In a Direct Acting Controller, how does the output respond to changes in input?

• A. As input increases, output decreases
• B. As controller input increases, controller output increases
• C. Output is independent of input
• D. Output only increases when temperature decreases

Answer: (B)

Direct acting means the controller has a positive gain: the output moves in the same direction as the input. In practice, the input is usually the error signal (setpoint minus process variable). When the error grows larger (input increases in the positive sense), the controller increases its output to drive the process variable toward the setpoint. When the error becomes smaller or negative, the output lowers accordingly. This is why the described behavior—output increasing as input increases—fits a direct-acting controller.

The other ideas don’t match how direct action works: a reverse-acting controller would move the output in the opposite direction of the input, a controller whose output is independent of input wouldn’t provide corrective action, and tying output changes to temperature in a fixed way ignores the general sign relationship between input and output in direct action.