Thermocouple is a kind of wide application of measuring instruments, has a very important role in many industries. The thermocouple in the application of the electric furnace is also very important, plays a vital role. When using thermocouple in electric furnace for its materials also have certain requirements. Commonly used electric thermocouple material requirements 1. High-temperature thermocouple temperature measurement range depends on high temperature performance of hot electrode, that is to say, in the high temperature medium, heat stable physical and chemical properties of the electrode, it is made of thermocouple temperature measurement range is wide. 2. Good - dominant again Electrode materials with the same two hot thermocouple, asking them to electric performance and stable phase, this can make the thermocouple batch production, and has good compatibility; 3. High sensitivity, good linearity requirements of galvanic thermoelectric potential is large enough, and has a linear relation with temperature; 4. Thermocouple for materials besides can satisfy the requirement of the above points, and hope the resistance coefficient and temperature coefficient of resistance as small as possible and the price is cheap, plentiful. Thermocouples used in electric furnace, when using, should according to the requirement of reasonable choice. At present there are several commonly used thermocouple 1. Platinum rhodium/platinum thermocouple - S degree, the anode is an alloy of 10% 90% platinum and rhodium, negative extremely pure platinum wire. The advantage of the thermocouple is high precision, high stability, suitable use in oxidizing and neutral atmosphere; Its high melting point, high temperature limit is. In the industrial measurement generally use it to measure the temperature of above 1000 ℃, under 1300 ℃ can be used for a long time continuously, short-term WenKeDa 1500 ℃. Platinum rhodium/platinum thermocouple disadvantage is that the price is expensive, thermoelectric power is small, the reducing gas, metal, metal oxide, and silicon oxide and sulfur oxide atmosphere use will soon be contamination and deterioration, so he must use it in the atmosphere and protect casing, in addition, the thermocouple thermoelectric performance of nonlinear is larger, the hot electrode can sublimate at high temperatures, make rhodium molecules penetrate into the platinum extremely contamination, it lead to thermoelectric potential instability. 2. Nickel chromium/nickel silicon thermocouple - Index number k, the positive component is 9 - Chromium, 0 10%. 4% of silicon, the rest of nickel, anode component of 2. 5 - 3% silicon, 3. Nickel chrome/constantan thermocouple - Dividing e, the anode nickel chrome components in 9 - 10% chromium, 0. 4% silicon, the rest is nickel; The cathode copper was 56% copper and 44% nickel test. Copper nickel chrome/test thermocouple thermoelectric potential is large, the advantages of cheaper prices. The shortcoming of the thermocouple is cannot be used to measure the high temperature, the temperature up to 800 ℃, use for a long time, will only be below 600 ℃, in addition, because the constantan alloys are susceptible to oxidation and deterioration, must be equipped with protective casing. 4. Platinum rhodium 30 / platinum rhodium thermocouple 6 - Referred to as double platinum rhodium thermocouple, index number is b. Across the electrodes of the thermocouple is platinum rhodium, just different proportion alloy content and the third, the anode containing rhodium 30%, anode containing rhodium is 6%, double platinum rhodium thermocouple of fouling resistance is strong, when the temperature of 1800 ℃ temperature is still a good stability. The temperature measurement accuracy is higher, suitable for oxidizing, neutral medium, can long-term continuous measuring 1400 - The high temperature of 1600 ℃, short-term measure up to 1800 ℃. Double platinum rhodium thermocouple sensitivity is low, when using, should display instrument of high sensitivity. At room temperature for thermoelectric potential minimal impact, so when using do not generally requires temperature compensation. 5. The copper/constantan thermocouple - Its index number for t, is extremely copper, negative extremely 60% / 40% copper nickel alloy. Its advantage is high temperature sensitivity, thermal electrode is easy to copy, cheap, good low temperature performance, can be measured, 200 ℃ low temperature. But its composition is easy oxidation of copper, so the average maximum temperature does not exceed 300 ℃.