National Instruments 9225E Operating Instructions And Specifications page 6

You can connect ground-referenced or floating signal sources to
the NI 9225E. Connect the positive signal of the signal source to
the AI+ terminal, and connect the negative signal of the signal
source to the AI– terminal. If you make a ground-referenced
connection between the signal source and the NI 9225E, make sure
the voltage on the AI+ and AI– connections are in the
channel-to-earth safety voltage range to ensure proper operation of
the NI 9225E. Refer to the
information about operating voltages and overvoltage protection.
Note
connection when connecting more than one wire to a
single terminal on the NI 9225E.
Refer to Figures 3 and 4 for illustrations of how to connect
grounded and floating signal sources to the NI 9225E.
© National Instruments Corp.
Specifications
You must use 2-wire ferrules to create a secure
section for more
5 NI 9225E Operating Instructions and Specifications