焊锡对热电偶测温误差影响分析

航天器真空热试验中为了消除焊锡可能带来的温差热电势，文章采用Keithley 2750数据测量系统，通过比较法对焊锡与铜、焊锡与康铜之间的温差热电势进行了测试分析。标准热电偶选择铜-康铜热电偶，测试温度范围为-195～+75℃。测试时，热电偶冷端为冰水混合物，热端为液氮浸泡过的不锈钢圆柱体或热水瓶。为了确保回路中的焊点处于相同的热环境条件，可采用多层隔热组件进行包覆，避免接插件直接接触热沉。

Effect of soldering tin on thermocouple measurement error

The thermo-emf between the Cu and SnPb and that between the CuNi and SnPb are studied with a comparative method. The type T (copper vs copper-nickel) thermocouple is chosen as a standard thermocouple, as is widely used in spacecraft thermal vacuum test. The experiment temperature ranges from -195 ℃ to 75 ℃. Keithley 2750 data acquisition system is used to record the measurements of the thermo-emf, which includes the 2750 digital multimeters, 7702 connection boxes, E5810 gateway and computer with special measurement software. The cold junction of the thermocouple is ice water mixture and the hot junction is stainless steel cylinder or thermos. The temperature difference and thermo-emf of the tin-copper and those of the copper-Constantan are treated by curve fitting. The results show that the thermo-emf of the CuNi-SnPb is 92% of that of type T thermocouple, and the thermo-emf of the Cu-SnPb is 7.1% of that of type T thermocouple with the same temperature difference. In order to eliminate the thermo-emf caused by CuNi, the solder joint of the loop should be kept in the same thermal boundary conditions, and some measures are taken, such as coating the thermocouple with multi-layer insulation components or making sure that the connector is some distance away from the heat sink.