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Патент USA US2408061

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Sept 24, 1946.
‘a. B. GRYA'CEI ETAL'
' 2,408,060
ELECTRICAL MEASURING INSTRUMENT
Original Filed June 12, 1943
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Attorney '
Patented Sept. 24, 1946
2,408,060
UNITED STATES PATENT OFFICE
2,408,060
ELECTRICAL MEASURING INSTRUMENT
Bertram Barnett Grace, John ‘,Handley, and ‘
Gilbert Gilliver, London, England, assignors,
by mesne assignments, to International Stand
ard Electric Corporation, New York, N. Y., a
corporation of Delaware
Originalapplication June 12, 1943, Serial No.
490,627. Divided and this application November
29, 1943, Serial No. 512,176. In Great Britain
July 17, 1942
6 Claims.
This invention relates to electrical measuring
instruments of the moving coil type in which
the permanent magnet is situated within the
moving coil while a ring of magnetic material
surrounds the magnet and coil assembly to de?ne
the outer periphery of the air gap in which the
coil swings and to complete the magnetic system,
and is a division of our co-pending application
(01. 171——95)
2
The pivot bearings, control springs and ad
justers are mounted on the two bridge pieces 38
which are attached to the framework by the
screws 39. The bridge pieces are insulated from
the frame by bushings and washers.
The open ends of the pole shoes l8 are ex
tended towards one another at a reduced width
and machined off ?at on their extended portions.
‘ .
The invention consists in using for the perma 10 A short-circuitingr screwed plunger 48 is provided
to short circuit or shunt the magnetic flux from
nent magnet on an element of an alloy of high
‘ one pole
shoe to the other and so reduce the ?ux
BH (max) which has been subjected to a steady
density in the gap for the purpose of ?nally ad
magnetic ?eld during cooling and in assembling
justing the de?ection of the instrument.
the parts so that the direction of maximum
The framework isiattached to the base ID of
magnetisability of said element as determined by 15
the instrument by four screws 42 which are
said treatment during cooling shall be coincident
screwed through the ‘base into lugs 472A on the
with the direction in which the element is then
Serial No. 490,627 ?led June 12, 1943.
magnetised after assembly.
7
The invention will now be described with refer
ence to the accompanying drawing, in which:
Fig. 1 is a front View with cover and scale re
rear end of the die castings M,
>
The scale plate 35 is attached to lugs on the
front of the die castings by screws 4|.
20
The permanent magnet I1 is made from ma
moved; and
terial having a very high BHmax, where B is the ‘
Fig. 2 is a top plan view with the base or rear
cover shown in section on the centre line.
remanence, H is the coercive force and BHmax is
the maximum product of these two values. The
best of such materials at present known are al
The framework of the mechanism consists of
a ring-shaped-pole-piece 19 to which two die cast 25 loys of aluminium, nickel and cobalt, which have
been so heat treated in a magnetic ?eld as to ‘en
supports I 4 are rigidly attached by rivets 24.
able a much higher BHmax to be obtained, when
The central permanent magnet I1 is cylindrical
subsequently magnetised in the same direction.
in shape but with a flat portion IT’ on one side
and it is ?tted within a cradle of non-magnetic 30 This gives a very high flux density in the arcuate
air gaps between the pole shoes and the ring. One
material comprising a pedestal 2| and a pair of
such permanent magnet material is sold under the
diametrically opposite pole shoes IS the pedestal
trade name of Ticonal 42/50.
being adjacent to the ?at portion on the magnet
The proportions of the magnet system are so
and insuring that the magnet is assembled in a
chosen ‘that the magnet produces its BHmax, a
de?nite angular position. When assembled the
condition that is dependent on the relationship
magnet is magnetised across its diameter, the
between: the cross sectional area of the magnet
magnetic axis being parallel to the ?at portion
S, the average length of the flux path in the
and corresponding to the direction of the mag
magnet L, the cross sectional area of the ?ux
netic ?eld in which the material was heat treated
during manufacture. Reference may be made for 40 path in the gap s, the combined length of the ?ux
paths in the two gaps Z, and the leakage factor f.
example to the article in “Nature” for July 30,
The proportions are then given by
1938, page 209 for such special process of mag
netisation. The magnet and pole shoe assembly
is held in the ring by the pedestal, which is lo
cated in one of the recesses [9' in the ring and 45
For Ticonal 42/50, BHmaX=4-22 x 106 where
secured by the screw 23.
B=8600 lines per sq. cm. and H=490 Gilberts per
The outer ring I9 is concentric with the mag
cm. so that
net and its polepieces, so that an arcuate air gap
B 8600
I8’ is formed between them with the centre of
F_T90 -17.5
the two opposite arcs coincident with the axis 50
. of the cylindrical magnet.
The moving coil 20 is of rectangular shape
embracing the magnet so that its opposite sides
7 swing in the air gap I 8’ on its pivots which are
coincident with the geometric axis of the magnet 55
and outer ring.
The dimensions of the magnet system therefore
are so proportioned that
£73,1-“: 17.5 approximately
The width of the air gap is no more than is
necessary to accommodate the coil with working
~
I
2,408,060
3
3. An electrical measuring instrument, com
clearances (say 1.2 m/m). The circumferential
prising, amoving coil, a permanentmagnet with
length of the gap is determined, by the ‘angular
co‘ "and pointer, and,
a (suitable
swing of :the
p _
I
‘
said coil, said.’ permanent‘, magnet consisting
of an element rendered magnetically anisotropic
diameter and length of magnet and the leakage
during heat treatment, a cradle comprising a
factor are calculated to give the correct ratio of.
B/I-I.
It will be understood that the _. invention. may
take other forms an example being that in which
the magnetic ?ux is not towb‘e uniformlydis
tributed throughout the length ofthe‘igapnwhichw
may be attained by non-circular curvatureucf
the poles or upstanding portions‘of the outer ring
or by these surfaces being eccentric in relation to
the axis of the magnet and pivotsaand producing
diametrically
opposite pole shoes: surrounding said permanent
magnet and means carried respectively by said
.p'ermanent'fmag'net. and said pedestal to locate
the permanent :magnet in the correct angular
' nonmagnetic pedestal and a pair of
I
positionto .haye it magnetized in a ?eld in the
same direction- asthe held in which it was heat
(waned, said direction being substantially per
p'endi’cular/to that of the path of said moving
0011:‘
air gaps of varying widths.
“
'
‘
pedestal and. a pair of, arcuate'pole shoes overly
ingthepoles .oflthe permanent magnet and a ?at
surfaceonisaid pedestal‘ engageable with the ?at
material 'overlyingthe-poles of the magnet; a
portioniof rtl'ielpermanent, magnet to locate the‘
magnet inithe, correct angular position to have
cradle» oiv-non-magneticumaterial toiwhich the
pole-pieces are secured in such positions that
they grip the magnet between them; a continuous
it magnetized ina ?eld in thesame direction as
the?eld in .whichit was heatvtreated, said direc
ringer highL ‘permeability . material surrounding
the- magnet-and-pole-shoq assembly coaxially
ti'ierewit-hj andpformed with- upstanding portions
in juxtaposition to the pole-shoes to de?ne there
tion- being substantially ‘perpendicular to. that V
of thepathof saidmovingcoil, and said flat sur
‘face being substantiallyparallel to said directien
of" magnetization.
with thatwo opposite :arcsof a cylindrical-arcuate
'5: Anins'trument accordingto claim 2, wherein
air-gap; and a movingcoilembracing the magnet
said. direction of-magnetization is substantially
perpendiculartothe direction'of the path of said
andfpoler-shoe , assembly ,_ and‘, pivoting centrally
about an axis coincidentwithri the axis of the
moving coil in its medium position.
i
6. An instrument according to claim 2, wherein
the _ , magnet-and-pole-shoe V as
said .movingcoil is, arrangedirotatably about an
40
2-. An ,electrical- measuringinstrument, com-»
directionbeing substantially perpendicular to that
of the path‘ oi said moving coil.
ing a cylindrical air gap to receive said moving
stantially perpendicular to the axis of said moving
prising, a moving: coil and a permanent magnet
magnetized in substantially one direction, said
axis, saidlpermanent magnet has pole pieces form
coil, and said direction of-magnetization is sub
.
within’ said‘ coil,_said permanent magnet consist
ingofgan element rendered =magnetically aniso
tropic ‘during heat treatment and permanently
i
cooling,‘ 2, cradlev comprising a non-"magnetic
drical-arcuate pole-shoes - of » high, permeability,
ring‘,
_.
beenjsubjectednto a'steady- magnetic ?eld vduring
across a diameter and has beenipermanently
niagnetisedalong, said diameter; a pair of cylin
sembly being accurately located with respect to
the-continuous, fring by» the seating .of ‘the cradle
inra gap between the upstanding portions of the
.
magnet within said coil, said magnet having a flat
portion on one side thereof and consisting of an
elementpof .an alloy, of high Bl-l max which has
nickel and cobalt whichyelement has been sub—.
jectedlduring cooling to a steady magnetic ?eld
magnet-system;
.
4. ‘An electrical measuring instrument, com
prising a moving coil, a cylindrical permanent
'
What is claimed is:
1. An electrical measuring instrument com
prising a permanent magnet consisting’ of
cylindrical element of an alloy of iron, aluminium,
coil.
45
BERTRAM-BARNETT GRACE.
JOHN I-I‘ANDLEY.
GILBERT GILLIVER,
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