Hello.
I have been pouring over information trying to find answers to my specific issues, but havent had much success, so I am asking here for some clarification. I have read over the field wiring guide, which has helped a lot, but it hasnt quite covered all of my bases.
Anyway, here is my situation and issue. I am using a 6343 multifunction DAQ, and usually measure all channels in differential mode. All of my input are via BNC connectors, so I have a junction box which has the BNC connectors connected to it, and then they are terminated inside with Cat 6, which then goes out to the DAQ itself. I use the solid of a color as AI+, and the striped of a color as AI- for each channel. Inside the junction box, every single wire is then connected via its own 11kohm resistor to the chassis ground point on the DAQ. Everything that requires power (a handful of piezoresistive pressure transducers and some thermocouple transmitters) are powered by an ungrounded 24v battery supply.
My issue is that I am suddenly working with a set of projects which will require more than the 16 differential channels that I have, and with rapidly changing sensor configurations. This has lead me to look into using either RSE or NRSE measurements on some of the channels so that I can open myself up to say, 22 channels. i.e. 10 differential channels, and 12 single ended. This, however, creates an issue in the junction box, as nothing is connected to AIGND or AISENSE, and each channel is using a bias resistor. To avoid removing the bias resistors, which would cause a major problem when I need to switch things around all the time, I am considering using NRSE for the 12 channels, since the field wiring guide shows these lines with bias resistors as a good practice.
That said, however, I do not have anything connected to AISENSE. This leaves me with a couple of options, and I do not know which would be best, or which is even reasonable.
-Option 1, I put an 11kohm bias resistor directing inside the DAQ between AIGND and AISENSE, and then change nothing else. This would leave the the NRSE channels with only a single wire, and absolutely no wires going to AISENSE. I am not even sure if this would work, but thought that since both sides are connected to AIGND, that it might work. This is desirable for me, because I would never need to rewire between system changes.
-Option 2, I do the same as in option 1 with the bias resistor, but then I have to make a negative line for each single ended device that goes back to the AISENSE. Either all of them terminated at the single AISENSE pin on the DAQ, or terminated together, with a single wire going to AISENSE.
Can anyone tell me if option 1 will even work? And possibly pitfalls of each? One assumes that there may be a more elegant solution, which I am also open for. But I would prefer that the junction box be rewired a maximum of one time, and not between each configuration change, so if it is possible to wire it in a way that I can remotely flip channels between differential and single ended at will, without needing to physically go there to rewire, I would be very open to suggestions.
Thank you very much for your time!
