Chapter 4
Analog Input
©
National Instruments
4-35
X Series User Manual
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.
Once 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.
Retriggerable Analog Input
The AI Start Trigger can also be config
u
red to be retriggerable. The timing
engine will generate the sample and convert clocks for the config
u
red
acq
u
isition in response to each p
u
lse on an AI Start Trigger signal.
The timing engine ignores the AI Start Trigger signal while the clock
generation is in progress. After the clock generation is finished, the co
u
nter
waits for another Start Trigger to begin another clock generation.
Fig
u
re 4-22 shows a retriggerable analog inp
u
t with three AI channels and
fo
u
r samples per trigger.
Figure 4-22.
Retriggerable Analog Input
Note
Waveform information from LabVIEW will not reflect the delay between triggers.
They will be treated as a contin
u
o
u
s acq
u
isition with constant t0 and dt information.
Reference triggers are not retriggerable.
AI
S
t
a
rt Trigger
AI
Sa
mple Clock
AI Convert
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