Chapter 4
Analog Input
©
National Instruments
4-49
X Series User Manual
Differential Connections for Floating Signal Sources
Fig
u
re 4-27 shows how to connect a floating (or non-referenced) signal
so
u
rce to a channel on an Sim
u
ltaneo
u
s MIO X Series device.
Figure 4-27.
Differential Connection for Floating Signals on Simultaneous MIO
X Series Devices
Fig
u
re 4-27 shows bias resistors connected between AI 0–, AI 0+, and the
floating signal so
u
rce gro
u
nd. These resistors provide a ret
u
rn path for the
bias c
u
rrent. A val
u
e of 10 k
Ω
to 100 k
Ω
is
u
s
u
ally s
u
fficient. If yo
u
do not
u
se the resistors and the so
u
rce is tr
u
ly floating, the so
u
rce is not likely to
remain within the common-mode signal range of the instr
u
mentation
amplifier, so the instr
u
mentation amplifier sat
u
rates, ca
u
sing erroneo
u
s
readings. Yo
u
m
u
st reference the so
u
rce to the respective channel gro
u
nd.
+
+
Floating
Signal
Source
Instrumentation
Amplifier
V
m
Measured
Voltage
I/O Connector
AI 0 GND
Bias
Current
Return
Paths
AI 0 –
AI 0 +
AI 0 Connections Shown
Bias
Resistors
–
+
–
–
Simultaneous X Series Device
V
s
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