Which of the following is NOT a component of a control loop?

The correct answer identifies that an indicator lamp is not a component of a control loop. A typical control loop consists of several key elements: the sensor, which continuously measures the process variable; the controller, which compares the sensor's readings to a setpoint and makes decisions based on that comparison; and the actuator, which adjusts the process based on the controller's commands.

An indicator lamp serves a different purpose. It might provide visual feedback to the operator about the status of the system or alert them when certain conditions are met, but it does not play a direct role in the regulation or management of the control process itself. Therefore, it is not considered a fundamental component of a control loop, which is designed to maintain or control specific variables within a system.