I've recently connected a network of 14 thermistors in parallel to a labjack t7 (outfitted with mux80 and 4x cb37 expansion boards). I used excitation circuit #4 - and confirmed voltage readings (and corresponding resistance/temp calculations). All 14 measurements are solid. However, when I introduce 3 differential voltage measurements (each measuring a battery voltage), all thermistor voltages drop significantly. My understanding was that by measuring the batteries as differential pairs, they are isolated from single-ended thermistor measurements. Any ideas as to why the battery voltage measurements are interacting with the thermistor voltages?
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Unfortunately, true isolated measurements are not possible on the T7 without external hardware. Your battery measurements as they are do not look valid; you must have a DC path to GND at the AIN inputs for bias current to flow. The following section has a related discussion. I would also recommend seeing the section about measuring power supplies in series:
http://labjack.com/support/app-notes/differential-analog-inputs#differen...
Another part of the issue might be the source impedance of the thermistor circuits. You could see channel settling issues with source impedance above 1kΩ. I would recommend seeing our settling time application note:
https://labjack.com/support/app-notes/SettlingTime