This bridge (Fig.1) measures mutual inductance in terms of a known self-inductance. The same bridge, slightly modified, was used by Campbell to measure a self-inductance in terms of known mutual inductance.
Fig. 1. Heaviside mutual inductance bridge
Let , M= unknown mutual Inductance ,
L1= self-inductance of secondary of mutual inductance ,
L2= known self-inductance ,
R1, R2, R3, R4= non inductive resistors,
At balance voltage drop between b and c must equal the voltage drop between d and c. Also the votage drop across a-b-c must equal the voltage drop across a-d-c. Thus we have the following equations at balance.
It is clear from Eqn. (2), that L1, the self inductance of the secondary of the mutual inductor must be known in order that M be measured by this method.
In case, R3=R4, we get,
This method can be used for measurement of self-inductance.