DAQ issues - multichannel output, different gnds, etc.

[dagda99]

Hi!

My DAQ card is behaving somewhat strangely - M series multifunctionDAQ PXI-6251.

I've created a Simulate Signal express VI [8V DC signal] wired to the DAQ output. When I ouput to ao1 it works fine [except for the 1 thing below], a multimeter shows that I'm getting the correct DC output. However, when outputting to ao1, there is no signal whatsoever. Multimeter reads 0.

The other odd behavior is with the Grounds - ao1 works fine in that the voltage is 10 V, but this is when I reference it [pin #21] to one of the AI Gnd pins [#24]. Referencing to one of hte AO Gnd pins [#54, or #55] does not show a voltage on the multimeter.

In DAQ Asst, Terminal Configuration (which I know is important for AI pin connections) is '<Let NI-DAQ choose>' because all the other options are grayed out.

I know the code works because I can attach a control in Labview to the DC offset and have it dynamically change the output voltage (of ao1 referenced to ai gnd); but for some reason ao0 doesn't work and the gnd pins seem to be doing something strange.

Any ideas?

Thanks!

-Pavan

[Otis]

Hi Pavan,

I see you're having a few problems getting your analog output lines working.  It sounds like this could be one of multiple problems.  My first hunch is that you might have fried your ao0.  However, since there are a couple of other problems, then it could be something else.

Here are a few troubleshooting steps that you may want to try:

1. Install the latest version of the DAQ Drivers 
2. Open Measurement and Automation Explorer (MAX) to test the device.
   1. If it doesn't pass let me know; otherwise, continue
   1. Wire the Analog Output to the Analog Input and see if you can read the voltage values.
   1. If you can read something on both channels then the device is working.
   2. If you cannot read anything, then you might have a broken card.  You will first want to check with the M-Series Help Manual to make sure that you have the right signal connections.
1. Go to My System > Devices and Interfaces > NI DAQmx Devices right-click on the PXI-6251 and click Self-Test
2. Right-click and open a Test Panel, try updating the voltage on channels 0 and 1.  Maybe try using a sine wave too.
3. If testing the device works, try running the device in LabVIEW.  If you experience problems, then it means there is something wrong with the code you are using.

If for some reason ao0 is broken then you should contact National Instruments to see about getting your board repaired.

Regards,

[dagda99]

Thanks for the help Otis!

-It passes self-test

-I can read from ao1, but not ao0 [0 V]

Other symptoms - using multimeter, there is no connectivity between AO Gnd and AI Gnd, or b/w AO Gnd and the other AO Gnd. There is connectivitiy between AI Gnd and another AI Gnd.

Using Max, Test panels, multimeter reads:

Output 10 V DC to ao0

0 V b/w ao0 and ao gnd

0 V b/w ao0 and ai gnd

Output 10 V DC to ao1

0 V b/w ao1 and ao gnd

10 V b/w ao1 and ai gnd

So the AO gnds are messed up, as is ao0.

Does this mean ao0 is fried? I haven't used it for anything previously, so there's no reason it should be...

Thanks!

-Pavan

[Otis]

Hi dagda99,

The voltages that the Analog Output produces (pins 21 and 22) are in reference to the Analog Output Ground (pins 55 and 54).  Ultimately all of the ground pins (aignd, aognd, dgnd) should be at the same potential too because they are referenced to the ground on the PCI bus. 

At this point it sounds like you may have a broken analog output channel, but I don't want to say that for sure because it is peculiar that you aren't reading a voltage potential between ao1 and aognd, but you are between ao1 and aignd.  I think the best thing for you to do now is to contact Technical Support and work with an engineer to see if there is anything that we might be overlooking in this forum.

Regards,