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Ground-
+
Referenced
V
Signal
s
Source
–
Common-
+
Mode
Noise and
V
cm
Ground
–
Potential
I/O Connector
Common-Mode Signal Rejection Considerations
© National Instruments Corporation
positive and negative inputs of the instrumentation amplifier. The
instrumentation amplifier rejects this difference. If the input circuitry of a
NI 783xR is referenced to ground in RSE input mode, this difference in
ground potentials appears as an error in the measured voltage.
Figure 2-8 shows how to connect a grounded signal source to a channel on
the NI 783xR configured for NRSE input mode.
AI+
AI–
AISENSE
AIGND
NRSE Input Mode Selected
Figure 2-8. Single-Ended Input Connections for Ground-Referenced Signals
Figure 2-5 and Figure 2-8 show connections for signal sources that are
already referenced to some ground point with respect to the NI 783xR.
In these cases, the instrumentation amplifier can reject any voltage caused
by ground potential differences between the signal source and the device.
With differential input connections, 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 when V+
their specified input ranges. Refer to Appendix A, Specifications, for more
information about input ranges.
Chapter 2
+
Instrumentation
Amplifier
–
and V–
in
in
2-13
Hardware Overview of the NI 783xR
+
Measured
V
m
Voltage
–
(input signals) are both within
NI 783xR User Manual
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