By Bob Rice1 and Doug Cooper

The control objective for the pumped tank process is to maintain liquid level at set point by adjusting the discharge flow rate out of the bottom of the tank. This process displays the distinctive integrating (or non-self regulating) behavior, and as such, presents an interesting control challenge.

The process graphic below (click for a large view) shows the pumped tank in automatic mode (also called closed loop):

 

The important variables for this study are labeled in the above graphic:
CO = signal to valve that adjusts discharge flow

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