multiple DAQ cards

[mgilorma]

Ed,

Due to some massive oversights on my part, I realized that I'd better output any NIDaq exceptions instead of ignoring them.  What I found is that I am getting the samples no longer available exception when just aquiring 4 cards with 10 channels at 100000 S/s.  I get the same error when recording 4 cards x 64 chans x 15625 S/s.  So I guess the first thing I need to do is figure out how to aquire 4 cards x 10 chans x 100000 S/s?   Sorry I didn't catch this earlier.

thanks for all the help

[Ed W]

Hi Mike,

This error can be avoided by doing just as the message says – increase your buffer size.  A good guideline to follow is to create a buffer size that is 10% (in bytes) of your channel count times your sample rate (in Hz).

buffer size B = 0.1 x  (# channels) x (sample rate Hz)

So if on each 6071E, you’re sampling at 10,000Hz on 10 channels, use a buffer size of 10,000 B for each device.

Best regards,

Ed W.

Applications Engineer
National Instruments

[mgilorma]

Ed,

I was having trouble understanding how to increase the "buffer", because I wasn't aware that I could increase the buffer size since I was doing a continuous aquisition.  But I found the documentation that told me how to do just that using Task->Stream->Buffer->set_InputBufferSize( int ).  However I found that in order to get things to run smoothly for the case where I had 4 cards with 10 chans per card running at 100,000 S/s I had to set my buffers to 1,000,000.  It seems that for all the combinations of chans*rate that = 1 M S/s the size of the buffer can use the defaults for rates < 31250 S/s but above that I found that the buffer size would have to be around 10 times the sampling rate.  At this point the CPU still is running at 100% but I am able to aquire with no exceptions and also record the data to the disk.  Hopefully I have not overlooked anything and this will be the end of this thread!

Thanks for the help