Thermocouple&RTD Knowledge

Difference between thermal resistance and thermocouple?

Difference between thermal resistance and thermocouple?Thermal resistances and thermocouples are temperature sensors, and are widely used in agriculture, transportation, science and technology, environmental protection, national defense, culture, education and health. Although the thermal resistance and thermocouple are the most commonly used temperature detection elements in the industry, the two also show the following differences in use.
1.The principle of temperature measurement is different
Two ends of two different composition conductors (called thermocouple wires or thermal electrodes) are connected to a circuit. When the temperature of the two junctions is different, electromotive force is generated in the circuit. This phenomenon is called the thermoelectric effect, and This electromotive force is called thermoelectric potential. Thermocouples use this principle for temperature measurement.
Thermal resistance temperature measurement is based on the characteristic that the resistance value of a metal conductor increases with temperature. The temperature measurement principle of thermal resistance is based on the characteristic that the resistance value of a conductor or semiconductor changes with temperature to measure temperature and temperature-related parameters.
2. Different characteristics
Technical advantages of thermocouples: The thermocouple has a wide temperature measurement range and relatively stable performance. The measurement accuracy is high, and the thermocouple is in direct contact with the measured object without being affected by the intermediate medium. The thermal response time is fast and the thermocouple responds flexibly to temperature changes. The measuring range is large, the thermocouple can continuously measure temperature from -40 ~ + 1600 ℃; the thermocouple has reliable performance and good mechanical strength. The device has a long service life and is easy to use.
The main advantages of thermal resistance thermometers are: high measurement accuracy and good reproducibility; a large measurement range, especially at low temperatures; easy to use in automatic measurement, and also convenient for long-distance measurement. Similarly, the thermal resistance is also defective, and its accuracy is not good in high temperature (greater than 850 ° C) measurement; it is easy to oxidize and not resistant to corrosion.
3. Different application scope
In the temperature measurement, the application of the thermocouple is extremely extensive. It has many advantages such as simple structure, convenient manufacturing, wide measuring range, high accuracy, small inertia, and easy transmission of the output signal. In addition, because a thermocouple is a passive sensor, it does not require an external power supply for measurement and is very convenient to use. Therefore, it is often used to measure the temperature of gas or liquid in boilers and pipes and the surface temperature of solids.
The most widely used thermal resistance materials are platinum and copper: platinum has high resistance, is suitable for neutral and oxidizing media, has good stability, has a certain non-linearity, the higher the temperature, the smaller the rate of change in resistance; copper resistance is in the temperature measurement In the range, the resistance value and the temperature have a linear relationship. The number of temperature lines is large, which is suitable for non-corrosive media. It is easy to be oxidized above 150 ° c.


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