On 09/16/2003 10:55 AM, Bernard Cleyet wrote:
>
> BTW a much less expensive method of detecting phase (than a PAR,
> Stanford Research, etc.) is to use a center tapped secondary
> transformer. In this case the primary is driven by the speaker,
> unloaded (isolated) by a cathode follower (emitter follower for the
> modern, op. amp. for the "really" modern). The output is compared to
> the source (oscillator output) using another transformer, Its
> secondary is in series with other's center tap and the center of a
> balanced rectifier (the other legs of the rectifier go the the
> secondary of the first transformer). The output of the rectifier is
> proportional to the input signal and the polarity indicates the
> phase. Unfortunately, unless the signal (and the reference) are
> constant, this device does not give the phase angle, only whether it
> leads or lags the reference. This device was invented for use with
> strain gauge bridges.
>
> If your library hasn't discarded Hill's Electronics in Engineering,
> (because it's so old, 1949) look on page 247 for the circuit and
> description.
For the "really, really" modern, just do it in software.
Practically all computers have a sound-card that will
record stereo. Hook up
left = reference / excitation / independent variable
right = dependent variable
and turn the crank. Software adequate for present purposes
shouldn't take more than an afternoon to write. Hint:
scilab can read .wav files, and can do FFTs.