Chapter 4
Analog Input
X Series User Manual
4-26
ni.com
Posttriggered data acq
u
isition allows yo
u
to view only data that is acq
u
ired
after a trigger event is received. A typical posttriggered DAQ seq
u
ence is
shown in Fig
u
re 4-14. The sample co
u
nter is loaded with the specified
n
u
mber of posttrigger samples, in this example, five. The val
u
e decrements
with each p
u
lse on AI Sample Clock,
u
ntil the val
u
e reaches zero and all
desired samples have been acq
u
ired.
Figure 4-14.
Posttriggered Data Acquisition Example
Pretriggered data acq
u
isition allows yo
u
to view data that is acq
u
ired before
the trigger of interest, in addition to data acq
u
ired after the trigger.
Fig
u
re 4-15 shows a typical pretriggered DAQ seq
u
ence. AI Start Trigger
(ai/StartTrigger) can be either a hardware or software signal. If AI Start
Trigger is set
u
p to be a software start trigger, an o
u
tp
u
t p
u
lse appears on
the ai/StartTrigger line when the acq
u
isition begins. When the AI Start
Trigger p
u
lse occ
u
rs, the sample co
u
nter is loaded with the n
u
mber of
pretriggered samples, in this example, fo
u
r. The val
u
e decrements with
each p
u
lse on AI Sample Clock,
u
ntil the val
u
e reaches zero. The sample
co
u
nter is then loaded with the n
u
mber of posttriggered samples, in this
example, three.
Figure 4-15.
Pretriggered Data Acquisition Example
1
3
0
4
2
AI
S
t
a
rt Trigger
AI
Sa
mple Clock
AI Convert Clock
Sa
mple Co
u
nter
n/
a
0
1
2
3
1
0
2
2
2
AI
S
t
a
rt Trigger
AI Reference Trigger
AI
Sa
mple Clock
AI Convert Clock
Sa
mple Co
u
nter
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