What is the function of a 'deadband' in a control system?

A deadband in a control system is a range of input values for which the controller produces no output. Its function is to prevent the controller from making small, unnecessary adjustments in response to minor fluctuations or noise in the process variable. These small adjustments can cause excessive wear and tear on the control valve or other actuators and can also lead to instability in the system. The deadband introduces a region around the setpoint where the controller takes no action. Only when the process variable deviates outside this region will the controller begin to adjust the output. The size of the deadband is a design parameter that can be adjusted to optimize the performance of the control system. A larger deadband will reduce the frequency of controller action but may also result in larger deviations from the setpoint. A smaller deadband will provide tighter control but may lead to more frequent actuator movements. The deadband is particularly useful in systems where there is significant noise or hysteresis in the process or the actuator.