Although the resistance value of most metals varies with temperature, not all metals can be used as thermal resistors for measuring temperature. AsThermal resistance measurementThe metal material should have the following characteristics: high temperature coefficient of resistance, high electrical resistivity, and low thermal capacity; Stable physical and chemical properties should be present throughout the entire temperature measurement range; The relationship between resistance and temperature is best approximated as linear or a smooth curve; And it requires easy processing, good reproducibility, and affordable price. However, it is actually difficult to meet the above requirements for thermal resistance materials at the same time. The most widely used thermal resistance materials at present are platinum and copper, which have been made into standard thermometers. At the same time, thermometers made of materials such as nickel, iron, and indium are also used.

1、 Platinum resistance

The characteristics of platinum resistors areHigh precisionGood stability and reliable performance. Platinum is widely recognized as the best material for manufacturing thermal resistors due to its highly stable physical and chemical properties in oxidizing atmospheres, even at high temperatures. Platinum resistors are mainly used as standard resistance thermometers and are also commonly used in industrial measurements. In addition, it is widely used for the transmission of temperature benchmarks and standards. Platinum resistance thermometer is currently the most reproducible thermometer, with a long-term stable reproducibility of up to 10 * K, which is superior to all other thermometers.

2、 Copper resistance

Platinum is a precious metal and expensive, so in situations where the temperature measurement range is relatively small (-50~+150 C), copper made temperature measuring resistors can be used, known as copper resistors. Copper has good stability within the above temperature range, with a relatively large temperature coefficient and a nearly linear relationship between resistance and temperature. And the material is easy to purify and the price is cheap. The disadvantage is that the measurement accuracy is slightly lower than that of platinum resistors, and the resistivity is small.

3、 Iron resistance and nickel resistance

Iron and nickel have high temperature coefficients of resistance and high electrical resistivity, so they can be made into small-sizedHigh sensitivityThe disadvantage of the resistance thermometer is that it is prone to oxidation, has poor chemical stability, is difficult to purify, has poor reproducibility, and has a poor linear relationship between resistance value and temperature. Currently, it is not widely used.