National Instruments E Series - Manual (Page 56)

Chapter 4 Signal Connections
DAQCard E Series User Manual 4-20  National Instruments Corporation
Figure 4-7 shows how to connect a grounded signal source to a channel
on a DAQCard configured for NRSE mode.
Common-Mode Signal Rejection Considerations
Figures 4-4 and 4-7 show connections for signal sources that are
already referenced to some ground point with respect to the DAQCard.
In these cases, the PGIA can reject any voltage caused by ground
potential differences between the signal source and the DAQCard. In
addition, with differential input connections, the PGIA can reject
common-mode noise pickup in the leads connecting the signal sources
to the DAQCard. The PGIA can reject common-mode signals as long
as V+in and V-in are both within
±
11 V of AIGND. The
DAQCard-AI-16XE-50 has the additional restriction that (V+in + V-in)
added to the gain times (V+in - V-in) must be within
±
26 V of AIGND.
At gains of 10 and 100, this is roughly equivalent to restricting the two
input voltages to within
±
8 V of AIGND.
Figure 4-7. Single-Ended Input Connections for Ground-Referenced Signals
V
s
+
+
+
-
-
-
V
m
Measured
Voltage
ACH<0..15>
AIGND
Instrumentation
Amplifier
I/O Connector
AISENSE
V
cm
+
-
Selected Channel in NRSE Configuration
Common-
Mode
Noise
and Ground
Potential
Ground-
Referenced
Signal
Source
PGIA
Input Multiplexers