National Instruments SCXI-1121 - Manual (Page 36)

Chapter 2 Configuration and Installation
SCXI-1121 User Manual 2-20 www.natinst.com
Analog Input Channels
The positive input channels are located in column A. Their corresponding
negative input channels are located in column C. Each input corresponds to
a separate amplifier and is fully isolated from the other channels and from
earth ground. The inputs are designed in a floating single-ended
configuration, hence the measured signal can be referenced to a ground
level with common-mode voltage up to 250 V
rms
. For better noise
immunity, connect the negative input channel to the signal reference. If the
measured signals are floating, connect the negative input channel to chassis
ground on the terminal block. Figure 2-4 shows how to connect a
ground-referenced signal. Figure 2-5 shows how to connect a floating
signal. Figures 2-6 and 2-7 show how to connect AC-coupled signals.
Figure 2-4. Ground-Referenced Signal Connection with High Common-Mode Voltage
Figure 2-5. Floating Signal Connection Referenced to Chassis Ground for Better
Signal-to-Noise Ratio
V s
V
cm
High
CMV
V
out
+
–
+
–
+
–
+
Module
+
V
s
V
out
+
–
+
–
Module