DAQ and signal processing simultanously with different rates

[Griza]

Hello,

I have a question. I have a PXI-8106 Controller and a PXI-6123. For my project I need to sample (after a trigger signal) 8 analog input channels with 500kHz for 10s. Up to now I have created a DAQmx task for this, with which I read all channels until the number of samples is reached. Afterwards I log the data. But now I simultaneously want to take one Sample of data (all 8 channels) every 10 ms for signal processing. Is this possible without effecting/disturbing the RealTime Performance? I've already tried this with a)shared variables and b) a while loop where I read one sample each iteration, but I'm not sure if this is the right way.

Thanks a lot

Griza

[RebeccaFo]

 Hello Gizra,

normally this should work without a problem but it depends from some things like how you program it and so on.

Do you have troubles with it?

Thanks,

[Griza]

Hello,

yes, I have a problem, because I'm not sure how to implement it. Is it better to aquire only one sample each iteration of a timed loop? Can a timed loop "run" with a period of 5µs? Or shall this period be 10ms and I aquire 5000 Samples and then  only read the last elementsin the array (or calculate the average)? And how do I communicate between the two loops? Local variables or RT FIFO? I don't have enough experience with LabView to solve this on my own.

Thank you

Griza

[RebeccaFo]

The easiest way for sharing data is to use the Realtime Communication Wizard. it is descirbed in the follwoing link:http://zone.ni.com/devzone/cda/tut/p/id/4676

I´ve also searched some more information material for you:

Real-time FIFO: http://zone.ni.com/devzone/cda/tut/p/id/3934

Shared Variables: http://zone.ni.com/devzone/cda/tut/p/id/4679

http://zone.ni.com/devzone/cda/tut/p/id/3898

Hope this helps,

[Griza]

Hi,

thanks so far, but I'm sorry, I forgot to say that both data aquisition and signal processing have to run on the PXI-8106. Because I have implemented an algorithmus which is based on an abel inversion method and needs a lot of calculation capacity. Up to now we have reduced the period for one calculation to 10 ms. But the data aquisition mustn't be affected! That's why I'm not sure if it is possible. Because what to do in the time critical loop: DAQ or signal processing? If I do the calculation in the non-determistic loop does it have influence on the time critical loop? Or does the aquisition still work with 500kHz then and the signals are "stored" in a buffer on the daq card(PXI-6123)?

Thanks again!