Справочник Пользователя для National Instruments AT E Series
Chapter 4
Connecting Signals
© National Instruments Corporation
4-55
Field Wiring Considerations
Environmental noise can seriously affect the accuracy of measurements
made with the AT E Series device 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 to the device, although
they also apply to signal routing in general.
made with the AT E Series device 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 to the device, although
they also apply to signal routing in general.
You can minimize noise pickup and maximize measurement accuracy by
taking the following precautions:
taking the following precautions:
•
Use differential analog input connections to reject common-mode
noise.
noise.
•
Use individually shielded, twisted-pair wires to connect AI signals to
the device. 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.
the device. 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 device carefully. Keep cabling away from noise
sources. The most common noise source in a PC DAQ system is the
video monitor. Separate the monitor from the analog signals as much
as possible.
sources. The most common noise source in a PC DAQ system is the
video monitor. Separate the monitor from the analog signals as much
as possible.
The following recommendations apply for all signal connections to the
AT E Series device:
AT E Series device:
•
Separate AT E Series device signal lines from high-current or
high-voltage lines. These lines are capable of inducing currents in or
voltages on the AT E Series device 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.
high-voltage lines. These lines are capable of inducing currents in or
voltages on the AT E Series device 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.
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, at
and Noise Consideration for Analog Signals, at
ni.com/zone
.