42.

Principles of Induction Coil.

a. Comparison with transformer. The induction coil is essentially a transformer. This similarity may be noted

by comparing the circuit diagrams of the transformer and induction coil in figure 36. Electrically, the action of an

induction coil is the same as that of a transformer, and the same basic principles apply to it. The transformer in its

simplest form consists of two conducting coils which have mutual inductance between them. The common connection

between the windings of the induction coil does not affect the mutual inductance between the coils. As a result of the

mutual inductance, a varying current in one winding induces an ac voltage in the other. The value of the induced ac

voltage depends on the turns ratio and on the rate at which the current changes: the higher the rate of change, the greater

the induced voltage. The induced voltage has the waveshape of the changing current. This action of the transformer is

explained in detail in TM 11-681.

FIGURE 36. Comparison of Transformer

and Induction Coil.