Multifunction DAQ

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Problem with external sample clock and sample rate


Thanks again for your help.

I have checked the trigger problem that you said number2(never start AUX task). The result of AvailSampPerChan indicators shows 0. which A.C.E didn't start. So when I remove the trigger at CI and AI(Main channel), it still doesn't fit at the right time but with the trigger, it has a too many points at XY graph. 

To check that problem, I did

1. I changed the Aux signal(trigger0) to a chirp signal (600 to 1200Hz) , so this signal is not faster than 10kHz. 

2. I added digital input vi, which I could see the TTL signal made by A.C.E.

3. I added the 'counter period Graph X' to check trigger0 signal is properly changed to TTL signal and make sample point at falling part of trigger0 signal.




As you can see from the photo below, the results show that TTL signal(Digital Waveform Graph) has almost 0.04sec delay. 

What I think, this TTL signal is used for the Main channel clock source, so the signal from Main will lose signal about 0.04sec at the front part. so the result of Trigger1 signal and XY graph show delay.




Also, I found some problems with the sample point at 'counter period Graph X'(3rd photo).Sample points from 'counter period Graph X' are made by Trigger0 signal at AUX&Main Graph. As you can see from the photo, the high frequency part of the signal at trigger0 has 8 falling edges, so it will make 8 sample points. but the result shows at 'counter period Graph X' shows 11 sample points. Does this mean AUX&Main graph doesn't show all signals?


It seems that trigger(synchronization) is necessary.. but using a trigger, still too many XY points. I did a few tests of triggers using only CI and  Main AI channel. The results are like this and I don't get it... I also attach vi that i use. Thanks


nicky15_5-1601988664637.png(using trigger only CI)


nicky15_6-1601988717593.png(using trigger only AI(Main channel)


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Message 11 of 12

That's an awful lot to try to digest.  I really only have time for a couple brief remarks.


- I can't immediately get concerned about the seeming "delay" in DI data or some other things about the data that appear *on the surface* to be a little off in the timing.  Waveforms and waveform graphs want to show data sampled at equal time intervals, much of your data is coming at variable intervals, some oddities are inevitable.  Don't have time now to track down every little nuance and detail.  


- I focused especially on the graph of individual counter periods.  The first and last ones shown made a lot of sense.  Their range (800-1700 microsec) matches the periods corresponding to the chirp freq range of 600-1200 Hz.  They also appear to be quantized at 100 microsec boundaries, which in turn appears to correspond to the AI sample rate.  I didn't *know* to expect this, but it seems sensible in retrospect.  It seems that the analog comparison event status is sync'ed to the AI sample clock.  I can buy that.

   The middle one shown is very, very different.  It seems to show a lot of samples right at 100 microsec, several that dip down to a small fraction of that amount, and none at all that exceed 600 microsec.  Something was different about that run.  I have no way of knowing what it was, and don't have any educated guesses offhand, but I'd encourage you to keep a close eye on those individual periods and figure out what corresponds to the times they don't make a lot of sense.



-Kevin P

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Message 12 of 12