07-15-2009 09:44 AM
Hi. I'm using a DAQ board to acquire triggers using the retriggerable setting. I'm acquiring waveforms and it is working great, except the times are incorrect.
If you take a look at the attached VI, the front panel controls the acquisition rate (default 250 kHz) and the number of samples to record after each trigger (default 10). The DAQmx Read VI is called each time the 10 samples are read to read them into the computer as a waveform.
After outputting all of the waveforms as an array and looking at the t0 for each, the t0 values are not what they should be. Instead, the first t0 value is correct, and the rest are separated by exactly 4x10^-5 seconds. That would be correct if there was no pause between triggers (reading 10 samples at 250 kHz takes exactly 4x10^-5 seconds). But when reading in triggers that occur 10 times a second, the t0 values should be separated by 0.1 seconds, right?
Is there any way to stop the DAQ board from pausing its internal clock while it waits for the next trigger?
Thanks!
Jeremy
07-16-2009 11:38 AM
Can someone at least run this program on their computer so I know if it's just me with this problem?
Thanks,
Jeremy
07-16-2009 04:14 PM - edited 07-16-2009 04:14 PM
07-16-2009 04:22 PM
Thanks for helping, although it seems to me like you've got the same problem. You're down to 500 Hz, so the first timestamps are separated by exactly 0.02 seconds, no matter how far apart the triggers come in.
Jeremy
07-16-2009 05:18 PM
Hi Jeremy,
I want to clarify for myself what your goal here is. Are you wanting to only timestamp when the triggers occur and have no timestamp associated with the individual samples?
Also, what data acquistion board are you using and what version of the DAQmx driver are you using?
Thanks!
07-17-2009 09:24 AM
07-17-2009 10:34 AM
Thanks. I guess I'll just go with Windows timestamps (although they're rounded to the nearest millisecond or so for me).
I'm using the NI DAQ-6251 USB with NI-DAQmx 8.8.
Jeremy
12-19-2018 10:15 AM
Has somebody found a solution for that. I have very similar issue that is posted HERE.