Chapter 4
Analog Input
X Series User Manual
4-42
ni.com
•
AI FIFO
—Sim
u
ltaneo
u
s MIO X Series devices can perform both
single and m
u
ltiple A/D conversions of a fixed or infinite n
u
mber of
samples. A large first-in-first-o
u
t (FIFO) b
u
ffer holds data d
u
ring A/D
conversions to ens
u
re that no data is lost. Sim
u
ltaneo
u
s MIO X Series
devices can handle m
u
ltiple A/D conversion operations with DMA or
programmed I/O.
Analog Input Terminal Configuration
Sim
u
ltaneo
u
s MIO X Series devices s
u
pport only differential (DIFF) inp
u
t
mode. The channels on Sim
u
ltaneo
u
s MIO X Series devices are tr
u
e
differential inp
u
ts, meaning both positive and negative inp
u
ts can carry
signals of interest. For more information abo
u
t DIFF inp
u
t, refer to the
Connecting Analog Input Signals
section, which contains diagrams
showing the signal paths for DIFF inp
u
t mode.
Caution
Exceeding the differential and common-mode inp
u
t ranges distorts the inp
u
t
signals. Exceeding the maxim
u
m inp
u
t voltage rating can damage the device and the
comp
u
ter. NI is
not
liable for any damage res
u
lting from s
u
ch signal connections. The
maxim
u
m inp
u
t voltage ratings can be fo
u
nd in the specifications doc
u
ment for each
Sim
u
ltaneo
u
s MIO X Series device.
Analog Input Range
Inp
u
t range refers to the set of inp
u
t voltages that an analog inp
u
t channel
can digitize with the specified acc
u
racy. The NI-PGIA amplifies or
atten
u
ates the AI signal depending on the inp
u
t range. Yo
u
can individ
u
ally
program the inp
u
t range of each AI channel on yo
u
r Sim
u
ltaneo
u
s MIO
X Series device.
The inp
u
t range affects the resol
u
tion of the Sim
u
ltaneo
u
s MIO X Series
device for an AI channel. Resol
u
tion refers to the voltage of one ADC code.
For example, a 16-bit ADC converts analog inp
u
ts into one of 65,536
(= 2
16
) codes—that is, one of 65,536 possible digital val
u
es. These val
u
es
are spread fairly evenly across the inp
u
t range. So, for an inp
u
t range of
–10 V to 10 V, the voltage of each code of a 16-bit ADC is:
Sim
u
ltaneo
u
s MIO X Series devices
u
se a calibration method that req
u
ires
some codes (typically abo
u
t 5% of the codes) to lie o
u
tside of the specified
range. This calibration method improves absol
u
te acc
u
racy, b
u
t it increases
the nominal resol
u
tion of inp
u
t ranges by abo
u
t 5% over what the form
u
la
shown above wo
u
ld indicate.
10V
10V
–
(
)
–
2
16
-----------------------------------
305
μ
V
=
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