In a basic feedback loop, what compares SP and PV?

Multiple Choice Questions Automation MCQ
1

In a basic feedback control loop, what compares the setpoint (SP) and the process variable (PV)?

A) Sensor
B) Actuator
C) Controller
D) Transmitter

View Answer

:white_check_mark: Correct Answer: C) Controller

:magnifying_glass_tilted_right: Detailed Explanation

In a closed-loop control system, the controller is the component that performs the comparison between:

Error = SP−PV

The controller continuously:

  1. Receives the setpoint (SP)

  2. Receives the process variable (PV) from the transmitter

  3. Calculates the error

  4. Applies the control algorithm (P, I, D)

  5. Generates the output signal (CO)

Without this comparison step inside the controller, automatic correction would not be possible.

:cross_mark: Why the Other Options Are Incorrect

A) Sensor
A sensor only measures the physical parameter (temperature, pressure, flow, etc.). It does not perform comparison.

B) Actuator
An actuator (e.g., control valve, VFD) executes the controller’s output. It does not calculate error.

D) Transmitter
A transmitter converts the sensor signal into a standardized signal (e.g., 4–20 mA). It does not compare SP and PV.

:fire: Control Loop Flow (Simple View)

Sensor → Transmitter → Controller (Comparison + PID) → Final Control Element → Process