Wheatstone bridge

A Wheatstone bridge is an electrical circuit used to measure an unknown electrical resistance by balancing two legs of a bridge circuit, one leg of which includes the unknown component.

The primary benefit of the circuit is its ability to provide extremely accurate measurements (in contrast with something like a simple voltage divider).

The resistance R2 is adjusted until the bridge is "balanced" and no current flows through the galvanometer Vg.

At the point of balance, Detecting zero current with a galvanometer can be done to extremely high precision.

Alternatively, if R1, R2, and R3 are known, but R2 is not adjustable, the voltage difference across or current flow through the meter can be used to calculate the value of Rx, using Kirchhoff's circuit laws.

The Wheatstone bridge illustrates the concept of a difference measurement, which can be extremely accurate.

Variations on the Wheatstone bridge can be used to measure capacitance, inductance, impedance and other quantities, such as the amount of combustible gases in a sample, with an explosimeter.

A Wheatstone bridge has four resistors forming the sides of a diamond shape. A battery is connected across one pair of opposite corners, and a galvanometer across the other pair.
Wheatstone bridge circuit diagram . The unknown resistance R x is to be measured; resistances R 1 , R 2 and R 3 are known, where R 2 is adjustable. When the measured voltage V G is 0, both legs have equal voltage ratios: R 2 / R 1 = R x / R 3 and R x = R 3 R 2 / R 1 .
Directions of currents arbitrarily assigned
Kelvin bridge