Why do I get grabled txt when use Tektronix DSA7000 driver to save data?

Here's the program I use to save waveform to data, but the txt file I get is always grabled. I'm not sure if I need to convert the data form or use other function other than the one I'm using 'write to binary file'.

Code:

txt file:

By the way, the file can be normaly read back to waveform.