What is the difference between the standard thermocouple and non-standard thermocouple _ instrument

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) Changes in temperature, will be affected 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. Thermocouple cold junction compensation is usually used in a composed of thermocouple cold end series bridge. The three bridge arms for standard resistance, in addition, there are a bridge arm by ( Copper) Thermocouple. When the cold end temperature change ( Rise, for example) Thermocouple thermoelectric potential will change (to produce Reduce) The thermocouple resistance in series, while the bridge will be change and make the change at the ends of the bridge voltage also ( Higher) 。 If the parameter is a good choice and wiring is correct, produced by the bridge voltage as it happens and thermoelectric potential changes over temperature equal to the amount, the thermocouple measurement circuit, the total output voltage ( Potential) Exactly reflect the measured temperature value. This is the thermocouple cold junction compensation principle. Industrial commonly used thermocouple in fact there are two types, one is a standard thermocouple is another kind of thermocouple. Standard thermocouple is what we normally use, its production standards comply with the national standard, either from the relationship between thermoelectric potential and temperature, the permissible error are in strict accordance with national standards. At the same time supporting digital display table is also customized according to the national standard. For non standard thermocouple is not does not meet the technical requirements, but the standard is not very widely used, suitable for individual industrial units, has a certain particularity. Domestic industrial products started a little bit late, to the standard production requirement of thermocouple should be back on January 1, 1988, the thermocouple custom made seven standards in China, s, b, e, k, r, j, t. S, r, b belong to precious metal thermocouple, n, k, e, j, t belong to cheap metal thermocouple. Then the seven standards respectively means what meaning? S degree, characterized by strong antioxidant properties, appropriate continuous use in oxidation, the inert atmosphere, the long-term use of temperature 1400 ℃, 1600 ℃ in the short term. Of (among) all the thermocouple, s degree, high precision grade, often used as a standard thermocouple; R degree, compared with s degree, in addition to the thermoelectric emfs big by about 15%, other properties are almost identical; J index number is characteristic of both can be used for oxidizing atmosphere ( Using the maximum temperature 750 ℃) , also can be used in a reducing atmosphere ( Using the maximum temperature 950 ℃) And resist the corrosion of gas h2 and co, used in refining and chemical industry; B dividing minimal thermoelectric emfs at room temperature, so the general without compensation conductor when measuring. Its long using temperature is 1600 ℃, 1800 ℃ in the short term. Can be used in the oxidation or neutral atmosphere, and also can be used under vacuum conditions in short term. K index number is characterized by strong antioxidant properties, appropriate continuous use in oxidation, the inert atmosphere, the long-term use of temperature 1000 ℃, 1200 ℃ in the short term. Widely used in all thermocouple; N the characteristics of the index number is 1300 ℃ high temperature oxidation resistance is strong, the long-term stability of the thermoelectric emfs and short-term thermal cycle of good repeatability, nuclear radiation resistance and low temperature resistance, can partially replace # s dividing thermocouple; E the characteristics of the index number is in commonly used thermocouple, the thermoelectric emfs, namely high sensitivity. Appropriate continuous use in oxidation, the inert atmosphere, using temperature 0 800℃; T index number of all the cheap metal thermocouple is the feature of high precision grade, usually used to measure the temperature under 300 ℃.