Why can't thermocouples use ordinary connectors?

Ordinary connectors, here we refer to connectors with copper alloy as the contact. Copper and copper alloys are widely used in electrical conductivity because of their excellent electrical properties. Thermocouple connectors are specially made for transmitting thermocouple signals.

We know that the positive and negative poles of thermocouples are made of special metal materials, which generate extremely weak electrical signals. In order to ensure accurate signals, thermocouple temperature measuring wires and extension wires must use thermocouple-specific materials. So why can't ordinary connectors be used to transmit thermocouple signals?

According to the intermediate conductor law, one of the four laws of thermocouples, a third conductor (intermediate conductor) is connected to the original thermocouple circuit. As long as the temperatures at both ends of the intermediate conductor are consistent, the connection of the intermediate conductor has no effect on the temperature measurement results. If the temperatures at both ends of the copper connector we use are inconsistent, measurement errors will be introduced. We have done experiments, using a hot air gun to heat up one end of the copper connector to increase the temperature difference at both ends of the copper needle. As a result, the thermocouple temperature measurement error is as high as tens or even hundreds of degrees Celsius, and the length of the copper connector is only about 2cm.

Since the temperature measurement principle of thermocouples is closely related to materials, there are requirements for the selection of materials, and generally special wires and connectors with specific graduation numbers are used.