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1. Scope The length of the metal sleeve from the measuring end is not less than 500mm.
Multiple armored lengths of 1m were combined into different lengths and tested at different calibration temperature points. Among them, the change of the calibration point at 800°C is more obvious, the variation with the length shorter than 500mm reaches -0.56°C, the maximum variation with the length of 500mm is -0.29°C, and the variation with the length greater than 500mm is smaller. Therefore, in JJF1262-2010, it is specified that the length of the metal sleeve to be sheathed is not less than 500 mm.
2. Metering characteristics The metering characteristics of armored thermocouples include room temperature insulation resistance and indication tolerance tolerance specifications.
(1) Insulation resistance at room temperature By measuring the insulation resistance at room temperature between the thermocouples and between the thermode and the metal case, the quality of the mating device can be judged. Therefore, JJF1262-2010 specifies the insulation resistance measurement item at room temperature.
(2) Tolerance of indication value It is judged whether the value of the inspection indication is within the tolerance limit, and the indication tolerances of level 1 and 2 are specified. Since the output signal of the armored thermocouple is terminated to the compensation wire, the compensation wire correction value is added to the deviation calculation formula of the indication value and the index table.
(3) Why does the new system do not anneal before calibration?
In the related standards of the mating couples, it is stipulated that after the new mating couples are annealed, the indicating values ​​are calibrated. In response to this problem, the drafting team selected different types of armored couples to perform a large number of tests before and after annealing (primary and secondary annealing) at different calibration temperature points, whether the first annealing or the second annealing. Compared with the value shown before annealing, the maximum difference is about one-tenth of the tolerance. The test results show that if the even-wire material is fully annealed before leaving the factory, whether or not the new anneal annealing is performed will have little effect on the calibration results. Therefore, JJF1262-2010 omitted the work of anneal before the calibration of the new system.
3. Calibration conditions (1) Environmental conditions Armored thermocouples require that the environment of the electrical test equipment comply with the requirements of their corresponding regulations; the environment of the thermostat equipment should be free of airflow disturbances.
In order to meet the requirements of the measuring zone on the measuring temperature zone (satisfying the length of the diameter of the 5 times thermocouple as the “minimum immersion depth†of the thermocouple), the drafting team designed a length of 80 mm, a hole depth of 65 mm, and an aperture ratio to be calibrated. The uniform metal temperature block with a large diameter (0.5-1.0) mm is used in the assembly, and the index of the tube-type furnace uniform temperature block obtained through a large number of tests is shown in Table 1 of JJF1262-2010. When calibrating, place the geometric center of the temperature block at the geometric center of the tube furnace.
4. Calibration method (1) Calibration of indication Although the measurement range of the mating device is wide, it is limited by the use range of the standard device and the constant temperature device, so the calibration zone is calibrated. The calibration of the armored and even indication values ​​uses a comparison method. According to the size of the diameter, at least 3 calibration temperature points are selected. When calibrating, the compensating wire must be connected to the signal output end (or the signal output terminal lead) of the armored thermocouple, and then the reference end should be placed in the freezing point thermostat.
(2) Depth of insertion of the temperature mounting box below 300°C When calibrating the mounting adapter below the temperature range of 300°C, the insertion temperature of the temperature sensing point of the standard unit and the measuring terminal to be calibrated shall not be less than 200mm. In the relevant standards, it is specified that the standard device and the inserted device have a depth of 300 mm. The drafting team used the first-class platinum resistance thermometer as an etalon, and tested the insertion depths of 200 mm and 300 mm in thermostatic oil tanks and dry well furnaces for different lengths of helium fittings. The maximum difference between the results was only -0.14. °C. The insertion depth of the measuring end should not be less than 200mm.
(3) The impact of the immersion depth of the standard mercury thermometer (original second grade) on the calibration result The standard mercury thermometer (formerly second class) was used as the standardizer. When calibrating an assembly, immersing in the upper or lower limit of the standard thermometer has little effect on the calibration result.
The drafting team immersed the standard mercury thermometer with a calibration temperature point of 200°C and a measuring range of 150°C to 200°C to the upper limit. The calibration results were compared with the calibration results using a standard platinum resistance thermometer as the standard. The maximum difference was 0.03°C.
The standard mercury thermometer with a range of 200°C to 250°C is immersed to the lower limit. The calibration result is compared with the calibration result using a standard platinum resistance thermometer as the standard. The maximum difference is 0.05°C.
(4) Depth of insertion of thermocouples in the temperature zone above 300°C. Standard thermocouples are fitted with high-aluminum protection tubes and are fitted into the holes of the temperature-equalization block in the tube furnace respectively. The measurement ends are in contact with the bottom of each hole. This thermocouple insertion depth is about 325mm.
(5) Appendix
Specification of Armored Thermocouple Specifications
Specification of Armored Thermocouple Specifications
(2) Constant temperature equipment The constant temperature device above 300°C should be equipped with a uniform temperature block, which is derived from the test result of the tube-type furnace installed with the "hole" metal material uniform temperature block. The test data in this area has been reported to the AQSIQ.