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
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
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.