National Instruments 700 - Manual (Page 28)

Chapter 3 Signal Connections
© National Instruments Corporation 3-9 DAQCard-700 User Manual
Differential signal connections reduce picked-up noise and increase common-mode signal and
noise rejection. With these connections, input signals can float within the common-mode limits
of the input instrumentation amplifier.
Differential Connections for Grounded Signal Sources
Figure 3-4 shows how to connect a ground-referenced signal source to a DAQCard-700 card
configured for DIFF input.
Ground-
Referenced
Signal
Source
Common-
Mode
Noise,
Ground
Potential,
and so on
Input Multiplexers
Instrumentation
Amplifier
V
m
Measured
Voltage
AIGND
-
+
-
+
V
s
V
cm
+
-
-
+
I/O Connector
DAQCard-700 Board in DIFF Configuration
3
5
7
17
4
6
8
18
1, 2
ACH<0..7>
ACH<8..15>
Figure 3-4. 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
DAQCard-700 ground (shown as V
cm
in Figure 3-4).