Anderson's Bridge - Construction, working, advantages and disadvantages

Anderson's Bridge is the modification of Maxwell's inductance-capacitance bridge. In Anderson's bridge, a standard capacitor is used for the measurement of self-inductance. The main advantage of this method is that it can be used for the wide range of self-inductance measurement.

The following figure shows Anderson's bridge for the balance conditions.

Anderson's Bridge


  • L1 = Self-inductance to be measured,

  • R1 = resistance of self-inductor,

  • r1 = resistance connected in series with self-inductor,

  • r, R2, R3, Ra = known non-inductive resistances,

  • C = fixed standard capacitor.

At balance,

1 2

Advantages of Anderson's Bridge:

1)      In Anderson's bridge, it is very easy to obtain the balance point as compared to Maxwell’s bridge.

2)      In this bridge, a fixed standard capacitor is used therefore there is no need of costly variable capacitor.

3)      This method is very accurate for measurement of capacitance in terms of inductance.

Disadvantages of Anderson's Bridge:

1) It is more complex as compared with Maxwell’s inductance bridge. It has more parts and hence complex in setting up and manipulate. The balance equations of Anderson's bridge are quite complex and much more tedious.

2) An additional junction point increases the difficulty of shielding the bridge.

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  1. What is the use of resistance r and capacitance C. Is it necessary for the circuit operation

  2. Krishna : The resistance r and capacitance C are essential to the operation of the bridge. Remember the purpose is to determine L1 and R1, but in the equation for the former both quantities r and C appear. Admittedly r and C do not appear in the expression for R1( I will address that latter consideration below).
    I assume your question is motivated by the idea that if C was not present at all and if r was simply shorted out then the bridge circuit as usually drawn would look more like other bridge circuits such as those of Wheatstone(for DC), Schering, Maxwell and Hay in that components exist only around the edges with nothing in the middle except the detector. Clearly it would be impossible to then balance the bridge because then arms BC, CD and DA would each be purely resistive but the remaining arm AB has both resistive and reactive contributions.
    It might be of interest to point out that the equation derived for determining R1 is the same as one would get if C was not built into the circuit( irrespective of whether r is present or not) and the bridge used with a dc source and treated as a Wheatstone bridge. From the preceding sentence one might reckon that the bridge be used first with a dc source to determine R1 then use an ac source to determine L1 - that indeed would be correct if the effective series resistance of the inductor is governed entirely by the resistance of the wire forming its coil, a situation very nearly valid for an air-cored coil. It would be less valid for an inductor with an iron core because of additional heating, equivalent to an effective resistive energy dissipation, arising from eddy currents and magnetic hysteresis in the core material. Thus to determine the EFFECTIVE series resistance under operating conditions of the inductor one should use the ac method as described by Mayuresh.