National Instruments NI 7831R - Manual (Page 29)

Chapter 2 Hardware Overview of the NI 7831R
NI 7831R User Manual 2-10 ni.com
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 7831R 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 Appendix A, Specifications , for more information about
input ranges.
Differential Connections for Nonreferenced or
Floating Signal Sources
Figure 2-7 shows how to connect a floating signal source to a channel on
the NI 7831R configured in DIFF input mode.
DIFF 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–