The level in a drain collection tank is being controlled by an automatic level controller, and is initially stable at the controller setpoint.
Flow rate into the tank increases, slowly at first, and then faster until a stable higher flow rate is attained.
As tank level begins to increase, the level controller slowly opens a tank drain valve.
The level controller output signal increases both as the tank level increases and as the rate of tank level change quickens.
After a few minutes, tank level returns to, and remains at, the original level with the drain flow rate equal to the supply flow rate.
The controller in this system uses __________ control.
A. proportional only
B. proportional plus derivative only
C. proportional plus integral only
D. proportional plus integral plus derivative
Show Answer
Answer: D
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