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3330B
the
Relay
Driver
Assembly
A4A9
and
relay
A6K2.
The
instrument
output
is
connected
to
the
normally
open
contacts of
A6K2.
When
the front
panel
CROWBAR-OFF
switch
is
depressed, the relay
is
de-energized and, conse-
quently, has
no
effect.
When
the
CROWBAR-ON
switch
is
pressed,
A6K2
is
energized,
through
the relay
driver,
and
resistor
A6R1
is
placed
across the
output
terminals
to
quickly
discharge the
output
capacitors.
3'111.
Control
Circuitry
and Front Mother Board
3-112.
The
Control
Circuitry for the
instrument
consists
of four
assemblies.
The
parent
assembly
is
the
(A3) Front
Mother
Board,
which
interconnects the
(A3A1)
Decade
Switch
assembly, the
(A3A2)
Switch Board,
and
the
(A3 A3)
I
Limit/V
Trip assembly,
and
distributes the
result-
ing control
signals
to the
appropriate
sections
of
the
instru-
ment.
Programming
inputs
from
the rear
panel
Remote
connector, except
for
the
operate, voltage
trip
range
and
vernier
and
current
limit are parallel
connected
with
the
limit circuitry
in
the
instrument.
The
Voltage
Trip range
is
determined by
the relay
switching
circuitry. ITie
operate
line
is
routed through
the
Front
Mother Board
in
order
for
both
local
and remote
modes
of operation
to
be con-
trolled
by
the inhibit circuitry
which
prevents
the
instru-
ment
from
being turned
on
before being placed
in
standby.
3-113.
FRONT
MOTHER BOARD
(A3).
The
Front
Mother Board
contains
the ladder
networks
for the
remote
current
limit
and
voltage
trip
vernier
control
features, a
greater
than 100
volt
output
detector, the status indicator
lamps,
and
an
inhibit
circuit.
The
current
limit
ladder con-
C-I
I
I
—
.
riiii-Mii
I-I^
^
sists
of
Q5
through Q8,
K2
through
K5, and
the
remote
se-
lection
'circuit
Q4
an3"Kl.
The
vo
ltag e trip
ladder
consists
of QlOlhiougli
Q13,
K7
through
KIO,
and
th^remo^le-
I
null
I
r
.ii
Ti
•Jtui.i
lection
circuit
Q9
and K6.
TransistorsQl through
Q3
form
the greater
than
100
volt
output
detector,
and
the
status
ln3icato7lampTl:onsisro
DSl
througtTDSlO.
TTie
cir
-
cuitry
of
Kll
thru
Kjj
,
Q17, and
Q18
form
the
V
oltage
^^THp Ykige.'EIen^nts of the
inhibit
circuitrjT^
fCl,
Q15,
3-114.
The
remote
current
limit
ladder
consists
of
relay
drivers
Q5
through
Q8
and
relays
K2
through
K5,
a
resis-
tive
ladder
network of
R17, R19, R21, and R23, and
the
remote
selection circuit
of
Q4
and Kl.
The
relay
drivers are
identical
PNP
switches
which
are
turned
on by
a
Logic
"1"
(0 to
0.5
'ftilts)
and turned
off
by
a
Logic
"0"
(+3.8
to
20
volts).
Each
transistor
receives a
—25
volt
dc
collector
voltage
through
the
associated
relay
which
is
connected
to
terminal
22.
Base
voltages
are
dependent
on
the
input
logic
signals
from
the
Remote
connector.
Diodes
CR7
and
CR8
convert
the
8-4-2-1
coded
input
to 4-4-2-1
code,
which
limits
the
maximum
digital
command
to a four
digit
word
of
eleven
or
110
milliamperes.
The
resistive
ladder
network
is
selected
in
various
combinations
by
relays
K2
through
K5
and
divides the
I
limit resistance
at
terminal
19
into
weighted terms of
elevenths.
The
remote
selection
circuit
of
Q1
and
Kl
is
activated
upon
the
presence of
a
Logic
"1" remote
current
limit
com-
mand
at
terminal 21
and
applies the ladder
output
to
terminal 19.
The
current
limit circuitry
in
the
instrument
receives
this
ladder output
and
limits the
maximum
output
current to the
level
established
by
the
coded
inputs
at
terminals
43
through
46
of
the
Remote
connector.
3-
115.
The
remote
voltage limit ladder
employs
relay
drivers
QIO
through
Q13,
relays
K7
through
KIO,
and
the
resistive
ladder
network
of
R26, R28, R30, and R32.
The
remote
selection
circuit
for
this
network
is
Q9
and
K6.
Operation of
the voltage
limit
ladder
is
essentially
the
same
as
that
of
the current limit ladder.
Collector
voltage for the
relay
drivers
is
obtained
from
the
—25
volt
source
in
the
same manner
described
for
the
current
limit
ladder.
CR9
and
CRIO
perform
the
8-4-2-1
to
4-
4-2-
1
decoding.
The
ladder
output appears
at the
remote
contact of
K6
and
is
coupled through
R40
to
the base
of emitter follower
Q14.
The
output
is
developed
across
R41
and
appears
on
terminal 92.
3-116.
The
Voltage
Trip
Range
circuitry
is
composed
of
Kll
thru
K13
and
associated elements.
Relay
K13
is
a
"Local-Remote"
relay for
this circuit
and
is
energized
by Q9.
With
pins 3
and 4
held
at
Logic "0",
the
10
volt
trip
range
is
activated.
When
a
Logic
"1"
is
applied
to
Q17,
the
100
volt
trip
range
is
called;
with
the
base of
Q17
held
at
a
Logic
"0" and
a
Logic
"1"
applied to
Q18,
the
1000
volt
trip
range
is
in
effect.
Both
relay drivers
are
PNP
switches
that
are identical to
the
current
limit
and
voltage
trip
switches.
3-117.
The
greater
than
100
volt
output detector of
Ql,
Q2
and
Q3
samples
the
output
and
illuminates
DS6
when
the
output
voltage
exceeds
100
volts.
This provides
a visual
indication that the
instrument has output
voltages
present that require caution
in their
application.
3-118.
The
configuration of
Q15, Q16, and quad
NOR
gate
ICi
forms an
inhibit circuit
which
prevents the
instru-
ment
from
going
into
operate before passing
through
stand-
by.
Refer
to Figure 3-8
for
a
simplified
diagram of
this
cir-
cuit.
The
flip-flop
is
set
initially
to
the
proper
state
by
the
Logic
"1" coming from S2
on
the
Switch Board
(A3A2),
when
the
standby
position
is
selected.
Should
the
instru-
ment
be
in
the
operate
mode when
the
power
is
turned
on,
3-14
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