Electricity: measuring and testing – Fault detecting in electric circuits and of electric components – Of individual circuit component or element
Reexamination Certificate
1999-11-15
2001-08-14
Metjahic, Safet (Department: 2858)
Electricity: measuring and testing
Fault detecting in electric circuits and of electric components
Of individual circuit component or element
C324S1540PB, C324S072500, C439S482000, C439S700000
Reexamination Certificate
active
06275054
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to electrical contact systems and more particularly to spring biased contacts used, for example, to interconnect test apparatus, analyzers and the like to circuit boards and the like to be tested.
BACKGROUND OF THE INVENTION
Electrical contact systems having spring loaded, movable contacts are employed in circuit board and electronic circuit test systems and the like in which electrical contact is made between a circuit or device and one or more test points. The electrical contact system generally comprises a metal barrel having a contact plunger telescopically slidable therein and a spring disposed within the barrel for biasing the contact plunger to a normally outward position. The contact plunger has an outer end provided with a probe tip of a selected configuration to engage a test pad or the like of a circuit board or other device. As test systems employ higher radio frequencies in testing procedures there is an increasing need to provide the shortest possible so-called electrical path in a matched impedance system. Contact assemblies have moving parts and inherently have a degree of mismatch within the manufacturing tolerances and materials employed. Any mismatches which do occur are directly related to the length of the contact assemblies so that the longer the assembly, the greater the mismatch. In copending U.S. application Ser. No. 09/145,914, now Pat. No. 6,053,777 which issued Apr. 25, 2000 and is assigned to the assignee of the present invention, the subject matter of which is incorporated herein by this reference, an electric contact assembly having an improved short length is described accomplished, inter alia, by attaching the ground plunger to the coaxial cable. The system has an inner contact assembly having an electrically conductive inner plunger barrel received on the signal conductor of the coaxial cable and spaced from the ground plunger in coaxial relationship therewith. An inner contact portion of an inner plunger of the contact assembly is received in the plunger barrel and biased by a first spring to extend a selected amount in a given direction beyond the ground plunger when in at rest position and a second spring biasing the ground plunger and coaxial cable in the given direction with the second spring having a spring force greater than the first spring. In operation, the inner contact portion which extends outwardly beyond the ground plunger and outer contact portion will engage the test site and be forced inwardly until it is coplanar with the outer contact portion of the ground plunger. Both contact portions, as well as the coaxial cable, will then move inwardly together for another selected distance to ensure that predicatable contact pressure is obtained for both the inner and outer contact portions. By combining the motion of the inner and the outer contact portions, the overall length of the assembly is shortened thereby minimizing any impedance mismatch. However in certain applications, it is preferred to mount the coaxial cable so that it is immovable relative to the test fixture.
The ground plunger and the inner contact assembly of the electrical assembly described in Ser. No. 09/145,914 are maintained in concentric, coaxial relation with one another using first and second spaced apart annular spacer members of dielectric material so that the effective dielectric therebetween approximates that of air. In a modified embodiment, the spacer members are formed into an integral structure with a reduced diameter intermediate web joining two spacer portions, the reduced diameter web providing an open annular space with a resulting near air dielectric.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide electrical contact apparatus for interconnecting test apparatus and the like with contact pads of a circuit board or other electrical device to be tested with a device having positive contact pressure which provides an improved short and direct electrical path. Another object of the invention is the provision of a coaxial contact assembly of the type described above in relation to Ser. No. 09/145,914 having an improved impedance matching for particular use with radio frequency electrical signals and the like yet one which includes a ground plunger which is movable relative to the coaxial cable. Another object is the provision of an improved electrical coaxial contact system having improved impedance matching for use with high frequency electrical signals which is relatively low in cost yet highly reliable, creating minimal electrical noise. Yet another object of the invention is the provision of a coaxial contact system having improved dielectric spacers to maintain the inner and outer contact assemblies in concentric, coaxial relationship with one another.
Briefly, an electrical contact system made in accordance with a first embodiment of the invention comprises a ground plunger barrel in which is telescopically, slidably received an electrically conductive, generally cylindrical interface ductor member having a hub portion from which a plurality of longitudinally extending fingers are formed, preferably with radially inwardly extending portions at their free distal ends and spaced from one another to form an opening. The hub is fixed to the ground conductor of a coaxial cable with the fingers received in the bore of the ground plunger barrel and biased into firm electrical engagement therewith. The electrically insulated signal conductor extends through the opening formed by the distal end of the fingers. The fingers are electrically isolated from an inner contact plunger mounted on a signal sleeve in turn disposed on the end of the signal conductor of the coaxial cable by an electrically insulative, generally annular, separator member. A dielectric spacer is fixedly mounted on the inner contact plunger barrel adjacent to the outer end of the ground plunger to maintain a coaxial relationship between the inner contact plunger and the ground plunger barrel. The ground plunger barrel is biased to a normally outward position by a coil spring received about the interface member and extending between the hub of the interface member and the inner end of the ground plunger barrel. The several parts are received in a fixed outer barrel and fixed thereto by means of crimping through the hub of the interface member.
According to a modified embodiment, the inner end of the ground plunger is formed with resilient fingers while the interface ductor member is a solid tubular member, i.e., it has no fingers. In yet another embodiment, a reduced diameter portion of the ductor member is received on the inner dielectric layer of the coaxial cable providing a space for the ground plunger spring to thereby enable a reduced diameter contact system. In other embodiments, dielectric spacers used to maintain the inner and outer contact assemblies in concentric, coaxial relation to one another are formed of a relatively thin tube of dielectric material which extends from a first diameter portion received on the inner contact assembly to a second diameter portion received within the ground plunger with the ratio of air to solid dielectric between the first and second diameters remaining substantially constant along the axial length of the spacer.
REFERENCES:
patent: 2480963 (1949-09-01), Quinn
patent: 3416125 (1968-12-01), Theve
patent: 3976352 (1976-08-01), Spinner
patent: 4012105 (1977-03-01), Biddle
patent: 4138643 (1979-02-01), Beck et al.
patent: 4174875 (1979-11-01), Wilson et al.
patent: 4245189 (1981-01-01), Wahl et al.
patent: 4397519 (1983-08-01), Cooney
patent: 4734046 (1988-03-01), McAllister et al.
patent: 4740746 (1988-04-01), Pollock
patent: 5175493 (1992-12-01), Langgard
patent: 5291129 (1994-03-01), Kazama
patent: 5576631 (1996-11-01), Stowers et al.
patent: 5850147 (1998-12-01), Stowers et al.
patent: 5936421 (1999-08-01), Stower et al.
patent: 6034532 (2000-03-01), Tarzwell
patent: 6053777 (2000-04-01), Boyle
Haug John A.
Metjahic Safet
Nguyen Jimmy
Rika Electronics International, Inc.
LandOfFree
Electrical contact system does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Electrical contact system, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Electrical contact system will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2498113