National Instruments NI 6014 - Manual (Page 38)

Chapter 4 Connecting Signals
NI 6013/6014 User Manual 4-12 ni.com
Differential Connections for Nonreferenced or
Floating Signal Sources
Figure 4-5 shows how to connect a floating signal source to a channel
configured in DIFF input mode on the NI 6013/6014.
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 unlikely to remain within the
common-mode signal range of the PGIA. The PGIA then saturates, causing
erroneous readings.
Selected Channel in DIFF Configuration
PGIA
–
+
–
+
–
+
Floating
Signal
Source
Bias
Current
Return
Paths
V
s
Bias
Resistors
(see text)
I/O Connector
AISENSE
AIGND
Input Multiplexers
Instrumentation
Amplifier
Measured
Voltage
V
m
ACH–
ACH+