Calibration is essential for any instrument as it makes it more precise and accurate. Through this process, we are also able to check if the instrument is still at their benchmark of accuracy. Instrument calibration can help to create a safe work environment for everyone. It can also help to generate factual data for any research publication or reference. So long as measurement accuracy is needed, instrument calibration will come in.
A thermocouple is a sensor that measures temperature and there are many different types. How often we should conduct a calibration of the thermocouple is dependent on the potential damage and frequency of its usage. For instance, when the thermocouple was accidentally dropped on the ground or when you use it to measure extreme temperatures. Both the mechanical and thermal shock subjected to the thermocouple can affect their accuracy. Hence, it is important that a thermocouple has frequent calibration or after-every-use calibration.
Calibration of a Thermocouple
There are various ways to calibrate a thermocouple and we will share 3 best ways with you.
- Fixed Point Calibration
Thermodynamic fixed points have to be considered in this method and it is usually the most accurate type of calibration. Fixed points represent the sources of controlled temperature. First of all, you have to establish a control temperature which can give a constant temperature which is stable. It must be evenly diffused and can cover an area big enough to immerse a thermocouple. One commonly used tool is the ice bath. The fixed temperature points of common substances where their physical state changes, will be compared against the thermocouple’s temperature readings. There will be a reference junction which is kept at 0-degrees-Celsius, and the thermal Electromotive Force (EMF) from the thermocouple is measured during the fixed-point transition where the metal materials transition from a solid to liquid state. This EMF will subsequently be compared with standard measurement charts to determine the thermocouple’s accuracy in measurement.
However, this may take some time and must be carried out by an experienced person.
- Liquid baths
This is another frequent method of thermocouple calibration and it will require a furnace or a stirred liquid bath depending on the temperature requirements. Firstly, the thermocouple will be immersed in a liquid bath, together with a calibrated sensor. Both of them will be stabilized at a determined temperature and the thermocouple reading will be used in comparison to the calibrated sensor.
- Dry block calibration
Regarding this type of calibration, it is usually not conducted in laboratories, unlike the first two ways of calibration previously mentioned. For this calibration, a special metal block calibrator is needed and it has holes which allow the thermocouple to fit nicely into it. The metal block will be heated or cooled to the predetermined temperature given by an internal sensor. Afterwards, the block temperature will be checked against the thermocouple reading. Your device will have moderate accuracy if you use this type of calibration.
If you realize that you may require equipment capable of producing the regulated temperature source for thermocouple calibration yet have none. Feel free to contact any specialized companies for professional help and inquiries. Make sure that their calibrations are traceable to the International System of Units (SI) through National Metrology Institutes.