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Commonly used thermocouple indexing, S, B, E, T, K, J, etc., these are all standard thermocouples. Which type K means nickel chrome - nickel and silicon thermocouple, it is a cheap thermocouple to measure high temperature. Because of this alloy has good high temperature oxidation resistance, may apply in oxidizing or neutral medium. It can measure 1000 - degree heat for a long time, short-term measurable to 1200 degrees. It cannot be used for reducing medium, otherwise, the decay quickly, in this case can only be used for measuring under 500 degrees. It is much cheaper than S type thermocouple, the repeatability is good, the thermoelectric potential is large, and thus the sensitivity is very high, and it has a good linear. Although its measuring precision degree is slightly lower, but can entirely meet the requirements of industrial temperature measurement, so it is the most commonly used thermocouple on industry. Summary: as the industrial temperature measurement, one of the most widely used temperature sensor of thermocouple, and the platinum thermal resistance, together accounting for about 60% of the total temperature sensor, thermocouple and display instrument, usually measured directly in the production of various - 40 ~ 1800 ℃ range of liquid, vapour and gas medium, as well as the surface temperature of the solid.10792
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Thermocouple principle: two different components of the conductor (called the thermocouple wire or hot electrode) synthesis loop at both ends, when the junction temperature is not at the same time, in the circuit will generate electromotive force, this kind of phenomenon called the thermoelectric effect, called the thermoelectric potential and the electric potential. Thermocouple is in using the principle of temperature measurement, which directly used to measure medium temperature is called at the end of the working end (also known as measuring side), the other end is called the cold end compensation (also known as end); Cold end connected to the display instrument and meter, display instrument will point out the thermocouple thermoelectric potential. Thermocouple is actually a kind of energy converter, it converts thermal energy into electricity, using thermoelectric potential generated by the measuring temperature, the thermocouple thermoelectric power, should pay attention to several problems as follows: (1) the thermocouple thermoelectric potential is a function on both ends of the thermocouple temperature difference, rather than a function of temperature difference on both ends of the thermocouple; (2) the size of the thermocouple thermoelectric potential produced by, when material is uniform thermocouple, has nothing to do with the length and diameter of the thermocouple, only with the thermocouple at the ends of the material composition and temperature difference; (3) when the two thermocouple wire thermocouple material component is determined, the size of the thermocouple thermoelectric potential, only associated with the temperature difference of thermocouple; If the thermocouple cold end temperature keeping, work it into the thermocouple thermoelectric power is just end the single value function of temperature.
Thermocouple, the basic structure: industrial measuring temperature with thermocouple, the basic structure includes thermocouple wire materials, insulation pipe, protecting tube and junction box, etc. A, commonly used thermocouple wire material and its properties 1, 10 - platinum platinum rhodium thermocouple (index number is S, also known as single platinum-rhodium thermocouple) the thermocouple of the positive components for containing rhodium platinum rhodium, 10% negative extremely pure platinum; Its characteristic is: (1) the thermal stable performance, strong oxidation resistance, appropriate for use in oxidizing atmosphere, the long-term use of the temperature can reach 1300 ℃, and above 1400 ℃, even in the air, or pure platinum wire recrystallization, coarse grains and fracture; (2) high precision, it is in all thermocouples, accuracy of the highest grade, usually used as a standard or measure high temperature; (3) has a wide range, good uniformity and interchangeability; (4) the main disadvantages are: differential thermoelectric power is small, and therefore have relatively low sensitivity; Price is more expensive, low mechanical strength, there is appropriate in a reducing atmosphere or metal vapor under the conditions of use. 2, 13 - platinum rhodium platinum thermocouple (index number is R, also known as single platinum-rhodium thermocouple) of the thermocouple is platinum rhodium alloy containing 13%, so it is a negative extremely pure platinum, compared with S type, its potential rate around 15%, other performance is almost the same, this kind of thermocouple industry in Japan, as a high temperature thermocouple used most frequently, but in China, with less; 3 6 30 - platinum rhodium, platinum, rhodium thermocouple (index number is B, also known as a dual platinum rhodium thermocouple) is the thermocouple of the anode containing rhodium platinum rhodium, 30% 6% negative extremely containing rhodium platinum rhodium, at room temperature, the thermoelectric power is small, so in general measurement without compensation conductor, negligible effect of cold end temperature change; Short-term for long-term use of temperature of 1600 ℃, 1800 ℃, for thermoelectric power is small, so it need to display instrument with high sensitivity. B type thermocouple is suitable for use in oxidizing or neutral atmosphere, can also be used in vacuum atmosphere in the short term; Even under the reducing atmosphere, its life is R or S type 10 ~ 20 times; Due to the electrode made of platinum rhodium, so there is no platinum rhodium platinum thermocouple all faults on the cathode, in a few big trend of crystallization at high temperature, and has great mechanical strength; And because it is less impurity absorption or rhodium migration effects, therefore its thermoelectric potential change after long-term use is not serious, disadvantage is expensive (relative to the single platinum rhodium). 4 silicon, nickel chrome - nickel (nickel aluminum) thermocouple (index number K) as the thermocouple is extremely 10% chromium nickel chromium alloy, negative is 3% of the nickel containing silicon silicon alloy (in some countries, the product is very pure nickel). Measurement of 0 ~ 1300 ℃ medium temperature, suitable for continuous use in the oxidizing and inert gas, short-term use temperature is 1200 ℃, the long-term use of temperature is 1000 ℃, the approximate linear relationship between thermoelectric potential and temperature, the price is cheap, is the most consumable thermocouples.