National Instruments NI 783xR - Manual (Page 32)

Chapter 2 Hardware Overview of the NI 783xR
© National Instruments Corporation 2-13 NI 783xR User Manual
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.
Figure 2-8. Single-Ended Input Connections for Ground-Referenced Signals
Common-Mode Signal Rejection Considerations
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+
in
and V–
in
(input signals) are both within
their specified input ranges. Refer to Appendix A, Specifications , for more
information about input ranges.
NRSE Input Mode Selected
–
+
–
+
–
+
–
+
V
cm
V
s
Ground-
Referenced
Signal
Source
Common-
Mode
Noise and
Ground
Potential
I/O Connector
AISENSE
AIGND
V
m
Measured
Voltage
Instrumentation
Amplifier
AI+
AI–