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e.
Linear interpolation and extrapolation is permissible.
For example, given
v
2
= -2.Sv,
V l
=
Ov,
v
1
-v
2
=+2.5v,
then, looking at Graph
II,
the line marked
V
2
= -2. 5v is the uppermost sloping line radiating
from the origin.
The uppermost line sloping downward corresponds to V 1 - V
2
= +2. 5v and
the resulting intersection is at Rl 1 = 1. 25 K, and R9 = 1. 75 K (R25 = 1. 25 K and
R23
=
1. 75 K for circuit B).
If V
2
=
-2. 5v and V
1
=
+2. 5v, then V
1
- V
2
=
+5. Ov.
The corresponding resistors
would be (by linear extrapolation) double those previously found, i.e., Rl 1
=
2. 5 Kand
R9
=
3. 5 K.
When the operating voltage (+6v) is reduced to +5v, then Graphs
I
and
II
are modi-
fied as follows.
( 1)
The maximum input is now reduced to +5v.
(2) Graph I must be modified by multiplying each labeled value of V
2
by (5/6), and
each labeled value of (V
1
- V
2
) must be multiplied by (2/3).
(3) Graph II must be modified by multiplying (V
1
- V
2
) by (2/3).
V
2
remains
unchanged.
External Level and Sensitivity Control. -- If Equations (
1)
through (5) yield un-
realistic resistance values (e.g., requiring excessive power dissipation), then an external
power supply must be used and jumper J 1 is replaced by an appropriate resistor.
Using the
same definitions for V
1
and V
2
, the external supply will be equal to V
2
and the value of re-
sistance replacing J 1 is determined from Equation (6).
R=
4.15
+
0.3
v
2
(6)
Switching Level Measurement. - - Switching levels may be measured in the fol-
lowing manner.
a.
Select and connect the appropriate network (internal or external) to pin 3 (pin 30
for circuit B).
b.
Connect a well-filtered de supply to the input.
c.
Set the de supply to +6v.
The output should be Ov.
d.
Lower the de input until the output switches to +6v.
This is the de negative-
going switching level, V
1
.
e.
Raise the de input until the output switches to Ov.
This is the de positive -going
switching' level, V
1
.
A-195
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