National Instruments PCI-6023E - Manual (Page 44)

Chapter 4 Signal Connections
© National Instruments Corporation 4-15 PCI-6023E/6024E/6025E User Manual
Differential Connections for Nonreferenced or
Floating Signal Sources
Figure 4-6 shows how to connect a floating signal source to a channel
configured in DIFF input mode.
Figure 4-6. Differential Input Connections for Nonreferenced Signals
Figure 4-6 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. The PGIA will then saturate,
causing erroneous readings. You must reference the source to AIGND. The
easiest way is to connect the positive side of the signal to the positive input
+
-
+
Floating
Signal
Source
Input Multiplexers
Instrumentation
Amplifier
V
m
Measured
Voltage
-
V
S
-
+
I/O Connector
AIGND
Bias
Current
Return
Paths
Bias
resistors
(see text)
ACH-
ACH+
AISENSE
Selected Channel in DIFF Configuration
PGIA
Programmable Gain
PCI.book Page 15 Wednesday, September 16, 1998 9:09 AM