1 | P a g e CCB 3072 PROCESS INSTRUMENTATION & CONTROL LAB PROJECT REPORT EXPERIMENT: TEMPERATURE CONTROL GROUP: 8 MEMBERS: Mohd Muizzuddin Bin Mohd Pauzi15401 Nurul Alia Bt Mohamad15607 Nuralia Syairah Binti Osman15669 Foo Wai Hun15303 Guilles, Arielaine Fe Cruzat17779 Lecturer: Dr Timothy Ganesan A/L Andrew Date Submission : 5th August 2014 2 | P a g e Table of Content No.TopicPage 1 Introduction 3 2 Methodology 4 3 Result of Experiment 5 4 Analysis of Instruments 6 5 Dynamic Model 11 6 Feedback Controller 15 7 Discussion 19 8 Conclusion 20 9 Reference 20 3 | P a g e Introduction InProcessInstrumentationandControlLab,weconductedTemperatureControlexperiment amongotherexperiments.Inthisparticularexperiment,theobjectivesaretodemonstratethe characteristicofProportionalOnlyControl(P),ProportionalBandandIntegralAction(PI)and Proportional Band, Integral Action and Derivative Action (PID) on a temperature process control loop. It is also conducted to demonstrate the loop tuning procedure on a temperature process control loop.TheAir Temperature Control has been designed on how a temperature loop for an exchanger canbecontrolledusingamicroprocessorbasedcontroller.Thecontrolpanelisconnectedtoa DistributedControlSystem(DCS),whichcanremotelycontroltheprocessplantusingsupervisory controlmode(SCADA)ordirectdigitalcontrolmode(DDC).Aselectorwithlocatedatthecontrol panelisusedtoselectbetweenSCADAorDDCmode.InSCADAmodetheDCScanmonitorand control the process through the process controller and in DDC mode; the DCS can directly control the plant through the Field Control Station. TheAirTemperatureControlModuleisanairprocesswhere6bar(g)compressedairis charged into the air receiver tank V-102 and regulated to about 4 bar(g) by the air regulator PCV-102. AirfromV-102 flowsthrough the process lineinto the air heater K-101 where it isheated up to 150 C and is then discharged to the atmosphere. 4 | P a g e Methodology Methodology of the Temperature Control Experiment: Firstofall,thecompressorwasstartedandwewillwaitforsufficientairpressuretobuildupinthe receiver tank. After that, the instrument main supply was swich on. Then, the controller was set to the manualmode with set point of 100 . A step input was introduced and the experiment was started with Proportionalonly control to observe the response produced, and then was repeated by replacing the P ControllerwithaProportional-Integral(PI)ControlandthenlastlytouseaProportional-Integral-Derivative (PID) Control. Methodology of the Project 1) A dynamic model of the process was first drafted out.2) Basic instruments to use for the process control system were analysed.3) A feedback control system was designed and the standard block diagram for the feedback control system was plotted.4) The stability of the feedback control system was analysed using Routh Stability Criterion as well as in MATLAB.5) The behaviour of the process control system when using 3 different types of Feedback controllers were analysed in MATLAB SIMULINK.6) The most suitable type of controller was determined based on the results in SIMULINK.7) The optimum parameters for the chosen controller were then determined by using MATLAB SIMULINK. 5 | P a g e Result of Experiment Graph of temperature against time by using PID controller Graph of temperature against time by using PI controller Graph of temperature against time by using P controller 0 50 100 150 200 01020 Temperature/C Time/min Closed Loop Response of PID Controller temperature by using PID setpoint temperature 0 50 100 150 200 01020 Temperature/C time/min Closed Loop Response of PI Rontroller temperature by using PI setpoint temperature 0 50 100 150 200 010203040506070 Temperature/C Time/min Closed Loop Response of P Rontroller temperature by using P setpoint temperature 6 | P a g e Analysis of Instruments Thefollowingdiagramshowsafeedbackcontrolloopwhichcomprisesoftheprocess,the measurement, the controller and thefinalcontrolelement. When all the various elements are interconnectedwitheachotherandthereexistsacontinuouspassingofinformationaround theloop,thentheloopbecomesaclosedloopcontrolandsimultaneously,anautomatic feedback exists. Figure 1 Closed Loop Control Furthermore, the actual setup of the instruments in the lab is also given in the figure below. Figure 2 Experimental Setup of Equipments PSV-302 PIC-302 PT-302 Receiver tank V-301 Control tank V-302 PT PC PSV-301 7 | P a g e 1.PID Controller (PIC-302) For this experiment, PID controller is perhaps the most important tool that can determine the success of meeting the objectives. P, I, and D stand for Proportional, which depends on present error, Integral, which is the accumulation of past errors and Derivative, which is the prediction of future errors, terms respectively. A simple block diagram of PID controller is shown below. Figure 3 PID controller block diagram PID controller is useful in processes such as those that have rapid and large disturbances. ItmustbeusedonlywhennecessarybecausethedesignandtuningprocessofaPID controller can initially appear to be conceptually intuitive but prove to be hard in practice. Nevertheless, this type of control proves itself useful for various processes.For the experiment, three different types of controller are being used in order to determine themostsuitablecontrollernamelyPcontroller,PIcontrollerandPIDcontroller.When thePcontrollerisusedalone,itresultswithanoffsetfromthesetpointoftheprocess variable. The magnitude of the offset varies depending on the value of the controller gain. Asthevalueofthecontrollergainincreases,the amount ofoffsetdecreases.Whenused withIcontroller,theoffseterrorbecomeseliminatedandthemovementoftheprocess towards thesetpointaccelerates.However,itisimportant tonote thatsincetheintegral termrespondstoaccumulatederrorsfromthepast,itcancausethepresentvalueto overshootthesetpointvalue.ThisiswheretheDcontrollerplaysitsrolebypredicting the system behaviour and improving settling time and stability as a result. 2.Recorder (PR-302) Thisinstrumenthasapairofpenchartrecorderwhich continuouslyrecordstheresponseoftheprocess instrumentoftheinputandoutputbythemeansofa graph. This instrument is crucial for this experiment because it enablesonetostudyandinvestigatethesystem responses in various tuning methods. 8 | P a g e 3.Pressure transmitter (PT-301) Pressureistheratioofforcetotheareaoverwhichtheforceisdistributed.Itis important to maintain the pressure at a specified level in order to prevent explosion or implosionoftanksduetoexpandingorshrinkingofgasesorliquidspresentinside. Pressuretransmitterisimportantforthesafetyoftheexperimentasitactsasa transducer which generates a signal as a function of the pressure. 4.Control Valve (PCV-302) Controlvalves,alsoknownasfinalcontrolelements,are valvesusedtocontroldifferentconditions(i.e.pressure, temperature)andwhichfullyorpartiallyopensorcloses dependingonthesignalsreceivedfromcontrollerswhich comparethesetpointtotheprocessvariable.Theopening and closing of the valves can either be done withthe help of electrical, hydraulic or pneumatic actuators. If different types ofvalveswithvarioussizesaresubjectedtothesame volumetric flow rate and differential pressure was kept contant, then all the valves will have an equal orifice pass area. 5.Vortex flow meter (FT-301) Flow meters are used to measure the flowoffluidssuchasliquidsor gasesinthesystem.Vortexflow meter works by placing a bluff body (calledashedderbar)inthepath of thefluid and as thefluid passes this bar,itcreatesdisturbanceswhich then results to vortices. The vortices trailbehindthecylinderorfrom each side of the bluff body. The flow rate of the liquid is then measured using the concept that thefrequencyatwhichthevorticesalternate sidesisproportionalto theflowrate of the fluid. 9 | P a g e 6.Pressure indicator (PI-301, PI-302, PI-303, PI-304) Pressuremeasurementsareoftentimesmaderelativeto somespecifiedreferencepoint.Someofthesereference pointsareabsolute,gaugeanddifferentialpressure. Absolutepressureiszero-referencedagainstaperfect vacuum which makes it equal to gauge plus atmospheric pressure.Gaugepressure,ontheotherhand,iszero-referencedagainstambientairpressurewhichmakesitequaltoabsolutepressureminus atmosphericpressure.Lastly,differentialpressureisthemeasureofthedifferencesin pressures at two different points. Forthisindicator,thepressureisequaltoabsolutepressureminusatmosphericpressure which makes it equal to a gauge pressure where the negative sign is omitted. 7.Process Tanks (V-301, V-302) In this experiment, the process tank is used to study the change in pressure by inserting air into the tank and it is crucial for safety that the pressure be kept at a high value in order to avoid damage to the tank. 8.Alarm annunciator (PAL-302, PAH-302) Analarmannunciatorwasusedintheexperimenttoensurethatifthepressurereaches criticallevels,theuserswillbemadeawareandcantakeprecautionarymeasures. Generally,thisinstrumentalertstheoperatorsoftheconditionsintheplanttoensure everyones safety. 9.Pressure Relief Valve (PSC-301,PSC-302) PressureReliefValve,alsoknownasPRV,isatypeofreliefvalvewhichcontrolsthe pressure in the system by releasing excess pressure build up caused by a process upset or instrument failure. This device is mechanically activated and works due to a spring which isloaded to normally close thevalve. If the pressureinside thesystemishigher than the spring tension, it pushes the spring up and causes the PRV to open in order to purge air to atmosphere to avoid overpressure in the tank. 10 | P a g e 10. Solenoid Valves (HV-301, HV-302, HV-303) Solenoid valves are electromechanically operated in which they are controlled by electric currentthroughasolenoid.Thistypeofvalveoffersfastandsafeswitching,hashigh reliability, long life cycle, low control power and compact design. 11. Air Regulator (PCV-301) Asthenameimplies,theairregulatorintheexperimentregulatestheairsupplytothe process receiver tank in order to ensure that the pressure limits are not exceeded. 12. D/P transmitter (PDT-301) A differential pressure transmitter or sensor connects two different points and measures its pressuredifference.Intheexperiment,theD/Ptransmitterfunctionsmainlyforthe process line and it is able to measure values between 0-60 psig. 13. Rotameter (FI-301, FI-302) A rotameter is another flow rate measuring device which measures liquid or gas flow rates enclosedinatube.Itisonetypeofvariableareameterswhichmeasuresflowrateby varying the cross sectional area where the fluid flows. In this experiment, it acts as a flow rate measuring device for the process line. 14. Hand Valve (HV-304, HV-309) A hand valveis a type ofisolation valve which stops the flowofprocessmediaatagivenlocationwhen necessary.Oftentimes,duringmaintenanceorforsafety purposes,theflowhastobecompletelystopped.Inthis experiment,thehandvalvesareisolationvalvesforthe input and output air and determines the directionas well as the load changes of the air flow. 11 | P a g e 15. Fault Simulation Switches (HS-30, HS-302, HS-303) Theseswitchesactasacut-offswitchforemergencypurposes.Inthisexperiment,it comesinhandywheneverthereisaleakageatthepressurecontroltank.Itcanalsobe used to shut off the outlet to the pressure control tank if the instrument air supply has been cut off for any reason. 16. Control Panel The control panelin this experiment acts as a motherboard of pressure control. It mounts thecontroller,alarmannunciator,recorder,pushbuttonpowersupplyswitchand changeover switch between the distributed control system (DCS) and local control. Dynamic Model Mass balance

Since density and volume is constant

Energy balance

12 | P a g e

Let

and

At steady-state

Laplace Transform:

Thus, the dynamic model for the heat exchanger is

Parameter values: Air temperature Based on density tables,

13 | P a g e

From previous equation,

While

Hence,

Characteristic Equation

14 | P a g e Lowest limit

Using Routh Array,

Therefore

The range of

is

15 | P a g e Feedback Controller For P Controller Block Diagram of the process with P Controller to control the output of temperature. 16 | P a g e For PI-Controller Block Diagram 17 | P a g e 18 | P a g e For PID Controller Block Diagram 19 | P a g e Discussion As the figures shown previously, the output of 3 types of controller, namely, P controller, PI controller and PID controller were compared and the results can be observed from simulink done.No Type of Controller Overshoot (%)Settling Time (s)Steady State error 1P-controller24.972.3Yes 2PI-controller6.26108No 3PID-controller8.5873.6No From the above observations, it is clear that PI controller gives the best result compared to other type ofcontroller.TheuseofP-onlycontrollerwhichnotonlygivemoreovershootandlongersettling time,butalsosteady-stateerrorforthesystem,henceisnotselected.WedecidedtochoosePI controllertocontrolforourprocessoverPIDcontrolbecauseofthelessovershootpercentageand also easier to be tuned compared to PID controller. Begin with PID controller, the outcome of simulink has given us a hint that the time taken to reach the new set point is shorter as compared to the actual experiment result.Asfor PIcontroller, the simulated result givesa better outcome ascomparison to the resultobtained fromtheexperimentconducted,offsetiseliminated.However,forthiscontroller,ittakeslengthier duration to reach the desired value as the order of the system increase that produce sluggish outcome. 20 | P a g e Finally,forPcontroller,intheconductedexperiment,thegraphobtainedhasshownanoffsetwhile reachingthesetpointvalue.Bycomparisontothegraphsassimulated,anexpectedofsluggish responseiscommon asit takesa long periodof time to respond. Bothgraphshave indicated that the desired set point value will not be achieved by using P controller alone as it is very sluggish.Transfer function and gain values included Simulink software may contribute to the errors or deviation fromtheactualexperimentresults.Thismaycausethedelayinthesystem.Besides,theinaccurate transferfunctionsandtheassumptionsofidealsystemmightcausetheresultsvaryfromtheactual results. The order of the transfer function plays an important role in producing accurateoutcome. The transferfunctionusedisfirstorder.Thismaynotbetrueasthesystemintheactualexperimentis more complex and may have transfer function other than first order.Conclusion Basedon the temperature controlexperiment done for theProcess, Instrumentation & Control Lab, a dynamicmodelforthephysicalappendageschemewasdevelopedusingthedataobtainedfromthe experiment.Ananalysisonthebasicinstrumentationusedforthesummonsarrangementwasalso done. Finally, a feedback controller arrangement was designed to fit the process system referring to the possibleparametersthatneededtobecontrolledusingdifferenttuningmethod.Basedontheresults obtained and figuring, the best controller system for this process is the PI-controller because of the less overshoot percentage and also it is easier to be tuned.Reference P.Sivakumar, D.Prabhakaran & T.Kannadasan. (2012). Temperature control of shell and tube heat exchanger by using intelligent controllers. International journal of computational engineering research, 2(8). Seborg D.E., T.F. Edgar and D.A. Melliechamp, Process Dynamics and Control, John Wiley andSons, New York, 1989, pp 116-118.The Controller. (n.d.). Retrieved 7 1, 2014, from Control Actions: http://www.see.ed.ac.uk/~jwp/control06/controlcourse/restricted/course/second/course/lecture5.html What is an Integral Control System? . (n.d.). Retrieved 7 1, 2014, from Integral Control Systems: http://www.facstaff.bucknell.edu/mastascu/econtrolhtml/intro/intro3.html