Slow acquisition with PXI-4071

[cb3]

I'm acquiring 7 voltages using 7 PXI-4071's in a PXI-1045 chassis. I've programmed the initialization, triggering (I've tried both Immediate & Software triggers) and fetching of multi point data using LabVIEW. I initiate the fetch, or data read of the 7 DMM's, all at the same time, letting the system sort out the results. I'm also using 7.5 digit resolution for accuracy.

Everything seems to be working fine. Voltages are accurate and consistant. However, acquisition time is slow. A complete scan of 7 DMM's takes about 1400 msec. I've found that I can scan from 1 to  4 DMM's in <700 msec. If I scan 5 or more DMM's the acquisition time jumps to just under 1400 msec.

 Am I running into a buffer problem and if so how do I reset buffer size? Does this problem have something to do with the triggering? Has anyone else run into a similar problem?

Thanks

[J_Bray]

Check if you have "Reset = True" on the niDMM_initialize VI.  If it is true, this will cause the firmware to be re-loaded which would contribute the bulk of that acquisition time.  So try setting this to false and re-evaluate the timing.

Also, if you are calling the "niDMM_Reset" VI at any point, remove it and try the acquisition again.

As a related question, are you taking multiple acquisitions on each board?  If so, be sure to only call initialize once per board.  Then in the beginning of the loop, simply re-initiate the board to start the subsequent acquisitions.

[cb3]

Jim - thanks for the timely responce. Your comments got me thinking and what I found in my code was that I was using the niDMM_initialize VI correctly, in that reset was set to False. However, I was using the niDMM Read Multi Point.vi instead of the niDMM Fetch Multi Point.vi with the niDMM Initiate.vi. Read Multi Point must be re-initializing each of the 7 boards for each loop.

Thanks again;

cb