EE Pro for TI-89, 92 Plus
Equations - Meters and Bridge Circuits
35
20.4 Maxwell Bridge
A Maxwell bridge is designed to measure the inductance Lx and its series resistance
Rx in a bridge circuit. The input stimulus to the bridge circuit is an AC source with
a variable frequency and an AC meter detecting a null. The first two equations
measure the unknown inductance Lx and its resistance Rx by varying the
capacitance Cs, and its parallel resistance Rs and bridge arm resistances RR1 and
RR2. The third and fourth equations measure the quality factor Q by using either
measured values of Lx and Rx or Cs and Rs. The final equation links the radian
frequency
ω
to the frequency f.
Eq. 20.4.1
Eq. 20.4.2
Eq. 20.4.3
Eq. 20.4.4
Eq. 20.4.5
Example 20.4-
Find the inductance and resistance of an inductive element using the Maxwell bridge. The
bridge are resistors are 1000_
Ω
each with a .22
µ
F capacitor and 470
Ω
parallel resistance. Compute Lx and Rx.
Entered Values
Calculated Results
Solution -
The first two equations are needed to solve the problem. Press
„
to display the input screen,
enter all the known variables and press
„
to compute the solution. The calculated results are shown in the
screen display above.
-PQYP8CTKCDNGU%U
A
µ
44
A
Ω
44
A
Ω
%QORWVGF4GUWNVU.Z
AJGPT[
4Z
A
Ω
20.5 Owen Bridge
The Owen bridge circuit is an alternative AC bridge circuit used to measure an inductance and
its series resistance. The input stimulus to the bridge circuit is typically an AC source with
variable frequency and an AC meter detecting a null. The inductance Lx is measured in terms of
the capacitor CC3, and the branch resistance RR1 and RR4. The series resistance Rx is
measured by a ratio of the capacitors CC3 and CC4 and tempered by RR2, the variable
resistance in the Lx arm of the bridge.
Lx
RR
RR
Cs
=
⋅
⋅
2
3
Rx
RR
RR
Rs
=
⋅
2
3
Q
Cs Rs
= ⋅ ⋅
ω
Q
Lx
Rx
= ⋅
F
HG
I
KJ
ω
ω
π
= ⋅ ⋅
2
f