National Instruments NI 785xR - Manual (Page 36)

Chapter 2 Hardware Overview of the NI 78xxR
© National Instruments Corporation 2-15 R Series Intelligent DAQ 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.
Figure 2-9. Single-Ended Input Connections for Ground-Referenced Signals
–
+
–
+
–
+
–
+
V
cm
V
s
I/O Connector
AISENSE
AIGND
V
m
AI+
AI–
Instrumentation
Amplifier
Measured
Voltage
Ground-
Referenced
Signal
Source
Common-
Mode
Noise and
Ground
Potential
NRSE Input Mode Selected