ADLINK DAQe-2214 - Manual (Page 40)

28 Signal Connections
Differential Input Mode
The differential input mode provides two inputs that respond to
signal voltage difference between them. If the signal source is
ground-referenced, the differential mode can be used for the com-
mon-mode noise rejection. Figure 3-3 shows the connection of
ground-referenced signal sources under differential input mode.
Figure 3-3: Ground-referenced Source and Differential Input
Ground-referenced Source and Differential Input
Figure 3-4 shows how to connect a floating signal source to the
DAQ-/DAQe-2213/2214 card in differential input mode. For
floating signal sources, you need to add a resistor at each
channel to provide a bias return path. The resistor value should
be about 100 times the equivalent source impedance. If the
source impedance is less than 100ohms, you can simply con-
nect the negative side of the signal to AIGND as well as the
negative input of the Instrumentation Amplifier without any
resistors. In differential input mode, less noise couples into the
signal connections than in single-ended mode.
Figure 3-4: Floating Source and Differential Input
AIxH
AIxL
x = 0, ..., 31
Ground
Referenced
Signal
Source
To A/D
Converter
AIGND
+
-
Instrumentation
Amplifier
V
cm
Common-
mode noise &
Ground
potential
+
-
Input Multipexer
AIxH
AIxL
x = 0, ..., 31
Ground
Referenced
Signal
Source
To A/D
Converter
AIGND
+
-
Instrumentation
Amplifier
+
-
Input Multipexer