US2062784A - Seismograph - Google Patents

Description

Patented Dec. 1, 1936 UNITED STATES PATENT OFFICE 9 Claims.

My invention relates to seismographs and more particularly to a device of this character embodying a coil and means associated therewith for generating an electrical current in the coil in response to vibrations or movements of the instrument.

In seismographs of the character now commonly used the armature carrying the coil is mounted on the case or support for movement therewith, and a relatively heavy magnet is yieldingly supported by the case so that upon movement of the case the magnet will tend to remain stationary, and electrical currents, having an amplitude directly proportional to the vibratory impulses transmitted to the instrument, will be generated in the coil. p

. In order that instruments of this type be responsive to vibrations or similar movements, it is necessary to employ heavy or weighted magnets and strong springs which impair the sensitiveness of the instrument and require comparatively large cases.

The principal object of my invention is, therefore, to provide a seismograph wherein the entire working mechanism constitutes the yieldingly suspended mass thus making it possible to not only decrease the relative size of the instrument, but also to increase its sensitiveness.

A further object of the invention is to embody means in an instrument of this type for adjusting the width of the air gap thereby permitting a widervariation in the stillness of the suspension springs used. As a result of the variable airgap it is also possible to adjust the instrument more easily for use in recording seismic disturbances near other sources of vibrations.

In accomplishing these and other objects of my invention I have provided improved details of structure, the preferred form of which is shown in theaccompanying drawing, wherein:

Fig. 1 is aperspective view of a seismograph embodying my invention and mounted on a support shown fragmentarily. Fig. 2 is a central vertical section of the instru- 45 ment showing particularly the mounting of the coil, armature and magnets.

Fig. 3 is a side elevational view illustrating the armature in contact with the supporting arm.

Fig. 4 is a diagrammatic view illustrating action of the armature responsive to vibrations.

Referring more in detailto the drawing:

l indicates a support which may comprise either a bar as shown, or a suitable case for hous- 55 ing a seismograph generally designated 2, and

includes a bracket 3 anchored in any convenient manner to the support as by bolts 4.

Secured to the upper and lower ends of the bracket by screws 5, or the like, are forwardly projecting spring blades 6 and 1 respectively, for yieldingly supporting therebetween a mass 8 comprising the electrical mechanism of the seismograph and including a U-shaped bar 9, having lateral-arms Ill.

Spacing plates H are inserted between the spring blades and the corresponding arms of the bar to permit free flexing oi the blades, and backing plates l2 are mounted over the outer ends of the blades;.screws l3 being extended through aligned openings in the backing plates, blades and spacing plates and threaded into openings M of the arms for securely connecting the several parts in operable relation.

A spacing bracket I5, having a lateral extens'ion I6, is secured to the lower arm in alignment with its outer end by a screw I1; and rastened to the lateral projection by screws l8 or the like is a permanent preferably U-shaped magnet l9 having the usual poles 20 directed upwardly and spaced from the corresponding poles of a cooperating magnet 2| arranged in opposed aligned relation to the magnet IS. The magnet 2| is mounted by means such as screws 22 to the lower face of the upper arm l0, and a plurality of shims 23 are inserted between the magnets and their mountings so that the space 24, reserved between the poles of the respective magnets, may be adjusted by removing or replacing shims to vary the width of the air gap formed by the spacing.

In order to support a coil 25 within the openings of the magnets, cross bars 26 are preferably provided having lateral flanges 21 secured in recessed portions 28 of the magnet poles by screws 29. The cross bar of the lower magnet further serves to pivotally support an armature 30 mounted thereon by a flexible spring blade 3| secured centrally both to the cross bar and to the armature by welding or the like. An outer end 32 of the armature projects from the instrument and is adapted to contact a boss 33 provided on a bracket arm 34 secured by means .of a foot portion 35 and screws 36 to the support. The armature is normally retained in contacting engagement with the bracket arm by a spring 31 having its upper end anchored to a hook portion 38 of .the armature and its lower end connected to a bolt 38 adjustably secured to the ear 39 of an anchoring plate 40, by means of adjusting nuts 4!, the anchoring plate being secured in any convenient manner to the instrument as by screws 42 threaded into openings 63 of the lower arm iii.

Wires E 4 and 65 leading fromi the coil may be connected to any suitable mechanism for recording the movements of the seismograph on film or paper by mechanical or electrical amplification.

Assuming a device to be constructed and assembled as described, its operation is as follows: The bracket 3 is attached to the support I and the support is mounted on a body, such as the earth, in which displacements or vibrations are imparted. Vibrations traveling through the 'earth are transmitted to the support 5 and through the bracket 3 to the arm 34. The tenthe support due to inertia andits resilient mounting by reason of the springs 6 and 1.; Since the armature 30 is attached to the mass through the flexible fulcrum 3|, the fulcrum point of the armature will also tend to remain stationary in parallel relation with the bars 26 and in the center of the space'or gap between the pole pieces of the respective magnets. However, since one end of the armature is held in contact with the boss 33 by 'means of the spring 31, the vibra- H tions imparted to the arm 34 will cause oscillatory or pivotal movement of the armature on its flexible fulcrum 3!, as shown in Fig. 4. For example, assuming that'the arm 34 moves upwardly, the armature will tilt in an anticlockwise direction so that one end moves toward the pole piece on the left-hand side of the lower magnet and its opposite end toward the pole piece on the right-hand side of the upper magnet (Fig. 2). The fulcrum 3|, being flexible, is thus capable of bending to allow rocking movement of the armature above described. This movement of the armature causes change of magnetic flux and sets up a current impulse in the coil. During movement of the armature, as above described,

. the spring 31 flexes to hold the armature against the boss 33 and prevents actual contact of the armature with the pole pieces. When the vibration is reversed and the'arm 34 moves downwardly, the spring 31 will contract to cause the armature to follow the arm and rock or oscillate 'in'the opposite direction so'that the ends thereof move toward the. other pole pieces of the respective magnets which causes another current impulse to be generated in the coil in an opposite direction. It is,,therefore, obvious that the armature will pivot or oscillate about the fulcrum in exact conformity tothe vibrations imparted to the arm 34 setting up'current fluctuations in the coil in conformity with the intensity and frequency of the vibrations. By suitable amplification means, galvanometers, and photographic apparatus, the fluctuations of the current may be amplified and recorded in a manner well known to those skilled in the art.

From the foregoing, it is apparent that I have provided a compact seismograph of simple construction, adapted to be enclosed in a relatively small case and which, due to employing the electrical mechanism as the mass or weight, is extremely sensitive.

What I claim and desire to secure by Letters Patent is:

1. A seismograph including a support vibratory in response to seismic waves, a pair of magnets having pole pieces for establishing a magnetic field, a frame member mounting the magnets with like pole pieces spaced from each other to form an air gap therebetween, bars connecting the poles of the magnets, a current conducting coil supported on the bars in the magnetic field of the magnets, an armature, a spring blade pivotally securing the armature on one of said bars, a pair of spaced resilient blades secured to the support and to the frame member for yieldingly suspending the mass including said frame mem-- ber, magnets and coil from the vibratory support whereby inertia of the mass retains the mass in immobility during vibratory movement of the support, a bracket arm on the support for engaging the armature, and a coil spring on the frame member yieldingly connected with the armature for holding the armature in contact with in said air gap and responsive to vibratory movement of the support to generate a current in said coil which is a function of said seismic waves.

2. In a device of the character described, a support, a pair of spaced resilient blades secured to the support, a frame member fixed to outer ends 'of the blades,-a pair of magnets having pole pieces for establishing a magnetic field, means mounting the magnets in the frame member with like pole'pieces spaced from each other to form an air gap therebetween, bars connecting the pole pieces of each magnet, a current conducting coil supported on the bars in the magnetic field of the magnets, an arm extending from said support, an armature, means for pivotally mounting the armature centrally on one of said bars and in contact with said arm, and yielding means connected with the armature for retaining the armature in contact with said arm so that the armature is pivoted in said air gap responsive to vibratory movement of said arm and inertia of said magnets to generate a current in said coil.

3. In a device of the character described, a support, a pair of magnets having poles for establishing a magnetic field, means mounting the magnets on the support with their poles in spaced aligning relation to form an air gap therebetween, an armature, means for pivotally supporting the armature centrally within said air gap, ,means for adjusting the magnets on said mounting to vary thewidth of the air gap.

the bracket arm so that the armature is pivoted a current conducting coil, means for supporting said coil in encircling relation with the armature and in the field. of the magnets, and means on the support engaging the armature for eflecting pivotal movement of the armature in response to vibratory movement of said support and inertia of said magnets to generate a current in said coil.

4. In a seismograph including a support vibratory in response to seismic waves, a pair of opposed U-'-shaped magnets for establishing a I magnetic field, a current conducting coil, cross bars connecting the poles of each magnet for supporting the coil in the field of the magnet, a pair of leaf springsyieldingly mounting the magnets and coil for vibratory movement on the support whereby inertia of the mass included in the magnets and coil retains the mass in immobility during vibration of the support, an

. i at tory in response to seismic waves, a pair of op-' posed U-shaped magnets for establishing a mag-' netic field, a current conducting coil, cross bars oi-connecting the poles of each magnet for supporting said'coil in the magnetic field oi the magnets, a pair of leaf springs yieldingly mounting the magnets and coil for vibratory move- 'ment relatively to the support whereby inertia of the mass including the magnets and 0011' retains the mass in immobility during vibration or the support, an armature, a spring blade fixed to-the "crossbar one magnet and to the armature for pivotally supporting the armature within the coil and magnetic field of the magnets, a bracket arm on the support having one end engaging the armature for eflecting pivotal movement of the armature in 'response'to vibratory movement of the support to generate a current in said coil which is a function of the seismic waves, and a coil spring for pivotally retaining the armature in engagement with said arm.

6. A seismograph including a support vibratory in response to'seismic waves, a pair of opposed U-shaped magnets having pole pieces establishing a magnetic field, a carrier for mounting the magnets with like 'pole pieces spaced from each other to form an air gap therebetween, a bar connected to the poles of one of the magnets, an armature, a spring blade secured to said bar and to said armature for pivotally mounting the armature on said bar intern mediate said poles of the magnets. a coil encircling said armature and supported by the magnets, springs for yieldingly mounting said carrier on the vibratory support whereby inertia of the massincluding said carrier; magnets, coil and bar retains said mass in immobility during vibratory 'movement or the support; a bracket arm on the support engaging the outer end of the armature to eflect pivotal movement oi the armature in response to vibratory movement oi the support for generating a current in said coil which is afunction of said seismic waves, and a coil spring mounted on the carrier and connected with the outer end of the armature for retaining the arcross bar for connecting the poles oi-the magnet mature in pivotal engagement with the bracket '1. A seismograph including a support, a frame, a magnet mounted in the frame for establishing a ma netic field, a current conducting coil, 1:,

supported by the carrier in the field of said I the mass including said magnet and coil retains the mass in immobility during vibratory movement of the support, a bracket arni connecting the armature with the support'for effecting pivotal movement oi! the armature in response to vibratory movement of the support to effect change or the magnetic field sothat a current is generatedin'said coil whichisganiunction 0! said seismic waves, and a coil spring mounted on the frame and having one end engaging the outer end of the armature for retaining the armature in pivotal engagement with the bracket arm.

8. A seismograph including a support vibratory in response to seismic waves, a pair of magnets having poles for establishing a magnetic field. a carrier for the magnets to retain the magnets in spaced aligning relation to form an air gap between the poles thereof, an armature, a spring blade centrally secured to one of the magnets and to the armature for pivotally supporting the armature within said air gap, a current conducting coil encircling the armature and carried by said magnets, a pair of resilient blades having respective ends fixed to the support and to said whereby inertia of the mass carried by said resilient blades retains the mass in immobility during vibratory movement of the support. a bracket arm mounted on the'support and engaging the armature for effecting pivotal movement of the armature simultaneously with vibratory movement of the support to generate a current in said coil which is a function of said seismic waves, and a coilspring mounted on the carrier and con-.- nected with the armature'to retain the armature in pivotal engagement with the bracket arm.

- 9. A seismograph including a support responsive to vibrations, a pair of magnets having pole pieces for establishing a magnetic field,-a carrier for themagnets to retain the magnets in spaced aligning relation to form an air gap between the.

poles thereof, a coil encircling the air gangland agnets, resilient means suspending said carrier from the support whereby inertia of the mass including said magnets and carrier causes it to remain immobile during vibratory movement of the support an armature. means pivotally mounting the armature midway betweewthe poles of the magnets, and means operably connecting an'end of the armature with the vibratory support, whereby vibrations in the support produce rocking movement of the armature on its pivotal mounting.

f WILLIAM G. dam.

' carrier for mounting the carrier onthe support

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