I have a PXIe-8840 connected to two SRS-630 at address 7 and 8 via the GPIB connector. When I run the "Scan for Instrument" out of MAX I don't see the instruments.
I have tried using my laptop and a GPIB-USB-HS+ and connect to the same instrument and it works fine. I have tried replacing all the cables. I have also tried just connecting to one instrument.
I have attached an NI-SPY trace capture.
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Did you try matching the GPIB port settings on NI MAX for both the inbuilt GPIB and USB GPIB methods?
What happens when you try to communicate with a particular instrument address by manually keying in the address though not automatically detected?
I get a timeout error when I manually try to talk to the instrument. I have a second PXIe-8840 configured the same way as the original one and it works fine.
It is not uncommon for the GPIB cards inside some of the older instruments to have problems or the GPIB cables to have a break in a wire. If at any step the wrong response is seen, continue through all steps to determine if there is more than a single issue.
GPIB card seating and wire breaks can be intermittent or dependent on how they are connected.
It appears to be an instrument issue. The SR630 locks the GPIB bus and doesn't release it until you power it off. I will get with the instrument vendor.