Non-Standard Thermocouple
The production process of the other thermocouple is not mature enough, the application scope and quantity are not as good as the standardized thermocouple, there is no unified scale, and there is no supporting display instrument. Most of these thermocouples meet some special measurement requirements, such as ultra-high temperature, very low temperature, high vacuum or nuclear radiation environment. This kind of thermocouple is called non-standard thermocouple.
The common non-standard thermocouples are as follows: tungsten-rhenium 3-tungsten-rhenium 25 / tungsten-rhenium 5-tungsten-rhenium 26 thermocouple: the recommended temperature range of this thermocouple is 0 ≤ 3000 ℃. Advantages: it is the best in high temperature thermocouple, good plasticity and stability at low temperature. Disadvantages: poor reproducibility, need to be divided separately. Suitable for: vacuum, reduction or neutral environment. Tungsten-rhenium 26 thermocouple: the recommended temperature range of this thermocouple is 0 ≤ 3000 ℃. Advantages: the upper limit of temperature measurement is the highest and the EMF rate is large. Disadvantages: poor reproducibility and need to be graded separately; tungsten is brittle when exposed to air. Platinum-rhodium 20-platinum-rhodium 5 thermocouple: the recommended temperature range of this thermocouple is 500 ≤ 1700 ℃. Advantages: the upper limit of temperature measurement is higher than S type, the stability is good, and there is no need for cold end compensation. Disadvantages: vulnerable to metal steam contamination, EMF rate is small. Suitable for: vacuum, oxidation or neutral environment. Platinum-rhodium 40-platinum-rhodium 20 thermocouple: the recommended temperature range of this thermocouple is 1000 ℃ 1850 ℃. Advantages: the upper limit of temperature measurement is high, the stability and reproducibility are good, and the influence of cold end can be ignored. Iridium rhodium-iridium thermocouple: the recommended temperature range of this thermocouple is 1000 ≤ 2200 ℃. Advantages: the only thermocouple can be used in oxidation atmosphere above 1850 ℃. Disadvantages: general stability and reproducibility, short life, easy brittleness, easy to be contaminated by iron, low EMF rate. Tungsten-Mo thermocouple: the recommended temperature range of this thermocouple is 1200 ℃. Advantages: the price is not expensive and can be used in a reductive atmosphere. Disadvantages: low EMF rate, polar shift of thermoelectric EMF at 1200 ℃, vulnerable to carbon, oxygen, silicon contamination. Boron carbide-graphite thermocouple: the upper limit of temperature measurement is 2200 ℃. Advantages: high EMF, stable physical and chemical properties, low price, simple structure. Suitable for: carbon or neutral environment.
