National Instruments Data Acquisition Device NI USB-621x - Manual (Page 64)

Chapter 4 Analog Input
© National Instruments Corporation 4-31 NI USB-621x User Manual
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.
Using Referenced Single-Ended (RSE) Connections
for Floating Signal Sources
Figure 4-21 shows how to connect a floating signal source to the
USB-6210/6211/6212 device configured for RSE mode.
Figure 4-21. RSE Connections for Floating Signal Sources
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.
Connecting Ground-Referenced Signal Sources
What Are Ground-Referenced Signal Sources?
A ground-referenced signal source is a signal source connected to the
building system ground. It is already connected to a common ground point
with respect to the device, assuming that the computer is plugged into the
same power system as the source. Non-isolated outputs of instruments and
devices that plug into the building power system fall into this category.
The difference in ground potential between two instruments connected to
the same building power system is typically between 1 and 100 mV, but the
difference can be much higher if power distribution circuits are improperly
connected. If a grounded signal source is incorrectly measured, this
Selected Channel in RSE Configuration
PGIA
Input Multiplexers
–
+
–
Floating
Signal
Source
V
s
I/O Connector
AI GND
AI SENSE
AI <0..n>
+
Programmable Gain
Instrumentation
Amplifier
Measured
Voltage
V
m
–
+