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425A
Service manual
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HP 425A Service manual

SA
ICR®
ETER
.
.®
CERTIFICATION
THE THAT
TESTED
MEET
IT
MEASUREMENTS NATIONAL
EXTENT BRATION
HEWLETT-PACKARD
THIS
ITS
WAS
ALLOWED
INSTRUMENT
AND
SHIPPED
BUREAU
FACILITY
FROM
ARE
OF
BY
.
COMPANY
WAS
SPECIFICATIONS
THE
THAT
THE
THOROUGHLY
AND
FACTORY
ITS
CALIBRATION
BUREAU'S
FOUND
WHEN
.
TO
TO
THE THE
CALI-
TO
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
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, Insulator,
Binding Binding Insulator, Insulator,
G-81Eto(~W
resistor
Delete
stock
."
stock
."
G74to(~W G74D
toStock
G74N
toStock
Replaceable
StockNo. StockNo.
No
entire
CHANGES
MODEL
Serial
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
.
G-74Nto0370-0035 G-76Jto5060-0625 G-81Eto1120-0306
listing
resistor descriptionto"60 description
425A
Prefixed:142-
Printed:12/63
prefixes
Instrument
Diagram,
ohms
ohms
Designator, to
description,
description,
StockNo.
number
Parts
Cep
post
and ground
post:red
triple:black, triple:black,
post:black post
:
red triple:black, triple:black,
from
and
and
0370-0025 No.0370-0026 No.0370-0035
.
to
5060-0632
to
5060-0633
to
0340-0087
to
0340-0091
listing
.
tolerance
to
"50
check
StockNo.
(rmo)
(rmo)
1120-0306
10%to1%
change
change
.
from
cycle cycle."
for
errata below,
Serial
Prefix
1902-0108
link:black
internal external
internal external
descriptionto"Part
descriptionto"Part
.
. .
. .
. .
.
.
. .
.
.
10%
.
"
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and
make
Make
Manual
.
ofA5;
ofA5;
Changes
not
separately
not
separately
5/5/64
L
SupplementAfor
425A-902
.
...
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
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
.
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
.
Cabinet
.
Modulator
.
DemodulatorReplacement
.
Range
.
Disconnecting
Resistor
.
Replacement
Resistor
.
Servicing ..Adjustments .
Adjustment
Bias
.
Adjustment
.
Meter
.
Performance
.
.
Voltmeter
.
Ammeter
.
(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
Section Table
I
1-1
1-1.Specifications
Table
Model
425A
VOLTMETER Voltage
Accuracy
Input
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
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
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
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
deliverupto
425A
The
.
which
and
input Model potentiometer
.
has
anditwill
Microvolt-Ammeter
ranges
circuit
425A
many
GENERAL
device
which
volt
and
currents
input
minimizes
Model
425A
are
off
ground
may
be
provides
or
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
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number
and medicine
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three
only
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this
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to
be
made to
prefix
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Model
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BETWEEN
425A
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directly
manual
in
Models
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Section
Paragraphs
currentsininsulators
and
biology:it
cell
potentials;andinphysics
425Aisusefulinionization
andcan
identifier, indicate
the
425A
monitor
INSTRUMENTS
(000-00000).The
andison the
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A
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supplement
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indicate
manual
to
which
1-1to1-6
will
digit
serial
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the
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make
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carryadifferent
measure
num-
prefix
title may manual
I
and
.
.
be
00130-
Figure 1-1
3
.Model
425A
DC
Microvolt-Ammeter
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
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
containedina
to
operate
under
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
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
.
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
.
which
zero
apply
not
will
00130-2
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
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
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
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,
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wire
"Advance",
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dif-
meter
cur-
425A
cabi-
under
and
ground
drop
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loop
the
metal
cabinet-
rear
.
the
and
tran-
range
dif-
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
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
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
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following
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. respecttoa
onamore
currents)
A
isolationofModel
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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
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
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deflectionofModel
.
Model
together
positiononits
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output
AMP
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to
of
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425A
and
select
scale
425A,
deflection
LITUD
ZERO
con-
meas-
425A
.
and
E
.
is
re-
3-2
00130-2
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
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)
Model
Section Table-5-1
V
Table
5-1
.Equipment
Required
425A
Instrument
Voltmeter
Low
Frequency
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
410B
Model Model
412A Vacuum Voltmeters
Model
Vacuum Voltmeter
Tube
412A
Tube
or
Model
425A
Paragraphs
Section
5-1
to
V
5-14
.
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
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
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