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Патент USA US3026488

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March 20, 1962
E. 6. DE MOTT ETAL
3,026,478
ELECTRICAL INSTRUMENT WITH A PERMANENT MAGNET CORE
Filed June 23. 1959
2 Sheets-Sheet l
ELMER G. DGMOTK
‘7
CHARLES E. .STEGNER and
GERALD STOLAR
"2
INVENTORS
B
W. M'Mé
TTOR/VE Y
March 20, 1962
'
E. G. DE MOTT ETAL
3,026,478
ELECTRICAL INSTRUMENT WITH A PERMANENT MAGNET CORE
Filed June 23. 1959
2 Sheets-Sheet 2
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- \ ELMER GZDOMOTT,
CHARLES E. STEGWER and
GERALD STOLAR
INVEN’fORS
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BY
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"
United States Fatent name
3,026,478
Patented Mar. 20, 1962
1
2
3,026,478
strument magnetic system in which the component parts
thereof are inexpensively manufactured and easily assem
ELEQTRICAL INSTRUMENT WITH A
PERMANENT MAGNET CQRE
Elmer G. De Mott, Chatham, Charles B. Stegner, Verona,
and Gerald Stolar, Linden, N.J., assignors to Daystrom,
Incorporated, Murray Hill, N.J., a corporation of New
Jersey
Filed June 23, 1959, Ser. No. 822,349
10 Claims. (Cl. 324-151)
bled and adjusted.
An object of this invention is the provision of an in
strument magnetic system comprising a movement bracket
having bearing supporting arms integrally formed thereon,
the said movement bracket including means formed there
on for easily and accurately relatively positioning a mov
abie coil, a core magnet with pole shoes, and a soft iron
yo e.
This invention relates to an electrical instrument and 10
An object of this invention is the provision of a novel
more particularly to a moving coil electrical instrument
core magnet and pole piece construction for use in an
of the permanent magnet core type.
core are well known in the art and comprise a transversely
electrical instrument with a uniform scale characteristic.
An object of this invention is the provision of an instru
for the magnetic ?ux. An annular air gap is de?ned by
ponents are held together by a single locking screw and
Moving coil instruments having a. permanent magnet
ment magnetic system which includes a core magnet,
magnetized, generally cylindrical-shaped core surrounded 15 movement
bracket having bearing supporting arms in
by an annular soft iron yoke which acts as a return path
the outer periphery of the core magnet and the inn-er pe
tegrally formed thereon, and a soft-iron yoke, which com
which will not separate even if the locking screw becomes
riphery of the soft iron yoke. A movable coil is arranged
slightly loosened.
20
to rotate, in the said annular air gap, the coil being pivot
These and other objects and advantages will become
ally carried in bearings supported in bearing supporting
apparent from the following description when taken with
arms, or brackets adjacent the opposite ends of the core
the accompanying drawings. It will be understood, how
magnet. The bearing brackets in the instrument of our
ever, that the drawings are for purposes of illustration
invention comprise an integral part of a movement bracket
which extends through the annular yoke. The core mag 25 and are not to be construed as de?ning the scope or limits
of the invention, reference being had for the latter pur
net, soft iron yoke and movement bracket may be held
pose to the appended claims.
together as a subassembly by a single locking screw which
In the drawings wherein like reference characters denote
is threaded to the yoke and engages the magnet. Novel
like parts in the several views:
means are provided on the movement bracket and coop
FIGURE 1 is a plan view of an instrument mechanism
erating members for accurately and precisely relatively lo 30 embodying
our invention removed from its case;
cating the magnet, yoke and bracket whereby, even if the
FIGURE 2 is an enlarged side elevational view of the
locking screw becomes slightly loose, as occasionally hap
mechanism shown in FIGURE 1 with the scale plate and
pens in use, the means for locating the magnet, yoke and
yoke broken away for clarity;
bracket function to limit relative shifting between such 35 FIGURE 3 is an enlarged sectional view taken on line
parts.
3-4 of ‘FIGURE 2;
In core magnet instruments, the magnet is often pro
FIGURE 4 is an enlarged sectional view taken on line
vided with a pair of pole pieces, or shoes, of soft iron
4—_4 of FIGURE 2 only showing the instrument pointer
which provide some compensation for irregularities in the
in full and a portion of the scale;
?ux density at the polar surfaces of the magnet which 40
FIGURE 5 is an enlarged vertical cross-sectional view
may arise from variations in the hardness or composition
of the novel movement bracket of our invention;
of the magnet at different regions thereof. In the instru
FIGURE 6 is an enlarged fragmentary isometric view
ment of our invention, the core magnet is provided with
thin pole pieces; the pole pieces being thin to provide for
a permanent magnet having a maximum magnet length.
The permanent magnet also has a ?at formed thereon at
the magnetic axis to provide an air space between the
magnet and one of the soft-iron pole pieces, which air
showing a ‘boss and projections formed on the upper sur
face of the top bearing supporting arm of the novel
bracket of our invention, for the proper positioning of
the scale plate therewith;
FIGURE 7 is an enlarged side view of the permanent
magnet core and movable coil; and
space increases the reluctance of the magnetic path and
FIGURE 8 is an enlarged fragmentary side elevational
results in a more uniform ?ux at the pole pieces. Further,
view
of a modi?ed form of movement bracket and yoke
50
the magnetic ‘axis of the core is located about 14° above
embodying our invention.
the center-scale position of the coil, as measured in the
Reference is ?rst made to FIGURE 1 of the drawings
direction of up-scale movement of the coil. The com
wherein there is shown an instrument scale plate, desig
bination of pole shoes, a ?at on the core magnet at the
nated by the reference numeral 10, which is provided
magnetic axis, and the positioning of the ?at above the
with a suitably calibrated scale 11. A pointer 12 co
center-scale position of the core provide means whereby a
operates with the scale 11 and is adapted to be moved
substantially uniform scale characteristic may be obtained.
therealong. Referring now, also, to FIGURE 2, the in
In the instrument of our invention the pole shoes, or
strument
mechanism comprises a substantially cylindrical
pole pieces, of the magnet assembly and the magnet
permanent magnet core 13 positioned within and spaced
are of maximum effective height without the necessity
from a soft-iron yoke 14 of annular cross-section which
of rounding the corners of the pole pieces to provide
provides a return path for the magnetic ?ux of the mag
clearance for the inside corners of the coil frame upon
netized core and also serves as a magnetic shield for a.
which the movable coil is wound. The expense involved
coil 16 Wound upon a coil frame 17 of the suitable non~
in rounding the pole piece corners is avoided by making
magnetic material. The wire-wound movable coil 16,
the pole pieces of a lesser height than the magnet where
which carries the pointer 12, has secured thereto pivot
65
by top and bottom surfaces of the magnet and pole pieces
stafr’s 15, 15 which are supported in conventional pivots
are axially displaced. A full height magnet may, there
or jewel bearings 18 and Y18’ which, in turn, are thread
fore, be employed which results in an increase in ?ux
edly engaged in top and bottom bearing supporting arms
when compared to a core in which the magnet and pole
19 and 21, respectively. The bearing supporting arms
pieces are reduced in height to provide clearance for the
70 comprise an integral part of a novel movement bracket,
inner radii of the movable coil ‘frame.
designated 22. The movable coil rotates through an
An object of this invention is the provision of an in
angle which varies with the magnitude of the current
3,026,478
3
flowing in the coil, the current being conducted thereto
through the spiral hair springs 23, as is well known in
this art. The spiral springs 23 also function to restore
the movable coil to a normal zero position with no cur
rent ?owing through the coil, as is also well understood
by those skilled in this art.
Reference is now made to FIGURE 3 of the drawings
A‘if
the cradle 29 between which the core magnet 13 snugly
?ts. Axial displacement of the magnet assembly is there
by prevented by the projections 33, 33 and accurate axial
placement of the magnet assembly on the bracket is as
sured.
The bearing supporting arms 19 and 21, which are
integrally formed on the movement bracket 22, extend
radially in one direction only from the axially extending
wherein it will be seen that the core magnet 13 is pro
portion of the bracket (FIGURE 5). Tapped top and
vided with pole shoes or pole pieces 26, ‘26 made of suit
able magnetic material, such as soft-iron. The pole shoes 10 bottom bearing holes 36, 36 are formed in the bearing
are centered on an axis extending through the center
scale position of the coil in a symmetrical arrangement.
The ferrous pole pieces are preferably made thin whereby
arms, which holes are easily accurately located with re
spect to the arcuate surface 31 of the magnet cradle 29
in the manufacture of the bracket. Since the core magnet
13 is accurately positioned on the bracket, in a manner
a permanent magnet having a maximum magnetic length
may be utilized. The soft-iron pole pieces provide some 15 described above, the accurately located bearing holes as
sure the accurate positioning of the pivot bearings 18,
compensation for irregularities in the flux density at the
18’ (FIGURE 2) and hence, the coaxial location‘ of the
polar surfaces of the permanent magnet which may arise,
coil with the magnet axis.
for example, from variations in the hardness or com
In the assembly of the instrument, the core magnet
position of the permanent magnet at different regions.
The permanent magnet 13 is provided with a ?at 27 20 13 with the attached pole pieces 26, is preferably ?rst
cemented, or otherwise suitably secured to the bracket
which is centered on the magnetic axis of the core magnet
22 containing the jewel bearings 18, 18’. The coil 16 is
to thereby provide an air space between the magnet and
then rotatably mounted within said bearings. Unlike
the soft-iron pole pieces 26. The air space so provided
most prior art constructions, the assembly which includes
increases the reluctance of the magnetic path and results
the bracket 22, magnet 13 and movable coil 16, and
in a more uniform ?ux distribution at the pole shoes.
associated parts, such as the hair springs 23, may be
The constructional features of the permanent magnet
inspected and the necessary adjustments made thereto
core, which include a flat formed thereon and pole shoes
without a surrounding yoke thereon to obscure and ham
secured thereto, are combined With a third feature to
per such inspection and adjustment.
provide for an instrument having a substantially linear
As seen in FIGURE 2, the radial length of the lower
scale. The third feature includes the rotation of the 30
bearing arm 21 is less than the inside diameter of the yoke
core, within the pole pieces, to locate the magnetic axis
14 whereby the yoke is easily slipped over the above-de
thereof, a suitable angle above the center scale position
scribed assembly of the bracket 22, magnet 13, coil 16
of the coil measured in the direction of the up-scale move
and associated parts. In order to properly orient the yoke,
ment of the coil. Reference is made to FIGURE 4 of
an outwardly radially extending, positioning lug, or pro
the drawings wherein the center scale position of the
jection 37, is formed on the outside wall of the axially ex
coil '16 is designated by a broken line CS—CS while the
tending portion of the bracket 22, which projection coop
magnetic axis of the core is designated by a broken line
erates with a radially extending hole 38 formed in the
M—M. In FIGURE 4, a clock-wise, or up-scale rotation
of the magnetic axis M—M of the core 13 from center
scale position, line CS—CS, of the coil 16, of about 14°
is shown, it being understood, however, that the invention
is not limited to this particular angular displacement.
The novelty of the core construction involves the use of
a magnet assembly in which a magnet, having pole shoes,
is provided with a ?at thereon which is centered on the
magnetic axis of the magnet and which magnetic axis is
rotated above the center-scale position of the coil; that
is, in the direction of the up-scale movement of the coil.
yoke. A locking screw 39 engages a tapped hole 41 dia
metrically opposed to the hole 38. The locking screw is
tightened into clamping relation with the magnet between
the pole piece 26 on the magnet to lock the yoke, magnet
and bracket together. The lug 37 and cooperating hole
38 serve to properly locate the yoke on the bracket both
axially and angularly. The outer surface 40 of the axially
extending portion of the bracket 22 is curved to ?t the
inner diameter of the yoke for surface engagement be
tween the yoke and bracket (see FIGURE 3). That is,
the inner and outer side walls 31 and 40, respectively, of
The above constructional features result in an instrument
having a substantially linear scale, or one on which the 50 the bracket are arcuately curved with the center of curve:
ture thereof at the instrument axis, and with the yoke
calibrations are uniformly spaced, without the use of
locked in place with the bracket and magnet, the said core
expensive and intricate magnetic system contours or coil
designs.
In the core construction, the pole shoes 26, 26 are
magnet and yoke are concentrically positioned.
The axial portion of the bracket 22 is enlarged at the
preferably cemented to the magnet 13, although they 55 forward end thereof as at 22', against which enlargement
or projection the yoke may abut (FIGURES 2 and 5).
may be soldered or otherwise suitably secured thereto.
For added bracket strength, a ?llet-like portion 22" is
Likewise, the magnet 13 is preferably secured to the
formed between the enlargement and the axial length of
movement bracket 22 by cementing in order to facilitate
the bracket, and the forward inner wall of the yoke 14 is
the assembly thereof. It will here be understood, how
ever, that the assembly of the instrument can be carried 60 chamfered, as at 42, to accommodate such ?llet-like por
tion on the bracket.
out with such cementing of the core to the bracket.
In prior art instrument mechanisms employing a core
Referring to FIGURE 3 and the longitudinal sectional
locking screw threadedly engaging the instrument yoke,
view of the bracket 22 shown in FIGURE 5, it will be
the core magnet is free to fall out of the yoke if the lock
seen that the axially extending arm portion of the bracket
is provided with a cradle-like member 29 having an arcuate 65 ing screw is slightly loosened thereby possibly greatly dam
aging the instrument moving coil system. In the instru
surface 31 of the same radius of curvature about the
ment of our invention, the magnet 13 is preferably ce
instrument axis as the magnet 13 and against which sur
mented to the bracket 22 and is thereby held captive even
face the magnet abuts. The longitudinal sides 32, 32
if the core locking screw 39 is loosened. Further, even if
of the magnet cradle 29 (as seen in FIGURE 3) abut
the spaced longitudinal pole shoe edges to thereby pre 70 the bracket 22 and core magnet 13 are not cemented to
cisely angularly position the magnet on the bracket 22.
The bracket 22 (FiGURE 5), which is preferably die
gether in the assembly of the instrument, they are retained
within the yoke 14 even if the locking screw becomes
slightly loosened by reason of the cooperating axially ex
tending lug 37 and hole 38. Hence, there is no resultant
dially extending projections 33, 33 adjacent the ends of 75 damage to the instrument even when the. lQcking screw 39
cast, but which may be made by any other suitable proc
ess, is provided with a pair of inwardly, generally ra
3,026,478
6
becomes slightly loose. The instrument magnetic system,
together with the bracket 22, is obviously easily disassem
bled by the removal, or su?icient loosening, of thersingle
locking screw 39, vfor disassembly of the instrument.
air gap, a separable movement bracket having an axial
arm portion extending through the yoke in abutting en
gagement ‘with the yoke and magnet, and locking means
extending between the yoke and magnet at a point diamet
rically opposed to the axial arm portion of the movement
Reference is now made to FIGURE 7 of the drawings
wherein it will be noted that the ferrous pole pieces 26, 26
extend less than the full height of the permanent magnet
bracket and clampingly seeming together the core mag
net, yoke and bracket, cooperating means formed on the
yoke and movement bracket relatively axially and angu
larly positioning the yoke on the movement bracket, and
13. Heretofore, in prior art instruments, the pole pieces
and magnet are made of the same height, and in order to
provide clearance space between the coil frame and pole 10
cooperating means on the movement bracket and core
shoes, the pole shoe edges at the top and bottom are
magnet relatively axially and angularly positioning the
rounded. ‘In our mechanism, the cost of rounding the
core magnet on the movement bracket, the said cooperat
corners is eliminated by making the pole pieces of less
ing
means preventing disassociation of the core magnet,
height than the magnet. In this manner, maximum effec
yoke and movement bracket when the said locking means
tive height of the magnet and pole pieces is obtained with
is only slightly loosened.
out the necessity of rounding the pole piece corners. The
2. The invention as recited in claim 1 wherein the said
full height magnet results in an increase .in magnetic ?ux
cooperating means formed on .the yoke and movement
bracket include means forming a hole in the yoke diamet
rically opposed to the said locking means, and means
as compared to a core in which the pole pieces and magnet
are reduced to provide clearance for the inner radius of
the movable coil frame. The pole pieces with squared 20
forming ‘a generally radial outwardly extending projection
ends are easily manufactured by a punching, rolling or ex
truding process at a very low cost.
on the movement bracket which cooperates with the said
hole in the yoke.
The novel instrument mechanism of this invention pro
33. The invention as recited in claim 1 wherein the co
vides means for accurately positioning the scale plate 10
relative to the instrument axis and in the proper angular 25 operating means on the movement bracket and core mag
net include a pair of spaced pole shoes secured to the mag
position. Reference is now made to FIGURE 6 wherein
net, the core magnet abutting the axial arm portion of the
it will be noted that a large boss 46 is formed on the upper
movement bracket ‘between the pole shoes with spaced
face of the top bearing supporting arm 19 and is located
edges of the pole shoes abutting the bracket to relatively
in a coaxial relation surrounding the tapped bearing hole
36 formed in the arm. A pair of radially extending pro 30 angularly position the magnet on the bracket, and a pair
of generally radial inwardly extending projections on the
jections ‘47, 47 are formed on the boss 46 for proper cir
axial arm portion of the movement bracket which pro
cumferential location of the scale plate 10 (see also FIG
jections cooperate with the upper and lower ends of the
URE 1). It will be seen that the scale plate is provided
core magnet to relatively axially position the said magnet
with a cut-out portion having the outline of the diagonally
on the bracket.
opposite rounded sides of the boss 46 and projections 47,
4. The invention as recited in claim 1 including gener
4-7, which cut-out portion snugly ?ts the said boss and pro
ally parallel, radially extending, upper and lower bearing
jections to properly orient the scale plate. Although not
shown in the drawings, the instrument mechanism may be
supporting arms integrally formed at the ends of the axial
arm portion of the movement bracket, a pair of coaxial
anchored within a suitable instrument case ‘by utilization
of the annular groove 48 formed in the yoke 14, for exam
ple, and the properly oriented scale plate may also be at
tached to the case by suitable fastening elements which
bearing members attached to the said bearing supporting
arms, a movable coil surrounding said core magnet and
pivotally supported in the bearing members ‘for angular
movement about an axis extending through the said core,
a pointer attached to the said coil and rotatable therewith,
a scale plate mounted on the upper bearing supporting
With a die-cast bracket 22, it will be apparent that the
scale plate positioning boss and projections, .the core cradle 45 arm, a boss formed on the face of the upper bearing sup_
porting arm at the instrument axis, projections formed on
29, projections 33 for axially locating the core, and the
the said upper bearing supporting arm and extending ra
projection 37 for axial and circumferential location of the
dially of the said boss, and means forming a cutout por
yoke on the bracket are all obtained at substantially no
tion in the scale plate which includes side walls which
extra cost once the die for forming the bracket is pro
closely abut the side walls of the said projections on the
duced. It will be apparent that the instrument assembly
upper bearing arm and a portion of the side walls of the
of our invention is amenable to low cost production due
said boss to thereby accurately coaxially and angularly
both to the low cost of manufacturing the parts and to the
position the scale plate on the upper bearing supporting
ease with which the parts may be assembled and tested.
arm.
Having now described our invention in detail, in accord
ance with the requirements of the Patent Office, various
5. In a magnetic ?eld structure for an electrical instru
changes and modi?cations will suggest themselves to those
ment, a transversely magnetized cylindrical core, a coil
skilled in this art. For example, ‘as shown in FIGURE 8
surrounding said core and pivotally supported for angular
of the drawings, another embodiment of our invention in
movement about an axis extending through the said core,
volves the use of a yoke 14a and a bracket 22a in which the
pole pieces of magnetic material secured to the said core,
relative axial position of the yoke and bracket is ?xed by 60 the length of the said pole pieces being less than the length
the positioning of the yoke between the enlargement or
of the core whereby the pole pieces terminate a spaced dis
projection 22’ at the forward end thereof and a projection
tance from the ends of the core to provide clearance
51 on the bracket which engages the bottom end of the
space between the inside corners of the moving coil and
pole pieces.
yoke. In the construction of FIGURE 8, it will be appar
ent that the necessity for the locating hole 38 in the bracket 65
6. An electrical instrument of the type including a gen
extend through the clearance holes 49, 49 (FIGURE 1)
formed in the said scale plate.
2
yoke and the cooperating projection 37 on the bracket (as
erally cylindrical-shaped transversely magnetized core,
seen in FIGURE 2) are eliminated. It is intended that
these and other changes and modi?cations shall fall within
the spirit and scope of the invention as recited in the fol
pole pieces secured to the said core and symmetrically
positioned with respect to the magnetic axis of the core,
a magnetic yoke surrounding the said core and spaced
lowing claims.
70 from the pole pieces on the core by a radial air gap de
creased as compared with that beyond said pole pieces, a
We claim:
1. In a moving coil electrical instrument of the type in
cluding a magnetic system comprising a generally cylin
dn'cal-shaped core magnet and a magnetic yoke surround
ing the said core magnet and spaced therefrom by a radial 75
coil surrounding said core and pivotally supported ‘for
angular movement about an axis extending through said
core, the said core having a plane polar surface normal to
the magnetic axis of the core whereby an air gap is formed
3,026,478
7
between a pole piece and the core, the magnetic axis of
the said core being positioned upscale from the center
scale position of the said coil.
7. The invention as recited in claim 6, wherein the up
8
ter-scale position of the coil, to thereby provide for a
scale on which calibrations are substantially uniformly
spaced.
9. An electrical instrument of the, type including a gen
scale positioning of said magnetic axis is about 14°.
erally cylindrical-shaped transversely magnetized core,
8. In a moving coil, electrical instrument of the type in
cluding a magnetic system comprising a transversely mag
netized generally cylindrical~shaped core magnet, a mag
netic yoke surrounding the said core magnet and spaced
therefrom by a radial air gap, 9. pair of spaced pole shoes
secured to the magnet and with inner surfaces of cylindri
positioned with respect to the core, a magnetic yoke sur
rounding the said core and spaced from the pole pieces on
the core by a radial air gap, a coil surrounding said core
and pivotally supported for angular movement about an
cal curvature corresponding with the engaged cylindrical
pole pieces secured to the said core and symmetrically
axis extending through said core, the said core having a
plane polar surface normal to the magnetic axis of the
core whereby an air gap is formed between a pole piece
outer surface of the magnet, means forming a plane polar
and the core, the magnetic axis of the core being posi
surface on the magnet normal to the magnetic axis of the
magnet whereby an air gap is formed between the magnet 15 tioned upscale from the center-scale position of the said
coil.
at the plane polar surface and the pole shoe secured to
10. The invention as recited in claim 9 wherein the up
the magnet, a separable movement bracket having an axial
scale positioning of the said magnetic axis is about 14°.
arm portion extending through the yoke in abutting en
gagement with the yoke and magnet, locking means ex
References Cited in the ?le of this patent
tending between the yoke and magnet at a point diametri 20
UNITED STATES PATENTS
cally opposed to the axial arm portion of the movement
bracket and clampingly securing together the core mag
1,022,795
McClair ______________ __ Apr. 9, 1912
net, yoke and bracket, the core magnet abutting the axial
2,650,349
Lamb _______________ __ Aug. 25, ‘1953
arm portion of .the movement bracket between the pole
2,719,267
Kunz ____' ___________ __ Sept. 27, 1955
shoes with spaced edges of the pole shoes abutting the 25 2,834,942
bracket to thereby relatively angularly position the magnet
2,901,702
on the bracket, a coil surrounding the said core magnet
and pivotally supported for angular movement about an
axis extending through the core magnet, the magnetic axis
of the said magnet being positioned upscale from the cen 30
Eggers ______________ __ May 13, 1958
Endlich _____________ __ Aug. 25, 1959
FOREIGN PATENTS
192,901
Great Britain __________ __ Feb. 15, 1923
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