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Chapter 4 Analog Input
© National Instruments Corporation 4-9 NI 6124/6154 User Manual
With these types of connections, the instrumentation amplifier rejects both
the common-mode noise in the signal and the ground potential difference
between the signal source and the device ground, shown as V
cm
in these
figures.
Common-Mode Signal Rejection Considerations
The instrumentation amplifier can reject any voltage caused by ground
potential differences between the signal source and the device. In addition,
the instrumentation amplifier can reject common-mode noise pickup in the
leads connecting the signal sources to the device. The instrumentation
amplifier can reject common-mode signals as long as V+
in
and V–
in
(input
signals) are both within the working voltage range of the device.
Differential Connections for Non-Referenced or Floating Signal Sources
Figure 4-5 shows how to connect a floating signal source to a channel on a
non-isolated S Series device.
Figure 4-5. Differential Connection for Non-Referenced Signals on
Non-Isolated Devices
+
+
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
Resistor
V
s
–
+
–
–
Non-Isolated S Series Device