Maxwell’s Bridge Circuit and the expression for the unknown element at balance

• Maxwell's Bridge:                    

 measures an unknown inductance in of standard arm offers the advantage of compactness and easy shielding.  The capacitor is nearly a loss-less component.

One arm has a resistance Rx in parallel with Cu and hence it is easier to write the balance equation using the admittance of arm 1 instead of the impedance.

The general equation for bridge balance is

From equation of Zx we get

Equating real terms and imaginary terms we have

Maxwell's bridge is limited to the measurement of low Q values (1 -10).The measurement is impartial of the excitation frequency.The scale of the resistance can be calibrated to understand inductance directly.

The Maxwell bridge working with a fixed capacitor has the disadvantage that there an interaction between the resistance and reactance balances. It can be avoids: by varying the capacitances, alternatively of R2 and ft, to obtain a reactance balance. Even so, the bridge can be made to read directly in Q.

The bridge is particularly suited for inductances measurements, since comparison on with a capacitor is more ideal than with another inductance. Industrial bridges measure from 1 – 1000H. With ± 2% error. (If the Q is very becomes excessively large and it is impractical to obtain a satisfactory variable standard resistance in the range of values required).