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Depending on the purpose of use, a variety of thermometers have been designed and manufactured. The design basis is: electrothermal constant temperature incubator using solid, liquid, gas under the influence of temperature and thermal expansion and contraction phenomenon; under constant volume conditions, the gas (or vapor pressure changes due to different temperatures; thermoelectric effect; The resistance changes with changes in temperature; the effect of heat radiation, etc.
In general, any physical property of any substance, as long as it changes monotonously and significantly with changes in temperature, can be used to mark the temperature and make a thermometer.
Uses and classification
With the development of science and technology and the needs of modern industrial technology, temperature measurement technology has also been continuously improved and improved. Due to the increasingly wide temperature range, according to different requirements, they have also produced different temperature measuring instruments. Here are a few of them.
1, gas thermometer: use more hydrogen or helium as a temperature measurement material, electric thermostatic blast oven because of hydrogen and helium liquefaction temperature is very low, close to absolute zero, so its temperature range is very wide. This kind of thermometer is very accurate and used for precision measurements.
2, resistance thermometer: Divided into metal resistance thermometer and semiconductor resistance thermometer, are based on the characteristics of resistance changes with temperature made of this feature. Metal thermometers are mainly used for platinum, gold, copper, nickel and other pure metals and ferronickel, phosphor bronze alloy; semiconductor thermometers are mainly used carbon, germanium and so on. Resistance thermometers are easy to use and have been widely used. Its measurement range is around -260°C to 600°C.