Characteristic Analysis And Experimental Method Study Of Thermocouple Inhomogeneity

Thermocouple (TC) inhomogeneity is the main factor which affects its temperature measurement accuracy improved. The paper described and analyzed the principle and the errors of TC inhomogeneity with measuring temperature. In order to improve TCs of platinum rhodium 10-platinum temperature measurement accuracy,a set of measurement system on basis of two medium method was built which could measure inhomogeneity of TCs reliably. For the poor temperature homogeneity of liquid bath, the method of adding auxiliary platinic resistance thermometer was we put forward, in order to correcting the changes of temperature of liquid bath.This paper, TCs are scanned at 250℃in a stirred-liquid bath. The inhomogeneity of new and old TCs was compared , and the uncertainty of measurement experiment was evaluate. From the scan results, old TCs often was used under the action of temperature gradient thermal environment in the long time, impurity, annealing, etc, making its inhomogeneity greatly bad. While new making TCs inhomogeneity are relatively small, and their inhomogeneity thermoelectric motive force(EMF)curve exist consistency. Through analyzing the character of old and new TCs inhomogeneity, the effect of high temperature in course of TCs'manufactured and used, the oxidation of thermoelements is the main factor which caused TCs inhomogeneity.In order to make sure the relationships of TC inhomogeneity at different temperature,in this paper,some scanning and analyzing of TC inhomogeneity was done in silver heat-pipe furnace(961.78℃). By means of comparing the scanning results of TC inhomogeneity at 25 cm long thermoelements in liquid bath and 12 cm long thermoelements in silver heat-pipe furnace, the possible conclusion that inhomogeneity at different temperature has direct proportion relations was got.According to the experimental results, the conclusion that there is some errors estimation at the evaluation of uncertainty of type S TCs inhomogeneity in the process of verification of TCs was achieved. A suggestion is put forward that uncertainty value should be given according to the specific measurement temperature, or accordance to the temperature of thermoelectric power relation.