National Instruments AT-MIO-16X - Manual (Page 46)

Chapter 2 Configuration and Installation
AT-MIO-16X User Manual 2-24 © National Instruments Corporation
Differential Connections for Nonreferenced or
Floating Signal Sources
Figure 2-8 shows how to connect a floating signal source to an
AT-MIO-16X board configured in the DIFF input mode. The
AT-MIO-16X analog input circuitry must be configured for DIFF
input to make these types of connections. Configuration instructions are
included in Chapter 4, Register Map and Descriptions.
Figure 2-8. Differential Input Connections for Nonreferenced Signals
Figure 2-8 shows two bias resistors connected in parallel with the signal
leads of a floating signal source. If the source is truly floating, it 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 AI GND. The best way is simply to connect the
positive side of the signal to the positive (+) input of the PGIA and
Floating
Signal
Source
+
-
+
Input Multiplexers
AI SENSE
PGIA
V
m
Measured
Voltage
AI GND
-
V
s
-
+
I/O Connector
AT-MIO-16X Board in the DIFF Input Configuration
Bias
Resistors
Bias
Current
Return
Paths
ACH<8..15>
ACH<0..7>
Gain