On Wednesday 23 December 2009, Dustin Monroe wrote:
>I looked at renting an oscilloscope and it is pretty pricey especially
>with the function generator. Will this work for tuning, anyone have
>experience with it:
>http://cgi.ebay.com/2x100MHz-PC-USB-Oscilloscope-Spectrum-Analyzer-Meter_W0
>QQitemZ120507410776QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item1c0ecd295
>8
>
>If this will work I think i will just buy it, I need my machine up and
>running asap.
>
>Thanks
The function generator will need a very fast, very low distortion booster
amplifier as it is using the audio of the pc for the output, way too low to
effectively drive the servo's for test at full speed. An lf357 op-amp might
be a good candidate, but check the specs for a good, rail to rail swing when
set at a gain of 10 to 20.
The spectrum analyzer functions are an interesting option if the feedback
from the servos tachs can be a/d'd into a velocity signal without too much
conversion latency, which was then compared to the driving waveform and the
various knobs tweaked for what the spec display would call minimum
distortion. Running at say 1/2 or 1/4 HZ for the servo drive signal, the
comparisons between the drive signal and the servo's response would represent
a very intuitive and educational display of stability and following error,
but one would have to insert a delay in the driving signal display that
matched the lags in the converted feedback from the tachs.
Heck, on second thought, screw the spec analyzer. Given the ability to delay
the driving signal by the same amount as the feedback conversion time lags,
and adjustable gain, just subtract the two waveforms leaving the errors,
ideally only following error. Timing errors due to the data conversions will
show as 's' curves in the baseline. If the delay is adjustable, just adjust
for minimum s curves in the baseline at reversal time.
I could see achieving a following error of .0001" at speeds of 200 ipm using
such a tuning tool, and doing it in less time than it would take to
transplant the test leads to the next channel/servo to be tuned.
Gah, that's what you get when an old fart CET starts thinking. I'll go
quietly.
Merry Christmas everybody.
--
Cheers, Gene
"There are four boxes to be used in defense of liberty:
soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
"We demand rigidly defined areas of doubt and uncertainty!"
-- Vroomfondel
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