National Instruments PCI-6281, User Manual

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4-19
M Series User Manual
When to Use Referenced Single-Ended (RSE)
Connections with Ground-Referenced Signal Sources
Do
not
use RSE connections with ground-referenced signal sources. Use NRSE or DIFF
connections instead.
As shown in the bottom-rightmost cell of Table 4-3, there can be a potential difference between
AI GND and the ground of the sensor. In RSE mode, this ground loop causes measurement
errors.
Using Differential Connections for Ground-Referenced
Signal Sources
Figure 4-10 shows how to connect a ground-referenced signal source to the M Series device
configured in DIFF mode.
Figure 4-10. Differential Connections for Ground-Referenced Signal Sources
Note (NI USB-62xx BNC Devices) To measure a ground-referenced signal source
on USB BNC devices, move the switch under the BNC connector to the GS position.
With this type of connection, the NI-PGIA rejects both the common-mode noise in the signal and
the ground potential difference between the signal source and the device ground, shown as V
cm
in the figure.
AI+ and AI- must both remain within ±11 V of AI GND.
M S erie s Device Config u red in DIFF Mode
PGIA
–
+
–
+
–
+
–
+
V
cm
V
s
Gro u nd-
Referenced
S ign a l
S o u rce
Common-
Mode
Noi s e a nd
Gro u nd
Potenti a l
AI GND
AI S EN S E
Inp u t M u ltiplexer s
V
m
Me asu red
Volt a ge
In s tr u ment a tion
Amplifier
AI+
AI–
I/O Connector