And unless you only want only the very last acquisition recorded, you're going to have to change your VI. When the while loop stops, all it passes to the write waveform is the very last 1D array captured. If you want all data saved, put the write inside the while so that with every iteration you append to the same file. Or, turn on indixing where the 1D array exits the while loop. This will create a 2D array of all data acquired. Also, using Write Waveforms to file is probably not the best function unless you are actually creating a waveform datatype with timing info. Write to Spreadsheet will write a 2D array of DBLs or create a waveform datatype inside the while loop