National Instruments NI 7831R - Manual (Page 33)

Chapter 2 Hardware Overview of the NI 7831R
NI 7831R User Manual 2-14 ni.com
positive and negative inputs of the instrumentation amplifier. The
instrumentation amplifier rejects this difference. If the input circuitry of a
NI 7831R is referenced to ground in RSE input mode, this difference in
ground potentials appears as an error in the measured voltage.
Figure 2-9 shows how to connect a grounded signal source to a channel on
the NI 7831R configured for NRSE input mode.
Figure 2-9. Single-Ended Input Connections for Ground-Referenced Signals
Common-Mode Signal Rejection Considerations
Figures 2-6 and 2-9 show connections for signal sources that are already
referenced to some ground point with respect to the NI 7831R. 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
x8 Channels
AI+
AI–