How Thermocouple calibration is done

Thermocouples calibration is not the same as other instruments because thermocouple drift or de-calibration is irreversible.

In fact when the term calibration with respect to thermocouple is used in laboratory it basically implies the validation of the thermocouple to produce required voltage which should match with values in TC emf chart.

It is done by comparison of the two curve the ideal and the plotted.

Procedure

1.)Put thermocouple in a thermal bath at different temperature

2.)Measure thermal emf produced.

If it does not matches or show some deviation sometimes the controller or display device which reads online temperature like thermometer,controller,data acquisition system etc is programed again to match that voltage to the actual temperature.The device does that by readjusting its voltage equation.

So in effect it is calibration of the thermocouple instruments like thermometer,controller,data acquisition etc.

For temperature bath

We use Standard temperature source large enough so that the thermocouple can be inserted into it like ice bath.We can use the boiling and/or freezing point of a series of pure solvents as those temperatures are well known at STP. Use an accurate thermometer to note down temperature.

Another such heat source is thermocouple calibration furnace.They have fast heating time.Accurate temperature display about+-0.5decC.Also they can be used to calibrate multiple thermocouples at the same time.

Ok but what does a calibrator does.

It is a thermocouple emf simulator.

It can simulate and reproduce ideal thermocouple sensor millivolts at its output when set to a temperature and type.

Use

1.)To check that the instrument is reading correct temperature .If not the instrument is adjusted to read correct temperature.

2.) To compare the value read by TC under test and actual temperature reading eliminating the use of charts.