What is a control loop's deadband and why is it important in DDC?

• A. The range around setpoint where no control action occurs; reduces chatter and actuator wear.
• B. The range around setpoint where action is always applied to prevent overshoot.
• C. A fixed offset applied to setpoint to account for sensor bias.
• D. A time delay in the control loop that slows response.

Answer: (A)

Deadband is a tolerance band around the setpoint where the controller does not issue any actuator command. In a DDC system, this means small errors due to noise or minor disturbances won’t cause the valves or dampers to chatter or cycle constantly. That pause in action keeps wear and tear, and energy waste to a minimum, while the system remains effectively near the desired value. When the process error grows beyond the deadband, the controller activates to correct it, then once back inside the band it can settle again without continuous movement. The width of the deadband is chosen based on sensor noise, actuator precision, and how much steady-state deviation is acceptable; a wider deadband reduces cycling but allows a larger deviation, while a narrower one improves responsiveness at the cost of more actuator activity.