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SA
ICR®
ETER
.
.®
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CERTIFICATION
THE
THAT
TESTED
MEET
IT
I)FURTHER
MEASUREMENTS
NATIONAL
EXTENT
BRATION
HEWLETT-PACKARD
THIS
ITS
WAS
ALLOWED
INSTRUMENT
AND
PUBLISHED
SHIPPED
CERTIFIES
BUREAU
FACILITY
INSPECTED
FROM
ARE
OF
BY
.
COMPANY
WAS
SPECIFICATIONS
THE
THAT
TRACEABLE
STANDARDS
THE
THOROUGHLY
AND
FACTORY
ITS
CALIBRATION
BUREAU'S
CERTIFIES
FOUND
WHEN
.
TO
TO
THE
THE
CALI-
TO
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OPERATING
MODEL
SERIALS
AND
SERVICE
PREFIXED
425A
:
142
MANUAL
-
DCMICROVOLT-AMMETER
001304
Copyright
1501
PAGE
HEWLETT-PACKARD
MML
ROAD,
PALO
ALTO,
-i"
COMPANY
CALIFORNIA,U.S.A.
1958
Printed:DEC
1963
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To
adapt
changes
Instrument
142-
ERRATA
this
manualtoinstruments
shownintables
Serial
Prefix
:
.
#
MANUAL
DC
MICROVOLT-AMMETER
Manual
Manual
with
other
Make
Manual
ERRATA
Figure
Table
Table
5-12,
R12:Change
R13:Change
6-1,
CR1,
CR2:Change
J2:Changetofollowing
5060-0625
5060-0633
0340-0087
0340-0091
J3:Changetofollowing
5060-0632
5060-0633
0340-0087
0340-0091
M1:Change
R68:Change
V7,
V8
:
replaceable
XV7,
XV8:Delete
replaceable
Under
MISCELLANEOUS,
Change
Change
Change
6-2,
Change~StockNo.
Change~WStockNo.
ChangeStockNo.
ChangeStockNo.
ChangeStockNo.
G30A,
Change
Change
ChangeStock
ChangeStockNo.
ChangeStockNo.
G-83P:Delete
0727-0077:Change
9110-0038:Change
9110-0039:Change
G30B:Delete
Cep
Changes
Schematic
value
value
IndexbyReference
Binding
Binding
Insulator,
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stock
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MODEL
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serial
to 0.953
to 0.28
G-29A-74
tolerance
number
StockNo.
AC-10C
AC-10D
AC-54B
AC-54F
G-29A-74to1902-0108
entire
G-74to0370-0025
G-74Dto0370-0026
.
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425A
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Instrument
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number
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listing
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check
StockNo.
(rmo)
(rmo)
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change
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for
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Serial
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1902-0108
link:black
internal
external
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descriptionto"Part
descriptionto"Part
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.
...
Model
425A
ListsofIllustrations
Table
of
Contents
and
Tables
Section
I
GENERAL
1-1.Description
1-3.Applications
1-5
.
II
PREPARATION
2-1.Introduction.. . . . . .
2-3
.
2-6.Power
2-10.Power
2-13.Installation
2-15.Repackaging
II
OPERATING
3-1.Introduction
3-3.Preliminary
3-4
.
3-7
.
3-9
.
3-12
.
3-14.Isolating
3-16
.
V CIRCUIT
4-1.General
V
MAINTENANCE
5-1
.
5-3.Test
5-6.Mechanical
INFORMATION
... . . . . .
... . . . .
Differences
Unpacking
Low-Level
Ground
AC
Operating
Operation
DESCRIPTION
Introduction.. . . . . . . . .
Equipment
between
FOR
USE
and
Inspection
Requirements
Cable
. . .
for
INSTRUCTIONS
Considerations
Electrical
Currents
Voltages
Procedure
the
Chassis
withaRecorder
.
. . . . .
.
. . . ... ... .
AdjustmentofMeter
. .
. ...
Instruments
. . .
. . . .
.
. ... . . .
Shipment
. . . . . .
Phenomena
.
. . . . . .
. ...
. ... . . .
.
.
. . . . . . .
. . . . . . .
.
. . . . . . .
TABLE
. . .
.
. .
. .
. . .
. . .
Zero
.
.
.
.
.
.
.
Page
1-1
1-1
2-1
2-1
2-1
2-1
2-1
2-1
2-1
3-1
3-1
3-1
3-1
3-1
3-1
3-1
3-2
4-1
4-1
5-1
5-1
5-1
5-1
. . ..1-1
. ...
.
. . . .
. .
. ...
. .
.
. . . .
. . . . .
.
. . . .
. . . ..3-1
... . .
OF
CONTENTS
Section
V
VI
MAINTENANCE
5-8
.
Troubleshooting
5-9
.
Introduction
5-11
.
Amplifier-Power
5-13
.
Chopper
5-15
.
Modulator
5-18
.
Demodulator
5-20.Repair
5-21
.
5-23
5-24
5-26
5-28
5-30
5-33
5-35
5-37
5-38
5-40
5-42
5-44
5-46
5-47
5-49
5-53
REPLACEABLE
6-1
6-4.Ordering
Introduction
.
Cabinet
.
Modulator
.
DemodulatorReplacement
.
Range
.
Disconnecting
Resistor
.
Replacement
Resistor
.
Servicing
..Adjustments
.
Introduction
.
Adjustment
Bias
.
Adjustment
.
Meter
.
Performance
.
Introduction
.
Voltmeter
.
Ammeter
.
Introduction
(Cont~d)
. . . . . . . .
. . . .
Assembly
Assembly
and
. .
Calibration
Assembly
Replacement
. . .
Removal
Replacement
Switch
Information.. . . .
Replacement.. . .
Input-Shunting
of
Input-Shunting
.
Etched
.
. . . . . .
.
of
Cathode
. . .
of
Twin-T
Check
. .
Check
Check
PARTS
. . .
. . . . .
Supply
. . . ...
. . . . . .
.
. .
. . .
.
. . ...
. . . .
. .
Circuit
. . . .
.
. . . .
.
. . .
. . . . . ...
. . . . . .
. . . .
Follower
. .
. . . .
Filters..
. .
. . . .
. . .
. .
. . .
. . .
. .
. . . .
. . . .
. ...
. . . .
Boards
. .
. .
. .
. .
. . .
. .
.
.
. .
. .
. .
. .
. .
. .
.
.
.
.
.
.
.
.
Page
.
.
5-1
5-1
5-1
5-1
5-2
5-3
5-3
5-3
5-3
5-3
5-4
5-4
5-6
5-6
5-6
5-6
5-6
5-6
5-7
5-8
5-8
5-8
5-8
5-10
6-1
6-1
6-1
Number
1-1
.Model
3-1
.
4-1
.Block
.
5-1
5-2
.
5-3
.Modulator
5-4
.Right
5-5
.Range
5-6
.Connection
5-7
.Left
Number
1-1.Specifications
5-1
.Equipment
5-2
.
Troubleshooting
5-3
.Voltmeter
00130-
4
425A
Operating
Diagram
A6,
Chopper
Modulator
Side
Switch
Resistor
Side
.3
MILLIVOLTS
Controls
Assembly
Waveform
View
Point
........,..
View
Required. . . . . .
Calibration(1VOLTS
LIST
Title
DC
Microvolt-Ammeter
... .. . . . ..
of
Model
425A
. ....
Assembly
Model
Detail........
of
Model
Title
. . . . . .
... . . . . .
. . . . . . .
.
. ... ... .
. . . .
425A
Input-Shunting
425A. .
ranges). . . . .
. . . . .
. . . .
. . . .
. . . .
through
OFILLUSTRATIONS
Page
. .
1-1
3-0
4-1
.
5-1
5-3
5-3
. .
5-4
5-5
5-6
5-7
LIST
OF
Page
. .
1-0
. . .
5-0
. .
.
5-2
.
5-9
Number
5-8
.Voltmeter
5-9
5-10.Ammeter
5-11.Voltage
5-12.Model
5-13.Function
5-14.Exploded
TABLES
Number
5-4
5-5
6-1
6-2
through
.Voltmeter
(100
VOLTS
and
.
Voltmeter
through
.Ammeter
.IndexbyReference
.Replaceable
Calibration
.3
Calibration
MICROVOLTS
ranges)
Calibration
and
425A
and
Viewof425A
11021A
Calibration
10
Calibration
Title
Test
Setup(1VOLTS
MILLIVOLT
...........5-8
Resistance
(Schematic
Range
(1000
:1
Title
MICROVOLTS
Designator
Parts
ranges)
Test
Setup
through10MICRO-
Test
Setup
Diagram
Diagram).. . .
Switch
. . .
Detail.. . .
(Standard)
Divider)
(100
.. . . . ....
Probes
MICROVOLTS
ranges)
. .
. . . . . . .
. ...
. . . .
. . .
. .
...5-9
. ..6-2
Page
.
Page
5-8
5-10
5-12
5-13
5-14
5-14
5-10
6-8
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Section
Table
I
1-1
1-1.Specifications
Table
Model
425A
VOLTMETER
Voltage
Accuracy
Input
MICROAMMETER
Current
Accuracy
Input
Range
Positive
end
scale
10
1,
3,
:
Within
variations
1
Positive
microamperes
scaleinan
Within
variationsof±
Depends
_+3%
Impedance
megohm
Range
:
±3%
Impedance
Range
10pl.a
30
100l.A
.3mt
1
3mpa
10m1a
30mga
.1l
.3l,
1g.
003
.01ma
.03
.1ma
.3ma
1
3
:
and
negative
to1volt
sequence
end
of
of
+5cps
:
±3%
:
and
negative
end
eighteen-step,
of
end
5 cps
:
on
range, 1
tiga
a
.a
mAa
a
a
a
ma
ma
ma
ma
voltages
end
scale;power-line
affect
currents
scaleto3
scale;power-line
affect
megohm
from
scaleinan
accuracy
from
milliamperes
1, 3,10sequence
accuracy
to0.33ohm
Imp
edanc
e
1
.000
megohm
1
.000
megohm
1.000
megohm
.000
megohm
1
megohm
1
.000
0.333
megohm
0.100
megohm
0
.033
megohm
megohm
0.010
3300
ohms
ohms
1000
333
ohms
100
ohms
33
ohms
10
ohms
3.3
ohms
1.0
ohms
0.33
ohm
10
microvolt
eleven-step,
frequency
less
than2%.
10
micro-
end
frequency
less than2%.
AMPLIFIER
Output
:
0to1
volt
ohm
shunt
output
Output
Noise
Drift
GENERAL
Power
Dimensions
Impedance
Depends
ohms
when
output
:
Less
than 0
peak-to-peak)
:
After15minutes
perday
115or230
50-cycle
Cabinet
referredtothe input
:
Mount:7-3/8in.
in.(29.83
(Cont'd)
for
end
potentiometer)1ma
:
on
settingofoutput
potentiometer
.2liv
referred
volts
operation
:
cqi)
scale
rms
warmup,
+10%,
also
high,
reading,
(typically
to
driftisless
60
available
(18.73
12 in.(30
adjustable (5000-
maximum
potentiometer;10
is
set for
the
input
cps,40watts
cm)
less
than1.2
than±4l
wide,
.48cm)
maximum
at
11-3/4
deep
1-volt
pv
.v
AMPLIFIER
Gain:100,
Rejection
AC
At
least
proximately
line
or
greater
000
maximum
:
3
dbat1.0
60dbor
twice-power-line
than
end
cps,50 db
more
scale
at 50
above60cps;a
frequency
causes
less
cps
and
ap-
power-
signal40db
than1%error
.
Weight
:
Cabinet
Rack
Accessory
11021A
Probe
volts.Division
10
Mount:Net17lb (7.718
Mount
Available
(formerly
increases
megohms
:Net21lb (9
:
425A-21B)
range
of
accuracyt2%,
kg)
.
534
kg)
1000:1Divider
Model425A
input
to
1000
resistance
00130-
2
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Model425A
1-1.DESCRIPTION
1-2.The
extremely
voltages
1
picoampere
of1megohm
due
measurements
tial,
from
whichwill
recorders.It
1-3.APPLICATIONS
1-4.The
example,inengineering:itisan
tor ordoamplifier,
Model
sensitive
from1microvoltto1
to
on
circuit
to
for
the
chassis
the
cabinet.The
drive
will
Model
.
425A
DC
measuring
3
milliamperes.An
all
voltage
loading
in
circuits
either
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425A
The
.
which
and
input
Model
potentiometer
.
has
anditwill
Microvolt-Ammeter
ranges
circuit
425A
many
GENERAL
device
which
volt
and
currents
input
minimizes
Model
1milliampere
425A
are
off
ground
may
be
provides
or
galvanometer
applications.For
excellent
measurevacuum
SECTION
is
measures
from
resistance
errors
can
make
poten-
isolated
an output
atIvolt
null
detec-
tube
INFORMATION
an
ber
.
The
page
this
included
apply
serial
1
grid
currents
capacitors;in
nerve
potentials
and
chemistry:the
chamber
and
galvanic
1-5.DIFFERENCES
1-6
.
TheModel
with a
changes
prefix,
of
manual
changes
directly
number
and
medicine
measurements
actions
three
only
whenachangeismadeinthe
then,isan
this
manual
applies
with
this
to
be
made
to
prefix
leakage
and
plant
Model
.
BETWEEN
425A
carriesafive
digit
prefix
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directly
manual
in
Models
.
Section
Paragraphs
currentsininsulators
and
biology:it
cell
potentials;andinphysics
425Aisusefulinionization
andcan
identifier,
indicate
the
425A
monitor
INSTRUMENTS
(000-00000).The
andison the
to
A
.
supplement
to
indicate
manual
to
which
1-1to1-6
will
thermocouple
digit
serial
instrument
which
instrument
the
necessary
make
the
carryadifferent
measure
num-
prefix
title
may
manual
I
and
.
.
be
00130-
Figure 1-1
3
.Model
425A
DC
Microvolt-Ammeter
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Model
425A
Z-1.INTRODUCTION
2-2
This
.
inspection,
425A
2-3.UNPACKING
2-4
.Unpack
for
it
surfaces,
damage,
warranty
2-5.An
as
soonaspossible
inspection,alistofperformance
V,
paragraph
testaspartofincoming
section contains
repacking
.
the
instrument
signsofphysical
broken
fileaclaim
page
electrical
knobs,
the
at
5-46.These
.
and
AND
damage
etc
with
the
rearofthis
inspection
after
receipt.To
quality-control
SECTION
PREPARATION
informationonunpacking,
installationofthe
INSPECTION
upon
receipt
suchasscratched
.Ifthereisany
carrier
procedures
and
manual
should
checksareinsection
be
aidinelectrical
Model
.
and
inspect
panel
apparent
refertothe
.
performed
makeagood
inspection
II
Paragraphs
Section
2-1to2-16
11
FOR
Z-10.POWER
2-11
withathree-conductor
ged
into
ment
connectoristhe
2-12.To
erating
three-prongtotwo-prong
on the
2-13.INSTALLATION
2-14
quiringnopermanent
is
.
for
mountmounts
USE
.This
anappropriate
.The
.The
offset
preserve
instrument
adapter
Model
bench
CABLE
Hewlett-Packard
ground
to
ground
top
inastandard
.
power
receptacle,
pinonthe
pin
the
protection
fromatwo-contact
adapter
.
.
425A
isaportable
installation
operation
instrumentisequipped
cable
which,
when
power
.
.The
19-inch
grounds
cable
and
.The
Model
three-prong
feature
outlet,
connect
instrument
Model
425AR
rack
.
the instru
plug-
when
op-
use
topigtail
re-
425A
rack
a
Z-6
.
POWER
2-7
.The
a
115-volt60cps
converted
changing
power
series
place
ampere,
figure
2-8
.The
which
line
quency
the
which
Most
well
power
power
instrument,
cause
2-9
.The
factory
source
source,
two
filters
designed
the
Model
for
use
the dual 115-volt
transformer
configuration
the1ampere,slow-blow
slow-blow
5-13, for
Model
is
tunedtoa
frequency.A
of
instrument
does
commercial
within
plants
line
sluggish
.To
twin-T
are
factory
signal
the
mustbeoperated
not
vary
these
may
frequency
butiflarge
meter
Model
equipped
convertitto
you
must
filters
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to
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under
REQUIREMENTS
425Aisnormally
power
details
425A
synchronous
power
425A
to
stock
supply, butitcan
froma230-volt,60cps source
from
a parallel configurationtoa
.At
the
fuse.See
.
uses an
frequency 5/6
appliedtothe
in
frequency
systems
limits
not
change
from
however,
;
Variations
.
do not
variations
response
is
normally
operate
operate
the
50
single
at41.7cps are
number
.
wired
primary
timeofthe
line
the
schematic
ac-coupled
designated
motor
fromapower
more
maintain
completely
and
lossofaccuracy
from
a
from
rejection
cps
to41.7 cps
plug-in
9110-0039
for
windings
change,
fuse
witha0
determines
amplifier
than_+5
small
from
designated
disable the
exist
shipped
60-cps
50-cps
a
frequency
unit
available
.
use
with
easily
of
the
re-
diagram,
amplifier
power
fre
.Thus
source
cps
frequency
portable
they
will
from
the
power
power
.Both
.Units
from
be
by
.5
of
Z-15.REPACKAGING
2-16.The
packaging
questions,
sales
a
.Ifpossible,
for the
b.Wrap
before
c.Use
of
the
strips
.
.
d.Use
house
bandstoseal the
e.Mark
Instrument",
If
Packard
tachtothe
owner
be
sure
number,
following
an
instrument
contact
representative
instrument
the
placingitin
plentyofpacking
instrument
.
heavy
the
instrument
the
the
instrument
and
accomplished.In
to
your
.
use
.
instrument
the
and
cardboard
container
packing
etc
.
Company
instrument
indicatingthe
identify
serial
listisa
for
authorized
the
shipping container
protect
and
box
Note
is tobeshippedtoHewlett-
for
the
prefix,
SHIPMENT
FOR
general
shipment.If
Hewlett-Packard
original
in
material
use
.
with
serviceorrepair,
any
instrument
container
heavy
paper
around
the
panel
carton
a
or
heavy
"Fragile", "Delicate
identifying
tag
serviceorrepair
correspondence
and
serial
guide for
you
or plastic
.
with
cardboard
wooden
tape
by
model
number
.
have
any
designed
all
sides
box
or
metal
atthe
to
be
.
re-
to
00130-
4
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.
Model
Section
Figure3-1
III
425A
1.Power
2.Pilot
3
.
4.RANGE
3-0
switch
Light.Lights
FUNCTION
;
atinVOLTAGE
o
switch.For
rent
range
Turns
.
switch.For
or
desired,
instrumenton.
when
instrumentison
selecting
CURREN
selecting voltage or
mode
Figure 3-1
of
.
oper-
cur-
5
6
7.OUTPUT
.Operating
ZERO
.
setting
Probe.Connected
.
voltageorcurrenttobe
shown)
drive
recorders
Controls
control
of
.Provides
either
.Used
meter
.
connector
potentiometer
.
to
an
to
INPUT
measured
(rear
output
adjust
of
electrical
connector,
here
instrument,
voltage
or
galvanometer
.
which
zero
apply
not
will
00130-2
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Model
425A
Paragraphs
Section
3-1to3-15
III
3-1.INTRODUCTION
3-2.This
and
information
on
the
3-3.PRELIMINARY
.LOW-LEVEL
3-4
3-5
.Stray
ent,inone
circuits.The
tween
age.Thus,
possibilityoflow-level
mocouples
cables
on
capacitors
two
terminals
vanic
of
the
3-6
.Errors
appreciable.The
to
haveavery
the
most
materials
(with their
istics
(84v/OC),
and
brass(24v/OC).As
wirewound
(known
and
"Ideal").If
sucharesistor
ference
volts
3-7
.GROUND
3-8
.Ground
zero
rents
differs
net
test
.They
leadofthe
is
addedtothe
and
eliminate
shorting strap
groundterminalsofOUTPUT
the
instrument
This
3-9
.AC
3-10
.The
Model
sients
the
instrument
ferent
00130-3
section gives
on the
Model
stray
action)
Model
versus
willbedeveloped
on
occur
procedure
425Aprovides
425A
low-level
form
or
Model
and
signal
when
using
(thermoelectric
(triboelectric
(dielectric
mounted
all
can
425A
.
duetothermal
probeofthe
low
thermoelectric
common
maybe
approximate
manganin
resistors
under
between
lower
from
power
VOLTAGES
when
than
electrical
encountered.Some
copper)
the
trade
the
and
the
CURRENTS
currents
rangesofthe
when
the
ground
flow
through
cable,
input
the
ground
between
(frontpanel on
isolates
low-pass
measuring
.By
the
line
Microvolt-Ammeter
function
CONSIDERATIONS
ELECTRICAL
electrical
another,
425A
voltages;it
the
electrical
effect),
onanimperfect
produce
are
(3
I4v/
are
namesof"Eureka",
Model
thereisa1.OOCtemperature
endsofthe
.
may
potentialofthe
producingavoltage
signal.To
.
filterinthe
adequate
do
usingamodulator
frequency,
OPERATING
.
preliminary
anduseofall
in
does
lower
effect),
apparent
absorption),
voltages within
voltages alone
Model
conductor
temperature-emf
constantan
aluminum
0
C),
an
example,
wound
425A
.
causeanoffset of
Model
potentialofthe
the
probe
break
currents,
chassis-groundand
connector
rack
chassis
rejectionofac
signals
considerations
.
PHENOMENA
phenomena
nearly
ranges,
with
is
from
stray
all
not
distinguish
measures
consider
phenomena.Ther-
flexing
residual
battery
insulator
425Ais
effect
with
.In
likelymaterials
(40
4v/
some
constantan
connected
resistor,40micro-
425A.These
Model
circuit
cable
the
ground
remove
on the
mount
instruments)
cabinet
input
circuitof
within
the
frequency
line-frequency
SECTION
controls
.
.
are
pres-
electrical
be-
net
volt-
of
coaxial
charges
action
(gal-
the
range
can
designed
copper,
use
other
character-
C),
O
steel
(3
4v/0Q,
high-grade
wire
"Advance",
across
dif-
meter
cur-
425A
cabi-
under
and
ground
drop
which
loop
the
metal
cabinet-
rear
.
the
and
tran-
range
dif-
INSTRUCTIONS
the
of
be
of
.
of
III
pickupisprevented
theacamplifier
3-11.AC
net
example,
chassis
the
mum
exceed
3-12.OPERATING
3-13.The
operating
a
b.Turn
minuteisrequired.For
ranges,
c.Set
d.Set
e.Clip
metertozero
maximum
ishing
f.Connect
ranges,
and
librium before
3-14
3-15.To
the
metal
voltages
without
full-scaledovalueofthe
.
Do
utes
most
Static
within
circuit
Do
on
ingresistors
overload
If
disconnectedinyour
of
To
externally
reconnect
graphs5-30to5-33)
.
affecting
line
and
cabinet
voltages
500
volts
following
the
Model
Attach
probetoinput
instrumenton.
allow
FUNCTION
RANGE
probe
range
effectonhigher
not
handle
priortomaking
sensitive
charges
the
probe
allow
sufficient
connection
not
overload
higher
.
the
one-megohm
the nine
use
these
ISOLATING
isolate
shorting
from
is
actually
can
frequency
between
peak
425A
approximately
switch
and
common
with
ZERO
of
about±50 l.v;
the
voltage
and
probe
to
considering
current
are
lowest
ranges,
withaone-megohm
input-shunting
chassisofthe
strap
producing
overdriven
exist
between
accuracyofthe
potential
canbe80to100dbgreater
chassis
.
PROCEDURE
isastep-by-step
.Proceed
connector
Warmup
maximum
15
switch
probe
must
the
THE
to
to
desired
clip
control
ranges
.
Note
for three or four
zero
and
temperature
have timetodissipate
circuit
time
for
points
reading
Note
instrument
ranges,
not
input-shunting
current
for
protected
instrument,
either
resistor
.
CHASSIS
between
any
error
.
chassis
instrument.For
difference
range
selected.Maxi-
and
cabinet
.
as
.
timeofabout
stabilityonlower
minutes
desired
range
together
ZERO
.
thusithas
adjustment
current
.On
to
rangesisaltered
more
probe,
reach
final
excessively
current-shunt-
from
resistor
calibration
shunt
instrument
resistor or
.
Model
chassis-ground
procedure
follows
warmup
function
.
and
control
on
ranges
gradients
common
thermal
.
extreme
(see
para-
425A,
and
must
min-
sensitive
two
remove
unless
cabi-
between
than
not
for
:
one
.
.
adjust
has
dimin-
.
.
clip,
equi-
is
.
and
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Section
Paragraph
cabinet-ground
catedonrearofinstrument
tween
peak
both
is itself
(precaution
3-16
chassis,
425A
III
3-16
chassis
.Isolate
a.Measurement
above
b.Measurement
Measurement
c
.
OPERATION
.
a.If
b.Connect
.
and
chassis
ground
isolated
against
conditions
also
isolate
recordertoOUTPUT
terminals
cabinet
under
is
between
potential
is
with
.
is
made
ground
WITH
require
recorder
of
OUTPUT
Potential
.
must
not
following
two
.
respecttoa
onamore
currents)
A
isolationofModel
chassis
connector
difference
exceed 500
conditions
points
ground
sensitive
.
RECORDER
.
connectorofModel
which
volts
:
which
range
.
425A
lo-
be-
are
Clip
probe
c
.
1
VOLT
adjust
on
control
trol.The
urements.Remember
proportional
gardlessofrange
range
d
f
recorder
.Set
e.Select
ZERO
meter
Calibrate
.
to
g.Set
meterofModel
(30
and
.
MICROVOLT
30
controltoproduce
microvolts)
systembyadjusting
produce
system
to
meter
common
zerotodesired
desired
is
now
selected
clip
rangeonModel
.
deflectiononrecorder
425A
to
ready
that
deflection
deflectionofModel
.
Model
together
positiononits
end-scale
output
AMP
zerowith
recordyour
to
of
recorder
425A
and
select
scale
425A,
deflection
LITUD
ZERO
con-
meas-
425A
.
and
E
.
is
re-
3-2
00130-2
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Model
425A
Paragraphs
Section
IV
4-1to4-3
4-1.GENERAL
.
4-2
If
theMode1425Ais
two
input
terminalsand two
de
amplifier
.Block
whatisbetween
signalisapplied
ac
superimposed
filter.Aphotoconductive
pass
filtered
5/6
The
ac-coupled
feedback
dctoasquare
power-line
outputofthe
amplifier
through
.
considereda
diagramoffigure
input
and
output
across
onthe
frequency
modulator
the
input
signalisattenuatedbythe
whose
wave
by
is
tunedtomodulator
a rejection-type
SECTION
CIRCUIT
black
boxwith
output
amplifiedbyahigh-gain,
terminals,itis
4-1
terminals.The
resistance,
modulator
converts
frequencyissetat
a
light-beam
frequency
filter
.A
indicates
input
and
any
low-
the
chopper
by
synchro-
Iv
DESCRIPTION
nous
demodulator,synchronized
the
light-beam
dc.A
a
.
second-rejection-type
maining
modulator
meter,
determines
4-3
.When
actually
input
resistance
all
but
drop
across
of
one
chopper, converts
fundamentalfrequency
output.A
output
voltage
operated
measures
five
lowest
the
millivolt
circuit,
.
inputofthe
.
de
and
gain
as
voltage
However,
ranges
o£
an
with
the
amplifier
filter
attenuates
component
cathode
feedback
the
ammeter,
drop
this
to
follower
attenuator
instrument
the
acrossacalibrated
resistance
keep
full
instrumenttoa
modulator
by
output
any re-
of
the
de-
drives
which
.
Model
425A
varies
on
scale voltage
maximum
to
a
VOLTAGE
INPUT
FUNCTION
Figure4-1
.
Block
Diagram
of
Model
RANGE
425A
(power-line
frequency=60
cps)
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Model
Section
Table-5-1
V
Table
5-1
.Equipment
Required
425A
Instrument
Voltmeter
Low
Frequency
Oscilloscope
Electronic
Ohmmeter
Divider
Type
Calibrator
Voltmeter
Minimum
Output
Signal
Accuracy:±0.25%
Sensitivity:0.01
Frequency
Sensitivity:1
Input
Accuracy:±
Ranges:at
100:1witharatio
Required
Voltage
.
001to300
Frequency
minimum
Response
flat
down
to 10
to
400
volts
Resistance
or
higher
least
full
scale
within±0.1%
sistanceof100,000
Specifications
Range
volts
do
volt/cm
cps
0
volt
.
full
scale
10
5%
25
accurate
andatotal
:
:
full
scale
megohms
megohms
re-
ohms+1%
Use
Calibration
Performance
Check
Troubleshooting
Troubleshooting
adjustments
Twin-T
Troubleshooting
Performance
and
filters
and
of
check
Recommended
Instrument
Model
Cep
Voltmeter
Cep
Chp
Fabricateasde-
scribedintext
738AR
Calibrator
Model
120B
Oscilloscope
410B
Model
Model
412A
Vacuum
Voltmeters
Model
Vacuum
Voltmeter
Tube
412A
Tube
or
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Model
425A
Paragraphs
Section
5-1
to
V
5-14
.
INTRODUCTION
5-1
5-2.This
information
performance
maybe
ifications
strument
recommended
and
adjustment
5-3.TEST
5-4
.GENERAL
in
table
fabricated
5-5
.100:1DIVIDER
voltage
andatotal
5-9)
.Manganin
sistors
thermal
5-6.MECHANICAL
METER
5-7
.When
over
the
when
instrumentis1)atnormal
ture,
2) in
off
.Zero-set
mechanical
section contains
for
Model
checkisincluded
used
toverifyoperationwithinpublished
.This
in
its
cabinet
test
procedures
EQUIPMENT
.
5-1
.Note
.
divider,
and
gradients
zero
witharatio
resistanceof100,000
wire
the
divider
.
ZERO
meter
calibration
its
normal
as
followstoobtain
stability
.
425A
check
.This
equipment,
Required
that
.
Fabricate
should be
ADJUSTMENT
.
isproperlyzero-set,
operating
:
test
Microvolt-Ammeter
(paragraph
should
some
be
section also includes
troubleshooting,
.
.
test
equipment
equipment
accurate
ohmsf1%
specified
assembly
mark
on
operating
position,
and
maintenance
made
with
needstobe
one
100:1resistive
withint0.1°
for the re-
should
OF
pointer
the
meter
and3)turned
best
accuracy
SECTION
MAINTENANCE
.
A
5-46)
that
spec
the in-
repair
is
listed
/n,
(see
figure
minimize
rests
scale
tempera-
and
V
reveal
ponent
table
have
shooting,
causes
5-11.AMPLIFIER-POWER
5-12.Amplifier
checkedbyvoltage-resistance
stitution.If
difficulty,
Voltages
these
from
5-13.CHOPPER
5-14
checked,itmust
bly,
locationofpartsinthe
follows
glow
tion of
blades
the
areaofthe
itself.To
5-2
andavoltage-resistance
been
included
gives a
.
return
and
are
typical voltages
instrumenttoinstrument
.
Before
A6,isworking
:
a.Remove
b.Check
whenpower
c
.Check
the
are
all
the
chopper
rotating
further
in this
listofsymptoms
and
tube
substitution
the
resistances
ASSEMBLY
the
modulator
bedetermined
properly.Refertofigure
cabinet
four
lamps
is
applied
light
assembly
.
faulty
section.Table
power
original
are
following
(paragraph
interrupterinthe cut
componentifnot
assistintroubleshooting,
chart
and
SUPPLY
supply
tubetothe
indicated
and
.
.
or
(D51-4)tomake
.
.
operation
readings
does
not
may
vary
demodulator
if
chopper
the
steps.Proceed
5-23)
to
seeifthe
figure
5-2,
their
andtube
correct
instrument
infigure
somewhat
.
sure they
away
the
com-
5-11
Trouble-
possible
is
best
sub-
5-11
can
assem-
5-1
por-
chopper
the
.
;
be
for
as
a.Allow
minutes;this
operating
b
.Turn
capacitorstodischarge
c.Rotate
wise
until
upscale
d.Continue
stop
when
shoots
e.When
ment
wise
.Thisisenoughtofree
the
meter
step
you
5-S.TROUBLESHOOTING
5-9.INTRODUCTION
5-10.The
in
the
many
00130-3
the
allows
temperature
instrument
mechanical
meter
toward
zero,
screw
must
localizing
cases
zero
to
pointer
repeat
pointerisexactly
approximately
suspension
repeat
following
visual
a
instrument
pointer
.
rotate
is
of
to
operate
meter
movement
.
off
and
allow30seconds
.
zero-adjustment
is to
leftofzero
adjustment
rightonzero.If
stepscandd.
on zero,
15
degrees
adjustment
.If
pointer
steps c
section
troublesinthe
inspectiono£the
.
throughe.
.
gives
informationtoaid
for
to
reach
screw
and
screw
pointer
rotate
counterclock-
screw
moves
Model
instrument
at
least20
normal
for
clock-
moving
clockwise
over-
adjust-
from
during
425A.In
all
this
will
;
L
D-5-618
Figure
5-1.A6,
Chopper
Assembly