My AO triggers were delayed by about 1 ms out of every 1000 ms

[Fuh]

Dear Corby_B,

Thank you for your invaluable comments.

I have three more questions.

(1) Where can I find the clock rate of the master time base of my DAQ6062E?   I have used the DAQmx Timing Property node and set it to "Sample Clock".  I also set the "source" terminal to be "OnboardClock".  I have attached the configuration as a .jpg file with this post.

(2) Can you tell me more about the "software manipulation" that I can do to go around this issue?  Given the actual output rate was 44095 Hz, I re-created a wave file with the same sampling rate (44095 Hz), and tested.  Still the delay is proportional to the number of data points presented throught the AO channel.  I think I am confuse on what to change in my software to go around with this problem.  Can you be more specific of what I shall do to manipulate my software and to go around with this problem?  Thanks a lot!

(3) Can NI PCI-6221 be a solution for my application?  During my early attempts, I tried to output my triggers through DO channels.  It didn't work because my DAQCard 6062E does not provide correlated "hardware-timed" DIO.  A NI representative has recommended me an alternative - to purchase a NI card (NI PCI-6221) that provides the option of correlated "hardware-timed" DIO.  If I purchase a NI PCI-6221 card and route my triggers through the DO channels, will this solve my problem?

My apologies for my ignorance on many things, but if you or anyone could help me with this, I would greatly appreciate it.

Sincerely,

Fuh

[Steve_B]

Hi Fuh,

The Master timebase for the 6052E counters is 20MHz and this can be found on the product page listed under Specifications. Corby was referring to using the Timing Property Node to determine the actual sample clock rate. I have included a screen shot of how this can be done. You can find the property node on the DAQmx palette listed as DAQmx Timing Property Node. When you place it on your Block Diagram you can select the appropriate property (Sample Clock>>Rate). It sounds like you tried creating a sound file that has 44095 points in it and that sounds like a good idea to try. I would recommend that you try setting your rate to an integer that can be created by dividing 20MHz by an integer. This would test the idea more simply than trying to generate fractional frequencies. As far as using a PCI-6221 for this application, the only benefit would be that you can use an 80MHz timebase to divide by an integer to create your frequency.

NI PCI-6052E
http://sine.ni.com/nips/cds/view/p/lang/en/nid/2601

[Fuh]

Dear Steve, Corby_B,  and Rob,

I created a wave file with a sampling rate of 40,000 samples/second.  I then set the sample clock rate to 40,000 Hz.  And you know what?   It worked!!!   Actually it worked perfectly.  I checked the timing and recorded data points in the Neuroscan recording system.  It is "exactly" the time length I would expect.  Thank you all so much for all your help.  I really appreciate that.

Sincerely,

Fuh