NI PXI 2800

[bholsinger]

In this setup I don't need to access the analog bus on the carrier backplane. There is only one switch card, 2834A. Do you interpret the documentation to say the front panel AB connections are not accessible unless the interlock resistor is in place? That's not how it works for me, as I can certainly access devices attached to the front AB pins, through the matrix, even without the interlock resistor.

[Kyle_A.]

It seems like whether you're able to use the 2834 with or without the interlock, the intended behavior is that an interlock is required for operation, even with a single module. It is defined by the carrier, so using just one module in the carrier should mean it is required. I would try using the interlock resistor to see if the behavior on AB0 goes away. It is good feedback to know there is still some functionality that works even without the safety interlock in place.

As for your thoughts on the interpretation of documentation, I take it as you should not be able to connect to any columns on any AB without the interlock resistor in place, and that the only functionality you'd be able to run on the switch block is the integrated relay test. The 11V you are seeing may be a part of that relay test.

[bholsinger]

This is the correct answer.  It's odd that the switchblock and matrix appears to work correctly, if you don't look too closely, without the interlock resistor.  But it turns out that the lack of a resistor will cause 11V on AB0 and 100K shunts on all the AB1-7 lines.  The documentation doesn't make it clear to me, but experience is the best teacher after all...  

Thanks to all for comments and answers.