Re: How good a "sine" wave to drive a selsyn/synchro?

Your post seems to be a continuation of another thread. As I
understand your problem, you need to provide drive for a synchro or
selsyn for some kind of motion control application. There is a common
misconseption that a selsyn/synchro is a 3-phase device. For the usual
motion control application, this is not true. Time-wise, the voltages
are either in-phase or 180 degrees out of phase with respect to a
reference. As the synchro shaft rotates at a constant rotational
velocity, the AMPLITUDES (forgive my shouting) vary sinusoidaly and are
120 degrees apart with respect to the MECHANICAL (I did it again)
position. To generate these voltages, you only need to generate a
single phase (electrically) sine (or pseudo-sine) wave of an
appropriate frequency, i.e., 400Hz. You then vary the amplitudes of
the other two voltages so that they vary sinusoidally 120 degrees apart
with respect to the desired mechanical position of the shaft.
~
There is one application that does require drive voltages that are 120
degrees apart electrically. If you want to generate a sine wave whose
electrical phase varies sinusoidally with respect to a reference, you
can drive the 3 stator windings with sine waves that are electrically
120 degrees apart. Now, as the shaft is rotated, the rotor voltage
electrical phase will vary linearly from 0-360 degrees as the shaft
position varies from 0-360 degrees.
~
I hope this helps.
Regards,
Jon

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