National Instruments Low-Cost Multifunction I/O Board for ISA..., User Manual

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Signal Connections Chapter 3
Lab-PC+ User Manual 3-8 © National Instruments Corporation
+
-
+
Grounded
Signal
Source
V
m
Measured
Voltage
-
V
s
-
+
I/O Connector
Lab-PC+ Board in DIFF Configuration
1
3
5
7
2
4
6
8
9
Common
Mode
Noise,
Ground
Potential,
and so on
ACH 0
AGND
11
AISENSE/AIGND
ACH 2
ACH 4
ACH 6
ACH 1
ACH 3
ACH 5
ACH 7
(not connected)
V
cm
-
+
Figure 3-3. Differential Input Connections for Grounded Signal Sources
With this type of connection, the instrumentation amplifier rejects both the common mode noise
in the signal and the ground potential difference between the signal source and the Lab-PC+
ground (shown as V
cm
in Figure 3-3).
Differential Connections for Floating Signal Sources
Figure 3-4 shows how to connect a floating signal source to a Lab-PC+ board configured for
DIFF input. Configuration instructions are included under Analog Input Configuration in
Chapter 2, Configuration and Installation.