National Instruments VXI-MIO Series - Manual (Page 62)

Chapter 4 Signal Connections
VXI-MIO Series User Manual 4-16  National Instruments Corporation
Differential Connections for Nonreferenced or
Floating Signal Sources
Figure 4-5 shows how to connect a floating signal source to a channel
on a VXI-MIO Series module configured in DIFF input mode.
Figure 4-5. Differential Input Connections for Nonreferenced Signals
Figure 4-5 shows two bias resistors connected in parallel with the signal
leads of a floating signal source. If you do not use the resistors and the
source is truly floating, the source is not likely to remain within the
common-mode signal range of the PGIA, and the PGIA will saturate,
causing erroneous readings. You must reference the source to AIGND.
The easiest way is simply to connect the positive side of the signal to
the positive input of the PGIA and connect the negative side of the
signal to AIGND as well as to the negative input of the PGIA, without
+
-
+
Floating
Signal
Source
Other Input Multiplexers
Instrumentation
Amplifier
V
m
Measured
Voltage
-
V
S
-
+
I/O Connector
AIGND
Bias
Current
Return
Paths
Bias
resistors
(see text)
ACH<8..15>
ACH<0..7>
AISENSE
Selected Channel in DIFF Configuration
PGIA