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

Let,

  • 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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Hay’s bridge for measurement of inductance

Hay’s bridge for measurement of inductance :

The Hay’s bridge is modification of the Maxwell’s bridge. The connection diagram of the Hay’s bridge is shown in figure below. This Hay’s bridge uses a resistor in series with a standard capacitor (unlike the Maxwell’s bridge which uses a resistance in parallel with the capacitor).

Hay's bridge for measurement of inductance
Hay’s bridge for measurement of inductance

Let

L1=unknown resistance having a resistance R1,

R2, R3, R4=known non-inductive resistance,

C4=standard capacitor.

At balance,

1

Separating real and imaginary term, we obtain:

2

Solving the above two equations we have,

3

The Q factor of the coil is :

4

Advantages of the Hay’s bridge:

1)      This bridge gives very simple expression for unknown inductance for high Q coils, and is suitable for coils having Q > 10.

2)      This bridge also gives the simple expression for Q factor.

3)      From expression of Q factor it is clear that for high Q factor the value of resistance R4 should be small.

Disadvantages of Hay’s bridge:

1)      The Hay’s bridge is suited for measurement of high Q inductors, specially those inductors having Q > 10. For inductors having Q values smaller than 10, the term (1/Q)^2 in the expression for inductance L1 becomes rather important and thus cannot be neglected. Hence this bridge is not suited for measurement of coils having Q less than 10 and for thse applications a Maxwell’s bridge is more suited.

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