US2154232A - Adjustable inductance - Google Patents

Description

Apri] ll, 1939.

P. S. DARNELL ADJUSTABLE INDUCTANCE Filed May l5, 1937 o o o 4.4249

/NVENTOR BVRSDRNELL A TTORNE Y Patented Apr. i1, 1939 i 2,154,232

UNITED- STATES PATENT ori-Ica ADJUSTABLE INDUUIANCE Paul S. Darnell, South Orange, N. J., signor to Bell Telephone Laboratories, Incorporated, New York, N.- Y., a corporation of New York Application my 1s, rim, sei-isi No. 14am 4 emma (ci. 1v1-11s) This invention relates to adjustable inductances type disclosed in the W. C. Ellis Patent 1,943,115, and more particularly to toroidal coils, the inissued January 9, 1934. ductance of which may be varied. The core as shown more clearly in -Il'igs. 2 an Toroidal coils have gone into wide use as load- 3, has a tapered hole 6 drilled completely through 5 ing or lter coils, transformers and the like due the core, the axis of the hole coinciding with a 5 to the inherent eiliciency of the magnetic circuit radius of the torus.l Within the hole is located and other recognized advantages. However, the a movable disc 1 of magnetic material mounted use of such coils in places where a high degree of on the end of a screw l of non-magnetic mateaccuracy of inductance is required has been limrial such as brass, which screw is adapted to move 1o ited due to the dliilculty of adjusting the inductin an internally threaded4 brass sleeve 9 suitably l0 ance of such coils to the accuracy required. Even secured to a plate I of Bakelite or other insuwith care in manufacture it has been found that latlng material which serves as a closure for the coils will diier suillciently in inductance from the outer end of hole 8 while the inner end of the required value to maketheir use dinlcult for cerhole is closed by a plate Il of insulating material l tain purposes. For example, placing toroidal such as ilbre. Plates I0 and Il may be suitably l5 coils in an enclosed case, impregnatlng the windheld in place. for example, by being cemented to ings or mounting the coils in proximity to other the surfaces around the core opening 0. It will apparatus may vary their inductance. be apparent that by turning screw 8 the disc 1 An object of this invention is a toroidal coll of magnetic material may be moved upwardly or 'whose inductance may be varied. downwardly to the dotted positions I2, I 3, its up- 20 Another object of the invention is a toroidal per position being reached when the upper edge coil whose inductance may be accurately adjusted of disc 1 strikes plate I0, and the lower position after the wound core has been impregnated with being reached when the lower surface of disc 1 a suitable compound. strikes cover plate Il. It thus will be noted that In accordance with the preferred embodiment the movement of disc 1 is conflned to a region ly- 25 of this invention a toroidal corevof magnetic maing Wholly Within the periphery 0f the cere. 'I'hc terial is provided with a cylindrical or tapered dimensions of disc 1 are preferably such that the hole whose axis coincides substantially with a side walls of the disc fit snugly against the walls radius of the torus and within the hole is adof hole 6 when the disc is in its lowermost D081- justably mounted a relatively thin disc or plate tion Il. 30 of magnetic material with the axis of the disc Since as previeilsly stated the disc 1 moves ensubstantially coinciding with the axis of the hole. tirely within the limits of the core surface, it A winding of a suitable number of turns is then follows that the multi-layer winding 4 may be applied to the core and the wound core lmpreguniformly distributed around the toroidal core nated in the usual manner and suitably mounted except for the Space Occupied by Sleeve 9, so that 35 in the casing after which the inductance of the the winding Space 10st by the Se 0f the adjustwinding may be accurately adjusted to the reable feature of this invention is not determined quired value by the movement of the disc. The by the diameter of hole 6 but merely by the diammaxlmum inductance will occur when the disc is eter of the small sleeve 9.

at the inner periphery of the torus while the min- After the hole 6 has been drilled in the core, 40 imum inductance will occur when the disc is at the core may be Coated With a Suitable enamel to the outer periphery, intermediate positions of the prevent wax during the impregnating process disc giving intermediate values of inductance. from being absorbed into the dust core and alter- Referring to the drawing, ing its permeability-temperature characteristic.

Fig. 1 is a perspective view in partial section and also to prevent the wax from entering the 45 of a toroidal core'inductance coil embodying feahole t. After the enameling the disc assembly tures of this invention; 1, Il, 9, III may then be mounted in place after Fig. 2 is a longitudinal sectional view of a por which the core is. ready to be wound with a suittion of the wound core of Fig. l; and able number of turns and layers to give the ap- Fig. 3 is a cross-sectional view of the core of proximate desired inductance with thedisc 1in its 60 Fig. l taken along the line I-S of Fig. 2. middle position. The wound core is then mount- Referring now to Fig. ll a multi-layer winding ed within a suitable casing I! and the remaining l is shown uniformly mounted upon a toroidal space fllled with a suitable potting compound such core I made preferably of highly compressed inas wax, or the coil may be centered in the case sulated magnetic particles, for example, of the in any other suitable manner. The ends of the winding are brought out to terminals il and l1 mounted at any convenient place on a suitable terminal plate while the head Il of the adjusting screw l projects through an aperture in the case to permit adjustment of disc 'i after the wound core has been potted. By means of a screwdriver or other tool the inductance may be brought accurately to the desired value by turning screw! in the proper direction alter which the screw l may be locked in any suitable manner to prevent further turning.

It will be noted that when the disc is in its lowermost position there is practically no alrgap between the disc and the main core since in this position the disc ilts snugly against the walls of hole l, but as the disc is moved upwardly there is a gradually increasing air-gap between the disc and the core due to the increasing size of the hole.

In explanation of the change in inductance with change in position of disc i we may assume that hole I is cylindrical and that disc 'l is also cylindrical and fits snugly into the hole in all positions. It can be shown under such conditions that the ilux density at the inner periphery of the torus is substantially times that at the outer periphery, where n is the inside radius and n the outside radius of the torus. Hence, by completing the magnetic circuit at the inner periphery the ilux in the core will be greater than if the magnetic circuit is completed at the outer periphery. When both the hole and the disc are slightly tapered as shown in the drawing with the disc fitting snugly into the hole only at the inner periphery of the torus. the inductance variations result trom two actions, the variation in air-gap and the alteration in iiux density, and the two actions are mutually aiding, thereby increasing the overall variation of the inductance with change in position oi' disc l.

As previously stated, the disc 1 is preferably of higher permeability than the main core although both the core and the disc i may be composed of iinely divided magnetic material insulated and compressed in accordance with the above-mentioned Ellis patent, where the magnetic material employed may be molybdeninn permalloy as disclosed in G. W. Elmen, U. S. Patent 1,768,443 issued June 24, 1930. In one example, the magnetic material of the core 5 had an effective permeability of 13.5 while the magnetic material of disc 1 had an eHective permeability of 125. With the construction shown in the drawing, it hm been found that a variation of 2 per cent of the inductance of the coil can be readily secured by the described arrangement and it has also been found that with the shown construction the percentage change in inductance is practically linear with change in position of disc i along the axis of tapered hole I. The thickness of disc 1 should preferably be small compared to its length of travel; for example, it has been found satisfactory to have the thickness of the disc about one-sixth of its length of travel.

While it is preferred to have hole l slightly tapered it is also contemplated that both the hole l and disc 1 may be cylindrical.

Itistobeunderstoodthatthisinventionis applicable to-a coil having a plurality o! windingsandisnotlimitedtoacollhaving onlya single winding as described. lhe adjustable feature may also be modiiied from that shown and the invention is, therefore, to be limited only by the scope of the appended claims.

What is claimed is:

1. An inductance device comprising a toroidalY core of magnetic material, a winding on said core, said core having a hollow chamber extending substantially between the inner and outer peripheries of said core, a movable member of magnetic material located wholly within said chamber, means for moving said member along an axis extending between the inner and outer peripheries of said core, said member having in the direction oi its movement a thickness substantially less than the distance between the inner periphery and the outer periphery oi said core, and means for coniining said movement between the inner periphery and the .outer periphery of said core.

2. An inductance device comprising a toroidal core of magnetic material, a winding on said core, said core having a hole extending substantially between the inner and outer peripheries of said toroid, with the axis of said hole substantially coinciding with a radius of said toroid, a thin plate of magnetic material mounted within said hole with the plate located substantially at right angles to the axis of said hole, a non-magnetic cover for the inner and outer ends of said hole, said winding extending over a substantial proportion of said cover, and means projecting through said cover for moving said plate in a direction along the axis of said hole.

3. An adjustable inductance in accordance with claim2lnwhichsaidplateisadisc andinwhich the surface defining said hole constitutes a portion of the surface of a cone with its greatest diameter at the outer periphery of the toroid, the diameter or said disc being substantially equal to the diameter of said hole near the inner periphery of said toroid.

4. An adjustable inductance device comprising a toroidal core, a winding on said core, said core having a hole extending through said toroid with the axis of the hole substantially coinciding with the radius of the toroid, a nonmagnetic cover for the inner end oi' said hole, a non-magnetic cover for the outer end of said hole, said outer cover having an aperture substantially coinciding with the axis of said hole. a sleeve extending beyond the outer periphery of said toroid with the axis of said sleeve substantially coinciding with the axis of said hole, a screw extending through said sleeve into said hole and a disc of magnetic material within said hole and mounted on said screw.

PAUL S. DARNHL.

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