Transmitters Used in Process Instrumentation

For a process to be adequately controlled and manipulated, the variable of interest in the process (e.g. Temperature, Pressure or Flow) often called the Process Variable (PV) needs to be measured by a sensor which converts the measurement into a suitable signal format (4 – 20mA or digital) and then transmit it to a controller which makes the control decision and finally acts on a final control element in the control loop. What does this signal transmission is referred to as a transmitter. The schematic below illustrates the interactions between all the elements in the control loop:

Elements of a Process Control Loop

 
What is a Transmitter?

A Transmitter is a device that converts the signal produced by a sensor into a standardized instrumentation signal such as 3-15 PSI air pressure, 4-20 mA DC electric current, Fieldbus digital signal etc., which may then be conveyed to an indicating device, a controlling device, or both. The indicating or controlling device is often located in a centralized control room. The transmitter often combines a sensor and the transmitter in a single piece. The sensor measures the process variable and generate a proportional signal. The transmitter then amplifies and conditions the sensor signal for onward transmission to the receiving or controlling device.

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