Electric meter including pivoted mag- net rotor surrounded by continuous pole faces
US 3275936 A
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3,2 75,936 UNDED BY P 27, 1966 w. D HUSTON ELECTRIC METER INCLUDING PIVOTED MAGNET ROTOR SURRO CQNTINUOUS POLE FACES Flled May 4, 1962 INVENTOR. WILLIAM D. HUSTON Patented Sept. 27, 1966 3,275,936 ELECTRIC METER INCLUDING PIVOTED MAG- NET ROTOR SURROUNDED BY CONTINUOUS POLE FACES William D. Huston, Rochester, N.Y., assignor to American Radiator & Standard Sanitary Corporation, New York, N.Y., a corporation of Delaware Filed May 4, 1962, Ser. No. 192,452 3 Claims. '(Cl. 324146) The present invention relates to voltmeters, and has to do primarily with a voltmeter of the general type having a coil mounted on a fixed armature, and a rotor including a permanent magnet.
Voltmeters of this type are inexpensive and rugged. Heretofore, however, they have been subject to relatively severe limitations with regard to their accuracy and sensitivity, because of the inherent tendency of the permanent magnet to align itself with the armature due to its own magnetic field. Because of this effect, it has heretofore been thought necessary in voltmeters of this general type to provide a relatively large spacing between the rotor permanent magnet and the pole faces of the armature, thus leaving a relatively large gap in the magnetic circuit of the armature. This construction makes for relatively high reluctance in the armature circuit; and previous meters of this type, therefore, have been characterized by a lack of sensitivity.
Accordingly, one important object of the present invention is to improve the sensitivity of voltmeters of this type without sacrifice of accuracy, reliability and other desirable characteristics.
Another object is to provide a voltmeter of the stated type in which the pivoted permanent magnet may be closely spaced from the pole faces of the armature without developing an angular bias on the magnet due to its own magnetic field.
Another object is to provide a voltmeter of the stated type which may be easily and quickly calibrated, thereby facilitating production.
A general object of the invention is to provide a voltmeter of the stated type which is relatively inexpensive to manufacture, compact, requires a minimum number of parts, yet is rugged and of long-lasting construction, and is well suited for mass production by relatively unskilled personnellar aperture in the armature, within which the permanent magnet rotor is pivoted for rotation in response to magnetic flux developed in the armature by current passing through the coil. By making the gap in the form of a circular aperture centered on the pivot axis of the rotor, the rotor is made insensitive to the relative orientation of the armature, and no torque is produced on the rotor due to the interaction of the magnetic field of the rotor magnet and the armature. The spacing between the poles of the pivoted permanent magnet and the armature is the same for all angular positions of the armature.
In the illustrated embodiment, a biasing, or restoring magnet is fixed relative to the armature adjacent to the rotor for urging the rotor toward a selected zero indicating position.
The meter movement forms a sub-assembly, which may be quickly and easily calibrated prior to mounting in the meter case, by simply bending one leg of the armature toward or away from the opposite leg. This action adjusts the reluctance of the magnetic circuit, and thereby adjusts the sensitivity of the movement by varying the magnitude of the flux produced in the armature in response to a given applied voltage.
Referring now to the drawing by numerals of reference, the voltmeter shown includes a cup-like case 10, preferably made of a magnetic material such as sheet steel so that it will shield the meter movement from external magnetic fields. The open end of the case 10 is coveredby a crystal 12, which is held in place by a conventional bezel 14 and a spacer ring .16. A graduated dial 18 is held in position near the open end of the easing .10 between the spacer ring 16 and inwardly extending bosses 20, which are struck from the sidewall of the case 10 at spaced points therearound.
The meter movement 22 is mounted within the case 10 mostly behind the dial 18, and includes a pointer 24, which extends through an aperture 26 in the dial 18,
' land which is arranged to swing across the dial to indicate the value of the voltage being measured. The movement 22 is secured by a grommet 32 to an insulating plate 28, which extends across the back wall of the case 10 and is angularly fixed relative thereto by engage- The foregoing and other objects and advantages of the j invention will become apparent from the following detailed description of a representative embodiment thereof, taken in conjunction with the drawing, wherein:
FIG. 1 is a front elevational view of a voltmeter made according to the presently preferred embodiment of the invention;
FIG. 2 is a plan view of this voltmeter;
FIG. 3 is a front elevational view, on an enlarged scale but with parts broken away, of this voltmeter, showing the arrangement of the internal parts thereof; and
FIG. 4 is a cross-sectional view of this voltmeter.
The voltmeter of the present invention, like previous voltmeters of the type having pivoted permanent magnet rotors, is of rugged construction, especially adapted for use on motor vehicles where relatively severe vibration and shock may be encountered. The voltmeter of the invention, however, has improved accuracy and sensitivity. It includes a magnetic armature, which mounts an energizing coil to which the voltage to be measured is applied. The magnetic gap is preferably formed by a circument with diametrically opposed bosses 30 struck inwardly from the side wall of the case 10.
The movement 22 includes an armature or core 34 made of .a paramagnetic material such as a silicon steel alloy having relatively low reluctance and low coercive force. The armature or core 34 is in the form of a relatively thin ribbon bent in a U-shape, and is secured to the insulator plate 28 by the grommet 32, which extends through both legs 38 and 40 of the armature, and which is of a non-magnetic material such as bras-s. A spacer bushing 36 is fitted around the grommet 32 between the front leg 38 of the armature and the insulating plate 28 to maintain the desired spacing between the two legs 38 and 40 of the armature. The bushing 36 is also of a non-magnetic material such as brass. The back leg 40 of the armature or core passe-s behind the insulating plate 28 and rests against an inwardly-protruding central boss on the back wall of the case 10. The energizing coil 42 is mounted on the front leg 38 of the armature or core, and is retained thereon between the grommet 32 and a pair of laterally extending shoulders 44 on the armature.
There is a circular aperture 50 in the front leg 38 of the armature or core 34 near the bight portion thereof,
constituting a gap in the low reluctance flux path of the armature or core. A rotor 46 is pivoted within the aperture 50 for rotation in response to a magnetic flux developed in the armature or core. The rotor 46 is pivoted on a stem 48 staked to the rear leg 40 of the armature or core in axial alignment with the aperture 50. The stem 48 includes a flange 52 for engagement by a nonmagnetic retainer cup 54, which fits within the aperture 50 in the front leg of the armature-or core, and which serves the dual purposes of maintaining the stem 48 in coaxial alignment with the aperture 50 and of retaining a restoring magnet 56 upon the ,stem. The restoring magnet 56 is annular in form, and is fitted around the stem 48 between the retaining cup 54 and the rear leg 40 of the armature or core. The restoring magnet 56 is magnetized in a direction parallel to the plane of rotation of the rotor 46 and at about 45 from the direction of the length of the armature or core 34. The rotor 46 includes a hub or bushing 58, which fits upon the stem 48 and is freely rotatable thereon, and a permanent magnet 60 of generally oval shape, which is staked, or otherwise fixed on the hub or bushing 58 along with the pointer 24. The rotor magnet 60 is magnetized in a direction parallel to its plane of rotation and approximately normal to the length of the pointer 24.
The movement 22, including the insulating plate 28 constitutes a sub-assembly, and is secured in the case by a pair of studs 62 and 64, which extend through the insulating plate 28 and through the back wall of the case 10. The studs 62 and 64 are electrically insulated from the case by appropriate insulating bushings and washers (not separately designated). The coil 42 is connected to the studs 62 and 64 by terminal rings 66 and 68, which are positioned between the heads of the studs 62 and 64 and the insulating plate 28. A resistor 70 is connected in series with the coil 42 between the ring 66 and the coil for limiting the current in the coil 42. The value of the resistor 70 is selected in accordance with well known principles in view of the magnitude of the voltage it is desired to measure with the voltmeter.
In operation, the restoring, or biasing magnet 56 urges the rotor 46 and the pointer 24 toward zero indicating position by reason of the magnetic attraction between the restoring magnet 56 and the rotor magnet 60'. The rotor magnet 60 tends to align itself with the restoring magnet. When current passes through the coil 42 in response to a voltage applied between the studs 62 and 64, a magnetic flux is established in the armature or core 34, and rotates the rotor 46 in proportion to the magnitude of the current. This flux tends to urge the rotor 46 in a clockwise direction as viewed in FIGS. 1 and 3. The manner in which the flux operates to rotate magnet 69 is not fully understood; but it is surmised that the narrow areas at opposite sides of the aperture 50 in a direction transverse of the armature or core tend to constrict the electrically induced flux, thus producing a saturated condition. The flux is, therefore, directed through rotor 60 as the easiest path. The restoring magnet 56 is oriented, and the direction of current flow in the coil 42 is chosen so that the rotor '46 is driven across the 135 angle between the restoring magnet 56 and the armature or core 34 rather than the complementary 45 angle. Full scale deflection may include an angle of 90, or more, without encountering severe variations from a linear response relative to the current passing through, and of the voltage applied across the coil 42. When the voltage is removed, the magnetic flux in the armature or core 34 ceases, and the restoring magnet 56 draws the rotor 46 back to its zero indicating position.
With the magnet 60 positioned in the center of the circular aperture 50, the magnet is not influenced by the soft iron armature or core 34 in any direction until coil .42 is energized. The soft iron armature or core insures that the magnetic flux will be concentrated in one direction, to rotate the magnet 60. The magnet 60 can be of a length approximately equal to the diameter of the aperture 50; only mechanical clearance is required between the aperture and the rotor magnet 60. The armature or core 34 extends completely around the rotor magnet 60, and the aperture 50 is circular so that the forces produced between the permanent magnet 60 and the armature or core 34 by the permanent magnet 60 are independent of the angular position of the magnet 60 and do not include an angular component for any position of the rotor 46.
The magnet 56 serves not only as a return magnet but also to retain the rotor 46 on the stem 48. No other retaining device is included. The dial 18, however, extends over the rotor 46 and serves as an abutment stop to keep the rotor 46 from escaping from the stem 48 in the event of exceptionally severe shocks.
A mounting clamp, or strap 72 is carried by the studs 62 and 64 for easy mounting of the meter on the instrument panel of a vehicle, or the like. The clamp 72 is insulated from the studs 62 and 64 by appropriate insulating bushings and washers (not separately designated). When the meter is to be used in a vehicle wherein one of the battery terminals is grounded, a shorting cup 74 is provided on one of the studs 62 and 64 for grounding the corresponding terminal of the meter to the mounting bracket 72.
In manufacture, preliminarily to mounting the movement 22 in the case 10, the movement 22 is calibrated by applying a voltage of known magnitude to it, and then bending the upper, free end of the rear leg 40 of the armature toward or away from the front leg 36 until the proper deflection of the pointer 24 is noted. Bending the rear leg 40 toward the front leg 38 reduces the overall reluctance of the magnetic circuit of the armature 34, thereby increasing the flux produced in response to a given voltage,-and increasing the meter reading. Bending the rear leg 40 away from the front leg 36 increases the reluctance, reduces the flux, and reduces the reading.
While the invention has been described in connection with a specific embodiment thereof, it will be understood that it is capable of further modification, and this application is intended to cover any variations, uses, or adaptations of the invention following, in general, the principles of the invention and including such departures from the present disclosure as come within known or customary practice in the art to which the invention pertains and as may be applied to the essential features hereinbefore set forth, and as fall within the scope of the invention or the limits of the appended claims.
Having thus described my invention, what I claim is:
1. An electrical meter comprising (a) a generally U-shaped core comprising a single sheet of thin, soft magnetic material,
(b) an electric coil mounted on one leg of said core for producing magnetic flux therein upon energization of said coil,
(c) said core having a circular aperture in one leg with a continuous circular wall, said aperture extending across the major part of the width of the core whereby two magnetically saturable portions of the core are disposed at either side of the aperture,
(d) a permanent magnet, means pivoting said permanent magnet in said aperture, said magnet being polarized in the plane of said aperture, and
(e) means for biasing said magnet toward -a preselected angular position relative to said core, and means for adjusting the reluctance of said core for calibrating said meter. 2. An electrical meter as claimed in claim 1, wherein, for the purpose of calibrating said meter, one leg of said core is bendable toward and away from the opposite leg thereof. 3. An electrical meter as claimed in claim 1, wherein said biasing means is an annular magnet coaxial with 5 said pivoting means, and said permanent magnet is ro- 2,411,997 tatable about the axis of said pivot. 2,498,726 2,867,768 References Cited by the Examiner 2 3 9 520 UNITED STATES PATENTS 5 1,985,082 12/1934 Fans 324-151 2,040,060 5/1936 Middleton 324140 Kelly 324-146 Towner 324-146 X Fribance 324-446 Chapman 324146 WALTER L. CARLSON, Primary Examiner.
R. V. ROLINEC, Assistant Examiner.