72
SPECIAL
DEVICES
circuits described in the Type 82 circuit description
section of this manual.
Static Circuit Conditions
A 2D21 thyratron tube (master card control)
is
connected
across
the DC machine circuit with a 2000
ohm resistor in the cathode circuit and a high
speed
relay in the anode circuit. Negative
bias
voltage
for
this tube
is
obtained from the standard
bias
oscillator
and rectifier and
is
applied
to
the grid in series with
two
500K resistors, making the grid approximately
40 volts negative with respect
to
the cathode. This
nega-
tive
bias
prevents the tube from firing when anode
vol-
tage
is
applied each
cycle
at the time commutator 2
makes.
The control grid of the tube
is
also connected to the
master rail brush through a
.05
mfd capacitor.
Firing the
MCC
Tube
Shortly before a master card reaches the card brush
station, the rail brush
senses
a corner cut in the lead-
ing edge of the card (Figure
51).
This applies a
posi-
tive
pulse to the control grid of the master card control
tube through commutator 2, the master rail brush, the
.
05
mfd capacitor, and the 500K resistor. This positive
voltage cancels the negative grid
bias
and
causes
the
tube
to
fire
since,
at this
time,
anode voltage
is
also
applied
to
the tube through commutator
2.
Firing of the MCC tube
picks
up
the
MC
relay in
the anode circuit, thus transferring the MCR points.
Opening of the N / C MCR point allows removal of the
anode voltage from all impulse storage tubes when
com-
mutator 3 breaks. This allows
any
storage tube (12
through
9)
which has been previously
fired
to
de-ionize,
thus clearing the impulse storage section.
Closing of the
N / 0 MCR point completes a circuit
as
follows: from the positive
side
of the line, through
contact roll cover switch
1,
the card lever contacts,
group sort switch
1,
to commutator
2,
commutator 3,
through A-3, MCR
N/O,
A-2,
to the outer brush
on the selecting commutator. This permits placing
a positive potential on the contact roll when the
inner brush
sweeps
across
the segments, thus allowing
the card brush to
sense
holes
in
the master card.
Just before 9 time at the start of the master card
cycle,
the center and outer selector commutator brushes
make. This happens before commutator 2 breaks at
-h" before 9. In conjunction with the MCR
N/O
point,
these brushes shunt around commutator 2, thus main-
taining a positive potential on the anode of the MCC
tube and keeping the
MC
relay energized until the end
of the master card
cycle
when the center brush breaks.
Commutator 3 makes at
3
5
2"
before 9, shunting the
N/C
MCR point (now open) and applying anode volt-
age
to
the impulse storage tubes.
Sorting the Master
Card
When the card brush
senses
a hole in the master
card, the full
DC machine circuit voltage
is
applied
to
the starting anode of the OA4G trigger tube. This
c;:auses
immediate firing of the OA4G and sorting of
the master card into the corresponding pocket. At the
same time, this positive voltage
is
applied through the
corresponding impulse emitter segment
to
a tube in
the impulse storage section.
Each impulse storage tube (2D21 thyratron)
is
con-
nected
across
the DC circuit with a 47K resistor in
series with its cathode. Negative grid
bias
for these tubes
is
obtained in the same manner
as
for the MCC tube.
The positive pulse from the impulse emitter segment
is
applied through a
.05
mfd capacitor and a 500K
resistor to the control grid of the storage tube
con-
nected
to
that emitter segment. This voltage cancels
the negative grid
bias
on the tube, causing it to
fire
.
Once fired
by
the action of a master card, the tube
re-
mains in conduction until the following master card
(or a trailer card)
is
sensed.
Since
the voltage drop
across
a conducting 2D21
is
approximately 8 volts, the
voltage on the cathode of the storage tube during
con-
duction
rises
almost
to
the full DC circuit potential. The
majority of the potential drop appears
across
the 47K
resistor in the cathode circuit.
At the end of the master card
cycle,
the center brush
on the selecting commutator breaks, de-ionizing the
MCC
tube and dropping out the MC relay. The
N/C
MCR points
close
before commutator 3 breaks, thus
maintaining anode voltage on the impulse storage tubes
and keeping that tube in conduction that
was
pre-
viously fired
by
punching
sensed
in the master card.
The
N/O
MCR point breaks the circuit to the selecting
commutator and the contact roll to prevent sensing of
detail card information
by
the card brush.
Sorting Detail Cards
If
the card immediately following the master card
is
a detail card, it will not
be
read
by
the sort brush
because
of the condition of the
N/O
MCR point. How-
ever, when the impulse distributor makes on the
seg-
ment corresponding
to
the value sensed in the previous
master card, a positive potential
is
applied to the
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