Chapter 4
Analog Input
X Series User Manual
4-4
ni.com
Working Voltage Range
On most MIO X Series devices, the PGIA operates normally by amplifying
signals of interest while rejecting common-mode signals
u
nder the
following three conditions:
•
The common-mode voltage (V
cm
), which is eq
u
ivalent to s
u
btracting
AI <0..
x
> GND from AI <0..
x
>–, m
u
st be less than ±10 V. This V
cm
is
a constant for all range selections.
•
The signal voltage (V
s
), which is eq
u
ivalent to s
u
btracting AI <0..
x
>+
from AI <0..
x
>–, m
u
st be less than or eq
u
al to the range selection of
the given channel. If V
s
is greater than the range selected, the signal
clips and information are lost.
•
The total working voltage of the positive inp
u
t, which is eq
u
ivalent to
(V
cm
+ V
s
), or s
u
btracting AI GND from AI <0..
x
>+, m
u
st be less than
±11 V.
If any of these conditions are exceeded, the inp
u
t voltage is clamped
u
ntil
the fa
u
lt condition is removed.
Analog Input Ground-Reference Settings
MIO X Series devices s
u
pport the following analog inp
u
t gro
u
nd-reference
settings:
•
Differential mode
—In DIFF mode, the MIO X Series device
meas
u
res the difference in voltage between two AI signals.
•
Referenced single-ended mode
—In RSE mode, the MIO X Series
device meas
u
res the voltage of an AI signal relative to AI GND.
•
Non-referenced single-ended mode
—In NRSE mode, the MIO
X Series device meas
u
res the voltage of an AI signal relative to one of
the AI SENSE or AI SENSE 2 inp
u
ts.
The AI gro
u
nd-reference setting determines how yo
u
sho
u
ld connect yo
u
r
AI signals to the MIO X Series device. Refer to the
Connecting Analog
Input Signals
section for more information.
Gro
u
nd-reference settings are programmed on a per-channel basis. For
example, yo
u
might config
u
re the device to scan 12 channels—fo
u
r
differentially-config
u
red channels and eight single-ended channels.
MIO X Series devices implement the different analog inp
u
t
gro
u
nd-reference settings by ro
u
ting different signals to the NI-PGIA. The
NI-PGIA is a differential amplifier. That is, the NI-PGIA amplifies (or
atten
u
ates) the difference in voltage between its two inp
u
ts. The NI-PGIA
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