List the major components of a basic closed-loop process control system.

• A. Sensor/transmitter, controller, actuator/valve, plant/process, power supply, signal conditioning or isolation, feedback path.
• B. Sensor/transmitter, controller, plant/process, power supply only.
• C. Transmitter, receiver, actuator, plant, energy source, interface module, monitoring panel.
• D. Sensor, processor, actuator, plant, network, maintenance log, output indicator.

Answer: (A)

Understanding a closed-loop control system means recognizing the essential parts that form a continuous feedback cycle. The major components are the sensor/transmitter to measure the process variable, the controller to compare that measurement to the desired setpoint and generate a control signal, the actuator or valve to apply the corrective action to the plant, the plant or process being controlled, a power supply to power the devices, signal conditioning or isolation to keep signals accurate and safe, and the feedback path that sends the measurement back to the controller for ongoing adjustment. Each piece plays a crucial role: the sensor provides real-time data, the controller determines what must change, the actuator makes that change happen, the plant is the system being controlled, power is the energy source, signal conditioning ensures signal integrity, and the feedback path closes the loop so deviations are corrected.

Optionally, you can see that this complete set is what’s described, making it the best choice. The other options omit one or more of these critical elements or substitute nonstandard terms (like receiver, monitoring panel, or maintenance logs) that don’t represent the basic closed-loop structure.