eFunda: Introduction to Wheatstone Bridges
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Wheatstone Bridges: Introdu
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Bridge circuits are widely used for the measurement of resistance, capacitance, a
inductance. The resistive bridge, also known as Wheatstone bridge, is discusse
this section.
Basic Wheatstone Bridge Circuit
A basic Wheatstone bridge circuit contains four resistances, a constant voltage in
and a voltage gage, as illustrated below.
For a given voltage input Vin, the currents flowing throug
and ADC depend on the resistances, i.e.,
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The voltage drops from A to B and from A to D are given
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The voltage gage reading Vg can then be obtained from,
Now suppose that all resistances can change during the measurement. The
corresponding change in voltage reading will be,
To
Balanced Wheatstone Bridge Circuit
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eFunda: Introduction to Wheatstone Bridges
http://www.efunda.com/designstandards/sensors/methods/wheatstone_b...
If the bridge is initially balanced, the initial voltage reading Vg should be zero.
yields the following relationship between the four resistances,
We can use this result to simplify the previous equation that includes the change
resistances. Doing so results in the solution for the change in Vg,
where h is defined by,
Moreover, when the resistance changes are small (< 5%), the second order term
approximately zero and can be ignored. We then have,
which is the basic equation governing the Wheatstone bridge voltage in strain
measurement. The coefficient
is called the circuit efficiency.
To
Equal-Resistance Wheatstone Bridge Circuit
In practice, one often uses the same resistance value for all four resistors, R1 =
= R4 = R. Noting that r = 1 in this case, the change in voltage can be further sim
to,
By thoughtfully selecting the target and reference resistances, the Wheatstone b
circuit can amplify small changes in resistance and/or compensate for changes in
temperature.
To
AIP Handbook of
Modern Sensors ,
2nd ed., by Fraden,
J.
Measurement and Instrumentation in
Engineering: Principles and Basic
Laboratory Experiments , , by Tse,
F.S., Morse, I.E.
Mechanical Measurem
5th ed., by Beckwith,
Marangoni, R.D., Lien
J.H.
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