Power connections, Field wiring considerations – National Instruments NI PXI-7831R User Manual
Page 42
Chapter 2
Hardware Overview of the NI PXI-7831R
© National Instruments Corporation
2-21
flash memory, repeat the procedure above but return switch 1 to the OFF
position in step 3.
Note
When the NI PXI-7831R is powered on with switch 1 in the ON position, the analog
circuitry does not return properly calibrated data. For this reason, the switch should only
be switched to the ON position while you are using software to reconfigure the
NI PXI-7831R for the desired power-up behavior. Afterwards, you should return switch 1
to the OFF position.
Power Connections
Two pins on each I/O connector supply +5 V from the computer power
supply using a self-resetting fuse. The fuse resets automatically within a
few seconds after the overcurrent condition is removed. The +5 V pins are
referenced to DGND and can be used to power external digital circuitry.
Power rating ........................................... +4.65 to +5.25 VDC at 1 A
(250 mA max per 5 V pin,
1 A max total for all +5 V lines
on the device)
Caution
Do not connect the +5 V power pins directly to analog or digital ground or to any
other voltage source on the NI PXI-7831R or any other device under any circumstance.
Doing so can damage the NI PXI-7831R and the computer. NI is not liable for damage
resulting from such a connection.
Field Wiring Considerations
Environmental noise can seriously affect the accuracy of measurements
made with the NI PXI-7831R if you do not take proper care when running
signal wires between signal sources and the device. The following
recommendations mainly apply to AI signal routing to the device, although
they also apply to signal routing in general.
Minimize noise pickup and maximize measurement accuracy by taking the
following precautions:
•
Use differential AI connections to reject common-mode noise.
•
Use individually shielded, twisted-pair wires to connect AI signals to
the device. With this type of wire, the signals attached to the AI+ and
AI– inputs are twisted together and then covered with a shield.
You then connect this shield only at one point to the signal source
ground. This kind of connection is required for signals traveling