Chapter 2
Hardware Overview of the NI 78xxR
R Series Multifunction RIO User Manual
2-30
ni.com
Field Wiring Considerations
(NI 783
x
R/784
x
R/785
x
R Only)
Environmental noise can serio
u
sly affect the meas
u
rement acc
u
racy of the
device if yo
u
do not take proper care when r
u
nning signal wires between
signal so
u
rces and the device. The following recommendations mainly
apply to AI signal ro
u
ting to the device, as well as signal ro
u
ting in general.
Take the following preca
u
tions to minimize noise pick
u
p and maximize
meas
u
rement acc
u
racy:
•
Use differential AI connections to reject common-mode noise.
•
Use individ
u
ally shielded, twisted-pair wires to connect AI signals to
the device. With this type of wire, the signals attached to the positive
and negative inp
u
ts are twisted together and then covered with a shield.
Yo
u
then connect this shield only at one point to the signal so
u
rce
gro
u
nd. This kind of connection is req
u
ired for signals traveling
thro
u
gh areas with large magnetic fields or high electromagnetic
interference.
•
Ro
u
te signals to the device caref
u
lly. Keep cabling away from noise
so
u
rces. The most common noise so
u
rce 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 783
x
R/784
x
R/785
x
R:
•
Separate NI 783
x
R/784
x
R/785
x
R signal lines from high-c
u
rrent or
high-voltage lines. These lines can ind
u
ce c
u
rrents in or voltages on
the NI 783
x
R/784
x
R/785
x
R signal lines if they r
u
n in parallel paths at
a close distance. To red
u
ce the magnetic co
u
pling between lines,
separate them by a reasonable distance if they r
u
n in parallel or r
u
n the
lines at right angles to each other.
•
Do
not
r
u
n signal lines thro
u
gh cond
u
its that also contain power lines.
•
Protect signal lines from magnetic fields ca
u
sed by electric motors,
welding eq
u
ipment, breakers, or transformers by r
u
nning them
thro
u
gh special metal cond
u
its.
Refer to the NI Developer Zone t
u
torial,
Field Wiring and Noise
Considerations for Analog Signals
, at
ni.com/zone
for more information.
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