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Lab view/DAQ problem

  1. Jun 24, 2009 #1
    I'm trying to use an accelerometer to take measurements. I have it physically wired to my computer's DAQ board (a NI 6025E). According to the manual, pin 1 is ground and pin 3 is analog input 0. Therefore, this is where I have the output from my accelerometer going. I checked the signal at those pins using an oscilloscope and confirmed that there is the correct signal at that location in the circuit. I'm trying to use one of the example Lab View files to view the data from the DAQ board. However, according to the graph in Lab view, the waveform just grows and eventually saturates. At that point, all the DAQ reads is a flat 10V. I know, however, that this is incorrect because the signal from the accelerometer is between 0 and 5 volts. I suspect that either Labview or the DAQ are not "seeing" ground correctly.

    Does any one have any suggestions on what might be wrong? Thanks.
     
  2. jcsd
  3. Jun 24, 2009 #2

    berkeman

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    Staff: Mentor

    Welcome to the PF. Are you using the NI Measurement & Automation Explorer to look at the ADC data?

    It took me a bit of googling to get the pinout (the NI page wasn't cooperating):

    http://www.ni.com/pdf/manuals/370719c.pdf (page 12)

    The pinout you mention in your post does not seem to match...?
     
  4. Jun 24, 2009 #3
    I actually solved this problem today. The connector from the external circuitry to the DAQ on the back of the computer wasn't tight enough, so the ground wasn't actually being properly connected. Why the signal saturates when there's nothing connected beats the hell out of me.

    At any rate, you wrote that the pin out I gave you was incorrect. However, the document you posted has exactly the same pin out. I'm looking at page 14 of that pdf. It says Al GND (Analog Ground) next to pin 1. Then it says Al 0 (Analog Input 0) next to pin 3. So the connections I posted before were correct.
     
  5. Jun 24, 2009 #4

    berkeman

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    Staff: Mentor

    Glad the problem is fixed. The AI input will float someplace if nothing is connected to it, so floating up is reasonable.

    Ah, on the pinout, I was looking at the wrong page. I was looking at the first page of 3 pages of pinouts, and didn't read that I was looking at the wrong card's pinout. Sorry for any confusion.
     
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