Chapter 4
Analog Input
4-20
ni.com
The polarity of AI Hold Complete Event is software-selectable, b
u
t is
typically config
u
red so that a low-to-high leading edge can clock external
AI m
u
ltiplexers indicating when the inp
u
t signal has been sampled and can
be removed.
AI Start Trigger Signal
Use the AI Start Trigger (ai/StartTrigger) signal to begin a meas
u
rement
acq
u
isition. A meas
u
rement acq
u
isition consists of one or more samples.
If yo
u
do not
u
se triggers, begin a meas
u
rement with a software command.
After the acq
u
isition begins, config
u
re the acq
u
isition to stop:
•
When a certain n
u
mber of points are sampled (in finite mode)
•
After a hardware reference trigger (in finite mode)
•
With a software command (in contin
u
o
u
s mode)
An acq
u
isition that
u
ses a start trigger (b
u
t not a reference trigger) is
sometimes referred to as a posttriggered acq
u
isition.
Using a Digital Source
To
u
se AI Start Trigger with a digital so
u
rce, specify a so
u
rce and an edge.
The so
u
rce can be any of the following signals:
•
(USB-6210/6211/6215 Devices)
PFI <0..3>
•
(USB-6212/6216 Devices)
PFI <0..15>
•
(USB-6218 Devices)
PFI <0..3>, PFI <8..11>
•
Co
u
nter
n
Internal O
u
tp
u
t
The so
u
rce also can be one of several other internal signals on yo
u
r DAQ
device. Refer to
Device Routing in MAX
in the
NI-DAQmx Help
or the
LabVIEW Help
in version 8.0 or later for more information.
Yo
u
also can specify whether the meas
u
rement acq
u
isition begins on the
rising edge or falling edge of AI Start Trigger.
Routing AI Start Trigger to an Output Terminal
Yo
u
can ro
u
te AI Start Trigger o
u
t to any o
u
tp
u
t PFI terminal.
The o
u
tp
u
t is an active high p
u
lse.
The device also
u
ses AI Start Trigger to initiate pretriggered DAQ
operations. In most pretriggered applications, a software trigger generates
AI Start Trigger. Refer to the
section for a
