National Instruments NI USB-621x - Manual (Page 62)

Chapter 5 Connecting AI Signals on the USB-6210/6211 Devices
NI USB-621x User Manual 5-12 ni.com
Using Differential Connections for Ground-Referenced Signal Sources
Figure 5-7 shows how to connect a ground-referenced signal source to the
USB-6210/6211 device configured in DIFF mode.
Figure 5-7. Differential Connections for Ground-Referenced Signal Sources
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 Series Device Configured in DIFF Mode
PGIA
–
+
–
+
–
+
–
+
V
cm
V
s
Ground-
Referenced
Signal
Source
Common-
Mode
Noise and
Ground
Potential
AI GND
AI SENSE
Input Multiplexers
V
m
Measured
Voltage
Instrumentation
Amplifier
AI+
AI–
I/O Connector