-10920 Error at low pulse frequencies when doing simultaneous AI DAQ

[Jamie Fraser]

Hi,

I am using a DAQCard 6036E (and in the past a DAQCard 6062E) to do a simultaneous AI DAQ and buffered period measurement.

The buffered period measurement fails with very low frequency pulses (~68Hz on a 700MHz PIII) when the AI DAQ is also running. However, when I change the interrupt generation from ND_AUTO (which defaults at the AI sample frequency in use to ND_INTERRUPT_HALF_FIFO) to ND_INTERRUPT_EVERY_SAMPLE the buffered period measurement copes with much higher frequencies (~2-3kHz min).

I understand that PCMCIA devices use interrupts not DMA, and also that the DAQ-STC has only one hardware save register for each counter, which I assume must be read by NI-DAQ before the next gate sign
al causes the counter value to be written into the save register.

My question though is why changing the AI interrupt generation method as described above should help as it seems counter-intuitive. I would expect better counter performance when there are less AI DAQ interrupts being generated (i.e. when there is only one interrupt being generated per half FIFO) and not when there are more being generated.

Any enlightenment would be appreciated.

Jamie Fraser

[Sarah Thompson]

Jamie,
You may have already seen this, but here is a KB article about the -10920 error: Why Do I Get Error -10920 When Doing Buffered Counter Operations? http://digital.ni.com/public.nsf/websearch/8FB9091CB9BB452B8525642000554799?OpenDocument. I hope this helps.

[Jamie Fraser]

Sarah,

Thanks for you note, but the article you mention does not address the problem. I hope somebody else can help.

Regards

Jamie Fraser

[Sarah Thompson]

Here is another post that talks about a similar issue - maybe this will help.
http://exchange.ni.com/servlet/ProcessRequest?RHIVEID=101&RNAME=ViewQuestion&HOID=50650000000800000067870000&ECategory=Measurement+Hardware.Counter%2FTimer.

[Jamie Fraser]

Sarah,

Thanks again. Your link is actually to a thread that I started myself that I had totally forgotten about. I have re-written my app to be multithreaded, but still get the same problem as I had before. I will consider further what the previous respondent had to say and may have to ask further questions.

Regards

Jamie Fraser