Chapter 3
Connecting Signals
©
National Instruments Corporation
3-11
Differential Connections for Floating Signal Sources
Figure 3-5 shows how to connect a floating signal source to a
DAQCard-700 configured for DIFF input mode. Configuration
instructions are included in the
section.
Figure 3-5.
Differential Input Connections for Floating Sources
The 100 k
Ω
resistors shown in Figure 3-5 create a return path to ground for
the bias currents of the instrumentation amplifier. If a return path is not
provided, the instrumentation amplifier bias currents cause stray
capacitances, resulting in uncontrollable drift and possible saturation in
the amplifier. Typically, values from 10 k
Ω
to 100 k
Ω
are used.
DAQCard-700 Device in DIFF Configuration
Floating
Signal
Source
Bias
Current
Return
Paths
V
s
I/O Connector
17
18
1, 2
Measured
Voltage
V
ACH<0..7>
ACH<8..15>
Input Multiplexers
AIGND
Instrumentation
Amplifier