Which component would be part of an automatic control system for a process?

• A. Indicator lamp
• B. Manual switch
• C. Control loop
• D. Boiler water gauge

Answer: (C)

In automatic process control, the essential element is the control loop—the closed path that continuously measures a variable, compares it with the desired setpoint, computes the needed adjustment, and automatically implements that change in the process. This loop typically includes a sensor to monitor the variable, a controller to determine the corrective action, and an actuator to apply that action, keeping the system on target without human intervention. An indicator lamp merely shows status and does not drive adjustments; a manual switch allows human control or override, potentially breaking automatic operation; and a boiler water gauge is a display of a parameter, not a mechanism that drives automatic regulation. So the control loop is the component that enables automatic control.