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US3188595A - Adjustable resistor - Google Patents

Adjustable resistor Download PDF

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Publication number
US3188595A
US3188595A US226874A US22687462A US3188595A US 3188595 A US3188595 A US 3188595A US 226874 A US226874 A US 226874A US 22687462 A US22687462 A US 22687462A US 3188595 A US3188595 A US 3188595A
Authority
US
United States
Prior art keywords
contactor
film
slider
protuberance
base member
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
US226874A
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English (en)
Inventor
Cheever A Hult
Bebel Joseph
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Weston Instruments Inc
Original Assignee
Weston Instruments Inc
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Weston Instruments Inc filed Critical Weston Instruments Inc
Priority to US226874A priority Critical patent/US3188595A/en
Priority to GB38104/63A priority patent/GB1046939A/en
Priority to FR949024A priority patent/FR1412377A/fr
Application granted granted Critical
Publication of US3188595A publication Critical patent/US3188595A/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01C—RESISTORS
    • H01C10/00—Adjustable resistors
    • H01C10/24—Adjustable resistors the contact moving along turns of a helical resistive element, or vica versa

Definitions

  • This invention relates to an adjustable electrical resistor wherein the resistance element is in the form of electrically conductive film and, more particularly, to a multi-turn film potentiometer having a high degree of resolution.
  • a potentiometer is formed having an extended helical resistive film path and a wiper adapted to continuously track the film path.
  • the electrically resistive element comprises a carbon or metal film deposited by evaporation or other known techniques upon the inner surface or wall of a tubular substrate or base member.
  • the inner surface of the substrate usually is glazed prior to metal deposition. Terminations of an electrically conductive material are provided On the tube ends and a portion of the outer surface at each end of the tube. These terminations provide the necessary electrical path from the resistive element to the end caps which are force fitted on the outer tube surface.
  • the resistive element is adjusted to a desired resistance value by a method known as spiralling. Spiralling is accomplished through the use of an electric probe or an abrasive wheel to form a helical cut in the resistive element on the inside of the tubular substrate such that the resistive path is in the form of a helix or spiral.
  • the resistance between the ends of the tubular substrate may be varied by changing the pitch of the spiral.
  • the pitch of the lead screw which drives the contactor or wiper along the helical film path is selected to be the same as the pitch of spiral cut.
  • a typical spiral lead screw and follower arrangement for causing a contactor to follow a helical path is described in a US. patent, 1,606,153, issued November 9, 1926, to Harry A. Douglas. As described in Douglas patent, a helix or spiral follower designed to carry a contactor is threaded on a lead screw having the same pitch as the spiral resistance element so that the contactor will follow the spiral path of such element.
  • Another object of this invention is to facilitate the positioning of an electrical contactor on an electrically conductive film.
  • Still another object of this invention is to provide an improved contactor for film type adjustable resistors.
  • the adjustable resistor consists of an electrically non-conductive tubular base member which has a helix of a thin film of an electrically resistive material deposited on its inside wall. Terminals are placed at either end of the tubular base member so as to contact at least a portion of the thin film. End caps, having openings, are placed over either end of the tubular base member. The openings in the end caps are such as to receive a slider, comprising a contactor mounted on a contactor support, threaded on a lead screw. A slotted tube, placed over the lead screw is adapted to rotate the contactor and contactor support about the lead screw. By selecting the pitch of the spiral film path and the pitch of the lead screw threads to be the same, the contactor traverses the entire length of the spiral film resistor path.
  • the contactor is mounted in the contactor support or follower such as to permit it to have one direction of freedom with respect to the contactor support which is normal to the surface of the resistive film.
  • This is accomplished by forming a contactor from a sheet of resilient material into the form of a cross.
  • an elongated protuberance having a major axis that is in substantial alignment with the film path to facilitate the protuberances following the film path.
  • the arms of the cross are inclined away from the protuberance.
  • Two of the opposite arms of the cross are short and are inclined at a shallow angle to locate the contactor in the follower and maintain its position in the follower during rotation. The end edge surfaces of the short arms do not contact the follower and, therefore, do not provide a spring action.
  • the remaining two arms of the cross are longer than the shorter arms and are inclined to rest upon circumferential grooves in the follower. Depression of the contactor at the protuberance forces these arms to a shallower tangential angle on the periphery of the circumferential grooves. This provides the necessary spring action and maintains the protuberance in contact with the film.
  • FIGURE 1 is an isometric view of an exemplary embodiment of an adjustable resistor formed in accordance with this invention
  • FIGURE 2 is a longitudinal section view of the adjustable resistor illustrated in FIGURE 1;
  • FIGURE 3 is an end section view of the adjustable resistor illustrated in FIGURE 1 taken along the section line 33 of FIGURE 2;
  • FIGURE 4 is a pictorial view of the contactor of this invention.
  • FIGURE 5 is a pictorial view of the adjusting mechanism of this invention.
  • the adjustable resistor or potentiometer shown in FIG- URES 1 through 5 comprises a tube 10 which may be formed of an electrically nonconductivematerial such as a ceramic.
  • the adjustable resistor includes a lead screw for an external electrical connection to both ends and to the follower of the adjustable resistor through pins 30, 31 and 32 in the terminal board.
  • the tubular base member consists of an electrically non-conductive tube on the smooth, cylindrical inside surface of which is deposited a thin film 26 of an electri cally conductive material, i.e., a resistance film.
  • the resistance film 26 may be any of the known films such as a carbon film or a nickel composition deposited by sublimation or other known methods upon the inner surface of the tubular base member 10.
  • the inner surface of the tubular base member 10 is glazed prior to metal deposition.
  • Terminations 24 of an electrically conductive material such as a metallic frit or gold plating are provided on the ends and on a portion of the outer surface of each end of the tubular base member 10. These terminations 24 provide the necessary electrical path from the ends of film 26 to end caps 28 and 29.
  • An external electrical connection to the end caps 28 and 29 is made through the respective pins 30 and 32 of a terminal board 22 to terminals 34 which are soldered to the respective end caps 28 and 29.
  • the film 26 is adjusted to the desired resistance value by that method known as spiralling. Spiralling is accomplished preferably through the use of an electric probe although an abrasive wheel may be used also. The use of the electric probe rather than an abrasive wheel is preferred to prevent contamination of the restistive path with particles of the glaze'or base member. Such particles, if not thoroughly removed, may be trapped and carried by the contactor 60. Because of their hardness these particles would cause the film to wear rapidly away. Using an electric probe, the film26 is vaporized leaving a smooth surface relatively free of particles. In a typical case the spiralling is such as to create a film helix having turns, each turn of which has a path width typically of .030 inch.
  • the end caps 28 and 29 are generally in the shape of cups having central openings therein to receive and mount the adjusting mechanism of the adjustable resistor.
  • the adjusting mechanism includes a header assembly 18, the lead screw 12, a sleeve 44 and the end assembly 16.
  • the header assembly 18 is made up of a slotted adjustment head 36 and a bushing 38 which are assembled into an integral unit by the use of a cylindrical molding 4 0, the header assembly being mounted for rotation within the encapsulant as indicated by the directional arrows in FIGURE 2.
  • the adjustment head 36 and bushing 38 are of a suitable metallic material whereas the molding 40 may be of a plastic such as Teflon which provides a good seal, has a low coefficient of friction, is somewhat flexible, and provides electrical insulation between the adjustment head 36, the bushing 38 and the end cap 29.
  • V a plastic such as Teflon which provides a good seal, has a low coefficient of friction, is somewhat flexible, and provides electrical insulation between the adjustment head 36, the bushing 38 and the end cap 29.
  • the lead screw 12 whose center portion is threaded, is gold plated for improved conductivity and corrosion resistance, and is supported at one end by the rotatable bushing 38.
  • the other end of the lead screw 12 is fixedly supported by the end assembly 16 which includes the fixed bushing 42 coaxially mounted with an insulating bushing 54.
  • a terminal is soldered to the fixed bushing 42 which in turn is soldered to the lead screw 12.
  • the terminal 35 is electrically connected to the center pin 31 on the terminal board 22.
  • the sleeve or carriage 44' is metallic and in the shape of a half cylinder axially cut, but with a portion 46 at either end extending more than around.
  • the right hand end (in the drawing) of sleeve 44 is force fitted onto the bushing 38 so that it is driven by rotation of the adjustment head 36.
  • the left hand (in the drawing) end portion 46 of sleeve 44 is loosely fit over the fixed bushing 42 to permit its free rotation about that bushing.
  • a slider'll3 includes a contactor support or follower 14.
  • the follower 14 is driven laterally with respect to the axis of the tubular base member 10 at the pitch angle of the lead screw 12 such that it traverses the film helix 26 substantially from one end to the other.
  • the follower 14 is normally made of any suitable material such as brass and preferably is rhodium plated for improved electrical conductivity, wear resistance, and core rosion resistance. It is threaded to allow mating with the thread of the lead screw 12.
  • the insulating bushing 54 may be any suitable material such as a plastic known commercially as Teflon. This bushing acts as a seal and also an electrical insulator between the fixed bushing 42 and the left hand end cap 28.
  • the header end of the resistor is sealed by the use of Silastic washers 56 and an additional Tefion bushing 58.
  • This additional Teflon bushingSS reduces wear on the molding 40 and aids in centrally locating theheader assembly 18 by locating the end of sleeve 44.
  • a cross shaped contactor 60 formed of a resilient, electrically conductive sheet material, such as 0.002 inch Ney Oro G metal. It is cross shaped so as to rest in the axial and circumferential grooves 50 and 52, respectively.
  • the contactor 60 is made into a single point type by forming an elongated protuberance 62, whose major axis 64 is canted to be in substantial alignment with the helical film path 26.
  • the protuberance 62 is of sufficient height such that only it contacts the'film 26.
  • the contactor 60 has a pair of short arms 66 and a pair of long arms 68.
  • the short arms 66 are inclined away from the protuberance 62 at a shallow angle and function to locate the contactor in the axial groove 50 of the follower 14 during its'rotation. The ends of these arms do not contact the bottom but only the sides of the axial groove 50, hence do not provide any spring action.
  • the longer arms 68 of the contactor 60 also are inclined away from the protuberance 62 but rest upon the bottom of the circumferential groove 52 of the follower 14. Upon depression 'of the contactor 60 at the protuberance 62, these longer arms 68 are forced against the bottom of radial groove 52 causing the arms to spread somewhatand maintain contact between the protuberance 62 and the film path 26.
  • the contactor protuberance 62 is elongated in accordance with this invention for several reasons. With the typical 0.002 inch material, the formation of the simple protuberance of spherical shape of a sufiicient height would tend to rupture the material. The elongated protuberance has less tendency to rupture the material. Any increase in material thickness, to permit the formation of such protuberance or dimple without rupture, would greatly increase contact pressure and hence increase wear. Also the elongated protuberance 62 reduces the pressure per unit area on the film due to' increased contact area and hence causes less wear of the film. Finally, the
  • the major axis; of the protuberance 62 is slightly canted such that it is in alignment with the pitch angle of the helical film path 26.
  • This particular contactor arrangement is such that the only force acting on the contactor 6i) is that normal to the film surface.
  • the contactor 69 is relatively in sensitive to the direction of its movement with respect to the film surface.
  • a spring 70 and a pair of washers 72 placed on either side of the spring 70 are placed on either end of the lead screw 12 to provide a clutch action.
  • the washers may be gold-plated brass and the spring berylium copper.
  • the spring is placed into compression by the washers 72 which are located upon shoulders formed at either end of the lead screw 12.
  • the follower 14 compresses either of the springs 70 such that upon reversal of rotation of the adjustment head 36, the compressed spring 70 forces engagement of the follower 14 with the threads of the lead screw 12.
  • the clutch action prevents damage to the unit through excessive rotation of the adjustment head 36.
  • spiral film element has several advantages over the conventional straight strip element of the type described in U.S. Patent 2,926,324, issued February 24, 1960, to Barden et al., for example.
  • the increased length of the helical spiral path provides improved resolution of resistance values.
  • tracking of the film by the follower 14 is continuous.
  • the larger film area thus permitted, i.e., the entire inside of the base member rather than a mere strip, permit a greater dissipation of heat.
  • the relatively narrow film path 26 tends to reduce errors in non-linearity of the resistance between the contactor and either end terminal due to field effects.
  • an improved adjustable resistor unit which has a high degree of resolution of resistance.
  • the contactor is formed such that it is relatively insensitive to the direction of its rotation.
  • an elongated protuberance is formed on the contactor and is canted so as to be in substantial alignment with the helical film path to facilitate tracking of the film path.
  • An adjustable resistor comprising:
  • an electrically non-conductive tubular base member having a smooth, cylindrical inside wall, a helix of a thin film of an electrically resistive material on said inside wall of said tubular base member,
  • a slider adapted to move along said helix, said slider including an electrically conductive contactor, said contactor having a protuberance adapted to engage said thin film,
  • said protuberance being elongated in the direction of its travel over said resistive film
  • An adjustable resistor comprising:
  • said slider including a contactor and a contactor support
  • said contactor support being generally cylindrical in shape and having axial and circumferential grooves therein
  • said contactor being formed from resilient sheet material into the form of a cross
  • junction area of said cross having a protuberance adapted to engage said film
  • the arms of said cross being inclined away from said protuberance and positioned in said grooves whereby the pressure per unit area of said protuberance on said film is substantially independent of the direction of movement of said slider.
  • An adjustable resistor comprising: an electrically resistive film element, slider means that is movable along the length of said resistive element, said slider means including a contactor and a contactor support, said contactor formed from electrically conductive resilient sheet material in the shape of a cross, the junction area of said cross having a protuberance adapted to contact said resistive film element, said contactor support having substantially mutually perpendicular grooves formed therein, the arms of said cross being inclined away from said protuberance and positioned in said grooves to permit movement of said contactor relative to said contactor supportonly in a direction normal to the surface of said resistive film element whereby the pressure per unit area of said protuberance on said film is substantially independent of the direction of movement of said slider means.
  • An adjustable resistor comprising:
  • said adjusting means including a threaded lead screw fixedly mounted coaxially within said tubular base member, I 1
  • a spring member coaxially positioned over at least one end of said lead screw, said slider th-readingly engaging said lead screw and adapted to be rotated by said sleeve member, said end of said lead screw being unthreaded thereby to permit the disengagement of said slider from the threads'of said lead screw when it has reached the corresponding end of said helix by compressing said spring member, thereby to facilitate the reengagement of said slider on the threads of said lead screw upon a reversal of the rotation of said sleeve member,
  • said slider including a contactor and a contactor supsaid contactor support being generally cylindrical in shape and having axial and circumferential grooves therein,
  • said contactor being formed from resilient sheet material into the form of a cross
  • the arms of said cross being inclined away from said protuberance and positioned in said grooves to permit movement of said contactor relative to said con tactor support only in a direction normal tothe surface of said thin film whereby'the pressure per unit area of said protuberance on said film is substantially independent of the direction of movement of said slider.
  • An adjustable resistor comprising:
  • an electrically non-conductive tubular base member having a smooth, cylindrical, inside wall
  • electrically conductive slider means adapted to move along said helix
  • said slider means including a contactor, said contactor having a protuberance adapted to engage said thin film, 1
  • said protuberance being elongated in one dimension thereby to reduce the pressure per unit area of said contactor on said film
  • said adjusting means including a threaded lead screw fixedly mounted coaxially within said tubular base member,
  • a contactor support member for carrying said contactor threaded on said lead screw and adapted to be rotated by said sleeve member
  • a spring member coaxially positioned over atleast one end of said lead screw, said end of said lead screw being unthreaded and of reduced diameter thereby to permit the disengagement of said slider means from the'threads of said lead screw when it has reached said end of said filin helix by compressing said spring member thereby to facilitate the reengagementof said slider means on the threads of said lead screwnpon a reversal of the rotation of said.

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  • Engineering & Computer Science (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Measuring Leads Or Probes (AREA)
  • Adjustable Resistors (AREA)
US226874A 1962-09-28 1962-09-28 Adjustable resistor Expired - Lifetime US3188595A (en)

Priority Applications (3)

Application Number Priority Date Filing Date Title
US226874A US3188595A (en) 1962-09-28 1962-09-28 Adjustable resistor
GB38104/63A GB1046939A (en) 1962-09-28 1963-09-27 Adjustable resistor
FR949024A FR1412377A (fr) 1962-09-28 1963-09-28 Perfectionnements aux résistances ajustables

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US226874A US3188595A (en) 1962-09-28 1962-09-28 Adjustable resistor

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US3188595A true US3188595A (en) 1965-06-08

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US226874A Expired - Lifetime US3188595A (en) 1962-09-28 1962-09-28 Adjustable resistor

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US (1) US3188595A (fr)
FR (1) FR1412377A (fr)
GB (1) GB1046939A (fr)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3621438A (en) * 1964-07-01 1971-11-16 Charles S Wright Variable resistors
US5488349A (en) * 1993-12-02 1996-01-30 Erickson; Bruce L. Multiple range variable resistor

Citations (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1606153A (en) * 1926-01-27 1926-11-09 Harry A Douglas Rheostat
US2358991A (en) * 1942-03-02 1944-09-26 Morgan Crucible Co Variable electric resistance
US2665355A (en) * 1952-02-07 1954-01-05 Borg George W Corp Potentiometer
US2798140A (en) * 1953-04-06 1957-07-02 Wilbur M Kohring Resistance coatings
US2813182A (en) * 1955-03-10 1957-11-12 Borg George W Corp Potentiometer adjuster
US2826663A (en) * 1954-06-09 1958-03-11 Kingston Products Corp Rheostat switch
US2839642A (en) * 1953-10-13 1958-06-17 Allen Bradley Co Variable resistance device
US2938186A (en) * 1956-10-30 1960-05-24 Yucaipa Instr Ltd Inc Trimming potentiometer
US3059197A (en) * 1952-06-07 1962-10-16 John G Ruckelshaus Potentiometer

Patent Citations (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1606153A (en) * 1926-01-27 1926-11-09 Harry A Douglas Rheostat
US2358991A (en) * 1942-03-02 1944-09-26 Morgan Crucible Co Variable electric resistance
US2665355A (en) * 1952-02-07 1954-01-05 Borg George W Corp Potentiometer
US3059197A (en) * 1952-06-07 1962-10-16 John G Ruckelshaus Potentiometer
US2798140A (en) * 1953-04-06 1957-07-02 Wilbur M Kohring Resistance coatings
US2839642A (en) * 1953-10-13 1958-06-17 Allen Bradley Co Variable resistance device
US2826663A (en) * 1954-06-09 1958-03-11 Kingston Products Corp Rheostat switch
US2813182A (en) * 1955-03-10 1957-11-12 Borg George W Corp Potentiometer adjuster
US2938186A (en) * 1956-10-30 1960-05-24 Yucaipa Instr Ltd Inc Trimming potentiometer

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3621438A (en) * 1964-07-01 1971-11-16 Charles S Wright Variable resistors
US5488349A (en) * 1993-12-02 1996-01-30 Erickson; Bruce L. Multiple range variable resistor

Also Published As

Publication number Publication date
GB1046939A (en) 1966-10-26
FR1412377A (fr) 1965-10-01

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