On Friday, 26 February 2021 at 13:23:46 UTC, Don Pearce wrote:
On Fri, 26 Feb 2021 01:57:59 -0800 (PST), "
wrote:
** You sure about "any" ?
Square waves have cascading, odd numbered harmonics.
The ringing one would merely be out of step with the others.
Ringing and how it works was brought home to me when I had to set up a
CNC mill. Part of the setup was automatic, and was for the movement
servos to characterize themselves. When they come to a fast stop, the
heavy stuff attached rings (wobbles), and that has to be prevented. So
the servos use feedback to find the frequency of that ring. Then they
use a convolution algorithm to notch that frequency out of the
transient edge. Result - fast stops and no ringing or oscillation.
In linear systems frequencies can't be created out of nothing. All
frequencies are present in a fast edge, and this is where the energy
for the ring comes from. Remove that frequency from the edge and you
will not see any ringing. Note - this is not the same as harmonics of
the square wave. It is a continuous sinc curve of energy associated
with each edge.
This is super non-intuitive but provided there is no non-linearity, it
works.
d
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This Pultech clone has "catastophic ringing" with a 1kHz square wave, almost identical to the example posted.
A 600 ohm resistor alone reduces level by almost half, but the ringing remains at the same proportion of the square wave amplitude.
A 100ohm resistor in series with 10nF reduces the catastophing ringing initial spikes hugely, but nowhere near to "mild ringing", and has a slight rolloff on a sine wave at 10 and 20 kHz but not 1kHz.
A 100ohm resistor with 68 nF has way too much hf rolloff, but the ringing is eliminated entirely with a sloping squarewave wavefront showing the hf cut.
A 100 ohm resistor with 4.4nF to 1nF causes full amplitude oscillation, very bad.
The 10nF seems to be the most useful. Anything higher does eventually elliminate the ringing, but with unacceptable rolloff.
Thanks,
Gareth.