The correct answer is C. Electropneumatic converter.
A control valve is a final control element that is used to control the flow of fluids in a process. A potentiometer is a variable resistor that is used to measure or control voltage. A servomotor is a motor that is used to control the position or motion of a mechanism. An electropneumatic converter is a device that converts electrical signals into pneumatic signals.
A control valve is a final control element because it is the last device in a control loop that directly affects the process variable. The control valve is controlled by the controller, which receives feedback from the process variable. The controller then sends a signal to the control valve, which opens or closes to regulate the flow of fluid.
A potentiometer is not a final control element because it is not used to control the flow of fluids in a process. A potentiometer is used to measure or control voltage. The potentiometer is connected to a voltage source and a load. The voltage across the load is proportional to the position of the wiper arm on the potentiometer.
A servomotor is a final control element because it is used to control the position or motion of a mechanism. The servomotor is controlled by the controller, which receives feedback from the process variable. The controller then sends a signal to the servomotor, which rotates to regulate the position or motion of the mechanism.
An electropneumatic converter is not a final control element because it is not used to control the flow of fluids in a process. An electropneumatic converter is a device that converts electrical signals into pneumatic signals. The electropneumatic converter is used to control the flow of air in a pneumatic system.