You can connect floating signal sources and ground-referenced signal sources to the USB-6421.

Floating Signal Sources (Not Connected to 
Building Ground)

Examples of floating signal sources include ungrounded thermocouples, signal conditioning with isolated outputs, and battery devices.

Figure 13. Differential Mode Floating Signal Sources Connections


Figure 14. Non-Referenced Single-Ended (NRSE) Mode Floating Signal Sources Connections


Figure 15. Referenced Single-Ended (RSE) Mode Floating Signal Sources Connections


Ground-Referenced Signal Sources

Examples of ground-references signal sources include plug-in instruments with non-isolated outputs.

Figure 16. DIFF Mode Ground-Referenced Signal Sources Connections


Figure 17. NRSE Mode Ground-Referenced Signal Sources Connections


NI does no recommend connecting ground-referenced signal sources in RSE mode.

Figure 18. RSE Mode Ground-Referenced Signal Sources Connections


Refer to the following sections for more information on connecting signals to the USB-6421