How to Find the Value of Self-Inductance and its Inherent Resistance of a Given Coil Using Anderson Bridge

Anderson Bridge:-

The Bridge is used to measure the self-inductance of a coil in terms of standard known capacitor. The bridge and its connection diagrams are as shown below:

Anderson Bridge

Connection Diagram

The first figure shows the Anderson Bridge circuit diagram and second figure shows the connections to be made in the kit. It indicates the headphones detector, Galvanometer G, 1KHz Supply, 3V D.C Supply and inductance.

For null detection which occurs when the bridge is in balanced condition, it can be shown that the self inductance is given by L = CR(Q + 2r)

Procedure for Anderson’s Bridge:-

1. Make connections as shown in the connection diagram.
2. Here Galvanometer is the detector and 3V D.C supply is the source to the unknown inductance.
3. Adjust the dial R to get balance point with the galvanometer.
4. Using the resistance dial ‘S’ for fine balancing, note down the values of R
5. Replace D.C supply with A.C supply of 1KHz frequency. Replace the galvanometer with headphones for getting null point.
6. Set standard capacitance ‘C’ at position 0.1mF and adjust resistance dial ‘r’ till you get balance point as indicated by minimum sound in the headphones. Note the values resistance ‘r’ and calculate unknown inductance using the formula L = CR(Q + 2r). The range of Q factor for Anderson Bridge is 1 < Q < 10
7. Repeat above steps choosing different values of inductance and capacitance and tabulate the results.

Here in the Anderson Bridge, the term Bridge Sensitivity (S_B) is defined as the deflection of the galvanometer for unit fractional change in the unknown quantity. And besides vibrational galvanometers, other 2 types of detectors that are used most are headphones and tunable amplifier detectors.

Advantages of Anderson Bridge:-

• Fixed capacitor is used instead of variable capacitor as in case of maxwell’s bridge.
• The bridge is used for accurate determination of inductance in terms of capacitance.

Disadvantages of Anderson Bridge:-

• Bridge is more complex.
• An additional junction point increased the difficulty of shielding the bridge.
• Complex balance equations.