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Chapter 2 Hardware Overview of the NI 78xxR
© National Instruments Corporation 2-31 R Series Intelligent DAQ User Manual
Field Wiring Considerations
(NI 783xR/784xR/785xROnly)
Environmental noise can seriously affect the measurement accuracy of the
device 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, 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 signals 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. The most common noise source in a PXI DAQ system is the
video monitor. Keep the monitor and the analog signals as far apart as
possible.
Use the following recommendations for all signal connections to the
NI 783xR/784xR/785xR:
• Separate NI 783xR/784xR/785xR signal lines from high-current or
high-voltage lines. These lines can induce currents in or voltages on
the NI 783xR/784xR/785xR 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.
Refer to the NI Developer Zone tutorial, Field Wiring and Noise
Considerations for Analog Signals, at
ni.com/zone for more information.