Hi Bernd,
I don't have some of the IMAQ VIs that your application is using, but if the IMAQ VIs are returning values with double precision, then you can change the number of digits of precision of the number. You can either right-click on the number and change the Format & Precision to display more digits of precision. Also, you can use the To Double Precision Float.vi which will add additional precision to your number.
The precision is not really something that is handled by File I/O VIs since those merely write the value of the number to a file and does not actually modify the precision of the number. You'll want to look into actually increasing the precision of t
he number instead.
Thanks and have a great weekend too! 🙂
Kileen C.