Which of the following best distinguishes on-off control from PID control in terms of output behavior?

• A. On-off control provides continuous control for precise regulation.
• B. On-off toggles output fully on/off causing possible oscillations.
• C. PID control tends to produce more hysteresis.
• D. On-off control reduces oscillations more than PID.

Answer: (B)

The main idea is how the actuator output behaves: on-off control delivers a bang-bang signal that is either fully on or fully off, while PID control provides a continuous, gradually varying output. With on-off control, the actuator switches between extremes based on the error, which often causes the process variable to swing around the setpoint and produce oscillations, especially when there’s a deadband or slow system response. A PID controller, by contrast, adjusts the output smoothly using proportional, integral, and derivative terms, damping rapid changes and typically reducing oscillations. The option that states the output toggles fully on/off and can lead to oscillations best captures this difference. The other statements mischaracterize on-off control as continuous, or misstate how hysteresis and oscillations behave with PID versus on-off.