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Wheatstone Bridge

A Wheatstone bridge consists of four resistors connected in a diamond shape, and is used to measure very small resistance changes, for example from a strain gauge. When the bridge is balanced, the output voltage is zero; a small change $\Delta R$ in one arm gives a small, measurable differential voltage that can be amplified.

\Delta R = GF\cdot\varepsilon\cdot R

resistance change from strain in a strain gauge

Symbols

$GF$	gauge factor (the strain gauge's sensitivity)
$\varepsilon$	strain
$R$	the resistor's nominal value	$\Omega$
$\Delta R$	resistance change	$\Omega$

Example

$GF=2$ , $\varepsilon=0.001$ , $R=120$ Ω:

$\Delta R=2\cdot0.001\cdot120=0.24$ Ω.

When balanced the output voltage is zero – even a small

\Delta R

then gives a clear reading.

Practise measurement for free →

← Sampling and Nyquist

Part of Embedded Systems and Instrumentation: Measurement.