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Chapter 4
Analog Input
X Series User Manual
4-52
ni.com
common-mode rejection ratio (CMRR). These methods are o
u
tlined in the
Connecting Analog Input Signals
section.
AI GND is an AI common signal that ro
u
tes directly to the gro
u
nd
connection point on the devices. Yo
u
can
u
se this signal if yo
u
need a
general analog gro
u
nd connection point to the device.
Analog Input Timing Signals
In order to provide all of the timing f
u
nctionality described thro
u
gho
u
t this
section, Sim
u
ltaneo
u
s MIO X Series devices have a flexible timing engine.
Refer to the
Clock Routing
section of Chapter 9,
Digital Routing and Clock
Generation
.
Sim
u
ltaneo
u
s MIO X Series devices
u
se AI Sample Clock
(ai/SampleClock) to perform sim
u
ltaneo
u
s sampling on all active analog
channels. Since there is one ADC per channel, AI Sample Clock controls
the sample period on all the channels in the task.
An acq
u
isition with posttrigger data allows yo
u
to view data that is acq
u
ired
after a trigger event is received. A typical posttrigger DAQ seq
u
ence is
shown in Fig
u
re 4-28. 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 4-28.
Typical Posttriggered DAQ Sequence
An acq
u
isition with pretrigger data 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 4-29 shows a typical pretrigger DAQ seq
u
ence. The AI Start Trigger
signal (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 pretrigger 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
1
3
0
4
2
AI Start Trigger
AI Sample Clock
Sample Counter
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