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Working Principle Of Thermometer
Oct 31, 2017

Different thermometers have been designed and manufactured according to the purpose of use. Its design is based on: the use of solids, liquids, gases under the influence of temperature and expansion of the phenomenon of expansion and contraction, under constant conditions, the pressure of gas (or vapor) to vary the temperature, the effect of thermoelectric effect, the resistance to change with the temperature and the effect of heat radiation.

1. Gas thermometer: Use hydrogen or helium as a temperature-measuring material, because the liquefied temperature of hydrogen and helium is very low, close to absolute 0 degrees, so its temperature range is very wide. This thermometer is highly accurate and is used for precision measurement.

2. Resistance thermometer: Metal resistance thermometer and semiconductor resistance thermometer, are based on the resistance value with the temperature of the change in this feature. Metal thermometers are mainly used in platinum, gold, copper, nickel and other pure metal and rhodium-iron, phosphor bronze alloy, semiconductor thermometer mainly with carbon, germanium and so on. Resistance thermometer is easy to use and reliable, and has been widely used. Its measurement range is 260 ℃ to 600 ℃.

3. Thermocouple Thermometer: It is a kind of temperature measuring instrument widely used in industry. The use of thermoelectric phenomenon is made. Two different wires are welded together to form the working end, and the other ends are connected with the measuring instrument to form a circuit. Put the work end at the measured temperature, the working end and the free end of the temperature is not at the same time, there will be electromotive force, so there is current through the loop. The temperature of the other place can be determined by measuring the electrical quantity, using the temperature of the known place. It is suitable for two kinds of substances with large temperature difference, and is used for high temperature and low turbidity measurement. Some thermoelectric couples can measure up to 3,000 ℃ of high temperature, some can measure near absolute 0 degrees of low temperature.

4. Pointer thermometer: A thermometer, such as a dashboard, also known as a thermometer, used to measure room temperature, is made of metal expansion and contraction principle. It is a bimetal film as a temperature sensing element to control the pointer. Bimetallic sheets are usually riveted with copper and iron sheets, and the copper piece is left and the iron sheet is on the right. Because of the effect of copper expansion and contraction than iron significantly more, as a result, when the temperature rises, the copper sheet pulls the iron sheet to the right curved, the pointer is deflected by the bimetallic sheet to the right (pointing to the high temperature).

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