Chapter 4
Analog Input
4-10
ni.com
Analog Input Digital Triggering
Analog inp
u
t s
u
pports three different triggering actions:
•
Start trigger
•
Reference trigger
•
Pa
u
se trigger
Refer to the
sections for information abo
u
t these triggers.
A digital trigger can initiate these actions. All USB-621
x
devices s
u
pport
digital triggering. USB-621
x
devices do not s
u
pport analog triggering.
Field Wiring Considerations
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 apply
mainly to AI signal ro
u
ting to the device, altho
u
gh they also apply to signal
ro
u
ting in general.
Minimize noise pick
u
p and maximize meas
u
rement acc
u
racy by taking the
following preca
u
tions:
•
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
t channels 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.
Refer to the NI Developer Zone doc
u
ment,
Field Wiring and Noise
Considerations for Analog Signals
, for more information. To access this
doc
u
ment, go to
ni.com/info
and enter the info code
rdfwn3
.
Caution
Electromagnetic interference can adversely affect the meas
u
rement acc
u
racy of
this prod
u
ct. Refer to the
NI USB-621x Specifications
for more information abo
u
t the
performance of this prod
u
ct.
