AVO AVOMETER Mk II Service manual

MK II

WORKING INSTRUCTIONS

AVO

AVOCET HOUSE, 92-96, VAUXHALL BRIDGE ROAD, LONDON,

ENGLAND

LIMITED

THE

MODEL 8 UNIVERSAL

AVOMETER

Mk II

INSTRUCTIONS FOR USE

AVO

AVOCBT HOUSE, 92-96 VAUXHALL BRIDGE ROAD, LONDON, S.W.l.

Teleph one: V ictoria 3404 (9 lin es ) ENGLAND Tel egrams: Avocet, Sow est, London

LI M IT K I)

FOREWORD

For more than a quarter of a century we have been engaged in the design and
manufacture of “ AVO ” Electrical Measuring Instruments. Throughout that time
we have consistently pioneered the design of modern multi-range instruments and
have kept abreast of, and catered for, the requirements o f the epoch-making develop
ments in the fields of radio and electronics.

The success of our steadfast policy of maintaining high standards of performance
in instruments of such wide versatility, and making such instruments available at
reasonable cost, is reflected in the great respect and genuine goodwill which “ AVO ”
products enjoy in every part of the world.

It has been gratifying to note the very large number o f instances where the satisfac
tion obtained from the performance of one of our instruments has led to the auto
matic choice of other instruments from the “ AVO ” range. This process, having
continued over a long period of years, has resulted in virtual standardisation on our
products by numerous Public Bodies, The Services, Railway Systems, and Post

Office and Telegraph Undertakings throughout the world.

Our designers have thereby been encouraged to ensure that new instruments or
accessories for inclusion in the “ AVO ” range fit in with existing “ AVO ” apparatus
and serve to extend the usefulness of instruments already in being. Thus, the user
who standardises on “ AVO ” products will seldom find himself short of essential
measuring equipment, for, by means of suitable accessories, his existing equipment

can often be adapted to most unusual demands.

It is with pleasure that we acknowledge that the unique position attained by

“ AVO ” is due in no small measure to the co-operation of so many users who
stimulate our Research and Development staffs from time to time with suggestions,
criticisms, and even requests for the production of entirely new instruments or
accessories. It is our desire to encourage and preserve this relationship between
those who use “ AVO ” instruments and those who are responsible for their design
and manufacture, and correspondence is therefore welcomed, whilst suggestions will
receive prompt and sympathetic consideration.

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THE MODEL 8 AVOMETER MK. II

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CONTENTS

F o r e w a r d

I n t r o d u c t i o n

T ab l e o f R a n g es

G e n e r a l D e s c r i p t i o n

L im i t s o f A c c u r a c y ..

D esi g n a n d C o n s t r u c tio n

R a n g e C o n t r o l s

T h e M o v em e n t

Sc a l in g

R e p l a c e m e n t o f I n t e r n a l B a t t e r y a n d C e l l

M o v e m e n t R e v e rs e C o n t r o l

O v e r lo a d P r o t e c t i o n

O p e r a t i o n o f In s t r u m e n t

C u r r e n t M e a s u re m e n t

V o lta g e M e a s u r e m e n t

R e s i s ta n c e M e a s u re m e n t

I n s u l a t i o n R e s i s ta n c e M e a s u re m e n t

Low R e s i s t a n c e M e a s u r e m e n t

D e c ib e l s

A c c es s o ri e s

D.C. V o l t a g e M u l t i p lie r

R e s is ta n c e R a n g e E x t e n s io n U n i t
T r a n s f o r m e r s

C o n c l u s i o n ......................................................................................................

C ir c u it D ia g r a m o f t h e M o d e l 8 U n iv e r s a l A v o M e t e r

P a ge

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COPYRIGHT

No inform a ti o n or d ia g ra m s in whole or in pa r t m ay be copied or repro duced without th e p rior permi s s i o n

in writing of Avo Limited

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INTRODUCTION

Sin c e its con c eptio n in 1923, t he Av oMeter has m aint aine d a dist i nct l ead upon all
its co mp etitor s , and c an tod ay q u i te rig h t l y be t e rme d t he mos t popul ar instrumen t
of its type in t h e worl d , fo r in no other in strume nt can one f in d s uch a unique c ombi
natio n o f r anges and comp rehen sive aut om ati c over l oad p rot e ction, in addi t i on to
a high de gree of a c cura c y , reliabili t y and si mpl i c ity of u se .

M uch ti me an d tho ught is conti nually d evo ted b y ou r des i g n dep artment t o the
im prove ment of o ur pr oducts an d it is for the Ele ctronic Rad io and Te l evi s i on
En gine er that thi s new inst r ument ha s been primari l y pr o duc ed. The Mo de l 8
A vo Meter Mk. II has th e hi g h D . C. vo l tag e sensi t i vity of the H igh Re sist ance Avo-

Meter Mode l s 1 and 2, but in additi on, prov i s ion is mad e for t he me a sur e ment of
A . C. curr e n t. A fur th e r us e f ul fe ature which ha s b ee n incorpo r ated is a push button
change - ove r switch which enables the dir ectio n of the cur r e n t th rou gh the mo vin g

co i l to be revers e d , thus obvia t ing t he nece ssit y of changing lead s when wor kin g

with D. C. vo l tag es an d curre n t s whi ch m ay be e i t h e r positive or n egat i ve in res p e c t

to a bas i c te s t p osi t ion. The excellent qu alities of pre vious models in cludin g th e

“ AVO ” automati c cut - out h ave bee n re t a ined, an d w e ha v e gr e a t con fid enc e tha t

given a rea s onable amount o f care and att enti on, not forge t ting the removal of

exhausted batt e r i e s , thi s i nstrumen t will g i v e lastin g sat i s f a c tion .