STUDY OF I/P AND P/I CONVERTER

Transcription

1 STUDY OF I/P AND P/I CONVERTER Product Code 310 Instruction manual Contents 1 Description 2 Specifications 3 Installation requirements 4 Installation Commissioning 5 Troubleshooting 6 Components used 7 Packing slip 8 Warranty 9 Experiments 10 components details Im310 Page 1

2 Description The I/P and P/I converter setup is designed for understanding basic principles of electronic and pneumatic signal conversion. The setup consists of I/P converter, P/I converter, digital calibrator, pressure gauges and air regulator and air filter regulator. The Digital calibrator is used as source to supply 4-20 ma DC to I/P converter and to measure the output in ma DC from P/I converter. I/P converter gives the output as 3-15 psig and P/I converter gives output as 4-20 ma DC. All the components along with necessary piping and fittings are mounted on support housing designed for tabletop mounting. Set-up enables study of I/P and P/I converter working, calibration and characteristics of linearity, hysteresis, accuracy, and repeatability. Air supply Digital calibrator Regulator P/I Converter Vent Input Pressure Filter Regulator I/P Converter Supply Pressure Pressure Im310 Page 2

3 Specifications Product Study of I/P and P/I converter Product code 310 Pressure Transmitter Type Two wire, Range 0 1 bar, 4 20 ma I/P converter Input 4-20mA, 3-15 psig Signal Isolator Input: 7.2 to 20mA, output 4-20mA Digital Calibrator Measure/source, milliamp/millivolt mode Air regulator Range kg/cm 2 Air filter regulator Range kg/cm 2 Pressure gauge Range kg/cm 2 (2No), Range 0-7 kg/cm 2 (1Nos) Overall dimensions 550Wx300Dx400H mm Optional Mini compressor Shipping details Gross volume 0.10m 3, Gross weight 23kg, Net weight 14kg Installation requirements Air supply Clean, oil and moisture free air, pressure 2 Bar, consumption 50 LPH Support table Size: 800Wx800Dx750H in mm Im310 Page 3

4 Installation Commissioning Preparing set up for commissioning Place the set up on support table. Connect compressed air supply. Check supply voltage as L-N 230 +/- 10 V AC and L-E 1-5 V AC. If supply voltage is not as per specified then rectify the fault then proceed for commissioning the set-up. Commissioning Switch on the mains supply. Switch on the compressed air supply. Adjust the air supply to 25 psig and lock the air regulator by pressing the red ring around the knob. Set the digital calibrator to source/measure mode by pressing the side push button. Increase the (Source mode) from digital calibrator by rotating the round adjust knob clockwise from 4 ma to 20 ma. Check the pressure on output pressure gauge at the output of I/P converter, which is varying from 3 to 15 psig. If the same is not found as per specified above, calibrate I/P converter. (Calibration is to be done by experienced persons with extensive care, otherwise it may damage the unit) Now release the air to 0 psig by rotating air regulator anticlockwise. Now set the digital calibrator to Measure mode by releasing the push button. Now increase the pressure to P/I converter from 3 to 15 psig by varying regulator slowly. Check the output from P/I converter is 4 to 20 ma is indicated on digital calibrator. If the same is not found as per specified above, calibrate P/I converter. (Calibration is to be done by experienced persons with extensive care, otherwise it may damage the unit) Now set up is ready for experimentation. Shutting down the set up Switch off the compressed air supply. Release the air by rotating air regulator in anticlockwise direction. Switch off the digital calibrator Im310 Page 4

5 Troubleshooting Note: For component specific problems refer components manual Problems I/P converter not functioning or low signal pressure P/I converter not working and pressure transmitter not working Digital calibrator not working Possible causes / remedies Clogged restrictor hole. Clean it. Ensure 25-psig air supply. Check output line for no air leakage. Ensure calibrator is in the source mode. Ensure input pressure 3-15 psig. Check input air piping for no leakage. Check electric supply of signal isolator. Check electric supply/dc adpto Im310 Page 5

6 Components used Components Details Pressure Transmitter Make Wika, Model A-10, 4-20mA(2 wire), Supply 24VDC, Range 0-1 bar, Process conn. 1/4"BSP(male), Accuracy +/-1% I/P converter Make Control air inc, Type T500-AC, Input 4-20 ma DC, output 3-15 psig, end connection 1/4 NPT Signal Isolator Make Precision converters, Input 7.2 to 20mA, 4-20mA. Supply 230VAC. Digital calibrator Make Agrawal electronics, model SE , battery operated Air filter regulator Make Airmatic, Model MB VD-PAP, Range 0-2 Kg/cm^2, Type Relieving Air regulator Make Airmatic, Model MR10-021PA, Mounting panel, Connection ¼ BSP, Range 0-2 Kg/Cm^2, with lock nut. Pressure gauge Make Waaree, Code: PW2.5GNNNS /4"B, Dia.2.5", Gly. filled, Brass internals, S.S. casing, Range Kg/cm 2, 1/4"BSP (M) back connection Pressure gauge Make Waaree, Code: PW2.5GNNNS /4"B, Dia.2.5", Gly. filled, Brass internals, S.S. casing, Range 0-7 Kg/cm 2, 1/4"BSP (M) back connection Packing slip Box No.1/1 Size W575xD350xH475 mm; Volume:0.10m 3 Gross weight: 23kg Net weight: 14kg 1 Set up assembly 1 No 2 Test leads and cords set 1 No 3 Instruction manual CD (Apex) 1 No Im310 Page 6

7 Warranty This product is warranted for a period of 12 months from the date of supply against manufacturing defects. You shall inform us in writing any defect in the system noticed during the warranty period. On receipt of your written notice, Apex at its option either repairs or replaces the product if proved to be defective as stated above. You shall not return any part of the system to us before receiving our confirmation to this effect. The foregoing warranty shall not apply to defects resulting from: Buyer/ User shall not have subjected the system to unauthorized alterations/ additions/ modifications. Unauthorized use of external software/ interfacing. Unauthorized maintenance by third party not authorized by Apex. Improper site utilities and/or maintenance. We do not take any responsibility for accidental injuries caused while working with the set up. Apex Innovations Pvt. Ltd. E9/1, MIDC, Kupwad, Sangli (Maharashtra) India Telefax: , support@apexinnovations.co.in Web: Im310 Page 7

8 THEORY In recent years the performance requirements for process plants have become increasingly difficult to satisfy. Stronger competition, tougher environmental and safety regulations, and rapidly changing economic conditions have been key factors in the tightening of plant product quality specifications. A further complication is that modern processes have become more difficult to operate because of the trend toward larger, more highly integrated plants with smaller surge capacities between the various processing units. Such plants give the operator little opportunity to prevent upsets from propagating from one unit to other interconnected units. In view of increased emphasis placed on safe, efficient plant operation, it is only natural that the subject of process control has become increasingly important in recent years. In fact, without process control it would not be possible to operate most modern processes safely and profitably, while satisfying plant quality standards. Commonly used terms in process control Linearity Linearity indicates for each value of the input variable there exists one unique value of the output variable. We see that linear relationship can be represented by the equation of a straight line: y=mx+c Where, y = output of measure m = slope of straight line x = Variable to be measure C = offset or intercept of straight line Hysteresis Hystersis is a predictable error resulting from differences in the transfer functions when a reading is taken from above or below the value to be measured. Hystersis = at decreasing Input at increasing input. Accuracy This term is used to specify the maximum overall error (The algebraic difference between the indicated value & the actual value of a measured variable is called Im310 Page 8

9 the error) to be expected from a device, such as measurement of a variable. Accuracy usually is expressed as the inaccuracy and can appear in several forms: 1. Measured variable, as the accuracy is +/-2 o C in some temperature measurement. Thus, there would be an uncertainty of +/- 2 o C in any value of temperature measured. 2. Percentage of the instrument full-scale (FS) reading. Thus, an accuracy of +/- 0.5% FS in a 5-volt full-scale range meter would mean the inaccuracy or uncertainty in any measurement is +/ volts. 3. Percentage of instrument span, that is percentage of the range of instrument measurement capability. Thus, for a device measuring +/-3% of span for a psi range of pressure, the accuracy would be(+/-0.03)(50-20)= +/-0.9psi. 4. Percentage of the actual reading. Thus, for a +/-2% of reading voltmeter, we would have an inaccuracy of +/-0.04 volts for a reading of 2 volts. Repeatability Repeatability is the value of same output for given input in repeated trials is defined as repeatability of instrument. Repeatability can be found out in % of each reading. Final control Pneumatic signals Flapper nozzle system A very important signal conversion is from pressure to mechanical motion and Im310 Page 9

10 vice versa. This conversion can be provided by a flapper/nozzle system (sometimes called a baffle /nozzle system). A diagram of this device is shown in Fig.I below. A regulated supply of pressure, usually 20 psig, provides a source of air through the restriction. The nozzle is open at the end where the gap exists between the nozzle and flapper, and air escapes in this region. If the flapper moves down and closes off the nozzle opening so that no air leaks, the signal pressure will rise to the supply pressure. As the flapper moves away, the signal pressure will drop because of leaking of the leaking air. Finally, when the flapper is far away, the pressure will stabilise at some value determined by the maximum leak through the nozzle. Fig. II Fig II shows the relationship between signal pressure and gap distance. Note the great sensitivity in the central region. A nozzle/flapper is designed to operate in the central region where the slope of the line is greatest. In this region, the response will be such that a very small motion of the flapper can change the pressure by an order of magnitude Im310 Page 10

11 Fig. III Working principle and calibration procedure of I/P converter. Working Principle Current flowing through the operating coil energizes all I/P converters. They can be operated from a voltage supply from which the corresponding will be drawn (Ohms law V = IR). Units calibrated from a source are I/P ( to pneumatic) and voltage source is E/P (voltage to pneumatic) these don t differ essentially from each other except in minor manufacturing adjustment. The to pressure (I/P) converter, is very important element in process control. Often, when we want to use the low-level electric signal to do work, it is much easier to let the work be done by a pneumatic signal. The I/P converter gives us a linear way of translating the 4-20 ma into 3-15-psig signal. There are many designs for these converters, but the basic principle almost always involves the use of a flapper nozzle system. Refer Fig. III below. The through coil produces a force that will tend to pull the flapper down and close off the gap. A high produces a high pressure so that the device Im310 Page 11

12 is direct acting. Adjustment of the springs and perhaps the position relative to the pivot to which they are attached allows the unit to calibrated so that 4 ma corresponds to 3 psig and 20 ma corresponds to 15 psig. Current to pneumatic converters are two-wire precision instruments designed to convert standard industrial electrical input signals into proportional pneumatic output signal. They are force balance instruments using a coil suspended in a magnetic field to operate a flapper valve against a air nozzle to create back pressure on the control diaphragm of a booster relay. They are compact robust instruments suitable for panel or field mounting applications. Input signal: 4-20 ma DC. signal: 3-15 psi Supply pressure: 20 psig Calibration procedure Generally I/P converter is calibrated for standard industrial signals as 4-20 ma input and 3-15 psig output. These are standard factory settings and need not to be changed. Refer following steps to calibrate I/P converter: 1. Set digital calibrator in source mode. 2. Remove the top cover from the unit by gently prying up on the two snap-in cover tabs. 3. Connect 20-psig supply pressure and connect input signal i.e ma. 4. Set the input signal to 4 ma and check the output pressure on gauge as 3 psig. 5. If the pressure is showing more or less than 3 psig then adjust zero. Turn zero adjustment screw slowly by very small turn to obtain 3-psig pressure. More turning of zero adjustment may damage the I/P converter. Counterclockwise rotation increases the pressure, and clockwise rotation decreases the pressure. 6. Set the input signal to 20 ma and check the output pressure on gauge as 15 psig. 7. Turn the span adjustment potentiometer very slowly by small turn to obtain 15-psig pressure. More turning of span adjustment may damage the I/P converter Im310 Page 12

13 8. Repeat step 4 to check that the desired low value (4 ma ~ 3 psig) has not changed after adjusting the span. If necessary repeat steps 3 through 4 to fine-tune the unit. 9. Snap the top cover in the place. (Note: It is strongly recommended NOT to change the calibration set per standard factory setting.) Im310 Page 13

14 Working principle and calibration procedure of P/I converter. Working Principle Pressure to (P/I) converters is two-wire precision instrument designed to convert standard pneumatic input signals into proportional output electrical signal. They are compact robust instruments suitable for panel or field mounting applications. Input signal: 3-15 psig. signal: 4-20 ma DC Supply voltage: 24 VDC Calibration procedure Generally P/I converter is calibrated for standard industrial signals as 3-15 psig input corresponds to 4-20 ma DC output. These are standard factory settings and need not to be changed. To adjust the zero and span settings proceed as follows: Two adjustments for zero and span are provided in front face of unit. 1. Set digital calibrator on measure mode. 2. Connect input signal i.e psig. 3. Set the input signal to 3 psig and check the output as 4 ma. 4. If the is showing more or less than 4 ma then adjust zero on the isolator. 5. Set the input pressure signal to 15 psig and check the output 20 ma. 6. Turn the span adjustment potentiometer on signal 7. Repeat step 3 to check that the desired low value (3 psig ~ 4mA) has not changed after adjusting the span. If necessary repeat steps 3 through 4 to fine-tune the unit Im310 Page 14

15 Experiments + P/I converter Power on Milli Amp Measure + I/P converter Power on Milli Amp Source Im310 Page 15

16 Experiment No. 1: Linearity of I/P converter Procedure Start up the set up as mentioned in commissioning part above. Put digital calibrator in source mode. Give input in the step of 4 ma from 4 to 20 ma by slowly rotating the knob of digital calibrator. Note down corresponding pressure on output pressure gauge in psig. Tabulate above readings in the observation table given below. Observations Sr. Input Standard Actual No. Pressure Pressure Calculations Linearity: Linearity of I/P converter is 5% maximum of output span between 3 to 15 psig (as stated by manufacturer). Therefore 5/100 * (15-3) = 0.6 psig. This is the maximum deviation in the output. Plot graph of Input on X axis and output pressure on Y-axis. Draw a straight line that best fits all the points. The graph shows the straight line. Observe the maximum deviation in output and compare with specified by manufacturer. Conclusions We may observe some deviation in actual linearity of I/P converter from manufacturer s specification, as it depends upon accuracy of pressure gauges used, accuracy of digital calibrator and visual error in recording the readings Im310 Page 16

17 Experiment No. 2: Hysteresis of I/P converter Procedure Start up the set up as mentioned in commissioning part above. Put digital calibrator in source mode. Give input in the step 4 ma from 4 to 20 ma by slowly rotating the adjust knob on digital calibrator. Note down corresponding output pressure on output pressure gauge in psig. Now note the output pressure in psig by applying input in decreasing mode from 20 ma to 4 ma. Tabulate above readings in the observation table given below. Observations Sr. Input Sr. Input Hysteresis No. Pressure No. Pressure psig (X) (Y) (Y)-(X) Increasing input Decreasing input Calculations Hystersis: Hystersis of I/P converter is 0.5 psig typical (as stated by manufacturer). Calculate hysteresis by using formula: Hystersis = at decreasing Input at increasing input. Plot the graph showing hysteresis as input (increasing and decreasing) on X axis and corresponding output on Y-axis. Conclusions We may observe some deviation in hysteresis of I/P converter as it depends upon accuracy of pressure gauges used accuracy of digital calibrator and visual error in recording the readings Im310 Page 17

18 Experiment No. 3: Accuracy of I/P converter Procedure Start up the set up as mentioned in commissioning part above. Now put digital calibrator in source mode. Give input in the step of 4 ma from 4 to 20 ma by slowly rotating the knob of digital calibrator. Note down corresponding pressure on output pressure gauge in psig. Observations Sr. No. Input Standard Pressure (X) Actual Pressure (Y) Deviation (Y) (X) Calculations Accuracy: Accuracy can be calculated with reference to above definitions in theory part Im310 Page 18

19 Experiment No. 4: Repeatability of I/P converter Procedure Start up the set up as mentioned in commissioning part above. Now put digital calibrator on source mode. Give input in the step 4 ma from 4 to 20 ma by slowly rotating the adjust knob on digital calibrator. Note down corresponding output pressure on output pressure gauge in psig. Now repeat the above steps for more trials. Tabulate above readings in the observation table given below. Observations Sr. Input Sr. Input Deviation in No Pressure No. Pressure output psig (X) (Y) (Y)-(X) Trial 1 Trial Sr. Input Sr. Input Deviation in No. Pressure No. Pressure output psig (X) (Y) (Y)-(X) Trial 3 Trial Im310 Page 19

20 Calculations Repeatability: Note down the values of output for same input in repeated trials. Repeatability can be found out in % of each reading Im310 Page 20

21 Experiment No. 5: Linearity of P/I converter Procedure Start up the set up as mentioned in commissioning part above. Now put digital calibrator on measure mode. Give pressure input in the step of 3 psig from 3 to 15 psig by slowly rotating the air regulator. Note down corresponding output on digital calibrator in ma. Tabulate above readings in the observation table given below. Observations Sr. Input Standard Actual No. Pressure Calculations Linearity: Plot graph of Input pressure on X-axis and output on Y-axis. Draw a straight line that best fits all the points. The graph shows the straight line. Observe the maximum deviation in output Im310 Page 21

22 Experiment No. 6: Hysteresis of P/I converter. Procedure Start up the set up as mentioned in commissioning part above. Now put digital calibrator on measure mode. Give pressure input in the step of 3 psig from 3 to 15 psig by slowly rotating the air regulator. Note down corresponding output on digital calibrator in ma. Now note the output in ma by applying input pressure in decreasing mode from 15 psig to 3 psig. Tabulate above readings in the observation table given below. Observations Sr. Input Sr. Input No. Pressure (X) No. Pressur e ) (Y) Increasing input Decreasing input Hysteresis ma (Y)-(X) Calculations Hystersis: Calculate hysteresis by using formula: Hystersis = at decreasing Input at increasing input. Plot the graph showing hysteresis as input (increasing and decreasing) on X axis and corresponding output on Y-axis Im310 Page 22

23 EXPERIMENT NO. 7: ACCURACY OF P/I CONVERTER. Procedure Start up the set up as mentioned in commissioning part above. Now put digital calibrator measure mode. Give pressure input in the step of 3 psig from 3 to 15 psig by slowly rotating the air regulator. Note down corresponding output on digital calibrator in ma. Tabulate above readings in the observation table given below. Observations Sr. Input Standard No. Pressure (X) Actual Current (Y) Deviation (Y) (X) Calculations Accuracy: Accuracy can be calculated with reference to above definitions in theory part Im310 Page 23

24 Experiment No. 8: Repeatability of P/I converter Procedure Start up the set up as mentioned in commissioning part above. Now put digital calibrator in measure mode. Give pressure input in the step of 3 psig from 3 to 15 psig by slowly rotating the air regulator. Note down corresponding output on digital calibrator in ma. Now repeat the above steps for more trials. Tabulate above readings in the observation table given below. Observations Sr. Input Sr. Input Deviation No. Pressure No. Pressure in output psig (X) (Y) (Y)-(X) Trial 1 Trial Sr. Input Sr. Input Deviation No. Pressure No. Pressure in output psig (X) (Y) (Y)-(X) Trial 3 Trial Im310 Page 24

25 Calculations Repeatability: Note down the values of output for same input in repeated trials. Repeatability can be found out in % of each reading Im310 Page 25

26 Components Manuals Electro pneumatic transducer (I/P) The ControlAir Type 500X converts a input signal to a linearly proportional pneumatic output pressure. Technical specifications Model Make Input Min./Max supply pressure Linearity Repeatability Hysteresis Air consumption Port size Principle of operation 500X-AC ControlAir 4-20 ma 3-15 psi Min. 18 psig, Max 100 psig +/-0.75 % of span <0.5% of span <1% of span 0.05 scfm midrange typical ¼ NPT The unit is a force balance device in which a coil is suspended in the field of a magnet by a flexure. The flexure moves towards the nozzle and creates back pressure which acts as a pilot pressure to an integral booster relay. Input signal increase causes increase in proportional output pressure. Zero and span are calibrated by turning adjust screws on the front face of the unit. Adjustment of the zero screw repositions the nozzle relative to the flexure. The span adjustment is a potentiometer that controls the amount of through the coil Im310 Page 26

27 Troubleshooting Problem No output or low output Leakage Low or improper span Erratic operation Check Zero adjustment Supply pressure too low Clogged orifice Connections Zero and span adjustments Supply pressure too low leakage Electrical input signal Loose wires or connections Liquid in air supply Calibration 1 Open protective covers to expose zero and span adjustment screws. 2 Connect the recommended air supply to the inlet of the transducer and an accurate pressure gauge at the outlet. 3 connect the electrical input and set it to 4 ma. 4 Observe the output pressure. If necessary adjust zero screw until reaching minimum output pressure setting (3 psi). Turn zero screw counter clockwise to Im310 Page 27

28 increase pressure, clockwise to decrease pressure. If unable to achieve output during calibration process, turn zero adjustment screw counter clockwise for up to 30 revolutions, until output pressure rises. 5 Increase electrical input to 20 ma 6 Observe the output pressure. If necessary adjust the span screw until output pressure reaching 15 psi. Turn span screw counter clockwise to increase pressure, clockwise to decrease pressure. 7 The zero span adjustments are interactive. After adjusting the span it will be necessary to recheck the zero. Repeat steps 3-6 until both end points are at the required values. Manufacturer s address Control Air Inc. 8 Columbia Drive, Amherst, NH USA sales@controlair.com Indian supplier: Control teknics 5,Aboorva Flats, old No.6, New No. 11 7th main road, Raja Annamalaipuram Chennai controlteknics@eth.net Im310 Page 28

29 Mini combination air filter regulator These modular series filter regulator are high flow, low pressure, and high accuracy. Technical specifications Make Airmatic Model MB VD-PAP Range 0 2 Kg/cm 2 Type Diaphragm, Relieving Connection ¼ BSP Body Aluminium Bowl Polycarbonate Element Porous material Drain Brass Seals Buna N Diaphragm Buna N Spring pressure Spring steel Zn plated Spring valve Stainless steel Spring cage and nob Acetyl resin Gauge ports Two Element rating 25 micron Drain Manual Bowl capacity 30 ml Max. pressure 12kg/cm 2 Max. temperature 50 0 C Overall dimensions 40diameter x 155 H mm Weight 220 gm Im310 Page 29

30 Manufacturer s address Shah pneumatics, 28/30, Navketan Industrial Estate, Mahakali Caves Road, Andheri (E), Mumbai Shahpneu@bom3.vsnl.net.in Web: Im310 Page 30