AC Bridge.

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Transcript AC Bridge.

Balaji Engineering College
Measurement of inductance by using AC bridge
Prepared by:Lakhnotra Kanji(131090109021)
Nandaniya Jayesh(131090109022)
Odedra Nagajan(131090109023)
Contain:1.Introduction
2.Operation of AC Bridge
3.Maxwell’s Bridge
4.Hay’s Bridge
5.Anderson Bridge
6.Owens's bridge
Introduction
(1/2)
• A.C. Bridges are those circuits which are used to
measured the unknown resistances, capacitance
,inductance, frequency and mutual inductance.
• Inductance and capacitance can also be measured
by four-arm bridge.
• In this case the alternating current source is
employed by a vibration galvanometer.
(2/2)
Operation of AC Bridge:
 When the specific circuit conditions
apply, the detector current becomes
zero, which is known as null or
balance condition.
 Since zero current, it means that
there is no voltage difference
across the detector, Figure .
 Voltage at point b and c are equal.
I 1 Z1  I 2 Z 2
 The same thing at point d.
I1 Z 3  I 2 Z 4
 From two above equation yield
general bridge equation;
Figure Equivalent of Balance
(nulled) AC Bridge.
Figure : (a) and (b) are Simple AC Bridge Circuit.
Maxwell’s Bridge
• In the Maxwell’s bridge measure an unknown
inductance then becomes known in terms of
the capacitance. As shown in fig.
• It is used to measure unknown inductances
with capacitance standard.
•
Because the phase shifts of inductors and
capacitors are exactly opposite each other, a
capacitive impedance can balance out an
inductive impedance if they are located in
opposite legs of a bridge.
1<Q<10
R2 R3
Rx 
R1
Lx  R2 R3 C1
•
The impedance of the arm can be written as,
1
Z1 
1 / Rc  jC1
Z 2  R2
•
Substitute in the balance equation,
•
Set real and imaginary part,
Z 3  R3
Z 4  R x  jX LX
1
( R x  jX LX )  R2 R3
1 / R1  jC1
R x  jX LX 
L x  R2 R3 C1
R2 R3
 jR2 R3 C1
R1
Hay’s Bridge
• It is also a modification of the Maxwell’s
Bridge and is particularly useful if the
phase angle of the inductive impedance is
large.
• It used as resistance in series with
capacitor. For large angel phase angle R1
have a very low value, this circuit is used
for measuring high Q.
Hay Bridge
• The Hay circuit is used for
measuring high-Q .
• Hay bridge for inductance
measurements --------------------
• Impedance triangles illustrate
inductive and capacitive phase
angles ------------------------------
10<Q
Z x  Rx  j Lx
1  j R3C3
1
Z3  R3 

jC3
jC3
Z1  R1 
 Known, fixed
Z 2  R2 
 2 R1R2 R3C32
Rx 
1   2 R32C32
R1 R2C3
Lx 
1   2 R32C32
Quality factor , Q   Lx 
Rx
1
 R3C3
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.
Owens's bridge
Measuring high Q
Equation for Owen’s bridge
The owen’s bridge is used for measurement of inductance
such that the inductance is expressed in term of
capacitance.
There no frequency components in L1 and R1
 Balance condition is obtained much easily, because of
R2 and C2 are in same arm.