Chapter 4
Analog Input
X Series User Manual
4-2
ni.com
•
Mux
—Each MIO X Series device has one analog-to-digital converter
(ADC). The m
u
ltiplexers (m
u
x) ro
u
te one AI channel at a time to the
ADC thro
u
gh the NI-PGIA.
•
Ground-Reference Settings
—The analog inp
u
t gro
u
nd-reference
settings circ
u
itry selects between differential, referenced single-ended,
and non-referenced single-ended inp
u
t modes. Each AI channel can
u
se a different mode.
•
Instrumentation Amplifier (NI-PGIA)
—The NI programmable gain
instr
u
mentation amplifier (NI-PGIA) is a meas
u
rement and instr
u
ment
class amplifier that minimizes settling times for all inp
u
t ranges. The
NI-PGIA can amplify or atten
u
ate an AI signal to ens
u
re that yo
u
u
se
the maxim
u
m resol
u
tion of the ADC.
MIO X Series devices
u
se the NI-PGIA to deliver high acc
u
racy even
when sampling m
u
ltiple channels with small inp
u
t ranges at fast rates.
MIO X Series devices can sample channels in any order, and yo
u
can
individ
u
ally program each channel in a sample with a different inp
u
t
range.
•
A/D Converter
—The analog-to-digital converter (ADC) digitizes the
AI signal by converting the analog voltage into a digital n
u
mber.
•
AI FIFO
—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 AI acq
u
isitions
to ens
u
re that no data is lost. MIO X Series devices can handle m
u
ltiple
A/D conversion operations with DMA or programmed I/O.
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 MIO X Series device.
The inp
u
t range affects the resol
u
tion of the 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:
10V
10V
–
(
)
–
2
16
-----------------------------------
305
μ
V
=
Artisan Technology Group - Quality Instrumentation ... Guaranteed | (888) 88-SOURCE | www.artisantg.com
