engleski

TESTING OF THERMOCOUPLES FOR INHOMOGENEITY

It is good calibration practice to test thermocouples for homogeneity of the Seeback’ s coefficient during calibration process. If change in homogeneity the coefficient, commonly known as inhomogeneity is not detected, thermometer although calibrated might not be able to measure temperature correctly. Several different testing techniques are developed, depending on type of the thermocouple and the equipment available. In order to automate process of thermocouple inhomogeneity testing for all applicable testing methods a Thermocouple Inhomogeneity Testing Device was developed in Laboratory for Process Measurement (LPM), University of Zagreb. The device is mostly used for the testing of thermocouple inhomogeneity in conjunction with heater moving along the thermocouple. The sled for mounting of the heater or the thermometer is translated by a threaded shaft and a step motor in horizontal axis, vertical axis or its sliding direction can be tilted in six steps between those two positions. Sled is mounted on shafts guides with precision linear ball bearing, which allow for smooth translation. The frame of the device is designed with adjustable height and distance between legs, which allows testing in most available metrological baths or furnaces. System is controlled by custom made program on LabView platform, with ability to automatically acquire, store and analyze data test data. Variation of the thermovoltage recorded during measurement is used in calculation of the uncertainty of the calibration. This paper describes the techniques for inhomogeneity testing and design of the testing device. Interpretation of the measurement results and calculation of inhomogeneity related component of the uncertainty budget is presented

inhomogeneity testing; thermocouple

nije evidentirano