National Instruments DAQCard-1200 - Manual (Page 34)

Chapter 3 Signal Connections
DAQCard-1200 User Manual 3-12 © National Instruments Corporation
Figure 3-5. Single-Ended Input Connections for Floating Signal Sources
Single-Ended Connections for Grounded Signal Sources
(NRSE Configuration)
If you measure a grounded signal source with a single-ended configuration,
you must configure the DAQCard-1200 in the NRSE input configuration.
The signal is connected to the positive input of the DAQCard-1200
instrumentation amplifier and the signal local ground reference is
connected to the negative input of the DAQCard-1200 instrumentation
amplifier. Therefore, you must connect the ground point of the signal to the
AISENSE pin. Any potential difference between the DAQCard-1200
ground and the signal ground appears as a common-mode signal at both the
positive and negative inputs of the instrumentation amplifier and is
therefore rejected by the amplifier. On the other hand, if the input circuitry
of the DAQCard-1200 is referenced to ground, such as in the RSE
configuration, this difference in ground potentials appears as an error in the
measured voltage.
Figure 3-6 shows how to connect a grounded signal source to a
DAQCard-1200 configured in the NRSE configuration. For configuration
instructions, see the
Analog Input Configuration section in Chapter 2,
Installation and Configuration .
Vs
+
+
+
–
–
–
Vm Measured
Voltage
ACH 0
AISENSE/AIGND
AGND
Front I/O Connector
1
2
3
8
9
DAQCard-1200 in RSE Configuration
11
ACH 1
ACH 2
ACH 7
Floating
Signal
Source