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Oscilloscope resolution

Discussion in 'Electronic Equipment' started by J. Clouse, Feb 11, 2008.

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  1. J. Clouse

    J. Clouse Guest

    Hi all,

    Help please.

    I'm not new to electronics, but not well versed in scopes.

    Just purchased a new Tektronix TDS1001B scope (~$800).
    In testing a piece of equipment, the 28 KHz (28,000 Hz) ringing on a
    pulse (about 2 Hz) is not nearly as well defined as it
    was on our Gould OS4100 (before it broke). In fact the
    ringing is barely visible at 250 microseconds sweep.
    The ringing was about 5 % of the pulse height on the Gould
    at this sweep rate. Do we need a higher sample rate,
    other than an LCD screen or what to get better detail
    on the ringing? Thanks.

    ns
     
  2. Jim Yanik

    Jim Yanik Guest

    (J. Clouse) wrote in
    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?
     
  3. J. Clouse

    J. Clouse Guest

    --------------------------------------------------------------

    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
     
  4. 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
    www.alciom.com
     
  5. nospam

    nospam Guest

    '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.
    --
     
  6. Joerg

    Joerg Guest

    Best to post a screen shot, either on a.b.s.e. or on a web site.
     
  7. Some newer scopes have some more noise (CCD-Working Devices)
    than older Flash A/D-Converter designs. Maybe the Noise
    masks your Signal?


    Jorgen
     
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