Oscilloscope sample ratings

Discussion in 'General Electronics Chat' started by jody, Aug 10, 2014.

  1. jody

    Thread Starter Member

    Nov 12, 2012
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    hi all
    im a little confused over oscilloscope sample ratings. one scope quotes in ms/s and another in mhz. so what would a 200mhz sample rate be in ms/s.
     
  2. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    200Mhz is 5nana seconds (0.005 uSec)
     
  3. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    I think your are confused about the use of m=milli(10^-3) vs M=Mega(10^6)

    mHz
    MHz
    ms
    MegaSamples/s
     
  4. DerStrom8

    Well-Known Member

    Feb 20, 2011
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    I think Mike is right. It is most likely Ms/S, or "Mega-samples per second". 200 mega-samples per second is the same as 200 Mega-hertz.
     
  5. jody

    Thread Starter Member

    Nov 12, 2012
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    yes see where i was confused now did mistake the description. thanks a lot was driving me dotty:):):)
     
  6. hexreader

    Active Member

    Apr 16, 2011
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    I believe that scopes usually have a greater sampling rate (measures in Megasamples per second) than the bandwidth that is quoted in MHz.

    A 100 MHz scope will have an input amplifier capable of handling 100MHz sine wave with minimal distortion.

    If you want to view that 100MHz sine wave, then you will need a sampling rate much higher than the input bandwidth to give a reasonably accurate display. If the sampling rate were 100M Sa/s, then you only sample and display once per input cycle. It is pure luck where on the sine wave your sample comes.

    My cheap scope has 70MHz bandwidth, but 250M Sa/s.

    These are two different specifications and both are important
     
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  7. DerStrom8

    Well-Known Member

    Feb 20, 2011
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    This is correct, I'm not quite sure what I was thinking. I just bought a Rigol with a 50MHz bandwidth but 1Gs/S. They are completely different specifications and do not mean the same thing.

    Ms/S still means "meg-samples per second", though.
     
  8. hexreader

    Active Member

    Apr 16, 2011
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    Sorry to nit-pick, but are you sure?

    Shouldn't there be a little s for seconds?

    I will not argue over case for "samples" though, since this is not exactly an SI abbreviation.
     
  9. MrChips

    Moderator

    Oct 2, 2009
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    No, you are not nit-picking.

    The proper SI unit for seconds is s.

    Accepted practice for 1 giga samples per second is 1Gs/s.
     
  10. DerStrom8

    Well-Known Member

    Feb 20, 2011
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    I was trying to remember which "s" was used for seconds vs. samples. I think you're right, samples should be "S" and seconds should be "s", in which case that would be MS/s. And actually, I'm beginning to think they often include a small "a" after the S, so it would be MSa/s. That looks more realistic to me....
     
  11. MrChips

    Moderator

    Oct 2, 2009
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    S is the SI unit for siemens.

    However, Tektronix uses 1GS/s, for example.

    I think either 1Gs/s or 1GS/s is acceptable when used as sampling rate specification.

    Obviously, this would be dimensionally incorrect in an equation.
     
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  12. crutschow

    Expert

    Mar 14, 2008
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    The minimum sample rate per the Nyquist criteria is twice the highest frequency of interest. Any frequency higher than that will be "aliased" into the passband as a spurious signal. I have seen this in some early digital oscilloscopes where a sine-wave frequency above the scope sample frequency appeared as a lower frequency sinewave.

    To avoid this aliasing, the sample rate of a good digital scope is much higher than two times the scope frequency rating (often ten times or more). Then the input amplifier low-pass filters the signal so that any signal frequencies about 1/2 the sample rate are so small that they produce a negligible aliased signal on the screen.
     
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