1. ‘ELECTRICAL MEASUREMENTS AND MEASURING INSTRUMENT
Subject Code: Gujarat Technological University (GTU)

2. Bachelor of Engineering
Electrical Engineering
Department of Electrical Engineering
Government Engineering College, Dahod
Jhalod Road, Dahod
Gujarat

3. INDEX INTRODUCTION A.C.Bridges Wheat Stone Bridge Maxwell’s Bridge
Hay’s Bridge
Anderson Bridge
Heaviside Mutual Inductance Bridge
De-Sauty Bridge
Schering Bridge

4. A.C.Bridges

5. A.C.Bridges are those circuits which are used to measured the unknown resistances, capacitance ,inductance ,frequency and mutual inductance.

6. Wheat Stone Bridge
Wheatstone bridge operates on d.c supply and the detector used to detect the balanced condition of bridge.
The bridge is said to be under condition when galvanometer shows zero deflection.
This method is used for measurement of medium resistance very accurately.

7. Fig. a
R R R 1 R 3 = R 2 R4
R R 3

8. Inductance and capacitance can also be measured by a similar four-arm bridge, as shown in fig.b.
In this case the alternating current source is employed by a vibration galvanometer.

9. Fig.b

10. Maxwell’s Bridge
In the Maxwell’s 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.

11. Fig.
Q=wR1C1

12. 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.

14. 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.

15. Fig
L3= C1 R2 R R3= w C1 R1 R2 R4
1+w R1 C w R1 C1

16. Heaviside Mutual Inductance Bridge
It is a mutual inductance bridge and is used for measuring self-inductance over a wide range in terms of mutual inductometer readings.
The connections for Heaviside’s bridge employing a standard variable mutual inductance.

17. The primary of the mutual inductometer is inserted in the supply circuit and the secondary having self-inductance L2 and resistance R2 is put in arm 2 of the bridge.
The unknown inductive impedance having self- inductance of L1 and resistance R1 is placed in arm 1.
The other two arms have pure resistance of R3 and R4. as shown in fig.

19. De Sauty bridge
We will consider only De Sauty bridge method of comparing two capacitances the bridge has maximum sensitivity when C2 = C3.
The simplicity of this method is offset by the impossibility of obtaining a perfect balance if both the capacitors are not free from the dielectric loss.
A perfect balance can only be obtained if air capacitors are used. as shown in fig.

20. Fig.
C2= C3 R1 R2

21. 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.

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

23. PANDEY LEENA S. 130180109052 SAXENA MONALI A. 130180109099
MADE BY:-
PANDEY LEENA S.
SAXENA MONALI A.
RATHOD NIKITA S.