This document discusses several types of AC bridges used to measure unknown resistances, capacitances, and inductances. The Maxwell's inductance bridge uses two known impedances on one side and two pure resistances on the other to measure an unknown impedance. The Maxwell's capacitance bridge can measure unknown inductance by compensating the positive phase angle of inductance with the negative phase angle of capacitance. The Anderson bridge precisely measures unknown inductance over a wide range by using a known capacitance and resistance.

1. A.C.Bridges
By :-
Ranjal Agrawal (0105EC131087)
EC 3rd Sem.

2.  A.C.Bridges are those circuits which are
used to measured the unknown resistances,
capacitance and inductance.

3. Maxwell’s inductance Bridge
 In the Maxwell’s inductance bridge ,there
are two pure resistances used for balance
relations but on other side or arms the two
known impedances are used.
 The known impedances and the resistances
make the unknown impedances as Z1 and
Z2.Such a network is known as Maxwell’s
A.C.. Bridge. As shown in fig.

4. Fig.
(R1 + jwL1 )R3 = (R4 + jwL4 )R2

5. Maxwell’s Capacitance Bridge
 In the Maxwell’s capacitance Bridge the
positive phase angle of the inductance may
be compensated by the negative phase
angle of the capacitance impedance put in
the opposite arm.
 The unknown inductance then becomes
known in terms of the capacitance. As
shown in fig.

6. Fig.
R2 R4 + jwL1 R2 = R1 R3 + jwCR1 R2 R3

7. Anderson Bridge
 In the Anderson Bridge the unknown
inductance is measured in terms of a known
capacitance and resistance.
 This method is capable of precise measurements
of inductance over a wide range of values from
a few micro-henrys to several henrys and is the
best bridge method.

9. Hay’s Bridge
 It is also a modification of the Maxwell’s Wien
Bridge and is particularly useful if the phase
angle of the inductive impedance is large.
 In this case a comparatively smaller series
resistance R1 is used instead of a parallel
résistance.( which has to be of a very large
value) as shown in fig.

10. Fig
L3= C1 R2 R4 R3= w C1 R1 R2 R4
1+w R1 C1 1+w R1 C1

11. Schering Bridge
 Schering bridge used for the measurement
of capacitance and dielectric loss of a
capacitor.
 It is a device for comparing an imperfect
capacitor C2 in terms of a loss-free
standard capacitor C1. As shown in fig.

12. Fig.
C3 = C2 ( R1 / R2 ) R3 = R2 ( C1 / C2 )

13. Wien Series Bridge
 It is a simple ratio bridge and is used for
audio-frequency measurement of
capacitance over a wide range. As shown
in fig.

14. Fig.
R1=R2R4/R3 C1=C4(R3/R2)

15. Wien Parallel Bridge
 It is also a ratio bridge used mainly as the
feedback network in the wide range audio-
frequency R-C oscillators.
 It is may be used for the measurement of
the audio-frequency but it is not as
accurate as the modern digital frequency
meters. As shown in fig.

16. Fig.
C2 = R2 = R3
C1 R1 R4

17. THANK YOU