Instrumentation and Process Control

Courseware Sample

31446-F0

�

INSTRUMENTATION AND PROCESS CONTROL

COURSEWARE SAMPLE

bythe Staff

ofLab-Volt (Quebec) Ltd

Copyright © 2004 Lab-Volt Ltd

All rights reserved. No part of this publication may bereproduced, in any form or by any means, without the priorwritten permission of Lab-Volt Quebec Ltd.

Printed in CanadaJune 2004

III

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Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Courseware Outline

Multi-Process Station

Sample Exercises Extracted from Multi-Process Station

Ex. 2 Level Measurement II – Calibration of a Level Transmitter . . . . . 3

Ex. 6 Level Process Characteristics with Variable Speed Pump . . . . . 11

Ex. 15 Ultimate Period Tuning of a Level Process . . . . . . . . . . . . . . . . 19

IV

V

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The Lab-Volt Mobile Instrumentation and Process Control Training System,Series 3500, consists of self-contained workstations designed for hands-on trainingin the measurement, control, and troubleshooting of pressure, flow, level,temperature, heat exchange, and analytic processes. The stations can operateindependently, or be interconnected into several configurations to simulate complexprocesses. All processes are sized to be "real-world" in time lag and processresponse. Process dynamics can be altered by various means to provide severaldegrees of stability and damping. The Flow, Level, Heat Exchanger, Multi-Process,and Analytic Process Stations utilize water as the process media, while thePressure and Temperature Process Stations utilize air. All Process Stations includea microprocessor-based controller, a dual-speed strip chart recorder with single ordual pen, and alarm lamps, with all connections terminated by banana jacks on thestation main control panel.

VI

MULTI-PROCESS STATION

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VII

Exercise 1 Level Measurement I – Dry Method using a Bubble Pipe

Exercise 2 Level Measurement II – Calibration of a Level Transmitter

Exercise 3 Pressure Measurement

Exercise 4 Flow Measurement: Differential Pressure vs Flow Using a Venturior Orifice Plate

Exercise 5 Level Process Characteristics with Control Valve

Exercise 6 Level Process Characteristics with Variable Speed Pump

Exercise 7 Flow Process Characteristic with Control Valve

Exercise 8 Pressure Process Characteristic

Exercise 9 Proportional Control – Level Process with Control Valve

Exercise 10 Proportional Control – Flow Process with Variable Speed Pump

Exercise 11 Proportional Plus Integral Control – Level Process with ControlValve

Exercise 12 Proportional Plus Integral Control – Pressure Process

Exercise 13 Proportional Plus Integral Plus Derivative Control – LevelProcess with Control Valve

Exercise 14 Proportional Plus Integral Plus Derivative Control Flow Processwith Variable Speed Pump

Exercise 15 Ultimate Period Tuning of a Level Process

Exercise 16 Ultimate Period Tuning of a Flow Process – ApproximationMethod

Exercise 17 Open Loop Tuning of a Level Process using the Reaction RateMethod

Exercise 18 Open Loop Tuning of a Pressure Process

Exercise 19 Troubleshooting a Level Control Process

Exercise 20 Operation of a Two Element Control Process

MULTI-PROCESS STATION

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VIII

Exercise 21 Three-Element Control Process

Exercise 22 Auto-Tune Controller

Appendix A Symbols Used in DiagramsB Venturi Tube Flow Curve

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3

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OBJECTIVES

At the completion of this exercise, you will be able to calibrate a differential pressuretransmitter, using the process, to measure level.

DISCUSSION

A Differential Pressure (D/P) Transmitter may be used for the measurement of liquidlevel or flow of a fluid in a pipe. In this exercise you will calibrate the DifferentialPressure Transmitter by varying the height of the water column in the level tank.

A Differential Pressure Transmitter measures the difference of pressure appliedacross its measuring element. The differential pressure detected by the DifferentialPressure Transmitter is related to a column of fluid by the following relationship:

Pressure = Density of fluid x Height of fluid

Differential pressure transmitters produce an output proportional to the differencein pressure across its high pressure, and low pressure ports.

The height of fluid is normally expressed in inches/centimeters of water. If thedensity of the fluid remains constant, which is normally the case, then the pressureis directly related to the height of the fluid. Therefore, accurately determined,reproducible pressures can be applied to a Differential Pressure Transmitter byvarying the height of a column of fluid of a known density.

Calibration of a Differential Pressure Transmitter is the process of matching the zeroand full scale outputs of the transmitter to the minimum and maximum differentialpressures applied. The actual differential pressures that are to be applied to theDifferential Pressure Transmitter are derived from the specific application. As formost transmitters, the two adjustments available for the calibration are the zero andspan of range.

It is necessary to determine the upper and lower range values of differentialpressures which will be applied to the transmitter. The level process tank isgraduated in centimeters and inches. The bottom of the tank has two pressure taps,and mini valves labelled V6 and V7. If the tank overflow valve V13 is opened, thenthe tank will be vented to atmosphere, and we need only to connect the highpressure part of the D/P transmitter to V6 and V7. The tank level will provide apressure on the D/P cell proportional to its height, and the D/P electronics will givea current output of 4-20 mA equivalent to the range the D/P cell is calibrated to.

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4

When we connect the D/P cell to the bottom of the tank, two problems occur:

1) The air trapped in the tubing will compress as the water column height increases.This requires that the D/P cell be opened to release the trapped air, which is atechnique called “bleeding” the sensing lines and the D/P cell.

2) The “bottom” of the tank is not necessarily the real bottom of the water column.The actual “bottom” is the lowest point of the tubing in relationship to the heightof the D/P cell.

To solve 1) we must “bleed” the tubing and the D/P cell to ensure no air is trapped.All D/P cells have small vents to permit this.

To solve 2) we must adjust the electronics to “elevate” or “suppress” the zero outputof the D/P cell (4.0 mA) to be equal to the real level “zero” in the tank. Again this isnot always the bottom of the tank.

In this exercise we calibrate the transmitter for a zero = 4" of water and a span of20 inches of water. This means our range will be 4-24 inches of water.Range � span = zero.

EQUIPMENT REQUIRED

DESCRIPTION MODEL

Multi-Process Station 3505-M0D/P Transmitter (LT)

Digital Multimeter

INSTRUMENT DATA

DEVICE MODEL SERIAL NO. CALIBRATED

LT 0-30" WC/4-20 mA

PROCEDURE

CAUTION!

Water and electric power are present in this laboratory exercise.Be careful of possible electrical shock hazard.

� 1. Connect the equipment as shown in Figure 2-2. Open or close the valvesas shown.

� 2. Program the variable speed drive for manual operation. Close valve V8.

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5

� 3. Start the pump and fill the level tank to 26 inches (65 cm) and close valveV2. Stop the pump.

� 4. In this step you will bleed the air from the tubing between V7 and the D/Pcell. Using a small wrench, open the D/P cell high side vent, and bleed thecell into a small cup. You need to bleed 2 or 3 inches of water into the cupto ensure all air is out. Close the D/P cell vent.

� 5. Check again that the water level in the tank is exactly 24 inches (60 cm).If not, add or release water until correct.

� 6. Following the procedure in the manufacturers’ manual for the specific D/PTransmitter, set the span adjust so that the transmitter output, as indicatedon the DMM, reads 20.0 mA.

� 7. Open V8 and drain the tank level down to 4 inches or 10 cm and close V8.As for step 6, follow the manufacturers’ instruction for setting zero, and setthe zero adjust so that 4.0 mA is indicated on the DMM.

� 8. Refill the tank to 24 inches (60 cm) and reset the span adjust for 20 mA.Drain the tank to 4 inches (10 cm) and reset the zero to 4 mA.

Some transmitters require that you repeat this several times because thezero and span adjustments are often interactive. New microprocessorbased instruments have virtually no interaction, and the zero/span needonly to be set once.

� 9. Note that we have set the zero at 4 inches (10 cm) and upper range to24 inches (60 cm) for a 20 inches (56 cm) span. If time permits recalibratethe D/P transmitter to a zero of 10" (25 cm) and an upper range value of20" (50 cm).

� 10. Complete the calibration data sheet and plot a graph of the results. Checkto see if there is any non-linearity on hysteresis visible.

CONCLUSION

In this exercise you learned to calibrate a Differential Pressure Transmitter. Youobserved the interaction of the zero and span adjustments for a specified range ofoperation. The zero adjustment does not normally affect the span/range adjustment.However, the span/range adjustment does affect the zero adjustment. You alsolearned that a Differential Pressure Transmitter needs to be vented to producecorrect readings.

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6

CALIBRATION DATA SHEET

APPLICATION DATA INSTRUMENT NAMEPLATE DATA

INSTRUMENT NUMBER: MANUFACTURERS NAME:

FUNCTION: MODEL NUMBER:

LOCATION: SERIAL NUMBER:

INPUT RANGE: OUTPUT RANGE:

REQUIRED ACCURACY:

DATE OF CALIBRATION:

INPUT % SPANDESIREDOUTPUT

ACTUALOUTPUT

REMARKS

0

25

50

75

100

75

50

25

0

ALARMS

ALARM FUNCTION:

ALARM SETTINGS:

LOW SETPOINT

ACTUALTRIP POINT

HIGH SETPOINT

ACTUALTRIP POINT

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7

Figure 2-1.

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8

+ −

VSD

24 V − DC

SUPPLY FREQUENCY INPUT

ABOVE 70 Hz OR

DAMAGED

DO NOT SET F max.

PUMP MAY BE

CAUTION:

F2F1

24 V − DC

ALM−1

ALARM INDICATORS

ALM−2

1-5 V − DC

CONTROL OUT

AUXILIARY OUT

RATED 24 V − 1 A − DCRELAY 1 ISOLATED

CONTACT OUT

OUTPUTS

COM.

COMMUNICATIONS

COM.

1-5 V − DC

1-5 V − DC

1-5 V − DC

1-5 V − DC

ANALOG INPUTS

DRY CONTACTINPUTS

+5.0 V OPEN CIRCUIT

250

250

250

250

141315

−+ +

RS−485

4-20 mA 27

38

26

CO 2CO 1

(31)(32)−

+ +

20

23

7

4

4

3

2

1

4-20 mA

4-20 mA

4-20 mA

4-20 mA

B

A

22

25

24

30

18

21

5

2

2829

−+

−+

2D / P

1D / P

4-20 mA RLRL4-20 mA

PEN 1

SPAN

INPUT1-5 V − DC

SPAN

INPUT1-5 V − DC

PEN 2

250 250

TO PUMP

+ −4-20 mA

INPUTSIGNAL

100 mA

REMOTE24 V − DC OPEN CIRCUIT

DRY CONTACTMAINTAINEDMAINTAINED

3505MULTI-PROCESS STATION

I / P

INTERLOCK

PUMP-HEATER

MAINS

SUPPLY

PUMPSUPPLY

100 mA

SOLENOIDVALVE SV-1

DRY CONTACT

REMOTE24 V − DC OPEN CIRCUIT

TO+24 V − DC

SUPPLY24 V − DC

4-20 mA

3-15 psi20-102 kPa

20 psi / 140 kPa

−

+

140 kPa20 psi

SUPPLY

Figure 2-2A.

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9

V−11

V−7V−6OVERFLOW

V−10

U−1

U−9U−8

COLUMNLEVEL

V−3

V−4

V−14

SV-1

TE

U−6U−7

HA−2

V−9

0-3 psi0-20 kPa

U−3

V−8

V−13

PRR−1

U−4

V−5

CV−1

SUPPLY

75 LITRES20 GALLONS

HOLDING TANK

100 psi700 kPa

PUMP

U−5

V−12

U−2HA−1

FI

V−1

V−2

1

4-20 mA

+24 V − DCTO

D / P

LH

Figure 2-2B.

REVIEW QUESTIONS

1. What is the function of a Differential Pressure Transmitter in a levelmeasurement channel?

2. Why is it necessary to purge all air from the transmitter before using water asthe calibration medium?

10

11

8 mA

12 mA

STEP CHANGE

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OBJECTIVES

At the completion of this project, you will be able to use standard processinstrumentation to determine the characteristics of a level process, controlled by avariable speed pump.

DISCUSSION

Understanding how a process responds to changes is important for the individualwho must calibrate the instruments used for controlling the process. It is alsoimportant to know how quickly the output of the measuring instrument responds tochanging conditions.

In the previous exercise, we used a pneumatic control valve, which is a relativelyslow control element.

In this exercise, we will do exactly the same experiment, but use a much fastercontrol element.

Procedural Notes

1. The procedure involves a step change to the calibrator (Figure 6-1), performedby quickly increasing the output from 8 to 12 mA. Increasing the Variable SpeedDrive input signal will increase the flow.

Figure 6-1.

2. The process will take some time to react to the “instantaneous” step change.This is due to several factors, including the time it takes for the water to travelthrough the system and the water level to increase.

The actual step change will be considered instantaneous to simplify calculations.The step change and resulting process reaction are shown in Figure 6-2.

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12

8 mA

12 mA

T = 63.2%

to dtTIME

(A) STEP CHANGE

(B) PROCESS REACTION

VARIABLE SPEEDDRIVE INPUT

Figure 6-2.

where to = Initial Timetd = Dead Time (time taken by the process to start to react to the step

change)T = Process Time Constant (time taken by the process to reach 63.2% of

final steady state value)

EQUIPMENT REQUIRED

DESCRIPTION MODEL

Multi-Process Station 3505-M0Differential Pressure Transmitter (LT)Strip Chart Recorder (LR)Current to Pressure Converter (I/P)

Electronic Calibrator 3550-M0

INSTRUMENT DATA

DEVICE MODEL SERIAL NO. CALIBRATED

LT 0-30" WC/4-20 mA

LR 4-20 mA/0-100%

I/P 4-20 mA/3-15 psi

PROCEDURE

CAUTION!

Do not run pump for prolonged periods with a shut off head!

� 1. Set up and connect equipment as per the loop diagram. Close or openvalves as shown in Figure 6-4. Program the variable speed drive for manualoperation and 40 Hz.

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13

� 2. Fill the tank to approximately 10 in./25 cm water and bleed the HP side ofthe transmitter.

� 3. The low pressure side of the transmitter is left open and will thereforemeasure atmospheric pressure. The high pressure side is connected tovalve V7 and measures the pressure of the column of water plusatmospheric pressure. The difference between the two is the pressure, andtherefore the height, of the column of water. Because we are calibrating thistransmitter using water, it is necessary to purge the air from the highpressure side. Hold a cup under the HP vent and loosen the vent plug untila constant stream of water is flowing through. Tighten the vent plug.

� 4. Temporarily connect the I/P Converter input to the PID Controller output.Place the controller in manual and adjust the output to 100% (20 mA).Adjust the variable speed pump (and V2 if necessary) to a flow rate of5 GPM (18 lpm) with inflow to tank at maximum.

This step will permit the process to stabilize at approximately 24 to 30" ofwater in the column. When we switch between 8 and 12 mA the processwill stabilize at two lower levels.

� 5. Set the calibrator output to 8 mA.

� 6. Allow the process to stabilize. Adjust V8 (tank inflow) to balance the inflowand outflow.

� 7. Start the recorder at 10 in./min (1500 mm/s) and rapidly change thecalibrator from 8 to 12 mA. When the process has stabilized, stop therecorder.

� 8. Record the change in process level as read on the tank scale.

L start L finish

� 9. Perform calculations (see NOTES/CALCULATIONS).

NOTES/CALCULATIONS

Level start (Ls)

Level finish (Lf)

Level change Lc = Lf � Ls =

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14

Process Gain

1. Convert the Level Change (Lc) to a percent of transmitter span:

Lc/30" x 100% =

2 Express the variation of the VSD input signal as a percent.

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Process Dead Time

4 Process Dead Time (td) = time difference between point when the VSD inputsignal was changed from 8 to 12 mA and when process level started to rise

Process Time Constant

5 Process Time Constant (�) = time taken to reach 63.2% of final steady statevalue

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15

Figure 6-3.

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16

20-102 kPa3-15 psi

VSD

24 V − DC

SUPPLY FREQUENCY INPUT

ABOVE 70 Hz OR

DAMAGED

DO NOT SET F max.

PUMP MAY BE

CAUTION:

F2F1

24 V − DC

ALM−1

ALARM INDICATORS

ALM−2

1-5 V − DC

CONTROL OUT

AUXILIARY OUT

RATED 24 V − 1 A − DCRELAY 1 ISOLATED

CONTACT OUT

OUTPUTS

COM.

COMMUNICATIONS

COM.

1-5 V − DC

1-5 V − DC

1-5 V − DC

1-5 V − DC

ANALOG INPUTS

DRY CONTACTINPUTS

+5.0 V OPEN CIRCUIT

250

250

250

250

141315

−+ +

RS−485

4-20 mA 27

38

26

CO 2CO 1

(31)(32)−

+ +

20

23

7

4

4

3

2

1

4-20 mA

4-20 mA

4-20 mA

4-20 mA

B

A

22

25

24

30

18

21

5

2

2829

−+

−+

2D / P

1D / P

4-20 mA RLRL4-20 mA

PEN 1

SPAN

INPUT1-5 V − DC

SPAN

INPUT1-5 V − DC

PEN 2

250 250

TO PUMP

+ −4-20 mA

INPUTSIGNAL

100 mA

REMOTE24 V − DC OPEN CIRCUIT

DRY CONTACTMAINTAINEDMAINTAINED

3505MULTI-PROCESS STATION

I / P140 kPa

20 psiSUPPLY

INTERLOCK

PUMP-HEATER

MAINS

SUPPLY

PUMPSUPPLY

100 mA

SOLENOIDVALVE SV-1

DRY CONTACT

REMOTE24 V − DC OPEN CIRCUIT

TO+24 V − DC

SUPPLY24 V − DC

4-20 mA

3-15 psi20-102 kPa

20 psi / 140 kPa

−

+

−+

CAL.8-12 mA

Figure 6-4A.

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17

V−11

V−7V−6OVERFLOW

V−10

U−1

U−9U−8

COLUMNLEVEL

V−3

V−4

V−14

SV-1

TE

U−6U−7

HA−2

V−9

0-3 psi0-20 kPa

U−3

V−8

V−13

PRR−1

U−4

V−5

CV−1

SUPPLY

75 LITRES20 GALLONS

HOLDING TANK

100 psi700 kPa

PUMP

U−5

V−12

U−2HA−1

FI

V−1

V−2

VM7VM5

VM6

1

4-20 mA

+24 V − DCTO

D / P

PT

H L

Figure 6-4B.

REVIEW QUESTIONS

1. Why did the process level reach a steady state value rather than completelyfilling the tank to the overflow line?

18

19

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OBJECTIVES

At the completion of this laboratory exercise you will be able to use standardprocess instrumentation to observe and analyze the effects of setpoint and gainchanges on a controller and, using the observed information, determine theoptimum settings required to tune the controller.

DISCUSSION

The basic purpose of tuning is to match the P + I + D settings within the controller,to the dynamics of the process. There are two basic approaches to loop tuning:

a) Open loop, which we will examine later, andb) closed loop, which places the process in oscillation.

The desirable goal is to upset or disturb the process just enough to determine thePID values without upsetting the plant. There are many theoretical tuning methods.In this exercise we will examine the ultimate period or Ziegler-Nichols method.Because overall plant efficiency relies heavily on optimum tuning of all processesin the plant, it is important to understand this method of tuning.

In Exercises 9 and 12 we have observed that increasing the controller gain maylead to increased instability. Any control loop will oscillate in the controller gain (KP)is high enough. The period of the oscillation is called the natural or ultimate period(PU).

The ultimate period method requires placing the process in continuous amplitudeoscillation and then using the controller setting and measurements from the stripchart to determine the optimum settings of gain, Integral action and derivative actionfor the controller and the process.

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20

TIME

VARIABLEPuMEASURED

Figure 15-1.

EQUIPMENT REQUIRED

DESCRIPTION MODEL

Multi-Process Station including: 3505-M0Microprocessor PID Controller (LIC)Differential Pressure Transmitter (LT)Variable Speed Pump (VSP)Strip Chart Recorder (LR)

INSTRUMENT DATA

DEVICE MODEL SERIAL NO. CALIBRATED

LT 6-26" WC/4-20 mA

I/P 4-20 mA/3-15 psi

LR 4-20 mA/0-100%

Controller Configuration (See note in Exercise 9)

1. Setpoint = 50 %2. Gain = 1 (PB = 100 %)3. Reset = minimum rep/min (max. integral time min/rep)4. Derivative = 0.05 min.5. Auto/Manual = Auto6. Action = Reverse

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21

PROCEDURE

CAUTION!

Do not run pump for prolonged periods with a shut off head!

� 1. Set up and connect equipment as per the loop diagram. Valve settings asper diagram Figure 15-3. Configure the VSP to provide 0-10 GPM (36 lpm)for an input signal of 4-20 mA.

� 2. Calibrate the level transmitter for 6-26" WC.

� 3. Set the controller as per the Controller Configuration.

� 4. Manually adjust the controller output until the measured variable equals thesetpoint. Start the recorder and place the controller in automatic. Theprocess will stabilize close to the setpoint.

� 5. Disturb the process by increasing the setpoint for 5 seconds then reduceit back to 50 %. If the chart recorder displays the process as being incontinuous amplitude oscillations proceed with step 9. Otherwise proceedwith step 6.

� 6. Allow the process to stabilize until the process stabilizes.

� 7. On the controller, increase the gain (decrease the proportional band) togive more proportional action. The normal practice is to make steps infactors of 2 (i.e. PB = 100 % �50 % � 25 % � 12 % � 6 % … etc.)

� 8. Repeat steps 5 to 7 until the process responds with constant amplitudeoscillations.

� 9. Use the proportional setting and the period of oscillation in the Ziegler-Nichols equations to determine optimum controller settings.

Note: Some texts show slightly different coefficients on theequations.

� 10. Using the three calculated settings, evaluate the controller response tosupply and demand disturbances. Fine tuning may be necessary. Changesin process gain due to transmitter and VSP calibration variations will resultin values differing as much as 20 % or more.

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22

NOTES/CALCULATIONS

Kp = Calculated controller gain settingPB = Calculated proportional band settingTi = Integral time (min/repeat)RPM = Reset (repeats/min)td = Derivative time (min)Ku = Controller gain setting which resulted in constant amplitude oscillationsPu = Period of oscillation (minutes)

Proportional

Kp = 0.5 Ku = PB = 2 Pbu =

Proportional and Reset

Kp = 0.45 Ku = PB = 2.2 PBu =

Ti = Pu/1.2 = RPM = 1.2/Pu =

Proportional and Reset and Rate

Kp = 0.6 Ku = PB = 1.66 PBu =

Ti = Pu/2 = RPM = 2/Pu =

td = Pu/8 =

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23

Figure 15-2.

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24

20-102 kPa3-15 psi

VSD

24 V − DC

SUPPLY FREQUENCY INPUT

ABOVE 70 Hz OR

DAMAGED

DO NOT SET F max.

PUMP MAY BE

CAUTION:

F2F1

24 V − DC

ALM−1

ALARM INDICATORS

ALM−2

1-5 V − DC

CONTROL OUT

AUXILIARY OUT

RATED 24 V − 1 A − DCRELAY 1 ISOLATED

CONTACT OUT

OUTPUTS

COM.

COMMUNICATIONS

COM.

1-5 V − DC

1-5 V − DC

1-5 V − DC

1-5 V − DC

ANALOG INPUTS

DRY CONTACTINPUTS

+5.0 V OPEN CIRCUIT

250

250

250

250

141315

−+ +

RS−485

4-20 mA 27

38

26

CO 2CO 1

(31)(32)−

+ +

20

23

7

4

4

3

2

1

4-20 mA

4-20 mA

4-20 mA

4-20 mA

B

A

22

25

24

30

18

21

5

2

2829

−+

−+

2D / P

1D / P

4-20 mA RLRL4-20 mA

PEN 1

SPAN

INPUT1-5 V − DC

SPAN

INPUT1-5 V − DC

PEN 2

250 250

TO PUMP

+ −4-20 mA

INPUTSIGNAL

100 mA

REMOTE24 V − DC OPEN CIRCUIT

DRY CONTACTMAINTAINEDMAINTAINED

3505 MULTI-PROCESS STATION

I / P140 kPa

20 psiSUPPLY

INTERLOCK

PUMP-HEATER

MAINS

SUPPLY

PUMPSUPPLY

100 mA

SOLENOIDVALVE SV-1

DRY CONTACT

REMOTE24 V − DC OPEN CIRCUIT

TO+24 V − DC

SUPPLY24 V − DC

4-20 mA

3-15 psi20-102 kPa

20 psi / 140 kPa

−

+

Figure 15-3A.

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25

V−11

V−7V−6OVERFLOW

V−10

U−1

U−9U−8

COLUMNLEVEL

V−3

V−4

V−14

SV-1

TE

U−6U−7

HA−2

V−9

0-3 psi0-20 kPa

U−3

V−8

V−13

PRR−1

U−4

V−5

CV−1

SUPPLY

75 LITRES20 GALLONS

HOLDING TANK

100 psi700 kPa

PUMP

U−5

V−12

U−2HA−1

FI

V−1

V−2

VM6

VM7VM5

1

4-20 mA

+24 V − DCTO

D / P

LH

Figure 15-3B.

REVIEW QUESTIONS

1. Is the ultimate period method an open-loop or closed-loop method of controllertuning? Explain.

2. For the ultimate period method, why is the calculated gain value different for PIcontrol and straight proportional control?

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26

3. What information must be obtained to tune a controller using the ultimate periodmethod and what is it used to determine?