NI PCI-6221 - Input signals drop when board is installed in one PC but not another

[JoeUser]

We are trying to troubleshoot a field situation where a NI PCI-6221 board is installed in a specific PC and the input signals seem to drop 1/2 volt when connected to the NI board, but this voltage drop does not happen when the board is installed in another PC.  The board was moved to all PCI slots in the specific PC but that did not make any difference.

The signal being input is coming from a force transducer (I expect to have more details about that signal shortly).

What is the input impedance of the NI PCI-6221 input ports?

I don't know if the input channel being used by the NI PCI-6221 is single-ended or differential mode (I assume the board can do both).  I wonder if the computers and associated signal conditioners are connected to different main-power circuits, thus are not sharing a common ground or neutral power line, and this could be a ground-loop phenomena.

[JoeUser]

I have verified that this is not  a ground-loop problem because all equipment is powered off the same power bar.

I would like to know what power requirements the NI PCI-6221 card has.  For example, which of the available power bus lines (+5, +12, -5, -12) does that card use from the PCI bus.  I wonder if this could be a computer power-supply problem.

[AnalogKid2DigitalMan]

Strange situation.

Here's a link to the specs:

http://www.ni.com/pdf/manuals/371290g.pdf.

Analog inputs >10Gohm powered on, 820 ohms powered off.

Power consumption <3W, see pg 10 for the voltage/current breakdown.

Board can do bot SE and DIFF.

-AK2DM

[JoeUser]

So if the front-end amplifier is not being powered, the input impedance will be 820 ohms - low enough to drag down the output signal of an external device.

The manual indicates that the board is using the 3.3, 5 and 12 volt supply lines.  The board logic and PCI interface will be using 3.3 volts, so most likely the front-end amplifier or a/d chips are using either +5 or +12 volts, and the lack of one of those voltages would result in a low input impedance.

So without applying a volt meter directly to the NI card to see if the card is getting +5 and +12 volts as is should, does the board have any diagnostic capability to detect the condition of those power supply lines and report their state to the user?  Does the board have the ability to know if any of the front end chips are working or powered up - or not?

[AnalogKid2DigitalMan]

If you have the NI Measurement and Automation Explorer (MAX) utility installed, it can run self tests on various portions of the cards.

One external test you could do is program the analog outputs to send a voltage out of +10 and -10 V. If it can do that I think the +12V supply is working.

Just curious, are you running the same versions of NI drivers and software on the PC's?

-AK2DM

[BROhan]

Hi JoeUser,

As per you question about the diagnostic capabilities of the device, you can use the DAQ Diagnostic Utility. This utility performs Counter, AI, AO, DIO tests on the board.

[JoeUser]

The voltage was checked on the PCI bus for all the various 3.3, 5, -5 and -12 voltage sources (about 2 dozen of them) and they all check out fine.  So there is nothing wrong with the power being provided by the PCI bus to the NI card.

The state of the NI drivers and the use of the NI diagnostic software will be looked at next.

Does this board have dedicated analog input and output lines?  Or can any given analog line be configured as either an input or output.  I wonder if the signal to be captured is being connected to a channel that has been configured as an output line.

[AnalogKid2DigitalMan]

Analog I/O's are dedicated, refer to manual link I posted above. I have been pondering this and do not have any ideas yet. Can you test out measuring a voltage from a battery with the same card between different PC's?

-AK2DM