## Objective

This bridge measures mutual inductance in terms of known self- Inductance.

Figure 1 shows a modified Heaviside Bridge. This modification is due to Campbell. This is used to measure a self inductance in terms of a mutual Inductance. In this case an additional balancing coil L, R, is included in arm ad in series with inductor under test. An additional resistance r is put in arm ab. Balance is obtained by varying M and r. A short circuiting switch is placed across the coil R_{2}, L_{2} under measurement. Two sets of readings are taken one with switch (K) being open and other switch being closed. Let values of M and r, be M_{1} and r_{1} with switch open, and M_{2 }and r_{2 }with switch closed.

Fig.1.

Applying voltage across abc is equal to voltage across adc.

Switch (K) open

and with Switch(K) closed

This is a good example of the methods adopted to eliminate the effects of leads etc.