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Chapter 3 Connecting the Signals
© National Instruments Corporation 3-13 DAQCard-1200 User Manual
Figure 3-6. Single-Ended Input Connections for Grounded Signal Sources
Common-Mode Signal Rejection Considerations
Figures 3-4 and 3-6 show connections for signal sources that are already
referenced to some ground point with respect to the DAQCard-1200.
In these cases, the instrumentation amplifier can reject any voltage caused
by ground-potential differences between the signal source and the
DAQCard-1200. In addition, with differential input mode connections, the
instrumentation amplifier can reject common-mode noise pickup in the
leads connecting the signal sources to the DAQCard-1200.
The common-mode input range of the DAQCard-1200 instrumentation
amplifier is the magnitude of the greatest common-mode signal that can be
rejected.
The common-mode input range for the DAQCard-1200 depends on the size
of the differential input signal (V
diff
= V
in+
– V
in–
) and the gain setting of the
instrumentation amplifier. In unipolar mode, the differential input range is
0 to 10 V. In bipolar mode, the differential input range is from –5to+5V.
V
in–
should remain within a range of –6to+6Vinbipolarmodeand
DAQCard-1200 in NRSE Input Configuration
Ground-
Referenced
Signal
Source
Front I/O
Connector
V
s
+
–
1
2
3
8
9
11
ACH 0
ACH 1
ACH 2
ACH 7
AISENSE/AIGND
AGND
+
–
+
–
Measured
Voltage
V
m
V
cm
+
–
Common-Mode
Noise