Why is the 9206 C Series Module considered Bank isolated if there is only one COM?

[SeanDonner]

The 9206 C-Series Module is quoted as "Bank isolated; ideal for fuel cell measurements."  When I looked up what NI considers Bank Isolation, I found the following image which clearly shows the different banks.  However, if you look at the 9206 connector image from the manual, you notice that it only has a single COM pin and this adds the limitation that none of the 16 channels can be more than 10V away from this COM pin.   So my question is, if this 9206 is Bank isolated, where are the banks?  I was expecting at least two COM pins, one for each bank.

[ahmad191]

9206 just has a single bank of input channels which can either perform 32 single ended measurements or 16 differential measurements. Here Bank Isolation just means that the inputs are not channel to channel isolated, rather the whole bank of inputs is isolated from earth ground.

[SeanDonner]

That's what It seems like but NI went out of their way to differentiate bank-isolation from channel-to-earth isolation in their isolation white paper. As far as I can tell, ALL C-Series modules are at least channel-to-earth isolated so why point out for this module that it is bank isolated? It seems like there must be more to it than you and I are thinking.

[dousley]

In the white paper you are referring to, http://digital.ni.com/public.nsf/allkb/CF71091043A6193B862573D70077138B, it says under the Channel-to-Earth section that:

"This is the most fundamental type of isolation, this protection is covered by bank and channel-to-channel isolation."

The 9206 is indeed channel-to-earth isolated. As Ahmad191 pointed out, the specific kind of channel-to-earth isolation that it has is a bank style of isolation. And it only has one bank.

[SeanDonner]

So when NI states in their description of C Series modules that "In most cases, the CompactRIO modules provide isolation from channel-to-earth ground." would that imply that said modules are also bank isolated with at least a single bank? 

I guess what I'm trying to get at is if Channel-to-Earth isolation is a strict subset of Bank isolation or can there be a Channel-to-Earth isloated module that is *not* Bank Isolated?

If indeed Channel-to-Earth isolation is a strict subset of Bank isolation (with just one bank), why did NI go out of their way to call out Bank isolation for this one module but only call out Channel-to-Earth isolation for the other modules with only a single bank?

It is worth noting that this 9206 has a single DO and PFI line, are those part of the same bank as the AI channels too? 

[ahmad191]

They said "Bank" because more than one channels were grouped together to form a bank. If it were a single channel I guess they would have just called out "Channel to Earth isolated"