The w indings of coils 1 and 2 are connected into an a-с circuit
in such manner th at they set up magnetic fluxes in opposite
directions. Therefore, in the m id d le position of arm ature 3 w ith
the secondary w ind in g, the resultant flux equals zero and there
is no current in the w in d in g of armature 3. W hen armature 3
is displaced by the force to be measured, the fluxes in coils 1
and 2 are no longer equal, a flux is set up in armature 3 that generates
an emf in its w in d in g proportional to the displacement of
the arm ature and to the force being measured. The emf induced
in the w in d in g of armature 3 can be measured by ferrodynamic
instrument 4 having independent excitation.
$4388$SmE,M$