Dear Rikud,
I checked the Command Set mode and the device is indeed in the SCPI mode.
I tried to use the Keithley 2460 connected to a cRIO-9030 through USB and it seems to work much better or at least with less connection failure (still the VISA Read box which outputs an error).
I take the opportunity to join my VI exhibiting this connection issue (although it is entirely based on the library example of the Keithley 2450) because I was wondering if it was possible to realize a measure of the current in less than 60ms which is what I actually measure. It corresponds to a 15Hz sampling frequency which is extremely low for my application. Is there a way to increase it although the VI can almost not be simplified ?