The 3478A is an old device with limited GPIB commands.
To trigger it you need to send a GPIB Trigger (aka, Group Execute
Trigger). ?It's a bus control sequence, not a text command.
Likewise, a full reset is done via a GPIB Clear sequence (aka, Device
Clear).
The trigger command "Tn" sets a particular trigger mode from 1 to 5,
but does not itself cause a trigger. ?And "Hn" is selecting one of
eight presets, 0 to 7, which are described in the manual.
You could put it the same mode as a reset by sending "F1RAN5T1Z1D1".
Note that it only accepts upper case.
If you just perform a read from the 3478A with no command, it will
return the reading after the next trigger. ?So, if you leave it on
internal trigger mode (T1) and do a read, you'll always get the latest
reading.
-mark
