A, k type 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; Second, the advantages of S type thermocouple: 1, high measurement precision, S type thermocouple of all the thermocouple measuring precision is very high; 2, physical and chemical performance is stable, good reproducibility. 3, good oxidation resistance at high temperature; Three, k type thermocouple shortcomings: 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; Four, S type thermocouple shortcomings: 1, precious metal thermocouple, the cost is high, 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;