Time Stamp Offset Issue when Reading TDMS

I am having an issue when reading a TDMS file and displaying it on a waveform chart in LabVIEW. My waveform chart will always display the time stamp with a negative offset of 18,000 samples.
To make that easy, let's say I am sampling at 1000 samples per second and I log my data to TDMS. When I read that TDMS and display my waveform chart data, the chart displays the data read from the TDMS 18 seconds earlier than the recorded wf_start_time stated within the TDMS. If my wf_start_time is 08:00:20.000 AM 12/02/2014, then my waveform chart displays a start time of 08:00:02.000 AM 12/02/2014. Likewise if I sample at 4000 samples per second, my start time is off by starting 4.5 seconds earlier.
I am setting my Xscale.offset = wf_start_time and it reads back correctly, but the start time on the waveform chart is still wrong.
Because I am dealing with larger TDMS files (500mb+), I sometimes decimate the data to view it due to memory issues. Here, this issue occurs again. If I decimate the data to only display 1 out of every 10 data points, that offset is further shifting by a factor of 10x; going from 18 seconds to 180 seconds.
Is this some kind of UTC/system clock time stamp discrepancy or something else?
Solved!
Go to Solution.
Attachments:
VI edit tdms.png ‏41 KB

It's okay to mark your own post as a solution if it really is the solution, as it is in your case. That way, people that have the same problem know it was solved and they can see what you did to solve it.
Bill
(Mid-Level minion.)
My support system ensures that I don't look totally incompetent.
Proud to say that I've progressed beyond knowing just enough to be dangerous. I now know enough to know that I have no clue about anything at all.

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First, let me congratulate you on taking your first steps to learning LabVIEW. If you have not already done it, I highly recommend you go through the online tutorials. You have an actual project to work on, so application of what you learn will be fairly immediate.
For your actual program issue, you need to read the data from the Excel file and convert it to a timestamp before you set your filename. The order of operation of your program is to set the TDMS file name while simulataneously reading from the Excel file. After you have already created the TDMS file, you convert the data to a timestamp and write this to your timestamp front panel control. Note that the first point you write to the TDMS file may or may not be what you think it is. It could easily be the same 180000.000 value you are using to name the TDMS file. You have what is known as a race condition. The order of operation between the read and write of the timestamp control is not known and can be variable. It is one of the reasons that you should NEVER use local variables to pass data around. Use wires. In LabVIEW, wires are the data and take the place of variables in a text base language. Front panel controls should be used only for user interace reasons. In your loop, you should wire the timestamp from its current conversion (wired into the timestamp on the front panel) directly to the TDMS write (currently wired from a local variable of timestamp).
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This account is no longer active. Contact ShadesOfGray for current posts and information.

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Do you work with Novell technologies at a university, college or school?
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Time Stamp Offset Issue when Reading TDMS

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