US1807806A

US1807806A - Signors to the s

Info

Publication number: US1807806A
Authority: US
Publication date: 1931-06-02
Anticipated expiration: 1948-06-02

Description

June 2, 1931. T. A. SWARTZ ET AL VARIABLE RESISTANCE UNIT Filed Jan. 27, 1925 FIG: 2.. FIG 51 anon H 01;

FIG: 7. J6 AH 55 6965 1 WW cum 3 a y: a; 6 7m W Patented June 2, 1931 UNITED STATES PATENT OFFICE TORRENCE A. SWARTZ AND WILMER P. UHLER, OF TOTTENVILLE, NEW YORK, AS- SIGNORS TO THE S. S. WHITE DENTAL MANUFACTURING COMPANY, OF PHILADEL- PHIA, PENNSYLVANIA, A CORPORATION OF PENNSYLVANIA VARIABLE RESISTANCE UNIT Application filed January 27, 1925.

Our invention relates particularly to that class of resistance devices in which the resistance elements are subjected to different degrees of pressure to form a more or less intimate contact between said resistance elements, whereby a consequent variation in the current passing therethrough is attained; and is especially directed to such devices as may be employed in connection with radio receiving and transmitting apparatus.

It is a well known fact that microphonic noises are caused in certain circuits, such as the grid circuit of a radio receiving instrument or set, by the sliding contacts of the relatively movable elements of the circuit varying mechanism, and that such noises detract materially from the pleasure of listening in.

The principal objects of our invention are to provide a resistance unit that is so constructed andarranged as to avoid the use of sliding contacts, whereby the undesirable microphonic noises incident to such sliding contacts may be eliminated.

Other objects of our invention are to provide a resistance medium that in itself will tend to refine the sound vibrations, and to further tend to dampen any microphonic sounds by providing yielding means connecting said resistance medium with means for varying the resistance of said resistance medium,

Our invention further includes a variable resistance unit in which the resistance medium is disposed in separate piles formed of a plurality of individual blocks and arranged to be yieldingly compressed by balanced adjusting mechanism.

Specifically stated, the form of our invention as hereinafter described, comprises a casing of non-conducting material through the wall of which, electric terminal bindingposts extend, being connected through a plurality of blocks of especially prepared conductive resisting material forming what is commonly termed a pile, and a connecting or'bridge bar which may be yieldingly engaged therewith by springs adjustably maintained under pressure by an adjusting screw, actuated by means of a knob, and bearing Serial No. 5,015.

Our invention also includes all of the various novel features of construction and ar- L rangement as hereinafter more definitely specified.

In the accompanying drawings, Figure 1 is a sectional elevational view of a resistance unit, conveniently embodying our invention; Fig. 2 is a perspective view-of one of the terminal binding-posts and its terminal plate, illustrated in Fig. 1; Fig. 3 is a perspective view of one of the blocks of resistance material, of which the resistance piles illustrated in Fig. 1 are composed; Fig. 4. is a perspective view of the connecting bar of electrical conducting material, which connects the resistance piles shown in Fig. 1; Fig. 5 is a perspective view of one of the spring seatplates illustrated in Fig. 1, which may preferably be composed of insulating material; Fig. 6 is a perspective view of the balancing lever or teeter bar arranged to equalize the pressure of the springs as illustrated in Fig. 1; and Fig. 7 is a sectional elevational view similar to Fig. 1, showing a modified form of resistance unit embodying a single pile.

In said figures, the preferred embodiment of the resistance unit is shown in Fig. 1 and comprises the casing 1 forming achamber 2 divided by the transverse wall 3, and having the closure comprising the lid or cap 5 conveniently secured to said casing, all of which is formed of insulating or non-conducting material.

The rear wall of thecasing 1 is provided with the apertures 6 and 7, through which the terminals 01 the binding-posts 9 and 10 extend so as to protrude exterior to the easing for the convenient connection of the

wires

12 and 13 which are arranged to be secured by the

set screws

15 and 16, as shown in Fig. 1.

The inner ends of the binding-posts 9 and 10 are headed to provide the

plates

17 and 18 respectively, which afford seats for the piles 19 and 20 composed of the blocks 21 of resistance material. As shown, the piles ill iii

19 and 20 are disposed upon opposite sides of the transverse wall 3, which serves as a battle to prevent induction leaks, and said piles are conveniently connected by the electrical conducting bridge-bar 22, having the reduced connector 23, which serves to bridge and thereby complete the circuit including the

wires

12 and 13. The reduced connector 23 which constitutes the central portion of the bridge bar 22 operates to render this bridge bar flexible so that theend portions will make and maintain intimate contact with the ends of the resistance elements. 7

The resistance of the piles 19 and 20 may be conveniently varied by variation in pressure tending to bring the blocks of resistance material into more or less intimate contact, and for this

purpose springs

25 and 26 are provided, preferably in co-axial relation with the respective piles 19 and 20.

The

springs

25 and 26 may preferably bear upon the connecting-bar 22 and be insulated therefrom by the

spring seats

27 and 28, which may preferably be of insulating material, and pressure applied thereto and varied at will by the adjusting screw 29 whose head 30 bearscentrally against the balancing lever or equalizing teeter beam or bar 32, the end portions of which engage the

respective springs

25 and 26, so that any axial movement of the screw 29 efiected by rotation of its knob 33 tends to vary the pressure equally upon both of said piles 19 and 20.

In the form of our invention as shown in Fig. 7, the resistance unit comprises the easing 41 having the closure comprising the lid or cap l2 enclosing the chamber 43 into which a portion of the rear wall is extended to provide a seat 15 for the contact plate 46 forming the head of the binding-post 47 extended through the aperture 48 in said rear wall, to protrude exterior to the casing, being pro vided with the set screw 4.9 by which the lead wire 50 is engaged to said binding-post.

The contact plate 16 is electrically connected by the conducting bar 52 with the pile 53 composed of a plurality of blocks 55 of resi,

' .tance material, seated upon the contact plate gas 56 forming the head of the binding-post 57 extended through the aperture 58 in the rear wall of the casing 41 to protrude exterior thereto, being provided with the set screw 59 by which the lead wire 60 is engaged to aid binding-post.

The resistance of the pile 53 may be conveniently varied by the adjusting'screw 62 which is in threaded engagement with the closure 42 and which has the knob 63 by which I it may be rotated, and the head 65 arranged to bear against the balancing or teeter bar 66, at its medial region, to maintain the

springs

67 and 68 on the

insulated spring seats

69 and 70, under varying degrees of compression and thereby vary the resistance of said pile 53, said

springs

67 and 68 being co-axial with the binding-posts 47 and 57, and equally spaced upon opposite sides of the axis of said adlusting screw 62. 7

Our invention is advantageous in'that the resistance maybe varied by the rotation and consequent axial movement of the adjusting screw 29 whose head 30 bears upon the equaliz'ing teeter bar 32 and rotates thereon at a point, to vary the degree of compression on the

springs

25 and 26 and yieldingly vary the compression of the piles 19 and 20 and thereby vary the flow of current merely by such variation of pressure. varying the resistance, there are no wiping or scraping contacts, and as the cause of microphonic noises is eliminated, a consequent purity of tone results. 7

7e are aware that there are on the market certain variable resistance units having two.

tion 21, are connected by the electricalconducting bridge plate 22 having reduced connector 23. It can easily be seen by referring to Fig. 1 or Fig. 7 that this connector bridge completes the electrical circuit, between the two'piles of composition blocks 21, and thereby all slidin or relatively movable parts of the unit are entirely outside of the electric circuit, and are, in fact, insulated therefrom by

insulating pieces

27 and 28 in Fig. 1, or

pieces

69 and 70 in Fig. 7 by our construction and arrangement of the parts.

In other known types of compression units, slight movements of metal to metal contacts which are included in the electrical circuit are possible, and have been found to cause microphonic noises, especially as the higher resistance range of the unit is approached and when the direction of rotation of the knob is reversed. These sliding contacts may not necessarily be a part or function of such units, but may be an inherent def come by our construction and design.

We do not desire to limit our invention to the precise details of construction and arrangement as herein set forth, as it is obvious that various modifications may be made therein without departing from the essential features of our invention as defined in the appended claims. 7

Having thus described our'invention, we claim: 1. A variable resistance unit free from all sliding contacts in the electrical circuit comprising a casing, a plurality of pressure-re sponsive resistance elements, a bridge bar in electrical contact with one end of each of said elements, an equalizing bar, springs interposed between said bars, and means to move said equalizing bar to vary the compression of said springs.

By this method of ect which is over- 2. A variable resistance unit free from all sliding contacts in the electrical circuit, comprising a casing, two parallel resistance elements adapted to vary in resistance according to the pressure thereon, a bridge bar in electrical contact with adjacent ends of the elements so that said elements and bar are connected electrically in series, an equalizing bar, springs interposed between the ends of said bars, and means to move said equalizing bar to vary the compression of said springs.

8. A variable resistance unit comprising a support, a pair of parallel resistance elements adapted to vary in resistance according to the pressure upon the ends thereof, a bridge bar electrically connected to adj aoent ends of the elements and adapted to exert mechanical pressure thereon, and means including two springs disposed coaxially with the resistance elements to exert pressure upon the bridge bar and therethrough upon the resistance elements.

4. A variable resistance unit free from all sliding contacts in the electrical circuit, comprising a casing, two parallel resistance elements adapted to vary in resistance according to the pressure thereon, a bridge bar in mechanical and electrical contact with the other ends of the element-s so that said elements and bar are connected electrically in series, an equalizing bar parallel to said bridge bar, springs interposed between the ends of said bars whereby to exert pressure at the ends of said bridge bar, and an adjusting device operating against said equalizing bar intermediate its ends, said equalizing bar being capable of rocking movement with respect to said adjusting device.

5. A variable resistance unit free from all sliding contacts comprising a casing, a plurality of pressure-responsive resistance elements, a bridge bar having its respective end portions in electrical contact with said resistance elements, and independent yielding means engaging the ends of said bridge bar for moving the said ends toward said resistance elements, said bridge bar having the central portion thereof cut away in order to render said bar flexible whereby the end portions will make intimate contact with the resistance elements.

In witness whereof, we have hereunto set our hands the 8th day of J an., A. D., 1925.

TORRENCE A. SWARTZ. WILMAR P. UHLER.