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When the-jcircuit is closed w ith switch 5, b im e ta llic strips 2
are heated and bend in the directions shown by the arrows.
Strips 2 continue to bend u n til they reach contact springs 6.
Further bending of the strips leads to retraction of contacts 3
from movable element 1. This breaks the circuit. After this,
bim etallic strips 2 oscillate about movable element 1. At this,
the temperature of each strip is m aintaine d at a definite level.
The temperatures of the two strips can be equalized by varying
the distances between strips 2 and contact springs 6. Now, when
element 1 is displaced from its m iddle position, one strip is
heated to a higher temperature and the temperature of the
other strip is lowered. This establishes a temperature drop that
can be measured w ith differential thermocouple 7 and galvanometer
4. The reading depends directly on the displacement
of element 1.