The document discusses different types of bridge circuits. It describes the Wheatstone bridge, which converts variations in resistance into variations in voltage. When balanced, the output voltage is zero, but any change in a resistive element results in an unbalanced condition and a non-zero output voltage. It also discusses AC bridges for detecting changes in inductance and capacitance. Examples are provided for calculating voltage offset in a Wheatstone bridge and determining constants of an arm in an AC bridge. Finally, it briefly mentions comparison bridges for measuring unknown capacitance or inductance compared to known values, and the Maxwell bridge for measuring inductance in terms of a known capacitance.

1. Bridge Circuits
Dr. Ashraf Saleem
Dr. Ashraf Saleem 1

2. Bridge Circuits
g
Wheatstone Bridge: The primary application of this
g p y pp
bridge in signal conditioning is to convert variations of
resistance into variation of voltage
Dr. Ashraf Saleem 2

3. Wheatstone Bridge
g
VO will equal zero. In this situation, the bridge is said to be
BALANCED. Any change in any resistive element will result in an
UNBALANCED condition, hence VO will be non-zero.
,
Dr. Ashraf Saleem 3

4. Wheatstone Bridge
g
If we replace R3 with an active strain gauge, RG, which
will vary b ∆R when pressure i applied (th arrow
ill by h is li d (the
through the resistor shows that it has a variable value),
then
Dr. Ashraf Saleem 4

5. Example 1:
p
The resistors in a bridge are given by
R1=R2=R3=120Ω and R4=121Ω. If the
supply is 10V Find the voltage offset?
10V.
Dr. Ashraf Saleem 5

6. AC Bridges
g
AC bridges are used mainly to detect changes
in inductance and/or capacitance
At balance condition
Dr. Ashraf Saleem 6

7. Example 2:
p
An ac bridge is in balance with the
following constants: arm AB, R = 200 Ω
in series with L = 15 9 mH ; arm BC R =
15.9 BC,
300 Ω in series with C = 0.265 µF; arm
CD,unknown;
CD unknown; arm DA = 450 Ω The
DA, Ω.
oscillator frequency is 1 kHz. Find the
constants of arm CDCD.
Dr. Ashraf Saleem 7

8. Comparison Bridge: Capacitance
p g p
Measure an unknown capacitance by comparing it with a
p y p g
Known capacitance.
Dr. Ashraf Saleem 8

9. Comparison Bridge: Inductance
p g
Measure an unknown inductance by comparing it with a
y p g
Known inductance.
Dr. Ashraf Saleem 9

10. Maxwell Bridge
g
Measure an unknown inductance in terms of a
known capacitance
Dr. Ashraf Saleem 10