Module I-3 Pressure Instruments
Content
TASK DETAILING MANUAL -
Practical Demonstration of
PRESSURE INSTRUMENTS
MODULE NO. : I-3 MODULE SUBJ.: Pressure Instruments
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TASK DETAILING MANUAL Tasks: I-3.1 Demonstrate Demonstrate servicing and calibration of different types of pressure gauges. I-3.2 Service and calibrate a high/ low pressure switch.
I-3.3 Service and calibrate a differential pressure switch
I-3.4 Describe the meaning of the terms, zero, span, linearity when calibrating a pressure transmitter.
I-3.5 Demonstrate servicing and calibrating a pneumatic pressure transmitter.
I-3.6 Demonstrate Demonstrate calibration of a smart transmitter using a h hand and held communicator.
I-3.7 Demonstrate Demonstrate servicing and calibrating an electronic transmitter
I-3.8 Demonstrate Demonstrate iisolation solation procedure from process an and d electrical supply on a pneumatic/electronic pneumati c/electronic pressure tran transmitter. smitter.
I-3.9 Check function / ad adjustment justment / m maintenance aintenance of pressure regulators ffor or process lines. lines.
I-3.10 Service and calibrate a pneumatic in indicating dicating con controller. troller.
MODULE No.: TASK No.:
I-3 Pressure Instruments I-3.1 Demonstrate servicing and calibration of different types of pressure gauges.
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TASK DETAILING MANUAL Reference:
OJT Instructor to arrange reference catalogue for pressure gauges relevant relevant to each working area.
Materials:
1. Different types of pressure gauges as model models. s. 2. Cleaning rags
Equipment & Tools: 1. Tool Box 2. Pressure gauges tool kit
Conditions:
None.
Requirements By Trainee:
To study the task and familiarize himself.
Be able to identify pressure gauges types.
Be able to calibrate different types of pressure gauges.
Be able to disassemble and reassemble any pressure gauge.
Perform adjustments and service the pressure gauges.
Describe an understanding to his trainer.
Write observations and procedures in his work book.
TASK No.: I-3.1
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Details: Pressure Gauges A pressure gauge is a device, which senses pressure and provides a visual representation of that pressure. Most pressure gauges have bourdon tube sensors. Vacuum gauges and low-range gauges often use bellows sensors.
Differential-pressure can manufacturer use piston or and bellows sensors.range. The sensor type is usually dictated by thegauges preferred the required
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TASK DETAILING MANUAL Pressure gauges should be selected so that the expected operating pressure is in the center third of the gauge range. It is also important that the highest pressure that will ever be applied to the gauge be below the maximum reading. rea ding. Usually, the gauge can be selected so that the gauge maximum is above the set pressure of the system relief valve and the normal pressure is in the readable range. Pressure gauges are sometimes liquid filled. This is to protect the gauge dial and movement from the atmosphere. The liquid fill also provides some pulsation or vibration dampening. Glycerin is the most common fill liquid. Pressure gauges lose accuracy when exposed to hot fluids. When the process temperature is above approximately 180ºF (82ºC) a siphon should be installed. If the process fluid will not condense, at ambient temperature, the siphon can be filled with a suitable fluid such as ethylene glycol or glycerin. Differential-pressure gauges are useful when a pressure difference that is small compared to the static pressure needs to be measured. Differential-pressure gauges differ from static-pressure gauges in that they have two pressure connections. Differential gauges must be installed with an equalizing valve so that they will not be overranged while while disconnecting disconnecting..
TASK No.: I-3.1
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TASK DETAILING MANUAL Calibration Check To check the calibration of a gauge it must be removed from the line or equipment eq uipment and installed on a dead-weight tester, or test gauge manifold. Check calibration as illustrated at 1/3, 1/2, and 2/3 of the dial range. If the readings are outside of the tolerance limits, the instrument requires recalibration. Remove the front ring, glass
front (lens) and gasket. Then recalibrate as follows: fo llows:
TASK No.: I-3.1
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Recalibration
There are three specific adjustments, these are: A. Zero adjustment, B. Range adjustment, and C. Linearity adjustment. (A)
Zero Adjustment
If the gauge shows an equal amount of incorrect reading, either too high or too low over the entire range, adjustment is made by resetting the indicating pointer. These are furnished in three types, i.e. micrometer, slotted and plain. The micrometer type is adjusted by holding the pointer firmly with one hand and turning the micrometer screw with the other. Follow the same procedure for the slotted type, except rotate the slotted hub with a screwdriver. For gauges equipped with plain pointer make minor adjustments by rotation the slotted scale. Where this adjustment is not sufficient, remove the pointer (using a hand jack ), and reset in desired position. (B)
Range Adjustment
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TASK DETAILING MANUAL If the gauge readings show a progressively increasing (plus or minus) error, from the lower to the upper end of the range, loosen the two slide screws (1) and proceed as follows: For plus plus error, the slide (2) must be moved outward; for minus error, the slide must be moved inward. After attaining proper adjustment, retighten the slide screws (1). (C)
Linearity Adjustment
Assuming the gauge reads accurately at high and low points (1/3 and 2/3 of gauge range) but inaccurate at the center of the scale linearity adjustm adjustment ent is required. A linearity adjustment, being the most difficult adjustment of the three due to the geometric function of all components, may in some instances be accomplished in the field by loosening the two movement mounting screws (3) and rotating the
TASK No.: I-3.1
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movement. Without a technical gauge background this would be a trial and error adjustment. After each adjustment (which should require no more than a few degrees), the gauge should be re-tested through the complete range, after setting pointer at approximately 5% of scale range. Make a zero and/or range adjustment if required. Pointer Adjustment, Removal and Reassemble.
In case where pointer adjustment is necessary, the following procedure should be followed: For liquid filled gauges drain the liquid from the case. Loosen the ring using a strap wrench or equivalent. A slotted screwdriver blade is required so that the screwdriver’s blade b lade will properly engage the slot on the pointer hub and clear the tip of the pinion shaft protruding from the hub. hub. While holding the tail of the pointer, pointer, a clockwise rotation of the pointer’s hub will result in a counterclockwise pointer motion and vice versa. Care must be taken so as not to apply an excessive axial force to the pointer. If liquid filling is required, hold the gauge in a horizontal position and slowly fill the gauge with filling fluid. Should it be necessary to remove the pointer, the standard hand jack set should be used. When reassembling the pointer on lower connected gauges care must be
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TASK DETAILING MANUAL taken to support the pinion shaft. This is accomplished acco mplished by removing the fill plug in the back of the case and placing a support against the pinion shaft from the back side. On back connected gauges, position the driver against the pointer hub and push until the pinion stops against the socket. Contact will be felt. Hold the driver in this position and strike it lightly. In both cases, care must be taken to ensure the pinion shaft is not bent by heavy blows on the pointer driver. Gauge calibration must be checked aafter fter reinstalling the pointer. Tighten the ring to the case using a strap wrench.
MODULE No.: TASK No.:
I-3 Pressure Instruments I-3.2 Service and calibrate a high/ low pressure switch
Reference:
OJT Instructor to arrange reference catalogue / service manual for pressure switches relevant to each working area.
Materials:
Cleaning rags.
Equipment & Tools: 1. Tool Box 2. Digital Maltimeter 3. Pneumatic / Hydraulic pressure calibrator.
Conditions:
Work permit
Requirements By Trainee:
To study the task and familiarise himself.
To select the proper tools / equipment to perform this t his task.
Draw / Sketch the calibration set-up in his work book.
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TASK DETAILING MANUAL
Recognises the difference between high & low switch in calibration procedure.
Be able to perform routine service of a pressure switch.
Discuss an understanding to his trainer.
Write observations and procedure in his work book.
TASK No.: I-3.2
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Details: Pressure Switches A) Electric Pressure Switches An electric pressure switch senses pressure and opens or closes a switch element at a set pressure to signal another electrical device. Electric pressure switches are available in a wide variety of styles.
Most pressure switches trip at a pressure above atmospheric, and are called gauge pressure or simply pressure switches. switches. Switches can also also be manufactured to tri trip p at a pressure referenced to a complete vacuum and are called absolute pressure switches. Those set to trip below atmospheric pressure are called vacuum switches and those which can be set either above or below atmospheric pressure are called compound switches. Some switches are manufactured so that the trip point is factory set, while while others are fi field eld adjustable. Pressure switches are set to trip at a certain point with rising or falling pressure. When the pressure is returned to within the acceptable range, the switch does not reset at exactly the same point that it tripped. The difference in the trip point and the set point is called dead band or reset. reset . The electrical switch is usually either single-pole, double-throw or double-pole, double-throw. Figure 23 shows these types, as well we ll as others less frequently used. The number of poles determines the number of separate circuits that can be controlled by the switch, single pole for one circuit and double-pole for two circuits. The double-throw term means that a common terminal is connected to either of two other terminals, normally open or normally closed. B) Pneumatic Pressure Switches/Pressure Pilots A pneumatic pressure switch senses pressure and opens or closes a small valve at a set pressure to supply s upply or vent a pneumatic signal
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TASK DETAILING MANUAL to another pneumatic device. Pneumatic pressure switches are commonly known as pressure pilots. They T hey are frequently used when p pneumati neumaticc sshutdown hutdown and control
TASK No.: I-3.2
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systems are selected. Often, pressure pilots are used in Division 1 areas, such as on wellheads even when the primary process control is electronic. Devices, which are similar to electric pressure switches, are called pneumatic pressure switches. Pneumatic pressure switches are equipped with a two-way or three-way valve instead of an electrical switch. The two-way valve is either open or closed. A three-way valve connects a common port with one of two other ports, depending on whether the switch is tripped or not. Devices, which have been designed to be pneumatic, are usually called pressure pilots. The most common types of pilots are the piston-actuated, known as stick pilots, and the bourdon tube actuated pilots. Stick pilots are more often used on wellheads and bourdon tube pilots pilots are more often used on process equipment. Dead band or reset is equally important for pneumatic pressure switches /pressure pilots as for electric pressure switches. Pneumatic devices tend to have an even larger dead band than electric devices because more movement is required for actuation. Most pressure pilots are equipped with three-way pneumatic valves so that they can be used either as a high-pressure pilot or a low-pressure pilot depending on how they are connected. Pressure Switch Calibration;
Switch operating set point shall be verified at intervals to make sure the healthiness of the switch and the associated circuit. For any switch with a tag number prefix ending LL or HH, a maintenance by pass is provided on the shut down panel. Care must be taken to operate the correct switch by an authorised person. Switch must be isolated, depressurised and drained in order to hook up the test equipment.
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TASK DETAILING MANUAL TASK No.: I-3.2
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TASK No.: I-3.2
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To calibrate a pressure switch, follows:
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TASK DETAILING MANUAL Normally Closed:
1. Clean the switch. 2. Connect the switch to Wallace calibrator. 3. Adjust the Multimeter to measure Ohm. 4. Connect the red and brown leads of the switch to the meter. 5. Increase the pressure slowly till you reach the fixed set point, (the meter reads open circuit). 6. Decrease the pressure slowly and observe the Multimeter indication, record the pressure value when when meter read closed circuit. 7. Calculate the dead band value. Normally Open:
1. Clean the switch. 2. Connect the switch to Wallace calibrator. 3. Select resistance measurement “OHM” for the multimeter. multimeter. 4. Connect the multimeter to the switch to red and brown leads. 5. The meter reads open circuit. 6. Increase the pressure more than the set point, till the meter reads zero OHM. 7. Decrease the pressure slowly till the meter reads open circuit. 8. Check the set point with the name plate set point.
MODULE No.: TASK No.:
I-3 Pressure Instruments I-3.3 Service and calibrate a differential pressure switch s witch
Reference:
OJT Instructor to arrange reference catalogue / service manual for diff. Pressure switches relevant to each
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TASK DETAILING MANUAL working area.
Materials:
Cleaning rags.
Equipment & Tools: 1. Tool Box, 2. Digital Multimeter, and 3. Pneumatic / Hydraulic pressure calibrator.
Conditions:
Work permit
Requirements By Trainee:
To study the task and familiarise himself.
To select the proper tools / equipment to perform this t his task.
Draw / Sketch the calibration set-up in his work book.
Recognises the difference between high & low switch in calibration procedure.
Be able to perform routine service of a differential pressure switch.
Discuss an understanding to his trainer.
Write observations and procedure in his work book.
TASK No.: I-3.3
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Details: Deferential Pressure Switches Description; These switches act on the difference between pressures acting on either diaphragm or bellows. There are two kinds of differential d ifferential pressure switches: Single switches; these switches control only one differential pressure to one limit. Double Switches; these switches control the differential pressure to two limits.
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TASK DETAILING MANUAL
Differential Pressure Switch TASK No.: I-3.3
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TASK DETAILING MANUAL
Calibration Set-up of Diff. Press. Switch
Calibration Procedure
1. Open the low pressure port to the atmosphere. 2. Apply the setting pressure to the high pressure port. 3. Adjust the multimeter to (OHM) position. 4. Connect the multimeter leads to the terminal strip. (Normally open). 5. Use a suitable open-end wrench to turn HEX adjusting nut. 6. Adjust the setting point until the multimeter measure the continuity of the micro switch. 7. Repeat step 6 till you get a precise set point.
MODULE No.: TASK No.:
I-3 Pressure Instruments I-3.4 Describe the meaning of the terms, zero, span, linearity when calibrating a pressure transmitter.
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TASK DETAILING MANUAL Reference:
Materials:
None.
Equipment & Tools: None.
Conditions:
None.
Requirements By Trainee:
To study the task and familiarise himself,
Be able to define Zero, Span and Linearity of a pressure transmitter,
Discuss an understanding with his trainer, and
Write the definition of each in his work book.
TASK No.: I-3.4
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Details: Zero Pressure
Is the bottom scale value of measuring range, for example if measuring range of a press transmitter is from (-2 to 40 psi), psi), zero press. is equal to (-2 psi). Span
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TASK DETAILING MANUAL The difference between the Upper Range Value (URV) and the Lower Range Value (LRV) of an instrument, on instrument starting at zero, the span equal to the range, for above example the span = 42 psi. Linearity
Linearity is the degree to which the calibration curves of matches a straight line, the linearity error is generally the greatest departure from the t he best straight line that can be drawn through the measured calibration points.
MODULE No.: TASK No.:
I-3 Pressure Instruments I-3.5 Demonstrate servicing and calibrating a pneumatic pressure transmitter
Reference:
OJT Instructor to arrange reference catalogue / Service Ser vice manual for pneumatic pressure transmitter model relevant to each working area.
Materials:
Cleaning rags with solvent.
Equipment & Tools: 1. Tool Box, 2. Hydraulic or Pneumatic pressure calibrator, and
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TASK DETAILING MANUAL 3. Standard output gauge.
Conditions:
Work permit.
Requirements By Trainee:
To study the task and familiarise himself,
Be able to describe the operation principle of the pneumatic press. transmitter,
Be able to identify the main parts of a pneumatic transmitter,
Perform periodic adjustments / calibration of a pneumatic transmitter, tra nsmitter,
Perform periodic and corrective maintenance or replace parts of a pneumatic transmitters,
Draw / Sketch calibration set-up of a pneumatic press. transmitter,
Discuss an understanding with his trainer, and
Write observation and procedures in his work book.
TASK No.: I-3.5
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Details: Pressure Transmitters Pressure 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. tra nsmitters. Other signals can be used if required b by y tthe he receiver, b but ut 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.
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TASK DETAILING MANUAL 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 possible and the unit unit is called a absolute 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 pressure transmitter, these are: 1. Bellows 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-3.5
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TASK No.: I-3.5
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Clibration
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 substanti s ubstantially. ally. 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 pressure transmitter are listed in the reference cataloguee or service manual of the applied model. Consult your trainer. catalogu
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TASK DETAILING MANUAL Maintenance and Servicing
Maintenance and servicing of pneumatic 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, 4. Clean booster relay Restrictor, 5. Replace Booster Relay, 6. Change Range Bar, 7. Remove / Replace Bellows 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.
MODULE No.: TASK No.:
I-3 Pressure Instruments I-3.6 Demonstrate calibration of a smart transmitter using a hand held communicator.
Reference:
OJT Instructor to arrange reference catalogue / service manual smart transmitter model relevant to each workingfor area..
Materials:
None.
Equipment & Tools: 1. Function generator, 2. Digital Multimeter, and 3. Pneumatic / Hydraulic pressure calibrator. 4. HHC for Smart Transmitter model. Conditions:
None.
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TASK DETAILING MANUAL Requirements By Trainee:
To study the task and familiarise himself,
Be able to describe using of HHC keypad,
Be able to define de fine the difference between the electronic press. transmitt transmitter er and smart type,
Perform adjustments and calibration of Smart transmitters, transmitters,
Be able to maintain and troubleshoot Smart pressure transmitters,
Draw / Sketch calibration set-up,
Discuss an understanding to his trainer, and
Write observations and procedures in his work book.
TASK No.: I-3.6
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Details: Smart Transmitters Microprocessor-based Micropro cessor-based pressure ttransmitters, ransmitters, sometimes called smart transmitters are offered by several companies. These transmitters can be remotely programmed for any desired range, either by the main process computer or by a special programmer. These transmitters are usually used in sophisticated computer control schemes. Smart transmitters uses an integrated circuit sensor to measure the process variable . This integrated circuit contains microprocessor-based electronics and
digital communication circuitry to add functions over the same two wires used to transmit power and the measurement signal. The next figure shows electronics assembly of Foxboro 863DP smart transmitter. trans mitter.
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TASK DETAILING MANUAL
Smart Press. Transmitter, Electronic Parts. TASK No.: I-3.6
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Smart Press. Transmitter Calibration Set-up;
Calibration equipment equipment should be a minimum of three times more accurate than the desired accuracy of the transmitter.
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4 to 20 mA Calibration Setu
TASK DETAILING MANUAL Calibration is performed by simulating the process pressure. This done by applying a pressure equal to the transmitter range pressure. Field Calibration is performed without disconnecting the process piping. To perform field calibration, refer to detail procedure in the reference doc., Consult your trainer. Bench Calibration set-up requires disconnecting the process piping To calibrate the transmitter , use the detailed procedure of the reference doc., consult your trainer.
TASK No.: I-3.6
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Fault Analysis;
Fault analysis of Foxboro Smart Press. Transmitter (863 DP) is accomplished
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TASK DETAILING MANUAL through the following flow shart.
TASK No.: I-3.6
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Fault Analysis Flowchart “Continue”
TASK No.: I-3.6
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TASK DETAILING MANUAL Maintenance;
These transmitters when used in hazardous area, must be deenergised deenergised before removing the covers or performing any maintenance. Maintenance is limited to the replace electronics modules assembly, sensor and housing assembly, cover Orings, and optional indicator. Detailed procedure to replace these parts, refer to the t he reference catalogue or maintenance manual of the smart transmitter model, consult your trainer.
MODULE No.: TASK No.:
I-3 Pressure Instruments I-3.7 Demonstrate servicing and calibrating an electronic transmitter
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TASK DETAILING MANUAL Reference:
OJT Instructor to arrange reference catalogue / Service Ser vice manual for electronic pressure transmitter model relevant to each working area.
Materials:
Cleaning rags with solvent.
Equipment & Tools: 1. Tool Box, 2. Hydraulic or Pneumatic pressure calibrator, and 3. Function Generator and digital Multimeter. Conditions:
Work permit.
Requirements By Trainee:
To study the task and familiarise himself,
Be able to describe the operation principle of the electronic presser transmitter, tra nsmitter,
Be able to identify the main parts of an electronic e lectronic transmitter,
Perform periodic adjustments / calibration of an electronic transmitter,
Perform periodic and corrective maintenance or replace parts of an electronic transmitters,
Draw / Sketch calibration set-up of the electronic press. transmitter,
Discuss an understanding with his trainer, and Write observation and procedures in his work book.
TASK No.: I-3.7
“Continue” “Continue”
Details: Electronic Pressure Transmitters
Electronic transmitters with 4-20 milliamp outputs are the most common. Pressure transmitters are available in a variety of ranges. The ranges available vary from one manufacturer to another, so it is necessary to consult manufacturer's
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TASK DETAILING MANUAL literature before selection. The range and the span are two different parameters. The span is the actual pressure range to be measured after the transmitter has been adjusted. The range is the 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, 3 psig, or 20 kPa) at zero pressure, or the bottom of the span if elevated zero is used. The span is adjusted so that the o output utput is maximum (20 ma, 15 psig, or 100 kPa) 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 shows the main parts of an el electronic ectronic pressure transmitter;
Sensing module, and
Electronic housing contains; header assembly board, DC ampilfier board, and calibration board
TASK No.: I-3.7
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TASK DETAILING MANUAL
Electronic Press. Transmitter, Main Parts.
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TASK DETAILING MANUAL TASK No.: I-3.7
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Principle of operation;
This electrical block diagram illustrates the operation of the electronic pressure transmitter. The process pressure 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.
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 .
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TASK DETAILING MANUAL TASK No.: I-3.7
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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 need 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 any where 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 pressure transmitter is 4 mA.
The zero and span adjustment potentiometers are accessible externally and are located behind the name plate of the transmitter.
TASK No.: I-3.7
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TASK DETAILING MANUAL The recommended procedure for zero and span adjustment detailed in the reference catalogue / service manual of the electronic 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. board.
Calibration procedures for adjusting or changing ranges are outlined in the calibration section of the transmitter catalogue, 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 trouble shooting guide. Test Terminal; to assure that their 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. Thesection detail of procedure to checkout the sensing are listed in the maintenance the transmitter’s catalogue, consultmodule your trainer. 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-3.7
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TROUBLESHOOTING
1) SYMPTOM: HIGH OUTPUT
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TASK DETAILING MANUAL Potential Source and Corrective Action. Impulse Piping Check for leaks or blockage. b lockage. 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. b lockage. Check for entrapped gas in liquid lines. Check for sediment in transmitter process flanges.
TASK No.: I-3.7
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Transmitter Electronics Connections 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.
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TASK DETAILING MANUAL Transmitter Electronics Failure Determine faulty circuit board by trying spare boards. Replace faulty circuit board. OUTPUT 3) SYMPTOM: Potential SourceERRATIC 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. Transmitter Electronics Connections
Check for intermittent shorts or open circuits. Make sure that bayonet connectors are clean and check the sensor se nsor connection connections. s. 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.
MODULE No.: TASK No.:
I-3 Pressure Instruments I-3.8 Demonstrate isolation procedure from process and electrical supply on a pneumatic/el pneumatic/electronic ectronic pressure transmitter.
Reference:
Materials:
1. Soap Solution, and 2. Cleaning Rags
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TASK DETAILING MANUAL Equipment & Tools: 1. Tool Box, and 2. Pneumatic or Hydraulic Pressure Source.
Conditions:
Work Permit
Requirements By Trainee:
To study the task and familiarise himself,
Be able to demonstrate safe process isolation procedure for the pressure devices,
Be able to perform safe electrical e lectrical isolation procedure procedure for tthe he pressure devices, Discuss an understanding to his trainer, and
Write observations and isolation procedures in his work book.
TASK No.: I-3.8
“Continue” “Continue”
Details: Preparations
1. Fill in work permit. 2. Use soap solution and brush to check any gas or air leakage. 3. If there is any leakage from fittings, tighten it by a suitable open-end wrench. Flushing the transmitter impulse line ; the figure below show typical installation of the pressure transmitter for either liquid or gas services, follow the next procedure for safe process isolation. isolation.
1. Close isolating valve A.
2. Slowly open drain valve C. 3. Slowly open isolating valve A to flush the impulse line. 4. After flushing the impulse line, close valve C, slowly open A, and put the
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TASK DETAILING MANUAL
Typical Pressure Transmitter Piping
MODULE No.: TASK No.:
I-3 Pressure Instruments I-3.9 Check function / adjustment / maintenan maintenance ce o off pressure regulators for process lines.
Reference:
OJT Instructor to arrange reference catalogue / Service manual for pressure regulators models in each working area.
Materials:
Cleaning Rags
Equipment & Tools: 1. Tool Box, 2. Standard test gauges, and 3. Continuou Continuouss air ssupply upply pressure.
Conditions:
Work permit.
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TASK DETAILING MANUAL Requirements By Trainee:
To study the task and familiarise himself,
Be able to identify pressure regulators types,
Be able to describe the principle of operation of continuous bleed regulator,
State the advantages and disadvantages of continuous and continuou co ntinuouss bleed regulators,
Be able to dismantle, inspect, clean and replace a regulator,
Discuss an understanding to his trainer, and
Write observations in his work book.
TASK No.: I-3.9
“Continue” “Continue”
Details: Pressure Regulators
If a steady constant pressure is required either for instruments supply or process operations. This is ensured by fitting a pressure regulator in the line. A standard pressure regulator consists of a body in which is fitted a flexible diaphragm. The diaphragm is connected to a valve and is top loaded by a spring which can be adjusted. System or primary air pressure is led to the underside of the diaphragm. The diaphragm flexes, opening the valve and allowing air to pass to the outlet side where it is known as secondary air. A small amount of secondary air is bled to the top side of the diaphragm which, together with the spring, forces the diaphragm down and operates the valve. Any change in primary air pressure will cause movement of the diaphragm opening or closing the valve and stabilising the secondary air pressure. Permanent changes in secondary air pressure can be made by adjusting the the pressure on the spring with a screw. There are two types of pressure regulators; 1. Continuou Continuouss bleed , and 2. Non continuous continuous bleed
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TASK DETAILING MANUAL
TASK No.: I-3.9
“Continue” “Continue”
Page 35
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TASK DETAILING MANUAL Continuous Bleed Press. Regulator
MODULE No.: TASK No.:
I-3 Pressure Instruments I-3.10 Service and calibrate a pneumatic indicating controll controller er
Reference:
OJT Instructor to arrange reference catalogue / Service Ser vice 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.
Requirements By Trainee:
To study the task and familiarise himself,
Be able to identify the major components of pneumatic controller,
To describe the pricible of operation of pneumatic indicating controller, controller,
Be able to perform periodic adjustments / calibration of the controller,
To perform previntive maintenance, service, parts replacement of the controller,
Draw/ Sketch calibration set-up in his work book, Discuss an understanding to his trainer, and
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TASK DETAILING MANUAL
Write observations and procedure in his work book.
TASK No.: I-3.10
“Continue” “Continue”
Details: Pressure Controllers A pressure controller is a device, which senses the pressure in the process and vary an a n 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. signal.
Pressure controllers can be categorized either as indicating or blind 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. po int. 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 press ure 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 pneu pneumatic matic for fieldfield-mounted 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-3.10
“Continue” “Continue”
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TASK DETAILING MANUAL 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 the to manual regulator output to thetransfer automatic output transfer to manual or thematch set point the process variable b efore before 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. Panelmounted, 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 convenient when the valve is accessible access ible..
TASK No.: I-3.10
“Continue” “Continue”
Principle of operation
This figure explains in steps how the pneumatic indicator controller works;
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TASK DETAILING MANUAL
TASK No.: I-3.10
“Continue” “Continue”
Clibration
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.
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TASK DETAILING MANUAL 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 controllerer are listed in the reference cataloguee or service manual of the applied model. Consult your trainer. catalogu 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. 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 indicating controller mod model. el. Consult your trainer.
