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8.4.8
Twenty-Segment Functions
Provision is made for operating a pair of ten-segment DFG's as a single
twenty-segment unit.
The unused output amplifier of the second DFG is
then available for independent use as an inverter.
Twenty-segment opera-
tion can serve either of two purposes:
increased accuracy through the use
of more segments, or the generation of functions
~rom
an input that ranges
over both polarities.
For the former purpose, two DFG's of the same type
(both
"+"
or both
"_II)
are used together; for the latter, one
u+"
and one
It_If
are used together. 'In most connnon arrangement, the first DFG in a pair
is the
"+"
type and the second is the
If_If
type.
However, either type may
be put in any position, so that it is possible to obtain (for example)
twenty
bre~kpoints
in the interval 0
~
x
~
1.
The PARALlAX controls on two connected DFG's perform the same function, each
of them is simply a bias adding a constant (positive or negative) voltage to
the output o In twenty-segment operation, only one of these controls is needed,
the other should be turned offo
Similarly, the controls marked CENTER SLOPE (i.e., the
~S
position on slope
switch 1) determine the slope at x ='0.
This slope is determined by a pot
and input resistor; like the PARALLAX controls, one of these is redundant
in twenty-segment operation.
However, unlike the PARALLAX control, the
CENTER SLOPE control may be used as an ordinary segment
w~en
not needed for
central slope.
This capability is described in Paragraph 8
0
4.6,
If
Eleven-
Segment Functions".
In the case of a DFG with positive and negative inputs, some thought should
be given to the problem of setting the values in the interval around zero.
What is desired is a straight-forward method of setting the values of x and
f(x)
at all breakpoints.
If there is no breakpoint at x
=
0, then the func-
tion values of the two breakpoints nearest zero (one positive, one negative)
cannot be set directly and independently.
Over the interval containing zero,
no diodes are conducting, and the output is simply a linear function of the
input.
The PARALLAX pot allows setting the y-intercept of this function,
i.e o , the value when x
=
O.
The CENTRAL SLOPE pot, which is Slope Pot 1
on either the
+
or the -DFG, allows setting the slope'of this line.
Since
these two parameters completely characterize the line, they can be set to
pass the line through any two points; i.e
o ,
they can be set to give the
correct values at the two breakpoints (one positive, one negative)o
8-19
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