Hello,
Check into the Timeout feature of VISA. In the Instrument IO/VISA/VISA Advanced pallette, you should find a "set timeout" VI (resembling a property node) that will allow you to tell the VISA Read how long to wait before it moves on and gives a timeout error. Then, all you will need to do is add a condition that stops the loop whenever the error cluster contains that same "VI_ERROR_TMO" error. If you would like more information on this function and these errors, see the LabVIEW online help or the VISA programmer's reference, located at http://digital.ni.com/manuals.nsf/websearch/87E52268CF9ACCEE86256D0F006E860D?OpenDocument&node=132100_US
Scott B.
Applications Engineering
National Instruments