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The disadvantage of the S-type thermocouple is that the thermoelectric rate is small
2012-2-28 8:25:16

The installation location of the s-type thermocouple should be convenient for construction and maintenance. Avoid near the furnace door, or too close to the heating body and strong magnetic field, the temperature at the junction box does not exceed 100 ℃. The installation position should be as vertical as possible, but it must be installed obliquely when there is a flow rate. The outlet of the terminal box should face downward.
Thermocouples with porcelain protection tubes must be protected from rapid cooling and explosion, and should be explosion-proof. When installing, choose a place that does not prevent the heated object from moving. Porcelain jackets cannot measure liquid temperature.
The thermocouple should be wired in accordance with regulations, the lead should avoid the heat source, and the polarity of the compensation wire should not be reversed when wiring. The condition of the protective tube should be checked frequently, and measures should be taken immediately if oxidation or deformation is found. Check regularly.

Thermocouple technology standards

)铂铑10-铂热电偶铂铑10-铂热电偶(S型热电偶)为贵金属热电偶。 ( S-type thermocouple ) Platinum rhodium 10-platinum thermocouple Platinum rhodium 10-platinum thermocouple (S-type thermocouple) is a precious metal thermocouple. The diameter of the wire is specified as 0.5mm, and the allowable deviation is -0.015mm. The nominal chemical composition of the positive electrode (SP) is platinum-rhodium alloy, which contains 10% rhodium, 90% platinum, and negative electrode (SN) is pure platinum. Commonly known as single platinum rhodium thermocouple. The long-term maximum use temperature of this thermocouple is 1300 ° C, and the short-term maximum use temperature is 1600 ° C.
The S-type thermocouple has the highest accuracy, the best stability, the wide temperature range and long service life among the thermocouple series. It has good physical and chemical properties, good thermoelectric stability and good oxidation resistance at high temperatures, and is suitable for oxidizing and inert atmospheres. Because the S-type thermocouple has excellent comprehensive performance and conforms to the international temperature scale, the S-type thermocouple has long been used as an interpolated instrument of the international temperature scale. Although "ITS-90" stipulates that it will no longer be used as an internal inspection instrument of the international temperature scale, However, the International Advisory Committee on Temperature (CCT) believes that S-type thermocouples can still be used to approximate the international temperature scale.
不足之处是热电势,热电势率较小,灵敏读低,高温下机械强度下降,对污染非常敏感,贵金属材料昂贵,因而一次性投资较大。 The shortcomings of S-type thermocouples are thermoelectric potential, small thermoelectric potential, low sensitivity reading, low mechanical strength at high temperature, very sensitive to pollution, expensive precious metal materials, and therefore a large one-time investment.

(R-type thermocouple) Platinum-rhodium 13-platinum thermocouple Platinum-rhodium 13-platinum thermocouple (R-type thermocouple) is a precious metal thermocouple. The diameter of the wire is specified as 0.5mm, and the allowable deviation is -0.015mm. The nominal chemical composition of the positive electrode (RP) is platinum-rhodium alloy, which contains 13% rhodium, 87% platinum, and negative electrode (RN) is pure platinum. The maximum operating temperature is 1300 ℃, and the short-term maximum operating temperature is 1600 ℃.
The R-type thermocouple has the highest accuracy, the best stability, the wide temperature range and long service life among the thermocouple series. Its physical and chemical properties are good, thermoelectric potential stability and oxidation resistance at high temperature are good, it is suitable for oxidizing and inert atmosphere. Because the comprehensive performance of R-type thermocouples is comparable to that of S-type thermocouples, it has been difficult to promote it in China. Except for temperature measurement on imported equipment, domestic temperature measurement is rarely used. From 1967 to 1971, three major research institutes, the British NPL, the American NBS, and the Canadian NRC, conducted a cooperative study. The results showed that the R-type thermocouple has better stability and reproducibility than the S-type thermocouple. No research in this area has been carried out.
The shortcomings of R-type thermocouples are thermoelectric potential, small thermoelectric potential, low sensitivity reading, low mechanical strength at high temperature, very sensitive to pollution, expensive precious metal materials, and therefore a large one-time investment.

(Type B thermocouple) Platinum-rhodium 30-platinum rhodium 6 thermocouple Platinum-rhodium 30-platinum rhodium 6 thermocouple (type B thermocouple) is a precious metal thermocouple. The diameter of the wire is specified as 0.5mm and the allowable deviation is -0.015mm. The nominal chemical composition of the positive electrode (BP) is a platinum-rhodium alloy, which contains 30% rhodium, 70% platinum, and the negative electrode (BN) is a platinum-rhodium alloy. The amount of rhodium is 6%, so it is commonly called double platinum rhodium thermocouple. The long-term maximum use temperature of this thermocouple is 1600 ℃, and the short-term maximum use temperature is 1800 ℃.
The B-type thermocouple has the highest accuracy, the best stability in the thermocouple series, a wide temperature range, a long service life, and a high temperature limit. It is suitable for oxidizing and inert atmosphere, and can also be used in vacuum for a short time, but it is not suitable for reducing atmosphere or metal or non-metal vapor atmosphere. An obvious advantage of the B-type thermocouple is that it does not need to be compensated with a compensation wire, because the thermoelectric potential is less than 3μV in the range of 0 ~ 50 ° C.
The shortcomings of the B-type thermocouple are the thermoelectric potential, the thermoelectric potential is small, the sensitivity is low, the mechanical strength decreases at high temperatures, it is very sensitive to pollution, and the precious metal materials are expensive, so the one-time investment is large.

(K-type thermocouple) nickel-chromium-nickel-silicon thermocouple nickel-chromium-nickel-silicon thermocouple (K-type thermocouple) is currently the largest amount of cheap metal thermocouples, the amount of which is the sum of other thermocouples. The nominal chemical composition of the positive electrode (KP) is: Ni: Cr = 90: 10, the nominal chemical composition of the negative electrode (KN) is: Ni: Si = 97: 3, and its operating temperature is -200 ~ 1300 ° C.
K-type thermocouples have the advantages of good linearity, large thermoelectromotive force, high sensitivity, good stability and uniformity, strong oxidation resistance, and low price. They can be used in oxidizing inert atmosphere. Widely used by users.
K-type thermocouples cannot be used directly at high temperatures in sulfur, reducing or reducing, oxidizing and vacuum atmospheres, and are not recommended for use in weakly oxidizing atmospheres.

(N-type thermocouple) Ni-Cr-Si-Ni-Si thermocouple Ni-Cr-Si-Ni-Si thermocouple (N-type thermocouple) is a cheap metal thermocouple, which is the latest internationally standardized thermocouple. Developed successfully by the Australian Ministry of Defence laboratory, it overcomes two important shortcomings of the K-type thermocouple: the K-type thermocouple is unstable at 300 ~ 500 ℃ due to the short-range order of the nickel-chromium alloy's lattice; At about 800 ℃, the thermoelectromotive force caused by the preferential oxidation of nickel-chromium alloy is unstable. The nominal chemical composition of the positive electrode (NP) is: Ni: Cr: Si = 84.4: 14.2: 1.4, the nominal chemical composition of the negative electrode (NN) is: Ni: Si: Mg = 95.5: 4.4: 0.1, and its operating temperature is -200 ~ 1300 ℃.
N-type thermocouple has the advantages of good linearity, large thermoelectromotive force, high sensitivity, good stability and uniformity, strong oxidation resistance, cheap price, and not affected by short-range ordering. Its comprehensive performance is better than K Type thermocouple is a promising thermocouple.
N-type thermocouples cannot be used directly at high temperatures in sulfur, reducing or reducing, oxidizing alternate atmospheres and vacuum, nor are they recommended for use in weakly oxidizing atmospheres.

(E-type thermocouple) Nickel-chromium-copper-nickel thermocouple nickel-chromium-copper-nickel thermocouple (E-type thermocouple), also known as nickel-chromium-constantan thermocouple, is also a cheap metal thermocouple. The positive electrode (EP) is : Ni-Cr 10 alloy with the same chemical composition as KP. The negative electrode (EN) is a copper-nickel alloy with a nominal chemical composition of 55% copper, 45% nickel and a small amount of manganese, cobalt, iron and other elements. The use temperature of this thermocouple is -200 ~ 900 ℃.
The E-type thermocouple has a large thermoelectromotive force and a high sensitivity, which is the highest among all thermocouples. It should be made into a thermopile to measure small temperature changes. It is not very sensitive to corrosion in a high humidity atmosphere and should be used in a high humidity environment. E thermocouple also has good stability, oxidation resistance is better than copper-constantan, iron-constantan thermocouple, cheap price and other advantages, can be used in oxidizing and inert atmosphere, widely used by users.
E-type thermocouples cannot be used for sulfur directly at high temperatures, and the thermoelectric potential is poor in a reducing atmosphere.

(J-type thermocouple) iron-copper-nickel thermocouple iron-copper-nickel thermocouple (J-type thermocouple), also known as iron-constantan thermocouple, is also a cheap metal thermocouple. The nominal chemical composition of its positive electrode (JP) is pure iron, and the negative electrode (JN) is a copper-nickel alloy, which is often vaguely called constantan. Its nominal chemical composition is: 55% copper and 45% nickel and a small amount But very important elements such as manganese, cobalt, iron, etc. Although it is called constantan, it is different from nickel chromium-constantan and copper-constantan constantan, so it cannot be replaced by EN and TN. Covering temperature range of iron-constantan thermocouple is -200 ~ 1200 ℃, but the commonly used temperature range is 0 ~ 750 ℃
J-type thermocouple has the advantages of good linearity, large thermo-electromotive force, high sensitivity, good stability and uniformity, and cheap price. It is widely used by users.
J-type thermocouples can be used in vacuum, oxidation, reduction and inert atmospheres, but the positive electrode iron oxidizes faster at high temperatures, so the use temperature is limited, and it cannot be used directly in a sulfurized atmosphere at high temperatures without protection.

(T-type thermocouple) Copper-copper-nickel thermocouple Copper-copper-nickel thermocouple (T-type thermocouple), also known as copper-constantan thermocouple, is also an optimal low-temperature thermocouple for measuring low-cost metals. Its positive electrode (TP) is pure copper, and its negative electrode (TN) is copper-nickel alloy. Often it is constantan. It is common with nickel-chromium-constantan constantan EN, and iron-constantan constantan JN. Although they are called constantan, the cover temperature range of copper-copper-nickel thermocouples is -200 ~ 350 ° C.
T-type thermocouple has the advantages of good linearity, large thermoelectromotive force, high sensitivity, good stability and uniformity, and cheap price. It is especially used in the temperature range of -200 ~ 0 ℃, with better stability and annual stability. The property can be less than ± 3μV, and it can be used as a second-class standard to transmit low-temperature magnitude after low-temperature test.
的正极铜在高温下抗氧化性能差,故使用温度上限受到限制。 The positive electrode copper of s-type thermocouple has poor oxidation resistance at high temperature, so the upper limit of the use temperature is limited.

1Cr18Ni9Ti -200∽800 has high temperature corrosion resistance, usually used as general heat-resistant steel

304 -200∽800 Low carbon content, good resistance to intergranular corrosion, usually used as general heat-resistant steel
316 -200∽750 Low carbon content, good resistance to intergranular corrosion, used as heat resistant steel
316L -200∽750 Ultra-low carbon content, good resistance to intergranular corrosion, used as heat-resistant steel
310S -200∽1000 With high temperature oxidation resistance and corrosion resistance, usually used as heat-resistant steel
GH3030 0∽1100 Nickel-based superalloy steel has excellent oxidation resistance and corrosion resistance, usually used as heat-resistant steel