What is a deadband vs a hysteresis in control systems?

• A. Deadband is the same as hysteresis; both describe a loop in output.
• B. Deadband is a range around setpoint with no action; hysteresis is the difference in output when the input rises vs falls, creating a loop.
• C. Hysteresis is a fixed offset; deadband is a time delay.
• D. Deadband is a rate limit; hysteresis is a threshold.

Answer: (B)

Deadband and hysteresis describe how a controller decides to act when the measured variable is near the target, but they do so in different ways. A deadband means there is a neutral zone around the setpoint where no action is taken at all. Small fluctuations within that band don’t cause the actuator to respond, which helps avoid chatter and unnecessary switching. Once the error moves outside the band, the controller acts again.

Hysteresis is about history: the action depends on the direction the input is moving. The system uses different thresholds for turning the output on versus turning it off, so the path from a lower input to a higher input yields a different switching point than the reverse path. This creates a loop in the input–output behavior.

So the statement that best fits is that a deadband is a range around the setpoint with no action, while hysteresis is the difference in output when the input rises versus falls, producing a loop. An example helps: a thermostat with a deadband simply stays idle while the temperature stays within a small range, but with hysteresis it switches on and off at two different temperatures depending on whether the temperature is climbing or falling, forming a loop in the control response.