07-17-2009 03:13 PM
Hello,
I am unable to achieve desired poll rates from the Read ADC vi on my PXI-7356 card. I ran the Test_Motion_AI_Rate.vi form the article below and I am only getting 100 Hz update. My system specs are better than what was indicated in the article. I have a 3.16 GHz Intel Core 2 Duo with 4 GB RAM running Window XP. I would like to achieve the reported 500 Hz update that was indicated in the article.
http://digital.ni.com/public.nsf/allkb/41FDFB251D251C7F86256FE2007B412B
Any suggestions?
Adam
07-17-2009 04:20 PM
I found an issue. I have other routines running on the RT target which is significantly reducing the rate at which it can perform the Read ADC. So that aside...
When I just run the Read ADC test script I get 660 Hz for a single channel and 108 Hz for 6 channels (number of channels i am using). i'd like to be able to run 6 channels at 200Hz, but that doesn't seem possible.
07-20-2009 03:11 AM
The Read ADC rate depends on many factors like application complexity, processor speed, motherboard type and so on. The main purpose of the analog inputs on NI motion control boards is to provide analog feedback signals to the onboard control loop, but it was never meant to be a meaurement device. Due to the asynchronous nature of the data transfer you also will never be able to acquire signals with a deterministic timing.
For fast and accurate measurements I strongly recommend a DAQ device like a PXI-6220. These devices also can be synchronized with your motor operations (e. g. correlate analog signals to motor positions).
Kind regards,
Jochen Klier
National Instruments