In a process control loop, which element transmits the sensor signal to the controller?

• A. Transmitter
• B. Sensor
• C. Controller
• D. FCE

Answer: (B)

The sensor provides a signal that represents the measured process variable, but that raw signal is typically weak and needs conditioning for reliable use by the controller. The transmitter takes that sensor signal, conditions and often converts it to a standardized form (like 4-20 mA), and then transmits it to the controller. This makes it possible for the controller to read the value accurately over the field wiring and distance. The controller uses the received signal to determine the corrective action, and the final control element then implements that action on the process. So, the transmitter is the part that transmits the sensor signal to the controller, while the sensor does the sensing, and the controller and final control element handle processing and actuation.