The water level in a tank is being controlled by an automatic level controller using proportional-only control as shown in the figure below.
Initially the tank level is stable at 50 percent, but then the flow into the tank increases and stabilizes at a higher flow rate.
As tank level increases, the controller positions the drain valve more open than necessary to stabilize the level.
As tank level decreases, the controller positions the drain valve more closed than necessary to stabilize the level.
This cycle is repeated continuously, never reaching a stable tank level or drain valve position.
The excessive valve cycling described above can be reduced if the controller’s gain is ____________ or if the controller’s proportional band is ____________.
A. increased; widened
B. increased; narrowed
C. decreased; widened
D. decreased; narrowed
Show Answer
Answer: C
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