US 2019457 A
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Description (OCR text may contain errors)
Oct. 29, 1935. 5, ape 2,019,457
RESISTOR Filed Feb. 20, 1951 Patented Oct. 29, 1935 UNITED 1 STATES PATENT OFFICE usss'roa tollughllbmmh m February :0. m1. Serial No. man
s mum. (cl. m-sa) tacttoaresistancewindingatthepermanentpositionofthecontactonthewinding,andtoclectroplatethcwindingand subsequently solderthe contact to 'thewinding without intermediately diitufrblns the contact position.
4 herw p eistosclectivelyeiectroplate thepartsofaresistoratwhichcontacttothe resistoristobemadebypassingcurrenttothe resistorin the platingbathatthepoints atwhich plating is desired, and maintaining the'plating voitagelowenoughsothatduetotheresistance of the resistor itself, the current density at points remote from those at which current enters the $2212: bath will not rise high enough 'to permit Afurtherpurposeistotapareslstorbymeans of spring contacts secured at its extremities and also, if desired, at an intermediate point or points, soldering the contacts to the plated surface of the resistance winding.
dfurtherl urposeistoslotacontacttoaresistor to facilitate soldering to the plated.surface of the resistor.
A further purpose is to apply solder at spaced points on a iixed resistor determining the extent of solder application by the extent of preliminary treatment of the resistor.
Afurtherpurposeistomakecontacttoaresistance winding by caps which are soldered to an electroplated deposit upon the winding.
A further purpose is to use a solder band for clamping purposes to ensure good electrical contact with a fixed resistor.
Further purposes will appear in the specification and in the claims My invention relates both to the methods in-- volved and to apparatus by which the methods maybe carriedout.
In the drawing! illustrate only a few of the many variations in which my invention may. be embodied,-as well as =1 illustrations 5 of the apparatus required. The forms shown have been selected because of their case of construction, satisfactory operation and convenient illustration of the principles involved.
l 'igureiisaperspectiveviewillustratingmy resistor in position upon a winding machine.
I'igureSisaticviewofaneleotroplatingbathshowingmyresistorinpcsltion iorp atins.
I'laure4isaperspectiveviewofmyresistor platingoftheends. v
is a perspective view of a fragment is a fragmentary central vertical sece soldered resistor. 7showsamodiiiedformofresistorin view. 8 is a perspective view of a somewhat form of resistor showing the parts ted. Figureilisscents-a1verticalsectionofaresistor diifering slightly from that of Figure 8.
In the drawing like numerals refer to like radio manufacturer and the electrical industry generally demand a fixed resistor which, besides being mechanically sturdy has an accurately predetermihed and reproducible resistance. because the design of the circuit as a whole and oi the instruments in it presupposes a deflnite resistance. Much progress has been made in producing resistance wire of fairly uniform cross-section, but the connections to the resistance wire from the main circuit have not always been satisfactory either as to mechanical strength, contact resistance or accuracy of positioning.
In the past resistors have been prepared by winding the resistance wire on a form, regulating the pitch and length of the winding as accurately as commercial winding conditions will permit, and then securing to the winding" contacts 59 spaced a predetermined distance a art. Resistors prepared by this method will vv nlybe of the desired standard resistance if the resistance wire is of uniform cross section throughout, if the pitch of the winding is always uniform, if the u on Of diameter of the form upon which the coil is wound is invariable and if the contact resistances are always the same. None of this is strictly true. so that as a result the fixed resistors heretofore prepared have varied considerably in resistance.
By my invention I permit accurate standardization of the resistors and eliminate most of the variables referred to above. After the winding is finished, I bridge it by the contacts which are to be permanently affixed to the resistor, but instead of initially making permanent attachment, I temporarily secure the contacts and measure the resistance across them, varying their distances apart until the resistance between the contacts is that desired for the standardized resistor.
Then, having temporarily aflixed the contacts at the points desired for the predetermined resistance, I permanently secure them to the winding without intermediately changing the positions of the contacts. Once the resistance is standardized, no variation in resistance, or at most a very slight and definite variation, is subsequently permitted.
My method of attachment of the contacts to the resistor, while particularly suitable to a resistor which has been standardized by measurement of its resistance between contacts only temporarily secured to the winding, is also generally useful as a means of physical attachment of contacts to a resistance winding, whether or not the resistance has been previously measured.
The standardizing of a resistor is clearly illustrated in Figure 1. A winding 20 of suitable resistance wire, preferably a nickel chromium iron alloy of which one is very well known under the trade name of nichrome, is in position upon a winding machine. Of the winding machine the chuck 2| alone is shown with the wire 22 leading off to the supply spool of the machine. The chuck 2| rotatably supports a coil form 23, which I prefer to make of porcelain, or other ceramic material, desirably but not necessarily unglazed, as for example that sold under the trade name of "Isolantite. The form 23 may either be solid as shown in Figures 1, 2 and 4, or hollow, as shown at 23 in Figures 5 and 8. If the form 23 is not itself electrically insulating, I cover it with suitable insulating material.
At spaced points along the winding 20 I place metallic clip contacts 24 and 25, each of which comprises a slightly resilient curved gripping end 25 and a lateral extension 21, which is desirably provided with notches 28 and a hole 29 to assist in connecting to the external electric circuit. The gripping end 26 is preferably outwardly bent at its extremity an to assist in spreading its opposing sides when the clip contact is placed upon the winding. The gripping end 26 is longitudinally slotted at 3| to permit the introduction of solder and to facilitate electroplating as later explained. I
After winding the coil 20 in any suitable manner, the clip contacts 24 and 25 are snapped upon the coil at spaced points as shown and current is passed from the contacts through the coil by connections 32 and 33 from a source 34. The circuit includes a suitable current-measuring instrument G upon which the resistance between the contacts 24 and 25 may be determined.
After the initial determination of the resistance, the spacing between the contacts 24 and 25 will if necessary be changed, either manually or mechanically, until the reading upon the current-measuring instrument G indicates that the resistance between the contacts 24 and 25 has reached the correct value. Once this has been determined, the clip contacts 24 and 25 will be subsequently retained in their previous positions 5 so that the resistance of the winding will not be changed after standardization.
While I believe that my method of standardizing the resistance of the resistor is in itself highly desirable, without regard to the means of perma- 10 nent attachment of the contacts to the winding, and, in fact, without need of permanent attachment, I find that the method of permanent attachment invented by me greatly assists in placing the resistor in use without variation of its 15 resistance subsequent to standardization. Of course my method of attachment is also applicable to resistors which are not standardized.
In Figure 3 I illustrate a conventional electroplating equipment comprising a vat 35 contain- 20 ing a solution 36 in which are located a suitable anode 31 connected to a current source through a lead 38 and a cathode 39 consisting of a resistance winding 20 electrically connected to the current source through the contacts 24 and 25, the 25 electrically conducting supporting frame 40 and the lead 4i 'Since the resistance of the winding 20 is fairly high, and since current flowing from the lead 4| to the central portion of the winding 20 must 30 traverse the winding 20 from the nearer of the contacts 24 or 25, the current density upon the surface of the winding 20 rapidly decreases from a maximum at the ends 42 and 43, adjacent to the contacts 24 and 25, to a minimum at the cen- 35 ter 44. By regulating the voltage between the plating terminals, I maintain the current density at the mid-portion of the winding 20 sufiiciently low so that no plating takes place there while I have a high enough current density adjacent to 40 the contacts 24 and 25 so that plating takes place upon the winding at the ends 42 and 43.
It will readily be seen that plating of the portion of the winding 20 intermediate the contacts 24 and 25 would be undesirable as it would 45 coat the wire with an electrically conducting material and, especially where copper plating is used, would greatly reduce the resistance of the winding.
It will of course be evident that if electroplat- 5O ing were desired in any other localized zone of the winding other than the ends, it could be obtained by simply making contact to the winding in the plating bath at the point at which plating was desired. 55
To some extent the slit 3| in the gripping end 26 of the contact assists in plating by allowing free access of the plating solution to the resistance wire beneath the contact.
Plating with copper is particularly desirable 50 where the resistance wire used is nichrome, because soldering of nichrome wire is diflicult, while soldering upon the copper-plated surface of the nichrome wire is relatively easy.
In practice I maintain a current density low 65 enough so that the only plating which takes place occurs upon the turns of the wire immediately adjacent to the contacts 24 and 25 and upon the surface of the contacts 24 and 25, particularly upon the inner surface of the curved gripping ends 26 of the contacts 24 and 25.
Subsequent to plating I wash the resistor to remove all traces of the plating solution and dry it carefully before soldering.
Thus the juxtaposed surfaces of the contacts 24 or 2! and the winding II are electroplated as indicatedinI'lgure4,inwhichathincover-ing of plating. preferably copper,'is present upon the winding and the contacts at the ends I! and 43. After plating I solder the contacts, preferably by flowing molten solder through the longitudinal slits ii of the contacts. The solder unites with the electroplated turns of the winding and with the contacts I and II, thus firmly scaring the contactstothewinding asseeninl'igure'sb and 6. Solder is indicated at It around the turns of the winding 20 and between the winding and the gripping end 28 of the slip contact. I
Where nichrome wire is used, the solder will not extend beyond the plated portion of the wire,
so that thereis no danger of short-circuiting by solder turns .of the winding beyond the contacts.
The bar if made of some such material as nichrome, can, therefore, be plated or otherwise coated at the predetermined and can then befiooded with solder to short-circuit the turns which are coated with (as in Figure 5) or without (as in Figure 5a) attachment of terminalsatthetime. Itcanthenbesoldinthis condition for later use in connection with ter- -minals or can have the terminals applied to it by the solderaspartof the'sameoperationorby subsequent soldering. Since the coated nichrome wire will take solder freely where coated and will not take is otherwise, the solder can be applied by dipplns and automatically will be limited to the coated section. Moreover a solder covering about the wire (with or-without prior coating of the nichrome to. cause the solder toadhere to it) acts as a clamp to ti hten the wire upon the mount as the solder contracts in cooling. This also tightens the solder about the wire. giving a good contact from theclamp action where there is any soldering.
The product will of course ordinarily be lacquered to make it water-proof and to hold the wire-in place,
It will be noted that no change'in the positions of the contacts 24 and it takes place subsequent to the final setting of the contacts during of the winding between the contacts 24 and Ills produced during permanent attachment of the contacts to The only resistance change which is possible isachangeinthecontactreaistancebetween the contacts 24 and 25 and the winding. and this I had to be very slight and to be nearly uniform for diil'erent resistors, so that allowance for it can be made in the original standardization.
My invention is by no nieans limited to securing contacts to the ends of a resistor. For example, in Figure 7 I illustrate an intermediate tap It which is fastened to the winding in the manner which I have outlined and whose position is determined by measurement tween the tap 46 and either of the contacts 24 and 28 in the manner previously discussed for positioning the contacts 24 and 25. In plating the resistor of Figure 7, contact is made at 24, 46 and 25.
My invention may also be applied to resistors of the cartridge type intended to be held by spring contacts. In Flgurefi Iillustrate such a resistor winding 20 upon -a hollow form 23', as
- well as contact caps 41 and it. The extremities oi'the resistance be- 3 position P atory for plating. The caps may beprovided either withopenendsasinl'igures, sothattheymaybemovedalongthewindingto provide any desired space, or they may have closed ,ends as shown 'at 41' and I8 in Figure 9. The form of Figure 8-has the advantage that penetration of the plating solution into the inierior of the caps occurs-more readily.
While plating of the resistors when the contacts are in position is much preferable to] plating before the contacts are applied, it will be understood that part of the advantage of my invention could be obtained by initially plating and subsequently applying the contacts. In that case. special contacts for use-in the plating bath alone could be applied at the points at which the permanent contacts were to be afilxed, and the platingcontactsmightthenberemovedtopermit attachment of permanent contacts.
It will be evident that, by platingthe parts in 2 their final positions, I avoid shifting of the contacts subsequent to standardization, and insure that plating is restricted to the portion of the winding close to the contacts.
Inviewoimyinventionanddisclosurevariations and modifications to meet individual whim 'or particular need will doubtless become evident predetermined areas and at predetermined 40 pwinssalongthewiretheextentofthewire between the determining the resistance .01 the resistor, metallic contacts located at the electrodeposited areas and solder between the electrodepcsited coatings and the metallic cbnis tacts, the distribution of, the solder being restricted Substantially to 1 the electrodeponted areas and covering substantially the entire width of the'electroplated areas, whereby the resistance at the contacts is reduced to a minimum 60 and the resistance ofthe resistor is due to the predetermined spacing of the electrodeposited areas.
2. Inafixedresistor,atuhularform,awinding upon the form of metallic resistance wire which takes solder with diillc'ulty, a plurality of areas ofreadily solderable metallic coatings upon the wire, the spacing between the areas being predetermined according to the desired resistance of the resistor, spring metallic contacts gripping the winding at the areas and solder between the contacts and the metallic coatings, the solder short-circuiting the turns at the coated areas for substantially the entire width of the coated areas and being substantially restricted in its 65 distribution to the coated areas, whereby the resistance of the resistor is due substantially whoily to the predetermined spacing of the coated areas and the contact resistance is reduced to a minimum' 3. In a fixed resistor, a tubular form, a windingupontheform of metallicresistance wirewhich takes solder with difliculty, a plurality of areas of readily solderable metallic coatings upon the wire, thespacing between the areas being predetermined according to the desired resistance of the resistor, spring metallic contacts gripping the winding at the areas, each contact having a soldering opening adjoining its coated area and solder between the coatings and the contacts and along' the edges of the openings through the contacts, the solder short-circuiting the turns at the coated areas and extending substantially for the axial extent of the coated areas and the distribution of the solder being substantially restricted to the coated areas, whereby the uncertainty in resistor manufacture due to the contact resistance is reduced to a minimum and the reproducibility of the resistance is improved because the resistance of the resistor is due substantially wholly to the predetermined spacing of the coated areas.
EDMUND GILBERT LODGE.