Two NI-5114's (PCI) behave differently in the same computer with the same signal

[Karl T.]

Hi,

I have two NI-5114 (PCI) cards in the same computer, and we're using them to acquire signals from a charged particle detector (channeltron) put through a pre-amp.  The signals going into the card should be a negative pulse of amplidtude 0.5V.  We set a trigger at -0.1V, and run the program which simply counts the number of events, which should be around 10Hz.

The issue is that we've been using both cards interchangeably, but we just found out that one measures a much lower rate: ~0.5Hz instead of ~10Hz.   By simply switching from one 5114 to another (same hardware otherwise), we can see a vastly different rate of signal.  Is there an issue with having two of these cards in a computer at the same time?  Is there something wrong with one card, and are we even seeing the full rate with the other?

Any insight would be appreciated.  I've attached the VI to help diagnose problems.

Thanks!

Karl 

[The_Red_Barron]

Hey Karl,

To summarize what we discussed on the phone (for the sake of others reading this forum):

When using a function generator to produce -0.5V pulses the working card properly counts the pulses and the broken card does not count anything.  Changing the offset of the function generator by about 0.1V allows the broken card to start counting triggers properly.

It seems that there is an ~0.1V offset on the trigger either due to a problem in the circuitry or the card being out of calibration.

Swapping PCI slots does not resolve the issue so we can rule out PCI slot grounding/power as the cause.

Regards,