SOLUTION

The error signal is the input to a controller.

Detailed Explanation

Closed-Loop Control

• A closed-loop control system utilizes a measure of the actual output to compare the actual output with the desired output response.
• The measure of the output is called the feedback signal. The elements of a general closed-loop feedback control system are shown in Figure.

• A closed-loop control system compares the measurement of the output with the desired output (reference or command input).
• The difference between the two quantities (the error signal) is then used to drive the output closer to the reference input through the controller and actuator. Here the input signal to the controller is an error signal
• Often the difference between the output of the process under control and the reference input is amplified and used to control the process so that the difference is continually reduced.