US2878350A - Variable trim resistor - Google Patents

Description

March 17, 1959 Q AMSLER VARIABLE TRIM RESISTOR Filed Sept. 24, 1956 'ff/1y.

INVENTOR. CL V05 ,4A/.SL59 7- BY United States Patent O 2,878,350 VARIABLE TRIM RESISTOR Clyde Amsler, Santa Monica Canyon, Calif., assignor to Hycon Mfg. Company, Pasadena, Calif., a corporation of Delaware My invention relates to variable resistors and has particular reference to a miniature resistor construction wherein precise adjustment can be obtained by rotating an outer shell relative to an inner member.

The production of precise electronic equipment inv ariably depends upon precise components of which reslstors constitute a principal part. Fixed resistors frequently are so inaccurately constructed as to be of limited value and adjustment to some other circuit component or condition is frequently desired. Variable resistors accordingly constitute a desirable component for precision circuits. Such resistors are referred to as trim resistors, that is, adjustable to a precise value as compared to resistors that are intended to be variable during operation.

While variable resistors have been used for decades, they are of limited utility, generally being of considerable bulk and requiring manual manipulation to adjust them to the desired value. The usual external slidersv are a short circuit hazard and the physical assembly of these variable resistors is diticult in miniature circuits.

I have devised an adjustable resistor or trim resistor that is compactly constructed and simple to adjust. A simple rotation of an inner shell effects minute and precise changes in the eiective resistance values. The design lends itself to miniature trim resistors, making practical high precision adjustable resistors that are an inch or less in length.

It is therefore a general object of the invention to provide improved wire wound resistors that are precisely adjustable in resistance.

Another object is to provide a resistor that is adjustable in resistance by rotation of an outer shell with respect to an inner member.

A further object is to provide a variable resistor that is wire wound and the wiper element is threaded upon internal threads on an outer case.

Other objects and advantages of my invention will be apparent in the following descriptions and claims considered together with the accompanying drawings forming an integral part of this specification and in which:

Fig. l is a sectional view through one form of embodi ment of the invention wherein the wiper is threaded to the outer case.

Fig. 2 is a sectional view along the line II--II of Fig. 1.

Fig. 3 is a sectional view through another embodiment of my invention wherein the variable resistor is disposed within the central opening of a toroidal winding.

Fig. 4 is a sectional view along the line IV-IV of Fig. 3.

Fig. 5 is a sectional view through a third modification of the invention wherein differential threads advance a winding with respect to a wiper.

Fig. 6 is an end view taken along the line VI--VI of Fig. 5.

Fig. 7 is a sectional view through another modied form of the invention.

Referring to Figs. 1 and 2 the resistor is referred to generally by numeral 10 and may have a first member in the form of an outer shell 11, a second member in the form of a wiper or contact 13, preferably formed of electrically conductive material. The wiper 13 may be generally tubular in shape and may be externally threaded to engage internal threads on the shell 11 so that the wiper may be moved inwardly and outwardly of the shell by relative rotation. A loop or terminal 14 may be soldered or otherwise electrically connected to the wiper 13.

The resistor core 12 may be secured to the shell 11 in any suitable manner and there is illustrated a terminal eye 16 projecting through the closed end of the shell 11 and Ithe resistor core 12 may be mechanically secured to this terminal eye by threads or other mechanical connection. In the form illustrated in Fig. l the conductor core 12 may be formed of insulating material about which may be wrapped a helically wound resistor wire 17, one end of which may be electrically connected to the terminal eye 16. To stabilize the resistor core 12 within the shell 11 a tubular sleeve 18 may be inserted between the wiper 13 and the wire windings 17.

In operation the device of Figs. l and 2 is adjusted for resistance by relative rotation between the wiper 13 and the outer shell 11. The wiper 13 may have one or more inwardly projecting wiper points 13a, preferably on one end thereof, which may engage the resistance wire 17 disposed about the core 12. As the wiper 13 moves to the left in Fig. 1 it will contact an increasing length of the resistance wire 17 increasing the electrical resistance between the terminals 16 and 14. In this fashion a very precise resistance adjustment may be obtained. lf the pitch of the wire windings 17 is the same as the threads between the shell 11 and the wiper 13 there will be no sliding of the wiper transverse to the resistance wire and the resistance adjustment will be most precise in ythat it operates along the length of a wire rather than jumping from one wire winding to the adjacent wire winding.

Illustrated in Figs. 3 and 4 is a trim resistor embodying the invention in combination with a winding which may be either an inductive or resistance winding, depending upon the application. A spool 21 may have wire windings 22 disposed thereon and may be closed if desired by a cylindrical cover 23. One end of the wind# ing 22 may be electrically connected to a terminal 24 and the other end may project toward the center of the spool as at 22a. Disposed within the center of the spool 21 may be an externally threaded wiper 26 having a pair of inwardly projecting points 26a to engage a resistance wire 27 wrapped about a resistor core 28. This resistor core 28 may be of electrically conductive material if desired so that it may be riveted within the spool 21, or may be of insulating material such as plastic which is headed with heat so as to define a rivet head 29 to retain the core within the spool. The free cantilever end of the core 28 may be supported within the tubular wiper 26 by a close fitting cap 31 positioned on the end of the resistor core. The wiper 26 may be slotted at its outer end as at 32 to permit screwdriver rotation and may have a hole 33 therethrough to act as an electrical terminal.

The operation of the device of Figs. 3 and 4 is similar to that of Fig. l in that relative rotation of the wiper 26 and the spool 21 causes the wiper to advance along the windings 27 to vary the effective length of the resistance wire 27.

Illustrated in Figs. 5 and 6 is an embodiment of the invention wherein extremely precise resistance adjustments are obtained by means of diierential screws. In those gures an outer shell 36 may be cylindrical in shape and may have the bore through one end slotted lengthwise as at 37. The other end of the bore may have inserted therein a resistance core member 38 that is not only rotatable within-the shell but is movable lengthwise of the shell. This resistance core 38 may be formed of conductive material and may have a reduced diameter shoulder on which is disposed a layer of insulating material 39 either as a iilm of paint oras a ribbon of solid material. Helically wound on this insulator 39 may'be a continuous resistance wire d havingV one end 41a' electrically connected to the resistance core 3E.

Inserted in the left end of the shell of Fig. may be a rotatable cap 42 of conductor material having a screwdriver slot i3 and a pair of holes which receive driving pins 44 passing through the rotatable resistance core 38. These pins may likewise be of'conductor material. The cap 42 may beV retained in the shell 38 in aV suitable manner as by the snap ring 46 and may be electrically contacted at al1 times by the terminal ring 47.

Projecting centrally inwardly from the cap 42 may be a threaded stem 4S engaging internal threads on a tubular member 49 iitted in the other end of shell 36. This tubular member 49 may have a transverse pin 51 inserted therethrough which rides in the slot 37' to prevent rotation of that tube. Accordingly, rotation of the stem 4S will reciprocate the threaded tube 49 inwardly and outwardly of the shell 36.

The tube 49 is also externally threaded as at 52 to engage internal threads 53 on the resistor core 38. Therefore, as the tube 49 reciprocates it tends to reciprocate with it the resistor core 38. However, the resistor core 3S is also rotatable in the same pitch direction as the stem 48 so as to counteract the reciprocating action of the tube 49. By making the threads SZ and S3 of a slightly different pitch from those on the stem 48, a dierential threading action is obtained so that the actual reciprocation of the resistor core 38 is but a very tiny fraction per revolution of the cap 42 of the pitch dimension of the threads on stem 4S. A terminal member 54 may project through the wall of the shell 36 to contact the resistance wires 41 to thereby create a conductive path through the resistance wires 41 from the terminal 47. By making the pitch of the resistance wires 41 equal that of the differential between the'threads, very precise resistances can be obtained because of the single wiper 54.

The operation of the device of Figs. 5 and 6 is eiected by rotating the cap 42 which, in turn, causes the same degree of rotation of the stem d8 and the resistor clore 38. The differential between the threads 52 and those of the stem 48 causes a diierential reciprocation of the resistor core 38 with respect to the shell 36 and the longitudinally movable tube 49.

Illustrated in Fig. 7 is a modication of the invention wherein the resistor core is threaded within the outer shell. Accordingly, an outer cylindrical shell 56 may have a reduced diameter end plate 57 threaded to receive an externally threaded resistor core 58 having a terminal eye 59 formed on one end thereof. This resistor core 53 may have a reduced diameter end portion 58a having a suitable insulating film thereon upon which may be wrapped or wound a resistance wire 6l. This wire may be electrically connected to the resistor core 58 as at 61a. A tubular wiper 62 may be inserted within the shell 56 and may have wiper points 62a engaging the resistance wire 61. A terminal 63 may be electrically connectedl to the wiper 62.

The operation of the device of Fig. 7 is accomplished by rotating the core 58 relative to the shell 62 moving the resistance windings 61 relative to the wiper 62.

While I have described my invention with respect to speciic embodiments thereof,.I do not limit myself to these embodiments,nor otherwise, but claim all modiiications and variations that come within the true spirit and scope oli` the invention.

lclaim:

l. A variable resistor of high adjustment precision comprising an outer insulating shell;l a screw mounted for rotation within the shell; a core rotatable within the shell; a resistance wire wound onthe core; means driving the core in rotation with the screw and providing free movement of the core lengthwise of the screw; diterential thread means interconnecting the screw and shell and core; al wiper mounted' on the shell and contacting the resistancewire; and a terminal connected to one endl of thev resistance "wire, whereby relative rotation of the screw and shell cause dierential movement of the core toy give every exact adjustment of the wiper on the wire.

2,. A resistor that is adjustable in resistance comprising4 a rst member forming an outer insulator shell; a second member forming a resistor core disposed within the shell; a third member of conductive material forming a wiper disposed between the core and the shell' and connected to a terminal; resistance wire disposedV on said core and connected to a terminal at one end; and difierential thread means interengaging at least two of said three members so that-relative rotation between said two members will reciprocate the wiper member relative to the corejmemben'so that a variable resistance is developed between* the terminals.

y3. A variable resistor of'highradjustment precision comprising an outer vshell of insulating material; an internally and-- externally threaded tubular member disposed withinl the shell; means kmounting said tubular threaded member for reciprocation within the shell and preventing relative rotation with respect to the shell; a core disposed within the shell; a rotatable cap formed of electrical conductor material and disposed within the shell at one end thereof; a tubular core slidingly mounted on the core for reciprocation within the shell and rof tatably driven by the cap and disposed within the shell and internally threaded to engage the external threads on the tubular memberya screw secured to the cap c oaxially with the tubular member and threadedly engaging the internal' threads on that tubular member; resistance Wire wound on the exterior of the core and having one end electrically connected to the cap; and a wiper connected' to the shelland engaging the resistance wire and having one end projecting lbeyond the shell to act as a terminal, characterized by the internal threads on the tubular member being of a diierent pitch than the external threads on the tubular member, so that rotation of the cap gives rise to a dilerential movement of the core to give precise resistance settings.

References Cited in the iile of this patent UNITED STATES PATENTS 2,481,682 Payne Sept. 13, 1949 2,704,800 Graybeal et al Mar. 22, 1955 2,778,908 Altieri Jan. 22, 1957

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