Using Non-Referenced Single-Ended (Nrse) Connections For Ground-Referenced Signal Sources - National Instruments NI 6221 User Manual

Chapter 4 Analog Input
Using Non-Referenced Single-Ended (NRSE) Connections for
Ground-Referenced Signal Sources
I/O Connector
Ground-
Referenced
Signal
Source
Common-
Mode
Noise
and Ground
Potential
M Series User Manual
Figure 4-11 shows how to connect ground-reference signal sources in
NRSE mode.
AI <0..15>
or AI <16.. n >
+
V
s
–
Input Multiplexers
+
AI GND
or AI SENSE 2
V
cm
–
M Series Device Configured in NRSE Mode
Figure 4-11. Single-Ended Connections for Ground-Referenced Signal Sources
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 one of
AI <0..15> and connect the signal local ground reference to AI SENSE.
You also can connect the signal to one of AI <16..79> and connect the
signal local ground reference to AI SENSE 2. AI SENSE (or AI SENSE 2)
is 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.
Instrumentation
Amplifier
+
PGIA
–
AI SENSE
(NRSE Configuration)
4-24
+
Measured
V
m
Voltage
–
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