Question:
What is meant by a direct-acting controller?
Options:
A) PV↑ → Out↓
B) PV↑ → Out↑
C) SP↓ → Out↑
D) Err = 0
View Answer
Correct Answer: B) PV↑ → Out↑
Detailed Explanation
A direct-acting controller is defined by the relationship between the process variable (PV) and the controller output.
In direct action:
- If PV increases,
- The controller output also increases.
The output moves in the same direction as the PV.
Example
Cooling system:
- Temperature (PV) rises
- Controller output increases
- Cooling valve opens more
- Temperature reduces
The controller output increases when PV increases — hence direct acting.
Why Other Options Are Incorrect
A) PV↑ → Out↓ → That describes reverse-acting control.
C) SP↓ → Out↑ → Direct/reverse action is defined by PV behavior, not SP.
D) Err = 0 → That describes steady-state, not controller type.