US2833989A - Long scale electrical instruments - Google Patents

Description

May 6, 1958 A. L. NYLANDER [LONG SCALE ELECTRICAL INSTRUMENTS 2 Sheets- Sheet 1 Filed May 26. 1953 Fig.

Fig.3.

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Inventor: ATnold L. Nylander;

His Attor ney.

y 1953 A. L; NYLANDER 2,833,989

LONG SCALE ELECTRICAL INSTRUMENTS Filed May 26. 1953 2 Sheets-Sheet 2 Inventor: Arnold L. Nylahder, y WMMGT -His Attorney.

LONG SCALE ELECTRICAL INSTRUMENTS" Arnold-L. Nylauder, Swampscott, Mass, assignor to General 'El e'ctric Company, a corporation oiNew York Application May 26,1953, Serial-N0.--357,6 15

4 Claims. (Cl. 324'-'150) My invention relates to improvements in long-scale atent electrical instruments, and its' chief object is'toprovide instruments having greater sensitivity and much lower manufacturing cost than those previously" available. Other objects and advantages will appear asthe' description proceeds;

Brieflystated, in accordance with one aspect ofmy invention; I provide improved instruments-having permanent magnets whioh'are magnetized in'a single"strai ght line direction. This makes practical the-use 'of oriented perm'anent'magnet materials having a preferreddirectionof magnetization, which, when magnetized inth' eir preferred direction; possess exceptionally high" values of coercive force and residual magnetism. Consequently, highvalues at magnetic flux'density are obt ained'atlow cost, and these high'flux' densities give gre-ater'sensitivity" and improve other characteristics of the instruments. Furthermore, magnetizing the magnets and adjustiug'thei r strength for calibration purposes arefacil-itatedby"straight line magnetization; which reduces manufacturing'costs. An even'greater' cost reduction results from the'fact that my improved instruments do not require permanent rrra'gnets having complex shapes or'precise dimensions; which would necessitate costly 'grindingioperations, since "the common high-strength permanent magnet materials gen'-" erally cannot be machined by standard metal-working tools. Instead, my improved 'instruments'cornprise pole piecesand a yoke which are preferably precisionmoulded of powdered iron, whereby precise shapes anddimensions" are obtained at low cost. My invention" has reducedithe manufacturing cost of the. magnet and polepiecestruo ture of one type instrument .to'one-third the previous cost; and. at the same time hasimpr-oved the sensitivity andother characteristics of the instrument.

My invention will be better understood from the fol lowing description. taken in connection with'th'e accompanying drawings, and its 'scope -will be pointed out in the appended claims. To. improve the clarity of the drawings ,and description, certain conventional parts, such as the instrument case, calibrated scale, and electricalterminals, have been omitted, since it is believed that those skilled in the art willhave no difficulty in supp-lying such parts. In the drawings,

Fig. 1 is a plan view of an electrical instrument mechanism embodying principles of my invention,

Fig. 2 is a section taken general-1y along the line 2--2 of Fig. 1,

Fig. .3 is-a plan View of another electrical instrument mechanism embodying principles of my invention,

Fig. 4 is an end view of the mechanism shown in Fig. 3,

Fig. 5 is a plan view of still another electrical instrument mechanism embodying principles of my invention,

Fig. 6 is a section taken generally along the line 66 of Fig. 5,

Fig. 7 is a plan view of still another electrical instrument mechanism embodying principles of my invention,

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Fig. 8 is a section taken generally along the line 8--8 of Fig.7.

Referring now to Figs. 1 and 2 of the drawings, the instrument mechanism comprises a substantially annular inner pole piece 1 and an outer pole piece 2 having a C- shaped inner pole face which is substantially concentric with the inner polejpiece. A' conventional moving coil 3is mounted so that 'a 'portion" of'the coil is movable along the circular air gap between the inner and outer pole 'pie'ces,'as is usual in long-scale electrical instruments. Coil 3 is attached toa rotatable shaft 4 pivoted in conventional jewels Sand 6; The'jewels' may be supported by 'a bracket 7 extending inwardly from annular pole piece 1. Electricalconnections'tocoil' 3 are'made through conventional lea-'d inspirals Sand 9. A pointer 10'wl1ich'co'op'erates with" a calibrated scale', notshown, moveswith coil 3 and'shaft 4 to display 't-he-v-alne'of current flowing through the'coil. Bias torquetending to return the pointer to its zero current position maybe supplied by the lead inspirals 8 and "9 in the'conventional manner.

A substantially annular yoke- 11 extends"circumferential-ly around the outer pole-piece- 2,"but.not"in"direct contact therewith. Yoke 11 has an inwardly extending tongue portion 12, to which "the" inner pole' piec'e-l is directly connected by suitable means such as" screw" 13'. The pole piece 1 may have a smallradialslot,f'asshowh in. Fig. 1, to facilitate insertion of the. coil" 3 durin-gas portions'of' pole piece *1 on opposites-ides 'ofthisra' 'dial" slot. 7

Permanentmagnets 14 and 15' are'bonn'ected b'e'twe'e'n magnets preferably has'substantially the-shaped a teetangular"parallelepiped; Preferably, the't'wo magnetsare located on diametrically opposite sides of"polepiece"2,

as shown, andare respectively magnetized" iu"oppositef strai'gh'tfline directions. In the clrawiiigs, the'lettersN' and S"respec'tively' represent 'north and? south'poles of the magnets. The magnets 14 and '15 "provide "magnetic whicha portion of coil 3 moves,"throu'g"h pole piece 1 can bemade of any suitable ferromagnetic materiaL such' assoftirn or anne'ale'd'steel, they" arepreferably'made of precision moulded powderediron. When" sofmade,

these parts can be shaped and dimensioned very precisely,"

thus providing a high quality instrument, with very low manufacturing cost. The pennanent'magnets" 14 and 15 -are"preferably made of oriented" permanent ma net mater'ial having extremely high coercive force and residual" magnetism. For example, permanent ma 'rretaubys of the i'oriented Alnicotype may be usedi Because "oftheir rectangular shape, and the fact thatlittleifany grinding is required, 'these permanent ma'gnetscanbe -madeait rue; ti've1y"'low"co'st.' The'out'er polepiece 2 andthe yoke 11 may 'be placed in a suitable] jig, to hold thempreci'sely' in '.th"desired'relative position] i nets may then be bonded betweerirthe"outf'pole piece and the yoke to form a permanent unitary structure. This structure is then removed from the jig, and the other parts of the instrument are assembled.

Figs. 3 and 4 show a modified form of the instrument mechanism. The instrument shown in Figs. 3 and 4 is similar to that shown in Figs. 1 and 2, except that the yoke and the permanent magnets are somewhat differently shaped. The yoke 16 is substantially Cshaped, as shown, with the tongue portion '17 extending inwardly from its the permanent thaga) center. The permanent magnets 18 and 19 are shaped substantially like truncated wedges, as shown. This wedge-like shape of the magnet permits intimate magnetic joints while still maintaining pole piece 2 in a central position, even though the thickness of individual magnets may vary considerably. This construction increases the coil flux and maintains a uniform circular air gap with resulting advantages in instrument sensitivity and scale markings.

Figs. 5 and 6 show still another form of instrument which may be used where small radial dimensions are required. The annular inner pole piece is substantially the same as the inner pole pieces shown in the preceding figures. The outer pole piece 21 is substantially C-shaped, as shown. The yoke comprises an annular portion 22 and a tongue portion 23. The annular portion 22 is coaxial with, and spaced axially apart from, the pole piece 21. The tongue 23 extends parallel to the common axis of the annular portion and the pole pieces. The inner pole piece 20 is connected directly to tongue portion 23 by suitable means, such as screw 24. A C-shaped permanent magnet 25 is connected between pole piece 21 and the annular portion 22 of the yoke, as shown. C- shaped magnet 25 is magnetized in a direction parallel to its axis, so that it provides magnetic fiux through pole piece 21, across the air gap in which a portion of coil 26 moves, through pole piece 20, and back through tongue 23 and annular portion 22. of the yoke.

Figs. 7 and 8 show another form of improved instrument mechanism having a simple, inexpensive construction with external pivots. The moving coil 29 has a low resistance because of its short mean length of turmmaking this construction particularly useful in those applications (millivoltmeters) requiring low resistance. The substantially C-shaped yoke 27 and the substantially annular inner pole piece 28 may be moulded as a single unitary part. A portion of a coil 29 is movable along an air gap between the inner pole piece 28 and an outer pole piece 30 having a substantially C-shaped inner pole face. The moving coil is supported by pivots 31 and 32 which cooperate with conventional jewels, not shown, attached to the instrument frame. Conventional lead-in spirals are shown at 33 and 34. Permanent magnets 35 and 36, preferably shaped substantially like truncated Wedges, are connected between the yoke 27 and the outer pole piece 30, as shown. This provides magnetic flux from the north poles of permanent magnets 35 and 36 through the outer pole piece 30, across the air gap to inner pole piece 28, and back through yoke 27 to the south poles of the permanent magnets.

In all the embodiments described, it will be noted that the permanent magnets are substantially straight in their direction of magnetization, and that all of the permanent magnets are magnetized in a single straight-line direction, so that the magnetic lines of flux are substantially straight and parallel as they pass through the permanent magnets. As has been explained, this makes practical the use of oriented permanent magnet materials, with consequent advantages in greater sensitivity and improved instrument characteristics.

It will be understood that my invention is not limited to the specific embodiments herein illustrated and described, and that the following claims are intended to cover all changes and modifications which do not depart from the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters- Patent of the United States is;

1. In a long-scale electrical instrument of the moving coil type the combination of a substantially annular inner pole piece, an outer pole piece having a C-shaped inner pole face substantially concentric with said inner pole piece, a C-shaped yoke extending about a portion of said outer pole piece but not in direct contact therewith, said yoke having a tongue portion extending inwardly from its center, means connecting said inner pole piece direotly to said tongue portion, and a pair of permanent magnets connected between said yoke and said outer pole piece, said magnets each having substantially the shape of a truncated wedge, said pair of magnets being respectively located on diametrically opposite sides of said outer pole piece and being respectively magnetized in opposite straight-line directions to provide magnetic flux between said pole pieces, each of said magnets having pole faces of like polarity in juxtaposition to the pole face of said outer pole piece.

2. In a long-scale electrical instrument of the moving coil type the combination of a substantially annular inner pole piece, an outer pole piece having an outer pole face and a C-shapcd inner pole face substantially concentric with said inner pole piece and spaced therefrom to form an air gap, a ferromagnetic yoke member connected to said inner pole piece and having portions thereof spaced radially outwardly from portions of said outer pole piece, and a pair of wedge-shaped permanent magnets connected between said outer pole piece portions and said yoke portions, said pair of magnets being respectively located on diametrically opposite sides of said outer pole piece and being symmetrically aligned with and on diametrically opposite sides of said annular inner pole piece, said magnets being respectively magnetized in opposite straightline directions to provide magnetic flux between said pole pieces, each of said magnets having pole faces of like polarity in juxtaposition to the outer pole face of said outer pole piece portions.

3. In a long-scale electrical instrument of the moving coil type the combination of a substantially annular inner pole piece, an outer pole piece having an outer pole face and a C-shaped inner pole face substantially concentric with said inner pole piece and spaced therefrom to form an air gap, at substantially C-shaped ferromagnetic yoke member having a centrally located inwardly extending tongue portion to which said inner pole piece is connected and having portions which are spaced from portions of said outer pole piece, and a pair of wedge-shaped permanent magnets connected between said outer pole piece portions and said yoke portions, said pair of magnets being respectively located on diametrically opposite sides of said outer pole piece and being respectively magnetized in opposite straight-line directions to provide magnetic flux between said pole pieces, each of said magnets having pole faces of like polarity in juxtaposition to the outer pole face of said outer pole piece portions.

4. The combination defined by claim 3 in which said yoke is in the form of a moulded powdered iron member and said inner pole piece is formed as an integral portion vthereof.

References Cited in the file of this patent UNITED STATES PATENTS 2,586,831 Knudsen Feb. 26, 1952 FOREIGN PATENTS 787,424- France Sept. 23, 1935

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