1. Field of the Invention
The present invention relates to hermetic terminals used to carry electrical current to a compressor. More specifically, the present invention relates to identifying relative electrical capacities of conductor pins used in hermetic terminal assemblies, and identifying relative electrical capacities of completed hermetic terminals.
2. Description of Related Art
Hermetic terminals of the general type of this invention are well-known in the art, and examples of same are illustrated in U.S. Pat. No. 3,988,053 to Dodenhoff, dated Oct. 26, 1976 and U.S. Pat. No. 3,551,191 to Elbling et al., dated Dec. 29, 1970. Terminals of this type traditionally comprise a generally cup-shaped metallic body having a plurality of openings in the end wall of the body, through each of which a conductor pin extends, the pin being hermetically sealed to the body, by means of a glass to metal seal, for example.
The aforesaid conductor pins have traditionally been constructed of solid stainless steel, such as No. 446 stainless steel. For many applications, solid stainless steel conductor pins are suitable because steel is a satisfactory electrical conductor for most applications, and particularly since the coefficient of thermal expansion of the steel pin relates closely to the coefficient of thermal expansion of the glass and the cup-shaped metallic body. Another desirable feature of stainless steel is that it is corrosion resistant, it being understood that in hermetic compressor terminals of the type with which the present invention is concerned, one end of the conductor pins will be extending outside of the enclosure housing of the compressor, and in many cases will be exposed to the ambient, whereby corrosion of the exposed ends is possible if the conductor pins are not constructed of a corrosion resistant material.
It will be understood that it is the usual practice to weld tabs to the exposed outer ends of the conductor pins, which tabs are adapted to receive terminal clips carried by the wiring which extends from the source of electrical power. Thus, the electrical current is transmitted from the wiring to the conductor pins by means of the mechanical interconnection which exists between the terminal clips and the tabs. The current then passes through the conductor pins into the enclosure, the pins being connected at their inner ends to the terminals of the compressor by any suitable means.
The problem with the above described solid stainless steel conductor pins is that steel possesses limited current carrying capability, which becomes a concern when used with a compressor which requires high current. For compressors involving high current applications, it is known to use a stainless steel pin having a copper core. This way, the corrosion-resistant and thermal properties of steel are coupled with the high electrical conductivity of copper. Because such copper-cored pins perform well when used in high current applications, they are widely used in hermetic terminals.
Manufacturers produce hermetic terminals for varying applications. Thus, manufacturers use both solid stainless steel conductor pins as well as conductor pins having the above described copper core. The problem manufacturers experience is that it is difficult to distinguish a stainless steel conductor pin having a copper core from a conductor pin of pure stainless. Thus, the two types of pins can possibly be confused.
It is known to mark the pins with identifiers such as colored tabs, but such an approach is inadequate because the tabs are typically installed in one of the last steps of terminal assembly, by which time a "mix-up" of the pins may have already occurred. Furthermore, colored tabs can be difficult to see when the terminal is welded into a refrigeration compressor, for example.
In a related application, with electrical cables having more than one conductor within an insulation layer, it has been known to mark one or more of the conductors with a groove, or other formation along the longitudinal axis of the conductor. Thus, with a long length of cable, the conductors at one exposed end can be identified at the other exposed end by locating the conductor having the identifying mark. The other conductors can then be identified by their positions relative to the conductor having a marking. However, this method is unsuitable as a cost effective means to clearly distinguish stainless steel conductor pins from those pins having a copper core.