2-38
|
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Chapter 2
Analog Input and Temperature Sensor Measurements
Figure 2-37.
SCB-68A Circuit Diagram for Single-Ended Analog Input Attenuation on AI <i>
Install resistors in positions B and F, or positions D and G, depending on the channel you
are using on the SCB-68A. Use the following equation to calculate the gain of the circuit:
where
R
B
or
D
is the resistance of the resistor in position B or D, and
R
F
or
G
is the resistance
of the resistor in position F or G.
Analog Input Voltage Dividers
When calculating the values for
R
1
and
R
2
, consider the input impedance value from the point of
view of
V
in
, as shown in Figure 2-38.
Figure 2-38.
Input Impedance Electrical Circuit
The following equation shows the relationship among all of the resistor values:
AI
i
AI
i
+
8
y
S
C
x
E
A
F
G
B
C
D
+
+
+
+ 5 V
AI GND
+ 5 V
AI GND
AI
i
AI
i
+
8
G
R
B
or
D
R
B
or
D
R
F
or
G
+
(
)
-------------------------------------------
=
R
2
V
in
+
–
+
–
R
1
Input
Impedance
