What is deadband in controller operation?

• A. The range around setpoint where the controller responds to small errors
• B. The range around setpoint where the controller does not respond to small errors
• C. The time delay after setpoint change
• D. The difference between actual and commanded value

Answer: (B)

Deadband is a region around the setpoint where small deviations do not trigger a control action. This keeps from chattering due to sensor noise or minor fluctuations and lets the system remain stable. The controller only reacts when the error grows beyond that zone, so action is taken only for larger, more significant deviations. The width of the deadband is chosen based on how much noise or fluctuation is acceptable and how aggressively you want the system to respond, balancing smooth operation with accuracy. In a thermostat, for example, temperatures within the deadband keep the heater or cooler idle, and action starts only when the temperature moves far enough from the setpoint. This concept isn’t about a time delay, nor is it simply the raw error value itself—it's about the range in which the controller deliberately ignores small errors to avoid unnecessary switching.