practical demonstration of flow instruments

TASK DETAILING MANUAL

Module I-4 www.arfanali.webs.com

Practical Demonstration of

FLOW INSTRUMENTS

MODULE NO. : I-4

MODULE SUBJ.: Flow Instruments

http://www.arfanali.webs.com/



Tasks:

I-4.1 Describe the procedures used to remove an orifice plate from a Daniel’s

senior orifice fitting.

I-4.2 Demonstrate servicing and calibration of a pneumatic differential

pressure flow transmitter.

I-4.3 Demonstrate servicing and calibration of an electronic differential

pressure flow transmitter.

I-4.4 Demonstrate ability to isolate the transmitter from process without

damage to equipment.

I-4.5 Perform zero check procedure (static zero adjustment).

I-4.6 Perform servicing of a turbine meter. Check magnetic pickup for

damage. Calibrate pulse to mA converter.

I-4.7 Perform service and check of a Rotameter.

I-4.8 Service and calibrate a Foxboro 43AP controller.

I-4.9 Calibrate square root extractor.

I-4.10 Troubleshooting 3 way / 5 way valve manifold.

MODULE No.: I-4 Flow Instruments

TASK No.: I-4.1 Describe the procedures used to remove an orifice

plate from a Daniel’s senior orifice fitting.




Reference:

Materials: None.

Equipment & Tools: None.

Conditions: None.

Requirements By Trainee:

To study the task and familiarise himself,

Be able to identify parts of Daniel’s senior orifice,

Be able to state the differences between Senior / Junior and flange orifices,

Be able to remove and reinstall an orifice plate from senior orifice fitting,

Draw / Sketch types of orifice fittings used in his working area,

Describe an understanding to his trainer, and

Write observations and procedures in his workbook.

TASK No.: I-4.1

“Continue”

Details:

Orifice Plates

Orifices are the most common form of custody transfer meter for Oil and Gas

production facilities. Numerous types of devices are available for transmission,

recording, and accumulation of data from orifice meters.




An Orifice plate is a thin metal plate with a precisely machined circular opening

be inserted in the flow stream. As flow passes through the opening (orifice) some

of the upstream pressure head is converted into velocity head. The velocity head is

greatest and pressure head smallest at the "vena contracta" located slightly

downstream of the orifice. The differential pressure across the orifice is related to

velocity by Bernoulli's equation. When the differential pressure and static pressure

are measured, and the orifice size, pipe size, and the gas properties are known, the

flow rate can be calculated.

TASK No.: I-4.1

“Continue”

Figure I-4.1A, Senior Orifice Fitting




To Remove Orifice Plate

(a) Open No. 1 (Max. two turns only).

(b) Open No. 5.

(c) Rotate No. 6.

(d) Rotate No. 7.

TASK No.: I-4.1

“Continue”

(e) Close No. 5.

(f) Close No. 1.

(g) Open No. 10 B.

Figure I-4.1B




(h) Lubricate through No. 23.

(i) Loosen No. 11 (Do not remove No. 12).

(j) Rotate No. 7 to free Nos. 9 and 9A.

(k) Remove Nos. 12,9 and 9A.

To Replace Orifice Plate

(a) Close 10B.

(b) Rotate No. 7 slowly until plate carrier is clear of sealing bar and gasket level.

Do not lower plate carrier onto slide valve.

(c) Replace Nos. 9 A, 9 and 12.

(d) Tighten No. 11

(e) Open No. 1.

(f) Open No. 5.

(g) Rotate No. 7.

(h) Rotate No. 6.

(i) Close No. 5.

(j) Close No. 1.

(k) Open 10 B.

(l) Lubricate through No. 23.

(m) Close No. 10 B.


TASK No.: I-4.2 Demonstrate servicing and calibration of a pneumatic

differential pressure flow transmitter.

Reference: OJT Instructor to arrange reference catalogue / service

manual for pneumatic DP flow transmitter relevant to

each working area.




Materials: Cleaning rags.

Equipment & Tools: 1. Tool Box,

2. Standard Output gauge, and

3. Pneumatic / Hydraulic pressure calibrator.

Conditions: Work permit



To select the proper tools / equipment to perform this task,

Understand the principle of operation of pneumatic DP flow transmitter,

Be able to perform calibration adjustments of the pneumatic flow transmitter,

Draw / Sketch the calibration set-up in his workbook,

Be able to perform routine service of a pneumatic flow transmitter,

Discuss an understanding to his trainer, and


TASK No.: I-4.2

“Continue”

Details:

Differential Pressure Transmitters (DPT.)

These transmitters are used when the controller, recorder, or indicator needs to be

located in a control room or panel where it is undesirable to pipe the process fluid.

They are also used when several devices are to be operated from a single

measurement or when elevated zero is required. The output is usually 4-20,

milliamps for electronic transmitters or 3-15 psig (20-100 kPa) for pneumatic

transmitters. Other signals can be used if required by the receiver, but these are the

most common and should be used if possible.

Elevated zero occurs when the base value of the measured variable is not at

atmospheric pressure. Most transmitters have this as an option, while most




controllers do not. Elevated zero is used when the pressure range of interest is

narrow and at a fairly high level.

Suppressed zero, where the base value of the measured variable is below

atmospheric pressure, is sometimes available. Usually, the zero is as near to

perfect vacuum as possible and the unit is called a absolute pressure transmitter.

The use of pneumatic transmitters is decreasing; however, a number of

manufacturers still make them for the replacement market and some new

installations are still being made. Pneumatic transmission may be advantageous

when existing equipment is pneumatic with which operating personnel are already

familiar.

The next figure shows the main parts of a pneumatic differential pressure

transmitter, these are:

1. Twin diaphragm Capsule as a sensing element,

2. Force Bar,

3. Leaf Spring,

4. Range Adjusting Bar,

5. Booster Relay, and

6. Feedback Bellows.




TASK No.: I-4.2

“Continue”

TASK No.: I-4.2

“Continue”

Calibration

Figure I-4.2A, Pneumatic Differential Pressure Transmitter.




Calibration is required if the transmitter has been taken apart for cleaning or for

parts replacement, if a change of range is desired, or if the amount of zero

elevation or suppression is changed substantially.

If the capsule was removed or the flexure cap screw loosened, before calibrating,

make the flexure cap screw adjustment above.

The transmitter to be calibrated to 3 to 15 psi signal pressure range, at which the

receiver signal is used.

Calibration procedures; detailed bench calibration and in-line calibration

procedures of the pneumatic differential pressure transmitter are listed in the

reference catalogue or service manual of the applied model. Consult your trainer.

TASK No.: I-4.2

“Continue”

Maintenance and Servicing

Maintenance and servicing of pneumatic differential pressure transmitter are

limited to clean or replace its parts, such as:

1. Supply Air Filter blow out at least once a day,

2. Replace Screen Filter of the process inlet,

3. Clean Nozzle Assembly,

Regulate air supply to pressure at

which transmitter will be operating

Calibrating

Air Supply

Bleeder Valve

Test gauge or reading input signal pressure. manometer for

Vent low-pressure

side of transmitter.

0 to 20 psi

Output test gauge

Figure I-4.2B, DP flow transmitter calibration setup




4. Clean booster relay Restrictor,

5. Replace Booster Relay,

6. Change Range Bar,

7. Remove / Replace Diaphragm Capsule, and

8. Adjusting Flexure Cap Screw.

Disassembly;

Normal servicing of the transmitter does not require the removal of any parts other

than those already mentioned. Further disassembly is not recommended because

of possible loss of accuracy or damage to the transmitter, detailed servicing

procedures are mentioned in maintenance section of the selected transmitter

model. Consult your trainer.


TASK No.: I-4.3 Demonstrate servicing and calibration of an electronic

differential pressure flow transmitter.

Reference: OJT Instructor to arrange reference catalogue / Service

manual for an electronic differential pressure flow

transmitter model relevant to each working area.

Materials: 1. Cleaning rags, and

2. Solvent.





2. Hydraulic or Pneumatic pressure calibrator, and

3. Function Generator and digital Multimeter.

Conditions: Work permit.



Be able to describe the operation principle of the electronic DP transmitter,

Be able to identify the main parts of an electronic DP transmitter,

Perform periodic adjustments / calibration of an electronic transmitter,

Perform periodic and corrective maintenance or replace parts of an electronic

DP transmitter,

Draw / Sketch calibration set-up of the electronic DP transmitter,

Discuss an understanding with his trainer, and

Write observation and procedures in his work book.

TASK No.: I-4.3

“Continue”

Details:

Electronic Differential Pressure Flow Transmitters

Electronic transmitters with 4-20 milliamp outputs are the most common.

Differential pressure flow transmitters are available in a variety of ranges. The

ranges available vary from one manufacturer to another.

The range and the span are two different parameters:

The span; is the actual differential pressure range to be measured after the

transmitter has been adjusted.

The range; is the differential pressure range within which the span can be adjusted.

Most transmitters have two adjustments, zero and span:




The zero; is adjusted so that the output is minimum (4 mA) at zero differential

pressure, or the bottom of the span if elevated zero is used.

The span; is adjusted so that the output is maximum (20 mA) when the pressure is

at the top of the span.

But the zero must always be rechecked after the span has been adjusted and the

span checked after the zero adjustment.

Next figure shows the main parts of an electronic differential pressure transmitter;

Sensing module, and

Electronic housing contains; header assembly board, DC amplifier board, and

calibration board

TASK No.: I-4.3

“Continue”




Figure I-4.3A, Electronic Differential Press. Transmitter, Main Parts.




TASK No.: I-4.3

“Continue”

Principle of operation

This electrical block diagram illustrates the operation of the electronic differential

pressure transmitter.

The process pressure is transmitted through an isolating diaphragm and oil fill

fluid to a sensing diaphragm located in the centre of the cell. The position of

the sensing diaphragm is detected by the capacitance plates, the sensor is

driven by an oscillator.التذبذب

Demodulator consists of a diode bridge, which rectifies the ac signal to dc to

drive the oscillator.

Voltage regulator provide a constant voltage of 6.4 V dc for the reference and 7

V dc to supply the oscillator.

Current control amplifier drives the current control circuitry to a level that

causes the current detector to feedback a signal.

The current limit prevent output current from exceeding 30 mA in case of

overpressure .

Figure I-4.3B




TASK No.: I-4.3

“Continue”

This figure shows the signal terminals, which are located in the electrical housing

in a separate compartment. All power to the transmitter is supplied over the signal

wiring and there is no additional wiring required. Signal wiring needs to be

shielded, but twisted pair should be used for best result. Output current is limited

to 30 mA dc on the 4-20 mA dc unit.

Calibration

Span Adjustment Range; is continuously adjustable to allow calibration anywhere

between maximum span and 1/6 of maximum span.

Zero Adjustment Range; Transmitter’s zero is the lowest value of the transmitter

range, at which the output of the electronic DP transmitter is 4 mA.

The zero and span adjustment potentiometers are accessible externally and are

located behind the nameplate of the transmitter.

TASK No.: I-4.3

“Continue”

Figure I-4.3C




The recommended procedure for zero and span adjustment detailed in the

reference catalogue / service manual of the electronic differential pressure

transmitter model, consult your trainer.

Linearity Adjustment; this is a factory calibration adjusted for optimum

performance over the calibrated range of the instrument and is not normally

adjusted in the field, however only maximise linearity over particular range be

applicable.

Damping Adjustment; the output amplifier boards are designed to permit damping

of rapid pulsations in the pressure source by adjusting the control marked

“Damping” located on the solder side of the amplifier board.

Calibration procedures for adjusting or changing ranges are outlined in the

calibration section of the transmitter catalogue, consult your trainer to proceed.

Maintenance

Maintenance is a technique for checking out the transmitter components, the

method for disassembly and reassembly, and a troubleshooting guide.

Test Terminal; to assure that there is no leakage current through the diode

when a test reading is resistance of the test connection or meter should not

exceed 10 ohms.

Sensing Module Checkout; the sensing module is not a field repairable and

must be replaced if found to be defective. If no obvious defect, such as a

punctured isolating diaphragm or loss of fill fluid is observed, the sensing

module may be checked. The detail procedure to checkout the sensing module

is listed in the maintenance section of the transmitter’s catalogue. Consult your

trainer.

Circuit Boards Checkout; the printed circuit boards “Amplifier board and

Calibration board” can most easily be checked for a malfunction by

substituting into the circuit

TASK No.: I-4.3

“Continue”

Troubleshooting

1) SYMPTOM: HIGH OUTPUT




Potential source and Corrective action.

Impulse Piping

Check for leaks or blockage.

Check for liquid in dry lines.

Check for sediment in transmitter process flanges.

Transmitter Electronics Connections

Make sure bayonet connectors are clean and check out the sensor connections.

Check that bayonet pin #8 is properly grounded to the case.

Transmitter Electronics Failure

Determine faulty circuit board by trying spare boards.

Replace faulty circuit board.

Power Supply

Check output of power supply.

2) SYMPTOM: LOW OUTPUT OR NO OUTPUT

Potential source and Corrective action

Loop Wiring

Check for shorts and multiple grounds.

Check polarity of connections.

Check loop impedance.

Impulse Piping

Check that pressure connection is correct.

Check for leaks or blockage.

Check for entrapped gas in liquid lines.

Check for sediment in transmitter process flanges.

TASK No.: I-4.3

“Continue”


Check for shorts in sensor lead.

Make sure bayonet connectors are clean and check the sensor connections.

Check that bayonet pin #8 is properly grounded to the case.

Test Diode Failure

Replace test diode or jumper test terminals.







3) SYMPTOM: ERRATIC OUTPUT

Potential source and Corrective action

Loop Wiring

Check for intermittent shorts, open circuits and multiple grounds.

Process Fluid Pulsation

Adjust electronic damping pot (4-20 mA dc only).

Impulse Piping

Check for entrapped gas in liquid lines and for liquid in dry lines.


Check for intermittent shorts or open circuits.

Make sure that bayonet connectors are clean and check the sensor connections.

Check that bayonet pin#8 is properly grounded to the case.





TASK No.: I-4.4 Demonstrate ability to isolate the transmitter from

process without damage to equipment.

Reference: None

Materials: Cleaning Rags.




Equipment & Tools: Tool Box.

Conditions: None.



Be able to select proper tools to perform this task,

Be able to demonstrate safe isolation procedure of a flow transmitter in service,


Write observations and procedure in his workbook.

TASK No.: I-4.4

“Continue”

Details:




TASK No.: I-4.4

“Continue”

To perform safe isolation of a DP transmitter in service, follow the next:

1. Fill in your work permit.

Figure I-4.4A, Piping and Tubing arrangement of a DP transmitter




2. Using Soap solution and brush, check for any process leakage.

3. In case of crude oil (only visual inspection). If there is any leakage from fitting,

tighten it.

4. Close the high and low blocking valves.

5. Open the by pass valve.

6. Slowly open high and low drain plugs.

7. Slowly start to open high pressure blocking valve to flush the high

pressure impulse line, then close it.

8. Slowly open low pressure blocking valve to FLUSH THE LINE, then

close it.

9. Fix high and low drain plugs, and tighten them.

10. Open high and low blocking valves.

11. Close the By-pass valve so that the transmitter in service.


TASK No.: I-4.5 Perform zero check procedure (static zero adjustment).

Reference:

Materials: 1. Cleaning rags, and

2. Solvent.




Equipment & Tools: 1. Tool Box, and

2. Standard output gauge.




Be able to select proper tools to perform this task,

Be able to perform static zero adjustment of a DP flow transmitter,


Write observation and procedures in his workbook.

TASK No.: I-4.5

“Continue”




Details:

Figure I-4.5A, illustrates piping and tubing arrangement of a field mounted flow

recorder as an example to proceed static zero adjustment.

TASK No.: I-4.5

“Continue”

Static Zero Check;

If the instrument has a static pressure element, perform the following check:

Figure I-4.5A, Field Mounted Recorder Piping Arrangement




With no pressure applied, check static pressure zero. If minor adjustments are

required, make adjustments using the zero adjust screw.

Leak Checking and Zero Adjustment:

1. OPEN block and shut-off valves,

2. CLOSE block valves,

3. OPEN equaliser valve(s),

4. OBSERVE DP pen position, with calibration chart installed:

If pen position is slightly off of zero, make fine adjustment using pen zero

adjust screw.

5. CLOSE equaliser valve(s),

6. OBSERVE DP pen position:

a) If pen position at ZERO, no further check required,

b) If pen position UPSCALE, possible leak on low-pressure side (Check /

tighten connections), and

c) If pen position DOWNSCALE, possible leak on high-pressure side (Check /

tighten connections).


TASK No.: I-4.6 Perform servicing of a turbine meter. Check magnetic

pickup for damage. Calibrate pulse to mA converter.

Reference: OJT Instructor to arrange reference catalogue / service

manual for turbine meter model relevant to each

working area.




Materials: 1. Cleaning Rags, and

2. Solvent.

Equipment & Tools: 1. Frequency generator / counter,

2. Digital Multimeter, and

3. Function generator.




Be able to describe the main parts of a turbine flow meter and its principle of

operation,

Be able to define the meter factor of a turbine flow meter,

Understand flow calculation of using turbine flow meter,

Perform periodic maintenance and troubleshooting of turbine flow meter,

Be able to calibrate turbine flow analyser,

Draw / Sketch calibration set-up,



TASK No.: I-4.6

“Continue”

Details:

Turbine Meters

Turbine meters consist of:

1. A propeller mounted in a precisely machined housing, and

2. One or two pickup devices are mounted externally in the body in the same

plane as the rotor blades.

Principle of Operation;




Fluid flowing through the meter causes the rotor to rotate at a speed proportional

to the flow velocity and viscosity. As each blade tip passes the pickup a signal

pulse is generated. The number of pulses per unit time allows calculation of the

flow velocity, which can be used to determine flow rate.

Q = T f / K

Where

Q is the volumetric flow rate (gallon/min.),

K is turbine meter factor, pulses per volume unit ( pulses/gal ).

f is number of frequency (Hz).

T is a time constant ( such as 60 for gpm ).

Most turbine meters are threaded or mounted between flanges. Some turbine

meters are available which insert into user supplied piping.

Flow Analyser; receives an electronic pulse train from a flow meter and provides

a registration of totalised flow and an indication of flow rate by utilisation of its

microprocessor-based circuitry. The totalised flow and flow rate are displayed on

two six digit liquid crystal displays (LCD’s). Both displays are properly labelled

with respective units of measurement.

TASK No.: I-4.6

“Continue”




0

Maintenance and Repairs;

1) Turbine flow meter is virtually maintenance-free.

The frequency of periodic checks depends on the service to which the meter is

applied.

TASK No.: I-4.6

“Continue”

The following suggestions may prove helpful toward determining when to inspect

the meter for possible wear or damage:

a) Significant variations from normal flow rates should be sufficient notice to

remove the meter from the line and examine its internal parts for damage or

wear.

b) Other operators may prefer to make periodic inspections even though marked

variations from normal flow rates have not been observed.

Figure I-4.6A, Turbine Flow Meter, Main Parts.




TASK No.: I-4.6

“Continue”

2) A specific sequence of steps and certain precautions should be observed in

removing the meter from the line, disassembling and reassembling it. Particular

care should be given to note the direction-of-flow arrows on the various parts

of the meter.

Preparing for Installation:

1. Remove magnetic pickup or protect it to prevent damage.

2. Remove the three socket head capscrews from each end of the housing.

3. Remove upstream and downstream bearing supports and rotor.

Figure I-4.6B, Turbine Flow Meter Principle of Operation.




If bearing supports are stuck, drive them out with a small wooden or plastic rod

and hammer. Use extreme caution in prying on the beam supports since the

internal parts may break or shatter. Tap alternately on blades of supports to

prevent damaging housing.

4. Clean bore of housing with a swab and remove any burrs or rough spots.

5. Clean screw hole area to insure proper seating of new capscrews.

Installing Replacement Kit:

1.Grease and insert downstream bearing support so direction of flow arrow

corresponds with the arrow on outside of housing. Align the index marks (punch

marks) on the bearing support and the edge of the housing.

2. Install downstream retaining capscrews and tighten.

3. Insert rotor with direction arrow properly aligned. Be sure its shaft enters the

downstream bearing.

4. Grease and insert upstream bearing support in housing and align the index

marks. It may be necessary to spin the rotor to permit its shaft to enter the

bearing. “ Do not force the bearing support down against the rotor as this may

break the rotor shaft.

5. Install upstream retaining capscrews and tighten.

6. Be sure rotor is free to spin before placing meter in flow line.

TASK No.: I-4.6

“Continue”

7. For positive factor identification, wrap strap of plastic tag bearing factor around

conduit adapter, thread end through hole in tag and pull tight. Cut off excess

strap length.

8. Screw magnetic pickup in all the way and then screw out 1/4 tum. Lock pickup

retainer nut.





TASK No.: I-4.7 Perform service and check of a Rotameter.


manual for the Rotameter model relevant to each

working area.

Materials: 1.Cleaning rags, and

Figure I-4.6C, Turbine Flow Meter Parts Replacement.




2. Solvent.

Equipment & Tools: 1. Tool Box, and

2. Digital Multimeter.


Requirements by Trainee:

To study the task and familiarize himself,

Understand the operation principle of the variable area flow meter,

Be able to identify the main parts of the Rotameter,

Understand the difference between Orifice flow meter and Rotameter,

Perform periodic and corrective maintenance or replace parts of Rotameter,

Draw / Sketch process piping arrangement of the Rotameter,


Write observation in his workbook.

TASK No.: I-4.7

“Continue”

Details:

Variable Area Meters

Variable area meters, which are also known as “rotameters” have a vertical

tapered tube, which is partially blocked by a piece of material, called the float.

The float is not actually buoyant in the process fluid and is constructed from a

heavy material, often stainless steel. When fluid enters the bottom of the rotameter

it exerts Pressure on the float and causes the float to rise in the tube. As the float

rises, the space around the float in the tube increases and allows the pressure

above and below the float to equalize. When the difference in pressure is such that

the weight of the float is counter balanced, the float becomes stationary and the

flow can be determined. The float height is proportional to the flow rate.

The tube can be transparent to allow direct observation of the float if the pressure

is low enough for safety. If the pressure is high enough to cause safety concerns or




the fluid is considered too dangerous for other reasons, the tube can be made of

stainless steel and the position of the float sensed magnetically. This type is

known as an armored rotameter

As illustrated in figures I-4.7A&B, at equilibrium there are three forces working

on the float:

1. A downwards directed force exerted by the gravity which is constant.

2. An upwards directed buoyancy (Archimedes law) which is constant if the

density of the measured liquid or is constant.

3. An upwards directed force exerted by the flowing liquid or gas.

TASK No.: I-4.7

“Continue”

Figure I-4.7A, Float at equilibrium position




TASK No.: I-4.7

“Continue”

Maintenance

There is no routine maintenance to be performed of the Rotameter. If meter

operation is affected by defective parts these parts to be replaced.

Detailed procedures to service or replace Rotameter parts are listed in the

reference service manual. Consult your trainer to perform the following:

1. Float and 0-ring Replacement,

2. Magnetic Switch and Relay replacement,

3. Indicator Reference Mark (Zero) Adjustment,

4. Alarm Set Point Adjustment, and

5. Adding the Alarm Option.

Figure I-4.7B, Rotameter, main parts




TASK No.: I-4.7

“Continue”


TASK No.: I-4.8

Figure I-4.7C, Metal Rotameter with Magnetic Indicator




Service and calibrate a Foxboro 43AP controller.


manual for pneumatic controllers models relevant to

each working area.

Materials: 1. Plastic / St.St. Tubing,

2. Regulated Air Supply.

Equipment & Tools: 1. Pneumatic calibrator bench or Druck Pump,

2. Standard test gauges,

3. Service/ Repair Kit, and

4. Tool Box.

Conditions: None.



Be able to identify the major components of pneumatic controller,

To describe the principle of operation of pneumatic indicating controller,

Be able to perform periodic adjustments / calibration of the controller,

To perform preventive maintenance, service, parts replacement of the

controller,

Draw/ Sketch calibration set-up in his work book,



TASK No.: I-4.8

“Continue”

Details:

43AP Controllers

43AP controller is a device, which senses the pressure in the

process and develops an output, which controls a device to regulate that pressure.

The control device, or end element, is usually a pneumatic-control valve. The




controller output is usually either a 3-15 or 6-30 psig (20-100 or 40-200 kPa)

pneumatic signal.

These controllers can be categorized either as indicating or blind. The indicating

controller has a mechanism so that the operator can read the process pressure

directly from the controller. The blind controller has no direct-reading mechanism

and the operator must rely on an adjacent pressure gauge or other device to know

the process pressure. The indicating controller set point is usually marked on the

indicator; thus it is easy to adjust to the desired point.

Adjustment of the blind controller is more of a trial and error process. Indicating

controllers are somewhat more expensive than blind controllers, but the cost

difference is moderate if a pressure gauge can be eliminated.

Pressure controllers must provide an output to control the end element. This can

be an electric or pneumatic signal, but is most often pneumatic for field-mounted

controllers. The pneumatic signal is usually 3-15 psig (20-100 kPa), but it can be

6-30 psig (40-200 kPa) if required to reduce the control valve actuator size. The

control action needed for pressure control is proportional plus integral, or P and I

(integral is also referred to as reset by some manufacturers).

The proportional action varies the output in proportion to the difference between

the measured pressure and the set pressure. The integral or reset action gradually

increases the amount of the correction until the measured pressure is returned to

the set point. A more extensive discussion of control modes and controller tuning

can be found in the controller’s catalogue or service manual, consult your trainer.

TASK No.: I-4.8

“Continue”

Preparations

A common option for pressure controllers is an auto/manual switch. This is a

valve, which allows the output of a manual regulator to be directed to the end

element (valve actuator) instead of the controller's automatic output. The transfer

can be either bumbles where the outputs are automatically matched to each other

when the auto/manual switch is transferred, or manual balance where the operator

must match the manual regulator output to the automatic output transfer to manual

or the set point to the process variable before transfer to automatic.




Pressure controllers are either surface, panel, pipe-stand, or yoke mounted.

Surface-mounted controllers are fastened to a wall or other vertical surface. Panel-

mounted, also called flush-mounted, controllers are mounted in a cutout in a

control panel. Pipe-stand mounting occurs where a vertical or horizontal pipe

support is constructed and the controller is provided with a bracket and U-bolts to

attach it to a two-inch pipe-stand. It is not a good idea to support controllers on

process piping. Yoke mounted controllers are fastened to the valve yoke with

special brackets. Yoke mounting is convenient when the valve is accessible.

TASK No.: I-4.8

“Continue”

Principle of operation

Figure I-4.8A, explains in steps how the pneumatic indicator controller works;




TASK No.: I-4.8

“Continue”

Control Adjustments

Proportional Controller (P controller);

Figure I-4.8 A, Controller’s Principle of Operation.




Figure I-4.8B, illustrates the effect of various proportional band settings

Proportional plus Reset Controller (PI Controller);

Figure I-4.8C, illustrates the effect of various Reset Times

TASK No.: I-4.8

“Continue”

Calibration

Calibration is required if the controller has been taken apart for cleaning or for

parts replacement, if a change of range is desired, or if the amount of zero is

changed substantially.

Figure I-4.8B, PB Effects at Various Settings

Figure I-4.8C, Effects of Various Reset Times




If the capsule was removed or the flexure cap screw loosened, before calibrating,

make the flexure cap screw adjustment above.

The controller to be calibrated to 3 to 15 psi signal pressure range, at which the

receiver signal is used.

Calibration procedures; detailed bench calibration and in-line calibration

procedures of the pneumatic indicating controller are listed in the reference

catalogue or service manual of the applied model. Consult your trainer.

Maintenance and Servicing

Maintenance and servicing of pneumatic indicating controller are limited to clean

or replace its parts, such as:

1. Supply Air Filter blow out at least once a day,

2. Replace Screen Filter,

3. Clean Nozzle Assembly,

4. Clean booster relay Restrictor,

5. Replace Booster Relay,

6. Change measuring Range ,

7. Remove Measurement Pointer or Set Point Index, and

8. Adjusting controller’s Alignment.

Disassembly; normal servicing of the controller does not require the removal of

any parts other than those already mentioned. Further disassembly is not

recommended because of possible loss of accuracy or damage to the controller,

detailed servicing procedures are mentioned in maintenance section of the selected

pneumatic indicating controller model. Consult your trainer.


TASK No.: I-4.9 Calibrate square root extractor.


manual for Square root extractor model in each

working area.

Materials:





2. Standard test gauges / Digital Multimeter, and

3. Pneumatic calibrator / Function generator.




Understand the function of the square root extractor,

To state the purpose of using the square root extractor in a control loop,

Be able to calibrate, inspect and replace square root extractor unit,


Write observations in his workbook.

TASK No.: I-4.9

“Continue”

Details:

Function:

Pneumatic or Electronic Square-Root Extractor receives a pneumatic or electronic

analogue input signal, and provides a pneumatic or electrical output signal

proportional to the square root of the input signal.

Principle:

This instrument solves the equation A = Square root of E, where E and A are

input and output signals, respectively.

It is used for linearising, differential pressure flow signals

Method of Operation:

To understand square root extractor method of operation, figure I-4.9A illustrates

ECKARDT pneumatic square root extractor as an example and the following steps

explains its method of operation




TASK No.: I-4.9

“Continue”

The input signal is applied to a

1) Diaphragm which causes the

2) Force beam carrying the

3) Flapper to move towards the

4) Nozzle. The thereby increased nozzle back pressure is applied to the

5) Roll diaphragm which is displaced upwards against the pressure of the

6) Spring. The movement of roll diaphragm (5) is transmitted without loss of

movement via the

7) Piston rod and a tape-driven

8) Segment to the

9) Shaft. A root extracting, or respectively, function generating

10) Cam is rigidly attached to the external extension of this shaft. By means of

11) Cam follower and

Figure I-4.9A, Pneumatic Square root Extractor Operation Method




12) Tension spring, the rotary movement is converted into a vertical movement

which, by being applied to force beam (2), opposes the force generated by

diaphragm (1), so as to bring forces into equilibrium. The rotation of shaft (9)

is also transmitted via the

13) Tape drive which alters the tension of the

14) Spring, and thereby alters the tension of the

15) Force beam and attached flapper in relation to the

16) Nozzle, the change in back pressure so generated being applied to the

17) Double diaphragm in the amplifier unit. The resultant output pressure is fed

back to the

TASK No.: I-4.9

“Continue”

18) Input diaphragm acting on the force beam (15) which is then brought to a

position of equilibrium.

Calibration:

Square root extractor is factory calibrated at a reference supply pressure. To

maintain specified accuracy at a different supply pressure, the instrument must be

recalibrated to the new pressure, figure I-4.9B illustrates calibration setup of our

model device. The instrument to be calibrated in the same position of service

installation. Detailed calibration procedure is listed in the reference catalogue or

service manual. Consult your trainer.




TASK No.: I-4.9

“Continue”

Maintenance:

Maintenance of a pneumatic square root extractor is limited to periodic checks of

supply pressure or input / output signals and clean or replace parts, such as; supply

air filter, clean restrictor, replace relay, replace screen filters and service the

service manifold.

Fault Finding:

1) Output signal rises but does not reach full value, possible cause is input signal

line not pressure tight, or blocked restrictor, check connections or clean

restrictor.

2) Output signal fluctuates, possible cause is cam follower track or roller dirty,

clean cam, track and follower roller.

Figure I-4.9B, Square root Extractor Calibration Setup.





TASK No.: I-4.10 Troubleshooting 3 way / 5 way valve manifold.


manual for manifold type relevant to each working

area.

Materials: 1. Cleaning Rags, and

2. Solvent

Equipment & Tools: Tool Box

Conditions: Work permit






Select proper tools to perform this task,

To understand the purpose of using manifolds for DP measurement,

To perform preventive maintenance, service, parts replacement of manifolds,

Draw/ Sketch manifold process piping in his workbook,



TASK No.: I-4.10

“Continue”

Details:

Function:

Meter manifolds are made for use with field meters or differential pressure

transmitters to achieve meter operation, calibration and service in easy and safe

way.

Features:

There are two types of meter manifolds, 3-valve and 5-valve. In 3-valve

manifolds, there are two main block valves and one block equalising valve. In 5-




valve manifolds, there are two main block valves along with double block and

bleed for the bypass line. Manifolds are available in both hard or soft seat

configurations, to withstand process pressure and temperature.

TASK No.: I-4.10

“Continue”

Figures I-4.10 A&B, illustrates 5-valve manifolds status in case of normal

operation and meter calibration. Consult your trainer for safe isolation procedure.

Figure I-4.10B, 5-Valve Manifold in case of meter calibration.


practical demonstration of flow instruments

Documents