Although they are all contact temperature measuring instruments, their temperature measurement ranges are different.

Thermocouples are used in environments with high temperatures because their output thermoelectric potential is very small in the medium and low temperature regions. When the potential is small, anti-interference measures and secondary meter requirements are very high, otherwise the measurement will be inaccurate. In addition, in the lower temperature region, the relative error caused by changes in cold junction temperature and environmental temperature becomes prominent and difficult to fully compensate for.

At low to medium temperatures, a thermistor is generally used to measure temperatures within the range of 200~500 ℃, and even lower temperatures can be measured (such as using a carbon resistor to measure low temperatures of around 1K) The platinum thermistor Pt100 is currently being used normally. There are also Pt50 and copper resistors used in industry, but the temperature measurement range is relatively small, between -50~150 ℃ In some special occasions, there are indium resistors, manganese resistors, etc.

Principle of Temperature Measurement

The basic principle of measuring temperature with a thermocouple is the thermoelectric effect, and a secondary meter is a voltmeter or an electronic potentiometer used to improve accuracy.

Resistance works based on the characteristic of the resistance value of conductors and semiconductors changing with temperature, and a secondary meter is an unbalanced bridge.