optimize PXI chassis by placing boards in a different way?

[ArtBB]

Given that PXI runs at high frequency, does anybody know if I can optimize stability and/or performance by positionning the PXI boards in a  particular order in the chassis?

Thanks in advance,
Arthur

[Collin M]

In an 8-slot and larger chassis the lower number slots (slots closest to the PXI controller) will have more bandwidth available when there is contention on the PXI bus. By contention I mean more than 1 card trying to transfer data at the same time. This is because the PCI arbiter in the chipset in the PXI controller typically supports fewer bus masters than the number of slots in an 8-slot or larger chassis, and so two or more slots end up "sharing" bandwidth. Note that the bandwidth limitation only occurs when more than one PXI card is trying to move data across the PXI bus, and the PXI cards have large sustained transfer rates. By large sustained transfer rate I mean a significant transfer rate compared to the 132MB/s available on the PXI bus. This is a limitation is PCI systems as well as PXI systems.

As far as stability, there should be no difference among the slots.

[ArtBB]

I was thinking of potential EMC problems inside the chassis, that would cause some random instabilities... we have some matrix cards but also a multimeter card with some current going through... what do you think about that?

[Collin M]

I know that cards made by NI that are succeptible to EMI have metal shielding around their sensitive circuits. I've never heard of a problem caused by inter-card EMI.

Are you having a specific problem or just asking a question?

[ArtBB]

Actually i hadn't understood our problem very well, i apologize for that!

We are experiencing instability, and my colleague remembers having read somewhere, that there might be some trouble related to the bus' waveguide behavior, which would make stationery waves if the cards are inserted in certain places (for exemple: 2 cards in the first to slots, and nothing else in the chassis).

[edit: wow, sorry for the complicated sentence, hope it's clear, though!]

Ever heard of such a thing?

Thanx again,
Art

Message Edité par ArtBB le 08-30-2005 05:12 AM

[Collin M]

What configuration (chassis, controller, and cards) are you using that is causing instability? How do you know this instability occurs? I've never heard of a case of inter-card interference but that doesn't mean it can't happen.