Glossary term
Wheatstone Bridge
A four-resistor bridge circuit used to detect or measure small resistance changes through differential voltage imbalance.
Definition
deviceA Wheatstone bridge is a four-resistor bridge circuit used to detect or measure small resistance changes by comparing two voltage divider legs.
Wheatstone bridges convert resistance imbalance into a differential voltage. They are widely used with strain gauges, load cells, pressure transducers, temperature sensors, precision resistance measurement, and metrology circuits where small changes must be measured against a stable reference.
A Wheatstone bridge has two voltage-divider branches. When the resistor ratios are equal, the bridge output is zero or balanced:
Small resistance changes unbalance the bridge and create a differential output voltage. This makes the circuit useful for sensors whose resistance changes by a very small amount relative to nominal resistance.
Engineering use
Strain gauges often use quarter-bridge, half-bridge, or full-bridge arrangements. A full bridge can improve sensitivity and compensate temperature or bending effects if the active gauges are arranged correctly. Load cells, torque sensors, pressure diaphragms, and force transducers commonly use bridge circuits with instrumentation amplifiers.
Important design choices include excitation voltage, self-heating, resistor tolerance, temperature coefficient, lead-wire resistance, common-mode voltage, amplifier offset, filtering, shielding, grounding, and calibration. Ratiometric measurement can reduce error from excitation drift when the analog-to-digital converter reference shares the bridge excitation.
Bridge configurations
Quarter-bridge, half-bridge, and full-bridge circuits trade component count, sensitivity, and compensation. A quarter bridge is simple but more exposed to lead resistance and temperature effects. A half bridge can compensate bending or temperature when gauges are placed carefully. A full bridge gives high sensitivity and can reject common effects, but only if the active elements follow the expected strain pattern and wiring polarity.
Common mistakes
A common mistake is assuming a bridge output is linear over a large resistance change. Many bridge equations are linear approximations around balance. Another is ignoring lead-wire resistance and temperature gradients in quarter-bridge measurements. A strong Wheatstone-bridge review states bridge configuration, excitation, nominal resistance, expected resistance change, lead-wire compensation, amplifier gain, filtering, calibration method, uncertainty, and temperature behavior.