Transcript 11-Wheatstone bridgex

WHEATSTONE BRIDGE
Maram Odeh
Anwaar Haimoor
Bridges
A bridge circuit is a type of electrical circuit in
which two circuit branches (usually in parallel
with each other) are "bridged" by a third
branch connected between the first two
branches at some intermediate point along
them.
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A bridge circuit is a type of electrical circuit in which two circuit branches (usually in parallel
with each other) are "bridged" by a third branch connected between the first two branches
WHY DO WE USE THEM??
The bridge was originally
developed for laboratory
measurement purposes and one of
the intermediate bridging points is
often Why do we use them ??
adjustable when so used.
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EXAMPLES :
Diode bridge
Kelvin bridge
Maxwell bridge
H bridge
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WHEATSTONE BRIDGE:1) the best-known bridge circuit .
2) is used for measuring an unknown resistance.
3) it minimize the error
measurement (precise system).
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TO MEASURE AN UNKNOWN RESISTANCE ….
First we can try measuring a resistor connected to a
battery ,using ohms law….
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CURRENT MEASUREMENT
Based on ohms law :The current is directly proportional to the voltage
and inversely proportional to the resistance.
Current measurement
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SO …
the primary benefit of a Wheatstone bridge is
its ability to provide extremely accurate
measurements (in contrast with something like a
simple voltage divider)
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Rx : is the unknown resistance to be measured. R1,R2 and
R3 : are resistors of known resistance.
r2 is adjustable
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MEASUREMENT USING WHEATSTONE
BRIDGE:
A Wheatstone bridge
as shown below can be
used to measure the
resistance of the
resistor “R”:
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IN MOST CASES the
Wheatstone bridge
is unbalanced and it
is so called when
some current is
flowing through the
galvanometer.
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BUT in the case,
when no current flows
through the bridge
galvanometer ; this
state is called the
balanced state of
Wheatstone bridge.
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APPLICATION OF WHEATSTONE
BRIDGE:
* Measuring the value of an unknown
resistor.
* It is also used in electrical sensors like
temperature sensor , light sensor etc.
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Some Wheatstone bridge
designs include two variable
resistors to improve the
sensitivity of the system.
(vg) is proportional to the
difference in the transducers’
resistance values relative to
the reference resistance in
the bridge configuration
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The design of the
circuit reduces the
effects of noise
on the output
voltage.
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IF the input voltage
varies, it does not
influence the output
voltage since it is
related to the ratio of
the resistances.
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Also, a variation in
temperature affects all
the resistor elements
equally and therefore
cancel each other out.
therefore, this circuit
greatly suppresses
electrical noise and
thereby improves the
signal to noise ratio.
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When the Wheatstone bridge is used in a pressure
sensor, the resistors are oriented such that R1 and R4
are variable under the stress of a flexible membrane
on which they are made.
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The resistors in the
Wheatstone bridge
are made of a
piezoresistive
material, a material
which changes its
resistance when
mechanical stress is
applied.
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. A change in pressure
creates a deflection of
the diaphragm. This
deflection causes the
variable resistors of the
bridge to expand,
increasing circuit
resistance indicating a
change in pressure
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