I don't know much about the 830 lock-in amplifier, but most instruments use the same commands regardless of whether you use GPIB or RS232.
So, I suggest that you download the LabVIEW driver from http://ni.com/idnet/, and modify it to work with the serial port. It may work with no changes. Or, you may have to modify the Initialize VI by adding "VISA Configure Serial Port" to set the baud rate, parity, handshaking and other RS232 settings. Let us know if this works. I hope this helps. Brian
