What is meant by “manipulated variable” in PID control?

Multiple Choice Questions Automation MCQ
1

Question:

What is meant by “manipulated variable” in PID control?

Options:

A) Process variable
B) Error signal
C) Sensor signal
D) Controller output

View Answer

:white_check_mark: Correct Answer: D) Controller output

:magnifying_glass_tilted_right: Detailed Explanation

The Manipulated Variable (MV) is the variable that the controller changes to influence the process.

In practical terms:

  • The controller calculates an output (CO).
  • This output adjusts the final control element (valve, VFD, damper, heater).
  • That adjustment changes the process variable (PV).

So, the manipulated variable is essentially the controller output signal applied to the actuator.

:repeat_button: Control Relationship

SP → Compare with PV → Controller → Manipulated Variable (MV) → Process → PV

The MV is what we “manipulate” to bring PV toward SP.

:cross_mark: Why Other Options Are Incorrect

A) Process variable → That is what we measure, not what we change.
B) Error signal → Error is SP − PV, not the manipulated quantity.
C) Sensor signal → That represents PV measurement, not control action.

:fire: Practical Example

Temperature Control Loop:

  • SP = 150°C
  • PV = 140°C
  • Controller increases output
  • Valve opens more
  • Steam flow increases

Steam valve position = Manipulated Variable

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