Single-Ended Connections For Grounded Signal Sources (Nrse Input Mode) - National Instruments PXI-7811 User Manual

Single-Ended Connections for Grounded Signal
Sources (NRSE Input Mode)
To measure a grounded signal source with a single-ended input mode, you
must configure the NI 783xR/784xR/785xR in the NRSE input mode. Then
connect the signal to the positive input of the NI 783xR/784xR/785xR
instrumentation amplifier and connect the signal local ground reference to
the negative input of the instrumentation amplifier. The ground point of the
signal should be connected to AISENSE. Any potential difference between
the NI 783xR/784xR/785xR ground and the signal ground appears as a
common-mode signal at both the positive and negative inputs of the
instrumentation amplifier. The instrumentation amplifier rejects this
difference. If the input circuitry of a NI 783xR/784xR/785xR 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 783xR/784xR/785xR configured for NRSE input mode.
Ground-
+
Referenced
V
s
Signal
–
Source
Common-
+
Mode
Noise and V
cm
Ground
–
Potential
I/O Connector
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AI+
AI–
AISENSE
AIGND
NRSE Input Mode Selected
Figure 2-9. Single-Ended Input Connections for Ground-Referenced Signals
2-15
Chapter 2 Hardware Overview of the NI 78xxR
+
Instrumentation
Amplifier +
Measured
– V
m
Voltage
–
R Series Multifunction RIO User Manual