A Wheatstone bridge precisely measures unknown resistance by comparing it against known values. When balanced, no current flows through the center galvanometer. The bridge is the foundation of many sensor measurement circuits.
⚠The bridge is most sensitive near balance. For precise measurement, use a high-resolution adjustable R3 and sensitive null detector. Temperature affects all resistor values.
What is a Wheatstone Bridge?
The Wheatstone bridge, invented by Samuel Hunter Christie in 1833 and popularized by Sir Charles Wheatstone, is a circuit for measuring unknown electrical resistance. It consists of four resistors in a diamond configuration with a voltage source across one diagonal and a galvanometer across the other. When balanced, the ratio of two adjacent resistors equals the ratio of the other two.
Balance Condition
R1/R2 = R3/Rx. When balanced, Vout = 0 and no current flows through the center. Solve for any unknown resistor.
Sensitivity
Maximum sensitivity when all resistors are equal. Use high-resolution adjustable R3 (decade box) for precise null detection.
Unbalanced Output
Vout = Vin × (R3/(R3+Rx) - R1/(R1+R2)). Near balance, Vout ≈ Vin × ΔR/(4R) for small changes. Used in strain gauges.
Temperature Effects
Resistors change value with temperature. Use precision resistors with low temperature coefficient (ppm/°C) for accurate measurements.
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