Which control structure uses two PID controllers in series?

Multiple Choice Questions Automation MCQ
1

Question:

Which control structure uses two PID controllers in series?

Options:

A) Feedback
B) Cascade
C) Ratio
D) Split

View Answer

:white_check_mark: Correct Answer: B) Cascade

:magnifying_glass_tilted_right: Detailed Explanation

Cascade control uses two PID controllers arranged in series:

  1. Master (Primary) Controller
  2. Slave (Secondary) Controller

The output of the master controller becomes the setpoint of the slave controller.

Structure:

Master PID → sets SP → Slave PID → Final Control Element → Process

The slave loop responds faster to disturbances, improving overall stability and disturbance rejection.

:repeat_button: Typical Example

Heat exchanger control:

  • Master PID controls temperature
  • Slave PID controls steam flow

The inner (flow) loop reacts quickly before temperature is affected.

:cross_mark: Why Other Options Are Incorrect

A) Feedback → Uses a single PID loop.
C) Ratio → Maintains proportion between two variables.
D) Split → Splits one output to multiple actuators, not two controllers in series.

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