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Thermocouple temperature measurement method of experimental design _ instrument

by:JVTIA     2020-10-28
Rapid temperature measuring thermocouple calibration method and the device is a kind of metallic melts fast thermocouple calibration method and device. The device is mainly composed of a measured accidentally end can accommodate two quartz tube flat heating coil, two measured accidentally calibration of the same shape and thermocouple and the corresponding temperature control display output device. Verification method is to first use two calibration thermocouple find the two calibration in this flat heating coil accidentally thermoelectric potential of the same point, were I to replace one of the calibration accidentally, in the case of other conditions unchanged, after being checked my reading stability compared with the calibration accidentally readings can be accidentally quantities are accurate. This method provides a rapid temperature measuring thermocouple laboratory verification method, but the temperature point of rapid temperature measuring thermocouple in multiple test and comprehensive assessment. Thermocouple cold junction compensation method of properly resolve industrial thermocouple cold junction compensation method, is very important, because, there is no right choice the accurate measurement of cold junction compensation method can lead to correct or not, the error is very big, easy to have an accident, according to field experience, some mistakes because of the cold end compensation methods product quality problem is the shoe to see not fresh, which is what is called: thermocouple cold junction compensation? Measure the end for the hot end, by the end of the lead connected to the measurement circuit is called the cold end, thermocouple measuring temperature for its cold side temperature is kept constant, the thermoelectric potential size had certain proportion relationship with measuring temperature. 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 types commonly used thermocouple could be divided into two types: standard thermocouple and non-standard thermocouple. Using standard thermocouple refers to the national standard specifies its thermoelectric potential and the relationship between temperature, permissible error, and a unified standard score table of thermocouple, it has with matching display instrument to choose from. Non-standard thermocouple or on the order of magnitude less than the range using standardized thermocouple, generally no unified indexing table, mainly used for the measurement of some special occasions. 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. Thermocouple is don't need to cold junction compensation, because of the cold junction compensation refers to the thermocouple thermoelectric potential is zero for the standard measurement, it does not need to drive source. And instrument at room temperature, so for thermocouple, it is not at 0 degrees as a standard for measuring, thus the uncertainty. So in the circuit of instrument, is typically a cold junction compensation circuit. Thermocouple and thermocouple temperature measuring principle is different, it is to rely on their own resistance with the temperature change and change the principle of temperature measurement, we give platinum resistance for a current incentives, direct reading voltage on both ends, with almost no instrument in temperature. If the four wire measurement, the distance of the instrument and sensor can also be further. Thermocouple cold end temperature compensation because thermocouple material generally is special, and temperature measuring points are far away the distance to the instrument, in order to save thermocouple materials, reduce cost, usually adopt the compensating conductor (of the cold junction of the thermocouple The free end) Reaches to the relatively stable control indoor temperature and connected to the meter terminals. It must be pointed out that the role of the thermocouple compensation wire only extend thermal electrode, make moves to the control room of the cold junction of the thermocouple meter terminal, it itself does not eliminate the cold end temperature change on the influence of temperature, no compensation. So, still need other correction method is used to compensate the cold end temperature t0 indicates influence on measuring temperature 0 ℃. Must pay attention to when using thermocouple compensating conductor model match, cannot be wrong polarity, compensation conductor should be connected to the thermocouple temperature should not exceed 100 ℃.
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