Abstract: The thermocouple is a low-cost, sturdy and durable temperature sensor. In the comprehensive testing equipment part of the temperature measurement that does not require high test accuracy, thermocouples are usually used as sensors. Thermocouples are usually combined with extension cords and display instruments to form a set of measurement systems. In order to reduce the cost and cabinet installation design, sometimes it is necessary to introduce a relay to achieve the purpose of separate measurement. The addition of electrical components to the measurement system will affect the measurement accuracy and uncertainty. Analyze the principle of thermocouple temperature measurement and the working principle of relay structure. Analyze the influence of adding an electromagnetic relay in the thermocouple measurement system on the design of the signal conditioning circuit, and verify the influence of different circuit designs on the uncertainty of the measurement system through experiments, and give a set of suitable circuit design schemes. The test results show that there are two schemes: no relay connection in the measurement system and 1 relay normally open contact in the measurement system, and the measurement uncertainty is U<1℃. This research provides reference for the design of the subsequent thermocouple measurement system.

Key words: Thermocouple, Eelectromagnetic relay, Measurement uncertainty