Hi,
Take HP6624A for example,
Instrument Driver for HP6624A can be downloaded from
hereAfter installing the ID, please open its Application Function Example, "hp662xa Getting Started.vi"
You will find that any working VI should have the followings:
a. Initialisation
b. Action/ Measure etc
c. Close
PS: Initilisation (before entering main loop) and Close (when exiting program) should be executed only once, unless otherwise.
Regards,