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Патент USA US2127427

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‘Aug; 16, 1938.
Filed July 51, 1937
Marvel‘ W. Scheldor?
2,127,427 ‘
Patented Aug. l6, 1-938
stra'res PATENT OFFICE "
‘ _
PERMANENT MAGNET oarvanonm'raa
Marvel w. Scheldori', Schenectady, N. ‘ll., assign
or to General Electric fllompany, a corporation
I or New York
. Application July or, 1937, Serial No. 156,732 f
4 Claims.
My invention relates to permanent-magnet
(Cl. I'll-95)
it. The armature had a strong tendency to snap
galvanouieters o! the balanced armature type.
such as those employed in radio loud speakers,
magnetic pick-up devices, electrocardiographs,
% and the hire, is .1“. its object is to provide a gal
vanonleter whose response is more nearly pro
over against and bridge the pole pieces, the posi
tion indicated in dotted lines, as soon as there
was any" current flow in the exciting winding.
This tendency was due largely tothe tendency
of the armature to move to close the only air
gap in the permanent magnet ?ux circuit, and
portional to the variation of the current in its this tendency increased as the armature de; ‘‘
euciting winding than has been the caselwith parted from a'cent'ral position, making it im
prior galvanometers of this type.
practicable to offset‘this' magnetic pull by any
The ieatures oi the invention which are be
simple restraining device. For, these reasons, the
lieved to he novel and patentable will be pointed useful working range of the armature was quite
out in the claims appended hereto. For a better
and the de?ecting force dimcult to match
understanding otmy invention, reference is made limited
control by a restraining spring.
in the ioilowing description to the accompanying and
I have found that, if the permanent magnet 15
/ it drawing wherein a side view ot a preferred em
circuit is provided with additional air gaps, as,
‘hooliinent oi my invention is illustrated.
for example, by, placing nonmagnetic spacers it
Ili‘he fgalvanoineter illustrated is oi.‘ the bal
and it between the permanent magnet ll arid.
anced armature type. ‘It includes a pair oi U~ the pole-piece parts it and it, greatly improved
shaped colt-iron pole-pieceparts it and it with results are obtained. The permanent magnet
their open sides facing each other but separated must be of a larger size or produce a greater
to provitle a relatively large armature air gap. total ?ux than before because now appreciable
in which a magnetic vane armature it is sym
metrically mounted. The armature is biased to
a central neutral position by suitable restraining
means which may comprise a torsional rod it
on which the armature is fixed at its center.
The rotl iii may be clamped at one or both of
its ends, one" such clamp being indicated bash
oi the armature at it. an exciting winding
?ux leaks across between the pole pieces of the
permaneutmagnet asindicated by the dotted
lines til. However, the improved results more 26
than o?set the necessity of using a. stronger per
' 3“ made in two coils it and it surrounds opp lsite
‘ enol
rtions oi‘ the armature it.
These coils
will .be connected'iu series and excited by a cur
rent, such as the voice current of a radio loud
spealter, tending to poiarize the vane armature
it in the direction oi its length. Also a mirror
it$1 it moved by the armature and a light ray indi
cating system such as a lamp ti and scale it
ay he used.
_ ‘
A horseshoe-shaped permanent magnet ii is
m provided to create a unidirectional magnetome
tive torce between the pole pieces of the two
parts it and‘ it as indicated by the designa
tions “it” and “S”.
manent magnet.
It is evident that, with no" reluctance gap or
its equivalent at it and it when there is a de
?ection oi the armature from neutral position 30
maximum reluctance, the permanent magnet ?ux
increases and the magnetic pull on the armature
increases not only because of the reduction‘in
armature air gap reluctance wlth'deflectlon but
also because of the increase in permanent-mag
net. ?ux with such decrease in reluctance; that '
is, there is‘ a building up force condition that is
dimcult to control.
By increasing the reluctance of the permanent
magnet ?ux circuit by the air gap at it and
it, the relative decrease in total reluctance of
the magnetic circuit by movement-of the arms.
ture from neutral is of a much lower order than
it now the excitation of "before and the increase in permanent magnet
coils ill and ii is such as to polarize the arma
?ux is correspondingly less. The change in re
ture to produce a south pole at its right end and luctance of the magnetic circuit due to rotation
.45 north pole at its left end as indicated; the arma
of the armature from maximum reluctance to a
ture willtend to twist counterclockwise and, ii’ lower
reluctance position is thus minimized. The
the exciting current is reversed, it wlll‘tend to instability
of the armature is materially deéreased
turn in the‘ opposite direction against the re
straining iorce of‘ the torsional shaft l3. “
' 5
in the prior art device of this type, the perma
nent magnet ll abutted directly against the soft
iron pole-piece parts it and it so that the only
air gap of any consequence in the permanent ‘
55 magnet circuit was the gap between the pole
pieces it and it. _ Such prior art arrangement,
while operative, was not very satisfactory for
- some purposes because the armature was quite
unstable except, of course, in a central position
,60 with no exciting current ?owing in coils liand
and its sensitivity to current variations and its .
magnetic. regulation characteristics greatly im
proved. ‘It is possible to secure much better re
sults by using a large magnet at ‘H with the
air gap at It and i9 than with a magnet weak
enough to place directly on the pole-piece parts,
it and it without encountering instability.
The relative dimensions of the parts and of
~‘the air gaps shown in the drawing are satisfac
tory, but the invention; is by no means limited
to the relative dimensions illustrated. The total
length of air gap in series at 18 and I 9 should
preferably be not greater and may be less than
the length ‘of air gap between the north and
south pole pieces of the galvanometer with ar
a mature I! in the neutral position. The total
length of air gap in the useful flux path should
cuit excited by a permanent magnet and having
pole pieces defining an air gap, a magnetic vane
armature movably supported in said gap, means
for resiliently biasing said armature to a neutral
position of maximum reluctance in the flux path
across said air gap, and an exciting winding
which, when energized, polarizes said armature
obviously not be greater and should preferably
be less than the leakage flux gap at 20. With
the relative dimensions shown» in the drawing,
causing it to turn against its bias to a lower
reluctance position, said magnetic circuit con
taining an additional appreciable and intentional
10 there is a negligible change in flux density across
the armature air gap when the armature l2
air gap for the purpose of minimizing the per
manent magnet ?ux change in said magnetic
circuit whichis due to the movement of said
_ moves from the neutral to an extreme position,
and this useful flux is comparable in magnitude
to'the leakage of flux of the permanent magnet
II, the greater portion of which traverses the _. armature to a lower reluctance position.
2. A galvanometer having a magnetic circuit
path indicated at 20. If I make gaps I8 much
larger in proportion to the other gaps than here
represented, bene?cial results as regards sta
containing an armature air gap and a perma
nent magnet for producing a ?ux across said air
gap, a magnetic vane armature pivoted in said
bility will still be obtained but this will call
20 for a further increase in the size, strength and
cost of the permanent magnet that ceases to
be justifiable. The particular air gap dimen
sions and strength of flux to be used in any par
ticular case will depend upon the degree of sta
bility and sensitivity desired and the use for
which the device is intended.
'The strength of the permanent magnet used
may be such that the flux density in the useful
air gap is increased in comparison to prior gal
vanometers of this general type. In such prior
devices it, was the practice to fit the pole pieces
_ such as H and I! to the permanent magnet as
perfectly as possible. The result was that any
increase in ?ux strength for the purpose of in
pieces separated by an air gap, a permanent
I intentionally provide air gaps at points i8
and I9 and increase the strength of the perma
nent magnet used, but I do not wish to limit my
invention to any particular gap dimensions and
maximum reluctance with respect to the per
40 strength of permanent magnet because any ap- '
reasonable increase in size and cost of the per
manent magnet.
In accordance with the usual practice, the
magnet i1 is made of high grade permanent mag
. net material and is permanently magnetized to
50 provide an efiicient permanent magnet.
pole pieces l0 and II are made of soft iron and
the armature I2 is preferably made of the best
grade of soft, high permeability magnetic ma
terial obtainable.
By means of my invention, the useful range
of vibration of the armature is increased, its de
?ection is more nearly proportional to the exci
tation current, and a more suitable restraining
spring may be used.
It is evident that the structural relation of
the parts may be materially changed without de
parting from the principle of the invention.
In accordance with the provisions of the patent
statutes, I have described the'principle of opera
tion of my invention together with the apparatus
which I now consider to represent the best em
bodiment thereof but I desire to have it under
stood that the apparatus shown is only illus
trative and that the invention may be carried
out by other means.
What I claim as new and desire to secure. by
Letters Patent of the United States is:
1. A galvanometer comprising, a magnetic cir-»
additional appreciable and intentional air gaps
to minimize the change in reluctance of the
magnetic circuit caused by such movement of
said armature.
3. A galvanometer comprising, soft-iron pole
magnet for producing a unidirectional ?ux be
tween said pole pieces across said ,gap, a magnetic
vane-armature pivoted in said air gap, a spring
biasing said armature to a neutral position of
85 creasing sensitivity also decreased the stability.
preciable gap at the points l8 and i9 improves
the relation between sensitivity and stability and
is highly beneficial ‘up to the point where this
expedient becomes impracticable due to an un
air gap, said vane being resiliently biased to a
neutral maximum reluctance position with re
spect to the permanent magnetic flux crossing 20
said gap,
and an exciting coil which, when ener
gized, polarizes said vane causing itto turn from
a neutral maximum reluctance position against
its bias to an unstable lower reluctance position
with respect to the permanent magnet ?ux cross
ing said air gap, said magnetic circuit including
manent magnet ?ux crossing said gap, said ar
mature being movable in opposite directions from
such position to lower reluctance positions in 40
cluding positions where it may bridge said pole
pieces, an exciting winding which, when ener- ‘
gized, polarizes said magnetic vane armature.
causing it to turn from its neutral position to
intercept more of the permanent magnet ?ux
crossing said gap and lowering the reluctance of
said magnetic circuit, and nonmagnetic spacers
between said permanent magnet and said soft
iron pole pieces for the purpose of minimizing
the change in reluctance of the magnetic circuit '
due to such movement of said armature.
4. A galvanometer comprising, pole pieces sep
arated to form an armature air gap, a permanentv
magnet forming with said pole pieces a magnetic.
circuit for producing a unidirectional flux across
said gap, a magnetic vane armature pivoted at
its center in the center of said gap, resilient
means for biasing said vane to a neutral maxi
mum reluctance position with respect to the ?ux
crossing said air gap but permitting the vane 60
to turn in either direction from such position to
lower reluctance positions including positions
where the‘vane may bridge said pole pieces, the ’
permanent magnet being of horseshoe shape and
being magnetically spaced from the pole pieces 85
by reluctance gaps permitting a substantial leak
age ?ux between its pole pieces which does not
cross the armature air gap, and a coil which,
when energized, polarizes the magnetic vane ar
mature and causes it‘ to-de?ect from its neutral
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