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Data Acquisition

  1. Mar 9, 2007 #1

    jamesrc

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    Hi,

    I've got a little mental block with something I'm working on and was hoping someone could help out:

    I'm doing some data acquisition with a National Instruments PCI-6025E board using LabView (not a lot of experience with LabView by the way). Anyway, the board is supposed to be a 12-bit board and the input range (for the analog inputs) is supposed to be -10 to +10 V. If I do the math, my resolution should be 20/(2^12) = 4.9 mV, right? Why, then, when I read data using the program does it appear that my resolution is twice that (I see steps in the data recording spaced ~2.5 mV apart). Any hints on what I'm doing wrong?

    Thanks.
     
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  3. Mar 9, 2007 #2

    berkeman

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    Any chance you have it configured in single-ended mode? That will double the resolution. Or maybe it's in +/-5V range mode?

    Your math appears correct for the +/-10V range.
     
  4. Mar 9, 2007 #3

    jamesrc

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    That was it - it's in single ended mode.

    Thanks for the help.

    While I've got you and since you mentioned range, do you happen to know how the ranging works when you're using the DAQ assistant wizard (I know, this is what I get for using a black box component). I mean, I think the board specs allow for +/-50mV to +/-10V ranges; if you enter in the range you are using, will it adjust accordingly? What if you choose a range that isn't one of the board selectable ranges? Like if I enter +/-9V (not that I planned to) will it behave the same as if it were +/-10V? Thanks again.
     
  5. Mar 10, 2007 #4

    berkeman

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    Glad to help. I'm not of any help on your follow-up question unfortunately. But NI has pretty good support, so you should be able to just give them a call on Monday to ask about what kind of errors get thrown by the different parts of their software.
     
  6. Mar 11, 2007 #5

    jamesrc

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    OK. Thanks again.
     
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