working Principle: strip the two rolled each other plates of the metals with different coefficients of expansion (bimetal) that bends when the temperature changes.
the Bending is roughly proportional to the temperature. The bimetallic strip formed the basis of two different measuring elements:

– coil spring;
– spiral spring.

as a result of mechanical deformation of the bimetallic plate when the temperature changes in these elements there is a rotational movement. If the outer end of the bimetal measuring system is fixed securely, the other end without any intermediate element will rotate a pointer shaft. The ranges of the readings lie between -70 °C and + 600 °C during the measurements with the accuracy class 1 and 2 according to DIN 16203.