Basic Elements of a Control Loop

Process piants are composed of hundreds of control loops. These control loops are used to maintain pressure, temperature, flow, level, and analytical process variables. The basic elements of a control loop are  

Transmitter—a device designed to convert a measurement into a signal. This signal is transmitted to another instrument. 

Controller—a device designed to compare a signal to a setpoint and transmit a signal to a final control element. 

Transducer—a device designed to convert an air signal to an electric signal or an electric signal to a pneumatic signal. Sometimes referred to as an / to P or a converter. 

Final control element—the part of a control loop that actually makes the change to control the process. 

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