A Reverse Action controller has which relationship between input and output?

• A. As input increases, output increases
• B. Output remains constant as input changes
• C. As input increases, output decreases
• D. There is no relation between input and output

Answer: (C)

In a Reverse Action controller, the signal sent to the actuator moves in the opposite direction of the input (the error). The input is typically the difference between the setpoint and the process variable. So when the error increases, the controller’s output decreases; when the error decreases, the output increases. This inverse relationship is what defines a reverse-acting controller and is used to match how the actuator and process respond to the control signal. If the output were to increase with the input, that would be direct action; a constant output or no relationship would fail to correct the error.