A transmitter is a device which senses a process variable, convert it into a standard signal and transmit that signal to a monitor or a controller. Simply transmitter convert signal into 4 to 20 mA current signal. It is used to create a standard signal proportional to a process variable and transmit that signal from where transmitter is installed to another receiving device. Other thing transmitter do is that it maintain that 4 to 20 mA output proportional to for example applied pressure irrespective of applied power till it goes down well below require power to turn on transmitter.

The main functions of a transmitter are:

- Measure a process variable.

- To change process variable into a pneumatic or electronic signal. (3-15 psi or 4-20 mA)

- Transmitting these signal to a monitor or a controller.

The output range of transmitter is standardized to bring uniformity in construction of secondary instruments as well as to facilitate them for test and calibration purpose.


Transmitters are classified into two depending upon working supply and output. They are

1. Pneumatic transmitter (3 to 15 psi output)

2. Electronic/ electric transmitter (SMART transmitter - 4 to 20 mA output )

3. Hybrid transmitter (Analog + SMART)

In next article i will explain each type in detail and it's calibration procedure.




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