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National Instruments Corporation
15
NI sbRIO-961x/9612XT/963x/9632XT/964x/9642XT
Understanding Ground Connections
All of the grounds (D GND, AI GND, AO GND, ground lug P1, and the
plated mounting holes) are connected together internally on the NI sbRIO
device. The ESD protection diodes are connected to the plated mounting
holes with a lower inductive path than the path to D GND, so the best ESD
protection is provided by connecting the plated mounting holes and ground
lug P1 to a low inductive earth ground.
Care must be taken to
not
connect the grounds in such a way that stray
power supply currents traverse through the board. For example, when using
the NI sbRIO-964
x
/9642XT, the D GND connections on the 24 V DIO
connectors J5 and J6 should not be carrying more than a few tens of
milliamps of current. Ideally, only the return current for the 24 V inputs
should return through D GND on J5, and D GND on J6 should have no
current flow. For the remaining connectors, a good rule of thumb is current
flowing out of the connector should match current flowing in.
To verify correct grounding of the NI sbRIO device, make sure current
flowing into the power connector J3 equals the current flowing out of power
connector J3. These currents should be measured with a current probe after
final assembly of the end product and any current differences investigated
and removed.
All external power supplies should have their connected to a system ground
external to the NI sbRIO device. Do not use the NI sbRIO device as the
common system grounding point. Significant currents traversing through
the NI sbRIO grounds can result in digital component failures. If more than
3 A flows through the common (–) pin on the J3 power connector,
components start to fuse open.
Connecting the NI sbRIO Device to a Network
Use a standard Category 5 (CAT-5) or better Ethernet cable to connect the
RJ-45 Ethernet port to an Ethernet network.
Caution
To prevent data loss and to maintain the integrity of your Ethernet installation,
do
not
use a cable longer than 100 m.
If you need to build your own cable, refer to the
section for more
information about Ethernet cable wiring connections.
