Distinction between thermal resistance and thermocouple

In industrial temperature measurement equipment, we often encounter thermal resistance and thermocouples. Many people think that they are two things called a thing. In fact, they are two very different things.

They are all connected to the temperature measuring instrument, but their temperature measurement principle and temperature range are different. Let me talk about the thermal resistance. The thermal resistance is generally used for the measurement of low temperature. The principle is based on the fact that the resistance value of the metal conductor increases with the increase of temperature to measure the temperature. Most of the thermal resistors are made of pure metal materials. Currently, platinum and copper are the most widely used. In addition, thermal resistances such as nickel, manganese and tantalum have been used. Industrial thermal resistance is generally Pt100, Pt10, Cu50, Cu100, PT1000 platinum thermal resistance temperature range is generally minus 200-800 degrees Celsius, copper thermal resistance is minus 40 to 140 degrees Celsius.

Thermocouples are generally used for the measurement of medium and high temperatures. The working principle of thermocouples is based on the Seeback effect, that is, two different conductors are connected at both ends into a loop. If the temperature of the two terminals is different, a thermal current is generated in the loop. Physical phenomenon. Thermocouples have a wide measuring range. Platinum crucibles are commonly used - platinum (index S, measuring range 0 to 1300 degrees), nickel chromium - nickel silicon (index K, measuring range 0 to 900 degrees), nickel Chromium - Constantan (index E, measuring range 0 ~ 600 degrees), platinum 30 - platinum 6 (index B, measuring range 0 ~ 1600 degrees). Thermocouples are more expensive than thermal resistors because they are made of precious metals.

Usually, the thermocouple has only two lead wires. If there are three lead wires, it is a thermal resistor. If there are only two lead wires, it can be judged by measuring the resistance value with a digital multimeter. Since the resistance value of the thermocouple is small, the thermal resistance is almost zero; if the resistance value is small when measuring, it may be a thermocouple.

The thermal resistance at room temperature will also have a minimum resistance value greater than 10. You can also find an easily available heat source to judge and identify by heating the temperature measuring element. If the cup of hot water can be connected, put the measuring end of the temperature measuring component into the hot water, measure it with the DC millivolt of the digital multimeter, and measure whether it has a thermoelectric potential. If there is a thermoelectric potential, the thermocouple finds the thermocouple according to the thermoelectric potential. With the meter, you can determine what thermocouple is the index number. When there is no thermoelectric potential, the resistance value is measured. If there is a resistance value rising, the thermal resistance is the trend. The measurement end of the temperature measuring element can also be heated using an electric soldering iron or an electric oven to determine the identification.
For the four-wire thermal resistance and thermocouple, because it is not common, Huaheng Instrument  will not introduce it here.



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