Anderson's Bridge
Let us understand why there is need of Anderson's bridge though we have Maxwell bridge and Hay's bridge to measure quality factor of the circuit. The main disadvantage of using Hay's bridge and Maxwell bridge is that, they are unsuitable of measuring the low quality factor. However Hay's bridge and Maxwell bridge are suitable for measuring accurately high and medium quality factor respectively. So, there is need of bridge which can measure low quality factor and this bridge is modified Maxwell's bridge and known as Anderson's bridge.Actually this bridge is the modified Maxwell inductor capacitance bridge. In this bridge double balance can obtained by fixing the value of capacitance and changing the value of electrical resistance only. It is well known for its accuracy of measuring inductor from few micro Henry to several Henry. The unknown value of self inductor is measured by method of comparison of known value of electrical resistance and capacitance. Let us consider the actual circuit diagram of Anderson's bridge.(see figure given below).
Putting the value of ic in above
equations, we get
The above equation (7) obtained is more complex that we have obtained in Maxwell bridge. On observing the above equations we can easily say that to obtain convergence of balance more easily, one should make alternate adjustments of r1 and r in Anderson’s bridge.
Now let us look how we can obtain the value of unknown inductor experimentally. At first set the signal generator frequency at audible range. Now adjust r1 and r such that phones gives a minimum sound. Measure the values of r1 and r (obtained after these adjustments) with the help of multimeter. Use the formula that we have derived above in order to find out the value of unknown inductance. The experiment can be repeated with the different value of standard capacitor.
Phasor Diagram of Anderson's Bridge
Let us mark the voltage drops across ab ,bc, cd and ad as e1, e2, e3 and e4 as shown in figure above.Advantages of Anderson's Bridge
(1) It is very easy to obtain the balance point in Anderson's bridge as compared to Maxwell bridge in case of low quality factor coils.(2) There is no need of variable standard capacitor is required instead of thin a fixed value capacitor is used.
(3) This bridge also gives accurate result for determination of capacitance in terms of inductance.
Disadvantages of Anderson's Bridge
(1) The equations obtained for inductor in this bridge is more complex as complex as compared to Maxwell's bridge. (2) The addition of capacitor junction increases complexity as well as difficulty of shielding the bridge.Considering above all the advantages and disadvantages, Maxwell bridge is preferred over Anderson's bridge whenever use of variable capacitor is permissible.

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