SCXI 2000 Problems

[JonM]

I am currently having some fun with an SCXI 2000 rack,
and I wondered if anyone here could help (or has had this problem before, even if you don't have a solution).

I have an SCXI 2000 rack, containing SCXI 1200 and 1161 cards, connected to a PC running Windows NT 4.0 with an NI AT-485 card. I am performing continous analogue input from the SCXI 1200 card, with the card set to sample at 120, 150 or 200 samples per second, and I am sampling across 8 channels.

I have 2 problems with this system.

Firstly, the data I am getting back from the SCXI rack is 2.5 to 3 seconds behind real time. I realise this may be a limitation of the rack (or more pertinantly the 485 communications), but it seems a bit longer than I was expecting (I have tried syn
chronous and asynchronous acquisition, neither of which changes this delay).

My second (and more important) problem is that, after 2 to 5 days of continous running the software loses communications with the rack completely. The time it takes to sieze seems to vary almost randomly, and once communications have been lost they can only be re-established by rebooting both the PC and the rack.

At first I thought it might be the software overallocating some memory or buffer, but I have tried everything I can think of (including running NI's example VIs on their own) to stop this happening, and nothing makes any difference at all. I have also tried changing to NI-DAQ 6.6.0, 6.8.1, 6.9.1 and 6.9.2, none of which seem to make any difference. I've also tried LV 5.1 and 6.0.2 (also no change).

I'm fresh out of ideas, anyone got any suggestions?
Thanks,
Jonathan

[Filipe A.]

Hello;

As you aparently already covered all the basic troubleshooting procedures without luck, we can start wonder if the problem is not related to the hardware you have. One thing we can try is to take the NI-485 board out of the picture and hook up the 1200 module to one of the COM ports of your computer and change the communication protocol to RS-232 instead. By doing that we will isolate one variable out of the system, the 485 board.
Hope this helps.
Filipe

[JonM]

Thank you for your reply Filipe,
it is much appreciated.

I will try using 232 coms. If it works it will at least prove that it is a 485 communication issue (although the problem could lie with the NI-485 card or the SCXI rack, or both). Unfortunately the 232 communications only appear to work on the rack at 4800 baud (this is problem I encountered when developing for it), at any other baud rate higher than that it fails to communicate. I'm not sure if this is an inherent limitation of all SCXI 2000 racks? Or possibly another symptom of the problem? It may have been a function of the wiring used (a custom built cable).

Jonathan