Shaun,
The DAQ device should be set to NRSE mode when using the SC-2345. Version 2.1 of Measurement and Automation Explorer (MAX), which is included with NI-DAQ 6.9, will automatically set the card to NRSE mode when an SC-2345 is selected as the signal accessory.
Unfortunately, it is not possible to use the differential input mode with the SC-2345 and SCC family. Please refer to the SCC-AI User Manual, page 10, the section titled, "Connecting the Input Signals," for more information. You will find that the inputs are designed in a floating (nonreferenced) single-ended configuration.
SCC-AI Series Isolated Analog Input Modules User Guide
http://digital.ni.com/manuals.nsf/websearch/E270A0A15C11C3DB86256AEF006D5F02?OpenDocument
If you would like t
o perform differential measurements, perhaps you would benefit from an SCXI system.
Which DAQ System Is Right for You?
http://volt.ni.com/niwc/common.jsp?page=daq_10x_sig_cond_right&node=1603
Regards,
Justin Britten
Applications Engineer
National Instruments