In a control loop, which device typically directly drives the process?

In a control loop, which device typically directly drives the process?

• A. Actuator or valve.
• B. Sensor/transmitter.
• C. Controller.
• D. Power supply.

Answer: (A)

The device that directly drives the process is the actuator or valve. In a control loop, the sensor measures the process variable and the controller computes the required change, but it is the actuator (often a valve, motor, or hydraulic/pneumatic device) that actually applies that change to the process. It takes the controller’s signal and converts it into a physical action—opening a valve to change flow, moving a control rod, adjusting heat or pressure—so the process variable responds. The power supply simply provides energy to the system and does not directly alter the process.

The device that directly drives the process is the actuator or valve. In a control loop, the sensor measures the process variable and the controller computes the required change, but it is the actuator (often a valve, motor, or hydraulic/pneumatic device) that actually applies that change to the process. It takes the controller’s signal and converts it into a physical action—opening a valve to change flow, moving a control rod, adjusting heat or pressure—so the process variable responds. The power supply simply provides energy to the system and does not directly alter the process.