In reverse-acting control, output increases when?

Multiple Choice Questions Automation MCQ
1

Question:

In reverse-acting control, output increases when?

Options:

A) PV rises
B) Error zero
C) PV falls
D) SP rises

View Answer

:white_check_mark: Correct Answer: C) PV falls

:magnifying_glass_tilted_right: Detailed Explanation

In a reverse-acting controller, the controller output increases when the process variable (PV) decreases.

Using the standard error equation:

Error = SP - PV

If PV falls below SP:

  • Error becomes positive
  • Controller increases output
  • Final control element acts to raise PV

This is common in temperature and pressure control loops where increasing output increases the process variable.

:repeat_button: Example

Temperature control with steam valve:

  • PV drops below SP
  • Controller increases output
  • Valve opens more
  • More steam enters
  • Temperature rises

:cross_mark: Why Other Options Are Incorrect

A) PV rises → In reverse action, output decreases when PV rises.
B) Error zero → Output remains steady in ideal steady-state.
D) SP rises → Output may increase, but reverse/direct action is defined by PV behavior.