K type thermocouple and s type thermocouple what are the advantages and disadvantages of _ instrument

Thermocouple, in more extensive range of industrial applications, and to adapt to the environment is also very high, with the continuous development of science and technology, in order to better adapt to all kinds of bad environment, the types of thermocouple is gradually increasing, such as k type thermocouple and s type thermocouple. A advantages, k type thermocouple and s type thermocouple type k thermocouple advantages: 1, high temperature metal thermocouple cheap, cheap, widely used, the annual production of nearly half of all metal thermocouple; 2, good reproducibility, approximate linear relationship between thermoelectric potential and temperature; 3, thermoelectric potential: 52. 4 mv / 1300 ℃, high rate of thermoelectric potential: 41 uv / ℃; 4, good oxidation resistance can be used in oxidizing atmosphere and air medium and long term; S type thermocouple advantages: 1, high measurement precision, s type thermocouple of all the thermocouple measurement precision is very high; 2, physical and chemical performance is stable, good reproducibility. 3, good oxidation resistance at high temperature; Second, the two thermocouple type k thermocouple weakness weakness: 1, the stability is a bit poor, in the 150 - Magnetic change very easily within 200 ℃, 250 - 550 ℃ range, can appear the thermoelectric potential and heating process specification change not ( Back to the poor inconsistent) , if used at high temperature for a long time, the thermoelectric performance is unstable; 2, not suitable for in a vacuum, carbon, sulfur atmosphere; S type thermocouple shortcomings: 1, the precious metal thermocouple, high cost, in all thermocouple series, only slightly lower than b type thermocouple price; 2, poor mechanical strength, small thermoelectric potential, especially in low temperature, thermocouple is small, need measuring instrument with high sensitivity; 3, hot wire electrode diameter ( 0. 35mm- 0. 5毫米) Very fine, poor mechanical strength; Thermocouple temperature measurement is the basic principle of two kinds of different ingredients of closed loop conductor material composition, when when there is a temperature gradient at both ends, loop will have an electric current passes through, the existed between the electromotive force on both ends - — Thermoelectric emf, this is the so-called seebeck effect ( 塞贝克效应) 。 Two different components of homogeneous conductor electrode as heat, the temperature is higher for work at the end of the end, one end of the low temperature as the free end, usually free end under a constant temperature. According to the thermoelectric emf as a function of temperature, the thermocouple indexing table; Indexing table is free end temperature at 0 ℃, under the condition of different thermocouples with different indexing table. Access in the thermocouple loop when the third metal material, the two contacts at the same temperature as long as the material, produced by the thermocouple thermoelectric is set to remain the same, which is not affected by the third metal access in the loop. Therefore, when the thermocouple temperature measurement, can be connected to the measuring instrument, measured after the thermoelectric emfs, can know the temperature of the measured medium. Thermocouple measuring temperature to the cold end ( Measure the end for the hot end, by the end of the lead connected to the measurement circuit is called cold junction) Temperature remains constant, the size of thermoelectric potential and measured temperature in certain proportion relationship. When measuring, the cold end ( Environment) Temperature changes, will seriously affect the accuracy of measurement. Take action at the cold end compensation due to the impact of the cold end temperature change is called the thermocouple cold junction compensation is normal. Connected to the measuring instrument with special compensation conductor.