National Instruments PCI-1200 - Manual (Page 33)

Chapter 3 Signal Connections
© National Instruments Corporation 3-11 PCI-1200 User Manual
Differential Connections for Floating Signal Sources
Figure 3-4 shows how to connect a floating signal source to a PCI-1200
board configured for DIFF input. Configuration instructions are in the
Analog I/O Configuration section of Chapter 2, Installation and
Configuration .
Figure 3-4. Differential Input Connections for Floating Sources
The 100 k
Ω resistors shown in Figure 3-4 create a return path to ground for
the bias currents of the instrumentation amplifier. If there is no return path,
the instrumentation amplifier bias currents charge stray capacitances,
+
+
Floating
Signal
Source
V
m
Measured
Voltage
V
s
+
I/O Connector
PCI-1200 in DIFF Configuration
1
3
5
7
2
4
6
8
100 k Ω
Bias
Current
Return
Paths
ACH0
AGND 11
ACH2
ACH4
ACH6
ACH1
ACH3
ACH5
ACH7
100 k Ω
–
–
–