Chapter 10Control Loop Troubleshooting
Overall Course ObjectivesDevelop the skills necessary to function as an industrial process control engineer.SkillsTuning loopsControl loop designControl loop troubleshootingCommand of the terminologyFundamental understandingProcess dynamicsFeedback control
Objectives for Control Loop TroubleshootingBe able to implement an overall troubleshooting methodologyBe able to determine whether or not the actuator, process, sensor, and controller are functioning properly.Recall the major failure modes for each of the elements of a control loop.
Troubleshooting Loops in the CPI
Control Diagram of a Typical Control Loop
F1
TC
T1
F2
T2
TF
TT
Sensor System
Controller
Actuator System
Components and Signals of a Typical Control Loop
I/P
F1
T1
F2
T2
TF
3-15 psig
Thermocouplemillivolt signal
Air
Thermowell
4-20 mA
OperatorConsole
Transmitter
4-20 mA
DCSControl Computer
A/D
Tsp
Actuator System
Controller
Sensor System
D/A
What is Control Loop Troubleshooting?Control loop is suspected of not functioning properly.Poor overall control performanceErratic behaviorControl loop was removed from service.Identify the source of the problem.Correct the problem.Retune the controller and monitor.
Overall Approach to Troubleshooting Control LoopsCheck subsystem separately.Actuator systemControllerSensorProcessThen check performance of the entire control loopWhats been changed lately?
Checking the Actuator SystemApply block sine wave input changes to the setpoint for the flow controller.Determine the deadband of the flow control loop from a block sine wave test. Also, estimate the time constant for the flow control loop from the block sine wave test.If the time constant is less than 2 seconds and the deadband is less than 0.5%, there is no need to evaluate the actuator system further
Block Sine Wave Test
Chart1
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&A
Page &P
Setpoint to Flow Controller
Measured Flow Rate
Time
F16
7.25E-013.50E+023.50E+02
1.48E+003.50E+023.50E+02
2.23E+003.50E+023.50E+02
2.98E+003.50E+023.50E+02
3.73E+003.50E+023.50E+02
4.48E+003.50E+023.50E+02
5.23E+003.50E+023.50E+02
5.98E+003.50E+023.50E+02
6.73E+003.50E+023.50E+02
7.48E+003.50E+023.50E+02
8.23E+003.50E+023.50E+02
8.98E+003.50E+023.50E+02
9.73E+003.50E+023.50E+02
1.05E+013.50E+023.50E+02
1.12E+013.50E+023.50E+02
1.20E+013.50E+023.50E+02
1.27E+013.50E+023.50E+02
1.35E+013.50E+023.50E+02
1.42E+013.50E+023.50E+02
1.50E+013.50E+023.50E+02
1.57E+013.50E+023.50E+02
1.65E+013.50E+023.50E+02
1.72E+013.50E+023.50E+02
1.80E+013.50E+023.50E+02
1.87E+013.50E+023.50E+02
1.95E+013.50E+023.50E+02
2.02E+013.50E+023.50E+02
2.10E+013.50E+023.50E+02
2.17E+013.50E+023.50E+02
2.25E+013.50E+023.50E+02
2.32E+013.50E+023.50E+02
2.40E+013.50E+023.50E+02
2.47E+013.50E+023.50E+02
2.55E+013.50E+023.50E+02
2.62E+013.50E+023.50E+02
2.70E+013.50E+023.50E+02
2.77E+013.50E+023.50E+02
2.85E+013.50E+023.50E+02
2.92E+013.50E+023.50E+02
3.00E+013.50E+023.50E+02
3.07E+013.50E+023.50E+02
3.15E+013.50E+023.50E+02
3.22E+013.50E+023.50E+02
3.30E+013.50E+023.50E+02
3.37E+013.50E+023.50E+02
3.45E+013.50E+023.50E+02
3.52E+013.50E+023.50E+02
3.60E+013.50E+023.50E+02
3.67E+013.50E+023.50E+02
3.75E+013.50E+023.50E+02
3.82E+013.50E+023.50E+02
3.90E+013.50E+023.50E+02
3.97E+013.50E+023.50E+02
4.05E+013.50E+023.50E+02
4.12E+013.50E+023.50E+02
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4.80E+013.50E+023.50E+02
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4.95E+013.50E+023.50E+02
5.02E+013.50E+023.50E+02
5.10E+013.50E+023.50E+02
5.17E+013.50E+023.50E+02
5.25E+013.50E+023.50E+02
5.32E+013.50E+023.50E+02
5.40E+013.50E+023.50E+02
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5.55E+013.50E+023.50E+02
5.62E+013.50E+023.50E+02
5.70E+013.50E+023.50E+02
5.77E+013.50E+023.50E+02
5.85E+013.50E+023.50E+02
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6.45E+013.50E+023.50E+02
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6.60E+013.50E+023.50E+02
6.67E+013.50E+023.50E+02
6.75E+013.50E+023.50E+02
6.82E+013.50E+023.50E+02
6.90E+013.50E+023.50E+02
6.97E+013.50E+023.50E+02
7.05E+013.50E+023.50E+02
7.12E+013.50E+023.50E+02
7.20E+013.50E+023.50E+02
7.27E+013.50E+023.50E+02
7.35E+013.50E+023.50E+02
7.42E+013.50E+023.50E+02
7.50E+013.50E+023.50E+02
7.57E+013.50E+023.50E+02
7.65E+013.50E+023.50E+02
7.72E+013.50E+023.50E+02
7.80E+013.50E+023.50E+02
7.87E+013.50E+023.50E+02
7.95E+013.50E+023.50E+02
8.02E+013.50E+023.50E+02
8.10E+013.50E+023.50E+02
8.17E+013.50E+023.50E+02
8.25E+013.50E+023.50E+02
8.32E+013.50E+023.50E+02
8.40E+013.50E+023.50E+02
8.47E+013.50E+023.50E+02
8.55E+013.50E+023.50E+02
8.62E+013.50E+023.50E+02
8.70E+013.50E+023.50E+02
8.77E+013.50E+023.50E+02
8.85E+013.50E+023.50E+02
8.92E+013.50E+023.50E+02
9.00E+013.50E+023.50E+02
9.07E+013.50E+023.50E+02
9.15E+013.50E+023.50E+02
9.22E+013.50E+023.50E+02
9.30E+013.50E+023.50E+02
9.37E+013.50E+023.50E+02
9.45E+013.50E+023.50E+02
9.52E+013.50E+023.50E+02
9.60E+013.50E+023.50E+02
9.67E+013.50E+023.50E+02
9.75E+013.50E+023.50E+02
9.82E+013.50E+023.50E+02
9.90E+013.50E+023.50E+02
9.97E+013.50E+023.50E+02
1.00E+023.50E+023.50E+02
1.01E+023.50E+023.50E+02
1.02E+023.50E+023.50E+02
1.03E+023.50E+023.50E+02
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1.12E+023.50E+023.50E+02
1.12E+023.50E+023.50E+02
1.13E+023.50E+023.50E+02
1.14E+023.50E+023.50E+02
1.15E+023.50E+023.50E+02
1.15E+023.50E+023.50E+02
1.16E+023.50E+023.50E+02
1.17E+023.50E+023.50E+02
1.18E+023.50E+023.50E+02
1.18E+023.50E+023.50E+02
1.19E+023.50E+023.50E+02
1.20E+023.50E+023.50E+02
1.21E+023.50E+023.50E+02
1.21E+023.50E+023.50E+02
1.22E+023.50E+023.50E+02
1.23E+023.50E+023.50E+02
1.24E+023.50E+023.50E+02
1.24E+023.50E+023.50E+02
1.25E+023.50E+023.50E+02
1.26E+023.50E+023.50E+02
1.27E+023.50E+023.50E+02
1.27E+023.50E+023.50E+02
1.28E+023.50E+023.50E+02
1.29E+023.50E+023.50E+02
1.30E+023.50E+023.50E+02
1.30E+023.50E+023.50E+02
1.31E+023.50E+023.50E+02
1.32E+023.50E+023.50E+02
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1.33E+023.50E+023.50E+02
1.34E+023.50E+023.50E+02
1.35E+023.50E+023.50E+02
1.36E+023.50E+023.50E+02
1.36E+023.50E+023.50E+02
1.37E+023.50E+023.50E+02
1.38E+023.50E+023.50E+02
1.39E+023.50E+023.50E+02
1.39E+023.50E+023.50E+02
1.40E+023.50E+023.50E+02
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1.44E+023.50E+023.50E+02
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1.51E+023.50E+023.50E+02
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1.52E+023.50E+023.50E+02
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1.54E+023.50E+023.50E+02
1.54E+023.50E+023.50E+02
1.55E+023.50E+023.50E+02
1.56E+023.50E+023.50E+02
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1.69E+023.50E+023.50E+02
1.69E+023.50E+023.50E+02
1.70E+023.50E+023.50E+02
1.71E+023.50E+023.50E+02
1.72E+023.50E+023.50E+02
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1.73E+023.51E+023.50E+02
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1.76E+023.51E+023.50E+02
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1.87E+023.50E+023.50E+02
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2.10E+023.49E+023.50E+02
2.11E+023.50E+023.50E+02
2.11E+023.50E+023.50E+02
2.12E+023.50E+023.50E+02
2.13E+023.50E+023.50E+02
2.14E+023.50E+023.50E+02
2.14E+023.50E+023.50E+02
2.15E+023.50E+023.50E+02
2.16E+023.50E+023.50E+02
2.17E+023.50E+023.50E+02
2.17E+023.50E+023.50E+02
2.18E+023.50E+023.50E+02
2.19E+023.50E+023.50E+02
2.20E+023.50E+023.50E+02
2.20E+023.50E+023.50E+02
2.21E+023.50E+023.50E+02
2.22E+023.50E+023.50E+02
2.23E+023.50E+023.50E+02
2.23E+023.50E+023.50E+02
2.24E+023.50E+023.50E+02
2.25E+023.50E+023.50E+02
2.26E+023.50E+023.50E+02
2.26E+023.50E+023.50E+02
2.27E+023.50E+023.50E+02
2.28E+023.50E+023.50E+02
2.29E+023.50E+023.50E+02
2.29E+023.50E+023.50E+02
2.30E+023.50E+023.50E+02
2.31E+023.50E+023.50E+02
2.32E+023.50E+023.50E+02
2.32E+023.50E+023.50E+02
2.33E+023.50E+023.50E+02
2.34E+023.50E+023.50E+02
2.35E+023.50E+023.50E+02
2.35E+023.50E+023.50E+02
2.36E+023.50E+023.50E+02
2.37E+023.50E+023.50E+02
2.38E+023.50E+023.50E+02
2.38E+023.50E+023.50E+02
2.39E+023.50E+023.50E+02
2.40E+023.50E+023.50E+02
2.41E+023.50E+023.50E+02
2.41E+023.50E+023.50E+02
2.42E+023.50E+023.50E+02
2.43E+023.50E+023.50E+02
2.44E+023.50E+023.50E+02
2.44E+023.50E+023.50E+02
2.45E+023.50E+023.50E+02
2.46E+023.50E+023.50E+02
2.47E+023.50E+023.50E+02
2.47E+023.50E+023.50E+02
2.48E+023.50E+023.50E+02
2.49E+023.50E+023.50E+02
2.50E+023.50E+023.50E+02
&A
Page &P
Common Problems with the Actuator SystemExcessive valve deadbandImproperly sized control valveValve packing is tightened too muchImproperly tuned valve positioner
Check the Sensor SystemEvaluate the repeatability of the sensor during steady-state operation.Evaluate the sensor dynamics.This may require an independent measurement of the controlled variable.Or check the elements that could contribute to a slow responding sensor.
Most Common Sensor FailuresTransmitterImproperly calibratedExcessive signal filteringTemperature sensorOff calibrationImproperly located thermowellBuildup of material on the thermowellPressurePlugged line to pressure sensor
Most Common Sensor FailuresSampling system for GCPlugged line in sampling systemFlow indicatorPlugged line to differential pressure sensorLevel indicatorPlugged line to differential pressure sensor
Check the ControllerCheck the filtering on the measured value of the controlled variable.Check the cycle time for the controller.Check the tuning on the controller.
Factors that Affect the Closed-Loop Performance of a Control LoopThe type and magnitude of disturbancesPrimarily affects variability in CVCan affect nonlinear behaviorThe lag associated with the components of the feedback control loop (actuator, process, and sensor)Results in slower disturbance rejection which affects variability Precision of the feedback componentsDirectly affects variability
Testing the Entire Control LoopClosed-loop block sine wave testVariability of the controlled variable over a period of a week or more.
Closed-Loop Block Sine Wave Test
Chart1
350.0681350
350.0409350
350.0594350
349.945350
349.9884350
350.0893350
350.0633350
350.0175350
350.0045350
350.0757350
350.0081350
350.0125350
350.0889350
350.2316350
349.9383350
349.9233350
349.939350
349.9952350
349.9074350
349.8946350
350.1343350.1
350.0955350.1
350.0084350.1
349.9802350.1
350.0807350.1
349.9055350.1
350.0476350.1
350.0629350.1
349.8077350.1
349.9222350.1
349.8083350.1
349.9476350.1
350.0918350.1
349.9279350.1
349.8339350.1
350.1561350.1
349.9784350.1
349.8446350.1
349.9376350.1
349.757350.1
349.8901350
349.8534350
349.9452350
349.98350
349.9608350
349.9243350
350.0786350
350.0465350
350.001350
349.8404350
349.9857350
350.0891350
349.87350
350.0323350
349.856350
349.9857350
350.0505350
350.0213350
350.0022350
350.0683350
350.1343349.9
349.8893349.9
350.0427349.9
349.9895349.9
349.9885349.9
349.8347349.9
350.0004349.9
350.1152349.9
349.8545349.9
350.0398349.9
349.8488349.9
350.1078349.9
350.0184349.9
350.0991349.9
349.9845349.9
350.0973349.9
350.0974349.9
349.85349.9
350.0825349.9
350.0799349.9
350.0848350
349.9594350
349.9576350
349.935350
349.9919350
349.936350
349.9648350
349.9675350
350.1309350
350.1758350
349.9207350
350.0857350
349.9283350
349.8937350
349.9462350
350.0766350
350.0422350
349.8591350
349.8648350
349.8694350
349.9778350
350.0239350
349.8773350
349.8833350
350.0929350
349.8612350
350.1766350
350.078350
349.9336350
349.9995350
349.9487350
350.0143350
349.9005350
349.9639350
350.1099350
349.9993350
349.8196350
350.0702350
349.9776350
349.9209350
349.9873350.2
349.9647350.2
350.1203350.2
350.1822350.2
349.8557350.2
350.0559350.2
350.312350.2
350.1181350.2
350.1946350.2
350.1893350.2
350.335350.2
350.2851350.2
350.2507350.2
350.3789350.2
350.2317350.2
350.3282350.2
350.3551350.2
350.3029350.2
350.3157350.2
350.1262350.2
350.2095350
350.1639350
350.0829350
350.3145350
350.0868350
349.9049350
349.7893350
349.9795350
350.036350
349.808350
349.8515350
350.1134350
349.8751350
349.9756350
349.8861350
349.738350
349.8967350
349.9777350
350.0251350
350.1332350
350.094349.8
350.1033349.8
350.0383349.8
349.946349.8
349.8515349.8
349.9131349.8
350.0475349.8
349.9511349.8
349.8811349.8
349.9879349.8
349.6516349.8
349.682349.8
349.8803349.8
349.6339349.8
349.8425349.8
349.6048349.8
349.6215349.8
349.789349.8
349.8717349.8
349.7547349.8
349.8828350
349.7801350
349.9453350
349.9373350
349.927350
350.1255350
350.033350
349.9339350
350.1643350
350.1378350
350.0027350
350.1258350
350.1193350
350.0683350
350.086350
350.0323350
350.0536350
350.0135350
350.0745350
349.9519350
349.9705350
350.0073350
350.052350
350.0575350
349.87350
349.9363350
350.0869350
350.0706350
350.0203350
350.057350
349.9132350
350.1364350
350.1216350
349.9583350
349.8737350
349.9291350
350.1692350
349.9318350
350.111350
349.9733350
350.1918350.4
349.9318350.4
350.192350.4
350.1547350.4
350.0687350.4
350.2222350.4
350.3632350.4
350.4567350.4
350.4742350.4
350.5585350.4
350.5911350.4
350.4523350.4
350.7635350.4
350.5999350.4
350.6136350.4
350.6276350.4
350.4339350.4
350.3604350.4
350.3898350.4
350.3132350.4
350.2939350
350.3541350
350.188350
350.1362350
350.0426350
349.9696350
349.8913350
349.9947350
349.9707350
349.8641350
350.015350
349.879350
349.8609350
349.9176350
349.9101350
349.9918350
349.855350
349.9958350
350.1595350
350.0175350
350.0437349.6
350.0359349.6
349.8968349.6
349.9728349.6
349.8414349.6
349.7852349.6
349.6775349.6
349.6803349.6
349.607349.6
349.5895349.6
349.4994349.6
349.4349349.6
349.6507349.6
349.4123349.6
349.6163349.6
349.4839349.6
349.5827349.6
349.6848349.6
349.7514349.6
349.4637349.6
349.7435350
349.7264350
349.88350
349.91350
349.8657350
349.8719350
349.9204350
349.8661350
350.1737350
350.277350
350.0934350
350.1247350
349.8458350
350.1448350
350.1722350
350.0343350
350.0514350
350.0179350
349.8457350
350.0266350
349.9732350
349.9806350
350.1447350
349.7524350
349.9879350
349.9682350
349.8603350
349.9248350
349.9493350
349.9749350
349.9978350
349.9689350
349.9542350
350.1267350
350.1032350
349.9245350
350.151350
350.1867350
350.1392350
350.0087350
350.168350
350.0132350
350.0825350
350.024350
349.9023350
350.1226350
349.9966350
349.9678350
349.9686350
349.7466350
349.9118350
349.9564350
350.0111350
Setpoint
ControlledVariable
Time
F16
7.25E-013.50E+023.50E+02
1.48E+003.50E+023.50E+02
2.23E+003.50E+023.50E+02
2.98E+003.50E+023.50E+02
3.73E+003.50E+023.50E+02
4.48E+003.50E+023.50E+02
5.23E+003.50E+023.50E+02
5.98E+003.50E+023.50E+02
6.73E+003.50E+023.50E+02
7.48E+003.50E+023.50E+02
8.23E+003.50E+023.50E+02
8.98E+003.50E+023.50E+02
9.73E+003.50E+023.50E+02
1.05E+013.50E+023.50E+02
1.12E+013.50E+023.50E+02
1.20E+013.50E+023.50E+02
1.27E+013.50E+023.50E+02
1.35E+013.50E+023.50E+02
1.42E+013.50E+023.50E+02
1.50E+013.50E+023.50E+02
1.57E+013.50E+023.50E+02
1.65E+013.50E+023.50E+02
1.72E+013.50E+023.50E+02
1.80E+013.50E+023.50E+02
1.87E+013.50E+023.50E+02
1.95E+013.50E+023.50E+02
2.02E+013.50E+023.50E+02
2.10E+013.50E+023.50E+02
2.17E+013.50E+023.50E+02
2.25E+013.50E+023.50E+02
2.32E+013.50E+023.50E+02
2.40E+013.50E+023.50E+02
2.47E+013.50E+023.50E+02
2.55E+013.50E+023.50E+02
2.62E+013.50E+023.50E+02
2.70E+013.50E+023.50E+02
2.77E+013.50E+023.50E+02
2.85E+013.50E+023.50E+02
2.92E+013.50E+023.50E+02
3.00E+013.50E+023.50E+02
3.07E+013.50E+023.50E+02
3.15E+013.50E+023.50E+02
3.22E+013.50E+023.50E+02
3.30E+013.50E+023.50E+02
3.37E+013.50E+023.50E+02
3.45E+013.50E+023.50E+02
3.52E+013.50E+023.50E+02
3.60E+013.50E+023.50E+02
3.67E+013.50E+023.50E+02
3.75E+013.50E+023.50E+02
3.82E+013.50E+023.50E+02
3.90E+013.50E+023.50E+02
3.97E+013.50E+023.50E+02
4.05E+013.50E+023.50E+02
4.12E+013.50E+023.50E+02
4.20E+013.50E+023.50E+02
4.27E+013.50E+023.50E+02
4.35E+013.50E+023.50E+02
4.42E+013.50E+023.50E+02
4.50E+013.50E+023.50E+02
4.57E+013.50E+023.50E+02
4.65E+013.50E+023.50E+02
4.72E+013.50E+023.50E+02
4.80E+013.50E+023.50E+02
4.87E+013.50E+023.50E+02
4.95E+013.50E+023.50E+02
5.02E+013.50E+023.50E+02
5.10E+013.50E+023.50E+02
5.17E+013.50E+023.50E+02
5.25E+013.50E+023.50E+02
5.32E+013.50E+023.50E+02
5.40E+013.50E+023.50E+02
5.47E+013.50E+023.50E+02
5.55E+013.50E+023.50E+02
5.62E+013.50E+023.50E+02
5.70E+013.50E+023.50E+02
5.77E+013.50E+023.50E+02
5.85E+013.50E+023.50E+02
5.92E+013.50E+023.50E+02
6.00E+013.50E+023.50E+02
6.07E+013.50E+023.50E+02
6.15E+013.50E+023.50E+02
6.22E+013.50E+023.50E+02
6.30E+013.50E+023.50E+02
6.37E+013.50E+023.50E+02
6.45E+013.50E+023.50E+02
6.52E+013.50E+023.50E+02
6.60E+013.50E+023.50E+02
6.67E+013.50E+023.50E+02
6.75E+013.50E+023.50E+02
6.82E+013.50E+023.50E+02
6.90E+013.50E+023.50E+02
6.97E+013.50E+023.50E+02
7.05E+013.50E+023.50E+02
7.12E+013.50E+023.50E+02
7.20E+013.50E+023.50E+02
7.27E+013.50E+023.50E+02
7.35E+013.50E+023.50E+02
7.42E+013.50E+023.50E+02
7.50E+013.50E+023.50E+02
7.57E+013.50E+023.50E+02
7.65E+013.50E+023.50E+02
7.72E+013.50E+023.50E+02
7.80E+013.50E+023.50E+02
7.87E+013.50E+023.50E+02
7.95E+013.50E+023.50E+02
8.02E+013.50E+023.50E+02
8.10E+013.50E+023.50E+02
8.17E+013.50E+023.50E+02
8.25E+013.50E+023.50E+02
8.32E+013.50E+023.50E+02
8.40E+013.50E+023.50E+02
8.47E+013.50E+023.50E+02
8.55E+013.50E+023.50E+02
8.62E+013.50E+023.50E+02
8.70E+013.50E+023.50E+02
8.77E+013.50E+023.50E+02
8.85E+013.50E+023.50E+02
8.92E+013.50E+023.50E+02
9.00E+013.50E+023.50E+02
9.07E+013.50E+023.50E+02
9.15E+013.50E+023.50E+02
9.22E+013.50E+023.50E+02
9.30E+013.50E+023.50E+02
9.37E+013.50E+023.50E+02
9.45E+013.50E+023.50E+02
9.52E+013.50E+023.50E+02
9.60E+013.50E+023.50E+02
9.67E+013.50E+023.50E+02
9.75E+013.50E+023.50E+02
9.82E+013.50E+023.50E+02
9.90E+013.50E+023.50E+02
9.97E+013.50E+023.50E+02
1.00E+023.50E+023.50E+02
1.01E+023.50E+023.50E+02
1.02E+023.50E+023.50E+02
1.03E+023.50E+023.50E+02
1.03E+023.50E+023.50E+02
1.04E+023.50E+023.50E+02
1.05E+023.50E+023.50E+02
1.06E+023.50E+023.50E+02
1.06E+023.50E+023.50E+02
1.07E+023.50E+023.50E+02
1.08E+023.50E+023.50E+02
1.09E+023.50E+023.50E+02
1.09E+023.50E+023.50E+02
1.10E+023.50E+023.50E+02
1.11E+023.50E+023.50E+02
1.12E+023.50E+023.50E+02
1.12E+023.50E+023.50E+02
1.13E+023.50E+023.50E+02
1.14E+023.50E+023.50E+02
1.15E+023.50E+023.50E+02
1.15E+023.50E+023.50E+02
1.16E+023.50E+023.50E+02
1.17E+023.50E+023.50E+02
1.18E+023.50E+023.50E+02
1.18E+023.50E+023.50E+02
1.19E+023.50E+023.50E+02
1.20E+023.50E+023.50E+02
1.21E+023.50E+023.50E+02
1.21E+023.50E+023.50E+02
1.22E+023.50E+023.50E+02
1.23E+023.50E+023.50E+02
1.24E+023.50E+023.50E+02
1.24E+023.50E+023.50E+02
1.25E+023.50E+023.50E+02
1.26E+023.50E+023.50E+02
1.27E+023.50E+023.50E+02
1.27E+023.50E+023.50E+02
1.28E+023.50E+023.50E+02
1.29E+023.50E+023.50E+02
1.30E+023.50E+023.50E+02
1.30E+023.50E+023.50E+02
1.31E+023.50E+023.50E+02
1.32E+023.50E+023.50E+02
1.33E+023.50E+023.50E+02
1.33E+023.50E+023.50E+02
1.34E+023.50E+023.50E+02
1.35E+023.50E+023.50E+02
1.36E+023.50E+023.50E+02
1.36E+023.50E+023.50E+02
1.37E+023.50E+023.50E+02
1.38E+023.50E+023.50E+02
1.39E+023.50E+023.50E+02
1.39E+023.50E+023.50E+02
1.40E+023.50E+023.50E+02
1.41E+023.50E+023.50E+02
1.42E+023.50E+023.50E+02
1.42E+023.50E+023.50E+02
1.43E+023.50E+023.50E+02
1.44E+023.50E+023.50E+02
1.45E+023.50E+023.50E+02
1.45E+023.50E+023.50E+02
1.46E+023.50E+023.50E+02
1.47E+023.50E+023.50E+02
1.48E+023.50E+023.50E+02
1.48E+023.50E+023.50E+02
1.49E+023.50E+023.50E+02
1.50E+023.50E+023.50E+02
1.51E+023.50E+023.50E+02
1.51E+023.50E+023.50E+02
1.52E+023.50E+023.50E+02
1.53E+023.50E+023.50E+02
1.54E+023.50E+023.50E+02
1.54E+023.50E+023.50E+02
1.55E+023.50E+023.50E+02
1.56E+023.50E+023.50E+02
1.57E+023.50E+023.50E+02
1.57E+023.50E+023.50E+02
1.58E+023.50E+023.50E+02
1.59E+023.50E+023.50E+02
1.60E+023.50E+023.50E+02
1.60E+023.50E+023.50E+02
1.61E+023.50E+023.50E+02
1.62E+023.50E+023.50E+02
1.63E+023.50E+023.50E+02
1.63E+023.50E+023.50E+02
1.64E+023.50E+023.50E+02
1.65E+023.50E+023.50E+02
1.66E+023.50E+023.50E+02
1.66E+023.50E+023.50E+02
1.67E+023.50E+023.50E+02
1.68E+023.50E+023.50E+02
1.69E+023.50E+023.50E+02
1.69E+023.50E+023.50E+02
1.70E+023.50E+023.50E+02
1.71E+023.50E+023.50E+02
1.72E+023.50E+023.50E+02
1.72E+023.51E+023.50E+02
1.73E+023.51E+023.50E+02
1.74E+023.50E+023.50E+02
1.75E+023.51E+023.50E+02
1.75E+023.51E+023.50E+02
1.76E+023.51E+023.50E+02
1.77E+023.51E+023.50E+02
1.78E+023.50E+023.50E+02
1.78E+023.50E+023.50E+02
1.79E+023.50E+023.50E+02
1.80E+023.50E+023.50E+02
1.81E+023.50E+023.50E+02
1.81E+023.50E+023.50E+02
1.82E+023.50E+023.50E+02
1.83E+023.50E+023.50E+02
1.84E+023.50E+023.50E+02
1.84E+023.50E+023.50E+02
1.85E+023.50E+023.50E+02
1.86E+023.50E+023.50E+02
1.87E+023.50E+023.50E+02
1.87E+023.50E+023.50E+02
1.88E+023.50E+023.50E+02
1.89E+023.50E+023.50E+02
1.90E+023.50E+023.50E+02
1.90E+023.50E+023.50E+02
1.91E+023.50E+023.50E+02
1.92E+023.50E+023.50E+02
1.93E+023.50E+023.50E+02
1.93E+023.50E+023.50E+02
1.94E+023.50E+023.50E+02
1.95E+023.50E+023.50E+02
1.96E+023.50E+023.50E+02
1.96E+023.50E+023.50E+02
1.97E+023.50E+023.50E+02
1.98E+023.50E+023.50E+02
1.99E+023.50E+023.50E+02
1.99E+023.50E+023.50E+02
2.00E+023.50E+023.50E+02
2.01E+023.50E+023.50E+02
2.02E+023.50E+023.50E+02
2.02E+023.50E+023.50E+02
2.03E+023.49E+023.50E+02
2.04E+023.49E+023.50E+02
2.05E+023.50E+023.50E+02
2.05E+023.49E+023.50E+02
2.06E+023.50E+023.50E+02
2.07E+023.49E+023.50E+02
2.08E+023.50E+023.50E+02
2.08E+023.50E+023.50E+02
2.09E+023.50E+023.50E+02
2.10E+023.49E+023.50E+02
2.11E+023.50E+023.50E+02
2.11E+023.50E+023.50E+02
2.12E+023.50E+023.50E+02
2.13E+023.50E+023.50E+02
2.14E+023.50E+023.50E+02
2.14E+023.50E+023.50E+02
2.15E+023.50E+023.50E+02
2.16E+023.50E+023.50E+02
2.17E+023.50E+023.50E+02
2.17E+023.50E+023.50E+02
2.18E+023.50E+023.50E+02
2.19E+023.50E+023.50E+02
2.20E+023.50E+023.50E+02
2.20E+023.50E+023.50E+02
2.21E+023.50E+023.50E+02
2.22E+023.50E+023.50E+02
2.23E+023.50E+023.50E+02
2.23E+023.50E+023.50E+02
2.24E+023.50E+023.50E+02
2.25E+023.50E+023.50E+02
2.26E+023.50E+023.50E+02
2.26E+023.50E+023.50E+02
2.27E+023.50E+023.50E+02
2.28E+023.50E+023.50E+02
2.29E+023.50E+023.50E+02
2.29E+023.50E+023.50E+02
2.30E+023.50E+023.50E+02
2.31E+023.50E+023.50E+02
2.32E+023.50E+023.50E+02
2.32E+023.50E+023.50E+02
2.33E+023.50E+023.50E+02
2.34E+023.50E+023.50E+02
2.35E+023.50E+023.50E+02
2.35E+023.50E+023.50E+02
2.36E+023.50E+023.50E+02
2.37E+023.50E+023.50E+02
2.38E+023.50E+023.50E+02
2.38E+023.50E+023.50E+02
2.39E+023.50E+023.50E+02
2.40E+023.50E+023.50E+02
2.41E+023.50E+023.50E+02
2.41E+023.50E+023.50E+02
2.42E+023.50E+023.50E+02
2.43E+023.50E+023.50E+02
2.44E+023.50E+023.50E+02
2.44E+023.50E+023.50E+02
2.45E+023.50E+023.50E+02
2.46E+023.50E+023.50E+02
2.47E+023.50E+023.50E+02
2.47E+023.50E+023.50E+02
2.48E+023.50E+023.50E+02
2.49E+023.50E+023.50E+02
2.50E+023.50E+023.50E+02
&A
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F16
&A
Page &P
Setpoint
ControlledVariable
Time
Closed-Loop Block Sine Wave TestClosed-loop deadbandIndication of the effect of actuator deadband, sensor noise, and resolution of A/D and D/A convertersClosed-loop settling timeIndication of the combined lags of the control loop componentsA means of determining if all the major problems with in a control loop have been corrected.
SPC ChartA Method for Evaluating the Long-Term Performance of a Controller
Chart1
4-1
4.51
4.50
4-1
40
-2-1
-11
2-0.5
-40
2-1
1-0.5
-50.5
4-0.5
-41
41
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Upper Limit
Lower Limit
Time (days)
Product Composition
F1A
0.00E+004.00E+00-1.00E+00
5.00E-014.50E+001.00E+00
1.00E+004.50E+000.00E+00
1.50E+004.00E+00-1.00E+00
2.00E+004.00E+000.00E+00
2.50E+00-2.00E+00-1.00E+00
3.00E+00-1.00E+001.00E+00
3.50E+002.00E+00-5.00E-01
4.00E+00-4.00E+000.00E+00
4.50E+002.00E+00-1.00E+00
5.00E+001.00E+00-5.00E-01
5.50E+00-5.00E+005.00E-01
6.00E+004.00E+00-5.00E-01
6.50E+00-4.00E+001.00E+00
7.00E+004.00E+001.00E+00
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Long-Term Measurement of VariabilityDirect measure of control performance in terms that relate to economic objectivesTakes longer to develop than closed-loop block sine wave test
Troubleshooting ExampleSymptom- The variability in the impurity level in the overhead product of a distillation column is greater than the specified limit.Step 1 Check the actuator systemBy applying a series of block sine wave tests, it was determined that the deadband and time constant of the flow control loop were 0.3% and 1.5 second which indicates that the actuator system is functioning properly.
Troubleshooting Example (cont)Step 2 Check the controllerThe filtering on the product analyzer reading was found to be excessiveThe controller was retunedThe control performance was improved but at times it was still not meeting the product variability specifications
Troubleshooting Example (cont)Check the product analyzerThe repeatability was determined by observing steady-state periods and was found to be well within the product variability specifications.The cycle time of the controller was found to be appropriate.Excessive transport delay in the sample system was identified and a new sample pump installedThe composition controller was retuned and control performance met specifications.
Troubleshooting ExerciseStudents pair up into groups of two.One student represents the process and the other, who is acting as the control engineer, performs the troubleshooting.The process student must choose a loop fault and the control engineer requests the results of certain tests from the process.After the engineer identifies the problem and fixes it, the students switch roles and repeat the exercise.
Overview of CPI TroubleshootingIn order to ensure that a control loop is functioning properly, the control engineer must have a thorough knowledge of the proper design and operation (Table 2.3) of the various components that comprise the control loop.
Troubleshooting in the Bio-Tech Industries
Overall ApproachFor the CPI, troubleshooting usually involves evaluation of one control loop at a time.For the bio-tech industries, it usually involves evaluating the operation of a bio-reactor.For the bio-tech industries, poor operation of a bio-reactor can involve poorly performing control loops or poorly performing sensors. Therefore, troubleshooting is a global problem.
Expert SystemsExpert systems for troubleshooting a bio-reactor are based on distilling the experience of experts into a set of if-then-else rules that guide the operator to the root problem(s).Expert systems can identify batches that can be returned to a normal operating window. Otherwise, the batch can result in off-specification products that are useless.
Actuator SystemsBlock sine wave tests can be used to determine the deadband and time constant for the actuator system.See Table 2.3 for desired performance levels.
Sensor SystemsCoriolis flow meters- require periodic calibration.Ion-specific electrodes (DO, pH and Redox)- require regular replacement and proper location is important.DO- membrane should be replaced regularly.pH- calibration drift a problem requiring calibrationRedox- regular calibration a problem
Sensor SystemsTurbidity sensor- cell can accumulated in the measurement cell.Mass spec- highly reliable due to regular calibration with air samples.HPLC- use guard columns to reduce fouling of the HPLC column.FIA- malfunctioning valves a major problem.
Overview of Bio-Tech TroubleshootingExpert systems are used to guide the troubleshooting activity.Troubleshooting bio-reactors is a global problem requiring a complete understanding of the entire system.Effective troubleshooting of bio-reactors can greatly reduce the frequency of bad batches and is, therefore, economically important.