The DIO channels connect to the FPGA through buffers, which have overvoltage and
undervoltage protection as well as over current protection. Refer to the device specifications
on
for more information about the maximum voltage and current.
When the system powers on, the DIO channels are set as input low with pull-down resistors.
To set another power-on state, you can configure the NI PXIe-7846R to load a VI when the
system powers on. The VI can then set the DIO lines to any power-on state.
All the high-speed DIO channels on Connector 1 are routed with a 50 Ω characteristic trace
impedance. Route all external circuitry with a similar impedance to ensure best signal quality.
NI recommends performing signal integrity measurements to test the affect of signal routing
with the cable and connection accessory for your application.
Field Wiring Considerations
Environmental noise can seriously affect the measurement accuracy of the device if you do not
take proper care when running signal wire between signal sources and the device. The
following recommendations mainly apply to AI signal routing to the device, as well as signal
routing in general.
Take the following precautions to minimize noise pickup and maximize measurement
accuracy:
•
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 signal attached to the positive and negative 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 through
areas with large magnetic fields or high electromagnetic interference.
•
Route signals to the device carefully. Keep cabling away from noise sources, such as
video monitors and analog signals.
Use the following recommendations for all signal connections to the NI PXIe-7846R:
•
Separate NI PXIe-7846R signal lines from high-current or high-voltage lines. These lines
can induce currents in or voltages on the NI PXIe-7846R signal lines if they run in
parallel paths at a close distance. To reduce the magnetic coupling between lines, separate
them by a reasonable distance if they run in parallel or run the lines at right angles to each
other.
•
Do not run signal lines through conduits that also contain power lines.
•
Protect signal lines from magnetic fields caused by electric motors, welding equipment,
breakers, or transformers by running them through special metal conduits.
+5 V Power Source
Use the +5 V terminals on the I/O connector 5 V referenced to DGND to power
external circuitry.
Caution
Never connect the +5 V power terminals to analog or digital ground or
any other voltage source on the NI PXIe-7846R or any other device. Doing so can
NI PXIe-7846R User Manual
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© National Instruments
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