National Instruments Data Acquisition Device E Series - Manual (Page 57)

Chapter 2 Analog Input
E Series User Manual 2-24 ni.com
With this type of connection, the 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 this figure.
Common-Mode Signal Rejection Considerations
Ground-referenced signal sources with differential connections to the
device are referenced to some ground point with respect to the device. In
this case, the PGIA can reject any voltage caused by ground potential
differences between the signal source and the device. In addition, with
DIFF input connections, the PGIA can reject common-mode noise pickup
in the leads connecting the signal sources to the device. The PGIA can
reject common-mode signals as long as AI + and AI – (input signals) are
both within ±11 V of AI GND.
Differential Connections for Non-Referenced or Floating Signal Sources
Figure 2-10 shows how to connect a floating signal source to a channel
configured in DIFF mode.
Figure 2-10. Connecting a Floating Signal Source to a DIFF Mode Channel
E Series Device Configured in DIFF Mode
PGIA
–
+
–
+
–
+
Vs
Ground-
Referenced
Signal
Source
Bias
Current
Return
Paths
AI GND
AI SENSE
Input Multiplexers
Vm
Measured
Voltage
Instrumentation
Amplifier
AI +
AI –
I/O Connector
Bias
Resistors
(see text)