The application principle of thermocouple

Thermocouple temperature test is commonly used in industry one of the measuring element. The strengths of the thermocouple is numerous, another is: 1, the survey precision of high temperature due to the thermocouple direct contact with the object being measured, not affected by middle medium. Heat quickly and accurately. 2 and surveying the temperature range of commonly used thermocouple from - 50 ~ + 1600 ℃ can be continued exploration, some special thermocouple to - can be obtained 269℃（ www。 wuxiyibiao。 com） , great to + 2800 ℃ ( Such as tungsten - Rhenium) 。 3, simple construction, convenient use thermocouple is usually composed of two different kinds of metal wire, and is not affected by volume and the limit of the opening, have tried my best to take care of outside casing, extremely convenient to use. Basic principle of thermocouple temperature measurement will be two different material A conductor or semi-conductor A and B welding together, constitute A closed loop, as shown in figure 2 1 - 1. When conductor A and B two persistent point temperature difference between 1 and 2, between the initiation of electromotive force, thus forming A volume of current in the circuit, this kind of phenomenon called the thermoelectric effect. Thermocouple is in using this effect to office. Thermocouple category and structure formation of the category a, thermocouple commonly used thermocouple can be divided into two categories, thermocouple and non standard thermocouples. Deployment by using standard thermocouple is refers to the state standard specifies its thermoelectric potential and the relationship between temperature, permitted error, and unify the norm tables of thermocouple, it has exposed its composed of a set of instruments to choose from. Non-standard thermocouple number in the b range or level than standard thermocouple, however, are usually not unify indexing table, mainly used in the survey of some special occasions. Standardized thermocouple since January 1, 1988 in our country, the thermocouple and thermal resistance is all according to IEC international standard production, and specify the S, B, E, K, R, J, T seven standardization thermocouple for our country to unify the default type thermocouple. Second, the structure of thermocouple ceremony in order to guarantee reliable and safe office thermocouple, requirements for its structure as follows: 1, the composition of the thermocouple two hot electrode welding must be strong. 2, two hot electrode insulation between you and me should be better, in case of short circuit. 3, to repay the conductor and the free cod of a thermocouple petition to convenience dependable. 4, try to take care of casing should be able to guarantee thermal electrode and harmful medium filling the middle partition. The thermocouple cold end temperature pay for thermocouple materials are usually more high value ( Surprise is that the right and use expensive metal) And the temperature measurement points to instrument are far away, in order to save heat bimetallic material, reduce costs, generally considered appropriate and repay use wire thermocouple cold end (the The free end) Extended to more reliable stem indoor temperature, a petition to the meter terminals. Is important to point out that, the effect of repay thermocouple wires only extend thermal electrode, make moves to curb chamber of the cold junction of the thermocouple meter terminal, in itself does not eliminate the cold end temperature change on the influence of temperature, can't afford to pay the utility. Because of this, still need to see fit and use other modified square method to repay the cold end temperature t0 indicates influence on measuring temperature 0 ℃. Make sure to type when in use repay thermocouple wires are suitable, the polarity miss wrong, repay the conductor and the thermocouple petition the temperature not over 100 ℃.