National Instruments NI 785xR - Manual (Page 32)

Chapter 2 Hardware Overview of the NI 78xxR
© National Instruments Corporation 2-11 R Series Intelligent DAQ User Manual
Differential Connections for Ground-Referenced
Signal Sources
Figure 2-6 shows how to connect a ground-referenced signal source to a
channel on the NI 783xR/784xR/785xR configured in DIFF input mode.
Figure 2-6. Differential Input Connections for Ground-Referenced Signals
With this connection type, the instrumentation amplifier rejects both the
common-mode noise in the signal and the ground potential difference
between the signal source and the NI 783xR/784xR/785xR ground, shown
as V
cm
in Figure 2-6. In addition, 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 the NI R Series Intelligent DAQ Specifications, available at
ni.com/manuals , for more information about input ranges.
DIFF Input Mode Selected
–
+
–
+
–
+
–
+
V
cm
V
s
I/O Connector
AISENSE
AIGND
V
m
AI+
AI–
Ground-
Referenced
Signal
Source
Common-
Mode
Noise and
Ground
Potential
Measured
Voltage
Instrumentation
Amplifier