Field Instrumentation

What are transmitters and how is it useful for process industries?


A transmitter can be described as a transducer, which would convert a measurement variable into a transmission signal. These transmitters are inevitable in process industries, in the process industries the control instruments would be located away from the process and so the measurements must be transferred from a remote location and this can be done by using a transmitter. The industrial transmitter can be explained as merging between the transducer and the signal conditioning circuit.

What are the functions of a transmitter?

The major function of a transmitter is to change or convert the values from a sensor into a signal which is then transmitted to a controller. The transmitter is used to transfer signals from remote locations to the controller because most of the instruments will be away from the controller so transferring the signal can be achieved by using a transmitter.

What are the types of transmitters?

Types of industrial transmitters

Analog transmitters

The transmitters that are used for industrial applications would transmit the measured information by using the analog current signal and the current range would be 4-20mA and the current is dependent on the measured value. In this type of transmitter, the connection is done from the transmitter to the rest of the system is by using two wires and these two wires are used for power and signal transmission.

Smart transmitter

It is similar to the analog transmitter, it uses the similar two-wire connection that can be seen in analog transmitters but the difference is that the signal from the sensor is digitized and then the signal is transmitted with the help of a microprocessor and it also uses digital to analog converter so that it can create an analog current signal.

Intelligent transmitters

This type of transmitter does digital two-way communications and this transmitter has an industrial communication interface such as Fieldbus. This has great advantages for signal transmission, so an intelligent transmitter can be considered as a transmitter that has digital two-way communication and digital signal processing.

How does a transmitter works and what are the types of signals used in the transmitter?

A transmitter will receive the measurement values from the instruments and these values will be converted that can be easily transmitted to the controller. So the values will be converted to signals. A transmitter is known as a secondary transducer, it can convert the physical signal and also they are capable to transfer the information to a good distance too. Mostly in a process industry, three kinds of signals are used to transfer the measured value of the instrument to the control system and they are Pneumatic signal, analog signal, and digital signal.


What are the required factors for a transmitter? How to select a transmitter?

  • It must have good power
  • It must be efficient
  • It must have good accuracy
  • Stability is an important factor
  • Short circuit condition must be considered too, if the output is shorted then there won’t be any damage to the transmitter
  • Mounting position effect must be considered too
  • It must be selected according to the service
  • It must be selected according to the range
  • The power supply must be considered
  • It must be selected according to the location
  • Temperature and pressure limit must be considered while selecting a transmitter
  • It must be selected according to the maintenance requirements

We must consider the process parameter while selecting the transmitter also we need to consider the measurement type as if it is direct or indirect. The output type must be considered while selecting it and the mounting must be considered too. A transmitter must be selected according to the type of signal transmitted and also we need to consider the receiving facility.

Why do we need transmitters?

  • The signals that are generated by instruments must be transmitted to the control system and it is done by using the transmitter
  • The receiving system or control system will only receive a standard signal, so we would need transmitters for this
  • Long-distance transmission of signals is achieved by this device
  • There could be interference for sensor output

What are the advantages of smart transmitters?

  • Its size is small
  • It has a good range
  • Good reliability
  • Easy to use and costs less
  • It has features like self-correction and auto display
  • It has an electronic data storage feature
  • It can do self-diagnosis and remote calibration is possible too

What are the applications of transmitters?

  • It is used in the petrochemical industry
  • Transmitters are used in the pulp and paper industry
  • Fertilizer industry
  • It is also used in chemical and sugar factory

So we can say that a transmitter is an inevitable device for most of the industrial applications it is also used for automation applications.


post-graduate in Electronics & communication.

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