NI 9871 Operating Instructions
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You must connect an external power supply to the NI 9871.
This power supply provides the power for the RS485/RS422
transceivers on the module. You can use the included female
four-position pigtail to connect to an external voltage source.
Figure 1 lists the connections between an external voltage source
(of +8 V to +28 V) and the NI 9871.
Caution
To ensure the specified EMC performance, do not
connect the power input to a d.c. mains supply or to any
supply requiring a connecting cable longer than 30 m
(100 ft.). A d.c. mains supply is a local d.c. electricity supply
network in the infrastructure of a certain site or building.