Practical Demonstration of FLOW INSTRUMENTS

Transcription

1 Practical Demonstration of FLOW INSTRUMENTS MODULE NO. : I-4 MODULE SUBJ.: Flow Instruments Module I-4 Page 1

2 Tasks: I-4.1 I-4.2 I-4.3 I-4.4 I-4.5 Describe the procedures used to remove an orifice plate from a Daniel s senior orifice fitting. Demonstrate servicing and calibration of a pneumatic differential pressure flow transmitter. Demonstrate servicing and calibration of an electronic differential pressure flow transmitter. Demonstrate ability to isolate the transmitter from process without damage to equipment. Perform zero check procedure (static zero adjustment). I-4.6 I-4.7 Perform servicing of a turbine meter. Check magnetic pickup for damage. Calibrate pulse to ma converter. 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.: TASK No.: I-4 Flow Instruments I-4.1 Describe the procedures used to remove an orifice plate from a Daniel s senior orifice fitting. Module I-4 Page 2

3 Reference: TASK DETAILING MANUAL 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 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. Module I-4 Page 3

4 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 Figure I-4.1A, Senior Orifice Fitting Module I-4 Page 4

5 Figure I-4.1B 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 (e) Close No. 5. (f) Close No. 1. (g) Open No. 10 B. Module I-4 Page 5

6 (h) Lubricate through No. 23. TASK DETAILING MANUAL (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. MODULE No.: TASK No.: I-4 Flow Instruments 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. Module I-4 Page 6

7 Materials: Cleaning rags. Equipment & Tools: 1. Tool Box, 2. Standard Output gauge, 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 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 Write observations and procedures in his workbook. TASK No.: I-4.2 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 ( 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 Module I-4 Page 7

8 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. Module I-4 Page 8

9 TASK No.: I-4.2 Figure I-4.2A, Pneumatic Differential Pressure Transmitter. TASK No.: I-4.2 Calibration Module I-4 Page 9

10 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. Regulate air supply to pressure at which transmitter will be operating Calibrating Air Supply Vent low-pressure side of transmitter. Bleeder Valve Test gauge or reading input signal pressure. manometer for 0 to 20 psi Output test gauge TASK No.: I-4.2 Figure I-4.2B, DP flow transmitter calibration setup 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, Module I-4 Page 10

11 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. MODULE No.: TASK No.: Reference: Materials: I-4 Flow Instruments I-4.3 Demonstrate servicing and calibration of an electronic differential pressure flow transmitter. OJT Instructor to arrange reference catalogue / Service manual for an electronic differential pressure flow transmitter model relevant to each working area. 1. Cleaning rags, and 2. Solvent. Module I-4 Page 11

12 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 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 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: Module I-4 Page 12

13 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 Module I-4 Page 13

14 Figure I-4.3A, Electronic Differential Press. Transmitter, Main Parts. Module I-4 Page 14

15 TASK No.: I-4.3 Principle of operation Figure I-4.3B 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 التذبذب. oscillator driven by an 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. Module I-4 Page 15

16 TASK No.: I-4.3 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 Figure I-4.3C 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 Module I-4 Page 16

17 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 Troubleshooting 1) SYMPTOM: HIGH OUTPUT Module I-4 Page 17

18 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 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. Module I-4 Page 18

19 Transmitter Electronics Failure Determine faulty circuit board by trying spare boards. Replace faulty circuit board. 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. Transmitter Electronics Connections 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. Transmitter Electronics Failure Determine faulty circuit board by trying spare boards. Replace faulty circuit board. MODULE No.: TASK No.: I-4 Flow Instruments I-4.4 Demonstrate ability to isolate the transmitter from process without damage to equipment. Reference: None Materials: Cleaning Rags. Module I-4 Page 19

20 Equipment & Tools: Tool Box. Conditions: None. Requirements By Trainee: To study the task and familiarise himself, Be able to select proper tools to perform this task, Be able to demonstrate safe isolation procedure of a flow transmitter in service, Discuss an understanding with his trainer, and Write observations and procedure in his workbook. TASK No.: I-4.4 Details: Module I-4 Page 20

21 Figure I-4.4A, Piping and Tubing arrangement of a DP transmitter TASK No.: I-4.4 To perform safe isolation of a DP transmitter in service, follow the next: 1. Fill in your work permit. Module I-4 Page 21

22 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. MODULE No.: TASK No.: I-4 Flow Instruments I-4.5 Perform zero check procedure (static zero adjustment). Reference: Materials: 1. Cleaning rags, and 2. Solvent. Module I-4 Page 22

23 Equipment & Tools: 1. Tool Box, and 2. Standard output gauge. Conditions: Work permit. Requirements By Trainee: To study the task and familiarise himself, Be able to select proper tools to perform this task, Be able to perform static zero adjustment of a DP flow transmitter, Discuss an understanding with his trainer, and Write observation and procedures in his workbook. TASK No.: I-4.5 Module I-4 Page 23

24 Details: TASK DETAILING MANUAL Figure I-4.5A, Field Mounted Recorder Piping Arrangement 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 Static Zero Check; If the instrument has a static pressure element, perform the following check: Module I-4 Page 24

25 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). MODULE No.: TASK No.: Reference: I-4 Flow Instruments I-4.6 Perform servicing of a turbine meter. Check magnetic pickup for damage. Calibrate pulse to ma converter. OJT Instructor to arrange reference catalogue / service manual for turbine meter model relevant to each working area. Module I-4 Page 25

26 Materials: TASK DETAILING MANUAL 1. Cleaning Rags, and 2. Solvent. Equipment & Tools: 1. Frequency generator / counter, 2. Digital Multimeter, and 3. Function generator. Conditions: Work permit. Requirements By Trainee: To study the task and familiarise himself, 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, Discuss an understanding to his trainer, and Write observations and procedures in his workbook. TASK No.: I-4.6 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; Module I-4 Page 26

27 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 Module I-4 Page 27

28 Figure I-4.6A, Turbine Flow Meter, Main Parts. 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 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. Module I-4 Page 28

29 Figure I-4.6B, Turbine Flow Meter Principle of Operation. TASK No.: I-4.6 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. Module I-4 Page 29

30 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 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. Module I-4 Page 30

31 Figure I-4.6C, Turbine Flow Meter Parts Replacement. MODULE No.: TASK No.: Reference: I-4 Flow Instruments I-4.7 Perform service and check of a Rotameter. OJT Instructor to arrange reference catalogue / Service manual for the Rotameter model relevant to each working area. Materials: 1.Cleaning rags, and Module I-4 Page 31

32 2. Solvent. Equipment & Tools: 1. Tool Box, and 2. Digital Multimeter. Conditions: Work permit. 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, Discuss an understanding with his trainer, and Write observation in his workbook. TASK No.: I-4.7 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 Module I-4 Page 32

33 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 Figure I-4.7A, Float at equilibrium position Module I-4 Page 33

34 Figure I-4.7B, Rotameter, main parts TASK No.: I-4.7 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. Module I-4 Page 34

35 TASK No.: I-4.7 Figure I-4.7C, Metal Rotameter with Magnetic Indicator MODULE No.: TASK No.: I-4 Flow Instruments I-4.8 Module I-4 Page 35

36 Service and calibrate a Foxboro 43AP controller. Reference: Materials: OJT Instructor to arrange reference catalogue / Service manual for pneumatic controllers models relevant to each working area. 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 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, Discuss an understanding to his trainer, and Write observations and procedure in his workbook. TASK No.: I-4.8 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 Module I-4 Page 36

37 controller output is usually either a 3-15 or 6-30 psig ( or 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 ( kpa), but it can be 6-30 psig ( 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 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. Module I-4 Page 37

38 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 when the valve is accessible. TASK No.: I-4.8 Principle of operation Figure I-4.8A, explains in steps how the pneumatic indicator controller works; Module I-4 Page 38

39 Figure I-4.8 A, Controller s Principle of Operation. TASK No.: I-4.8 Control Adjustments Proportional Controller (P controller); Module I-4 Page 39

40 Figure I-4.8B, illustrates the effect of various proportional band settings Figure I-4.8B, PB Effects at Various Settings Proportional plus Reset Controller (PI Controller); Figure I-4.8C, illustrates the effect of various Reset Times Figure I-4.8C, Effects of Various Reset Times TASK No.: I-4.8 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. Module I-4 Page 40

41 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. MODULE No.: TASK No.: Reference: I-4 Flow Instruments I-4.9 Calibrate square root extractor. OJT Instructor to arrange reference catalogue / Service manual for Square root extractor model in each working area. Materials: Module I-4 Page 41

42 Equipment & Tools: 1. Tool Box, 2. Standard test gauges / Digital Multimeter, and 3. Pneumatic calibrator / Function generator. Conditions: Work permit. Requirements by Trainee: To study the task and familiarise himself, 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, Discuss an understanding to his trainer, and Write observations in his workbook. TASK No.: I-4.9 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 Module I-4 Page 42

43 Figure I-4.9A, Pneumatic Square root Extractor Operation Method TASK No.: I-4.9 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 Module I-4 Page 43

44 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 ) 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. Module I-4 Page 44

45 Figure I-4.9B, Square root Extractor Calibration Setup. TASK No.: I-4.9 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. Module I-4 Page 45

46 MODULE No.: TASK No.: I-4 Flow Instruments I-4.10 Troubleshooting 3 way / 5 way valve manifold. Reference: Materials: OJT Instructor to arrange reference catalogue / Service manual for manifold type relevant to each working area. 1. Cleaning Rags, and 2. Solvent Equipment & Tools: Tool Box Conditions: Work permit Module I-4 Page 46

47 Requirements by Trainee: TASK DETAILING MANUAL To study the task and familiarise himself, 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, Discuss an understanding to his trainer, and Write observations and procedure in his workbook. TASK No.: I-4.10 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- Module I-4 Page 47

48 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 Figure I-4.10B, 5-Valve Manifold in case of meter calibration. 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. Module I-4 Page 48