Electricity: circuit makers and breakers – Electric switch details – Contact
Reexamination Certificate
1999-12-20
2001-02-20
Friedhofer, Michael (Department: 2832)
Electricity: circuit makers and breakers
Electric switch details
Contact
C200S246000, C200S271000, C200S275000
Reexamination Certificate
active
06191375
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to electrical switches and more particularly to such switches having improved reliability in closing a circuit path upon contact engagement of a movable electrical contact with a stationary electrical contact and to electrical contacts which provide such improved reliability.
BACKGROUND OF THE INVENTION
There are many applications in which a condition is sensed, for example, pressure of a fluid source, by a condition sensing device which provides an electrical signal upon the occurrence of a selected change in the condition; for example, a dished shaped diaphragm placed in fluid receiving relationship with a fluid pressure source to sense a change in fluid pressure. The diaphragm moves a motion transfer member when the diaphragm moves from one dished shaped configuration to an opposite dished shaped configuration with the motion transfer member applying a force to a movable contact arm, carrying a movable electrical contact, causing the movable contact to move into contact engaging relation with a stationary electrical contact to close a circuit path thereby providing an indication of the change in fluid pressure. Reliability of circuit closure is essential to ensure that the pressure indicator of the system using the pressure source operates as intended. A potential problem which can interfere with normal switch operation is for a small, e.g., microscopic, particulate contamination to find its way on the surface of the contacts at the point of engagement thereby preventing electrical closure of the circuit path even though the contacts have moved into physical engagement with one another. Although the problem normally occurs very rarely, for example, on the order of about 100 ppm, i.e., a 1 in 10,000 probability, this is considered to be unsatisfactory with regard to present day manufacturing standards where zero ppm is the goal.
In order to improve reliability, it is known to provide switches having multiple contact wipers, i.e., essentially a plurality of movable contact arms acting in electrical parallel, wherein the probability of having at least one contact wiper free of contaminants is essentially infinite; however, typically this involves some type of mechanical and electrical interconnection structure as well as a means for providing sufficient force to actuate the multiple wipers. This may be suitable for a more expensive and larger electrical switching systems but is not suitable in low cost indicator switches.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an electrical switch free of the above noted prior art limitations. Another object is the provision of an electrical switch having improved reliability which is low in cost and simple and compact in structure and to electrical contacts for such switches.
Briefly stated, an improved reliability electrical switch and improved reliability electrical contacts for such switches comprises a switch having a movable contact arm mounting a movable contact thereon with the movable contact movable into and out of engagement with a stationary contact. According to a preferred embodiment of the invention, the movable contact arm is an elongated, twistable arm having a center line along the long, or longitudinal axis, and being cantilever mounted with the movable contact having a base with first and second protrusions extending from the base formed on opposite sides of the center line. A force transferred through the movable contact arm will cause the movable contact to move into engagement with the stationary contact with both protrusions coming into contact therewith. If a contaminant is disposed at one of the switching points a moment in the direction of the second uncontaminated point will be generated taking advantage of the natural torsional flexibility of the contact arm with the second contact point forced into electrical engagement with the stationary contact thereby closing the circuit path between the contacts. The probability of contaminants occurring at both contact points decreases from approximately 1 in 10,000 to approximately 1 in 100,000,000. According to a preferred embodiment, a groove is formed in the movable contact by two converging surfaces, the groove extending along and in the direction of the center line of the long axis of the movable contact arm. According to one embodiment the angle formed by the two surfaces is approximately 125° while in a second embodiment the angle is approximately 158°. According to another preferred embodiment, the movable contact is formed with first and second generally semi-hemispheric protrusions spaced from one another on opposite sides of the center line of the long axis of the contact arm.
REFERENCES:
patent: 3189721 (1965-06-01), Lee
patent: 3283108 (1966-11-01), Collier
patent: 3502836 (1970-03-01), Woolley
patent: 3962659 (1976-06-01), Kawase et al.
patent: 5391847 (1995-02-01), Gallone
patent: 6043440 (2000-03-01), Sun et al.
Ney Contact Manual published by Pitney (Electrical Contacts for Low Energy Uses), copyright 1973.
Cardona Dario A.
Leyes Louis J.
Baumann Russell E.
Friedhofer Michael
Telecky , Jr. Frederick J.
Texas Instruments Incorporated
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