Maxwell Bridge (Measurement of Inductance)

 Maxwell Bridge (Measurement of Inductance)

Maxwell bridge can be used to measure inductance by comparison either with a variable standard self-inductance or with a standard variable capacitance. These two measurement methods can be done by using two different Maxwell bridge forms.

Maxwell Inductance Bridge

In this bridge arrangement the value of unknown inductance is measured by comparison with a variable standard self-inductance. Figure 2.12 shows the circuit arrangement and phasor diagram for Maxwell’s inductance bridge under balance condition. Two branches bc and cd consist of non-inductive resistance R₃ and R₄. One of the arms ad consists of variable inductance L₂ of fixed internal resistance r₂ connected in series with variable resistance R₂. The remaining arm ab consists of unknown inductance L_x of resistance R_x. A source of current is applied to two opposite junctions across ac and a null detector is connected to the other two junctions b and d.

Hence, the impedances of four arms are

                                      Z₁ = R_x + jwL_x

                                      Z₂ = R₂ + r₂ + jwL₂

                                     Z₃ = R₃

                                        Z₄ = R₄