Which statement about a PID controller is true?

• A. The integral term adds immediate correction based on current error.
• B. The proportional term eliminates steady-state error.
• C. The derivative term ignores the rate of error change.
• D. The full PID uses proportional, integral, and derivative actions to minimize error and stabilize the system.

Answer: (D)

A PID controller combines three actions to manage error over time and keep the system stable. The proportional term provides an immediate correction proportional to the current error, giving a quick response but not necessarily removing any remaining offset. The integral term sums past errors, so it gradually eliminates steady-state error by applying corrective action based on accumulated history. The derivative term looks at how fast the error is changing and helps dampen the response to prevent overshoot, improving stability. When all three actions are used together, they minimize error and keep the system stable, which makes that statement true. The other statements mischaracterize the roles: the integral term does not provide immediate correction, as that is what the proportional term does; proportional alone cannot eliminate steady-state error; and the derivative term actually uses the rate of error change rather than ignoring it.