Thermal resistance temperature measurement is based on the metal conductor resistance changes with the temperature, the temperature field at higher temperatures, the thermocouple resistance increases, the temperature field at lower temperature, thermocouple resistance decrease. Commonly used thermocouple linear good platinum wire, also called platinum thermocouple or copper thermocouple. Apply to the temperature measurement of low temperature area, in the general temperature range: - 200℃～650℃. Commonly used Pt100. 1, in order to make the measurement end of the thermocouple, and had good heat exchange between the measured medium, should be a reasonable choice of observation, try to avoid the valve, elbow and thermocouple pipeline and equipment near the corner of installations. 2, with a thermocouple with heat transfer and heat loss protection casing, in order to reduce the measurement error, thermocouple and thermocouple should have enough: (insert depth 1) For thermocouple temperature between fluid, usually should be measuring end is inserted into the pipe (at the centre of the Vertical or inclined installation) 。 As the current body of pipe diameter is 200 mm, the thermocouple insertion depth should choose 100 mm; ( 2) For high temperature and high pressure and high velocity of temperature measurement, Such as main steam temperature) , in order to reduce cases of fluid resistance and prevent cases break under the action of a fluid, can take protecting tube shallow inserted way or use hot thermocouple. Shallow inserted type thermocouple protection tube, its depth into the steam pipe should be no less than 75 mm; Heat sets the standard of thermocouple insertion depth is 100 mm; ( 3) If is need to measure the temperature of flue gas, although the flue is 4 m in diameter, thermocouple insertion depth of 1 m. ( 4) When measuring the original insertion depth of more than 1 m, explosion-proof thermocouple shall be installed vertically, as far as possible or add racks and protect casing. Thermocouple temperature measurement principle is based on a conductor or semiconductor resistance changes with the temperature change and this feature to measure temperature and parameters related to the temperature. Thermocouple are mostly made of pure metal materials, the application is a lot of platinum and copper, now have begun to use the materials such as nickel, manganese and rhodium thermocouple. Thermocouple is usually need to get the resistance signal through wire transfer to the computer control device or other secondary instrument. Industry commonly used metal thermocouple, from the perspective of the change of resistance with temperature, most of the metal conductor has this property, but not all can be used for temperature measuring thermocouple, thermocouple as general requirements of metal materials, as far as possible big and stable temperature coefficient, resistivity ( Reduce the size of the sensor) under the same sensitivity , using temperature range has stable chemical physics performance, good replication of material and resistance change with temperature have the function relationship between ( A good linear relationship) 。 Commonly used in low temperature zone thermocouple is a kind of temperature detector. Thermocouple temperature measurement is based on the metal conductor resistance value increases with the increase of the temperature of the properties for temperature measurement. Its main characteristic is high accuracy, stable performance. The platinum thermocouple measuring accuracy is high, it is not only widely used in industrial temperature measurement, and is made into standard benchmark instrument. Thermocouples are mostly made of pure metal materials, the application is a lot of platinum and copper, in addition, now began to use the materials such as nickel, manganese and rhodium thermocouple. Metal thermocouple commonly used thermal material sort is more, it is commonly used platinum wire. Industrial measurement with metal material in addition to the platinum wire, thermocouple as well as copper, nickel, iron, iron - Nickel, etc.