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3330B
to the
proper
terminal
of
the
network
as a
function of
each
digital
input
bit.
3-38.
The
5
-line
current
limit
input
consists
of
a 4-bit
BCD
input
which
is
applied to the
remote
current
limit
circuit,
and
a
single
local/remote
line
which
is
applied
through
a
relay
driver
to
A3K1
and A3K6.
Upon
re-
mote
command, A3K1
closes
and
selects
the
current
limit
ladder.
The
circuit
then
performs
the
current
limit
adjustment
in
accordance with
the
BCD
input.
The
voltage
limit circuitry
is
arranged
in.
the
same
way.
The
local/remote input operates
relay
A3K6
which
selects
the
remote
voltage
limit
ladder.
Again,
the
BCD
input
controls the
decoder
which
accomplishes
the
adjustment
function.
3-39.
CIRCUIT DESCRIPTIONS
3-40.
The
following paragraphs describe
in detail
the
operation of each
circuit.
The
information
is
grouped
according to
individual
assemblies
found
in
the
Model
3330B.
To
find the description
of
a
particular
circuit,
first
determine
the
name
of
the
assembly
that the
circuit
is
located
on and
proceed
from
there.
For
example,
the
VCO
circuit
is
located
on
the
Series Pass
assembly
A4A5.
3*41.
Main Mother Board
(A4)
3-42.
Functioning
as
the
parent
assembly
for
assemblies
A4A1
through
A4A17,
the
Main Mother
Board
inter-
connects
all
the assemblies
found on
it
and
distributes
signal
paths
to
appropriate
sections
of
the instrument.
Individual
circuit
descriptions for
A4A1
through
A4A17
are
provided
in
the following paragraphs.
3-43.
Components mounted on
the
A4
board
consist
primarily
of diodes and
relays.
Diodes
CRl
through
CR28
are
associated
with
the ladder assemblies.
Relays
K3
and
K6
form
part
of
the
mode
selection
circuitry.
K2
is
energized
when
the
instrument
is
in
the
1000
volt range.
K1
is
energized
in
the
100
volt
range
and
de-energized
in
the 10 volt range.
Relay
K5
is
the
Standby/Operate
relay,
and
K4
is
the Polarity
relay.
3-44.
+10
Volt Reference
Supply {A4A1)
3-45.
The +10
Volt Reference Supply produces
an
extremely
stable
reference voltage
upon
which
the
instru-
ment's
stability
is
based.
Range
zero adjustments
and
a
resistor for
the current
mode
are also
located
in this
assem-
bly-
3-6
3-46.
10
VOLT REFERENCE
SUPPLY.
Tlris
is
a vol-
tage regulated
power
supply
consisting
of
a
stable reference
amplifier, a
differential
comparator
amplifier,
and
a series
regulator.
Reference
amplifier
IC2
contains a
matched
zener
reference
and
amplifier
elements
to
produce
an
extremely
stable
voltage
with
respect
to
time
and
termpera-
ture.
Voltage
variations
at
the regulator sense
line
(terminal
14) are
developed
across the voltage divider
RIO
through
R13
and
R2
and
are
applied
to the
other input
of
IC2.
Any
difference
between
the sense terminal voltage
and
the reference voltage
is
amplified
by
IC2
and ICl and
used
to
control the
conduction of
the
series
regulator
Q1
and
Q2, which
establishes a
+10
volt
dc reference voltage
at
terminal
15.
Variable
resistor
RIO
provides
adjustment of
the regulated
output
voltage.
3-47.
RANGE ZERO AND CURRENT
SHUNT.
The
voltage divider
of
R16
through
R21
allow zero adjustments
in
the voltage
mode
of
operation.
Resistor
R22
is
used
in
the current
mode
of
operation.
3-48.
Chopper
Amplifier
(A4A2)
3-49.
The Chopper
Amplifier
compares
low
frequency
and dc
control
signals
from
the
Ladder
summing
junction
to
the
+SENSE
terminal voltage
and
amplifies
any
differ-
ence.
The
Chopper
Amplifier
circuitry
consists
of an input
filter,
a
MOSFET
chopper, an
operational amplifier,
a syn-
chronous demodulator, an output
filter,
and
a
multivibra-
tor.
3-50.
Low
frequency
and
dc
control
signals at
terminal
6
are
passed through
the input
filter
C2,
Rl, and
C3
to
reject
frequencies
above
30
Hz.
The
MOSFET
chopper
Q1
modulates
the
signal
appearing
at
the
junction of
its
drain
and R2.
C4
couples the
resultant to
the
gate
of
JFET
Q2.
The
output
signal at
the drain
of
Q2
is
then
amplified
by
the operational amplifier
ICl,
which
has
a
gain
of approximately 420.
The
paraphase
amplifier
Q3
amplifies the
output of ICl and
provides
two
equal ampli-
tude,
but
180"
out-of-phase
signals.
The
collector
signal
of
Q3
is
coupled by
C16
to the
shunt
demodulator Q4.
The
resulting
demodulated
signal
appearing
at
the junction
of
C17
and
R24
is
filtered
by R24,
R26
and C18,
leaving
only the amplified dc
and low
frequency
signals.
The
emitter
signal
of
Q3
is
applied
through
CI4, R21, C15,
R25, R23, and
C22
to
C18, where
it
is
used
to cancel
any chopper
ripple
at
215
Hz.
3-51.
The
215
Hz
multivibrator
is
formed
by
Q6,
Q7
and
associated
timing networks,
in
addition to
a driver
Q5.
Variable
resistor
R43
adjusts the
level
of
the
signal
applied to the
driver
Q5, and
subsequently the
output
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