How to avoid opening file for writing each time?

Question

Hi!
I have real time data acquisition from a digitizer (NI PXI 5124, but it is not important for my question). Using several NI SCOPE examples I wrote a simple labview program that does the following things in a while loop: configures the digitizer, fetches data and display it in a waveform graph, calculates FFT and display it in a waveform graph, and while the “Save To TDMS File” button is pressed it writes data to a TDMS file. And it works almost fine and “almost” is because from time to time some data are not written to the file. I suppose that the reason is that I open and close the file each time. How can I open the file only once when the button “Save To TDMS File” becomes active and close it at the end, when the button “Save To TDMS File” becomes inactive? I had some ideas using local or global variables but I didn't’t manage to make them work.
Additionally, how can I make “File Path” control inactive while the “Save To TDMS File” is active?
Thanks!
Attachments:
SimpleDataAcq.vi ‏340 KB

Answer 1

You could save the button's value in a shift register.  Then you can see if the value changed.  If the value changed to TRUE, open the file and use a property node (Enabled) for the path control to disable it.  If the value changed to FALSE, close the file and re-enable the path control.  You will need to save the file reference in a shift register as well.
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