Maxwell-Wien Bridge

168

03:00:39

Measure unknown RL (top left) by varying RC (bottom right) independent of frequency.  Diagonal voltage (measured with voltmeter) must be zero.

Names of elements:
.   .   .   .   .   .   .
Rx                    .
Lx                    R3
.                        .
.                        .
.                   .   .   .
R2              R4     C4
.   .   .   .   .   .   .   .   .


Computation of unknown elements:
Zx / Z2 = Z3 / Z4
Zx = Z2 * Z3 / Z4
(everything on the right must be known!)

...some steps in between...

Rx = R2 * R3 * 1/R4
Lx  = R2 * R3 * C4

Problem: In practice, it is very difficult to find right R and C such that amplitude AND phase of the diagonal voltage is zero. You could e.g. use an oscilloscope in xy mode for that.

published 7 years ago

hurz

7 years ago

It is only working for coils with a Q >1 and below 10! But your coil is at 1.23kHz Q=0.15 so this bridge wont work. You can increase the frequency to e.g. 10kHz to be within the Q limits.

karlpet

7 years ago

Thanks i changed it

hurz

7 years ago

Here an example setup. Well you can set all resistors to 50 Ohm and a resulting cap to 400nF, but this is boring http://everycircuit.com/circuit/4929149767778304

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