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USB Oscilloscope 10x probe — Parallax Forums

USB Oscilloscope 10x probe

tmatma Posts: 27
edited 2010-02-05 19:23 in General Discussion
I am using the scope (and my digital voltmeter) to explore a vacume flourecent display circuit.

The power supply to the VFD drive circuit is 47V so I need an external probe to view the high voltage pulses from the VFD driver to avoid damaging the scope.

Most conventional scopes that I am familiar with have a 1 megohm input impedance so a 9 megohm resistor in series with the input will do the job.

Can anyone tell me what the input impedance is·for the USB oscilloscope?

Comments

  • dandreaedandreae Posts: 1,375
    edited 2010-02-03 16:08
    The input impedance is 1 meg ohm.

    Dave




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    Dave Andreae

    Parallax Tech Support·
  • tmatma Posts: 27
    edited 2010-02-04 20:33
    Thank Dave

    Using rudimentary methods I·had calculated the input R at 1.3 megohm and the input C at 130 pF.
    I expected a margin of error of +/- 50%.

    Do you consider my idea of putting a 9 meg ohm resistor in series a safe way (for the scope) to measure higher voltages?
    I expect 47 Volts but·I want to have a good margin for error.
    ·
  • dandreaedandreae Posts: 1,375
    edited 2010-02-05 16:00
    That should work just fine.·

    Dave

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    Dave Andreae

    Parallax Tech Support·
  • tmatma Posts: 27
    edited 2010-02-05 19:23
    Thanks again Dave.

    I'm building it today

    Tom
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