What is a deadband in a valve actuator?

• A. Range of input where no actuator movement occurs
• B. A threshold to begin movement
• C. Maximum actuator speed
• D. The slope of the input-output relation

Answer: (A)

Deadband is the range of control input values where the valve actuator does not move. This happens because of mechanical factors like friction, clearance, and stiction inside the actuator, so small input changes can be ignored until they exceed that threshold. Once the input crosses the boundary of the deadband, the actuator begins to move, and the speed or extent of movement then follows the system dynamics and external factors. If the deadband is large, the control loop can feel sluggish and less precise, since small signals are filtered out; if it’s very small, the system may chatter due to noise. This concept is distinct from the point where movement begins (the boundary) and from the actuator’s maximum speed or the input-output slope (gain).