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E L E C T R I C A L P R I N C I P L E S
139
Holf-Entry
The half-entry circuit permits correction to rhe
nearest decimal by adding 5 to the position just to
the right of the last rerained decimal position. This
half correction can be entered only in the first six
positions of the product counter as indicated by the
block diagram in Figure 12 5.
A half-entry switch is provided for each of the
first six positions of the product counter. These
switches are in the N chassis, and their suppressors
are normally biased well below cutoff. Once dur-
ing each computation 5 pulses are applied to the
grids of all six half-entry swirches.
Of course,
nothing happens unless the suppressor of a switch
is brought above cutoff.
This is done by wiring
on the control panel.
When a half-entry hub is
wired to the
f/2
common (+40 volts), the corre-
sponding switch tube is condirioned to conduct by
bringing its suppressor above cutoff. Then when
the 5 pulses are applied to its grid, these 5 pulses
are passed on to the corresponding position of the
products counter.
An examination of rhe circuit diagram for
N
chassis will show 'that the suppressors of the half-
entry switches ( N l , N4, N7, N10, N13, N16)
are all tied to -100 volts and are at that potential
unril wired to +40 volts through the control panel
wiring. When a half-entry switch is wired to +40
volts through the
f/2
common hub, its suppressor
rises well above cutoff. The .OF mfd capacitor be-
tween the .039 megohm resistors serves to by-pass
any transients enrering through the cable from the
punch.
The 5 positive pulses for half correction
are applied to post N42 through the .02 mfd coup-
ling capacitor to the grids of all six switches. The
grids are normally at about -3 5 volts as determined
by the voltage divider shown under switch N1.
When 5 positive pulses are applied to the grids, 5
negative pulses appear at the anodes of the switches.
It will be seen rhat the half-entry switches share
the load resistor with the corresponding column
shift switches. This arrangement is necessary be-
cause ~ulses from both half-entry switches and the
column shift switches enter the clippers and from
there pass to the product counter.
The carry
switches in turn share one of the
. O l
megohm re-
sistors in the load circuit of the clipper as part of
their load resistor.
The 5 half-correction pulses are produced by
the half-entry control circuits in the A chassis as
indicated in the block diagram of Figure 125. The
half-entry is made during rhe first primary cycle
of the last column shift cycle. Remember that no
multiplicand rolling can occur during the first pri-
mary cycle of each column shift cycle, because the
multiplier advancing pulse does not come until 12.
Consequently this first primary cycle is reserved
for half-entry.
However, the half-entry can be
made only once during a computation. Therefore,
only the first primary cycle of the last column shift
cycle is used. From the foregoing it is obvious that
provision must be made to:
( 1 ) permit half-entry only during the 6rh col-
umn shift cycle.
(2) permit half-entry only during the first pri-
mary cycle of the 6th column shift cycle.
(3) recognize 5 pulses only during this first
primary cycle of the 6rh column shift cycle.
(4) produce these 5 pulses with suflicient power
to operate the six half-entry switches.
The first of the above requirements is met by
blocking tubes A141 and A201 as indicated in Fig-
ure 125.
Trigger A1 5 together with follower
A142 fulfills the second requirement.
The third
requirement is met by the 5 pulse trigger A22 un-
der control of switch A21, while the last require-
ment is met by switch A23 and power rube A24.
The actual circuits for the half-entry controls will
be found in the circuit diagram for the A chassis
(Section 26).
I t will be observed that A141 and A142 are para-
llel with the
OFF
side of the 5 pulse trigger A22.
Therefore as long as either A141 or A142 is con-
ducting, A22 cannot turn
ON.
A142 is normally
cut off, but A141 conducts during the first five
column shift cycles under control of A201 which
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