Adjusting time stamp of AI waveform when using pause triggering

Question

Hi Everybody,
I've written a VI that acquires data (AI) at specified time intervals
by using pause triggering and a counter signal, but the resulting time
stamps associated with the data points in the AI waveform are NOT the
actual time relative to the start of the initial acquisition. I was
thinking of modifying the time stamps (post-acquisition) for each set
of data points per interval by adding the "off" time as set by the
counter signal, thereby adjusting the time stamps of the data to real
time. I then have a subVI that will convert the time stamps to elapsed
time. I also have an AO waveform being generated at the same time, and
was wondering if I could somehow use those time stamps values if they
were synced to the AI somehow, although this seems more difficult. The
adjustment does not need to be extremely accurate, and can vary on the
order of seconds (e.g., the last data point could be at 9990 seconds
for an acquisition that actually ended after 10000 seconds). Any
suggestions?
As an aside, the important point of this part of my program is to
reduce the amount of data being collected. I need a high sampling rate
to acquire waveforms with pulse widths on the order of milliseconds,
but typically run the experiment overnight (+12 hrs.) so the files get
really big (e.g., 3 GB!). I could try writing to binary files, but I
haven't figured out how to read the file and then split the data into
smaller files of user-defined size that can then be converted to
text/.xls files. If you have any ideas on how I might do this as well,
I'd greatly appreciate the help! Thanks!
Unagi

Answer 1

Unagi,
I am not exactly sure what you are trying to do, but I can
take a guess.  When performing analog input measurements the waveform is
composed of t0, dt and Y.  You can manipulate any of these values after
the data has been acquired.  If you set up the task the waveform should
contain an absolute time, not relative.  If relative is required, as you
suggested, this can be done post acquisition with the build waveform components
vi. 
I do not understand exactly what you want do with the
timestamps for the analog output.  Do you
want to use the relative time computed from the analog input data for the
analog output waveform?  If so, you could
build a waveform and use the t0, dt from the analog input processed/relative
time waveform.  Again this would be done with the build waveform components
vi.
Finally, a binary file would reduce the amount of memory
required when saving your data.  A binary file is fairly simple to save
and open in LabVIEW.  There are a couple examples in NI Example Finder (i.e.
Write Binary File and Read Binary File) that show you how to write and read
binary files.  If you write the data to a binary file during acquisition,
and modify/split it later you could open the binary file, retrieve the data in
LabVIEW, and write a small subset to a text file.  Alternatively, you could
perform some analysis of the data during acquisition and only save the set of
data that you require post acquisition.
Regards,
Jesse O.
Application Engineering
National Instruments
Jesse O. | National Instruments R&D