Low temperature environment measuring thermometer right?

Work in some special occasions, the temperature is lower, using a thermometer to measure temperature is better? Is the use of common bimetallic thermometer at ordinary times or platinum resistance thermometer? Although are metal thermometer, or recommended platinum resistance thermometer in low temperature environment. Generally know a truth, the resistance value of the metal material is varies with temperature, but be used to make resistance thermometer for material has certain requirements: (1) need to be in the temperature measurement range with high temperature coefficient of resistance, that is when the temperature change 1 ℃, the changes in the resistance of the nine can make sensitivity is higher, and the best resistance with temperature of relations is a linear relationship; (2) chemical stability is strong, easy purification and copy; (3) under a certain temperature on unit length, cross section conductor resistance is bigger ( That is greater than resistance) , in order to make the volume of the thermometer can small skills; (4) the price is cheap. Practice has proved suitable for making thermal resistance element material with platinum, copper, iron, nickel, etc. Platinum is a kind of ideal material, its chemical stability is strong, easy to get high purity platinum wire, larger than the resistance, high temperature measurement precision, in - 200 - 0 ℃ range into approximate linear relationship between internal resistance and temperature. The copper are cheap, high temperature coefficient of resistance, but the measuring temperature range is smaller than platinum, generally in - Between 150 ℃ and 50 than resistance is small, large volume, low sensitivity. Such as iron, nickel, though has a high temperature coefficient of resistance, but resistance is not linear relationship with temperature, and difficult to purification, seldom used in general. So measuring platinum resistance thermometer is commonly used in low temperature. It compared with thermocouple, at low temperature with high sensitivity and accuracy of the push, do not need cold junction compensation, facilitate far transfer concentration detection, so almost entirely on the air separation device ontology with platinum resistance thermometer. Commonly used models have WZB - The type 210, WZB2 & ndash; The type 210, WZB - The type 280 ( Measuring the turbine expander bearing temperature) ,WZB - 264 w, etc.