When two kinds of material with different components compose a
conductor loop, there is a temperature gradient, and will be current
through the loop. At this time, there will be the electromotive force
between the two ends and this is called the Seebeck effect (Seebeck
effect), which is the working principle of
thermocouple.
These two different homogeneous conductors work as the thermodes, and
the end with higher temperature is a working end, while the other one
with the lower temperature is a free end, the free end usually at a
constant temperature. According to the function relationship between
temperature and the electromotive force, we can make the thermocouple
indexing table; indexing table is obtained under the conditions that the
temperature of free end is at zero degree Celsius below, different
thermocouples with different indexing table.
When the
thermocouple loop is connected with the third metal material, as long as
the two contact of the material are in the same temperature, the
electromotive force generated by the thermocouple will remain unchanged,
which is not affected by the third kinds of metallic access in the
loop. Therefore, while the thermocouple is measuring the temperature, we
can access measurement instruments, and once the electromotive force is
measured, we can know the temperature of the measured medium.
