Need help with tracking exact time of data acquistions

[zwagaroo]

Hi!

So I'm working on a project using NI 9215 DAQs for voltage data acquisition. For my purposes I need to track the exact time at which a piece of data was logged to get precise numbers on how much time has elapsed between any 2 measurements. Eventually if an event happened (which I want to eventually analyze using python later) get a really good estimate on when it happened. I am very new to LabVIEW, and I'm not even sure if it's possible. I am using the DAQmx configure logging module to try to log my data into a TDMS. But the result only gives me a wf_increment for the entire dataset which is just how much time is supposed to pass between 2 measurements. But I'm a bit unconvinced that the DAQ will be able to always log exactly at the wf_increment as external forces especially testing in high energy environments could do things to the hardware. Is there a way to configure this to show timestamps with the default configure logging? Or do I need to implement custom logic in logging my data?

I have attached my vi.

Thank you so much for your help!

Thanks!

[ZYOng]

There is no VI attached.

Anyway, if you are using Sample Clock timing, you don't have to worry about the accuracy of the waveform. See Accuracy of the Waveform Timestamp Returned by NI-DAQmx for a detailed explanation.

If you are worried that your high-energy environment might affect the hardware, the analog signal might also be impacted. Perhaps you should consider using some shielding?

[RTSLVU]

Well I don't use DAQmx but in NI-Scope T0 can be in Absolute Time or Relative Time.

If DAQmx does not have an Absolute Time option then I would just take a timestamp each time you begin data acquisition.  

[mcduff]

A lot of what you can do depends on your exact timing needs and budget. I have a bit of involvement using various solutions:

t0 here within refers to the initial timestamp, ie, the start of acquisition.

1. Typically t0 for DAQmx is not precise except if use TSN capable DAQmx equipment. Then you can get microsecond accuracy for t0.
2. NI-Scope has hardware time stamping, but don't be fooled by what it means. Yes, you can get a trigger's timestamp in hardware but unfortunately that timestamp is not related at all to the absolute time. 
3. If you have a GPS that outputs a PPS then you can record your data and the PPS concurrently. You know the PPS is every integer second; using that and a semi-accurate t0 from your computer should give you a good approximation of the absolute time. You can also tell if your sample clock is drifting using this method.