What is the effect of a deadband in a valve actuator on control performance?

• A. It eliminates nonlinearity.
• B. It reduces sensor noise.
• C. It creates nonlinearity and may cause sustained error or oscillation.
• D. It increases system bandwidth.

Answer: (C)

Deadband in a valve actuator creates a gap where small control inputs don’t produce any valve movement, so the actuator response is not proportional to the command. That makes the system nonlinear, because there’s a flat region in the input–output curve. In a feedback loop, this means small errors may persist because the controller doesn’t get a response until the command crosses the deadband threshold. The result can be sustained error if the loop can’t overcome the threshold, or oscillation/hunting as the controller keeps pushing the signal past and back across the threshold. Deadband doesn’t eliminate nonlinearity, and it doesn’t mainly reduce sensor noise or increase bandwidth; it often reduces precision and can destabilize the fine-structure of the response.