By "ASC 11", do you mean ASCII (American Standard Code for Information Interchange)?
Start by looking at the Write to Text File.vi and Read from Text File.vi examples that ship with LabView. To find the examples, from any LabView window, goto Help >> Find Examples >> Search. Then enter File I/O in the box labeled Type a keyword to find. These examples are specific to tab-delimited spreadsheet-format files, but you'll see how to open a file, read from it, convert from string to numeric, and close the file.
On the String >> String/Number Conversion palette, there are several conversion functions. The most flexible function to convert to a number is Scan Value, where you can specify the numeric representation of the output number. LabView calls 32-bit floating poin
t numbers Single Precision.