale, and sketch the designed plate. (4)

Question 9 Draw labelled sketches to show how a bellows element may be

used to measure: a) differential pressure (2) b) absolute pressure. (2)

Question 10 Draw a labelled sketch of a pneumatic differential pressure transmitter. (6)

Question 11 Define flow rate of a fluid and give the SI unit for flow rate. (2)

Question 12 State Bernoulli’s law (in words). (4)

Question 13 State the advantages and disadvantages of the venturi tube. (4)

Question 14 State three methods of positioning the high pressure and low pressure

tap-points, that may be used when measuring flow rate with orifice plates. (3)

Question 15 Water flows through a horizontal pipe with

cross sectional area of 5�10-3

m2. A circular object, facing

the stream with an area of 2�10-3

m2, is placed in the flow,

as shown in Figure 2. The force on the object is measured

as 0.5 newton. Calculate the flow rate q of the water,

if the flow rate is given by: q =

��

��

�

2)1

/A2

(A1

)2

p1

2(p

2A ,

where p1-p2 is the pressure difference across the object,

A2 is the restricted flow area, A1 is the unrestricted flow

area (pipe area) and � = 1000 kg/m3 (for water). (3)

q

Object area = 2�10-3

m2

p1 p2

F=0.5 N

Pipe area = 5�10-3

m2

Figure 2

Question 16 Draw a labelled sketch of a transit time (transmissivity) flow meter. (3)


Process Instrumentation I EIPIN1 Unit 1 Final Assessment 21 April 2006 Memorandum Page 1

Process Instrumentation I EIPIN1 Unit 1 Final Assessment 21 April 2006 Memorandum

1. Time: second [1]

Amount of substance: mole [1]

[2]

2. A – Bulb [½]

Primary element [½]

B – Bourdon tube [½]

Secondary element [½]

[3] C – Pointer and scale [½]

Functional element [½]

3. Precision is the closeness [1]

with which (repeated measurements of the same quantity) [1]

[2] agree with each other.


between the readings obtained when a (given value of the measured

[3] variable is approached from below) [1]

and when the (same value is approached from above.) [1]

5. Level control valve

[2]

6. Pressure is defined as the force exerted over a unit area [1]

. The SI unit is newton per square meter

[2] (N/m2) or pascal (Pa).

[1]

7. 1.2×hatm×g = 13600×0.76×g � hatm = 8613 m

[3]

8. P1 – P2 = �hg.

for P1-P2=100 kPa: 100�103 = 13600�h�9.81

�h = 750 mm. [1]

�Distance from zero line to 100 kPa marking = 375 mm. [1]

[4]

9. a) Differential 10.

93.74mm[½]

375mm[½]

281.3mm[½]

187.5mm[½]

100 kPa

75 kPa

50 kPa

25 kPa

0 kPa Zero line

b) Absolute

[4]

[6] / 8

11. Flowrate is the volume of a liquid or gas passing a given point per unit time, [1]

and is measured

High

pressure

High

pressure

(P1) [½]

Low pressure

(P2) [½]


Bellows [½]

Vacuum [½]

(P1) [½]


(2)

(2)

High pressure (P1)

input [½]

Air supply [½]

Restriction [½]

Pilot relay [½]

Nozzle [½]

Flapper [½]

Pivot point

(range wheel

adjust) [½]

Range bar [½]

Output Po [½]

Feedback

bellows [½]

Zero adjust [½]

Pivot and seal [½]

Force bar [½]

Diaphragm

capsule [½]

Cross

flexure [¼]

Capsule

flexure [¼]

Low pressure (P2)

input [½]

Bellows [½]

[2] in cubic meter per second (m3/s).

[1]

12. If an (incompressible fluid is in a streamlined flow with no friction,) [1]

the sum [½]

of the




per unit volume [½]

, is constant [½]

.


13. Advantages: Pressure loss is small [½]

Operation is simple and reliable [½]

[2] Disadvantages: Highly expensive [½]

Occupies considerable space [½]

14. Corner taps [1]

Flange taps [1]

Radius taps (D&D/2 or throat taps) [1]

[3]/5 Vena-contracta taps [1]

Pipe taps [1]

15. p1 – p2 = F/Aobject = 0.5/2�10-3

= 250 Pa. [1]

and A2 = 5�10-3

- 2�10-3

= 3�10-3

[1]

�q =

��

��

�

2)

1/A

2(A1

)2

p1

2(p

2A = (3�10

-3)�

��

��

�� 2

)105/103(11000

2502

33

[3] = (3�10-3

)�

��

�� 2

)6.0(11000

500=(3�10

-3)�

0.64

5.0=(3�10

-3)�0.8839=2.652�10

-3 m

3/s

[1]

16.

Ultrasonic transceiver 2

(Piezoelectric crystals) [½]

Ultrasonic transceiver 1

(Piezoelectric crystals) [½]

L [½]

[1]

Flow [1]

[3]

Process Instrumentation I EIPIN1 Unit 2 Final Assessment 26 May 2006 Page 1

Question 1 Distinguish between direct methods and indirect methods of level

measurement and give an example of each method. (4)

Question 2 State the principle on which level measurement with the flexure tube

displacer (torque tube) level meter is based. (1)

Question 3 Draw a labelled sketch of a bubble meter (gas flushing system) for

level measurement (using a manometer) in an open container. (4)

Question 4 Define temperature and give the SI unit for temperature. (2)

Question 5 Define the following fixed points on the international temperature

scale: a) The boiling point. (2) b) The sulphur point. (2)

Question 6 Name three liquids used in a liquid in glass thermometer. (3)

Question 7 Draw a labelled sketch of a resistance thermometer construction with

protective tube and terminal head. (4)

Question 8 A Wheatstone bridge is used

to measure temperature with a type PT100

platinum resistance thermometer RT, as shown in

Figure 1. The resistance of the thermometer is given

by: RT = 100×[1 + (3.9692�10-3

)�t – (5.8495�10-7

)×t2],

where RT is measured in ohm and t in degrees Celsius.

Figure 1

– +

V

100�100�

10V

100� RT

Table 1

°C 0 1 2 3 4 5 6 7 8 9

0 0 39 79 119 158 198 238 277 317 357

10 397 437 477 517 557 597 637 677 718 758

20 798 838 879 919 960 1000 1041 1081 1122 1163

30 1203 1244 1285 1326 1366 1407 1448 1489 1530 1571

40 1612 1653 1694 1735 1776 1817 1858 1899 1941 1982

50 2023 2064 2106 2147 2188 2230 2271 2312 2354 2395

60 2436 2478 2519 2561 2602 2644 2685 2727 2768 2810

70 2851 2893 2934 2976 3017 3059 3100 3142 3184 3225

80 3267 3308 3350 3391 3433 3474 3516 3557 3599 3640

90 3682 3723 3765 3806 3848 3889 3931 3972 4013 4055

100 4096 4138 4179 4220 4262 4303 4344 4385 4427 4468

Calculate the reading V on the voltmeter, if the temperature of RT is 150 °C. (4)

Question 9 In Figure 2, a type K

thermocouple is shown with its

hot junction at 55 °C and its cold

junction at 18 °C . An excerpt

from the type K thermoelectric

voltage table (in microvolt) for

temperatures in degrees Celsius,

is given in Table 1. Use Table 1

to determine the reading V, on

the voltmeter. (3)

55°C 18°C

V

Figure 2

Question 10 A ship’s automatic steering control system, must steer the ship in an exactly

northerly direction, independent of the influences of the sea currents and winds. For this

purpose, the control system monitors the ship’s compass reading, and position the ship’s

rudder accordingly. Identify the following aspects regarding this specific control system:

a) Controlled variable. (1) b) Manipulated variable. (1) c) Disturbance variable. (1)

d) Measured value. (1) e) Desired value. (1) f) Error value. (1)

Question 11 Define on-off (bang-bang) control. (2)

Question 12 Give the equation that describes the output C, of a proportional, integral

and derivative (PID) controller, in terms of the error signal E and controller gains. (3)

Question 13 Draw a circuit diagram of the integral (I) block of an electronic

proportional, integral and derivative (PID) controller. Give an expression for the

output of the I block, in terms of the error input signal E. (3)

Question 14 Draw a labelled sketch of a reverse acting pneumatic control valve. (7)


Process Instrumentation I EIPIN1 Unit 2 Final Assessment 26 May 2006 Memorandum Page 1

Process Instrumentation I EIPIN1 Unit 2 Final Assessment 26 May 2006 Memorandum

1. Direct methods involve direct measurement of 3.

the fluid level as such. [1]

Examples: dipstick, overflow pipe, float

or sight glass [1]

Indirect methods involve measuring another

variable that is related to the fluid level. [1]

Examples: Pressure exerted by the fluid,

echo time of ultrasonic signals

[4] beamed to the fluid surface. [1]

2. Archimedes’s Principle.

[1] [4] /5

Pressure

regulator[1]

Air/gas

supply[1]

Dip tube [1]

Bubbler

sight glass [1]

Filter[1]

4. Temperature is defined as the degree of heat [1]

of 7.

[2] a body. The SI unit for temperature is Kelvin (K). [1]

5. a) The boiling point: The boiling point of pure

water: [1]

100 °C. [1]

b) The sulphur point: The boiling point of pure

[4] sulphur: [1]

444.6 °C.[1]

6. Mercury [1]

, Alcohol [1]

, Pentane [1]

, Toluene [1]

,

[3] /5 Creosote [1]

8. RT = 100×[1 + (3.9692�10-3

)�t – (5.8495�10-7

)×t2]

= 100×[1+(3.9692�10-3

)�150–(5.8495�10-7

)×1502]

= 100×(1 + 0.5954 – 0.01316)

= 100 + 59.54 – 1.316

= 158.2 � [2]

VRT = [158.2/(100+158.2)]×10

= 6.127 V [1]

�V = 6.127 – [100/(100+100)]×10 [4] / 5½

10V

– +

V

100�100�

100� RT

Socket [½]

Resistor bulb

(resistance

winding [1]

Stem

(protective

tube) [1]

Leads [1]

VRT

Connector

conduit [1]

Terminal

Cap [1]

[4] = 1.127 volt [1]

9. E0-55°C = E0-18°C + E18-55°C [1]

� 2230 = 718 + V � V = 2230 – 718 = 1512 �V [2]

[3]

10. a) Controlled Variable: Sailing direction. (1) 14.

b) Manipulated Variable: Rudder position. (1)

c) Disturb. Variable: Sea currents & winds. (1)

d) Measured value: Compass reading. (1)

e) Desired value: Northern direction. (1)

f) Error value: Degrees difference between

[6] north and compass direction. (1)

11. On-off control: A control strategy in which

the controller output switches the final

control element fully on or off [1]

to keep

[2] the controlled variable near set point. [1]

12.

[3]

13.

[3] [7] /8 IR

Valve

body [½]

Actuator

(Motor)[½]

Spring nut [½]

Spring [½]

Diaphragm plate[½]

Plug[½]

Gasket[½]

Stem connector[½]

Diaphragm [½]

Seat[½]

Travel indicator[½]

Stem [½]

Yoke [½]

Gland & packing

[½]

Bonnet[½]

Bonnet nut[½]

C=KPE [1]

+KI �Edt[1]

+KDdt

dE [1]

E

CI [1]

VI=- �Edt

IC

1 [1]

RI [1]

VI

Process Instrumentation I EIPIN1 Unit 1 First Assessment 8 September 2006 Page 1

Question 1 Define the working standard of measurement. (2)

Question 2 Define the range of an instrument. (2)

Question 3 Define the resolution of an instrument. (2)

Question 4 Identify the following power supply symbols:

WS, AS, ES, GS and SS. (5)

Question 5 Give the density of the following substances:

Water, Mercury, Air and Transformer oil. (4)

Question 6 Define Gauge Pressure. (2)

Question 7 With the aid of a labelled sketch, derive the expression that is used

to determine pressure with a well type manometer. (4)

Question 8 The reading h, on a well type mercury manometer, is 73 cm. when

measuring a pressure of 100 kPa.

(a) Calculate the ratio of the well diameter to the diameter of the tube. (4)

(b) Determine the change in level of the mercury in the well of the manometer. (2)

Question 9 Describe the operation of a C-type Bourdon tube gauge. (4)

Question 10 Give a formula used for Poiseuille’s law and explain each symbol

used in the formula. (3)

Question 11 A flow rate meter, uses a restriction in the flow stream, to measure the

flow rate of a liquid in a horizontal pipe. The pressure difference across the restriction

is determined by allowing the liquid into two vertical tubes installed on top of the pipe

and on both sides of the restriction. When the flow rate is 0,1 cubic meter per second,

the level difference of the liquid in the tubes is 0,3 meter. Calculate the flow rate when

the level difference of the liquid in the two tubes is 0,6 meter. (4)

Question 12 Give the advantages and disadvantages of orifice plates. (5)

Question 13 Explain the operation of the following meters:

(a) Target meter

(b) Reciprocating piston PD meter.


Process Instrumentation I EIPIN1 Unit 1 First Assessment 8 September 2006 Memorandum Page 1

Process Instrumentation I EIPIN1 Unit 1 First Assessment 8 September 2006 Memorandum

1. Workplace standards are used to calibrate instruments used in industrial applications and

instruments used in the field, for accuracy and performance. [1]

Working standards are checked

[2] against secondary standards for accuracy. [1]

2. The range of an instrument is the minimum and maximum values [1]

of the measured variable that

[2] the instrument is capable of measuring. [1]

3. Resolution is the smallest variation [1]

in the measured variable that can still be measured. [1]

[2]

4. WS - Water supply [1]

AS - Air supply [1]

ES - Electric supply [1]

GS - Gas supply [1]

[5] SS - Steam supply [1]

5. Water: 1000 kg/m3 [1]

Mercury: 13600 kg/m3 [1]

Air: 1.2 kg/m3 [1]

Trafo oil: 864 kg/m3 [1]

[4]

6. Gauge pressure, is the difference between the absolute pressure in a medium and local atmospheric

[2] pressure [1]

, when the pressure in the medium is higher than atmospheric pressure. [1]

P1

ZL

P2

d

h Sketch: 2 marks

�

7. P1 = P2 + �(h+d)g [½]

…………….……… (1)

A1d = A2h [½]

� d =

1A

2Ah

[½] …….…….. (2)

(2) in (1): P1 = P2 + � ��

�

�� h

1A

2Ah g

�P1–P2 = �hg(1 + A2/A1) [½]

[4] A1 A2

8. P1 – P2 = �hg(1 + A2/A1) [1]

�100�103 = 13600�(73�10

-2)�9.81�[1 + (A2/A1)]

[1]

�1 + (A2/A1) = 100�103/[13600�(73�10

-2)�9.81] � (A2/A1) = 0.027

[1] � (D2/D1)

2 = 0.027

�D2/D1 = 0.1643 [1]

(4)

b) d = (A2/A1)h [1]

= 0.027�73�10-2

[6] �d = 19.71 mm. [1]

(2)

9. Bourdon tube pressure gauges are usually used where relatively large static pressures are to

be measured. [½]

The Bourdon tube pressure gauge consists of a C-shaped tube with one

end sealed. [½]

The sealed end is connected by a mechanical link to a pointer on the dial of

the gauge. [½]

The other end of the tube is fixed and open to the pressure being measured. [½]

The inside of the Bourdon tube experiences the measured pressure, [½]

while the outside

of the tube is exposed to atmospheric pressure. [½]

Therefore, the tube responds to changes

in Pmeasured – Patm. [½]

Increasing this pressure will tend to straighten out the tube and move

the pointer to a higher scale position. [½]

[4]

10. Poiseuille’s law: q = )2

p1

(pL8

4R�

%�

[1]

where q is the liquid’s flowrate (m3/s)

[½] , R is the radius of the pipe (m)

[½] , % is the viscosity

of the fluid (PI) [½]

, L is the length of the pipe (m) and p1–p2 is the pressure differential across

[3] the pipe (Pa). [½]


11. q1 = k1

h [½]

� 0.1 = k 0.3 � k = 0.1/ 0.3 [½]

= 0.1826 [1]

[4] q2 = k2

h [½]

= 0.1826 0.6 [½]

= 0.1414 m3/s

[1]

12. Advantages

Orifice plates are cheap and easy to install. [1]

Orifice plates are reliable and require a minimum amount of maintenance. [1]

Orifice plates can easily be changed to accommodate widely different flow rates. [1]

Disadvantages

The orifice meter has a large permanent loss of pressure. [1]

[5] The higher pressure loss may be associated with higher cost. [1]

13. (a) The target meter (also called a drag

plate meter), uses a flat disk or

target positioned at right angle to

the fluid flow. [1]

The drag force

exerted on the target [1]

by the

approaching stream, is transmitted

via a force bar to a bonded strain

gauge bridge (or differential

pressure arrangement for pneumatic

output). [1]

The strain gauge

converts the mechanical stress

caused by the target, into an

electrical signal, representing the

flow rate. [1]

(4)

(b) In the reciprocating piston flow

meter shown, the piston is pushed

upwards by the incoming fluid and

when it reaches the top of its stroke,

a slide valve opens the top piston

chamber to the inlet port while the

outlet is connected to the bottom

chamber. The piston is now forced

downwards and when it reaches the

bottom of its stroke, the slide valve

shifts to its initial position and the

cycle repeats. [2]

During each cycle,

the meter dispenses a precise

amount of fluid and therefore the

total volume of fluid is represented

by the number of cycles in a given

period. [1]

(3)

[7]

Process Instrumentation I EIPIN1 Unit 2 First Assessment 13 October 2006 Page 1

Question 1

A DP transmitter must be calibrated to measure the level of a liquid in an open tank.

The density of the liquid is 1000 kg/cubic meter. The DP transmitter will be

mounted one meter below the bottom of the tank. The tank is full when the height of

the liquid in the tank is 5 meter and it is empty when there is only liquid in the high

pressure line connected to the DP transmitter. Determine the necessary calibration

specifications for an output signal of 4 to 20 mA. (4)

Question 2 Describe the operation of the following level meters:

2.1 Chain float level meter. (4)

2.2 Magnetic float switch. (4)

2.3 Flexure tube displacer (torque tube) level meter. (4)

Question 3

To set a temperature scale, at least two fixed points are needed.

What is the distance between these two fixed points called ? (1)

Question 4 Define the following fixed points on the international temperature scale:

4.1 The sulphur point. (2)

4.2 The boiling point. (2)

4.3 The gold point. (2)

Question 5

5.1 Sketch and describe the operation of a bi-metal thermometer. (5)

5.2 State the thermocouple law of homogeneous circuits. (2)

Question 6 Explain the following terms:

6.1 Feedback and feedforward control. (4)

6.2 Direct acting control and reverse acting control. (4)

Question 7

Draw a circuit diagram of the proportional (P) block of an electronic proportional,

integral and derivative controller. Also give the expression of the output of the P

block, in terms of the error input signal E. (3)

Question 8

A process is controlled by a proportional controller. The controller is programmed

for a positive gain (reverse acting controller) and proportional band of 70%, a set

point of 50% and a bias of 50%. Calculate the output of the controller when the

measured value is 70%. (4)

Question 9

Give an equation that describes the output C of a proportional and derivative (PD)

controller in terms of the error signal E and controller gains. (3)

Question 10

Define derivative control. (2)


Process Instrumentation I EIPIN1 Unit 2 First Assessment 13 October 2006 Memorandum Page 1

Process Instrumentation I EIPIN1 Unit 2 First Assessment 13 October 2006 Memorandum

Question 1

P2 P1 1 m

DP cell

Patm

20 mA

Full

Patm

5 m

P2 P1 1 m

DP cell

Patm

Patm

4 mA

Empty

1. Empty:

P1 = Patm + �hg

= Patm + 1000�1�9.81

= Patm + 9810

�P1 – P2 = 9810 Pa

Full:

P1 = Patm + �hg

= Patm + 1000�6�9.81

= Patm + 58860

�P1 – P2 = 58860 Pa

Calibration specification: Output = 4 mA when input = 9810 Pa (empty condition)

[4] Output = 20 mA when input = 58860 Pa (full condition)

Question 2

2.1 Chain Float: This type of float is linked to a rotating drum, by means of a chain. [1]

The

chain engages a sprocket, which turns the drum, and with it the level indicator. [1]

A tape, that

wraps around the drum, is also used, instead of a chain. [1]

A weight is attached to the other

end of the chain or tape, to keep the chain pulled straight while the float moves up or down

with the changing level. [1]

(4)

2.2 Magnetic Float Switch: The magnetic float switch is a point level device. When the level

reaches a certain point, the float magnet activates the magnetic reed switch. [1]

The electric

contacts are safely isolated from the inside (wet side) [1]

of the container by non-magnetic

material that allows magnetic interaction between the float magnet and magnetic switch. [1]

The contacts may be used to switch a pump on or off, to sound an alarm or for other control

purposes. [1]

(4)

2.3 Flexure Tube Displacer (torque tube) Level Meter: The displacer type liquid level

measuring instrument is not a float as such, for the displacer is heavier than the process fluid

and the displacer moves very little during changes in tank level (a definite advantage over

other float types). [1]

According to Archimedes’s law, the apparent weight of the displacer

when immersed in a liquid, is its nominal weight in air minus the weight of the displaced

liquid. [1]

The weight of the displacer will thus vary linearly from its weight in air (when the

tank is empty) to its apparent weight when fully immersed in the liquid (when the tank is

full). [1]

The weight of the displacer acting on the torque arm, will cause an angular

displacement of the free end of the flexible torque tube and this movement will be

transmitted to the outside world, by the torque rod. [1]

(4)

[12]

Question 3

3. The fundamental interval.

[1]

Question 4

4.1 The sulphur point: The boiling point of pure sulphur [1]

– 444.6 °C [1]

(2)

4.2 The boiling point: The boiling point of pure water [1]

– 100 °C [1]

(2)

4.3 The gold point: The melting point of gold [1]

– 1064.18 °C [1]

(2)

[6]


Pointer and scale

[½]

Shaft [½]

Helical

bi-metal

element [½]

Stem [½]

Sketch

2 marks

Question 5

5.1 A bi-metal thermometer uses a bi-metal [½]

strip, shaped in a helix [½]

or spiral form, as

shown in the sketch. The one end is fixed and

the other end is free to rotate [½]

as the helix

curls in or out with changing temperature. [½]

A

shaft and pointer is linked to the rotating helix,

to indicate the temperature. [½]

The stem is

filled with silicone fluid, to provide damping

and thermal conductivity between the stem and

bi-metal strip. [½]

(5)

5.2 If two thermocouple junctions are at T1 and T2,

then the thermal emf generated is independent

and unaffected by any temperature distribution

along the wires. (2)

[7]

Question 6

6.1 Feedback control: Measure the controlled variable to determine the control strategy. (2)

Feedforward control: Measure disturbance variables to determine the control strategy. (2)

6.2 Direct acting control: A control arrangement in which the controller output increases

if the measured value rises above the set point. (2)

Reverse acting control: A control arrangement in which the controller output increases

if the measured value drops below the set point. (2)

[8]

E

RPI [1]

RPF [1]

VP = -

PIR

PFRE

[1]

Op-amp VP

Question 7

[3]

Question 8

C = 100/PB(S – M) + R [1]

= (100/70)×(50 – 70) + 50 [1]

= 21.43% [2]

[4]

Question 9

C = KPE [1]

+ KDdE/dt [1]

+ R [1]

[3]

Question 10

A control strategy in which the controller output is proportional to the derivative of the error.

[2]

Process Instrumentation I EIPIN1 Unit 1 Final Assessment 6 October 2006 Page 1

Question 1

1.1 Define the secondary standard of measurement. (2)

1.2 Explain the controlling function of an instrument. (2)

1.3 Define the reproducibility of an instrument. (2)

1.4 Identify the following instrumentation symbol: (2) TRC

Question 2

2.1 A column of liquid in a vertical tank is 0,01 meter high and the liquid has

a density of 1100 kg/cubic meter. The tank has an internal diameter of

1 centimetre.

(a) Calculate the pressure exerted by the column of liquid, in pascal. (2)

(b) Calculate the force exerted by the column of liquid, in newton. (2)

2.2 With the aid of a sketch, derive an equation that can be used to determine

pressure with an inclined manometer. All the symbols that are used, must

be shown on the sketch. (4)

2.3 The inclined limb of an inclined manometer, forms an angle of 30 degrees

with respect to the horizontal plane. The liquid in the manometer has a

relative density of 1,9. The cistern of the manometer has a diameter of

10 centimetre and the inclined tube a diameter of 1 centimetre. The reading (L)

on the inclined limb is 45 centimetre.

(a) Calculate the applied pressure on the manometer in kilopascal. (3)

(b) Calculate the new density of the manometer liquid if the applied pressure

must be increased by 500 pascal and the manometer reading must stay

the same. (3)

2.4 Give the advantages and the disadvantages of transformer oil, when used as

a manometer liquid. (4)

2.5 Calculate the mass of the mass pieces of the hydrostatic test balance with a

piston diameter of 2 centimetre, to apply a pressure of 100 kilopascal to a

pressure gauge. The mass of the platform together with the piston is

500 gram. (3)

Question 3

3.1 Define the following flow terms:

volumetric flow, rate of flow, potential energy, kinetic energy and pressure energy. (10)

3.2 Sketch and describe the operation of a Doppler flow meter. (5)

3.3 Sketch and describe the operation of a rotameter used to determine the flow rate

in a flow line. (6)


Process Instrumentation I EIPIN1 Unit 1 Final Assessment 6 October 2006 Memorandum Page 1

Process Instrumentation I EIPIN1 Unit 1 Final Assessment 6 October 2006 Memorandum

1.1 Secondary standards are employed in industry [1]

as reference for calibrating high-accuracy

equipment and components. Calibration and comparison are done periodically by the involved

industries against the primary standards maintained in the national standards labs. The main

function of the secondary standards is to verify the accuracy of working standards. [1]

(2)

1.2 This is one of the most important functions of an instrument, especially in the field of

industrial control processes. In this case, the information provided by the instrument is used by

the control system to control the original measured quantity. (2)

1.3 Reproducibility is the closeness of the instrument readings when the same input [1]

is applied

under different conditions over a long period of time. [1]

(2)

1.4 Temperature recording controller, [1]

mounted on board. [1]

(2)

[8]

2.1 a) Pressure = �gh = 1100×9.81×0.01 = 107.9 Pa. (2)

b) P = F/A � F = PA = 107.9×[�×(1×10-2

)2/4] = 8.474 mN. (2)

2.2 Equating pressures in the XY plane:

P1 = P2 + �(h+d)g [½]

…….…..……… (1)

and with mercury incompressible:

A1d = A2L � d =

1A

2AL

[½] …….….... (2)

Also in triangle abc:

sin� = h/L � h = Lsin� [½]

…….….... (3)

(2) en (3) in (1):

P1=P2+� ��

�

�� L

1A

2ALsin g

�P1 – P2 = �Lg ��

�

��

1A

2Asin

[½] (4)

c b

a

A1

L

A2

ZL

d

�

P1

P2

�

Sketch

2 marks

h

X Y

2.3 a) P1 – P2 = �Lg(sin� + A1/A2) [1]

= 1900×0.45×9.81×(sin30° + 1/100) [1]

= 4278 Pa. [1]

(3)

b) � = (P1 – P2)/[Lg(sin� + A1/A2)] [1]

= 4778/(0.45×9.81×0.51) [1]

= 2122 kg/m3 [1]

(3)

2.4 Advantages: Low density for measuring small pressure differences. [1]

Unaffected by ammonia. [1]

Can be easily seen. [1]

Does not readily evaporate. [1]

Disadvantages: Tends to cling to inside of tubes. [1]

Density of transformer oil varies. [1]

(4)

2.5 Pressure = � �

� �pistonprimary of Area

pistonprimary and platform ofweight masspieces ofWeight � [½]

�100�103 =

��

��

� �

��

��

4

2)2-10(2�

9.81)3-10(500 9.81m

[½]

�(100�103)�(314.2�10

-6) = 9.81m + 4.905

�9.81m = 31.42 – 4.905 = 26.52 � m = 2.703 kg [2]

(3)

[21]


3.1 Volumetric flow is the total volume of a liquid or gas passing a given point over a certain

period of time, and is measured in cubic meter (m3). (2)

Rate of flow is the volume of a liquid or gas passing a given point per unit time, and is

measured in cubic meter per second (m3/s). (2)

Potential energy is the energy that a liquid has by virtue of its height above a given plane. The

potential energy per unit volume, equals �gh joule. (2)

Kinetic energy is the energy a liquid has by virtue of its motion. The kinetic energy per unit

volume equals ½�v2 joule. (2)

Pressure energy is the energy which a liquid has by virtue of its internal pressure. The

pressure energy per unit volume equals p joule. (2)

3.2 Doppler flow meters use the well

known Doppler frequency shift effect,

to determine the flow velocity of a

stream. [½]

In order to operate, the

liquid must contain some small

particles or bubbles. [½]

Ultrasonic

sound waves are transmitted at an

angle into the flow, by an ultrasonic

transmitter, [½]

and reflected back by

the moving bubbles or particles in the

stream. [½]

The receiver picks up the

reflected waves at a higher frequency

than the transmission frequency [½]

and the flow velocity is a function of

the frequency difference between

the received and transmitted

frequencies. [½]

(5)

Piezoelectric crystals

Receiver

Bubbles or solid particles

v

Transmitter

Sketch: 2 marks

3.3 The rotameter (also called a variable area flow meter)

consists of a gradually tapered transparent tube, [½]

mounted vertically in a frame with the large end up. [½]

The fluid flows upward through the tube and a metal

displacer or float, is suspended in the fluid. [½]

The

float is the indicating element and the reading is taken

on the scale in line with the top of the float. [½]

The

position in the tube where the float reaches

equilibrium, depends on the flow rate of the fluid. [½]

The greater the flow rate, the further up the tube the

float rises. [½]

The tube is often made of high strength

glass to allow for direct observation of the float

position, [½]

but if greater strength is required or if the

liquid is very dark or dirty, a metal tube is used and the

float position detected externally. [½]

(6) Flow

Tapered

tube

Scale

Float

(displacer)

Sketch: 2 marks

[21]

Process Instrumentation I EIPIN1 Unit 2 Final Assessment 3 November 2006 Page 1

Question 1

1.1 Distinguish between contact and non-contact level metering. (2)

1.2 Sketch and describe the operation of a ball float level meter. (5)

1.3 The level of a volatile liquid in a

closed container, is measured with

the aid of a U tube manometer, as

shown in Figure 1. The maximum

level of the liquid in the container is

5 meter. The relative density of the

liquid in the container is 0,9. The

manometer liquid is mercury with a

relative density of 13,6. The zero

level of the manometer, is 0.5 meter

below the bottom of the container.

Calculate the level H, of the liquid in

the container, if the manometer

reading is 0.25 meter. (4)

0.25 m

5 m

�=13.6

�=0.9 H

Zero line

0.5 m

Figure 1

1.4 State the disadvantages of a bubbler system used for level measurement. (4)

Question 2

2.1 Define the following fixed points on the international temperature scale:

(a) Ice point. (b) Silver point. (4)

2.2 Sketch and describe the operation of a mercury in steel thermometer as used

for the measurement of temperature. (5)

2.3 Draw a labelled circuit diagram to illustrate the three wire method that is used

to compensate for ambient temperature when measuring temperature with a

resistance thermometer. (3)

2.4 A Wheatstone bridge is used to measure temperature

with a resistance thermometer RT, as shown in

Figure 2. The three fixed resistors have a resistance

of 100 � each, and the bridge is powered by a 10 V

battery. When the temperature around the

thermometer is 0 °C, the resistance of RT is 100 �

and the bridge voltage reading is V = 0 volt. When

the temperature of RT is increased, the voltmeter

10V

– +

V

100�100�

100� RT

Figure 2

reading V, increases to 1 volt. Assume that the temperature coefficient of

resistance of RT is 0.00391 /°C and that the resistance change of RT with

temperature, is described by the equation Rt = Ro(1 + �ot). Calculate the

temperature of RT when the voltmeter reading is 1 V. (5)

2.5 State the thermocouple law of intermediate metals. (2)

2.6 Give the positive element material, the negative element material and the

temperature range of a type E thermocouple. (3)

.................... / Page 2

Process Instrumentation I EIPIN1 Unit 2 Final Assessment 3 November 2006 Page 2

Question 3

3.1 Define the following concepts with respect to a proportional only control system:

(a) Proportional control law. (1) (b) Proportional gain. (1)

(c) Proportional band. (1) (d) Offset. (1)

3.2 Name the two kinds of delays (lags) that may be identified when a system is

subjected to a step input. (2)

3.3 The set point of a proportional only control

system is 50%. The behaviour of the measured

value M, after a disturbance, is shown in

Figure 3. Sketch a graph of the possible

behaviour of the measured value, if the

disturbance occurred while the controller’s

integral control function, was also active. (2)

Time 40%

50%

M Disturbance

Figure 3

3.4 The output of a proportional only controller, changes by 20%, when the error

changes by 15%. Calculate the proportional band setting of the controller. (2)

3.5 Draw a circuit diagram of the integral (I) block of an electronic PID controller.

Give the expression of the output of the I block in terms of the error input

signal E. (3)

TOTAL 50

---ooo000ooo---

Process Instrumentation I EIPIN1 Unit 2 Final Assessment 3 November 2006 Memorandum Page 1

Question 1

1.1 A contact type device, such as a float, makes physical contact with the liquid in the container,

in order to determine the level. [1]

A non-contact device, such as ultrasonic or radar, does not

require contact with the material in the container to measure the level. [1]

(2)

1.2 Ball float: The float is attached to a

rod and rotary shaft, operating

through a packing and bearing in

the container wall, to the level

indicator as indicated in the sketch.

Practical considerations, limit the

shaft rotation to ± 30º from the

horizontal, and therefore the range

of the instrument as well. [3] (5)

Float

Rotary shaft

Packing and

bearing

Level

indicator

[2]

0.25m

5 m

�=13.6

�=0.9 H

Zero line

0.5 m

Y X

1.3 PX = PY

�900(H+0.5-0.125)g+13600�0.25g = 900�5.625g

�900(H+0.375) + 3400 = 5062.5

�900H + 337.5 + 3400 = 5062.5

�H = 1.472 m (4)

1.4 Disadvantages of the bubbler system:

a) the liquid’s density, influences measurement accuracy. [1]

b) the need for compressed air or gas. [1]

c) the end of the dip tube may become plugged or clogged. [1]

and the dip tube must periodically be purged. [1]

(4)

[15]

Question 2

2.1 a) The ice point: The melting point of pure ice [1]

- 0 °C. [1]

(2)

b) The silver point: The melting point of silver [1]

- 961.78 °C. [1]

(2)

2.2 The mercury in steel thermometer system, allows for rugged

construction and is used extensively in industrial applications.

The thermometer consists of a steel bulb, a steel capillary tube

and Bourdon tube, as shown in the sketch. An advantage of the

mercury in steel thermometer is that measurements can be taken

a distance away from the application, as the steel tube can be

made fairly long and flexible . The whole system is completely

filled with mercury under pressure and sealed off. When the

temperature around the bulb increases, the mercury inside the

bulb will expand. The effect of the mercury trying to increase its

volume within a confined space, will be an increase in pressure,

transmitted via the capillary tube, to the coiled Bourdon tube.

The increase in mercury volume and pressure inside the coiled

Bourdon tube, will result in the Bourdon tube starting to uncoil,

proportional to the temperature. A pointer, linked to the free end

of the Bourdon tube, will subsequently move over the scale to

indicate the temperature. [3] (5)

Steel bulb [½]

Mercury [1]

Steel tube [½]

Pointer

and scale[½]

Bourdon

tube [1]

[2]

Process Instrumentation I EIPIN1 Unit 2 Final Assessment 3 November 2006 Memorandum Page 2

2.3

(3)

Rlead

Rlead

RT

R2

R1

E V

R3 RTD – 1 mark 3 lead wires – 1 mark

Rlead

Wheatstone bridge (R1, R2, R3 and E)

Voltmeter connected to middle Rlead – 1 mark

2.4 VBC = (100/200)�10 = 5 V and V = VAB = 1 V

�VAC = VAB + VBC = 1 + 5 = 6 V [1]

�100RT

RT

��10 = 6 � 10RT = 6(RT+100)

�RT = 150 � [2]

�150 = 100(1 + 0.00391t) � 1 + 0.00391t = 1.5

�0.00391t = 0.5 � t = 127.9 °C [2]

(5)

VBC

B 10V

– +

V

100� 100�

100� RT

A

VAC

C

2.5 The law of intermediate metals states that a (third metal may be inserted into a

thermocouple system without affecting the emf generated,) [1]

(if, and only if, the

junctions with the third metal are kept at the same temperature.) [1]

(2)

2.6 Type Positive element Negative element Temperature range (°C)

E Chromel [1]

Constantan [1]

-200 to 800 [1]

(3)

[22]

Question 3

3.1 a) Proportional control: A control strategy in which the controller output is proportional to the

magnitude of the error. {C = KPE + R = (100/PB)�(S-M) + R} (1)

b) Proportional gain: Ratio of controller output change to error value change �C/�E. (1)

c) Proportional band: The error range that causes 100 % change in controller output. (1)

d) Offset: The steady state difference between the set point and the measured value. (1)

3.2 Dead time lag [1]

and first order lag. [1]

(2)

3.3

or

(2) Time

40%

50%

M Disturbance

Time 40%

50%

M Disturbance

3.4 KP = �C/�E = 20/15 = 1.333 [1]

3.5

�PB = 100/KP = 100/1.333 = 75% [1]

(2)

(3)

E

CI [1]

VI=- �Edt

IC

IR

1 [1]

RI [1]

VI

[13]


Question 1 State the base SI units for mass, current and luminous intensity. (3)

Question 2 Name the instrument parts specified as variable conversion elements. (2)

Question 3 Define the repeatability of an instrument. (2)

Question 4 Define random errors that may occur during measurement. (3)

Question 5 Identify the measured variable and instrument

function, for the instrument symbol shown in Figure 1. (2)

Question 6 Draw the instrument symbol for an orifice plate. (1)

PRC Figure 1

Question 7 Define atmospheric pressure and give the standard value (pascal). (2)

Question 8

The container in Figure 2 has a cross sectional area of A meter2

and is partially filled with a liquid of density � kilogram/meter3,

to a height of h meter. Starting with the expressions for the

volume and mass of the liquid, show that the pressure exerted by

the liquid on the bottom of the container, is given by P = �hg,

where g is the gravitational acceleration in meter/second2. (4)

P h

A Figure 2

Question 9 Convert a pressure of 15 kPa into a pressure expressed in meter water. (2) P1 P2 Question 10

A mercury (relative density of 13.6) u-tube

manometer, is shown in Figure 3. The left hand

leg is filled to 0.6 m and the right hand leg to

0.2 m with a liquid with relative density of 1,6.

Calculate the pressure difference, P1 – P2,

applied across the manometer. (3)

�=13.6

� = 1.6 0.6 m

0.2 m

Figure 3

Question 11 Draw a labelled sketch of pneumatic differential pressure transmitter. (6)

Question 12 Give an expression for the gauge factor (GF) of a strain gauge. (2)

Question 13 Define flow rate of a liquid and give the SI unit for flow rate. (2)

Question 14 Explain the significance and importance of the Reynolds number. (2)

Question 15 In Figure 4, a restricted

horizontal flow line is shown. The

pressure difference, p1 - p2, is measured

by taking the reading h, as shown in

Figure 4. Use Bernoulli’s theorem and

the principle of mass flow continuity,

to derive the flow equation, q = k h . (7)

v2 v1

p1 p2 q

h

� � A1 A2

Figure 4

Question 16 Sketch the configuration, including dimensions and labels, when

radius taps are used for flow rate measurement with an orifice plate. (3)

Question 17 Draw a labelled sketch of a magnetic flow meter (magmeter). (4)



1. Mass: kilogram [1]

Current: ampere [1]

Luminous intensity: candela [1]

[3]

[2] 2. Primary element (or bulb) [1]

Secondary element (or Bourdon tube) [1]

3. Repeatability is the closeness [½]

of the instrument readings when the same input [½]

is

applied (repetitively over a short period of time) [½]

with the same conditions. [½]

[2]

4. Random errors occur because of unknown and unpredictable variations [1]

that exist in all

measurement situations. This results in slightly different values [1]

obtained for each

repeated measurement (scattered evenly about the mean value) of the same [1]

input. [3]

[2] 5. Pressure [1]

Recording controller [1]

6.

7. Atmospheric pressure is the absolute pressure caused by the weight of the earth’s

atmosphere. [1]

Standard atmospheric pressure at sea level is 101326 pascal. [1]

PRC [1]

[2]

A

P

h 8. Volume of the liquid = V = Ah.

[1] Mass of the liquid = m = Ah�.

[1]

Weight of the liquid = w = mg = (Ah�)�g. [1]

Pressure on the bottom of container due to weight of the liquid: [4] P = w�A = Ah�g/A = �hg

[1]

P1 P2

0.4

0.2 m

�=13.6

0.6�=1.6

9. P = �hg � 15000 = 1000h×9.81 � h = 1.529 m [2]

[2]

10. P1 + 1600�0.6�9.81 = P2 + 1600�0.2�9.81+13600�0.4�9.81

�P1+9418 = P2+56505 � P1-P2 = 56505 – 9418 = 47087 Pa [3]

(=47.09kPa) [3]

11.

12. GF = (�R/R)/(��/�) = (�R/R)/&, 13. Flowrate is the volume of a liquid or gas passing

a given point per unit time, [1]

and is measured

in cubic meter per second (m3/s).

14. For Re under 2000 the flow is streamlined [1]

while at

Re over 3000, the flow becomes fully turbulent.[1]

16. 17.

D [½]

½D[½]High pres-

sure tap [½]

Flow [½]

Low pres-

sure tap [½]

D [½]

High pressure (P1)

input [½]

Nozzle [½]

Flapper [½]

Pivot point

(range wheel

adjust) [½]

Range bar [½]

Output Po [½]

Feedback

bellows [½]

Zero adjust [½]

Pivo[½]

t and seal Force bar

[½]

Diaphragm

capsule [½]

Cross

flexure [¼]

Capsule

flexure [¼]

Low pressure (P2)

input [½]

Air supply [½]

Pilot relay [½]

Restriction [½]

15.

From Bernoulli’s law:

½�v12+p1=½�v2

2+ p2

[1] ……...... (a)

Flow continuity demands: A1v1 = A2v2

� v1 = (A2/A1)v2 [1]

………....…. (b)

(b) in (a): ½�(A2/A1)v22+p1=½�v2

2+p2

� v22 = 2(p1-p2)/�[1-(A2/A1)

2]

�v2= ])/A(A-[1)/p2(p 2

1221 ��

[1] .. (c)

But p1 – p2 = �hg [1]

……..........…... (d)

(d) in (c): v2= ])/A(A-2gh/[1 2

12

[1] . (e)

Also q=A2v2 [1]

………….….…....… (f)

From (f) and (e):

q = A2 ])/A(A-2gh/[1 2

12 …... (g)

[note: 1 mark for either simplified v2


Defining k=A2 ])/A(A2g/[1 2

12� [1]

in Equation (g): q = k h .

v2 v1

p1 p2 q

h

� � A1 A2

[7]

[6]

/8

[2]

[2]

[2]

Electrodes [1]

Magnet coils [1]

Flow

v [1]

[4]

/5

D [1]

B [1]

[3]

Process Instrumentation I EIPIN1 Unit 2 First Assessment 4 May 2007 Page 1

Question 1 Draw a labelled sketch of a flexure tube (torque tube) displacer level meter. (5)

Question 2

The level of a volatile liquid in a closed container, is

measured with the aid of a U tube manometer, as

shown in Figure 1. The maximum level of the liquid

in the container is 5 meter. The relative density of the

liquid in the container is 0,8. The manometer liquid

is mercury with a relative density of 13,6. The zero

level of the manometer, is 0.5 meter below the

bottom of the container. Calculate the level H, of

the liquid in the container, if the manometer reading

is 0.2 meter. (4) Figure 1

0.2 m

5 m �=0.8 H

�=13.6

Zero line

0.5 m

Question 3 Convert 50 degrees Fahrenheit to Rankine, degrees Celsius and Kelvin. (4)

Question 4 Define the silver point and gold point on the international temperature scale. (2)

Question 5 Draw a labelled sketch of a vapour pressure thermometer. (4)

Question 6 A resistor thermometer measures 100 � at 0 °C, and 145 � at 100 °C.

Assuming that the relationship between resistance and temperature is described by

the linear equation, Rt = R0(1 + �0t), calculate:

a) The resistance of the thermometer at 150 °C. (4)

b) The temperature when the resistance of the thermometer is 200 �. (2)

Question 7 State the thermocouple law of intermediate metals. (2)

Question 8 Give the positive element material, the negative element material and

the temperature range of a type S thermocouple. (3)

Question 9 A water level control system that aims

to keep the water level in the container half full (50%)

by regulating the inflow to compensate for changes

in the outflow, is shown in Figure 2. Explain the

following concepts regarding the system in Figure 2:

Container

Level

detector

and

controller

Inflow

valve

OutflowWater inlet

Inflow

a) Controlled variable. (1)

b) Manipulated variable. (1)

c) Disturbance variable. (1)

d) Desired value. (1)

e) Measured value. (1)

f) Error value. (1)

Question 10 Define feedback and feedforward control. (2)

Figure 2

Question 11 Sketch a graph of the output C (in %) versus the input error E (in %), for

a reverse acting proportional controller with proportional band of 50% and bias of 50%. (2)

Question 12 A digital PI controller is programmed with a proportional gain KP = 1,

an integral gain KI = 0.1, a set point S = 50% and a sampling period of T = 1 second.

The controller obtains the following sequence of samples for the measured variable M,

M(0) = 40%, M(1) = 30%, M(2) = 20% and M(3) = 30%.

a) Calculate the corresponding error values E(0), E(1), E(2) and E(3). (2)

b) Calculate the proportional part (P) of the controller output after M(3) was sampled. (1)

c) Calculate the integral part (I) of the controller output after M(3) was sampled. (2)

Question 13 Name the types of valves, that use a linear movement to operate. (5)



1. 2.

0.2m

5 m

PX = PY

�=0.8 H

Zero line

0.5 m

�=13.6

Y X

Displacer [1]

Chain [1]

Torque arm [1]

Torque tube [1]

Torque tube

flange [½]

Torque rod [1]

Level indicator [½]

�800(H+0.5-0.1)g +13600�0.2g

= 800�5.6g [1]

�800(H+0.4) + 2720 = 4480

�800H + 320 + 2720 = 4480

�800H = 1440 � H = 1.8 m [3]

[5]

/6 [4]

3. C = 5/9[F – 32] F = 5/9×[50 – 32] = 5/9×18 = 10 °C [2]

[4] R = F + 460 = 50 + 460 = 510 R

[1] K = C + 273 = 10 + 273 = 283 K

[1]

[2] 4. Silver: melting point of silver [½]

– 961.78 °C [½]

Gold: melting point of gold [½]

– 1064.18 °C [½]

5.

6. a) �o = (R100-R0)/100R0 = (145-100)/100×100 = 0.0045/°C [2]

RT = Ro(1 + �ot) = 100(1 + 0.0045×150) = 167.5 � [2]

(4)

b) RT = Ro(1 + �ot) � 200 = 100(1 + 0.0045t)

�0.0045t = 1 � t = 222.2 °C (2)

7. The law of intermediate metals states that a (third metal

may be inserted into a thermocouple system without affec-

ting the emf generated,) [1]

(if, and only if, the junctions

with the third metal are kept at the same temperature.) [1]

8

. Type

Positive

element

Negative

element

Temperature

range (°C)

S

90% Platinum

10% Rhodium [1] Platinum

[1] 0 to 1500

[1]

Vapour [1]

Steel bulb [½]

Volatile

liquid [1]

Steel tube [½]

Pointer

and scale[½]

Bourdon

tube [1]

[6]

[2]

[3]

[4]

/4½

9. a) Controlled variable: Water level (1) b) Manipulated variable: Water inflow (1)

c) Disturbance variable: Water outflow (1) d) Desired value: Level = 50% (1) [6] e) Measured value: Current water level (1) f) Error value: Desired val. –measured val. (1)

10. Feedback control: Measure the controlled variable to determine the control strategy. [1]

Feedforward control: Measure disturbance variables to determine the control strategy. [1]

[2]

12. a) E(0) = S – M(0) = 50 – 40 = 10% [½]

E(1) = S – M(1) = 50 – 30 = 20% [½]

E(2) = S – M(2) = 50 – 20 = 30% [½]

E(3) = S – M(3) = 50 – 30 = 20% [½]

(2)

b) P = KPE(3) = 1×20 = 20% (1)

c) I = KI[TE(0) + TE(1) + TE(2)] [1]

= 0.1×[1×10 + 1×20 + 1×30]

= 0.1×60 = 6% [1]

(2)

E

t 1 2 3

10 M(0)

M(1)

M(2)

M(3) 20

0

30

[5]

11.

[½]

[½]

C (%)

100%

25% [½]

E(%)

R=50%

-25% [½]

0%

[2]

[5] 13. Globe valve

[1] Gate valve

[1] Needle valve

[1] Pinch valve

[1] Diaphragm valve

[1]

Process Instrumentation I EIPIN1 Unit 1 Final Assessment 20 April 2007 Page 1

Question 1 Define measurement of a process variable. (2)

Question 2 State the basic functions of an instrument. (3)


Question 4 Define the error of hysteresis in an instrument. (3)

Question 5 Identify the instrument signal shown in Figure 1. (1)

Figure 1

Question 6 Define the density of a substance and give the SI unit for density. (2)

Question 7 With the aid of a labelled sketch, derive the expression that is used to

determine pressure with a well type manometer. (4)

Question 8 Name three manometer liquids and give their respective relative densities. (3)

Question 9 Draw a labelled sketch of a C-type Bourdon tube pressure gauge. (4)

Question 10 Draw a labelled sketch to show how a bellows element may be used to

measure gauge pressure. (2)

Question 11 A dead weight tester has a primary piston with a diameter of 1 cm.

The mass of the platform and primary piston together, is 500 gram. Calculate the

mass m, of the mass pieces, that must be placed on the platform to check a gauge

at 100 kPa. (3)

Question 12 Define viscosity of a liquid and give the SI unit for viscosity. (2)

Question 13 State Bernoulli’s law. (3)

Question 14 Draw a labelled sketch of a Pitot tube flow meter and give the

equation for flow velocity when using a Pitot tube. (4)

Question 15 A cylindrical object, suspended in a horizontal flow stream, has a

cross sectional area of 4�10-3

m2, which is positioned perpendicular to the flow.

If the object experiences an upstream pressure of 500 Pa and a downstream

pressure of 300 Pa, calculate the force exerted on the object, by the flow. (3)

Question 16 Name the three main types of orifice plates used. (3)

Question 17

a) Draw a labelled sketch of an electronic target flow meter. (4)

b) Give the operational equation that is used to calculate the flow rate q, from the

measurements made with a target flow meter. (2)



1. Measurement is defined as the determination of the existence [1]

or magnitude [1]

of a variable for [2] monitoring and controlling purposes.

2. Indicating function [1]

Recording function [1]

Controlling function [1]

[3]

[2] 3. Sensitivity is the rate of change [1]

of the output [½]

of a system with respect to input [½]

changes.


between the readings obtained when a (given value of the measured [3]

[1] variable is approached from below)

[1] and when the (same value is approached from above.)

[1]

5. Pneumatic signal.

6. Density of a substance is defined as the mass of a unit volume [1]

of a substance. [2] The SI unit is kilogram per cubic meter (kg/m

3).

[1]

7. P1 = P2 + �(h+d)g [1]

…….. (1)

A1d = A2h � d = 1

A

2A

h [1]

.. (2)

A1

P1

ZL

P2

d

h

Sketch:

1 mark

�

Transformer oil [½]

� = 0.864 [½]

Aniline [½]

� = 1.025 [½]

Dibutylphathalate [½]

� = 1.047 [½]

Carbon Tetrachloride [½]

� = 1.605 [½]

Tetrabromoethane [½]

� = 2.964 [½]

Bromoform [½]

� = 2.9 [½]

Mercury [½]

� = 13.6 [½]

8.

(2) in (1):

P1 = P2 + � ��

�� h

1A2A

h g [1]

[3]

/6A2 �P1–P2 = �hg(1 + A2/A1) [4]

Atmospheric

pressure [½]

P1 (Gauge

pressure) [½]

Bellows [½]

Pressure connection[½]

9. Pointer and scale

[½]

Pivot point[½]

Bourdon tube [1]

Pinion gear [½]

Sector gear[½]

Adjustable link[½]

Range adjust[½]

Hairspring [½]

10.

[2] Pressure indication [½]

P =pistonprimary of Area

piston prim. & platfrm masspcs,Weight

�100�103=22-

3-

)10(1/4)(

9.81)10(500 9.81m

��

�� [1]

�(100�103)�(78.54�10-6) = 9.81m + 4.905

�9.81m = 7.854 – 4.905 � 9.81m = 2.949

�m = 0.3006 kg. [2] = 300.6 gm

11.

[4]

/5

[3]

12. Viscosity is a measure of a fluid's resistance to flow. [1]

SI unit: poiseuille (PI). [1]

. [2]13. If an (incompressible fluid is in a streamlined flow with no friction,)

[½] the sum

[½] of the




per unit volume, is constant [½]

.

14. 17. a) Static pressure [1]

Stagnation pressure [1]

b) q = 2

d

8F4

)2

d2

�(D

��

� (2)

(4)

/5

Electronics

housing [½]

Target [1]

Force bar [1]

Pivot and seal [1]

Flow [½]

Strain gauge [1]

Impact hole [1]

v [½]

v =�

)statpstag2(p �[1]

[4]

/4½

[3]

15. F = PA = (500 – 300)×(4×10-3

) [1]

= 0.8 N [2]

16. Concentric, [1]

eccentric [1]

& [6]

segmental [1]

orifice plates. [3]


Question 1 Draw a labelled sketch of a chain float level meter. (4)

Question 2 During calibration of a Flexure tube displacer (torque tube) displacer

type level meter, it was found that the torque registered by the meter was 30 N-m,

when the tank was empty. If the length of the torque arm is 0.15 m, calculate the

torque that will be measured when the displacer, with a volume of 0.005 m3, is

fully immersed in the process fluid with density 1000 kg/m3. (4)

Question 3 Define temperature and give the SI unit for temperature. (2)

Question 4 Convert 537 Rankine to Kelvin. (4)

Question 5 Draw a labelled sketch of a liquid in glass thermometer. (4)

Question 6 A platinum resistance thermometer has a resistance of 100 � at 0 °C

and a resistance of 139.1 � at 100 °C. Calculate the temperature coefficient of

resistance (TCR) of the thermometer. (2)

Question 7 Draw a labelled circuit diagram to illustrate the four wire method that

is used to compensate for ambient temperatures when measuring temperature with

a resistance thermometer. (3)

Question 8 Define the Seebeck effect. (3) Table 1

Question 9 In Figure 1, a type K

thermocouple is shown, which is

used to measure an unknown

temperature T. The voltmeter

reading is 2390 microvolt, and the

temperature of the thermocouple

cold junction is 24 °C. An excerpt

from the type K thermoelectric

voltage table (in microvolt) for

temperatures in degrees Celsius, is

given in Table 1. Use Table 1 to

determine the temperature T of the

hot junction. (3)

°C 0 1 2 3 4 5 6 7 8 9

0 0 39 79 119 158 198 238 277 317 357

10 397 437 477 517 557 597 637 677 718 758

20 798 838 879 919 960 1000 1041 1081 1122 1163

30 1203 1244 1285 1326 1366 1407 1448 1489 1530 1571

40 1612 1653 1694 1735 1776 1817 1858 1899 1941 1982

50 2023 2064 2106 2147 2188 2230 2271 2312 2354 2395

60 2436 2478 2519 2561 2602 2644 2685 2727 2768 2810

70 2851 2893 2934 2976 3017 3059 3100 3142 3184 3225

80 3267 3308 3350 3391 3433 3474 3516 3557 3599 3640

90 3682 3723 3765 3806 3848 3889 3931 3972 4013 4055

100 4096 4138 4179 4220 4262 4303 4344 4385 4427 4468

2390 �V Figure 1 24°C T

Steam

control

valve

Thermometer

Hot water Steam outlet

TIC

Steam

supply

Cold water

Figure 2

Question 10 A heat exchanger that uses

steam to heat cold water and aims to deliver

hot water at a fixed temperature of 60°C, is

shown in Figure 2. Identify or explain the

following control variables and values, with

reference to the system in Figure 2:

(For example: Controlled variable: Temperature of hot water delivered)

a) Manipulated variable. (1) b) Disturbance variable. (1) c) Desired value. (1)

d) Measured value. (1) e) Error value. (1)

Question 11 Define open loop and closed loop control systems. (2)

Question 12 Define integral control reset time. (2)

Question 13 Draw a labelled sketch of a pneumatic proportional plus derivative controller. (4)

Question 14 Explain the valve term: ‘throttling’. (2)

Question 15 Draw a labelled sketch of a reverse acting pneumatic control globe valve. (6)



Needle valve rate adj. [½]

Set point S [½]

Reset

bellows [½]

Beam[½]

Bias value R [½]

Air

supply [½]

Flapper

and

nozzle [½]


Proportional

(feedback)

bellows[½]

Pilot

relay[½]

Controller

output C [½]

1.

3. Temperature is defined as the

degree of heat of a body. [1]

The SI unit is Kelvin (K). [1]

5. 7. 0

�

10. a) Manipulated variable:Steam flow. (1) 15.

b) Disturb. variable:Hot water demand

(steam pressure., ambient temp.). (1)

c) Desired val.:Required temp.-60°C. (1)

d) Meas. value:Thermometer reading. (1)

e) Error value:Difference between req.

temp. and thermometer reading. (1)

11. Open loop system: The input to the

system is not determined by the output. [1]

Closed loop system: The input to the

system is determined by the output. [1]

12. Reset or repeat time:Time taken [¼]

for

the integral control action [½]

to equal [¼]

the proportional control action [½]

under

the influence of a constant error. [½]

13.

8. Seebeck effect:

If two dissimilar metals [1]

are joined together to form a closed loop, and if

one junction is kept at a different temperature [1]

from the other, an electro-

motive force [1]

is generated and electric current will flow in the closed loop.

Level

indicator [1]

Drum [1]

Chain [1]

Weight [1]

Float [1]

[2]

[3]

[3]

Voltmeter return

across RT - 1 mark

Current source I

1 mark

Rlead

4. R = F+460 � F = R–460 = 537–460 = 77 °F [1]

�C = 5/9(F – 32) = 9/5(77 – 32) = 25 °C [2]

�K = C + 273 = 25 + 273 = 298 K [1]

Rlead

Rlead

Rlead

I

a

c RT

d

b

M 4 leadwires plus

RTD – 1 mark

6. �0 = 1000R

R100R � [1]

= 100100

100139.1

��

= 0.00391 /°C [1]

[3] 9. 24 °C � 960 �V [1]

� ET = 2390 + 960 = 3350 �V [1]

� T = 82 °C [1]

Scale

(etched) [1]

Bore [1]

Bulb [1]

Lens front

capillary tube

(stem) [1]

Liquid

column [1]

14. Throttling occurs when

the valve stem position

is between closed and

open (0 > x > 1) and the

valve is busy regulating

the flow stream. [2]

[6]

/8

Spring nut [½]

Spring [½]

Diaphragm plate [½]

Plug [½]

Diaphragm [½]

Actuator [½]

Valve

body [½]

Seat [½]

Stem connector [½]

Travel indicator [½]

Stem [½]

Yoke [½]

Gland and packing [½]

Bonnet nut [½]

Bonnet [½]

Gasket [½]

2. Weight of displacer in empty tank:

T = Fr � F = T/r = 30/0.15 = 200 N [1]

Weight of displacer in full tank

= Weight of displacer in empty tank

–Weight loss of displacer in full tank

= 200 – 0.005×1000×9.81 = 200 – 49.05

= 150.95 N [2]

�Torque measured in full tankTfull

= 150.95×0.15 = 22.64 N-m [1]

[4][4]

/5

[4][2]

[4]

/5

[5]

[2]

[2]

[4]

/5½

Process Instrumentation I EIPIN1 Unit 1 First Assessment 02 September 2011 Page 1

Question 1 Give the SI units for time and amount of substance. (2)

Question 2 Explain the recording function of an instrument. (2)


Question 4 State the elements that may be identified in an instrument. (5)

Question 5 Define pressure and give the SI unit for pressure. (2)

Question 6 Assuming that the density of the atmosphere is a constant value of 1.2 kg/m3 and that the atmospheric pressure at sea level is 760 mm. mercury, calculate the height of the atmosphere above sea level. (3)

Question 7 You are requested to design a scale plate for a U-tube manometer that uses mercury, with relative density of 13.6, as manometer liquid. You are told that the maximum differential pressure to be measured, will be 100 kPa. From the zero line upward, the following values must be marked off on the scale plate: 25 kPa, 50 kPa, 75 kPa and 100 kPa. Calculate the distances from the zero line to each marking on the scale, and sketch the designed plate. (4)

Question 8 Draw labelled sketches to show how a bellows element may be used to measure: a) differential pressure (2) b) absolute pressure. (2)

Question 9 Draw a labelled sketch of a pneumatic differential pressure transmitter. (6)

Question 10 Define flow rate of a fluid and give the SI unit for flow rate. (2)

Question 11 State Bernoulli’s law (in words). (2)

Question 12 State three methods of positioning the high pressure and low pressure tap-points, that may be used when measuring flow rate with orifice plates. (3)

Question 13 Water flows through a horizontal pipe with cross sectional area of 510-3 m2. A circular object, facing the stream with an area of 210-3 m2, is placed in the flow, as shown in Figure 1. The force on the object is measured as 0.5 newton. Calculate the flow rate q of the water,

if the flow rate is given by: q =

2)1

/A2

(A1

)2

p1

2(p

2A ,

where p1-p2 is the pressure difference across the object, A2 is the restricted flow area, A1 is the unrestricted flow area (pipe area) and = 1000 kg/m3 (for water). (3)

Question 14 Sketch the configuration, including dimensions and labels, when flange taps are used for flow rate measurement with an orifice plate. (2)

Question 15 a) Draw a labelled sketch of a rotameter (variable area flowmeter). (4) b) Why does the displacer in a rotameter move upwards with increasing flow rate? (1)

Question 16 a)The Reynolds number for a flow condition is determined as 4000. Is the flow streamlined or turbulent? (1)

b) Explain the function of a flow straightener (straightening vane) in a pipe. (2) ---ooo000ooo--- Total: 50

q

Figure 1

Object area = 210-3 m2

p1 p2

F=0.5 N

Pipe area = 510-3 m2


1. Time: second [1] Amount of substance: mole [1] 2. An instrument may provide the information of the value of a quantity under

measurement against time [1] or some other variable, in the form of a written record, [1] usually on paper.

3. Drift is the change in instrument indication over time [1] while the input and ambient conditions [2] are constant. [1] 4. Primary element [1] Data transmission element [1] Secondary element [1] Manipulation element [1] [5] and Functioning element [1] 5. Pressure is defined as the force exerted over a unit area [1]. The SI unit is newton per square meter [2] (N/m2) or pascal (Pa). [1] 6. 1.2×hatm×g1 = 13600×0.76×g1 hatm = 8613 m1

[3]

7. P1 – P2 = hg. for P1-P2=100 kPa: 100103 = 13600h9.81 h = 750 mm. [1] Distance from zero line to 100 kPa marking = 375 mm. [1] [4] 8. a) Differential b) Absolute [4] 9.

[2][2]

High pressure (P1)input [½]

Air supply [½]Restriction [½]

Pilot relay [½]

Nozzle [½]

Flapper [½]

Pivot point(range wheel

adjust) [½]

Range bar [½]

Output Po [½]

Feedbackbellows [½]

Zero adjust [½]

Pivot and seal [½]Force bar [½]

Diaphragmcapsule [½]

Cross flexure [1/2]

Capsule flexure [1/2]

Low pressure (P2)input [½]

[6]

Zero line 0 kPa

25 kPa

50 kPa

75 kPa

187.5mm[½]

281.3mm[½]

375mm[½]

93.74mm[½]

High pressure

(P1) [½]

Low pressure (P2)

[½]


Bellows [½]

(2) High pressure


Bellows [½]

(P1) [½]

(2) High pressure

Vacuum [½]


Bellows [½]

(P1) [½]

(2)


10. Flowrate is the volume of a liquid or gas passing a given point per unit time, [1] and is measured [2] in cubic meter per second (m3/s). [1] 11. If an (incompressible fluid is in a streamlined flow with no friction,) [1] the sum [½] of the [2] pressure energy, [½] the kinetic energy [½] and potential energy [½] per unit volume [½] , is constant ½]. 12. Corner taps [1] Flange taps [1] Radius taps (D&D/2 or throat taps) [1] [3]/5 Vena-contracta taps [1] Pipe taps [1]

13. p1 – p2 = F/Aobject = 0.5/210-3 = 250 Pa. [1] and A2 = 510-3 - 210-3 = 310-3 [1]

q =

2)1

/A2

(A1

)2

p1

2(p

2A = (310-3)

2)105/103(11000

2502

33

[3] = (310-3)

2)6.0(11000

500=(310-3)

0.64

5.0=(310-3)0.8839=2.65210-3 m3/s [1]

14. 15.(a) [2] / 2½ 15.(b) When the flow rate increases, the pressure difference across the float will increase, [½] which will tend to push the float upwards. As the float moves upwards, the restricted flow area will increase [½] due to the tapered tube. This will allow the pressure difference to decrease to its original value where the float [5] will remain suspended in its new position. (1) 16.a)Turbulent.1 [2]b)To streamline a flow1, if the flow is turbulent for measurement purposes.1

Highpressure

tap [½]

Flow [½]

Low pressuretap [½]

25mm [½] 25mm [½]

Flow [1]

Float (displacer) [1]

Scale [1]

Tapered tube [1]

Process Instrumentation I EIPIN1 Unit 2 First Assessment 14 October 2011 Page 1

Question 1Distinguish between direct and indirect level measurement, and give one example for each method. (4)

Question 2Draw a labelled sketch of a magnetic float level meter (magnetic coupled float and follower). (4)

Question 3a) Make a labelled sketch of a gas filled thermometer. (4) b) State which gas is normally used in a gas filled thermometer. (1)

Question 4State the most frequently used method of level measurement. (2)

Question 5The level of a liquid in an open container, is measured with the aid of a well type manometer, as shown in Figure 1. The ratio of the tube area to the well area is 0.01 (A2/A1 = 0.01). The relative densityof the liquid in the container is 1 (=1) and the manometer liquid is mercury with a relative density of 13.6 (=13.6). The zero level of the manometer liquid, is 1 meter below the bottom of the container. Calculate the level H, of the liquid in the container, if the manometer reading h, is 0.3 meter. (4)

Question 6Name three common metals used in resistance thermometers. (3)

Question 7Give the positive element material, the negative element material and the temperature range of a type T thermocouple. (3)

Question 8 Convert 40 °C to degrees Fahrenheit, Kelvin and Rankine. (3)

Question 9 Sketch and describe the operation of mercury in steel thermometer as used for the measurement of temperature. (5)

Question 10 Define dead time (transportation lag) in a control system. (2)

Question 11Draw a fully labelled block diagram of a feedback control system. (5)

Question 12 Define integral control reset time (2)

Question 13 Draw a labelled sketch of a pneumatic proportional plus integral plus derivative controller . (5)

Question14 Draw the graphs for the inherent valve characteristics for a quick opening valve, a linear valve and an equal percentage valve . (3)


Figure 1

= 13.6

h=0.3m

H = 1

Zero line

1 m


1. Direct acting method involves measuring the height of the fluid directly. [1] can be dipstick, overflow pipe, float or sight glass[1] Indirect method, another variable is measured that correlate to the liquid level[1] it can be measuring the weight of a substance in the container, pressure exerted on the bottom of the container or transmitting the ultrasonic beam to the level surface[1]

2. 3. (a) /5 (b) Nitrogen gas. [1] 4. Pressure measurement method [2]

5 . Ignore d and equate pressures on the zero line PA + 1000×(H+1)×g = PA + 13600×0.3×g [1] H = 3.08 m [3] Ignore d, calculate P1 on zero line and use well type manometer equation P1 = Patm + 1000(H + 1)g and P2 = Patm

P1–P2=1000(H+1)g & P1-P2=hg(1+A2/A1): 1000×(H+1)×g = 136000.3g(1+0.01) [1]

H= 3.121 m [3] Include d and equate pressures in line with mercury meniscus in well: PA+1000(H+1+0.003)g = PA+13600(0.3+0.003)g[1] H = 3.118 Include d and use well type manometer equation: P1-P2=1000(H+1.003)g=13600(0.3)g(1+0.01)[1] H = 3.118 m 6. Platinum, [1] Copper [1] and Nickel [1]

7.

Type Positive element Negative element Temperature range (°C)

T Copper [1] Constantan [1] -200 to 350 [1]

8 F=5

9C+32=

5

940+32=72+32=104 °F [1] R=F+460=104+460=564 R [1] K=C+273=40+273=313 K[1]

[4]

[2]

[3]

Non-magnetic dip tube [1]

Doughnut float with outer magnet [1]

Level indicator [1]

Indicator rod [1]

Follower with inner magnet [1]

Pointer and scale[1]

Bourdontube [1]

Steel tube [1]

Steel bulb [1]

Gas [1] (Nitrogen)

P1

= 13.6

h=0.3m

H = 1

ZL

1 m

P2

PA PA

Level indicator [1]

d=(A2/A1)h=0.003m

[3]

[4]

[4]

[1]

[3]

[4]/5


Needle valve rate time adjustment [½]

Restriction [½]

Set point S [½]

Resetbellows [½]

Beam[½]


Air supply [½]

Flapper andnozzle [½]


Proportional(feedback) bellows[½]

Pilot relay[½]

Controller output C [½]

Needle valve [½] Reset time adjust

9. The mercury in steel thermometer system, allows for rugged construction and is used extensively in industrial applications. The thermometer consists of a steel bulb, a steel capillary tube and Bourdon tube, as shown in the sketch. An advantage of the mercury in steel thermometer is that measurements can be taken a distance away from the application, as the steel tube can be made fairly long and flexible . The whole system is completely filled with mercury under pressure and sealed off. When the temperature around the bulb increases, the mercury inside the bulb will expand. The effect of the mercury trying to increase its volume within a confined space, will be an increase in pressure, transmitted via the capillary tube, to the coiled Bourdon tube. The increase in mercury volume and pressure inside the coiled Bourdon tube, will result in the Bourdon tube starting to uncoil, proportional to the temperature. A pointer, linked to the free end of the Bourdon tube, will subsequently move over the scale to indicate the temperature. [3]

10. Delay due to the time it takes information or material to be transported [1] from one point to another. [1]

11.

12. Reset or repeat time: Time taken [¼]

for the integral control action [½]

to equal [¼] the proportional control action

[½] under the influence of a constant error. [½]

13. 14.

[5]

[2]

Pointer and scale[½]

Bourdon tube [1]

Steel tube [½]

Steel bulb [½]Mercury [1]

[2]

[2]

Measured value [½]

Output [½]Controlled variable [½}

Sensor [1]

Manipulatedvariable [½] Control

unit [1]

Error value [½]

Desired value [½] Process [1]

Disturbancevariables [½] Comparator [1]

[5]

[3]

[5]/6½

=%[1] x

Quick[1]

Linear[1]

0 1

f(x)

1

0

Process Instrumentation I EIPIN1 Unit 1 Final Assessment 23 September 2011 Page 1

Question 1 Define measurement of a process variable. (2)

Question 2 State the basic functions of an instrument. (3)


Question 4 Define the error of hysteresis in an instrument. (3)

Question 5 Identify the instrument signal shown in Figure 1. (1)

Question 6 Define the density of a substance and give the SI unit for density. (2)

Question 7 With the aid of a labelled sketch, derive the expression that is used to determine pressure with a well type manometer. (4)

Question 8 The reading h on a well type mercury ( = 13.6) manometer is 1 meter, when measuring a pressure of 135 kPa.

a) Calculate the ratio (A2/A1) of the tube area (A2) to the well area (A1). (3) b) Determine the change in level (d) that the well mercury experiences. (2)

Question 9 Draw a labeled sketch of a C-type Bourdon tube pressure gauge. (4)

Question 10 A dead weight tester has a primary piston with a diameter of 1 cm. The mass of the platform and primary piston together, is 500 gram. Calculate the mass m, of the mass pieces, that must be placed on the platform to check a gauge at 100 kPa. (3)

Question 11 Define viscosity of a liquid and give the SI unit for viscosity. (2)

Question 12 Define a streamlined flow and a turbulent flow of a stream. (4) Question 13 Draw a labelled sketch of a Pitot tube flow meter and give the equation for flow velocity when using a Pitot tube. (4)

Question 14 (a) Explain the purpose of a vent hole. (1) (b) Explain the purpose of a drain hole. (1)

Question 15 Name the three main types of orifice plates used. (3)

Question 16 a) Draw a labelled sketch of an electronic target flow meter. (4) b) Give the operational equation that is used to calculate the flow rate q, from the measurements made with a target flow meter. (2) ---ooo000ooo--- Total: 50

Figure 1

Process Instrumentation I EIPIN1 Unit 1 Final Assessment 23 September 2011 Memorandum Page 1

1. Measurement is defined as the determination of the existence [1] or magnitude [1] of a variable for monitoring and controlling purposes. 2. Indicating function [1] Recording function [1] Controlling function [1] 3. Sensitivity is the rate of change [1] of the output [½] of a system with respect to input [½] changes. 4. Hysteresis is the difference [1] between the readings obtained when a (given value of the measured variable is approached from below) [1] and when the (same value is approached from above.) [1] 5. Pneumatic signal. 6. Density of a substance is defined as the mass of a unit volume [1] of a substance. The SI unit is kilogram per cubic meter (kg/m3). [1]

7. P1 = P2 + (h+d)g [1/2] …….. (1)

A1d = A2h d = 1A2A

h [/21] .. (2)

(2) in (1):

P1 = P2 +

h

1A2A

h g [1]....(3)

P1–P2 = hg(1 + A2/A1)[1] ...(4)

8. a) P1 – P2 = hg(1 + A2/A1)

[1] 135103 = 1360019.81[1 + (A2/A1)] = 133416[1 + (A2/A1)] 1+(A2/A1) = 135103/133416 = 1.0119 (A2/A1) = 0.0119 [2]

b) d = (A2/A1)h [1] d = 0.01191 [5] = 0.0119 m = 11.9 mm. [1] 11. Viscosity is a measure of a fluid's resistance to flow. [1] SI unit: poiseuille (PI). [1]. 12. Streamlined flow: In a streamlined flow, all the particles in the liquid, flow in the same direction

and parallel to the walls of the pipe, and the streamlines are smooth. [2] Turbulent flow: In a turbulent flow, the particles in the stream, flow axially as well as [4] radially, and the streamlines are in a chaotic pattern of ever changing swirls and eddies. [2]

[2]

[3][2]

[3][1]

[2]

[4]

Pivot point[½]

Bourdon tube [1]

Pinion gear [½]

Hairspring [½]

Adjustable link[½]

Sector gear[½]

Pointer and scale [½]

Pressure connection[½]

Range adjust[½]

[4]/5

A1

P1

ZL

P2

d

A2

Sketch: 1 mark

h

9.

P =pistonprimary of Area

piston prim. & platfrm masspcs,Weight

100103=22-

3-

)10(1/4)(

9.81)10(500 9.81m

[1]

(100103)(78.5410-6) = 9.81m + 4.905 9.81m = 7.854 – 4.905 9.81m = 2.949 m = 0.3006 kg. [2] = 300.6 gm

10.

[3]

[2]

Process Instrumentation I EIPIN1 Unit 1 Final Assessment 23 September 2011 Memorandum Page 2

13. 16. a)

14. a) Vent holes are provided to prevent (gasses when transporting liquids) [1/2] to accumulate at the top [1/2]

the pipe on the upstream side of the orifice plate.

b) Drain holes are provided to prevent (solid particles in liquids) and (condensate in gasses) [1/2] to accumulate at the bottom [½] of the pipe on the upstream side of the orifice plate. 15. Concentric, [1] eccentric [1] & segmental [1] orifice plates.

b) q = 2d

8F4

)2d2π(D

(2)

Electronicshousing [½]

v =ρ

)statpstag2(p [1]

Static pressure [1] Stagnation pressure [1]

Impact hole [1]

v [½]

[4]/4½

[2]

[3]

Target [1]

Force bar [1]

Pivot and seal [1] Flow [½]

Strain gauge [1]

(4)/5

[6]

Process Instrumentation I EIPIN1 Unit 2 Final Assessment 28 October 2011 Page 1

Question 1 Give three types of level indicators which can be used with the float in level measurement. (3)

Question 2 Mention the advantages and disadvantages of using the differential pressure method to measure level in a container. (4)

Question 3 Explain the term wet leg system, used in a closed container to determine level. (2)

Question 4 Differential pressure level measurement in a closed vessel is fundamentally different from level measurement in an open vessel. Mention those differences. (4)

Question 5 Draw a labelled sketch of a bubble meter (gas flushing system) for level measurement (using a manometer) in an open container. (4)

Question 6 When designing a temperature measuring device, the two fixed points must be defined. Mention and explain those two fixed points. (4)

Question 7 The resistance thermometers are based on what principle. (2)

Question 8 The thermocouples are used to measure temperature. Name the three laws of thermocouples. (3)

Question 9 The following equation is provided for a type K thermocouple, to calculate temperature (t in °C) from emf (v in μV) in the temperature range 0 °C to 500 °C. Use the equation below to calculate the temperature when the emf is 2602 μV t = (2.508355×10-2)v + (7.860106×10-8)v2 – (2.503131×10-10)v3 + (8.315270×10-14)v4 – (1.228034×10-17)v5 + (9.804036×10-22)v6 – (4.413030×10-26)v7 + (1.057734×10-30)v8 – (1.052755×10-35)v9 (4)

Question 10 Mention the main advantage of using compensating leads with thermocouples to measure temperature. (2)

Question 11 There are three main values associated with the controlled variable in process control. Mention them. (3)

Question 12 With examples, show how direct acting and reverse acting can be used in process control. (4)

Question 13 Most processes exhibit time delays between their input and output. Mention and explain first order lag in a process. (2)

Question 14 Explain the following terms in process control, when using proportional control: Bias, Proportional gain and Proportional band. (3)

Question 15 Draw a circuit diagram of the derivative (D) block of an electronic proportional, integral and derivative controller. Give the expression of the output of

the D block, in terms of the error input signal E (4)

Question 16 What is the main function of the control valves as used in control systems. (2) ---ooo000ooo--- Total: 50


1 Any three Chain float, Ball float[1], Magnet float(Magnetic coupled float and follower)[1],

Magnetic float switch[1] and Flexure tube level meter[1]

2. Advantages: (a) The equipment measuring the differential pressure, can be externally installed or retrofitted to an existing vessel[1]. (b) It can be also be isolated safely from the process using block valves for maintenance and testing [1].

Disadvantages: a) Leak paths could be the cause of many problems[1] b) Measurement errors occur due to changes or change of product, these variations must be compensated for, to maintain accurate measurements[1]

3. Wet system: when the outer leg[1] is allowed to be completely filled with the same process fluid as in the tank. [1]

4. With the closed vessel the high pressure will be connected to the outer leg[1], but with the open vessel the high pressure is at the bottom of the container [1]

With the closed vessel the differential pressure is zero when the tank is full[1/2] and maximum when the tank is empty[1/2], but with open tank the pressure is maximum when the tank is full[1/2] and zero when the tank is empty [1/2]

5. 6. Top fixed point: The temperature of (distilled water that boils) [1] at (standard atmospheric

pressure of 760 mm. mercury.) [1] Bottom fixed point: The temperature of ice (prepared from distilled water) mixed with distilled

water [1], at standard atmospheric pressure of 760 mm. mercury.[1]

7. Resistance thermometers are based on the principle that the resistance[1] of a metal increases with temperature[1]

8. a) Law of homogeneous circuits[1] b) Law of intermediate metals[1] c) Law of intermediate temperatures[1]

9. t = (2.508355×10-2)×2602 + (7.860106×10-8)×26022 – (2.503131×10-10)×26023

+ (8.315270×10-14)×26024 – (1.228034×10-17)×26025 + (9.804036×10-22)×26026 – (4.413030×10-26)×26027 + (1.057734×10-30)×26028 – (1.052755×10-35)×26029 [1]

t = 65.2674 + 0.5321609 – 4.409664 + 3.811584 – 1.464694 + 0.3042627 – 0.03563592 + 0.002222464 – 0.05755631[1]

= 63.95 °C[2]

10. Compensating leads are cheaper than thermocouple leads[1] and are used to connect the thermocouple to the measuring device at the reference junction a distance away. [1] 11. a) Measured value[1], b) Desired value (setpoint value)[1] c) Error value[1]

[3]

[4]

Pressure regulator[1]

Air/gassupply[1]

Filter[1]Bubbler

sight glass [1]

Dip tube [1]

[2]

[4]

[2]

[4]

[4]

[2]

[3]

[3]

[4]


12. Reverse acting: heating system[1] as temperature decreases, the demand on controller output

will increase[1] Direct acting: cooling system[1], as temperature increases the demand on the controller output

will increase.[1]

13. First order lag: delay due to the time it takes energy[1] to be transferred from one point or form to another[1]

14. a) Bias: the control effort that is maintained when the error is zero[1], b) Proportional gain: ratio of controller output change[1/2] to error value change[1/2], c) Proportional band: the error range that causes 100% change in controller output[1]. 15 16 .a) Control valves are used to regulate the flow rate of a medium[1] and serve as the correcting

element in many control systems.[1]

VD=-RDCDdt

dE [1]

E

CD [1]

RD [1]

Op-amp VD [1]

[4]

[2]

[3]

[4]

[2]


Question 1 Give the SI units for current and the amount of substance. (2)

Question 2 Define the significance of working standards in the hierarchy of instruments standards. (2)

Question 3 Define reproducibility and resolution. (4)

Question 4 Non linearity and Dead band are some of the typical instrument errors. Explain these typical instrument errors. (4) Question 5 Identify the following instrumentation symbol: (2) Question 6 The glass U-tube mercury manometer is 300 millimeter (mm) long and has a bore of 5 mm. The scale is movable for zero adjustment, and is calibrated from 0 to 250 mm. With the aid of a sketch calculate the maximum differential pressure which can be applied to the manometer. (4)

Question 7 With the aid of a sketch, derive an expression that is used to determine pressure with an inclined limb manometer.. (4)

Question 8 Draw a labeled sketch of a force-balance gauge calibrator (‘dead weight tester’). (5)

Question 9 The absolute pressure and vacuum pressure are two types of pressure. Explain what is absolute pressure and vacuum pressure. (4) Question 10 Draw a labelled sketch of a foil type strain gauge. (3)

Question 11 Draw a labelled sketch of a venture tube flow meter. Show the dimensions and relative sizes of the instrument clearly on your sketch. (4)

Question 12 State the advantages and disadvantages of the venturi tube. (4)

Question 13 Give a formula used for Poiseuille’s law and explain each symbol used in the formula. (3)

Question 14 Sketch and describe the operation of a transit time flowmeter. (5)

.


TRC


1. Current: amperes and amount of substance: mole 2. Workplace standards are used to calibrate instruments used in industrial applications

and instruments used in the field, [1] for accuracy and performance. Working standards are checked against secondary standards [1] for accuracy.

3. Resolution is the smallest variation [1] in the measured variable that can still be measured. [1] Reproducibility is the closeness of the instrument readings when the same input [1] is applied

under different conditions over a long period of time. [1] 4. Non-linearity is the maximum deviation [1] from a straight line

connecting the zero and full-scale calibration points. [1] Dead band is the largest change of input to which the

instrument does not respond due to friction or backlash effects 5. Temperature recording controller, [1] mounted on board. [1] 6 P1-P2 = hg[1] P1-P2 = 13600(250/1000)9.81[1] P1-P2 = 33.354 kPa [1] 7. Equating pressures in the XY plane: P1 = P2 + (h+d)g [½] …….…..……… (1) and with mercury incompressible:

A1d = A2L d = 1A

2AL [½] …….….... (2)

Also in triangle abc: sin = h/L h = Lsin [½] …….….... (3)

(2) en (3) in (1):

P1=P2+

L

1A2A

Lsin g

P1 – P2 = Lg

1A2A

sin [½]

8. 8. 9. Absolute pressure (total pressure)

is the pressure measured from absolute zero pressure.[2] Vacuum pressure is the difference between local atmospheric pressure and the absolute pressure in a medium[1], when the pressure in the medium is lower than atmospheric pressure[1]

10.

[2]

[2]

[4]

[2]

c b

a

A1

L

A2

ZL

d

P1

P2

Sketch 2 marks

h

X Y

[4]

[4]

Gauge under test [1]

Screw [1]

Primary piston [1]

Secondarypiston [1]

Platform [1]

Oil [1]

Mass pieces [1]

Backing material [1]Alignment marks[1] Solder tabs [1] Grid [1]

[3/4]

[2]

250

P1 P2

HG 1 Mark for sketch

[5]/7[4]


11. 12. Advantages: Pressure loss is small [1] Operation is simple and reliable [1] Disadvantages: Highly expensive 1] Occupies considerable space [1] ],

13. Poiseuille’s law: q = )2p1(pL8

4R

[1]

where q is the liquid’s flowrate (m3/s) [½] , R is the radius of the pipe (m) [½] , is the viscosity of the fluid (PI) [½] , L is the length of the pipe (m) and p1–p2 is the pressure differential across] the pipe (Pa). [½]

14. 2 MARK FOR SKETCH 3 MARKS OPERATION

The transit time flowmeter (also called transmissivity, time of flight or time of travel flowmeter) uses two ultrasonic transducers to beam a high frequency sound wave (ultrasonic wave), alternatively upstream and downstream at an angle θ, across the flow, as shown in[1]. The difference in times required for the sound waves to travel upstream (t12) and downstream (t21), can be used to calculate both the sound speed and the mean fluid velocity along the path followed by the sound[1]. This meter gives accurate results but is only applicable to clean liquids and gasses. It is however not easy to accurately measure the extremely short time intervals that are involved.[1]

D [½]

d/2 [½]D/2 [½]

High pressure tap(upstream tap) [½]

Low pressure tap (downstream tap) [½]

Flow [½]

d[½]

Throat [½]Inlet cone (19º-23º) [½]

Outlet cone (5º-15º) [½] d[½]

[4]

[5]

Ultrasonic transceiver 2 (Piezoelectric crystals) [½]

Ultrasonic transceiver 1(Piezoelectric crystals) [½]

L [½]

[1]Flow [1]

[4]

[4]

Process Instrumentation I EIPIN1 Unit 2 First Assessment 13 April 2012 Page 1

Question 1 A DP transmitter must be calibrated to measure the level of a liquid in an open tank. The density of the liquid is 1000 kg/m3. The DP transmitter will be mounted one meter below the bottom of the tank. The tank is full when the height of the liquid in the tank is 5 meters and it is empty when there is only liquid in the high pressure line connected to the DP transmitter. Determine the necessary calibration specifications for an output signal of 4 to 20 mA. (4) Question 2 Sketch and describe the operation of the following level meters: 2.1. Magnetic float switch level meter. (4) 2.2. Flexure tube displacer (Torque tube) level meter. (5) Question 3 Define the following fixed points on the international temperature scale: 3.1.Oxygen points (2) 3.2. Silver point (2) 3.3. The ice point (2) Question 4 Name three common metals used in resistance thermometer. (3) Question 5 Give the positive element material, negative element material and the temperature range of a type J thermocouple. (3) Question 6 Draw a labelled circuit diagram to illustrate the three wire method that is used to compensate for ambient temperature when measuring temperature with a resistance thermometer. (4) Question 7 State the thermocouple law of intermediate temperature. (2) Question 8 What is the main use of compensating leads, as used for temperature measurement. (2) Question 9 Explain the following terms: 9.1. Feedback and feedforward control systems. (4) 9.2. Direct acting control and reverse acting control systems. (4) Question 10 Draw a circuit diagram of the proportional (P) block of an electronic proportional, integral and derivative controller. Also give the expression of the output of the (P) block , in terms of the error input signal E. (3) Question 11 A process is controlled by a proportional controller. The controller is programmed for a positive gain (reverse acting controller) and proportional band of 70%,a set point of 50% and a bias of 50%. Calculate the output of the controller when the measured value is 70%. (4) Question 12 Define derivative control. (2)

TOTAL MARKS:50

Process Instrumentation I EIPIN1 Unit 2 First Assessment 13 April 2012 Memorandum Page 1

Question 1 1. Empty:

P1 = Patm + hg = Patm + 100019.81 = Patm + 9810 P1 – P2 = 9810 Pa Full: P1 = Patm + hg = Patm + 100069.81 = Patm + 58860 P1 – P2 = 58860 Pa

Calibration specification: Output = 4 mA when input = 9810 Pa (empty condition) Output = 20 mA when input = 58860 Pa (full condition) Question 2 1. Magnetic Float Switch:

The magnetic float switch is a point level device. When the level reaches a certain point, the float magnet activates the magnetic reed switch. [1/2] The electric contacts are safely isolated from the inside (wet side) [1/2] of the container by non-magnetic material that allows magnetic interaction between the float magnet and magnetic switch. [1/2] The contacts may be used to switch a pump on or off, to sound an alarm or for other control purposes. [1/2]

2. Flexure Tube Displacer (torque tube) Level Meter:

The displacer type liquid level measuring instrument is not a float as such, for the displacer is heavier than the process fluid and the displacer moves very little during changes in tank level (a definite advantage over other float types). [1/2] According to Archimedes’s law, the apparent weight of the displacer when immersed in a liquid, is its nominal weight in air minus the weight of the displaced liquid. [1/2] The weight of the displacer will thus vary linearly from its weight in air (when the tank is empty) to its apparent weight when fully immersed in the liquid (when the tank is full). [1/2] The weight of the displacer acting on the torque arm, will cause an angular displacement of the free end of the flexible torque tube and this movement will be transmitted to the outside world, by the torque rod. [1/2]

[4]

[4]

[5]

P2 P1 1 m

DP cell

5 m

Patm

Empty

P2 P1 1 m

DP cell

Patm

4 mA 20 mA

Patm Patm

Full

Float[1/2]

Swivel pin [½]

Float magnet [1/2]

Magnetic reed switch [1/2]

Non-magnetic housing [1/2]

Displacer [1/2]

Chain [½]

Torque arm [1/2]

Torque tube [1/2]

Torque tube flange [½]

Torque rod [½]

Process Instrumentation I EIPIN1 Unit 2 First Assessment 13 April 2012 Memorandum Page 2

Question 3 a) T b) The silver point: The melting point of silver [1] 961.78 °C. [1] c) The Ice point: the melting point of pure water[1] at 00C[1] Question 4 Iron, copper and aluminium. Question 5

Type Positive Isolation element colour element

Negative Isolation colour

Outer isolation

Temperature range (°C)

J Iron[1]

Constantan [1]

-200 to 750[1]

Question 6

Question 7 The law of intermediate temperatures states that the sum [½] of the emf developed by a

thermocouple with its junctions at temperatures T1 and T2, [½] and with its junctions at temperatures

T2 and T3, [½] will be the same as the emf developed if the thermocouple junctions are at

temperatures T1 and T3. [½]

Question 8 Thermocouple thermometers are normally installed some distance away from the voltmeter or computer that measures the emf generated by the thermocouple. For this purpose, cheaper and lower grade thermocouple wires, called extension wire or compensating leads, are used to connect the thermocouple to

the measuring device at the reference junction. Compensating leads have the same thermoelectric Question 9 Feedback control: Measure the controlled variable to determine the control strategy.[2] Feedforward control: Measure disturbance variables to determine the control strategy.[2] Direct acting control: A control arrangement in which the controller output increases

if the measured value rises above the set point.[2] Reverse acting control: A control arrangement in which the controller output increases if the measured value drops below the set point.[2]

Question 10 Question 11 C = 100/PB(S – M) + R [1] = (100/70)×(50 – 70) + 50 [1] = 21.43% [2] Question12 A control strategy in which the controller output is proportional to the derivative of the error.[2]

E

RPI [1]

RPF [1]

VP = -PIRPFR

E [1]

Op-amp VP

[6]

[3]

[3]

[4]

[1/2][1/2]

[1/2]

[1/2]

[1/2]

[1/2]

[1/2]

[1/2]

[1/2]

[2]

[2]

[8]

[3]

[4]

[2]

Process Instrumentation I EIPIN1 Unit 1 Final Assessment 23 March 2012 Page 1

Question 1 Define the International standard of measurements. (2)

Question 2 Instruments may be classified according to the functions they perform. Name and explain each function. (9)


Question 4 Define the Relative density of a substance. (2) Question 5 Explain the operation of a C-type Bourdon tube pressure gauge. (5)

Question 6 Discuss Aniline as a manometer liquid, with respect to its relative density, application, advantage and disadvantage. (4)

Question 7 U- tube manometers can be used to measure differential pressure, gauge pressure and absolute pressure. Give the formulae used to calculate those types of pressures. (3)

Question 8 A differential pressure transmitter is correctly calibrated for a process variable that varies from 0 kPa to 170 kPa. Determine the output of the DP transmitter when the process variable reaches 90 kPa (5)

Question 9 a) Draw a labelled sketch of a vortex flow meter. (3) b) Give the operational equation that is used to calculate the flow rate q, from the measurements made with a vortex flow meter. Define each symbol that appears in the equation.. (3) Question 10 Sketch the configuration, including dimensions and labels, when pipe taps are used for flow rate measurement with an orifice plate. (3)

Question 11 Describe the operation of a magnetic flow meter. (6) Question 12 Give the operational equation that is used to calculate the flow rate (q) from the measurements made with a magnetic flow meter. Define each symbol that appears in the equation. (3) .


Process Instrumentation I EIPIN1 Unit 1 Final Assessment 23 March 2012 Memorandum Page 1

1 International standards are defined by international agreement, representing units of measurements [1] to the best possible accuracy allowed by measurement technology [1]

2. Indicating function[1] an instrument may provide the information about the value of a quantity under measurement, in the form commonly known as an indicating function [2]. .Recording function [1] An instrument may provide the information of the value of a quantity under measurement against time or some other variable, in the form of a written record, usually on paper [2]. .Controlling function [1] This is one of the most important functions of an instrument, especially in the field of industrial control processes. In this case, the information provided by the instrument is used by the control system to control the original measured quantity [2].

3. Drift is the change in instrument indication over time [1] while the input and ambient conditions are constant. [1] 4. Relative density of a substance is defined as the ratio of the density of the substance [1] to the density of water. [1] 5.Bourdon tube pressure gauges are usually used where relatively large static pressures are to be measured. [1] The Bourdon tube pressure gauge consists of a C-shaped tube with one end sealed. [½] The sealed end is connected by a mechanical link to a pointer on the dial of the gauge. [½] The other end of the tube is fixed and open to the pressure being measured. [½] The inside of the Bourdon tube experiences the measured pressure, [½] while the outside of the tube is exposed to atmospheric pressure. [½] Therefore, the tube responds to changes in Pmeasured – Patm. [½] Increasing this pressure will tend to straighten out the tube and move the pointer to a higher scale position. [1] 6 Aniline Relative density: 1.025 [1] Applications: Suitable for pressure measurement in low pressure gas or air installations, with the exception of ammonia and chlorine [1]. Advantages: Low density for measuring small pressure differences. Evaporates slowly. Does not mix with water. Can be easily seen [1]. Disadvantages: Attacks paint. Poisonous, penetrates the skin and causes blood poisoning. Aniline darkens on contact with air [1]

7. (a) Differential pressure: P1-P2= ρ.g.h[1]

(b) Gauge pressure P1-Patm= ρ.g.h[1] (c) Absolute pressure Pabs= ρ.g.h[1] 8. At 170 kPa Po is 100 kPa [1] then Po= m (P1-P2) + 20 [1]

100 = m ( 170) + 20 m = 0.471 [1]

then at 90 kPa: Po = m (P1-P2) + 20 [1]

Po = 0.471 (90) + 20 [1]

= 62.353 kPa [1]

[2]

[9]

[4]

[5]

[5/6]

[3]

[2]

[2]

Process Instrumentation I EIPIN1 Unit 1 Final Assessment 23 March 2012 Memorandum Page 2

9

(b) ) q = AtS

fd [1] A = unblocked flow area [½] f = measured vortex frequency [½] d = width

of bluff body [½] St = Strouhal factor [½] constant 10.

11. Magnetic flow meters can measure the flow rate of any conductive liquid while offering no obstructions to the flow stream [1]. Magnetic flow meters are based on Faraday’s law of electromagnetic induction (e = B.v), which states that when a conductor is moved through a magnetic field, an emf e (volt) will be generated that is proportional to the velocity v (m/s) of the conductor, the length . (m) of the conductor, and the strength B (tesla) of the magnetic field [1]. The section of pipe that is part of the flow meter, contains the coils through which current is passed to produce the magnetic field [1] as well as the electrodes that produce the voltage that is proportional to the flow rate [1]. This section must be made of a material that is non-magnetic so as not to distort the magnetic field and also a material that is non-conductive so that the electrodes are not short circuited [1]. To ensure that the electrodes make contact with the liquid at all times, they should, preferably lie in a horizontal plane.[1]

12. q = keBD. [1] where D is the distance between electrodes or pipe diameter (meter), [1/2] B the magnetic flux density (tesla), [1/2] e the measured emf (volt) [1/2] and k a calibration constant (dimensionless).[1/2]

[6]

[3/4]Heat sensors in bluff body or ultrasonic sensors [1]

d

Eddies (vortices, whirls, swirls or Von Karman vortex street) [1]Bluff body

(vortex generator or shredder bar) [1]

v [1]

[3]

[3]

[3]


°C 0 1 2 3 4 5 6 7 8 9 0 0 39 79 119 158 198 238 277 317 357

10 397 437 477 517 557 597 637 677 718 758

20 798 838 879 919 960 1000 1041 1081 1122 1163

30 1203 1244 1285 1326 1366 1407 1448 1489 1530 1571

40 1612 1653 1694 1735 1776 1817 1858 1899 1941 1982

50 2023 2064 2106 2147 2188 2230 2271 2312 2354 2395

60 2436 2478 2519 2561 2602 2644 2685 2727 2768 2810

70 2851 2893 2934 2976 3017 3059 3100 3142 3184 3225

80 3267 3308 3350 3391 3433 3474 3516 3557 3599 3640

90 3682 3723 3765 3806 3848 3889 3931 3972 4013 4055

100 4096 4138 4179 4220 4262 4303 4344 4385 4427 4468

Question 1 Draw a labelled sketch of a chain float level meter. (4) Question 2 During calibration of a Flexure tube displacer (torque tube) displacer type level meter, it was found that the torque registered by the meter was 30 N-m, when the tank was empty. If the length of the torque arm is 0.15 m, calculate the torque that will be measured when the displacer, with a volume of 0.005 m3, is fully immersed in the process fluid with density 1000 kg/m3. (4) Question 3 Define temperature and give the SI unit for temperature. (2) Question 4 Convert 537 Rankine to Kelvin. (4) Question 5 Draw a labelled sketch of a liquid in glass thermometer. (4) Question 6 A platinum resistance thermometer has a resistance of 100 at 0 °C and a resistance of 139.1 at 100 °C. Calculate the temperature coefficient of resistance (TCR) of the thermometer. (2) Question 7 Draw a labelled circuit diagram to illustrate the four wire method that is used to compensate for ambient temperatures when measuring temperature with a resistance thermometer. (3)

Question 8 Define the Seebeck effect. (3)

Question 9 In Figure 1, a type K thermocouple is shown, which is used to measure an unknown temperature T. The voltmeter reading is 2390 microvolt, and the temperature of the thermocouple cold junction is 24 °C. An excerpt from the type K thermoelectric voltage table (in microvolt) for temperatures in degrees Celsius, is given in Table 1. Use Table 1 to determine the temperature T of the hot junction. (3)

Question 10 A heat exchanger that uses steam to heat cold water and aims to deliver hot water at a fixed temperature of 60°C, is shown in Figure 2. Identify or explain the following control variables and values, with reference to the system in Figure 2: (For example: Controlled variable: Temperature of hot water delivered) a) Manipulated variable. (1) b) Disturbance variable. (1) c) Desired value. (1) d) Measured value. (1) e) Error value. (1) Question 11 Define open loop and closed loop control systems. (2) Question 12 Define integral control reset time. (2) Question 13 Draw a labelled sketch of a pneumatic proportional plus derivative controller. (4) Question 14 Explain the valve term: ‘throttling’. (2) Question 15 Draw a labelled sketch of a valve positioner that helps the actuator of a pneumatic valve, to position its valve stem in the required position, as dictated by the value of the instrument signal. (6) ---ooo000ooo--- Total: 50

Table 1

T 24°C 2390 V Figure 1

Steamcontrolvalve

Thermometer

Hot water Steam outlet

TICCold water

Steamsupply

Figure 2


Needle valve rate adj. [½]

Set point S [½]

Resetbellows [½]

Beam[½]

Bias value R [½]

Airsupply [½]

Flapper and nozzle [½]


Proportional(feedback) bellows[½]

Pilot relay[½]

Controller output C [½]

Restriction [½]

Cam [1]

Air [½] supply

Valve stem [½]

Valve actuator [½]

Pilot relay [½]

Actuator Output [½]

Elasticforce-

balancebeam [1]

Pivot [½]

Instrument bellows [1]

Flapper and nozzle [1]

Instrument signal[½]

1.

3. Temperature is defined as the degree of heat of a body. [1] The SI unit is Kelvin (K). [1]

7.

10. a) Manipulated variable:Steam flow. (1) 15. b) Disturb. variable:Hot water demand (steam pressure., ambient temp.). (1) c) Desired val.:Required temp.-60°C. (1) d) Meas. value:Thermometer reading. (1) e) Error value:Difference between req. temp. and thermometer reading. (1)

11. Open loop system: The input to the system is not determined by the output. [1]

Closed loop system: The input to the system is determined by the output. [1]

12. Reset or repeat time:Time taken [¼]

for the integral control action

[½] to equal [¼]

the proportional control action [½]

under the influence of a constant error. [½]

13.

8. Seebeck effect: If two dissimilar metals

[1] are joined together to form a closed loop, and if

one junction is kept at a different temperature [1]

from the other, an electro-motive force

[1] is generated and electric current will flow in the closed loop.

[4]/5

Level indicator [1]

Drum [1]

Weight [1]

Float [1]

Chain [1]

[2]

[3]

[5]

[2]

[2]

[3]

2. Weight of displacer in empty tank: T = Fr F = T/r = 30/0.15 = 200 N [1] Weight of displacer in full tank = Weight of displacer in empty tank –Weight loss of displacer in full tank = 200 – 0.005×1000×9.81 = 200 – 49.05 = 150.95 N [2] Torque measured in full tankTfull = 150.95×0.15 = 22.64 N-m [1]

[2]

[4]

Voltmeter return across RT - 1 mark

Current source I 1 mark

Rlead

Rlead

Rlead

Rlead

I

a

c RT

d

b

M 4 leadwires plus RTD – 1 mark

6. 0 = 1000R

0R100R

[1]

= 100100

100139.1

= 0.00391 /°C [1]

[3] 9. 24 °C 960 V [1] ET = 2390 + 960 = 3350 V [1] T = 82 °C [1]

Scale (etched) [1]

Bore [1]

Bulb [1]

Lens front capillary tube (stem) [1]

Liquid column [1] [4]

/5

[4]

4. R = F+460 F = R–460 = 537–460 = 77 °F [1] C = 5/9(F – 32) = 9/5(77 – 32) = 25 °C [2] K = C + 273 = 25 + 273 = 298 K [1]

[4]/5½

14. Throttling occurs whenthe valve stem positionis between closed andopen (0 < x < 1)[1] andthe valve is busyregulating the flowstream.[1]

[2]

[6]/8

5.

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