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4 Thermocouples
Thermocouples may be insulated or non-insulated/grounded.
The non-insulated construction produces faster response times. However, no electrical insulation and
no galvanic isolation between the thermocouple and the protection tube can be provided here. Take this
into account when connecting the thermocouple, so as to prevent potential entrainments, etc.
4.2 Operating principle
The Seebeck effect (= thermoelectric effect) is the key factor determining how thermocouples operate.
Its basic principle is as follows:
If there is a temperature difference along a wire, this will cause the charge carriers to move. The extent
to which the charge carriers move depends on the electrical features of the material.
If two wires made of different materials are connected and exposed to a temperature difference, a volt-
age that depends on the prevailing temperature difference will be present at both open ends.
If the temperature at the open end is known, you can infer the temperature at the connection point.
To carry out the temperature measurement, the temperature at the open end (right) must be known. If
this is not the case, thermal cables will need to be used to extend the thermocouple into a zone that has
a known, constant temperature. If a constant temperature cannot be ensured, the temperature of the
cold junction will need to be acquired.
Insulated construction Non-insulated construction
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