Wheatstone bridge

An electric circuit used for measuring resistance. It is named after the British inventor Sir Charles Wheatstone (1802–1875)`, even though it was actually invented by the British scientist Samuel Christie. Wheatstone was the first to use this device for its primary modern application: the highly accurate measurement of electrical resistance.

The Wheatstone bridge consists of four resistors connected in a square circuit. For the classic application of resistance measurement, three of the four resistors are variable resistors of known values. The fourth resistor is unknown. If a bridge voltage is applied from a to c, then the electric current flowing through the bridge is split, flowing through R1 and R2 on one side, and R4 and R3 on the other side. If a voltmeter is connected from b to d, then by adjusting the three known variable resistors until the voltmeter reads zero the bridge can be "balanced" with equal currents flowing through both arms of the bridge. In a balanced bridge the unknown resistance can then be calculated from the values of the known resistances.

In a modification of this application, bridge circuits are frequently used to provide an amplified, highly sensitive output from transducers, by using such transducers as one or more elements of a bridge.

Related categories

• ELECTRICITY AND MAGNETISM
• INSTRUMENTATION

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