Campbell's Bridge

 Campbell's Bridge

This bridge measures unknown mutual inductance in terms of standard mutual inductance

Let   M1 = unknown mutual inductance,

         L1 = self-inductance of secondary of mutual inductance M1,

         M2 = variable standard mutual inductance,

          L2 = self-inductance of secondary of mutual inductance M2,

and   R1,R2,R3,R4 = non - inductive resistances.

There are two steps in balancing the process.

1.    Detacr is connected between b and d and the balanced point is obtained then the requirement of balance is :

                            L1/L2 = R1/R2 = R3/R4

This bridge may be balanced by adjustment of R3 ( or R4) and R1 ( or R2).

2.    Then we connected between b' and d' . Keeping adjustment in step1  then variable mutual inductance M2 is varied to get balance point Then 

                            M1/M2 = R3/R4

                            M1 = M2.( R3/R4 )