Which statement best describes the difference between a PI controller and a PID controller?

Which statement best describes the difference between a PI controller and a PID controller?

• A. A PI controller uses proportional and derivative actions; no integral.
• B. A PI controller uses integral and derivative actions; no proportional.
• C. A PI controller includes proportional and integral actions only; a PID adds a derivative term to anticipate changes and damp oscillations.
• D. A PI controller uses only proportional action.

Answer: (C)

The main idea is which terms are used to process the error. A PI controller combines proportional and integral actions, meaning it reacts to the current error (proportional) and also to the accumulation of past errors (integral) to eliminate steady-state error. It does not include a derivative term. A PID controller adds a derivative term that responds to how fast the error is changing, which helps anticipate future error and dampen oscillations for a faster, more stable response. So the statement that describes this difference—PI having only proportional and integral actions, while PID adds a derivative term to anticipate changes and damp oscillations—is the best fit. In other words, if you see a controller with only proportional action, that’s a P controller. If you see proportional plus derivative but no integral, that’s PD. If you see integral plus derivative with no proportional, that’s not a standard common controller.

The main idea is which terms are used to process the error. A PI controller combines proportional and integral actions, meaning it reacts to the current error (proportional) and also to the accumulation of past errors (integral) to eliminate steady-state error. It does not include a derivative term. A PID controller adds a derivative term that responds to how fast the error is changing, which helps anticipate future error and dampen oscillations for a faster, more stable response. So the statement that describes this difference—PI having only proportional and integral actions, while PID adds a derivative term to anticipate changes and damp oscillations—is the best fit.

In other words, if you see a controller with only proportional action, that’s a P controller. If you see proportional plus derivative but no integral, that’s PD. If you see integral plus derivative with no proportional, that’s not a standard common controller.