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Патент USA US2130213

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A. w O L ‘F
.n
2,130,213
AL
VIBRATION DETECTOR
Filed Oct. 23, 1935
PIC-‘1.2.
1'
.
A:
VE TOR 5
BY
1/L1AA/
r%¢// ATTORNEY
2,130,213
Patented Sept. 13,1938 ~
- ' UNITED
STATES“
PATENT OFFICE
2,130,213
VIBRATION DETECTOR
Alexander Wolf, Laurence G. Cowles, and William
S. Richardson, Houston, Tex., 'assignors to The
Texas Company, New York, N. Y., a corpora
tion of Delaware
Application October 23, 1935, Serial No. 46,242
6 ' Claims.
(Cl. 111-352)
This invention relates to vibration detectors,
more particularly to devices adapted to be placed
on or buried in the earth so as to be responsive
to, and to give indications of, vearth vibrations.
5 The device is especially well suited to the recep
tion or ‘detecting of compressional waves such as
are passed through the earth in the carrying out
of seismic methods of geophysical exploration.
The principal object of the invention is the pro
10 vision of an electrical earth wave detector of
rugged and simple construction in which electrical
damping is effectively used. A further object of
the invention is the provision of a detector hav
ing a high degree of sensitivity with a compara
15 tively weak magnetic ?eld.
. In a common form of electrical earth vibration
detector a strong permanent or electro-ma‘gnet
is adapted to be mounted in firm contact with
the earth so that it will be moved or vibrated in
20 accordance with variations in the surrounding
stratum. A coil of insulated wire is usually re
siliently suspended in the air gap of ‘the magnet
and the relative motion of the magnet and the
coil produces an E. M. F. in the coil which is
25 then registered by suitable means. Various modi
?cations of this type of detector are in use and
the electrical sensitivity of these devices depends
upon the strength of the magnetic ?eld and on the
space available in the air gap for coil winding.
so
In order to obtain a clear record of the waves
received by.the detector it is essential that some
means be used for damping the relative movement
of the magnet and coil and several di?erent types
of damping’ have been proposed‘ and tried out.
35 Damping is occasionally secured by ?uid friction,
increased by the presence of any inert material ~
such as insulating material in the coil. For a
given natural frequency of the coil and a given
magnetic ?eld strength the maximum damping is
obtained when the coil is entirely short-pircuited, 5
but obviously the sensitivity is then zero. In most
existing types of electrical earth vibration de
tectors used in seismic exploration by the re
?ection method the magnetic ?eld is so weak and
the natural frequency so high that it is either im- 10
practical or impossible to obtain good electrical
damping.
In accordance with this invention a vibration
detector has been provided in which electrical
damping is used, thus having the great advantage 15
of simplicity and independence of temperature for
all practical purposes for the reasons mentioned
hereinbefore. In providing the electrical damp
ing the pickup coil ordinarily suspended in the
air gap of the magnet is replaced by a solid ring 20
01 non-magnetic‘metal and the pick-up coil wind
ing is then mounted on one of the pole pieces of
the magnet. When the device is vibrated E. M.
F. induced in the solid ring produces variations in
the flux of the magnetic ?eld and hence an E. M. 25
F. in the pick-up coil. An added advantage is
obtained in the possibility of using for the solid
ring a material having a low product of resis
tivity by speci?c gravity such as aluminum,
whereas ‘aluminum cannot ordinarily be used in 30
a winding since insulated aluminum wire is not
readily obtainable.
For a better understanding of the invention
reference may be had to the accompanying draw
ing in which Fig. 1 is a sectional elevation of a :25
that is, by the movement of some element in
preferred embodiment of the invention taken on
either a liquid such as oil or a gas.
the line |-—| of Fig. 2; >
If oil is
used the damping changes rapidly with tempera
turebecause of viscosity-temperature variation.
40 To secure e?lcient air damping an elaborate sys
tem of ba?ie plates is usually required. If electri
cal damping is to be obtained it is usually neces
sary that the coil suspended in the air gap be
partially short-circuited so that the E. M. F.
45 induced in the short-circuited portion will pro
duce a current tending to resist or oppose the
relative motion between the magnet and the ‘coil.
This short-circuiting of a portion of the coil will,
of course, cause a loss in sensitivity and for a given
50 natural frequency of the coil and a given mag
netic ?eld strength the necessary loss of sensitivity
is determined entirely by the product of resistivity
by the speci?c gravity of the material forming
the winding. The loss of sensitivity increases
as with the increase of this product and it is also
Fig. 2 is a plan view of the device shown in Fig.
1, and
.
Fig. 3 is a sectional plan view taken on the line 40
3-3 of Fig. 1.
Referring to ‘the drawing, a permanent magnet
l0 having a cylindrical outer pole l2 and an axial
ly disposed inner pole I4 is adapted to be secured
to or buried in the earth in a manner such that it 45
will vibrate in response to compressional wave
vibrations passing through the surrounding stra
tum. The magnet ill may of‘ course be mounted
rigidly within a protecting casing if desired, the
‘casing then being placed in contact with the 50
earth. No casing has been shown in the drawing
for purposes of simplicity. An annular space i6
is thus formed between the two poles of the mag
net, this space serving to house the pick-up coil
as will be explained hereinafter. An annular 55
, 2
2,180,213
pole piece it having a depending body portion 20
and a ?ange portion 22 is secured to the upper end
of the outer pole i2 by any suitable means such
as by screws 2d. A smaller annular space 2b is
Cl \ formed between the inner surface of the body
portion of the pole piece it and the upper end of
the pole it and a metallic ring 28 of non-magnetic
material is resiliently suspended within the an
nular space 26 by means of an upper spring mem
10 ber 30 and a lower spring member 32. The spring
members 30 and 32 vare secured around their outer
edges to the pole piece it by suitable screws, the
spring members being separated from the pole
piece by means of suitable spacers or washers 36
of insulating material.
Although the spring
members 30 and 32 are shown as spring metal
discs having cut-out portions and radially pro
jecting tongues 36 secured to the ring 28, any
other suitable form of spring mounting for the
20 ring may be used.
inertia member of metallic non-magnetic mate
rial of a size to ?ll substantially all of said air
gap, means for resiliently suspending said inertia
member in said air gap, and a coil winding sur
rounding one of said poles a point spaced longi
tudinally from said air gap, said winding being
adapted to have induced therein an E. M. F.
produced by variations in ?ux caused by rela
tive movement between said inertia member and
the poles‘ of said magnet.
10
2. In a vibration detector, a member responsive
to vibrations, said member comprising a magnet
having an annular outer pole and a pole disposed
coaxially within said outer'pole, an inertia mem
ber comprising a metal ring, means for resil 15
iently suspending said ring between the ends of
the poles of said magnet, said ring being of a
size to ?ll substantially all of the space between
said magnet poles, and a coil winding surround
ing said inner pole and responsive to variations 20
The ring 28 thus forms an
inertia member which will tend to remain im . in ?ux produced by relative movement between
movable when the magnet member it is moved said magnet and said ring, said winding being
in response to earth vibrations. A pick-up coil disposed around said inner pole at a point spaced
comprising a winding 38 is placed in the annular from said inertia member.
space it around the inner pole id anda layer of
3. In a vibration detector a magnet having a
suitable insulating material 6t forms a spool for cylindrical outer pole and a pole disposed c0-' 25
this winding and serves to insulate the winding axially within said outer pole, an annular space
from the metal pole id.
being formed between said poles, a pole piece
When the magnet id is moved in response to secured to the upper end of one of said poles
earth vibrations the metal ring 23 will tend to ‘and extending laterally toward the other pole,
remain in its normal position and the relative an air gap being formed between one edge of 30
movement thus produced between the magnet said pole piece and said other pole, an annular
and the ring will cause currents to be induced metal ring of a size to ?ll substantially all of said
in the ring, these currents in turn producing air gap, means for resiliently suspending said
variations in the magnetic ?ux of the entire ring in said air gap anda coil winding disposed
system. These variations in the ?ux of the in said annular space at a point spaced longi 35
' magnetic circuit' will thus cause an E. M. F. to
be induced in the winding 23% and by connecting
the winding to any suitable indicating or re
cording device indications of the earth vibrations
may thus be obtained.
The currents induced in the metal ring 28 be
cause of relative movement between the ring and
tudinally from said air gap and adapted to have
an El M. F. induced therein, said E. M. F. being
produced by the variations in magnetic ?ux
caused by relative movement between said ring
and said magnet.
4. In a device for translating mechanical vi
brations into electrical energy, a member respon
sive to vibrations, said member comprising a
45 mal ?ux oi the magnetic circuit, which will thus magnet having an annular outer pole'and a pole
serve as a very emcient damping means. The disposed coaxially within said outer pole, an an 45
damping action produced on the ring 28 will be - nular space being formed between said poles, an
as e?’ective as could beobtained ii a short-cir
inertia member comprising a metallic ring 01
cuited winding of the same size and material non-magnetic material, means for
ently sus
,
to. were used in place of the solid ring.'
pending said ring in said annular space between
It will be observed that the annular space it the adjacent ends of said poles, said ring being to
is more than ample to house‘ the winding 38 and of a size to ?ll substantially all of said annular
since therefore the number of turns on this coil space, and a coil winding disposed in a portion
is practically unlimited, an extremely high sen
of the annular space between said poles and
55 sitivity. can be obtained. Since the only moving spaced longitudinally from said inertia member.
part of the device is the solid ring 2% it will be . the arrangement being such that an E. M. F. will 55
seen that a very rugged and inexpensive con
be induced in said coil by variations in ?ux
struction will result.
caused by relative movement between said
g
, While a permanent
gnet has been described net and said ring.
" so and shown, it is to be understood that an elec
5. In a vibration detector, a mber respon-=
tro~magnet may be used, the energizing wind= sive to vibrations, said member comprising a 430
ing for. such a magnet being placed in the an» magnet having an annular outer pole and a pole
the magnet will set up a ?ux opposing the nor
nular space l6.
-
obviously many modi?cations and variations
65 of the invention. as herelnbefore set forth, may
be made without departing from the spirit and
scope thereof, and therefore only such limita
. disposed coaxially within said outer pole, an an
nular space being formed between the poles of
said magnet, an inertia member comprising a
metal ring, means for resiliently suspending said
ring in said annular space between the adjacent
ends of said poles, said ring being of a size to
?ll substantially all of said
:1. -.
space, and
a coil winding; also disposed in said annular
1. ‘In a vibration detector, a member respon
space but separated longitudinally from said
sive to vibrations, said member comprising a inertia member and responsive to variations in
magnet having a pair of'poles substantially co
the ?ux produced by relative movement between
extensive and dispmed in parallel, the adjacent said magnet and said ring, the arrangement be
ends of said pole pieces forming an air‘ gap, an _ ing such that currents induced in said ring by 75'
3
2,130,213
relative movement between said magnet and said
ring will produce a ?ux opposing the normal
?ux oi’ the magnetic circuit, thus serving to
dampen the movement of said ring with respect
6. In a vibration detector, a member respon
sive to vibrations, said member comprising a
magnet having a pair of poles disposed concen
said ring being of a sizelsuch as to ?ll substan
tially all of the space in said air gap, and a coil
winding surrounding one of said poles at a point
spaced from said air gap longitudinally along
the axis of said pole, said winding being adapted
to have induced therein an E. M. F. produced
by variations in ?ux caused by relative move
ment between said inertia ring and the poles of
trically in parallel, said poles being substantially‘
said magnet.
to said magnet.
10 coextensive and the adjacent ends of said poles .
forming an air gap, an inertia member'comprls
ing a non-magnetic metal ring, means for re
siliently suspending said ring in said air gap.
»
ALEXANDER WOLF.
LAURENCE G. COWLES.
WILLIAM S. RICHARDSON.
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