scxi sample rate

[_Bryan]

Hello,

  I have a program that I can run on a laptop that has a sample rate of 20,000 and samples to read set at 60.  (It uses a PCMCIA 6036E card)  I put this program on a tower computer that has a PCI 6036E card and an SCXI chassis and when I try to run the program I get an error saying that the max sample rate is approx 7,000.  I noticed that if I delete a channel out of the task the error message would report a slightly higher sample rate is available.

  Is the SCXI chassis limiting my sample rate?  My task only has 6 channels in it.

Bryan

[Wallace_F]

Hello Bryan,

In your case, if you are using an SCXI module to connect to your signals for your six measurement tasks, it might be the sampling rate of the SCXI module that is the limiting factor. Are you using an SCXI module to connect to your signals? If so, what are the model numbers of both the SCXI chassis and module?

Best wishes,

Wallace F.

[_Bryan]

The modules are two 1102's and I am using a scxi 1000 chasis.

[Wallace_F]

Hello Bryan,

The scan rate of your data acquisition setup is dependent on four things:

1.      The sampling rate of your DAQ board.

2.      The sampling rate of the slowest SCXI module.

3.      The number of channels in your scan list.

4.      The resolution of your DAQ board.

In your case, the SCXI-1102s sample at 333kS/sec while the PCI-6036E has a sampling rate of 200kS/sec. That means that to start with, your limiting aggregate sampling rate is going to be 200kS/sec. Now take into account the number of channels in your scan list by dividing the sampling rate by 6 to get 33.33kS/sec.  When you take into account the minimum settling time required by you SCXI modules for a 16 bit resolution DAQ board, and this will reduce that 33.33kS/sec/channel quite significantly. In fact, the settling time required for a 16 bit DAQ board will reduce an aggregate sampling rate of 333kS/sec to an aggregate sampling rate of 50kS/sec.  When you divide this by 6, you get approximately 8kS/sec/channel.   Consider how much less this would be if you started with an aggregate sampling rate 0f 200 kS/sec instead of the 333kS/sec. For more information, please reference the knowledgbase article linked below.

http://digital.ni.com/public.nsf/allkb/410A70C25A4D12B486256A1E0070BDAE?OpenDocument

Best wishes,

Wallace F.

[moussj]

Is it possible to share the article related to the provided obsolete link below?

http://digital.ni.com/public.nsf/allkb/410A70C25A4D12B486256A1E0070BDAE?OpenDocument

Thanks.