Chapter 5
Adding Components for Special Functions
©
National Instruments Corporation
5-23
SCB-68 Shielded Connector Block User Manual
Figure 5-23.
Input Impedance Electrical Circuit
Z
in
is the new input impedance. Refer to Appendix A,
, in the
device user manuals at
ni.com/manuals
for the input impedance.
Equation 5-20 shows the relationship among all of the resistor values:
(5-20)
Special Considerations for Analog Output
When you use the circuit shown in Figure 5-19 for AO, the output
impedance changes. Thus, you must choose the values for
R
1
and
R
2
so that
the final output impedance value is as low as possible. Refer to
Appendix A,
, in the device user manuals at
ni.com/manuals
for device specifications. Figure 5-24 shows the
electrical circuit you use to calculate the output impedance.
Figure 5-24.
Electrical Circuit for Determining Output Impedance
Equation 5-21 shows the relationship between
R
1
,
R
2
,
and
Z
out
, where
Z
out
is the old output impedance and
Z
out2
is the new output impedance:
(5-21)
R
2
V
in
+
–
+
–
R
1
Input
Impedance
Z
in
R
1
R
2
Input Impedance
×
(
)
R
2
Input Impedance
+
(
)
---------------------------------------------------------
+
=
R
2
Output
Impedance
R
1
Z
out
Z
out2
Z
out
R
1
+
(
)
R
2
×
Z
out
R
1
R
2
+
+
---------------------------------------
=
