What is the _ instrument thermocouple and the working principle of the thermocouple

Thermocouple temperature measurement and control instruments commonly used in temperature measuring element, it directly measure temperature, and the temperature signals into a thermoelectric emfs, through electrical instrument ( Secondary instrument) Convert the temperature of the measured medium. The appearance of all kinds of thermocouple is often due to the need to vary, but their basic structure is roughly same, usually by the hot electrode, insulation sleeve to protect the main parts such as pipe and connection box, usually with digital display table, recording instrument and electronic regulator. Thermocouple temperature measurement is the basic working principle of two kinds of different ingredients of closed loop conductor material composition, when temperature gradient is at both ends, the 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 ( seebeckeffect) 。 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. Thermocouple cold junction compensation calculation method: from millivolt to temperature: measure the cold end temperature and conversion for the corresponding millivolt values, millivolt values with thermocouple, the temperature conversion; From temperature to millivolt: measure the actual temperature and the cold end temperature, the conversion of millivolt values, respectively, after subtracting the millivolt values, quick temperature high temperature alloy wear-resistant, using special heat-resistant and wear-resistant alloys as outside temperature protection tube, the inner core body, both has the high corrosion resistant performance of particle erosion, and under the condition of high temperature on the inner core body can play a good protective effect. Can adopt the flanged or threaded connection, between 0 ∽ 1200 ℃ temperature measurement for a long time, high temperature is used in metallurgical industry, wear-resisting material: environment ideal temperature sensor 3 yc52 or GH3030 heat-resistant wear-resistant alloy temperature: 0 ~ 1200 ℃ iron aluminum ceramic protection tube iron base containing aluminum and add A12O3 powder ably, namely system of iron and aluminum porcelain ( TLC） Special gold, iron and aluminum alloy porcelain made thermocouple ( Resistance) Protecting tube, become iron aluminum ceramic thermocouple (namely Resistance) Key parts of iron and aluminum ceramic protection tube. According to working temperature, wear condition, the type of medium, pressure equation, made into different series of iron and aluminum ceramic protection tube.