Chapter 4
Connecting Signals
©
National Instruments Corporation
4-39
Field Wiring Considerations
Environmental noise can seriously affect the measurement accuracy of the
NI 6115/6120 if you do not take proper care when running signal wires
between signal sources and the device. The following recommendations
apply mainly to AI signal routing, 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 ACH+ and
ACH– 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 PCI DAQ system is the
video monitor. Separate the monitor from the analog signals as far as
possible.
The following recommendations apply for all signal connections to the
NI 6115/6120:
•
Separate the NI 6115/6120 signal lines from high-current or
high-voltage lines. These lines can induce currents in or voltages on
the NI 6115/6120 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 NI Developer Zone tutorial,
Field Wiring
and Noise Consideration for Analog Signals
, available at
ni.com/zone
.
