National Instruments E Series , Common-Mode Signal Rejection Considerations

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
Vs
+
+
+
-
-
-
VmMeasured
Voltage
ACH<0..15>
AIGND
Instrumentation
Amplifier
I/O Connector






AISENSE
Vcm
+
-
Selected Channel in NRSE Configuration
Common-
Mode
Noise
and Ground
Potential
Ground-
Referenced
Signal
Source PGIA
Input Multiplexers