On 21 Aug 2013 10:10, "Ed Breya" <edbreya@...>
> Strictly speaking, the CT sweeping frequency could be
arbitrary, as long as it's fast enough to avoid flicker,
but slow enough to not have too much parasitic effects.
Clocking frequencies in equipment are often selected so
that they and their harmonics tend to land between those
of the basic 50 and 60 Hz line frequencies, so that there
is minimal interaction, and best line rejection.
> One possible reason for this in the CT may be to
minimize the interaction of the sweeping load with the
line frequency, within the scope mainframe power supply.
Maybe the maximum power level needed for the CT is a bit
too much, compared to "normal" plug-ins, so it would tend
to cause stability problems and beat frequency artifacts
in the display if it ran at or near line frequency.
Cool idea. I ask myself though if that is the
case. Iirc a new branch in the graph is selected every osc
cycle. If there were beating creating distortion, the
distortion would modulate 11 branches at a time. What one
wants is for the beating to be so fast that it is not
visible as such. If the beating were affecting deflection
then you want it to make a thicker line, rather than
jitter the traces erratically. So the beating freq would
need to be much higher but that is impractical. On the
other hand you might want the beating to be really slow,
so that it is just a slow drift so that you can still
measure against the graticule.