Lead for resistor element

A resistor device of simple construction particularly adapted for use as a precision, low ohmic value resistor. The terminal leads are axially aligned and extend outwardly from a molded housing. The inner end of each lead is shaped into a flat surface to facilitate the welding thereto of a resistor element and to minimize twisting of the embedded end of the lead. A radially extending disc shaped portion on each lead is adjacent the flat portion and is embedded in the molded housing to prevent axial movement of the embedded end of the lead. The embedded flat and disc shaped portions serve to minimize forces from acting on the weld joints to break the welds. The resistance element is free standing wire shaped into a serpentine configuration and embedded in the molded housing.

BACKGROUND OF THE INVENTION 
The present invention relates to molded electrical components and is 
particularly useful in resistor elements of low ohmic values that have a 
housing molded thereabout. Low value resistance elements are useful in the 
use of meters, such as voltmeters, wherein the meter is connected in shunt 
across the resistance element. It is desirable that the element have a 
very precise value of resistance and that it dissipate little energy from 
the circuit in which is it connected. From a manufacturing standpoint it 
is desirable that the resistance element have as few parts as possible, be 
simple to assemble (preferably automatically), and result in a high yield 
of commercially acceptable devices. 
In the manufacture of resistor elements themselves, and in their handling 
during shipping and during the process of their assembly and incorporation 
into an electronic system or end product, they sometimes are subjected to 
considerable physical abuse. 
It has been found in the past that resistor devices in which a resistance 
element was welded to electrical leads extending from a molded housing 
experienced an undesirably high failure rate because the weld joints 
broke. 
The present invention minimizes the above problem by providing a simple 
structure in which the ends of connector leads are so shaped that when 
embedded within the molded housing they substantially eliminate twisting 
and axial forces on the embedded ends of the leads, thereby minimizing 
destructive forces on the weld joints.

DESCRIPTION OF PREFERRED EMBODIMENT 
Referring in detail to the drawings, the resistor device 10 is comprised of 
a resistance element 12 that is made of a selected resistance material 
having a low ohmic value and is so constructed and arranged to provide a 
desired resistance value. Resistance element 12 may be any commercially 
available material and may be in any cross sectional shape. As examples, 
the resistance wires may range in diameter from 0.0035 inch to 0.0285 
inch. Representative values of resistance may be between 0.01 and 10 ohms. 
Suitable wires are sold under the trademarks Cupron and Evanohm by Wilber 
B. Driver Company, Newark, N.J. Resistance element 12 is secured, as by 
welding, at each end to a respective flat portion 14 and 16 at the 
adjacent ends of connector leads 20 and 22. Resistance element 12 and 
connector leads 20 and 22 are illustrated as having circular cross 
sections. It is desired that resistance element 12 be rigid enough to be 
self supporting in its desired position relative to leads 20 and 22 in the 
absence of any supporting means. 
Each lead has a disc shaped portion 26, 28 formed integrally thereon 
adjacent the respective flat portions 14 and 16. The integral flat 
portions 14, 16 and disc shaped portions 26 and 28 are formed on leads 20 
and 22 as by swaging. 
A housing 32 of an electrical insulating plastic material is molded around 
resistance element 12 and around the adjacent ends of leads 20 and 22. Any 
suitable molding material may be used. I have used a commercially 
available material identified as DC 307 Silicone Molding Compound, a 
product of Dow Corning Company, Midland, Mich. 
As illustrated, the flat portions 14, 16 and disc shaped portions 26 and 28 
of the leads are within the molded housing 32. Desirably, the flat 
portions 14 and 16 are wider than the diameters of connector leads 20 and 
22 to serve as anchors in the molded housing 32 to prevent twisting and 
rotation of the leads relative to resistance element 12. The flat surfaces 
14 and 16 also facilitate the welding of the resistance element 12 to 
leads 20 and 22. The embedded disc shaped portions 26 and 28 also serve as 
anchors to minimize axial movements of leads 20 and 22 relative to 
resistance element 12. The anchors minimize forces acting on the welded 
joints between the ends of resistance element 12 and leads 20 and 22 and 
thus minimizes broken welds, a source of component failure. 
The fact that the welded resistance element 12 is self supporting between 
leads 20 and 22 considerably simplifies the manufacture of the devices and 
adapts them for automatic assembly, thus minimizing cost. It is not 
necessary to wind the resistance element on a supporting core or bobbin, 
nor is it necessary to employ the stainless steel cup shaped end caps that 
are conventional in the art. The elimination of the end cups, or 
equivalent devices, eliminates additional welded or soldered joints and 
thus eliminates the respective thermal EMFs that unavoidably accompany 
such joints. 
The particular serpentine shape illustrated in the accompanying drawing is 
but one example of the shapes the resistance element may take. Other 
shapes may be used without departing from the teachings of the present 
invention. Similarly, the resistance element may have cross sectional 
shapes other than circular. 
The illustrated resistor device may be manufactured by employing known 
methods. Resistance element 12 may be shaped and formed in any suitable 
manner, either manually or automatically. Since the manner of forming the 
element is not the subject of this invention, it will not be further 
discussed. Resistance element 12 and leads 20, 22 may be clamped in a 
suitable jig to permit welding of the ends of the resistance element to 
the flat portions 14 and 16 on the leads. The illustrated unitary 
structure of leads 20 and 22 simplifies the manufacture of this 
subassembly. Subassemblies then may be inserted into molds and the 
housings 32 molded by any suitable molding technique. 
In its broader aspects, this invention is not limited to the specific 
embodiment illustrated and described. Various changes and modifications 
may be made without departing from the inventive principles herein 
disclosed.