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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 ). [ 1 ]
The best-known bridge circuit, the Wheatstone bridge, was invented by Samuel Hunter Christie and popularized by Charles Wheatstone, and is used for measuring resistance. It is constructed from four resistors, two of known values R 1 and R 3 (see diagram), one whose resistance is to be determined R x, and one which is variable and calibrated R 2.
Thus, considered as a Wheatstone bridge, the two resistances are X plus a length of bridge wire, and Y plus the remaining bridge wire. The two remaining arms are the nearly equal resistances P and Q, connected in the inner gaps of the bridge. A standard Wheatstone bridge for comparison. Points A, B, C and D in both circuit diagrams correspond.
The post office box was a Wheatstone bridge–style testing device with pegs and spring arms to close electrical circuits and measure properties of the circuit under test. [ 1 ] [ 2 ] Resistance measurement
However, the method went unrecognised until 1843, when Charles Wheatstone proposed it, in another paper [3] for the Royal Society, for measuring resistance in electrical circuits. Although Wheatstone presented it as Christie's invention, it is his name, rather than Christie's, that is now associated with the device.
Since the change in resistance measured by a single strain gauge is extremely small, it is difficult to accurately measure changes. Increasing the number of strain gauges applied collectively magnifies these small changes into something more measurable. A set of 4 strain gauges set in a specific circuit is an application of a Wheatstone bridge.
Bridge topology is an important topology with many uses in both linear and non-linear applications, including, amongst many others, the bridge rectifier, the Wheatstone bridge and the lattice phase equaliser. Bridge topology is rendered in circuit diagrams in several ways.
The operation of the Kelvin bridge is very similar to the Wheatstone bridge, but uses two additional resistors. Resistors R 1 and R 2 are connected to the outside potential terminals of the four terminal known or standard resistor R s and the unknown resistor R x (identified as P 1 and P′ 1 in the diagram).