US2633480A - Pencil galvanometer - Google Patents

Description

March 31, 1953 w. 3. STAFF 2,633,480

PENCIL GALVANOMETER Filed June 20, 1949. 2 SHEETSSHEET 1 II JJI II III/I ll Il/I/ III I I [III/III WILLIAM 3. STAFF INVENTOR.

BY QQ W AGENT March 31, 1953 w. s. STAFF PENCIL GALVANOMETER 2 SHEETS-SHEET 2 Filed June 20, 1949 FIG.30.

FIG.5

FREQUENCY anti:

FIG.

WILLIAM 3. STAFF INVENTOR.

BY a W AGENT Patented Mar. 31, 1953 UNITED STAT ()FFICE PENCIL GALvaNoMETEa of New York Application June 26, 1949, Serial No. 190,273

11 Claims. 1

This invention. relates to oscillograph galvanometers and more'particularly to. an improved pencil galvanometer of the type used in seismograph recording cameras.

Galvanometers used in seismic recording systems necessarily must be small to permit accom modation of a relatively large number in a small space for the recordation of a plurality of seismic signals on a relatively narrow film. Since the units are necessarily small physically, means for adjusting the tension of the suspension is not easily provided. The natural frequency of the suspension is dependent upon the tension as well as upon its moment of inertia. If a plurality of galvanometers in a common bank are to be matched to a selected standard, some means must be provided to adjust the natural ire uency. Once assembled, the inertia may not readily be changed and thus the tension generally is the final adjustment made. Under even the most favorable circumstances, the final adjustment is tedious and time-consuming.

The present invention is directed to the provision of a novel galvanometer embodying means for mounting a vibratory element and for ad justing the tensile force exerted thereon. Movement axially of the galvanometer to vary the tension is provided without introduction of any twisting or initial unwanted stress on the vibratory element.

More particularly, in a barrel type galvanometer with an anchoring member at oneend thereof, there is provided a vibratory element con, sisting of a galvanometer coil having a suspension fiber aiiixed at each end thereof, the vibratory element being of. length greater than the distance from the anchoring member to the other end of the barrel; A transverse pin is provided in the barrel near the end opposite the anchoring member. One end of the vibratory element is connected to the anchoring member. and with the other end threaded over the pin. Resilient means slidably mounted for longitudinal movement in the end of the barrel adjacent the pin is connected to the end of the vibratory element threaded over the pin. Means threadedly engaging the end of the galvanometer positions the resilient means to vary the tension on the vibratory element. The resilient means preferably has a yield point less than the ultimate strength of the vibratory element and greater than the maximum tension desired on the vibratory element.

For a further understanding of the present invention reference may now be had to the following description takenin conjunction with. the accompanying drawings in which:

Fig. 1 is an exploded view of the suspension sys tem;

Fig. 2 is an. elevation partly in section of the assembled galvanometer;

Fig. 3 is an enlarged View of the yoke-suspension coupling;

Fig. 3a is a modification of Fig. 3;

Fig. i is an enlarged view of the pin3 of Fig. 2; and

Fig. 5 is a frequency response curve for the galvanometer.

Referring now to Fig. 1, the elements of the galvanometer suspension. system have been illustrated as comprising a suspension fiber l0 an.- chcred, as by soldering, to the end of a pin or extension H which is fastened to or otherwise forms a part of a contact H2. The upper end of the suspension fiber id is terminated or connected in a spool l5 of ivory or similar non-conducting material. A second suspension element i6 is terminated or fastened to a similar spool H. A plurality of turns of fine wire wound on the spools I1 and i5 form the galvanometer coil is and together with the filamentary supporting means H3 and It form the vibratory element of the galvanometer. One terminal of the coil is is electrically connected to the element ill at point l9 while the other terminal is electrically connected at 2i! to the element It. A mirror 22 is fastened to and carried by the element it above the coil l8. Such a vibratory element may be assembled and tested before it is inserted for final mounting in a suitable metallic'. cylinder forming a galvanometer barrel.

When coil is is positioned in a magnetic field, flow of current therethrough causes the suspension to rotate about its axis for deflection of a beam of light suitably directed at mirror 22. The response of the galvanometer to a given signal will depend upon its inertia and the restraining forces exerted on coil 13 by the fibers it and It. The inertia is, of course, fixed by the weight and orientation of the various components. The restraining force will depend upon the material used in the fibers iii and it, the dimensions thereof and additionally upon their tension. For a galvanometer made up of given components, the tension is, of course, an independent variable by which several galvanometers may be adjusted and matched to a selected or predetermined standard.

In the embodiment illustrated in Fig. 1, a yoke 36 is utilized to anchor the upper end of the fiber IS. The yoke 30 has two depending arms 3| and 32. Arm 3i carries a resilient member or spring 33 extending downward therefrom. The free end of the spring 33 is formed in a coil or spiral as to be coupled or fastened to a loop 25 formed by the upper end of the suspension 18.

Referring to Figure 2, the galvanometer is illustrated assembled in a metallic barrel 35. The contact i2 connected to the lower end of the vibratory element is insulated from the lower end 36 of the galvanometer barrel 35 by a fiber plug 31. The vibratory element consisting of fiber l0, coil l8, and fiber i6, is preferably of length greater than the distance from the end of the contact l2 to the end 38 of the galvanometer barrel so that when the lower suspension fiber i9 is fixed to the end contact l2 and the contact inserted into the barrel 35 with the vibratory element therein, the free end of the vibratory element will extend slightly therebeyond for ready attachment to the other anchoring member as hereinafter described. A suspension supporting member or pin 39 is provided near the end 38 of the galvanometer barrel and extends trans versely thereacross. The pin or stationary support 39 is provided with an annular groove illustrated in Fig. 3a in length equal to the width of the fiber IS. The pin 39 is offset from center of the barrel so that one face of the groove in the pin is tangent to axis of the barrel 35. The pin 39 supports the vibratory element, positions the vibratory element at the axis of the barrel, and additionally guides the yoke 33 carrying the tensioning spring 33 to prevent twisting of the suspension when the tension is varied.

As viewed in Fig. 2 the fiber it initially is threaded on the left side of pin 33 slightly offset to the right of center. The arm 3| carrying spring 33 is connected to loop 25 and is then inserted into the barrel on the right hand side of the pin 39. Thus, the pin 39 acts as a support for the suspension fiber it. The combined length of the arm 3! and spring 33 in an unstressed state should be slightly greater than the distance that the vibratory element will extend beyond or inwardly of the pin 33 so that when the yoke 33 is forced a maximum distance into the galvanometer barrel to rest upon the pin 39, spring 33 will be stressed beyond its yield point and a maximum force will be exerted upon the fiber IS as determined by the yield point of the spring 33. A stud 4G threadedly engaging the upper end 38 of the galvanometer barrel may be rotated to adjust the position of yoke 30.

It will be recognized that the tensile force exerted on the fiber i6 and thus the rigidity of the whole galvanometer suspension will depend upon the dimensions and stiffness of the spring 33. As illustrated in the enlarged view of Fig. 3, the spring 33 carried by yoke 30 preferably is made of material such that its yield point is below the ultimate strength of the fiber l3 and greater than the maximum tension desired on the suspension. Thus, in assembling the galvanometer and making the initial adjustments, the yoke 30 is forced down on to pin 35 with the leg or extensions 3| in the space between the pin 39 and the wall of the galvanometer adjacent thereto at which point the spring 33 may be stressed beyond its elastic limit and take a permanent set. Thereafter, yoke 33 may be retracted to the point where the biasing force exerted by spring 33 is the desired value.

With the foregoing construction, the tension and thus the natural frequency of the galvanometer suspension may readily be adjusted by merely rotating the stud 33 in the upper end of the galvanometer barrel. Since the yoke 30 is bodily movable in the galvanometer barrel and slidably fits over the pin 39, the stud 43 may be rotated without subjecting the fiber it to any torque, i. e., the pin 39 assures that yoke 30 has a straight sliding motion toward and away from pin 39 and prevents rotation thereof. The adjustments may then be made without possibility of initially twisting the galvanometer suspension elements.

A modification of the yoke-spring arrangement of Fig. 3 is illustrated in Fig. 3a. A unitary formed spring 32 is utilized in this modification to anchor the end of the suspension element 16 threaded over the pin 33. For simplicity all portions of the galvanometer except the pin 39 and the suspension element it have been omitted. The spring 42 is formed into a single coil loop 43. One end of the spring extends downward at an angle of from the plane of coil 43. At least a portion of the length of the depending arm 34 is flattened as illustrated at 35 to reduce the stifiness of the spring. A hook it afiixed to or otherwise formed by the end of the arm 34 is coupled to the loop 23 in'the end of the suspension element it. By varying the position of the spring 32 in the end of the galvanometer barrel, the force exerted thereby on the suspension element 13 may be varied. The flattened or reduced cross-sectional portion 35 is so' dimensioned that it will take a permanent set or will yield before the suspension element it breaks. It will be observed that the spring 42 may rotate through a limited angle but in no case will the suspension element between the pin 33 and the galvanometer end terminal be subjected to any rotation. The maximum force exerted on the suspension element will then be determined by the yield point of the flattened portion 45 of the arm 33. In either of the modifications of Fig. 3 or 3a a member threadedly engaging the end of the galvanometer barrel may be varied in position to adjust the tension of the suspension.

In the final adjustment of the galvanometer, the coil H3 is mounted in a magnetic field whose direction is perpendicular to the axis of the suspension; Such a field may conveniently be provided by inserting the galvanometer between the faces of a permanent magnet structure including pole pieces 33 and 33, Fig. 2. When a signal is applied to the coil, the deflection of a beam of light 53 directed at the mirror 22 is noted. For example, alternating current from a source 51 of variable frequency may be applied to the galvanometer as by conductor 32 connected to the barrel terminal and conductor 53 connected to the contact !2. A control unit 53 including a meter or indicator may be included in the exciting circuit to adjust and maintain a constant amplitude current in the galvanometer at all frequencies. The frequency of the signal from source 5% may then be varied from a frequency below the seismic band to frequencies considerably above the seismic band.

As the signal frequency is varied from zero, Fig. 5, to the resonant frequency (j') of the galvanometer, the amplitude of deflection of a beam of light reflected from mirror 22 will increase rapidly to a maximum as the resonant frequency is approached if the galvanometer is undamped. Thereafter, the response decreases rapidly to 'a very low value at frequencies above resonance. For. a given set of galvanometers each having the same moment of inertia, the position of the stud 483 may be varied in the end of each galvanometer to change the tension exerted on suspension fiber l6 by the spring 33 until the maximum 6! Fig. 5, occurs at the selected resonant frequency (f). In actual operation, after calibration, a resistor 6! (shown dotted in Fig. 2) may be connected across the galvanometer terminal to provide the desired degree of damping so that the galvanometer will have a flat or desired response.

It will be recognized that if the tension is to be the final adjustment, each of a plurality of galvanometer suspensions must be made to have the same moment of inertia if they are to have the same response. Or" course, if sufficient care is exercised in manufacture and assembly of the suspensions, they will naturally have the same moment of inertia Without: further adjustment. However, slight adjustments well known in the art. may be made for minor variations of the moment of inertia. For example, a small drop of a glue or the like may be placed on the coil ['8 to vary its weight; alternatively, the coil It may be spread apart or altered in shape slightly. Such expedients are commonly used and may bemade before the galvanometer is inserted into the barrel. Thereafter, the resilient tension adjusting member is coupled to a loop in the end of the suspension and inserted into the end of the barrel. The position of the resilient member then determines the. tension on the suspension. which may be measured by noting the natural frequency.

In one form of the invention, the coil is comprised 20 turns of N0. 43 wire and made rigid by application of a thermo-setting glue. The

suspension element was beryllium-copper stock of dimensions approximately .0005" thick, and .005" wide. For acm. length of fiber the tension is preferably adjusted so that a torque in the order of. 1.5 dyne/cm. per radian rotation is. exerted. A high grade piano wire .006-.008 inch in diameter was used for spring 33. I

Though the invention has been illustrated in a particular modification, other modifications may now be apparent to those skilled in the art and it isintended by the; appended claims to cover all such modifications as fall within. the scope of the invention.

What is claimed is:

1. Means for mounting a galvanometer suspensionin a barrel having a transverse member-near one end thereof which comprises a suspension fiber threaded over and supported by said transverse member and anchored at the other end of said barrel, resilient means at said one end fastened to the end of said suspension fiber threaded over said support, an element having an extension carrying said resilient means and bodily movable toward said transverse member from said end of said barrel adjacent said transverse member, said extension engaging said transverse member to limit rotation of said element and means for positioning said element within said barrel for adjustment of the force exerted by said resilient means in said fiber.

2. Means for mounting a galvanometer suspension in a barrel having a supporting member in one end thereof comprising a suspension fiber anchored at one end and at the other end connected to the end of said suspension fiber, a

yokesuuatiy mounted for movement in said barrel adjacent said supporting member, said yoke having two extensions slidable relative to said supporting member to prevent rotation of. said yoke, one of said extensions carrying said spring adjacent an end thereof, and means threadedl'y engaging the end of said barrel for positioning said yoke to adjust the force exerted on said suspension by said spring.

3. Means for mounting a galvanometer suspension in a barrel having a supporting member adjacent one end thereof comprising a suspension fiber anchored at one end and at the other end threaded over said supporting member, resilient means having a yield point less than the ultimate strength of said suspension and connected to the end thereof, a yoke carrying 's'aid resilient means slidably mounted for movement inand longitu-r dinally of said barrel'with the arms of said yoke straddling said supporting member, and means for adjusting the position or said yoke infisaid barrel to stress said resilient member for application to said suspension of a predetermined force whose maximum value may not exceed said yield point.

' 4. A barrel type galvanometer provided withan anchoring member at one end thereof and comprising a vibratory element consisting of a galvanometer coil having a suspension fiber affi'xed to each end thereof and having a total length greater than the distance from the anchoring member'to the other end of the barrel, a shaft extending across and located a fixed distance from the other end of sai'd barrel, means for connecting one suspension fiber to s'aid' anchoring member, a yoke member carrying a spring coupled to the end of said-suspension fiber extending beyond saidother end of said barrel andirlsertalole from said other end into said barrel for threading said suspension fiber over said shattso thatsaid vibratory element lies along the axis of said barrel, and means fora'djustably positioning said yoke in the end of said barrel for varying th tension on said fiber threaded over the shaft.

5'. A pencil type galvanometer comprising a elon'gat'ed'barrel, a vibratory element including filamentary supporting means within said barrel, means for'anchoring a first end of said filamentary means at one end of -said barrel; a 'staticnary'supportcarried by'said barrel" adjacent the opposite end thereof with a 1 space between it and the; adjacentportion" of said barrelfthreading and; forces-applying structure coupled to't he 55 e d; 9? i fi ame tary. m n nc u i a leg portibn-of less orossgs'ectiunal' areathan that ofjsaid space for threading the filamentary means over said support and for "applying tension thereto by movement of said leg through said space and toward said first-named end of said barrel, and an adjusting member Within said barrel at said opposite end disposed in cooperative relation with said structure and movable lengthwise of said barrel for development of a desired biasing force upon said filamentary means to place it under predetermined tension.

6. A pencil type galvanometer comprising a thin elongated barrel, a vibratory element including filamentary supporting means within said barrel, means for anchoring said filamentary means at one end of said barrel, a stationary support carried by said barrel adjacent the opposite end thereof with a space between it and the adjacent portion of said barrel, threadingand forceapplying structure including a. leg portion of less cross-sectional area than that of said space for threading the filamentary means over said support and for applying tension thereto by movement of said leg through said space and toward said first-named end of said barrel, an adjusting member within said barrel at said opposite end disposed in cooperative relation with said structure and movable lengthwise of said barrel, and a spring disposed between the end of said filamentary means and said leg portion for development in response to movement of said adjusting member of a biasing force to place said filamentary means under predetermined tension.

7. A pencil type galvanometer comprising a thin elongated barrel, a vibratory element including filamentary supporting means within said barrel, means for anchoring said filamentary means at one end of said barrel, a stationary support carried by said barrel adjacent the opposite end thereof with a space between it and the adjacent portion of said barrel, threading structure connected to said filamentary supporting means and including a leg portion of less cross-sectional area than that of said space for threading the filamentary means over said support, and an adjusting member threadedly engaging said barrel at said opposite end and disposed in cooperative relation with said structure to produce longitudinal movement of said structure with said leg portion extending through said space for development of a desired biasing force upon said filamentary means upon rotation of said adjusting member with concurrent rotation of said structure limited by said leg extending through said space.

8. An adjustable anchor for one end of the vibratory suspension in a barrel type galvanometer which comprises a support within and adadjacent one end of the galvanometer barrel, a

resilient member insertable to beyond said sup- 9. In a totally enclosed galvanometer of the r barrel type having a vibratory element therein anchored at a first end to a barrel closure member, means for adjustably anchoring the other end of said element which comprises a rod extending transversely across the barrel adjacent the second end thereof, a yoke insertable from said second end and extending at least in part beyondsaid rod, a spring. mounted on theextended portion of said yoke, means for mechanically interconnecting the end of said vibratory element and said spring, and a member in said barrel for adjustment of the position of said yoke to vary the force applied to said vibratory element in dependence upon the position of said last-named member.

10. In a totally enclosed galvanometer of the barrel type having a vibratory element therein anchored at a first end to a barrel closure member, means for adjustably anchoring the other end of said element which comprises a rod extending transversely across the barrel adjacent the second end thereof, a unitary formed spring having a loop and an elongated extension tangent to said loop and normal to the plane there of, at least a portion of said extension being of reduced cross section having a yield point below the ultimate strength of said suspension, means for interconnecting the end of said vibratory ele ment and the end of said extension, and a closure member adjustably positioned in the second end of said barrel and mechanically engaging said loop for varying the tension on said vibratory element in dependence upon the position of saidunitary spring.

11. An adjustable anchor for one end of the vibratory suspension in a barrel type galvanometer which comprises a support within and adadjacent one end of the galvanometer barrel, a resilient member insertable to beyond said support from said end, means for coupling the end of said suspension to said resilient member for threading the suspension over said support; and an element adjustably positioned in the end of said barrel and on the side of said suport opposite said resilient means for movement toward said support to apply pressure on said resilient means for tensioning said suspension in depend ence upon the position of said element relative to said support.

' WILLIAM S. STAFF.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,193,979 Blondel Aug. 8, 1916 1,951,578 Peters Mar. 20, 1934 1,982,333 Thomander Nov. 27, 1934 2,149,442 Kannenstine Mar. 7, 1939 2,282,590 Miller May 12, 1942 2,291,713 Harley Aug. 4,1942

- 2,439,576 Morrow Apr. 13, 1948

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