finite data acquistion buffer, error -10089

[jonny e]

I have a 6071E and Labview 7.1, and I am trying to acquire a finite number of scans, but am running into a slight problem. 

Under certain conditions, get error -10089 in AI Control.vi  "NI-DAQ LV:  The total count is inconsistent with the buffer size and pretrigger scan count or with the board type."

This error occurs when the total number of scans I request (as an input to AI Start.vi) is greater than the buffer size I declare with AI Config.vi.

For instance, if I declare a buffer size of 4000 scans and I request 4001 (or more) scans, the error occurs.

This seems to be "logical" behavior, except that I thought acquisition was, by default, circularly buffered.  Thus the 4001st scan would just overwrite the 1st scan in the buffer, etc.  Or maybe it isn't?  If this is the case, what if I want to have an acquisition that lasts 20 min at, say 20 kHz over 50 channels...there's no way my computer memory would handle a buffer that size. 

I'm missing something obvious here.  Can someone please clue me in?

[Laura F.]

Hi Jonny,

I think your confusion over the error you see is that the circular buffer applies to continuous acquisitions, not finite.  With finite you cannot specify the number of points to acquire to be more than the buffer size. 

As for your application I would use a continuous acquisition and then use some timing condition to force your while loop to stop after 20 minutes. 

Let me know if that doesn't clear things up for you.

Laura

[jonny e]

Hi Laura-

Thanks very much for the info.

I figured this must be the case, all though it didn't seem to be well documented, if at all, in the NI manuals etc.

Good suggestion for the "long" finite acquisitions.  I think I'll just count the number of scans read with AI Read.vi, and terminate upon reaching enough scans.

thanks again,

jon