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OPTIMIZATION l TRAINING l CONSULTING

By Michel Ruel, P.E.By Michel Ruel, P.E.

Valve repairValve repair

FF Repair the valve and/or the positionnerRepair the valve and/or the positionnerFF Use a stronger actuatorUse a stronger actuatorFF Could be impossibleCould be impossible

The process could not be stoppedThe process could not be stopped Too expensiveToo expensive For fail safe a certain actuator must be usedFor fail safe a certain actuator must be used Type of valve used (ex Gate valve)Type of valve used (ex Gate valve)

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Stiction on the benchStiction on the bench

FF Usually worse than when the valve isUsually worse than when the valve isinlineinline not lubricatednot lubricated no noiseno noise no vibrationno vibration

Fighting stiction: strategiesFighting stiction: strategies

FF Add noise to the controller outputAdd noise to the controller output Ex.Ex.

Hydraulic system, a periodic 300 Hz addedHydraulic system, a periodic 300 Hz added

FF Use Derivative (loop controller)Use Derivative (loop controller)Adds noise to the controller outputAdds noise to the controller output

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Fighting stiction: strategiesFighting stiction: strategies

FFRetune the positionnerRetune the positionner If PID controllerIf PID controller

use Derivativeuse Derivativedo not use integral (reduce accuracy)do not use integral (reduce accuracy)

Some use a special algorithm to fightSome use a special algorithm to fightstictionstiction

Fighting stiction: strategiesFighting stiction: strategies

FF Use Proportional only or P+DUse Proportional only or P+D Such a control loop will have permanentSuch a control loop will have permanent

errorerror Removing the Integral will remove theRemoving the Integral will remove the

cyclingcycling

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Fighting stiction: strategiesFighting stiction: strategies

FF Use a PID controller with variableUse a PID controller with variableIntegral strengthIntegral strengthRemove the Integral action when theRemove the Integral action when the

error is small enougherror is small enoughIf |Error| < k Then If |Error| < k Then KiKi=0=0

Fighting stiction: strategiesFighting stiction: strategies

FF Use a PID-Gap controllerUse a PID-Gap controller If the error is small enough,If the error is small enough, the controller considers Error=0the controller considers Error=0and the output is frozenand the output is frozen

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Th a n k you !Th a n k you !

Boo th 2509Booth 2509