A Wheatstone bridge is an electrical circuit used to determine the resistance of a circuit element. It consists of four resistors split into two legs and is named after Sir Charles Wheatstone. By balancing one leg of the circuit against the one with the unknown resistor, the resistance of the component under test can be calculated. The circuit is designed to split the input current into two legs, which are bridged. Each leg has two resistive elements. One resistor of each leg has a fixed and known resistance.
A Wheatstone bridge is a type of electrical circuit known as a bridge circuit and is used to determine the resistance of a circuit element. This can be used to test the resistance of various components such as resistors, wire sections and any other electrical conductors. A typical Wheatstone-type bridge circuit uses four resistors split into two legs. By balancing one leg of the circuit with a fixed, known resistance against the one with the unknown resistor, the resistance of the component under test can be calculated.
Like many inventions and techniques, this type of test circuit is named not after the person who first invented it, but after the person who developed and perfected it. It was first developed in the early 19th century by a man named Samuel Christie, but was popularized by Sir Charles Wheatstone, by whose name it is now known. The principles by which a Wheatstone bridge circuit works and the methods by which it is used have not changed significantly since his invention, although many refinements and variations have been developed.
In its most basic form, a Wheatstone bridge consists of an electrical circuit with two legs, an electrical input source with a constant voltage, four resistors, two of which have a fixed and known resistance, one with a variable resistance that can be monitored as it changes and the resistance to be tested. You also need a voltage meter. This basic setup allows you to test any conductive material to determine its resistance with a very high degree of accuracy.
The circuit is designed to split the input current into two legs, which are bridged. Each leg has two resistive elements. One resistor of each leg has a fixed and known resistance. On one leg, this resistor is coupled with a variable resistor and there must be some means of monitoring the resistance as it changes. On the other side, the resistor with known resistance is matched to the component under test. When current is introduced, the variable resistor is manipulated until the voltage meter registers zero current flow, meaning that the resistances of each leg are exactly the same.
By controlling the resistance setting of the variable resistor, the resistance of the test component can then be easily calculated. It is possible to construct a Wheatstone bridge using three resistors with fixed resistances as long as all of their values are known. The calculations required to find the resistance of the test component are more complex when using such a Wheatstone bridge, but the basic principles involved are the same.
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