Specifically i would like to know what failure modes are possible on the input circuitry (Figure 1 in the schematic). The block diagram provides some info, but i need to confirm with NI. A schematic of the input circuitry would also be helpful.
Here are my guesses:
AI+/- Input fails open - For example the internal switch fails to provide the 4 mA excitation current AI+/- Input fails to supply - not probable for a single point failure, but perhaps the switch/excitation current circuit on AI+ looks different than in block diagram. And possible that the AI- op amp shorts to its supply. AI+/- Input fails to GND - not probable, depends on what the common mode bias current circuitry looks like
I am unable to determine the failure modes because the block diagram does not provide enough information. This is for a high reliability application and we need to confirm that it is safe to hook up the NI 9232 for test.
I took a look, and it does not appear that the information you are looking for is publicly spec-ed anywhere. That means we won't be able to release that information to you on the forums.
To pursue your question further, you'll need to create a Service Request with us by calling 866-275-6964. We can then work with R&D to see if the information you need is spec-ed and what we would be able to release to you.