Oscilloscope resolution

snipped-for-privacy@timbuck2.com (J. Clouse) wrote in news: snipped-for-privacy@news.supernews.com:

how does your ground connection to the scope probe look? thats a big source of ringing.

How do the two scopes BW/rise time compare?

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Jim Yanik
jyanik
at
kua.net

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It appears I was a little nondescriptive. We are viewing the microphone pickup signal from a metal dome loudspeaker tweeter. It has a mechanical resonance about 28 KHz. We excite this with the leading edge of a 2 Hz square wave (pulse it), which excites the ringing at 28 KHz. The scope screen (delayed trace so as to see the start of the trace) shows a vertical line with the

28 KHz ringing starting at the top and riding on the horizontal top of the 2 Hz square wave. The 28 KHz signal was clear and distinct (as a sine wave) on our Gould OS4100 scope before it broke, but is not nearly as well defined (especially as the ringing diminishes) on the Tektronik scope. Both scopes have a vertical resolution of 8 bits. Both scopes were set to the same horizontal sweep rate of course (250 us). The problem is we don't know which spec applies to get a higher resolution, in another digital storage scope.

ns

"J. Clouse" a écrit dans le message de news: snipped-for-privacy@news.supernews.com...

And don't know why you didn't get something close on both scopes, but why aren't you simply using a 28KHz bandpass filter between your source and the scope ? This would probably make you life far easier as you could increase the dynamic range through a gain only in your interesting bandpass, no ?

Cheers, Robert

'not nearly as well defined' doesn't really tell us much about what you think the problem is.

The scope has a sample rate at whatever timebase you are using and is going to put a pixel on the screen for each sample. I presume the sample rate is high enough for 28kHz so if it doesn't look like a 28kHz sinewave then probably the signal isn't a 28kHz sinewave.

Maybe the signal has high frequency noise which the old scope didn't see or the new scope and earthing arrangement is making the noise worse.

If the scope has a bandwidth limit try it, if it has a glitch capture mode try that to make the noise more visible. If it has an average mode and your trigger is stable enough try that to average out noise.

Best to post a screen shot, either on a.b.s.e. or on a web site.

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Regards, Joerg

http://www.analogconsultants.com/

Some newer scopes have some more noise (CCD-Working Devices) than older Flash A/D-Converter designs. Maybe the Noise masks your Signal?

Jorgen