US2173084A

US2173084A - Adjustable inductance

Info

Publication number: US2173084A
Application number: US134069A
Authority: US
Inventors: Nelson P Case
Original assignee: Hazeltine Corp
Current assignee: BAE Systems Aerospace Inc
Priority date: 1937-03-31
Filing date: 1937-03-31
Publication date: 1939-09-19
Anticipated expiration: 1956-09-19
Also published as: BE427257A; GB496912A

Description

Sept. 19, 1939. N. P. CASE 2,173,084

ADJUSTABLE INDUCTANCE Filed March 51, 1937 FIG.2.

l6 l3 l4 l5 FIG. 7.

INVENTOR. NELSON P. 35

ATTORNEY.

Patented Sept. 19, 1939 UNITED STATES BEISSUED PATENT OFFICE ADJUSTABLE INDUCTANCE Nelson P. Case, Great Neck, N. Y., assignor to Hazeltine Corporation, a corporation of Delaware Application March 31,

18 Claims.

This invention relates to adjustable inductance units which, while of general application, are especially adapted for use as tuning elements in the resonant circuits of a high-frequency signaling system for tuning the circuits over broad bands of frequencies.

In high-frequency signaling systems, it is generally desirable to maintain the antiresonant impedances of the resonant circuits at or near their maximum values as they are tuned over their respective ranges of frequencies in order that high gain may be obtained under all conditions. When an adjustable condenser is utilized as a tuning element of a tunable circuit, its capacitance becomes so large at the low-frequency end of the tuning range that the L/C ratio and the antiresonant impedance of the circuit, and hence the gain, are appreciably reduced. vHowever, if fixed condensers and adjustable inductance tuning elements are utilized in such resonant circuits, a high antiresonant impedance may be obtained over the entire tuning range.

Adjustable inductance units heretofore devised have been subject to various objections. In general, these units have been either of the type comprising fixed windings and an associated adjustable shield or of the well-known adjustable winding variometer type. Both of these types ordinarily are objectionable in that they' have relatively small ranges of inductance variation and the shield type also has relatively high power factors. While units of the variometer type have usually been the least objectionable in these respects, even they ordinarily have a relatively limited range of variation. For an adjustable reactance element suitable for tuning over a wide frequency range, such as the broadcast band, a variation of approximately 9:1 is required. Further, in conventional inductance units of the variometer type, very close spacing between windings is required for units of moder-' ate inductance and moderate dimensions, giving a large variation of distributed capacitance and limiting the tuning range when such unit is used as a tuning element of a resonant circuit. Moreover, inductance units of the variometer type heretofore devised have been relatively complicated and otherwise mechanically objectionable.

It is an object of the present invention, therefore, to provide a novel and improved adjustable inductance unit having a wide range of inductance variation.

It is a further object of the invention to pro- 1937, Serial No. 134,069

vide an adjustable inductance unit of the type described having one or more of the following characteristics: simplicity, compactness, ruggedness, and ease of operation.

In accordance with the present invention, there is provided a composite adjustable inductance unit which comprises a first winding means providing a first magnetic field of predetermined shape, intensity, and polarity. A second winding means, interleaving with said first winding means and having a mean diameter equal to that of said first winding means, is arranged to pro vide a second magnetic field of substantially the same shape and intensity as, but of an opposite polarity to, that of the first-mentioned winding means. An adjusting means is provided for substantially rectilinearly moving the two winding means with respect to each other. This relative movement is preferably from a first position, in which the two magnetic fields are substantially mutually exclusive and a maximum inductance is provided by the unit, to a second position, in which the fields are substantially coincident, so that the field of the second winding means substantially neutralizes or cancels the field of the first-mentioned winding means and a minimum inductance of a relatively small value is provided by the unit.

In one approved embodiment of the invention, three windings are individually disposed on three coaxial cylindrical forms. These forms are dimensioned for telescopic movement, one within the other two. The windings are so proportioned and arranged that the two windings on the outer and inner forms provide a first magnetic field as described above, and the winding on the intermediate form provides the second magnetic field. Preferably, the outer and inner forms are secured in relatively fixed telescopic relation, and means are provided operatively interconnecting a control element and the intermediate form so that equal adjustments of the control element over its range effect different displacements of the intermediate form relative to the outer and inner forms to vary the total inductance of the unit as described above. This manner of control renders the unit especially adaptable for use as a tuning element, in that equal adjustments of the control element may be made to effect equal variations in the resonant frequency of a circuit in which the unit is used as a tuning element.

As used in this specification, the term mean diameter is used to denote the effective diameter for purposes of inductance computation of winding systems to which the term is applied, and thus it may apply to a single layer winding, a multilayer winding, or a multiwinding system.

For a better understanding of the invention, together with other and further objects thereof, reference is bad to the following description taken in connection with the accompanying drawing and its scope will be pointed out in the appended claims.

In the accompanying drawing, Fig. 1 is a simplified circuit diagram illustrating one approved form of the present invention; Fig. 2 is a longitudinal sectional view of the windings of an inductance unit such as is illustrated in Fig. 1, indicating the magnetic fields produced by the windings; Figs. 3, 4, 5, and 6 are circuit diagrams illustrating various modified forms of the present invention; and Fig. 7 is a side elevation of a composite coupling unit embodying the present invention with certain portions shown in longitudinal section and certain portions broken away.

Referring in detail to Figs. 1 and 2, the inductance unit of the present invention illustrated by these figures comprises a pair of coaxial helical windings Ill and I I, disposed one within the other with an annular space therebetween, and an additional helical winding I2 coaxial with, and adapted to be telescoped within the annular space between, the windings I0 and II, the windings I0 and II and the winding I2 thus being interleaving. The cross sections of the windings may, of course, be of any desired shape other than circular, as shown. The radial dimension of the annular space between the windings I0 and II is preferably a small fraction of the mean diameter of the windings so that the magnetic field produced jointly by the two windings I0 and II is of substantially the same shape and intensity as that produced by the single winding I 2. For this purpose also, it is preferable that the di ameter of the wire used for the windings I0 and I I be small relative to the mean diameter of the windings.

In the arrangement of Fig. l, the winding I2 is wound in a direction opposite to that of the windings Ill and II so that the polarity of the field of the winding I2 is opposite to that of the field of the other two windings. The windings I0 and II are connected in parallel and the winding I2 is connected in series therewith. The three windings are so proportioned as to have substantially equal inductances so that the current through the winding I2 divides equally between the windings I0 and II. By virtue 0? this arrangement, as illustrated in Fig. 2, the windings Ill and II jointly provide a first magnetic field of a predetermined shape, intensity, and polarity, while the winding I2 provides a second magnetic field of substantially the same shape and intensity as,

. but of an opposite polarity to, that of the first L1L2 Li L2 (1) where L is the total inductance of the unit; Ll, La,

and La are the self-inductances of the windings I0, II, and I2, respectively; M1 is the mutual inductance between the windings I0 and I I and M2 is the mutual inductance between the pair of windings ID and II and the winding I2. The dimensions of the unit are so related that the maximum value of 2M2 approaches that of the expressionas closely as possible.

It will thus be seen that, with the winding I2 disposed in the position in which the two fields are substantially mutually exclusive, there is substantially no mutual inductance between the winding I2 and the windings III and I I, the value of M2 is inappreciable or substantially zero. In this position, therefore, the total inductance of the unit is a maximum. On the other hand, when the winding I2 is disposed in the secondmentioned position with the two fields substantially coincident, the mutual inductance M2 between the winding I2 and'the windings ID and II is a maximum and the total inductance of the unit is reduced to a minimum.

It will be noted that, in the arrangement 01 Fig. l, the high potential end of the winding I2 is adjacent the high potential ends of the windings Ill and II when the winding I2 is disposed within the other two windings. By virtue of this arrangement, thediiferences in potential of adjacent portions of the winding I2 and the other two windings is fairly small for all adjustments thereof and the variation of distributed capacitance between these windings has only a'small effect on the characteristics of the unit. Care should be taken that the power factors and impedances of the windings I0 and II are substantially equal at all frequencies at which the unit is to be operated so that the current through the two windings will be substantially equal under all conditions.

In Fig. 3 there is illustrated a modified form of the invention which is identical with that shown in Fig. 1, except that all three of the windings are wound in the same direction and the difference in polarities of the two fields is obtained by reversing the connections of the winding I2. While, in certain cases, substantially satisfactory results may be obtained with this arrangement, when the windings are completely telescoped, the low potential end of winding I2 is opposite to the high potential ends of the other two windings. so that the distributed capacitance therebetween is somewhat more effective than in the embodiment of Fig. 1.

In Figs. 4 and 5 two additional modified forms of the invention are illustrated which are similar to the embodiments of Figs. 1 and 3, respectively, except that all three of the windings are connected in series and the several windings are of correspondingly different relative proportions. In Fig. 4 the difference in polarity of the two fields is obtained, as in Fig. 1, by winding the element oppositely to the windings I6 and H. In Fig. 5, on the other hand, the difference in polarity is obtained, as in Fig. 3, by reversing the connections of the winding I2. In the embodiments of both Figs. 4 and 5, since all of the windings are connected in series, the total inductance provided by the unit maybe according to the formula:

L'=L1+L2+2M1+L3 2M2 3) in which corresponding terms representthe same factors as in Equation (1) In the embodiments of Figs- 4 and 5, also, the inductances of the windings I and II individually are preferably substantially equal, but, since the total inductance of these windings, L1+Lz+2M1, is approximately 4L1, the total inductance of the unit is Therefore, it is necessary that the inductance of the winding l2 be approximately four times that of each of the windings l0 and II in order that the total inductance may be reduced to approximately zero when the two fields are substantially coincident or M2 is at its greatest value.

In Fig. 6still another modified form of the invention is illustrated. Here, the three windings are all connected in parallel with the winding l2 wound in a direction opposite to that of the windings I0 and II in order to obtain the desired difference in polarity of the two fields. In this case, the winding I2 preferably has a self-inductance approximately equal to that of each of the windings I0 and II in order that the total inductance of the unit may be varied from its maximum value to a minimum value of approximately zero.

-The inductance of the unit of Fig. 6 may be determined according to the formula:

in which corresponding terms represent the same factors as in the other equations.

If then, L1 L2 L3=Ml=M2 Ll where unity 4 coupling between L1 and In is assumed, then for the minimum total inductance of the unit the following equation holds:

and for the maximum total inductance for the unit, where M 2:0, the following equation holds:

' LIZ L! L max.= ,M (6) It will be noted that this embodiment has the special advantage that the effect of the distribuuted capacitance is reduced to a minimum, since, when the windings are completely telescoped, there is no difference in potentials between adjacent parts of the windings.

Referring to Fig. 7, there is illustrated a physical construction of an inductance unit embodying the present invention. This unit comprises three coaxial cylindrical forms l3, II, and IS on which are disposed the windings III, II, and 12, respectively. The form It is disposed within the form I3, leaving an annular space therebetween and these two forms are rigidly secured to a suitable base l6, as shown. The form I5 is of a diameter intermediate between the diameters of the forms l3 and I4 and is adapted to be telescoped therebetween. An end piece I! is secured to the end of the form l5 remote from the base l6 and is provided with guide passages l8 and I9. There is also provided a fixed support 20 having transverse openings 2| and 22 corresponding to the openings l8 and I9, respectively, in the end piece IT. A guide rod 23 is rigidly secured in the opening 2| parallel to the common axis of the forms and extends through the passage I8 to prevent rotation of the form l5 while guiding axial movements thereof. A shaft 24 extends through the opening 22 and passage l9 and is provided with a suitable actuating knob 25 and annular collars 25 to prevent longitudinal movement thereof. A spiral screw thread 21, of a pitch gradually increasing in the direction of the support 20, is formed in the shaft 24 and engages a pin 28 in the end piece ll. This shaft and pin arrangement thus provides a nonuniform motiontransmitting means connecting the control element or knob 25 and the intermediate form. The windings H), H, and I2 may be proportioned, arranged, and connected in accordance with the embodiments illustrated in any of Figs. 1, 3, 4, 5 or 6.

In the operation of the inductance unit of Fig. '7 to adjust the inductance thereof, the knob 25 is rotated to rotate the shaft 24 and, because of the engagement of the pin 28 in the screw thread 21, the form I5 is axially moved relative to the forms l3 and M. The limits of movement of the form 85 are from its innermost position where the fields developed by the windings are substantially coincident and the total inductance of the unit is a minimum, to a position external to the forms l3 and H where the magnetic fields in question are substantially mutually exclusive and the total inductance of the unit is a maximum. The forms are so proportioned that the radial dimension of the annular space between the forms l3 and I4 is a small fraction of the mean diameters of these forms. By virtue of this arrangement, the magnetic fields produced jointly by the windings on these two forms is of substantially the same shape and intensity as that produced by the winding on the form l5 and when the form i5 is telescopically moved to its position between the other forms, the two fields are substantially coincident. It will be apparent that this result is not obtainable by a unit including only two telescopically engaging windings since, inasmuch as one of such windings must have a lesser diameter than the other in order to obtain telescopic engagement, the two fields will necessarily be of difierent shapes rendering coincident positioning thereof impossible. Due to the variation in the pitch of the screw thread 21, equal adjustments of the knob 25 from the first to the second extreme positions mentioned above effect gradually increasing adjustments of the winding 12. A unit of the type described is especially well adapted'for use as a tuning element in a resonant circuit since, with the pitch of the screw thread varying in a proper manner, equal adjustments of the knob 25 effect the proper adjustments of the total inductance of the unit to impart to the unit a straight-line frequency characteristic over its entire tuning range.

While there have been described what are :at present considered the preferred embodiments of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from this invention, including various other manners of connecting and positioning the windings of the unit in addition to those described in detail, and, therefore, it is aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of this invention.

What is claimed is:

1. A composite adjustable inductance unit comprising afirst winding means providing a and polarity, a second winding means interleaving with said first winding means and having a mean diameter equal to that of said first winding means and providing a magnetic field coaxial with, of substantially the same shape and intensity as, but of an opposite polarity to, that of said first means, and means for relatively axially moving said two Winding means.

2. A composite adjustable inductance unit comprising a first winding means providing a magnetic field of predetermined shape, intensity, and polarity, a second winding means interleaving with said first winding means and having' a mean diameter equal to that of said first winding means and providing a magnetic field coaxial with, of substantially the same shape and intensity as, but of an opposite polarity to, that of said first means, and means forrelatively axially moving said two winding means from a first position in which said fields are substantially mutually exclusive to provide a maximum inductance to a second position in which said fields substantially coincide to provide a minimum inductance.

3. A composite adjustable inductance unit comprising a first winding means providing a magnetic field of predetermined shape, intensity, and polarity, a second winding means interleaving with said first winding means and having a mean diameter equal to that of said first Winding means and providing a magnetic field coaxial with, of substantially the same shape and intensity as, but of an opposite polarity to, that of said first means, adjusting meansior relatively axially moving said two winding means, control means for said adjusting means, and nonuniform motion-transmitting means connecting said control means and said adjusting means whereby equal adjustments of the former over its range of adjustment effect predetermined difierent relative movements of said winding means.

4. A composite adjustable inductance unit comprising a first winding means providing a magnetic field of predetermined shape, intensity, and polarity, a second winding means interleaving with said first winding means and having a mean diameter equal to that of said first winding means and providing a magnetic field of substantially the same shape and intensity as, but of an opposite polarity to, that of said first means, adjusting means for relatively movingsaid two winding means while maintaining the polarities of said fields substantially unchanged from a first position with the fields of said two winding means substantially mutually exclusive to a second position with the fields of said winding means substantially coincident, control means for said adjusting .means, and nonuniform motion-transmitting means so connecting said control means and adjusting means that equal adjustments of said control means effect gradually decreasing relative movements as said windings are moved from said first position to said second position.

5. A composite adjustable inductance unit comprising a first winding means providing a magnetic field of predetermined shape, intensity, andpolarity, a second winding means interleaving with said first winding means and having a mean diameter equal to that of 'said first winding means and providing a magnetic field of the same shape and intensity as, but of an opposite polarity to, that of said first means, said two i winding means being coaxially disposed and dimensioned for telescopic movement, and means for relatively axially moving said winding means.

6. A composite adjustable inductance unit comprising a pair of relatively fixed windings providing a magnetic field of a predetermined shape, intensity, and polarity, an additional winding interleaving with said pair of windings and having a diameter equal to the mean diameter or" said pair of windings and providing a magnetic field of substantially the same shape and intensity as, but of an opposite polarity to, that of said pair of windings, and means for axially moving said pair of windings and. said ad'- ditional winding relative to each other.

7. A composite adjustable inductance, unit comprising a pair of relatively fixed coaxial windings one disposed within the other, an additional winding interleaving with said pair of windings and having a diameter equal to the mean diameter of said pair of windings and coaxially disposed with respect to said pair of windings and dimensioned for telescopic movement therebetween, and means for telescopically moving said pair of windings and said additional winding relative to each other from a substantially mutually exclusive position to provide maximum inductance to a position with said additional winding telescoped between the windings of said pair to provide minimum inductance.

8. A composite adjustable inductance unit comprising a pair of coaxial windings disposed one within the other and providing an annular space therebetween of a radial dimension which is a small fraction of the mean diameter of said windings, an additional winding coaxial with, and interleaving with, said pair of windings and dimensioned for telescopic movement therebetween, and means for relatively telescopically moving said pair of windings and said additional winding from a substantially mutually exclusive position providing maximum inductance to a position with said additional winding disposed in said annular space to provide minimum inductance.

9. A composite adjustable inductance unit comprising a first winding means, a second interleaving winding means, said two winding means having the same mean diameter and being coaxially disposed and dimensioned for telescopic engagement, and means for axially moving said two winding means, relative to each other, from. a first position with said two winding means substantially mutually exclusive to provide a maximum inductance, to a second position with said two winding means telescopically disposed to provide a minimum inductance, the high potential ends of both winding means being substantially adjacent in the last-mentioned position.

10. A composite adjustable inductance unit comprising a first winding means providing a magnetic field of a predetermined shape, intensity, and polarity, a second winding means interleaving with said first winding means and having a mean diameter equal to that of said first winding means and connected in series with said first means, said two winding means providing a magnetic field coaxial with, of substantially the same shape and intensity as, but of an opposite polarity to, that of said first means, and means for relatively axially moving said two winding means.

11. A composite adjustable inductance unit comprising a first winding means providing a magnetic field of predetermined shape, intensity, and polarity, a second winding means interleaving with said first winding means and having a mean diameter equal to that of said first winding means and connected in parallel with said first means, said two winding means providing a magnetic field coaxial with, of substantially the same shape and intensity as, but of an opposite polarity to, that of said first means, and means for relatively axially moving said two winding means.

12. A composite adjustable inductance unit comprising a pair of windings connected in parallel and arranged to provide a magnetic field of a predetermined shape, intensity, and polarity, an additional interleaving winding connected in series with the windings of said pair and arranged to provide a magnetic field coaxiaLwith. of substantially the same shape and intensity as, but of a polarity opposite to, that of said pair of windings, and means for relatively axially moving said pair of windings and said additional winding.

13, A composite adjustable inductance unit comprising a pair of concentric windings connected in parallel and providing a magnetic field of predetermined polarity, an additional interleaving winding connected in series and concentric with the windings of said pair and providing a, magnetic field coaxial with, but of a po-- larity opposite to, that of the first said field, all of said windings being proportioned to have substantially the same inductance, and means for relatively axially moving said pair of windings and said additional winding from positions with said fields substantially mutually exclusive to positions with said fields substantially coincident.

14. A composite adjustable inductance unit comprising a pair of windings connected in series and arranged to provide a magnetic field of a predetermined shape, intensity, and polarity, an additional winding interleaving with said pair of windings and having a diameter equal to the mean diameter of said pair of windings and connected in series with the said pair of windings, said additional winding being arranged to provide a magnetic field coaxial with, of substantially the same shape and intensity as, but of a polarity opposite to, that of said pair of windings, and means for relatively axially moving said pair of windings and said additional winding.

15. A composite adjustable inductance unit comprising a pair of concentric windings connected in series, having substantially equal inductances and providing a magnetic field of predetermined polarity, an additional winding ini terieaving with said pair of windings and having a diameter equal to the mean diameter of said pair of windings and connected in series and concentric with the windings of said pair, having an inductance approximately four times that of each of the windings of said pair and providing a second magnetic field coaxial with, and of a polarity opposite to, that of the -first said field, and means for relatively axially moving said pair of windings and said additional winding from positions with said field substantially mutually exclusive to positions with said fields substantially coincident.

16. A composite adjustable inductance unit comprising three coaxial cylindrical forms adapted to be telescoped one within another, the inner and outer forms being relatively fixed and having a mean diameter equal to that of the other of said forms, a winding disposed on each of said forms, said windings being connected in circuit and so dimensioned and disposed that the windings on the outer and inner forms provide a magnetic field of predetermined shape, intensity, and polarity and the winding on the intermediate form interleaves with the windings on the inner and outer forms and provides a magnetic field of substantially the same shape and intensity as, but of an opposite polarity to, that of said first field, and means for effectin relative movement between said outer and inner forms and said intermediate form.

17. A composite adjustable inductance unit comprising three coaxial cylindrical forms adapted to be telescoped one within another, the inner and outer forms being relatively fixed and having a mean diameter equal to that of the other of said forms, a winding disposed on each of said forms, said windings being connected in circuit and so dimensioned and disposed that the windings on the outer and inneriorms provide a magnetic field of predetermined shape, intensity, and

polarity and the winding on the intermediate form interleaves with the windings on the inner and outer forms and provides a magnetic field of substantially the same shape and intensity as, but of an opposite polarity to, that of said first field, a control element, and nonuniform motiontransmitting means connecting said element to said intermediate form, whereby equal adjustments of said element over its range of adjustment effect different movements of said intermediate form relative to said outer and inner forms.

18. 'A composite adjustable inductance unit comprising three coaxial cylindrical forms adapted to 'be telescoped one within another, the inner and outer forms being relatively fixed and having a mean diameter equal to that of the other of said forms, a winding disposed on each of said forms, said windings being connected in circuit and so dimensioned and disposed that the windings on the outer and inner forms provide a magnetic field of predetermined shape, intensity, and polarity and the winding on the intermediate form interleaves with the windings on the inner and outer forms and provides a magnetic field of substantially the same shape and intensity as, but of an opposite polarity to,

that of said first field, a control element, and

nonuniform motion-transmitting means so connecting said element and said intermediate form that equal adjustments of said element over its range of adjustment effect gradually decreasing movements of said intermediate form relative to said outer and inner forms from a first position substantially external to said outer and inner forms to a second position substantially completely telescoped therebetween.

NELSON P. CASE.