Hi,
I couldn't find an instrument driver for the Keithley 2400 at ww.ni.com/idnet. You mention the Keithley VI, Which VI is that?.
The best source of documentation is the instrument's user manual. If you have an instrument driver, you can compare the commands sent by the VI with the commands listed on the manual. If you don't have an instrument driver, the user manual has all the commands needed to control the device.
DiegoF.
National Instruments