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8-6
Each breakpoint, or "corner" in a DFG curve represents a diode that is
changing state; as the input voltage moves away from. the origin, in either
the positive or the negative direction, more and more diodes start to con-
duct.
Each diode, when it starts to conduct, increases or decreases the
slope of the curve.
The change in slope for a given segment is determined
by adjusting a potentiometer (the slope pot).
The change in slope intro-
duced at a given point has no affect on the value of the function at that
point, but does affect the value at subsequent points
o
For example, Fig-
ure 8.3 shows the affect of changing the slope pot for segment 5 on a par-
tially setup function. The incremental slope introduced at x5 does not af-
fect the function value at that point, but does affect the value at the next
breakpoint x
6
•
The tangent line represents the output with the SLOPE switch
OFF.
The DFG setup procedure is arranged so that the operator does not observe
slopes, but rather values of x and f(x).
Hence, the function value at the
sixth breakpoint is adjusted by means of the slope pot at the fifth and simi-
larly for the other breakpoints.
This fact is the key to understanding the
setup procedure.
In practice, the slope pot for a given segment does have an effect on the
value of the function at that point, due to the fact that the diode is not
·a perfect switch.
The "corner" at x
(Figure 8.3) is somewhat rounded,- and
a slight shift in f(x
5
) will ·occur
w~en
setting f(x
6
).
In many cases,. this
shift is negligible,
but in a few cases, it neceSSl.tates a later "trinuning"
adjustment.
8.4.3
Setting a Ten-Segment Function
Once the values of x and f(x) are tabulated, the function setup is quite
straight forward.
The 580 variable DFG has potentiometers for adjusting
slope and breakpoint for each segment.
The DFG setup panel allows direct
setting from a table of values; first adjust the breakpoint x (which may
be read directly on the DVM), and then set f(x).
As an example, consider the function in Table 8.1.
This is the same func-
tion that was given graphically in Figure 8.2.
Note that since 10 segments
are to be used, the function is tabulated at
11
points, including the
£
endpoints and 9 breakpoints.
A
"+"
DFG is assumed, and the endpoints are
fixed at 0 and-I.
In setting such a function, most computer operators will find it easiest
to set all breakpoints (x values) first, and then, set the function values
f(x)o
However, it is also possible to set the first .breakpoint x, then set
the corresponding f(x), and continue alternating in this mannero
In either
case, the procedure for setting a slope or a breakpoint is the same
0
The
procedure makes use of the DVM and signal selector, and the setup panel
(Figure 8.4), which is in the right half of the lower DFG drawer.
The unit
is marked TIME BASE AND. MDFG INPUT.
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