PCI-6221 analog input voltage wrong above 5V

[Bill I.]

I have a input problem that popped up during a power supply calibration.  You’ll see from the attached graph that above about 5.3 volts the input readings, as read from the Test Panel in NI-MAX, begin falling off.  I’ve put a meter on the signal from the amplifier and so I know the card is getting the correct signals.  My first thought was that the card, a PCI-6221, had been damaged, so I tried other cards.  I get exactly the same behavior from a brand new PCI-6221 and a used but working PCI-6552E.

I’ve checked that the inputs are configured to ±10V.  I’ve also completely deleted the devices and reinstalled them to no avail.  I’ve changed the connection boxes and cables, too.  At this point I’m convinced it’s a software/configuration or a computer problem, but I don’t know what else to do.

[crossrulz]

What kind of load is attached to the supply when running this test?  I'm guessing you have an additional load that is causing the supply to go into constant current mode.

[Bill I.]

I'm using a 1Ohm, 100W resister and the amplifier is controlled by the analog output of the card.  You can see from the picture below that I have meters on everything.  The card output is correct, the amplifier is responding correctly, and the signal at the input is correct for the programed current.  The problem is when I look at the input in the Test Panel in MAX.

[johnsold]

A grounding problem?

Lynn

[Kilometers]

Hi Bill,

What connector block are you using to interact with your PCI-6221? Since you are running into this issue with multiple cards it's likely the issue isn't with the card itself.

[borenhit2000]

i got the same problem with constant voltage around 10.68v, hope could find a solution for this.

[crossrulz]

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@borenhit2000 wrote:

i got the same problem with constant voltage around 10.68v, hope could find a solution for this.

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That one makes sense.  You do realize that the DAQ has a maximum input range of +/-10V.  So anything above that will likely be cutoff.  Anything about around 11V could damage the DAQ board. 

[Bill I.]

I'm using a BNC-2110.  I've tried changing that too.  Could it be a problem with the PCI bus in the computer?  I've had a PCI-6552E fail and take down the whole PCI power bus which led to the loss of all the outputs on every card on the bus.  Could this be an under-voltage on the bus?  The computer has a 460W Coursair power supply which should be enough to run 3 PCI-6221 and a PCI-GPIB.  I measured the outputs from the computer power supply and they're good, too.  I'm using an identical computer with 3 PCI-6552E's and the GPIB card and it's woking fine.  And yes, I tried a 6552E and it was exactly the same.

[Kilometers]

Are you able to test the PCI card in a different computer to see if it is infact the bus in your current computer?

[Bill I.]

Yes, they work fine in another computer. I swapped one with the PCI-6552E in the identical working computer.  Could an under-voltage to the card cause this behavior?