National Instruments VXI-MIO Series - Manual (Page 91)

Chapter 4 Signal Connections
 National Instruments Corporation 4-45 VXI-MIO Series User Manual
Field Wiring Considerations
Environmental noise can seriously affect the accuracy of measurements
made with your VXI-MIO Series module if you do not take proper care
when running signal wires between signal sources and the module. The
following recommendations apply mainly to analog input signal routing
to the module, although they also apply to signal routing in general.
Take the following precautions to minimize noise pickup and maximize
measurement accuracy:
• Use differential analog input connections to reject common-mode
noise.
• Use individually shielded, twisted-pair wires to connect analog
input signals to the module. With this type of wire, the signals
attached to the CH+ and CH- 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 module carefully. Keep cabling away from
noise sources. A common noise source in many data acquisition
systems is the video monitor. Separate the monitor from the analog
signals as much as possible.
The following recommendations apply for all signal connections to
your VXI-MIO Series module:
• Separate VXI-MIO Series module signal lines from high-current or
high-voltage lines. These lines are capable of inducing currents in
or voltages on the VXI-MIO Series module 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.
For more information, refer to the application note, Field Wiring and
Noise Consideration for Analog Signals available from National
Instruments.