I looked at your code and in order to append data as you want to a measurement file, you must add the new data as new channels. Measurement files are based on channels. Writing the same number of signals over and over will simply append the data to the end of the existing data. I already mentioned that you can merge your NEW data signals with the OLD data signals to get the desired effect.
Example, your 2D array has 4 rows...that creates 4 channels of data in the measurement file. If you take your 2D array of 4 rows and append data to make it 8 rows and then write to the measurement file, you will have 8 channels in the measurement file. If you already wrote 4 rows and then write 4 rows again, the new data will be appended to the existing 4 rows. This is one of the drawbacks of the Express VI. Otherwise, I would suggest using the TDMS file primitives.
