The difference between thermocouple and thermocouple _ instrument1

There are two kinds of structure of the thermocouple, regular and type. Ordinary thermocouples generally by the hot electrode, insulation tube, to protect casing and junction box parts, and the type of thermocouple is the thermocouple wire, insulation material and metal protective casing combination after assembly, after stretching processing from a combination of a solid. Thermocouple signals need to pass a special kind of conductor, the conductor we called compensation conductor. Different thermocouples require different compensation conductor, its main function is connected to the thermocouple, away from the power of the reference junction of the thermocouple, so that the reference temperature stability. Compensation wire is divided into compensation type and extended type two kinds, extend the chemical composition of the wire and the compensation of thermocouple is the same, but in practice, to extend the type of wire is not used is the same as the thermocouple material of metal, usually use and thermocouple wires to replace with the same electron density. Compensation and thermocouple wires of the wire are generally not very clear, the positive connection of the thermocouple compensating lead red line, while the cathode connecting the rest of the color. Most of the material compensating lead wires are commonly used copper nickel alloy. Choose the thermocouple used according to the temperature range, the required accuracy, atmosphere, the performance of the measured object, response time and the economic benefits and other comprehensive consideration. - 200 - 500 degrees of thermocouple, 0 1800 degrees of thermocouple. 1, the choice of measurement precision and temperature measurement range temperature at 1300 ~ 1800 ℃, requirements and high accuracy, generally choose B type thermocouple; Required accuracy is not high, atmosphere and allow tungsten-rhenium thermocouples are available, and higher than 1800 ℃ generally choose tungsten-rhenium thermocouples; Temperature at 1000 ~ 1300 ℃ requires accuracy and higher available S type thermocouple and N type thermocouple; Under 1000 ℃ in general with K type thermocouple and N type thermocouple, below 400 ℃ general use E type thermocouple; Negative temperature under 250 ℃, and usually measured in T thermocouple, T thermocouple during low temperature stability and high precision. 2, the choice of using atmosphere S type, type B, K type thermocouple is suitable for strong oxidation and weak reducing atmosphere, J type and T type thermocouple is suitable for weak oxidizing and reducing atmosphere, if use air tightness better protection tube, the atmosphere is not too strict. 3, durability and thermal response wire diameter of sexual selection of thermocouple better durability, but some response is slow, the heat capacity of thermocouple, response is slow, measure the gradient of temperature, in the case of temperature control, temperature control is poor. Requirements for fast response time and has certain durability requirements, choose more appropriate. 4, the nature of the measured object and state's choice of thermocouple motion object, vibration, temperature measurement requirements of high mechanical strength, high pressure vessel with chemical pollution of the atmosphere requires protecting tube, with electrical interference requirements under the condition of the insulation is quite high. Selection process: model - Index number - Explosion-proof grade - Precision grade - Installation of fixed form - Protecting tube material - The length or insert depth.