6023E DAQ and real-time PC-based ETS solution

[Jasiu]

Hello
I am using PCI-6023E DAQ card with a pc-based ETS system. While the card works properly on single pc non-rt system, when i try to run it on two machines (one with rt OS, and second one as a terminal), the card seems to aquire blocks of samples slower than it should. For example when i set block size to 100kS and sampling rate to 100kS (i am intentionally using huge blocks, but i belive same thing happens for smaller ones, only in lesser degree), waveform chart should be refreshed once in a second, but it refreshes at lower ratio (as i remember it was about 1.5s). What causes this? Can this problem be somehow solved?
I am using front panel communication. I've tried to use buffered aquisition (AI Config, AI Start etc), but only function that worked is Continous Aquisition (which i belive is buffered because you can set buffer size and block size there).

Thanks in advance

[Jeff M]

Hi Jasiu,

There are two very important considerations when changing from a single pc-based ETS system to a RT Target/PC Host Architecture.  The first item of consideration is to make sure your communication VI's are outside of the time-critical loop.  And secondly, keep in mind that large data packets might be limited by the TCP/IP bandwidth (which is a limitation of ethernet, in general).  This limitation does not occur on a single PC, regardless of whether it's an ETS system or Windows OS.  Take a look at the following KnowledgeBases for more detailed information on these two considerations:

1. Why is TCP Communication Slower in Time-Critical Loop?

http://digital.ni.com/public.nsf/websearch/62129235E2D254C286256D1D005A5D73?OpenDocument

2.  How Can I Determine the Optimal TCP/IP Transfer Rate between a Real-Time Embedded Process and My Host PC Using LabVIEW RT?

http://digital.ni.com/public.nsf/websearch/DA6777E0180003D0862569900059C048?OpenDocument

Hope this helps!

Regards,

Jeff M.

Applications Engineering

National Instruments

Message Edited by Support on 03-06-2006 11:05 AM