Thermocouple transmitter calibration

Introduction

A thermocouple is a sensor used to convert temperature into an electric signal. It consists of 2 dissimilar metals joined together to form junctions. In this session we are going to discuss about Thermocouple transmitter calibration

Working principle  

Seebeck effect: the emf produced in the thermocouple is proportional to the temperature difference between 2 junctions (hot &cold)

Different types of thermocouples

J type, k type, T type, E type, R type, S type

Equipments required for calibration

24 vdc supply, multimeter, transmitter, mill volt source(725 process calibrator)

 

 

 

 

 

Procedure for calibrating thermocouple transmitter.

  • Connect the circuit as shown in fig
  • Put multimeter into ma.
  • Let us look at this calibration procedure through an example

Example:

LRV=0 degree Celsius   and URV=200 degree Celsius

So 5 point calibration values be like this

4ma-0 degree Celsius

8ma-50 degree Celsius

12ma-100 degree Celsius

16ma- 150 degree Celsius

20ma- 200 degree Celsius

So right now we know the corresponding values of temp to ma

  • In process calibrator select thermocouple option.
  • And give different values of temperature in process calibrator and check the ma in multimeter and by adjusting zero and span potentiometer in the transmitter correct the ma values.
  • Repeat this procedure.

To know about Thermocouple basics and types of thermocouple.

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