Chapter 2 Connecting Signals
SCXI-1125 User Manual 2-4 ni.com
AC-Coupling
You can have an application where you wish to measure only AC voltages
and remove the DC component of a signal before amplification and
sampling. In such cases, you can connect a capacitor in series with one or
both input terminals of the SCXI-1125, as shown in Figures 2-3 and 2-4.
A resistor is connected across the input terminals of the channel to DC
reference the input stage of the SCXI-1125. You do not need to use a bias
resistor with any high-voltage terminal blocks, since the terminal blocks
already have a resistor between the input terminals, or with the SCXI-1305
BNC connectivity terminal block, since this terminal block already has an
AC-coupling option built in.
Figure 2-3. Connecting a Floating AC-Coupled Signal
Caution Connecting a signal source to chassis ground in Figures 2-2 and 2-3, breaks the
isolation barrier.
Figure 2-4. Connecting a Ground-Referenced AC-Coupled Signal
Module
+
–
++
–
I
Vout
VsRbias
Module
+
–
++
–
I
+
–
Rbias
High
CMV
Vout
Vs
Vcm