National Instruments NI 9215 - Manual (Page 10)

NI 9215 Operating Instructions and Specifications 10 ni.com
The NI 9215 with screw terminal has a 10-terminal detachable
screw-terminal connector. The NI 9215 with BNC has four BNC
connectors.
Each channel of the NI 9215 has an AI+ terminal or shield to which
you can connect the positive voltage signal, and an AI– terminal or
shield to which you can connect the negative voltage signal. The
NI 9215 with screw terminal also has a common terminal, COM,
that is internally connected to the isolated ground reference of the
module.
Note You must use 2-wire ferrules to create a secure
connection when connecting more than one wire to a
single terminal on the NI 9215 with screw terminal.