What is the output action of a controller when the process is not set at the value?

The output action of a controller when the process is not at the desired setpoint is to produce an output signal to correct the process. This process is fundamental to control systems, where a controller continuously monitors the conditions of a system and makes adjustments as needed to bring the output back to the setpoint or desired value.

When the measured value deviates from the setpoint, the controller calculates the error or deviation and generates an appropriate output signal. This signal may lead to actions such as opening or closing valves, manipulating pumps, or adjusting heaters in order to bring the system back into compliance with the desired operational parameters. Thus, the primary function of a controller is to respond dynamically to changes in the process and ensure that the system operates effectively at its setpoint.

In scenarios where the process is not set correctly, simply doing nothing or generating an alarm would not be useful actions, as they would not contribute to correcting the process. Reducing the input signal could potentially lead to further destabilization of the system rather than stabilization. Therefore, producing an output signal to correct the process is the most effective and direct method of achieving the desired control response.