Is there a way to read the value of the counter on board any cDAQ chassis along with sampling from other modules on the chassis? I want to try to use this as sort of timestamps for the acquired samples. Thanks in advance!

I'm basically repeating what others have said, just expanding on a couple things using different wording. Unless you go out of your way to configure otherwise, your AI task will sample at a *very* constant rate based on a clock in your cDAQ chassis. Any further timing info you try to get with a counter will be based on that same clock in the chassis, i.e., there will *not* be any new or better information available that way. If you were running your AI sample timing off some unknown *external* signal, then yes, timestamping those pulses with a counter *could* be useful. The t0 value of a waveform is a timestamp with sub-nanosecond *precision*. You can sample at 100 kHz, then iteration over a bunch of calls to DAQmx Read, and you'll see that the subsequent t0 values will *exactly* track and correspond to the dt value & the # samples previously read. The t0 value does *not* lose you any timing precision in your data. *Accuracy* is a different and trickier issue, but it's also usually not a significant consideration. Most data acq tasks don't *really* need to know if they started 2.24 seconds after 1:17 pm or 2.27 seconds after. Over the course of *very* long acquisitions, let's say 24 hours, you will probably see up to a few seconds timing skew between your PC's date and time clock and your DAQmx waveform timing info. Many data acq boards' clocks are spec'ed to be accurate to something like 50 parts per million. This works out to 1 part in 20 thousand. A 24 hour day has 86400 seconds in it, so one can expect an *inaccuracy* of up to 4+ seconds per day of continuous acquisition (or similarly, 1 second per 6 hours). But again, time-of-day accuracy usually won't matter, while the resolution & precision are far more than good enough for any sample rate a data acq device will support. -Kevin P

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Counters in DAQmx

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Wow, these are really great answers. Clears a lot many of my doubts. Thanks to everyone who took time to explain this.

Thanks and regards

Ashwin

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Counters in DAQmx

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