Single-Ended Connections For Grounded Signal Sources (Nrse Configuration); Common-Mode Signal Rejection Considerations; Figure 3-6. Single-Ended Input Connections For Grounded Signal Sources - National Instruments AT-MIO-16 User Manual

Chapter 3

Single-Ended Connections for Grounded Signal Sources (NRSE Configuration)

If you are measuring a grounded signal source with a single-ended configuration, you must
configure the AT-MIO-16 in the NRSE input configuration. Connect the signal to the positive
input of the AT-MIO-16 instrumentation amplifier and connect the signal local ground reference
to the negative input of the AT-MIO-16 instrumentation amplifier. Therefore, you must connect
the ground point of the signal to the AISENSE pin. Any potential difference between the
AT-MIO-16 ground and the signal ground appears as a common-mode signal at both the positive
and negative inputs of the instrumentation amplifier; the amplifier rejects this difference. On the
other hand, if the input circuitry of the AT-MIO-16 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 an AT-MIO-16 board in the NRSE
configuration. Configuration instructions are included in the Analog Input Configuration section
of Chapter 2, Configuration and Installation.
Ground-
Referenced
V
s
Signal
Source
Common-
Mode
V
cm
Noise
and so on
I/O Connector

Figure 3-6. Single-Ended Input Connections for Grounded Signal Sources

Common-Mode Signal Rejection Considerations

Figures 3-3 and 3-6 show connections for signal sources that are already referenced to some
ground point with respect to the AT-MIO-16. In these cases, the instrumentation amplifier can
reject any voltage caused by ground-potential differences between the signal source and the
AT-MIO-16. In addition, with differential input connections, the instrumentation amplifier can
reject common-mode noise pickup in the leads connecting the signal sources to the AT-MIO-16.
© National Instruments Corporation
ACH<0..15>
3
5
7
+
18
-
Input Multiplexer
19
+
1, 2 AIGND
-
AT-MIO-16 Board in NRSE Input Configuration
Instrumentation
+
-
AISENSE
3-11
Signal Connections
Amplifier
+
Measured
V
m
Voltage
-
AT-MIO-16 User Manual