US3541491A - Electrical resistors - Google Patents

Description

Nov. 17, 1970 N. G. wosTER ELECTRICAL REsIsToRs 2 Sheets-Sheet l Filed Dec. 19l 1968 rrys,

Nw, 17, 1970 N. G. woRs'rER 3,541,493i

ELECTRICAL RESISTORS Filed Dec. 19. 1968 2 Sheets-Sheet 2 31 f .PF/6.5'.

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United States Patent O U.S. Cl. 338-211 19 Claims ABSTRACT F THE DISCLOSURE Electrical resistor, particularly for use in electrical measuring instruments, comprising an elongated base strip of thin insulating material, such Mylar film, having printed thereon a meandering line pattern of electrical resistive material. From appropriate tapping points on such resistive line pattern printed connections are provided to a further electrically conductive deposit on the base strip with lan arrangement such that each or` the various resistive line sections between adjacent tappings is initially shunted by a part of the further conductive -deposit so that the overall resistance value between end connection terminals can be increased by breaking the continuity of Iat least one part of the further deposit as by means of a punch hole through the base member and the overlying conductive deposit.

This invention relates to electrical resistors and is more particularly concerned with the construction of a resistor using printed circuit methods for its initial manufacture. A particular, although -by no means exclusive, applica-tion of the invention is to the construction of electrical resistors for use in electrical measuring instruments Iand particularly those used for providing a moving coil type instrument with an overall coil circuit resistance of predetermined value. The invention is also applicable to resistors used in measuring instruments for range adjustment purposes.

Objects of the invention include the provision of an improved construction of resistor which permits easy adjustment of its resistance value to a particular chosen figure and which may, in its iinal manufactured state, be caused to assume a very small physical form.

In accordance with the invention a resistor comp-rises a thin film-like base member of electrical insulating material and a line pattern of electrical resistive material deposited thereon and -frorn tapping points on such resistive line pattern there are provided electrical connections to a further electrically conductive deposit o-n said base member, the arrangement being such that each of the various resistive line sections between adjacent tappings is initially shunted by a part of said further electrically conductive deposit whereby the overall resistance value between connection terminals connected to said line pattern may be increased by breaking the continuity of at least one part of said further deposit, e.g., by means of a punch hole through the base member and the overlying conductive deposit.

Preferably, the resistive line pattern is arranged with a sinuous or meandering form while the further conductive deposit may be located adjacent one of the edges of or near one end of an insulating base of elongated and relatively narrow strip form. After adjustment of the resistyance value, such a strip form insulating base may be rolled up into a cylinder of small diameter suitable for insertion into the casing o-f an electrical measuring or other instrument.

The resistive line pattern may be arranged as a plurality 3,541,491 Patented Nov. 17, 1970 of sec-tions of equal resistance value or, more conveniently, as a first group of sections each having a iirst, relatively high, resistance value, such as 10 ohms each, and a second group of sections each of a second, relatively low, resistance value, such as 0.5 ohm each. Coarse adjustment of the overall resistance value may rst be effected by placing one or more of the high value (10 ohm) sections into series circuit between end connection terminals of the resistor and iine adjustment then eiiected by placing one or more of the low value (0.5 ohm) sections into series circuit with the already chosen high value sections.

In a preferred form however, the respective resistance values of the various line pattern sections are arranged to have a substantially binary relationship with one another, that is to say, each section is of approximately twice the resistance of the next lower value section. By this means the number of individual punch or equivalent cricuit opening operations needed to adjust the overall resistance value to any chosen figure may be substantially reduced.

In order that the nature of the invention may be more readily understood -two particular practical embodiments -thereof will now be described in greater detail and by way of illustrative example only with reference to the accompanying drawings in which:

FIG. A1, by its two portions (a) and (b), illustrates the initial, unadjusted, form of one resistor construction in accordance with the invention;

FIGS. 2, 3 and 4 are enlarged scale fragmentary detail views of the construction of FIG. 1, illustrating the manner -of adjusting the resistance value.

FIG. 5, by its two portions (a) and (b), shows the initial, unadjusted, form of .a second and preferred embodiment of the invention;

FIG. 6 is an enlarged scale fragmentary detail view of part of the construction of FIG. 5, illust-rating the manner of resistance adjustment while FIG. 7 shows a final rolled-up form of either of the embodiments of FIGS. 1-4 or FIGS. 5 and I6 after its resistance value has been adjusted and in readiness for incorporation in an electrical apparatus, for instance in a moving coil type measuring instrument.

In FIGS. 1 and 5, the two sections (a) and (b) should be regarded as joined together at the lines P, P.

Referring first to the embodiment shown in FIGS. 1-4, this comprises a base member 10 in which the form of an elongated strip of constant, relativelynarrow, width and formed of a film of tlexible electrical insulating material such as that known under the registered trademark Mylan The film thickness used is conveniently 0.003 inch. Such base strip 10 has deposited thereon, by any convenient printed circuit technique, a sinuous or meandering line pattern 11 formed of electrical resistive material. Conveniently the deposited resistive material is copper/nickel 0.001 inch in thickness.

The electrical resistance element formed by the line pattern 11 is arranged as a Afirst group of ten sections 12, each of approximately ten ohms resistance value, and a second group of twenty-two sections 13 each of approximately 0.5 ohm resistance value. Such twenty-two sections 13 are conveniently arranged as two subgroups 14a, 14b each having eleven sections as shown.

The strip 1-0 is also provided with two electrically conductive connection terminal portions 15a, 15b at one end. Each of said terminal positions is located closely adjacent a longitudinal side edge of the base strip.

A further electrically conductive deposit is provided on the base strip 10. This comprises stripes 19, 20` closely adjacent the opposite side edges of the base strip. The wider end regions 19a, 20a of such stripes are electrically connected respectively to the terminal portions 15a, 15b while the other ends of the stripes 19, 20-` are electrically interconnected by a transverse coupling stripe 16. An additional short-circuiting strap connection 118 extends between the ends of the regions 19a, 20a, remote from the terminal portions 15a, 15b.

The various sections 12 of the first resistive line pattern group have their respective ends electrically connected to spaced-apart points of the stripe 19', the immediately adjacent ends of each pair of adjacent sections being connected to close spaced positions on the stripe as indicated, for example, at 17a in FIG. 1. The group of sections 12 can, therefore, be considered as a resistance having a plurality of spaced tapping points from which connections areitaken to spaced points of the stripe 19 which, initially, operates to shunt or short-circuit each of the resistance sections.

The various sections 13 of the respective subgroups 14a, 14b are connected in series between the strap connection 18 and the stripe regions 19a, 20a and have the spaced tapping points between adjacent resistance sections each connected by means of a tapping link 17b to the adjacent stripe region 19a or 20a so that each of such resistance sections is initially shunted and virtually short circuited by a conductive path of much lower resistance than the section itself.

In a resistance adjusting operation with this embodiment of the invention the short circuiting strap 18 is left intact when the final resistance value required is less than that of one of the sections 12, e.g., for a resistance of ohms or less. Within this range of resistance, an appropriate number of the lower valued sections 13 is placed in series circuit between the connection terminals 15a, 15b by making a punch hole through the base film 10 and the appropriate one of the stripe regions 19a, 20a, each punch hole being located, as indicated by way of example at the points x, FIG. l, and FIG. 2` between a pair of the links 17 which connect the related stripe regions 19a, 20a to the adjacent resistance section. Each break in the shunting stripe serves to increase the overall resistance value between the end connection terminals of the resistor. When, as is preferably the case, the stripe sections 19a, 20a, act as a virtual short circuit of the associated resistor sections each break operates to introduce an additionally low resistance value unit, e.g., 0.5 ohm, between the connection terminals 15a, 15b.

If a total resistance value greater than that of one section 13, e.g., greater than 10 ohms, is required, the short circuiting strap 18 is rst broken by means of a punch hole at the point y (see also FIG. 3). This makes the rst group of sections 12 available for insertion in series circuit between the connection terminals 15a, 15b. The required number of such high Value, l0 ohms, sections 12 may likewise be placed in series circuit between the connection terminals by making punchings through the base strip and the overlying connection stripe 19 at points such as those indicated at z in FIG. l and, to a greater magnied scale, in FIG. 4. The resistance of the inserted tirst group or high value sections 12 will, of course, be additional to that of any previously inserted second group or low value sections 13. lIn a normal adjustment or calibration operation, a number of the high value sections 12 would lirst be inserted by making appropriate punchings after breaking the short circuiting strap 18. Subsequent final adjustment would then be effected by making appropriate further punchings to place one or more of the low value sections 13 in circuit.

The base strip 10I is conveniently provided also with apertures 21a adjacent the connection terminal end to facilitate its securing after being wound up to form a cylindrical roll as shown in FIG. 7. Additional apertures, as shown at 2lb, may also be provided at chosen positions to assist in the accurate location of a punching tool when making the appropriate breaks in the continuity of the shunting deposit of stripes 19, 19a and 20a. Preferably, the strip-like element is placed within a punching mechanism having a plurality of separate punch tools which are aligned respectively with each of the different available positions, x, y and z by engagement of the apertures 21a, 2lb of the strip with suitable locating projections. Chosen ones of such punch tools may then be operated as required by push buttons or keys or by power means such as a solenoid if the resistance adjustment is being made automatically under the control of automatic Calibrating apparatus.

Referring now to the modied and preferred construction shown in FIG. 5, this comprises a base strip 10 of elongated form as in the first embodiment and which is also provided with a deposited line pattern 11 of resistance material to form the resistive elements. In this embodiment twelve resistance sections 22, 23, 24 31, 32 and 33 are employed, the length and shape of the resistive line pattern being so chosen that their respective resistance values have an approximately binary relationship to one another. For example, the smallest value section 22 may have a resistance of 0.25 ohm, the next larger resistance section 23, a value of 0.5 ohm, the section 24 a value of 1.0 ohm and so on with the highest value resistance section 33 having a value of 512 ohms. The various sections 22-23 are connected in series between end connection terminals 15a, 15b with the aid of junction areas 34-44 forming parts of a further deposit of electrical conductive material on the base film 10. These areas 34-44 are all located near to the end of the strip 10 having the terminal connections 15a, 15b. Such junction areas 34-44 are initially interconnected With one another by links or bridging strips as shown at 45 so that a low value shunting or short circuiting connection is present across each resistance section between the end connection terminals 15a, 15b. By breaking appropriate ones of said links 45 as by means of punch holes, as shown by way of example at q and r in the enlarged scale FIG. 3, any chosen one or more of the resistance sections 22, 23 32, 33 may be brought into series circuit connection between the end terminal connections.

In practice, on account of the tolerance in resistance value needed with each of the deposited resistive sections, a true binary relationship between the various section values may not be satisfactory. A relationship of somewhat less than 2 to l between adjacent sections is advisable. For example, with a tolerance of i15% in the resistance value of each deposited section, the section 22 may be nominally 0.25 ohm, the next section 23 one of 0.39 ohm, the section 24 one of 0.46 ohm and so on with the largest value section 33 having a value of 55 ohms.

In this embodiment apertures as shown at 21a and 2lb may be provided in the base film for securing and location purposes as in the 4first embodiment.

As resistance, once added by making appropriate punchings, cannot afterwards be removed from its connection in circuit between the strips end connection terminals 15a, 15b, the preferred adjustment technique involves the use of a range of external simulating resistances in series with the resistors under adjustment in a balance indicator circuit so that punching can be effected after trial insertion of resistance of substantially the same value.

The further electrically conductive deposits forming the connection terminal portions 15a, 15b, the stripes 19, 20, the straps 16, 18, the junction areas 34-44 and the links 45 are formed simultaneously with the resistive sections of the same resistive material at the line pattern.

After adjustment of the resistive value in the manner described, the base film strip is rolled up into the form of a tight cylinder as shown in FIG. 7 with the end thereof carrying the terminal connections 15a and 15b lying outermost. After securing such rolled-up form, as by means of ties 46 through the apparatus 21a, the resultant small cylindrical element is suitable for mounting within the casing of an electrical measuring instrument or for use as a component resistor in other electrical apparatus. With the embodiment shown in FIG. 5, the major part of the strip length may be rolled up to cylindrical form before the resistance adjustment operation is performed, since all of the positions where punching may be required are located in that part of the strip lying adjacent the end carrying the terminal connections a, 15b. Such a reduction in volume of the resistor during its adjustment enhances its convenience in use.

Various modilications may clearly -be made. For example, some or all of the resistance sections formed by the deposited line pattern may be arranged in parallel with one another by the interconnection of tapping points thereon through the further electrically conductive deposit. By breaking such interconnections at appropriate places, one or more of such parallel sections may be removed from the circuit path between the end connection terminals with resultant increase of overall resistance. Instead of using punched holes to break the shunting connections, notches may be cut in an edge region of the base strip to intersect the further deposit or the material of the latter removed mechanically by an abrasive or scraping action.

We claim:

1. An electrical resistor which comprises a thin ilmlike base member of flexible electrical insulating material and a single pattern of a single chosen electrical resistive material deposited thereon, said single pattern of resistive material including a shunting stripe part of substantial cross-sectional area and low resistivity extending between two opposite terminal-forming Iends and a plurality of resistance-providing sections of small crosssectional area and higher resistivity, each section having each of its ends united with said shunting stripe part at points on the latter which are spacially separated from one another whereby removal of at least part of said shunting stripe between said section ends is effective to remove the circuit continuity initially provided by said shunting stripe across any chosen section and thereby to bring such section into operative circuit between the terminal-forming ends.

2. A resistor according to claim 1 in which the circuit continuity of said part of said shunting stripe between said section ends is broken by removing a part of said deposit and the part of said base member upon which it is deposited.

3. A resistor according to claim 2 in which the circuit continuity of said part of said shunting stripe is broken by punching a hole in said base member.

4. A resistor according to claim 1 in which each of the resistive line sections is substantially short-circuited by the shunting stripe.

5. A resistor according to claim 1 in which said base member is of elongated strip form.

6. A resistor according to claim 5 in which said base strip is of constant width.

7. A resistor according to claim 5 in which each of said resistive line pattern sections is of a sinuous or rectilinear meandering form.

8. A resistor according to claim 7 in which the major part of the length of said meandering line pattern in each section is provided by rectilinear portions disposed transverse t0 the length of the base strip.

9. A resistor according to claim 5 in which said shunting stripe comprises a narrow linear stripe extending longitudinally of the base strip.

10. A resistor according to claim 9 in which said linear stripe is located closely adjacent one side edge of said base strip.

11. A resistor according to claim 5 in which said shunting stripe comprises a plurality of discrete junction areas forming tapping junctions between successive portions of said electrically resistive line pattern and readily removable bridging strips interconnecting adjacent ones of said junction areas.

12. A resistor accordance to claim 11 in which all of said tapping junction areas are located near one end of said base strip.

13. A resistor according to claim 1 which includes a plurality of resistive line pattern sections between tappings which are of substantially equal resistance value.

14. A resistor according to claim 13 which includes a irst group of resistive line pattern sections which each have a substantially equal first resistance value and a second group of resistive line pattern sections which each have a substantially equal second resistance value, the first resistance value being at least one order of magnitude greater than the second resistance value.

15. A resistor according to claim 1 in which the respective resistance values of said resistive line pattern sections have a substantially binary relationship to one another.

16. A resistor according to claim 1 in which the base member is of plastic lilrn.

17. A resistor according to claim 1 in which the deposited electrical resistive material is copper/nickel.

18. A resistor according to claim 1 in which the deposition of said resistive line pattern is effected by a printed circuit method.

19. An electrical resistor comprising a structure in accordance with claim 5 rolled into cylindrical form.

References Cited UNITED STATES PATENTS 1,586,240 5/1926 Cope 338-195 2,758,256 8/1956 Eisler 338-314 X 3,202,952 8/1965 Rayburn 338-308 X 3,441,804 4/1969 Klemmer 338-308 X E. A. GOLDBERG, Primary Examiner U.S.'Cl. X.R.

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