US2566911A

US2566911A - Variable resistance

Info

Publication number: US2566911A
Application number: US112722A
Authority: US
Inventors: Benjamin B Scott
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1949-08-27
Filing date: 1949-08-27
Publication date: 1951-09-04
Anticipated expiration: 1968-09-04

Description

Patented Sept. 4, '195i I l"UNITED As 'l'ir'rlss PATENT oFFicE g vAmlzsltz;;STANCl I Benjamin n."sam, seaman, s. Lautner,

toGeneralElec NewYork tric Company, a corporation of Application aum 21, isis, serial No. 112,122

. l y l invention 'relates to variable resistances, and more particularly to precision variable-resistances of the type in which the resistance'wire is wound i'n turns on 'a `suitable support and an electric contact is moved' over bared portions of tbe turns to vary the portion of the resistance included in an electrical circuit, and has for'its object means for reducing the resistance value of the steps in the change of the resistance as the contact'moves over the turns and for averaging variations in the resistance of the wire.

In the simplest form of variable resistance, which is a straight wire with a movable contact or brush, any desired change in resistance variation can be obtained as a function of the brush movement. Howeveix when this same wire is wound on a suitable support in a plurality of turns with a brush sliding over the turns, the resistance obviously changes in steps with 'brush movement. the value of each step being the resistance f a turn upon movement of the brush from one turn to the other. A reduction in value of resistance steps may'be obtained by suitably increasing the'length of the turn wound resistance so as to decrease the resistance of each turn but that is unsatisfactory when compactne'ss is required. Accordingly, a further object of the invention is 4a reduction in the step by step resistance change with brush movement while retaining the advantage of a short, compact re-V sistance unit.

Another disadvantage of turn wound resistances is that the unit length resistance of the wire itself varies becauseof manufacturing variations in the diameter of the wire and, accordingly, another object of my invention is to average substantially such variations in the resistance of the In carrying out my invention in one form, I provide at least two spaced apart brushes for a turn wound resistance, .which brushes are connected in parallel with a resistance in series with at least one brush and spaced apart a. distance sutlicient to include between them a plurality of the turns o! the resistance suillcient to averagethe inherent wire resistance variations. For minimum step by step resistance change, it is desirable'that the' currents in the brushes be substantially equal and, accordingly, in one form 'of my invention-when two brushes are used, I

single brush.

ll'or a more complete understanding of my invention,- reference should be had to the accompanyi'ng drawing, Fig. l of which is a diagrammatic representation of a wound resistance unit l1 Claims. (CL lOl-42) with two brushes embodying my invention: Fig. 2 is an enlarged fragmentaryview showing the relative arrangement of the brushes; Fig. 3" shows a--modiiied-form -of my invention utilizing brushes in spaced relation with each other; while Figs. 4 and 5 are modified forms showingfthe application of my invention to potentiometer resistances utilizing, respectively'gtwo and three bmsn'es. v

Referring to the drawing; in Fig. 1 the resistance wire i! is wound in turns/on an electrical insulating 'support or card Ii shown as a strip of suitable rigid electrically insulating material. such as a plastic or fiber material; Although the wire turns extend around,thc support, it will be understood that other tumshapes may be used such' as pass back' and fortlrjon one side of the-support. -For variation of the' amount of the resistance included in an electric circuit of which the conductors i2 and il 'form a part, two electric contacts, shown as brushes-.ll and II, are provided which engage bared portions of the turns on the upper edge, as shown, ofthe resistance unit. The brushes Il and ii aresuitably mounted on an electrically insulatinfgsupport'li which is movable in predetermined spaced parallel relation with the upper edge 'of 'the resistance unit so that the brushes, shown as made of a suitable tions having a diameter greater, and hence lower resistance,'than normal, thus producing plus and minus deviations from a desired linear output characteristic. Their Ainclusion in series between the two brushes in parallel with the resistance 2l has the effect of averaging the resistance variations at the brush contact points so that the resistance output at connection llfi'naterially improves linearity of the output characteristic of the unit. In a resistance 'wound-of .0015 inch diameter-wire, for example, the number of turns included between the brushes may be 500.

In precision wound resistors .each turn is exactly spaced from the preceding turn to given the' desired resistance characteristics with respect to the brush movement with consequent unequal spacing of the turnsA as turngresistan'ces vary. Because of this unequal spacing' of the turns. the brushes ordinarily do not each short circuit a turn at the same time-and, consequently, the resistance of the wire betweenothe brushes remains "substantially constant. This condition is shown in Fig. 2 of the drawing. in which the brush I i is about to move into the space between the turn portions II and I l upon further movement toward the right hand, as seen in the draw-` Ing, thereby to short circuit the turn between the portions I'I and Il while, at the same time, the brush I4 obviously maintains its engagement with the turn or portion I9. It will be obvious from` the'above description in connection with Fig. 2 that the ideal spacing between brushes Il and I l would be a spacing distance equal to an integral multiple of the anticipated `average resistor turn spacing plus one-half of the anticipated turn spacing in order that the brushes Il and Il be completely "out of phase in their travel across the resistor wire turns. Likewise, with the embodiments of Figs. 3 and 5, involving the use of three brushes, the ideal spacing would include a one-third turn spacing and for a larger 'number of brushes the fractional turn spacing being connected electrically to the conductor I2.

In the two-brush arrangement of Fig. 1, this resistance should be equal to the resistance between the brushes I4 and I5. It will be noted that the wire resistance between the brushes I4 and Il is connected in parallel with the resistance 20. With this arrangement, the resistance steps are reduced to the equivalent of one-half turn, because each turn is carrying one-half current in the parallel circuit. When each turn is added to the`circuit between conductor I3 and brush M, its current doubles, with consequent one-hall' turn resistance increase effect.

In the arrangement of Fig. 3, we have shown the use of three brushes, 2 I, 22 and 23, secured on a movable insulating support 24 so that the two outside brushes engage the resistance unit 25 in equally spaced relation with the central brush. In this case the values of resistors 23 and 21- are again chosen for equal brush current division. With `this arrangement, the current increases one-third in each turn as it is included in the circuit and ,each resistance step is reduced to one-third ascompared to a single brush.

In Figs. 4 and 5, I have shown suitable arrangements for use with potentiometer resistance units where the direction of current ow through the resistance unit to the brushes may not always be the same or where brush current is of negligible magnitude. In Fig. 4, the resistances 28 and 23 .may 4be equal, respectively, to substantially onehalt the resistance between the brushes 30'and 3|, attaining a reduction in resistance steps in a manner similar to that described above. The resistances 2l and 29 have a voltage take-of! point at their common connection, wire 32.

In the three-brush arrangement shown in Fig. 5, the

resistances

33, 34, and 35 may be each substantially' equal to one-half the resistance between the two

outside brushes

36 and 31, the two outside brushes being equally spaced from the central brush. It will be understood that in the embodiments. of Figs. 4 and 5 the brush resistances 28,129, and. 33, 34, and 35 may advantageously be o f higher resistance values than those stated, although the resistance values stated have been found to give satisfactory results and they should be taken as recommended minimum resistance values.

While I have shown a particular embodiment of my invention, it will be understood, of course, that I do not wish to be limited thereto since many modiilcations may be made and I therefore contemplate, by the appended claims, to cover any such modifications as fall within the true spirit and scope of my invention.

What! claim as new and desire to secure by Letters Patent -of the United States is:

1.l A variable resistor comprising a resistance wire wound in a plurality of turns on a support, a :pairv of electric contacts, means for supporting said contacts in spaced relation with each other in contact with saidy resistance wire, said support being movable` along said resistance wire thereby to move said contacts over said turns, electric connections for connecting said contacts together, a resistance included in said connections with at least one of said contacts, said electrically interconnected contacts together comprising one outgoing resistor connection.

2. A-variable resistor comprising a resistance wire wound in a plurality of turns on a support, a plurality of electric contacts, means for supporting said contacts in spaced relation with each other in contact with said resistance wire, said support being movable along said resistance wire thereby to move said contacts over said turns. electric connections for connecting said contacts together, and resistances included in saidconnections with said contacts 'having values such as to 'maintain substantially equal currents in said contacts, said electrically interconnected contacts together comprising one outgoing resistor con- A nection.

3. A variable resistor comprising a resistance wire wound in a plurality of turns on a support, a fixed outgoing connection at one end of said wire, a pair of, electric contacts, means for supsaid wire between said contacts so as to maintain: substantially equal currents in said contacts."' `y 4. A variable resistor comprising a resistance wire wound in a plurality of spaced turns on a support, a pair of contacts, means for supporting said contacts in spaced relation with each other in contact with said resistance wire, said support being movable along said resistance wire thereby to move said contacts over said turns, said contacts being mounted on said support in such spaced relative positions as to average variations in the resistance of said wire between said contacts, electric connections ior .connecting saidl lcontacts together, and `a resistance included in wire wound in a plurality of spaced turns on aI support, a plurality of electric contacts, means for supporting said contacts in spaced relation` with each other in contact with said resistance wire, said support being movable along said resistance wire thereby to move said contacts over said turns, said contacts being mounted on said.

support in such spaced relative positions as to average variations in the resistance of said wire between said contacts, electric connections for connecting said contacts together to form a movable outgoing resistor connection, and resistances included in said connections with said contacts having values such as to maintain substantially equal currents in said contacts.

6. A variable resistor comprising a resistance wire wound in a pluralityoi spaced turns on a support, a ilxedvoutgoing connection at one end of said wire, a pair of electric contacts, means for supporting said contacts in spaced relation with each other in contact with said resistance wire, said support being movable along said resistance wire thereby to move said contacts over said turns, said contacts being mounted on said support in such spaced relative positions as to average variations in the resistance of said wire between said contacts, electric connections for connecting said contacts together, and a resistance included in said connections with the one of said contacts nearest said fixed outgoing connection having a value substantially the same as the value of the resistance of said wire between said contacts so as to maintain substantially equal currents in said contacts thereby to reduce the effective resistance step to substantially onehalf turn.

7. A variable resistor comprising at least one iixed outgoing terminal and one movable outgoing terminal, said movable outgoing terminal being connected to a plurality of electrically and mechanically interconnected resistor contact brushes, said electrical interconnections including current-limiting resistors.

8. A resistance wire wound electrical resistor .having a movable contact device comprising a plurality o1' mechanically and electrically interconnected contact brushes for contacting axially closely spaced points on said resistor, said electrical interconnections including electrical resistance, and an outgoingterminal connected to said movable contact device.

9. A movable contact terminal device for a resistance wire wound electrical resistor, said device comprising at least two contact brushes, said brushes being both mechanically and electrically interconnected, said electrical intercon- 6 nection including electrical resistance, said brushes being axially spaced bya distance equal to an integral multiple of the anticipated average resistor turn spacing plus a fractional portion thereof, the fraction having a denominator equal to the number of brushes.

10. A movable contact structure for establish ing an outgoing connection for a resistance wire- Wound electrical resistor comprising a plurality of contact brushes for contacting the windings of said resistor, resistors connected in series with a number of said brushes at least as great as one less than the total number of said brushes, said brushes being mechanically connected and spaced from one another by distances equivalent to whole multiples of the anticipated average resistor turn spacing plus fractional multiples of said spacings, said fractional multiples comprising a fraction whose denominator is equal to the number of said brushes.

11. A resistance wire wound electrical resistor having a fixed outgoing connection at one end thereof, a movable outgoing connection contact nection, the higher value resistors being connected to the closer brushes.

BENJAMIN B. SCO'I'I.

REFERENCES CITED The following references are of record inthe ille of this patent: Y

UNITED STATES PATENTS OTHER REFERENCES zeitschrift Fur Instrumenenkunde. vol. 34, 1914, pages 142-151.