How is the Wheatstone bridge used in sensor circuits?

The Wheatstone bridge converts small resistance changes (from sensors like strain gauges, RTDs) into measurable voltage. In balanced state (R1/R2 = R3/R4), output voltage is zero. When sensor resistance changes, the bridge unbalances, producing output voltage proportional to resistance change: Vout = Vexc*(R3/(R3+R4) - R2/(R1+R2)). Quarter-bridge uses one active element; half-bridge uses two (temperature compensation or doubled sensitivity); full-bridge uses four (maximum sensitivity). Excitation can be voltage or current source. Amplification is needed for the small output voltages.