Termokopel data

On the other hand, commonly used thermocouple materials and their properties include: 1. Platinum rhodium 10 platinum thermocouple (also known as index number s, platinum rhodium thermocouple). The positive electrode of this thermocouple is a platinum rhodium alloy containing 10% rhodium, and the negative electrode is pure platinum; Its characteristics are: (1) stable thermoelectric performance, strong oxidation resistance, preferably used continuously in an oxidizing atmosphere, with a long-term use temperature of 1300 degree . When the temperature exceeds 1400 degree , even pure white gold wires will recrystallize in the air, and the grains will become coarse and destroyed. (2) high accuracy, which is the highest accuracy level among all thermocouples and is usually used as a standard or for measuring high temperatures. (3) wide range of use, good uniformity and interchangeability. (4) The main disadvantages are small differential thermoelectric potential, low sensitivity, high price, and low mechanical strength, so it is not suitable for use in reducing atmospheres and metal vapors. 2 . Platinum rhodium 13 platinum thermocouple (also known as index number r, single platinum rhodium thermocouple) The positive electrode of this thermocouple contains 13% platinum rhodium alloy, and the negative electrode is pure platinum. Compared with the S-type, the potential rate is about 15% higher, and other properties are roughly the same. This type of thermocouple is the most commonly used high-temperature thermocouple in the Japanese industry and is rare in China The platinum rhodium 30 platinum rhodium 6 thermocouple (also known as index number b, platinum rhodium thermocouple) has a positive electrode of a platinum rhodium alloy containing 30% rhodium and a negative electrode of a platinum rhodium alloy containing 6% rhodium. At room temperature, the thermoelectric potential is small, so the lead wire is not compensated during measurement. The long-term use temperature that can ignore the influence of cold end temperature changes is 1600 degree , and the short-term use temperature is 1800 degree . The thermoelectric potential is small, so a highly sensitive display is required. B-type thermocouples are suitable for use in oxidizing or neutral atmospheres. Even if they can be used in a reducing atmosphere for a short period of time in a vacuum atmosphere, their lifespan is 10-20 times that of r or s type thermocouples. Their electrodes are made of platinum rhodium alloy, so they have all the disadvantages of the negative electrode of platinum rhodium platinum thermocouples. At high temperatures, there is less tendency for crystallization, and they have greater mechanical strength. At the same time, due to the small influence of impurity absorption and rhodium migration, the change in thermoelectric potential is not severe after long-term use, and the defect price is high (compared to platinum rhodium). 4. Nickel chromium alloy (nickel aluminum) thermocouple (index number k) The positive electrode of the thermocouple is nickel chromium alloy containing 10% chromium, and the negative electrode is nickel chromium alloy containing 3% silicon (in some countries, the negative electrode is pure nickel). It can measure the temperature of the medium from 0 to 1300 degree and is suitable for continuous use in oxidizing and inert gases. The short-term use temperature is 1200 degree and the long-term use temperature is 1000 degree . The relationship between thermoelectric potential and temperature is basically linear and inexpensive, making it currently the most widely used thermocouple. K-type thermocouples are base metal thermocouples with strong oxidation resistance. When bare wires are used in an atmosphere of vacuum, sulfur-containing, carbon containing, and alternating oxidation-reduction, the chromium in the nickel chromium electrode is preferentially oxidized when the oxygen partial pressure is not ideal. The thermoelectric potential changes greatly, but the influence of metal gas is small. Therefore, metal protective tubes are often used. Disadvantages of K-type thermocouples: (1) The high-temperature stability of thermoelectric potential is worse than that of n-type thermocouples or precious metal thermocouples, and it is more prone to damage due to oxidation at high temperatures (such as over 1000 degree ) (the stability of short-term thermal cycling is poor in the range of 250-500 degree , that is, at the same temperature point, the displayed value of the thermoelectric potential is different during the heating and cooling process, and the difference can reach 2-3 degree ). The negative electrode undergoes magnetic changes in the range of 150-200 degree , and there are more deviations from the division value of the division table in the range of 230 degree at room temperature, especially when used in a magnetic field. Time independent thermoelectric potential interference often occurs. (4) Long term exposure to high-throughput system irradiation environment. The elements such as manganese (Mn) and cobalt (Co) in the negative electrode undergo denaturation, resulting in poor stability and significant changes in thermoelectric potential. 5. The main characteristics of nickel silicon thermocouple (index number n) are strong oxidation resistance under temperature regulation below 1300 degree , good long-term stability and short-term thermal cycle reproducibility, good radiation resistance and low temperature resistance. In addition, within the range of 400-1300 degree , The linearity of the thermoelectric characteristics of n-type thermocouples is superior to that of k-type even numbered 6, copper copper nickel thermocouples (division code T), and T-shaped thermocouples. The positive electrode of the thermocouple is pure copper and the negative electrode is copper nickel alloy (also known as constantan). Its main feature is that it is a base metal thermocouple with high accuracy and good uniformity of the thermoelectric electrode. Its operating temperature is -200~350 degree . Copper thermocouples are prone to oxidation, and due to the easy peeling of the oxide film, they should generally not exceed 300 degree when used in an oxidizing atmosphere. The sensitivity is high in the range of -200~300 degree . Copper constantan thermocouples have the characteristics of being cheap and the cheapest among commonly used standardized products. 7. Iron constantan thermocouple (division number J) J-type thermocouple, with pure iron as the positive electrode and constantan (copper nickel alloy) as the negative electrode, is inexpensive and suitable for vacuum oxidation-reduction or inert atmosphere. The temperature range is -200~800 degree , and the commonly used temperature is below 500 degree . When the temperature exceeds this limit, the oxidation rate of the ferroelectric electrode increases. If a thick wire diameter is used, it can still be used at high temperatures. The long-life thermocouple can withstand the corrosion of hydrogen (H2) and carbon monoxide (CO) gases, but cannot be used in a sulfur (s) atmosphere at high temperatures (such as 500 degree ). 8. Nickel chromium alloy (constantan) thermocouple (division number E) E-type thermocouple is a new product, with nickel chromium alloy as the positive electrode and copper nickel alloy (constantan) as the negative electrode. Its characteristic is that the thermoelectric potential is the highest among commonly used thermocouples, which means it has the highest sensitivity. Its application range is not as wide as K-type even numbers, but its sensitivity is high. The limiting conditions for use are the same as K-type, which is often selected under conditions of low thermal conductivity and allowable high resistance, but it is not very sensitive to corrosion, including high humidity environments. In addition to the 8 commonly used thermocouples mentioned above, non standardized thermocouples include tungsten rhenium thermocouples, platinum rhodium thermocouples, iridium germanium thermocouples, platinum molybdenum thermocouples, and non-metallic material thermocouples.