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What is Wein’s Bridge?
· The Wien’s bridge is a type of bridge circuit that was developed by Max Wien in 1891. The bridge consists of four resistors and two capacitors.
· At the time of the Wien bridge's invention, bridge circuits were a common way of measuring component values by comparing them to known values. Often an unknown component would be put in one arm of a bridge, and then the bridge would be nulled by adjusting the other arms or changing the frequency of the voltage source.
Usage of Wein’s bridge:
· used for precision measurement of capacitance in terms of resistance and frequency
· used to measure audio frequencies
Theory:
· The Wien bridge does not require equal values of R or C. At some frequency, the reactance of the series R2–C2 arm will be an exact multiple of the shunt Rx–Cx arm. If the two R3 and R4 arms are adjusted to the same ratio, then the bridge is balanced.
The bridge is balanced when:
w^2=1/RxR2CxC2 and Cx/C2=R4/R3-R2/Rx
The equations simplify if one chooses R2 = Rx and C2 = Cx; the result is R4 = 2R3.
In practice, the values of R and C will never be exactly equal, but the equations above show that for fixed values in the 2 and x arms, the bridge will balance at some ω and some ratio of R4/R3.
Advantages:
· By varying the two capacitor values simultaneously, by mounting them on the common shaft, different frequency ranges can be obtained.
· The perfect sine wave output is possible.
Disadvantages:
· instead of op-amp, transistorised amplifier is to be- used then more stages are required to obtain 0° phase shift between input and output. This increases the number of components and cost
· poor frequencies stability
VIDEO FOR WIEN BRIDGE
VIDEO FOR WIEN BRIDGE
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