US2430317A

US2430317A - Electrical measuring instrument

Info

Publication number: US2430317A
Authority: US
Publication date: 1947-11-04
Anticipated expiration: 1964-11-04

Description

Nov. 4, 1947. M. 5. WILSON ET AL summon. umsunme INsTnuuENT Filed Au 9, 1946 2 Sheets-Sheet l d w Y n n r o 0 M m @W A v h 00 MEW a r F Nov. 4, 1947.

M; 5. WILSON ETAL ELECTRICAL MEASURING INSTRUMENT Filed Aug, 9, 1946 2 Sheets-Sheet 2 Their Attorney Patented Nov. 4, 1947 ELECTRICAL MEASURING INSTRUMENT Myron S. Wilson, Lynn, and Francis M.

Maiden, Mala,

assignors to General Electri \Company, a corporation of New York Application August 9, 1946, Serial No. 689,422

9 Claims. (01. 171-45) Our invention reiatu ,to direct current, permanent magnet type, electrical measuring instruments, and its object is to provide a sensitive long scale measuring instrument in which the materials are efliciently used and the parts are compactly assembled, with provisions for removing the complete armature assembly as a unit without disassembly of the remaining stationary parts of the instrument. The structure is such as to assure a constant reluctance permanent magnet circuit after initial permanent assembly and polarization of such circuit without the use of a keeper.

The features of our invention which are believed to be novel and patentable will be pointed out in the claims appended hereto. For a better understanding of our invention, reference is made in the following description to the accompanying drawings in which Fig. 1 is a perspective top view of the armature assembly framework; Fig. 2 i a perspective top view of the permanent magnet and main portion of the magnetic circuit; Fig. 3 represents a small portion of the magnetic circuit structure which is fastened to and is removable with the armature assembly; Figs. 4 and 5 represent plan and sectional side views of the completedinstrument, Fig. 5 being taken on line 55 of Fig. 4, and Fig. 6 represents a modified form of integral permanent magnet field assembly which is magnetized after assembly and requires no keeper.

Referring now to the drawings, we employ a permanent magnet assembly as best shown in Fig.2 which is radially magnetized as in United States Letters Patent No. 2,272,767 to Corson. The permanent magnet material I used is of high corrosive force such as described in United States Letters Patent No. 1,947,274 or No. 1,968,569 to Ruder. Cast integral with the inner pole face of the magnet is a tubular soft iron pole shoe 2 having a circular inner periphery of approximately 250 degrees arc, defining the outer side of the circular armature air gap. The outer ring 2 and i central core I are made in one piece. These parts are preferably made of magnetic sintered iron and the magnet i is die cast within the inner and outer rings 2 and 2, and hence, these parts are permanently and intimately secured together providing a magnetic circuit of excellent efilciency. The structure is permanently magnetized after such assembly. The inner core 4 is divided into two similar nearly semi-circular parts and symmetrically joined to the outer ring 3 by divided tongue parts 5, leaving a key shaped opening between them. When the instrument is assembled, the key shaped opening is occupied by certain portions of the armature assembly to which is fastened a magnet part 6, Fig. 3, which fits into the gap at I and completes the circular inner core at this point. with the part 6 in place, a circular air gap of about 250 degrees arc length is completely defined by magnetic material and across which gap a uniform radially directed flux isforced by the permanent magnet I. We prefer to use an air gap which is circular anduniform and of a length of inch. It is to be noted that the division of the inner core into two symmetrical sections, symmetrically joined to the outer ring 2 and to the manetic plug 8, assures uniformity in the flux crossing the circular air gap. That is, the division of the magnetic circuit is symmetrical. The reason for the removable plug 8 i to permit the armature coil to be threaded over the core 4 with one side within the core and the other side in the circular air gap.

The armature assembly framework is shown in Fig.1 and comprises a die casting of nonmagnetic material comprising a top. plate 8 with upper threaded lugs 9 for mounting the scale plate lil (see Figs. 5 and 6) downwardly extended feet It with bolt openings therethrough for securing the frame to the .magnet by bolts l2, an upper bracket I3 for mounting the upper jewel screw it and upper lead-in spiral l5, and a lower bracket It for mounting the lower iewel screw l1 and lower lead-in spiral I 8. The downwardly extending lower bracket i8 is shaped and dimensioned to fit easily within the key shaped opening in the central part of the permanent magnet assembly of Fig. 2 and has a central sector shaped part is with a dovetailed key face 20 machined thereon which flts a dovetailed slot 2| in magnetic core part 8. Part 8 is mounted friction tight on part 20 and hence is removable with the armature assembly.

The armature assembly framework carries the armature coil 22, armature shaft 23, and pointer 24 as best shown in Fig. 5. The inner ends of the lead-in spirals I5 and I8 are secured to the shaft 23 and the shaft is pivoted in the upper and lower Jewel screws i4 and II. when the armatureassembly is removed but with the bolt openings therein for securing it to the magnet in alignment with the corresponding bolt openings in the magnet assembly part 2 shown at 25. Fig. 2, the shaft 23 is centrally aligned with respect to the center of the magnetic assembly, and the yoke of the lower bracket i8 is properly aligned with the portion 28 of the key shaped opening in the magnetic assembly with the sector shaped part i8 surrounding the shaft 23 and in alignment with one side of the central portion of the key shaped opening, and supporting magnetic core part 6 in place on keyway2ll and in alignment with part 1 of such opening. In inserting the armature assembly in place in the magnet assembly and likewise in withdrawing it, the armature coil 22 is first rotated directly over and surrounding plug 6 and hence in alignment with opening I.

a This is the armature position shown in Figs.

4 and 5. The coil is dimensioned relative to the opening at I so that the lower coil end can pass through such opening. Hence, as the complete armature assembly is lowered into the magnet assembly, the parts are guided by the shape of their aligned surfaces, and the lower side of coil 22 passes down through gap I followed by core part 6 which thus closes the opening as the armature assembly is lowered into proper position. We prefer to provide a slight taper to the yoke of bracket i6 and in the corresponding surface of the portion 26 of the opening in the magnetic assembly such that the bracket and opening are slightly larger at the top than at the bottom. We have used a taper of /2 degree here. The surfaces of parts 8, l9, and i6 and the corresponding surfaces of the core parts 4 and 5 where contact is made when the armature assembly is in place are finished and nicely fitted so that the armature assembly is rigidly locked in correct position, with the shaft 23 centrally aligned and with the armature coil22 free to rotate in the circular air gap provided. The outer surface of core part 6 is flush with the adjacent curved outer surfaces of parts 4 and conforms to and completes the circle thereof at this point to provide an unbroken circular inner pole piece.

The flux carrying capacity of the plug 6 is sumciently small in comparison to the remaining pole piece area that its removal does not disturb the permanent magnet strength by knockdown effect by reason of its removal. Thus the pole face area provided by plug 6 is about six per cent of the total effective pole face area of the inner core. Its presence improves the air gap flux distribution but has negligible effect on its magnitude. The air gap arc length of plug 6 is about 15 degrees. Also the air gap dimensions cannot be changed by reason of removal and insertion of the armature assembly. Hence the armature may be removed for inspection, repair, and adjustment without changing instrument calibration insofar as flux strength and air gap relations are concerned. The opening at 26 and its use for the purpose described effectively utilize what would otherwise be idle space, as it is not needed to carry magnetic flux. The resulting instrument is exceptionally rugged and compact, using a small number of parts and only a few fastening screws or bolts.

It is to be noted that the stationary support 21 for the lower spiral I8 is positioned in line with the core opening 1 so that it too may pass through such opening in the assembly and disassembly,

It is to be further noted that with the inner core parts 4 and 5 an integral part of the permanent magnet structure and never removed therefrom, no magnetic keeper or other precautions are necessary to prevent demagnetization of the permanent magnet after it has been magnetized. In other words, there can be no change in the reluctance of the magnetic circuit which would cause demagnetization because the parts of the magnetic circuit which determine mini- 4 mum reluctance are permanently assembled and comprise an integral structure. Other parts of the instrument not particularly mentioned may conform to usual practice.

The permanent magnet may therefore be magnetized at a high flux density and have a small knockdown corresponding to the reluctance of armature air gap in the magnetic circuit when the plug 8 is removed. This permits of exceptionally efllcient utilization of the permanent magnetic material and results in a rugged instrument of small size and high sensitivity.

The structure of Fig. 2 is polarized by employing a magnetizer with an inner C-shaped pole piece plug which fits within the inner periphery of the pole shoe 2 from one lateral side and is magnetically spaced from the inner core parts 4 and tongues 5 and an outer ring-shaped pole piece which embraces the outer periphery of the outer ring 3 from the other lateral side. When the magnetizer is energized, the permanent magnetic material i is polarized in a radial direction. The desirable features of a. permanently assembled one-piece field structure which is polarized after assembly, such as shown in Fig. 2, are not confined to that particular structure. For example,

the inner core and tongue may be in the form of a question mark as represented in Fig. 6.

In accordance with the provisions of the patent statutes we have described the principle of'oper-' ation of our invention, together with the apparatus which we now consider to represent the best embodiment thereof, but we desire to have it understood that the apparatus shown is only illustrative and that the invention may be carried out by other means.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. In an instrument,a permanent magnet flux path assembly comprising an inner circular tubular pole shoe of magnetic material, an outer circular yoke of magnetic material, an intermediate portion of permanent magnetic material extending between said pole shoe and yoke and polarized radially, said inner and intermediate portions having an open sector and said outer portion having a symmetrically divided two-part tongue projecting radially inwardly through such open sectors in symmetrically spaced relation to the intermediate and inner portions and forming a pair of similar sector shaped inner core parts spaced from said inner circular pole shoe by sector shaped gaps conforming to the same circle, said inner core parts being spaced apart a distance sufficient to pass the side of an armature coil therethrough, said permanent magnet flux path assembly being permanently assembled as an integral structure prior to polarization of the permanent magnet.

2. In an instrument, a permanent magnet flux path assembly comprising a C-shaped part and a ring shaped part embracing the outer periphery of the C-shaped part, a two-part inner core within the C-shaped part and joined to the ring part by tongue extensions through the opening in the C-shaped part, the inner periphery of the C-shaped part and the outer peripheries of the core parts forming concentrically disposed pole faces separated by a narrow concentric circular air gap of the order of 250 degrees arc, said parts being made from magnetic material and including permanent magnet material polarized to produce flux across said air gap between the C-shaped part and the inner core parts, all of the air gap arc and occupying less than ten per cent of such arc.

3. An electrical measuring instrument comprising a magnetic circuit which is closed by magnetic material except for a circular air gap extending over an arc of between 180 and 300 degrees, said material including a permanent magnet for producing flux across said gap. the magnetic inner core material forming the inner surface of said circular gap having an opening at the center of the circle conforming to the gap, a pivoted armature shaft extending through said opening, an armature coil carried by said shaft with one side adjacent the shaft within such opening and the other side in the circular air gap, said magnetic circuit being a permamently assembled integral structure, except for a section of the inner core which is removable for the purpose of threading the armature on such core, said removable core section being located at the center of the gap arc and having an air gap arc length not exceeding degrees. 4; A field structure for an electrical measuring' instrument comprising an inner O-shaped pole piece of magnetic material, an outer circular magnetic yoke, an inner magnetic core within the C-shaped pole piece Joined to the yoke by magnetic tongue means whichenters within the c-shaped pole piece through the opening in the 0 thereof and a c-shaped portion of permanent magnetic 'material between the outer yoke and inner pole piece, said parts being permanently and intimately united into a one-piece assembly and the permanent magnetic material being polarized in a radial direction after such assembly, theinner core being spaced fromthe inner pole piece by an air gap, an armature shaft opening within the inner core piece and an opening in the inner core piece for permitting an armature coil to be threaded thereon with one side in the shaft opening and the other side in the air gap. a

5. A field structure for an electrical measuring instrument comprising an inner C-shaped pole piece of magnetic material, an outer circular magnetic yoke, a magnetic core within and spaced from the C-shaped pole piece, magnetic tongue means joining the core to the yoke and entering the c-shaped pole piece through the opening in the C thereof, and a C-shaped portion of permanent magnetic material between the C-shaped pole piece and the yoke, the inner core and yoke being divided into two symmetrical sections leavshaped pole piece of magnetic material, a circular outer magnetic yoke. a magnetic core within and spaced from the inner O-shaped pole piece, magnetic tongue means securing the core to the yoke, and tongue means entering the C-sh'aped pole piece through the opening in the 0 thereof, permanent magnet material of c-shape between the inner C-shaped pole piece and outer yoke, the yoke, core and tongue portions being made of magnetic sintered oxide and all of said parts being permanently and intimately united by casting into an integral assembly, saidpermanent magnetic material being polarized in a radial direction after such assembly.

7. An electrical measuring instrument comprising a magnetic field structure comprising an outer circular magnetic yoke. a c-shaped permanent magnet having an inner pole piece of like shape supported within the yoke, an inner magnetic core forming a circular airgap with the said inner pole piece, magnetic tongue means joining the inner core with the outer yoke, said permanent magnet being radially polarized to produce a flux across said air gap, the core and tongue I being divided into two symmetrical parts by an intervening opening, an armature assembly frame having upper and lower bearing supports connected by a yoke, said yoke extending through the opening in said tongue, an armature shaft supported by said frame centrally of the inner core, an armature coil carried by said shaft and threading the core with one side adjacent the shaft and the other side in said air gap, and a. magnetic plug carried by said frame closing the opening in said core adjacent the air gap. said frame and the parts carried thereby being removable as a unit when the armature coil is turned into alignment with said plug.

8. An electrical measuring instrument comprising a magnetic field structure comprising inner and outer concentric magnetic pole pieces forming a circular air gap of the order of 250 degrees arc, a permanently magnetized magnetic circuit Joining said pole pieces and including a tongue part extending radially from the inner ole piece between the extremities of the air gap arc. the inner pole piece having a central axial opening which extends into the tongue part and a removable plug part adjacent the air gap opposite to the tongue part, an armature assembly frame having a yoke secured in the opening in said tonguepart, a shaft pivoted in said frame and extending centrally through the axial opening in said inner pole piece, an armature coil on said shaft with one side adjacent the shaft and the other in said air gap and surrounding the intervening portion of the inner ole piece, the removable plug of said inner pole piece being secured to said frame, said frame with the shaft, coil and plug parts carried thereby being axially removable as a unit when the coil is turned into alignment with said plug.

9. An electrical measuring instrument comprising magnetic circuit comprising a O-shaped permanent magnet having a c-shaped inner pole piece, an outer circular magnetic yoke, an inner core within the C-shaped pole piece and forming therewith an air gap of the order of 250 degrees arc, and; magnetic tongue Joining the core with the yoke through the opening in the C of the permanent magnet and its inner pole piece, the core and yoke being separated into .two symmetrical portions by an opening in line with the center of the tongue and core, all of said magnetic circuit parts being permanently and intimately united 7 into an integral assembly as by cast welding, and the permanent magnet being polarized ina radial direction after such assembly, an armature assembly comprising a framework of nonmagnetic material having upper and lower bearing supports, a yoke connecting the two, a shaft pivoted in the bearing supports, a coil carried by the shaft, and a magnetic plug supported from the yoke of the frame, the yoke of said frame being dimensioned to fit into the opening in the tongue of said magnetic circuit with the armature shaft coinciding with the axis of the core and with the magnetic plug closing the opening in the core, the plug being secured to the yoke of the frame by a support which curves around the shaft, the coil having one side adjacent the shaft and threading 8 the core with its other side in the air gap, said armature assembly and parts carried thereby being axially removable as a unit when the coil is in alignment with the plug.

MYRON 8. WILSON. FRANCIS M. LEARNED.

REFEllENCES CITED The following references are of record in the 10 file of this patent:

UNITED STATES PATENTS