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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 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
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 .
A standard Wheatstone bridge for comparison. Points A, B, C and D in both circuit diagrams correspond. X and Y correspond to R 1 and R 2, P and Q correspond to R 3 and R X. Note that with the Carey Foster bridge, we are measuring R 1 rather than R X. Let ℓ 1 be the null point D on the bridge wire EF in percent.
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.
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).
Resistance (, measured in ohms) is introduced as the constant in this relationship, independent of the current. Ohm's law is expressed in the equation = /. When applied to the 4 legs of the Wheatstone bridge circuit, the resulting equation is:
A Maxwell-Wien bridge. A Maxwell bridge is a modification to a Wheatstone bridge used to measure an unknown inductance (usually of low Q value) in terms of calibrated resistance and inductance or resistance and capacitance. [1] When the calibrated components are a parallel resistor and capacitor, the bridge is known as a Maxwell bridge.