National Instruments PCI-6281, User Manual

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Chapter 4 Analog Input
Using Non-Referenced Single-Ended (NRSE)
Connections for Ground-Referenced Signal Sources
Figure 4-11 shows how to connect ground-reference signal sources in NRSE mode.
Figure 4-11.
Single-Ended Connections for Ground-Referenced
Signal Sources (NRSE Configuration)
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.
AI+ and AI- must both remain within ±11 V of AI GND.
To measure a single-ended, ground-referenced signal source, you must use the NRSE
ground-reference setting. Connect the signal to an AI terminal and connect the signal local
ground reference to its AI SENSE. AI SENSE and AI SENSE 2 are internally connected to the
negative input of the NI-PGIA. Therefore, the ground point of the signal connects to the negative
input of the NI-PGIA.
Any potential difference between the device ground and the signal ground appears as a
common-mode signal at both the positive and negative inputs of the NI-PGIA, and this
difference is rejected by the amplifier. If the input circuitry of a device were referenced to
ground, as it is in the RSE ground-reference setting, this difference in ground potentials would
appear as an error in the measured voltage.
Using the DAQ Assistant, you can configure the channels for RSE or NRSE input modes. Refer
to the
Configuring AI Ground-Reference Settings in Software
section for more information about
the DAQ Assistant.
M S erie s Device Config u red in NR S E Mode
Inp u t M u ltiplexer s
I/O Connector
AI GND
AI S EN S E
or AI S EN S E 2
AI <0..15>
or AI <16.. n >
–
+
–
+
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
PGIA
–
+
–
+
V
m
Me asu red
Volt a ge
In s tr u ment a tion
Amplifier