User manual

Chapter 4 Connecting Signals
© National Instruments Corporation 4-13 NI 6034E/6035E/6036E User Manual
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 6034E/6035E/6036E device.
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. The PGIA then saturates, causing
erroneous readings.
PGIA
Selected Channel in DIFF Configuration
Programmable
Gain
Instrumentation
Amplifier
+
+
–
–
+
–
Input Multiplexers
AISENSE
AIGND
I/O Connector
V
cm
+
–
V
s
ACH+
ACH–
V
m
Bias
Current
Return
Paths
Bias
Resistors
(see text)
Floating
Signal
Source
Measured
Voltage
UM.book Page 13 Monday, May 14, 2001 10:32 AM