Table of Contents
Advertisement
3330B
Again,
Qll
and
Q12
together
with
Q3
act
to place the
instrument
in
standby
for
100
milliseconds.
The
momen-
tary
standby
function
is
also
invoked
by
application
of
a
polarity
change
command.
A
separate
inverter
QIO
together
with
associated
differentiator
circuits
provide
the
negative
trigger
to
Qll.
3-87.
Ladders
(A4A10
through
A4A16)
3-88.
There
are
seven
Ladders contained
in
the
instru-
ment.
Each
Ladder
consists essentially
of
the
same
cir-
cuitry
with
the
only
difference
being
the tolerance of the
divider
components.
The
Ladder
circuitry
consists
of
relay
driver/decoders
and
a ladder
network.
3-89.
RELAY
DRIVER/DECODERS.
Relay
Drivers
Q1
through
Q4
are
PNP
switches.
A
Logic
"1"
(0 to
+0.5
volts)
will
turn
the
drivers
on,
and
Logic
"0"
(+4.5
to
20
volts)
will
turn
them
off.
Each
transistor
re-
ceives a
-25
volt
dc
collector voltage
through
the
associa-
ted
relay
of
K1
through K4. Base
bias
voltage
is
dependent
upon
the input
logic signal
from
the
A3
assembly.
Diodes
CR5
and
CR6
convert the
8-4-2-1
coded
inputs
to a 4-4-2-1
code.
This conversion
is
necessary to
limit
the
maximum
digital
command
to
a
four
digital
word
of
eleven
which
corresponds
to
the
maximum
decade
range.
3-90.
LADDER.
Each deck
of
the seven ladder
decks
performs an
identical
function.
The
relative
position
of
the decks,
with
respect
to the
summing
junction,
deter-
mines
the
significance
of
that deck's
contribution
to the
ladder output.
For example, Ladder
no.
1,
which
is
nearest
the
junction,
determines
the
most
significant
portion
of
the
output,
and Ladder
no.
7,
which
is
farthest
from
the junction,
determines
the
least significant
portion.
Although
the
circuit
arrangement of each
ladder
is
the
same,
the
individual
assemblies
are
not
interchangeable,
because
component
tolerance
are different.
3-91.
Ladder
network
R1
through
RIO,
reed
relay
switches
K1
through K4,
and
switch
drivers
Q1
through
Q4
comprise
a four-bit,
weighted-resistor, digital-to-analog
decoder.
The
analog
output of
the
decoder
is
weighted
in
terms of
elevenths
of
the
reference voltage
(+10
volts)
so that
it
can
be
programmed by
input
digital
words
1
through
II.
The
ladder
network
functions
as
a voltage
divider,
where
resistors
R3
through
RIO
are, in
various
combinations, connected
in series
with
Ri
and R2, which
are
the
output
resistors.
Assume,
for
example,
the four-
bit
digital
word
0101,
representing
5,
is
present
at
the
decoder
input.
The
first
and
third
bits,
present
at
pins
16
and
14
respectively,
turn
on
drivers
Q2
and
Q4
and,
through them,
relays
K2
and K4,
while
the
second and
fourth
bits,
present
al
pins 15
and
13, bias drivers
Q3
and
Ql.
off.
With
K2
and
K4
energized,
+10
volts
is
applied to
R5
and R9.
The
parallel
combination
of
R5,
R6
and R9,
RIO
in series
with
Rl
,
R2
provide
an output
that
is
five-elevenths
of
the
available
decoder output.
This
decoder deck
together
with
the other
decoder decks
produces
a
combined
output
which
corresponds
to the
28-word
BCD
input.
An
important
characteristic
of
the
ladder
is
that
its
output impedance
is
constant
regardless
of
the
reed switch
positions,
thereby presenting
a
constant
load
to
the reference
supply.
3-92.
Referring
to the simplified
diagram
of Figure
3-6,
the
operation of
the
Ladders can be
more
easily seen.
The
numerals "4", "4", "2", and
"1"
refer to
the
BCD
com-
mands, and
the
IR, 2R,
etc.,
refer
to the
relative
weights
of
die
associated
Ladder
segments.
The
value
of
IR
is
25K,
so that
2R
is
50K,
etc.
Selecting various
combina-
tions
of
"R"
in
each Ladder
varies
the current supplied
to the
Range
resistors; this
current
is
available in incre-
ments of
1/11
from
each Ladder.
3-93.
Range/Shunt Networks (A4A17)
3-94.
The
Range/Shunt Networks
allow calibration
of
the various
voltage/current ranges
of
the instrument. Vari-
able
resistors
R21, R18,
and
R15
are
used
to calibrate the
full-scale
output
on
the
corresponding
10,
100,
and 1000
volt ranges.
Variable
resistors
Rl, R5, and
R9
are
used
to
calibrate
the
full-scale
output
on
the
corresponding
1,
10,
and 100
milliampere
ranges.
3-95.
Rear
Mother
Board
(A5).
3-96.
The
Rear
Mother
Board
contains
the
A5A1
power
supply assembly
and
the
A5A2
Pre-regulator
Assem-
bly.
Also located
on
the
board
are
Kl,
the
CURRENT
LTMIT/VOLTAGE
TRIP
FLAG
delay;
K2,
used
in
current
limit
and
voltage
trip
conditions;
and
K3,
the
CURRENT
LIMIT/VOLTAGE
TRIP FLAG. A5T1
on
this
assembly
couples the
VCO
pulses
from
the
A4A5
Series
Pass
Assem-
bly
to
the
A5A2
Pre-regulator
assembly.
3-97.
-25
and
-5
Volt
Power Supply (A5A1)
3-98.
The —25
and
—5
Volt
Power
Supply
consists
of
two
separate low-ripple
power
supplies that
produce
the
logic
power and
relay operating voltages for the
instrument.
The -25
volt
power
supply
consists
of
a
bridge
rectifier
CRI
through
CR4,
positive
rectifier
CR5
and
CR6,
the
regulator
Ql
through Q3, and
the
turn-on delay
circuit
Q4.
The
—5
volt
power
supply
consists
of
a
bridge
recti-
fier
CR7
through
CRIO
and
the regulator
Q5
through Q8.
3-11
Advertisement
Table of Contents
