US1286373A - Method of and apparatus for making electrical measurements. - Google Patents

Description

E. L. MCDONALD. METHOD OF AND APPARATUS FOR. MAKI NG ELECTRICAL MEASUREMENTS. APPLICATION FILED MAY 8, 1914.

Pafented Dec. s uns.

' 2 SHEETS-SHEET I- E. L. McDONALl METHOD OF AND APPARATUS FOR MAKING ELECTRICAL MEASUREMENTS. APPLICATION FILED MAY 8, 19M.

1,%86,373. I Patented Dec. 3, 1918. W7 2 SHEETS-SHEET 2.

W fig.

l 1 50 9 i I Ilh . ITED STATES PATENT ,OFFICE.

. I nnvair n mcnon'nnn, or SALT LAKE CITY, UTAH.

mnrnon or AND APPARATUS FORMAKING ELECTRICAL MEASUREMENTS.

1,286,373. Specification of Letters Patent. P t t D 3, 1913 Application fll'ed May a, 1914. Serial No. 837,317.

To all whom it may concern: 7 the connections for actual operation not be- Be it known that I, ERVAN L. MoDoN LD, ing shown.

a citizen of the United States, residing at Fig. 3 is a detail plan view of a contact Salt Lake City, in the county of Salt Lake member showing a portion of a coil with 5 and State of Utah, have invented certain which said member makes contact. A

new and useful Improvements in Methods Fig. 4 shows a side elevation of the conof and Apparatus for Making Electrical tact member. I

Measurements, of which the following is a Fig. 5 shows an elevation of the inner specification. side of one of the insulating rings of the' 65. 10 My invention relates to an improved adcontact member. a R

- justable inductance coil adapted for use in Fig. 6 shows a side elevation of the rotat making electrical measurements, and for ing conducting ring of the contact member. various other purposes,,in connection .with Fig. 7 shows a sectional view of the inelectric circuits connected to alternating'or sulating rings and the conducting ring in .15 pulsating electromotive force s. For -ex 7 assembled relation.

ample, the apparatus is of particular advan- Fig. 8 is an enlarged sectional view showtage in connection with my improved ing the means for maki contact with a method of measuring or comparing electrisingle turn of the coil; andv i cal resistances, capacities, inductance's, and ig. 9 is a partial side elevation of the 20 other characteristics of electrical circuits, conducting ring showing the means for maka s briefly-set forth herein, and as moreparing conta ct with a turn of-th'e coil.

ticularly described in my copending-appli Like numerals refer to like parts'iand elecation Serial No. 107,706, filed July 5,1916, 'rnents in the several figures of the drawings, whichis a division of this application..' in which my lnvention is shown as compris- 25 The principal object of this inventionvis ing two electrical conducting coils 10 and to provide an apparatus comprising an in- 11, which are inductively wound on the ductance coil mounted in fiXedpositionfin same core. Each coil is made up 'of a plu-' combination 'with a movable contact a r-. rality of turns which are "insulated from ranged to make contact with any desired eachother and from the turns of the other 30 turn of said coil throughout its-length and coil, the outer coil 11 being wound concenthroughout the periphery of the coil. A trically with the coil 10 and in close proxfurther object is to provide means for makimity thereto. The two coilsfareof equal ing contact with-the inductance coil at any length, preferably made up in sleeve-like desired point between its ends, in combinaform and mounted upon a base plate 12 '35 tion with means for accurately determining of insulating material, as shown in Fig. 2. the relative proportionsof thecoil on each The terminalsllO and 10 of the coil 10 side of the contact point. Still another obare connected by means of the electrical ject is to provide an improved contact for conductors 13 to binding posts 14, which making electrical connection with a-turn of are permanently fixed on the base plate 12.

40 the coil throughout the periphery thereof. The terminals 11 and 11 of the coil 11 Other objects relate to various features of are connected by means of the electrical construction and arrangement which will conductors 15 to the binding posts 16 and 17, appear more fully hereinafter. v .which are also permanently secured to the Other characteristics and advantages-of base plate. A portion of the peripheral sur 45 my invention will be set forth and made apface of the coil 11 is uninsulated, so that parent in the following specification, of each of the turns of-said coil is. exposed on which the accompanying drawings form a the outer periphery thereof, in order that an part. r electrical contact can be made with said In the drawings f I coil at any point between its ends. A guide 1 '50 Figure l is a diagrammatic view of the rod 18, preferably of rectangular cross secgeneral arrangement and connections of my tion, is mounted upon the base plate parapparatus, showingthe uniform and symallel to the coils 10 and 11, and has slidably metrical arrangement of the turns of the mounted thereon a-member 19 which carries inductive coils. v I the contact member 20 adapted to make an 65 Fig. 2 is a plan view ofmy apparatus aselectrical connection with the exposed porsembled in permanent form on a base plate, tions of the turns of the coil 11 at any point between the ends' of said coil. v A graduated '1 scale 21 is secured to the base plate parallel has fixed thereon the binding and 29. By means of the binding posts 14, the inner inductive coil 10 can be connected in circuit with a galvanometer 30, or other detector of feeble currents.

In order to insure greater accuracy in the adjustment of my apparatus I provide a contact member 20 of special form. The outwardly extending portion of the sliding member 19, which carries the contact member 20, is bifurcated, as shown clearly in Fig. 3, to form two forked arms 39, each of which is provided with an arcuate'flange 39 having an inner surface adapted to conform to a portion of the outer contour of an insulating ring 40. Each of these insulating rings is concentric with and has an inner diameter slightly greater than the outer diameter of the coil 11, and is secured to its corresponding arcuate flange 39 by suitable screws, or other means of fastening. The inner plane faces of the rings 40,,which are then spacedapart, serve as guides or bearings' for a rotatable conducting ring 41,

therewith,

which carries means for making electrical contact with a single turn of the coil 11 at any point around the periphery thereof after the sliding member 19 has been moved to the desired position longitudinally of the coil. The conducting ring 41 has an inner diameter greater than the inner diameter of the rings 40, and is provided on each side with a concentric annular flange 41 which is journaled in a corresponding annular groove 40 in the adjacent insulating ring 40. The ring 41 is thus maintained in proper relation to the coil 11, and is prevented from forming an electrical contact except as hereinafter described. The ring 41 is provided at some point on the inner side thereof with a notch 42 having an arcuate surface 43, upon which is mounted a spring connector 44', whose head 45 is adapted to make contact with the outer surface of a turn of the coil 11. .As shown in Fig. 8, the head has a surface conforming to the contour of the conductor of the coil, so that said head will-under the influence of its spring maintain contact with a single turn of said coil uponrotation of posts 37 28,

the ring 41. The head 45 is also beveled at each side of its contacting surface so that it will readily slide over successive turns of the coil, as the entire contact member 20 is I moved longitudinally of the coil on the guide rod 18. Radially outward of the head 45 the ring 41'carries a fixedpointer 46,

whose diametrically opposite points 46 project over graduations 4O on the insulating rings 40, as shown in Fig. 3.

The sliding member 19 carries. a binding post 47, 'to which the conductor 22 leading from the binding post 23 is fastened. The binding post 47 is preferably insulated from the member 19, and is provided with an insulated conductor 48, bymeansof which an electrical connection is made between the conductor 22 and a spring contact 49, which is secured'to, but preferably insulated from, an arm 39 of the member19 and adapted to project into a slot in one of the rlngs 40 to make electrical contact with the ring 41, as shown at 50. Since the operator of the apparatus moves the contact member longitudinally of the coil 11 by means of the sliding member 19, the binding post 47 and associated parts are, preferably insulated therefrom, as stated, in order that said member will form no part of the electrical cir-' cuit. 7 The member 19 is threadedly engaged by a stud 19*, which may be operated by means of a knurled head 19 to engage the guide rod 18, and thereby secure the contact member 20 in any desired position longitudinally of the coil 11. I

-'It will be apparent that by means-of a contact member 20, of the form just described, an electrical connection is made between the conductor 22 and a singleturn of the coil 11' at any point-around the'periphery thereof. A ring 40 being properly graduated to indicate the decimal parts of a turn of the coil 11, the operator may from the positions of the pointers 20 and 4t determine the number of turns and fractional parts thereof which are included in each portion of the coil 11 at each side of the point where an electrical contact is made therewith by the contact member 20. The rings 40 may he graduated to read in opposite directions, and two points 46 provided on the fixed pointer 46 so that the fractional part of aturn included in each portion of the coil 11 at corresponding sides of the con tact member 20 may be read directly or the graduations-may be placed-on the ring 41 and the indicators attached to the rings 40. In order to facilitate the reading of the po sition of the, pointer 46 when it is on the under side of the coil 11, a mirror or other suitable means may be adopted to indicate the reading to the operator in his position above the coil.

I have above described the parts of my apparatus which I prefer to assemble in permanent form on the base plate or standard, so that the apparatus may be conveniently moved from one position to another to be at alltimes in readiness for operation.. Referring to Fig. l, I have shown diagrammatically the connections of my apparatus which are used for measuring or comparing the resistance of electrical conductors. The two resistances 31 and 32, which are to be compared, are connected between'the respective pairs of binding posts-25 and 16 and 26 and 17, the binding posts 25 and 26 being electrically connected to the common connecting plate 27, or to the ground as preferred. The electrical conductors 33, leading from a source of alternating current E.

M. F. or other suitable supply are connected to the binding posts 23 and 24. Thus it will be seen that one terminal of the source of electric pressure is connected to the sliding contact member 20.. The other terminal of this source of pressure is connected to the common connecting plate 27, or to the ground, in case the binding posts 25 and 26 have been connected to the ground. Heferring to Figs, 1 and 2 it will be apparent that two parallel electric circuits are formed between the contact member 20 and the common connecting plate 27 as follows: the circuit 20, 11, 16. 21, 25, and 27, and the circuit 20, 11 17, 32 26 and 27.

It is therefore apparent that-the current entering th coil 11 from the contact member 20 will at any given instant be flowing in opposite directions from the contact member in the two portions of the coil at each side thereof. The inductive action ofone portion of the coil will therefore be opposed to that of the other portion, so that when these two actions are unequal a current will fiow in the coil 10, in response to the voltage induced therein, and cause a deflection or indication of the galvanometer or other detector 30. Then the inductive action of the two portions of the coil 11 on corresponding portions of the coil 10 just neutralize each other there will be no flow of current in the circuit 7 of the coil 10 and no deflection or indication of the galvanometer or other detector.

Having connected my apparatus as above described, the sliding member 19-is adjusted longitudinally of the coil 11 andthe contact member 20 manipulated until the inductive effect of one of the above named branch circuits just balances that of the other branch circuit. In making this adjustment the contact member 20 is moved longitudinally of the coil until a point is reached-w re the detector 30 indicates an approximate balance. The ring 41 is then adjusted within the insulating rings 40 until an exact halance is found. When this point of balance is 11 on each side of the contact member will just'neutralize each other, with the result that the voltages induced in the corresponding proportional parts of coil 10 will neutralize each other. Thus, the point of balance will be indicated by the galvanometer or detector 30, which will fail to register when this point in the adjustment has been reached. The scale 21 being graduated according to the number of turns in the coil 11, the relative number of turns and fractional parts thereof in the two portions of said coil at each side of the contact made by the contact member 20 can readily be determined by reading the indications made by the pointers 20 and 46 on their corresponding scales. The values of the resistances 31 and 32 will then be directly proportional to the number of turns in the two portions of the coil 11 at each side of the contact member, and if one of the resistances 31 or 32 be a known or standard resistance, the value of the other may readily be calculated from the proportion which the number of turns in" the two portions of the coil 11 bear to each other, all of which will be readily understood by anyone skilled in the art to which this invention appertains.

I preferably wind the coils 10 and 11 upon a core of non-magnetic material, since I have found that the results following the use of my apparatus are more accurate when an 9.11 core is used than when a core of magnetic material is employed. The accuracy of the results is also increased by constructing the coils of my apparatus with a relatively low resistance. The speed with which the apparatus may be used may be augmented by graduating the scale 21 to read in both directions, and this also provides a quick and convenient means for checking I have explained my invention in connec- 'tion with one particular form and arrangement of'apparatus', but it will be obvious that it may be embodied in other forms ofapparatus which may be operated upon the principles which have been set forth herein in connection with the particular form of apparatus described, and I do not therefore wish 7 -to be limited to the particular form and arrangement of apparatus herein described. It will be understood that I contemplate changes in form and arrangement and the substitution of equivalents without depart ing from the spirit of the invention as defined in the appended claims.

I claim 1. In apparatus of the class described, an.

electrical coil Wound in sleeve form, a guide extending around the periphery of said coil, and a movable contact element slidably mounted on said guide to contact with said coil at any point around the periphery thereof.

2. In apparatus of the class described, an electrical coil Wound in sleeve form, a guide extending around the periphery of said coil, a movable contact element slidably mounted on said guide to contact With said coil at any point around the periphery thereof, and supporting means for said guide adapted to permit movement thereof longitudinally of said coil. I 3. In apparatus of the class described,- a coil, a contact member movable longitudinally of said coil and arranged to contact.

with any desired turn thereof at any point around the periphery thereof, said contact member comprising relatively movable members, one of said members having graduations thereon, and a pointer carried by the other member.

4. In apparatus of the class described, an

electrical coil Wound in sleeve form With the turns thereof insulated frpm each other, and a contact member slidably mountedto move longitudinally of said coil, said contact mem: ber comprising a movable part adapted to extend around said coil'and to contact With any desired turn thereof at any point around the periphery cf'thef'coil;

5. In apparatus'of the class described, a coil'vvound in sleeveform and mounted in fixed position, the turns'of said coil being insulated from each other but having their outer surfaces uninsulated, a contact mem ber movable longitudinally of said coil, and a guide forsaid contact member mounted alongside said coil, said contact member comprising a part movable throughout the circumference of said coil to contact With any desired turn of said coil at any point throughout the periphery thereof.

6. In apparatus of the class described, an electrical conductor Wound in sleeve form to form a coil, an annular guide member extending around said coil, a contact member slidably mounted on said guide member and having a part adapted toengage any desired turn cf said coil, a supporting bracket for said guide member, and a member upon which said guide member is slidably mounted to move longitudinally of said coil.

7. In apparatus of the class described, an electrical conductor Wound in sleeve form to form a coil, a pair of annular insulating .menibers extending around said coil, 2. conducting member rotatably mounted between said insulating members, a contact element mounted on said conducting member to engage a turn of saidcoil, means to indicate the relative position of said contacting member With respect to said insulating members,

and means to permit bodily movement of said insulating members andsaid conduct ing member longitudinally of said coil.

8.In apparatus of the class described, an

engaged by said flanges, and a contact element resiliently mounted on said conducting member and adapted to engage a turn of said coil. v

. 9. In apparatus of the class described, an electrical conductor Wound in sleeve form to form a coil, a guide member mounted parallel to said'coil, supporting means slidably mounted on said guide member, a pair of annular insulating members carried by said -,,supporting means and extendin around said coll, an annular conducting member having lateral flanges, said insulat ing members having annular grooves to be 'slidably engaged by said flanges, a contact element resiliently mounted on said conducting member and adapted-to engage a turn 0 s around the periphery of the turn of'said coil engaged thereby. a

In testimony whereof, I- have subscribed my'name.

, nRvAN L'. MoDONALD. Witnesses R. W. MCDONALD, M. A- SULLIVAN.

aid coil, means to indicate the posi- 1 tion of said supporting means longitudi

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