Category Archives for Process Control

Controller Tuning – Ultimate Sensitivity Method

The ultimate sensitivity method ( Figure 300-24) is also a closed loop test. Adjust the integral time and/or the derivative time to their minimum values. Then narrow the proportional band (increase gain) in small steps, each time changing the setpoint … Continue reading

19. April 2018 by Juan
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Controller Tuning – Quarter Decay Method

The quarter decay method is a closed loop controller tuning method. This means that the controller remains in automatic while tuning adjustments are made. The quarter decay method defines the ultimate limit for tight controller tuning. Often, the tuning constants … Continue reading

19. April 2018 by Juan
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Feed-forward Control

Feed-forward control measures a disturbance before it can affect the controlled variable, and changes the manipulated variable to compensate for the disturbance. Of course, for feed-forward control to work properly, the magnitude and timing of the effect on the controlled … Continue reading

19. April 2018 by Juan
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Cascade Control

Cascade control should also be considered when the primary control variable is slow to react to disturbances. Like any feedback control loop, a cascade control loop has a controlled variable, a setpoint and a controller. However, instead of having a … Continue reading

19. April 2018 by Juan
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Derivative Control

With derivative action (also called rate action), the controller output is proportional to the rate of change of the error. This means the faster the change in level, the faster the change in controller output and control valve settings. By … Continue reading

19. April 2018 by Juan
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Integral Time

Integral time should be proportional to the time it takes for the process to respond to control action. When the process responds quickly, the integral time can be shorter. If the integral time is too short, the control valve reaches … Continue reading

19. April 2018 by Juan
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Integral Controllers Wind-up

A basic problem with integral controllers is that integral action continues as long as an error exists. Assume a proportional-plus-integral controller is used to maintain the level in the gas-liquid separator vessel in Figure 300-4. If a valve is closed … Continue reading

19. April 2018 by Juan
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Proportional-Plus-Integral Control

Proportional-plus-integral control is the recommended control action for most applications. Often called PI control, it combines proportional action and integral action in one controller. The resulting control action has the fast response and stability of proportional action, but no offset. … Continue reading

19. April 2018 by Juan
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Integral Control

Integral (reset) action is the result of an integration of controller error with time. With integral action, controller output is proportional to both the size and duration of the error. As long as a deviation from setpoint exists, the controller … Continue reading

19. April 2018 by Juan
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Proportional Control

(Controller output can go directly to a valve or to the setpoint of another controller. In the following discussions, it is assumed that controllers send their output directly to a valve.) Figure 300-7 shows the relationship between valve position and … Continue reading

19. April 2018 by Juan
Categories: Process Control | Comments Off on Proportional Control

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