2. INTRODUCTION
Different types of AC Bridges can
be used for measurement of either
inductance or capacitance. We can
measure unknown inductance by
using MAXWELL’S INDUCTANCE
BRIDGE.
CONSTRUCTION:
There are four different arms in
which:
First arm of the bridge contains
series combination of resistance
and inductance.
Third arm consists of series
combination of variable resistance
and variable inductance.
Second and fourth arm consists of
resistances respectively.
3. WORKING OF THE BRIDGE
• This coil is connected to AC supply when
alternating current flows through the coil
according to magnetic effect , it produces
magnetic flux lines.
• When these magnetic flux lines are cut by coil1
then according to FARADAY’s LAW of
ELECTROMAGNETIC INDUCTION emf is
induced in coil1.This emf is called as SELF
INDUCED emf ,denoted by E1.
• Mathematically E1=-L1(di/dt),where L is called as
‘SELF INDUCTANCE OF COIL’.
4. WORKING OF BRIDGE (CONTINUED)
• Similarly in this figure there are 2 different coils in which
coil1 is connected to AC supply and coil2 gets open.
• When AC supply is given then according to the magnetic
effect, magnetic flux lines are produced but some of the
magnetic lines cut by coil2and all the magnetic lines cut by
coil1.
• Hence according to FARADAY’S LAW emf will be induced
in both the coils.
•
• The emf induced in coil1 is called as SELF INDUCED EMF
and the emf induced in coil2 is called as MUTUALLY
INDUCED EMF.
• Using MAXWELL’S INDUCTANCE BRIDGE we can
measure only SELF INDUCTANCE of coil1.
5. DERIVATION
In adjacent figure ,
parameters L1 and R1 are
unknown parameters.
By using MAXWELL’S
INDUCTANCE BRIDGE
we have to find out these
parameters
6. DERIVATION
The mathematical balancing
condition of AC bridge is:
Z1.Z4=Z2.Z3
-----(1)
Where,
Z1=(R1+jωL1)
Z2=R2
Z3=(R3+jωL3+r3)
Z4=R4
Substitute the values in eq.(1)
R1R4+jωL1R4=
R2(R3+r3)+jωL3R2
7. FINAL EQUATION
Real part--- R1R4=R2(R3+r3)
Imaginary part---L1R4=L3R2
From these equations :
The above 2 equations are FREE FROM FREQUENCY ie the values of
unknown resistance and unknown inductance does not depend upon the
frequency of supply. So that ANY TYPE OF DETECTOR can be used
