Hi Noelia
VI-Logger only save data in ASCII format. If you want to save/retrieve in binary, you should use a programming language like LabVIEW to do so. Here is a link to a very in detail example about it
http://sine.ni.com/apps/we/niepd_web_display.display_epd4?p_guid=B45EACE3F12556A4E034080020E74861&p_node=201249&p_source=External
Hope it helps
Javier Gutiérrez
NI Aplication Engineering