The Vienna bridge is a type of bridge circuit that was developed by Max Wien in 1891 [1] The bridge consists of four resistors and two capacitors . At the time of the Wien bridge’s invention, bridge circuits were a common method of measuring component values by comparing known values. Often an unknown component will be put into one arm of a bridge, and then the bridge will be reduced to zero by adjusting the other arms or by changing the frequency of the voltage source. For example, see Wheatstone Bridge .

The Wien bridge is one of several common bridges. [2] Wien’s bridge is used for precise measurement of capacitance in terms of resistance and frequency. [3] It was also used to measure audio frequencies.

The Wien bridge does not need to be the same *value* as *R* or *C. *At some frequency, the reactance of the series *R *_{2} – *C *_{2} arm will be an exact multiple of the shunt *R *_{x} – *C *_{x arm. }If the two _{arms }*R3 *_{and }*R4* are adjusted to the same ratio, then the bridge is balanced._{}_{}_{}_{}_{}_{}

When the bridge is balanced:

\omega ^{2}={1 \over R_{x}R_{2}C_{x}C_{2}}And{C_{x} \over C_{2}}={R_{4} \over R_{3}}-{R_{2} \over R_{x}}\,।

If one chooses *R *_{2} = *R *_{x} and *C *_{2} = *C *_{x then the equations become simpler; }The result _{is }*r4* = _{2 }*r3* ._{}

In practice, the values of *R* and *C* will never be exactly equal, but for the values fixed in the above equations that the *2 and* X *arms* , the bridge will equilibrate on some _{and} some ratio of *R4* / *R3 *_{.}