EMI/RFI shielding assembly for cathode ray tube monitors

• US 4,710,591 A
• Filed: 10/06/1986
• Issued: 12/01/1987
• Est. Priority Date: 10/06/1986
• Status: Expired due to Fees

• Current Assignee: Unisys Corporation
• Original Assignee: Unisys Corporation
• Inventors: Rochester, Charles R. Jr.
• Primary Examiner(s): Grimley, Arthur T.
• Assistant Examiner(s): TONE, DAVID
• Application Number:
  US06/924,428
• Time in Patent Office: 421 Days
• Field of Search: 174/35 R, 174/35 GC, 219/10.55 D, 358/245, 358/246, 358/247
• US Class Current: 174/372
• CPC Class Codes: H01J 2229/8633 Meshes and patterns
• CPC Class Codes: H01J 29/868 Screens covering the input or output face of the vessel, e.g. transparent anti-static coatings, X-ray absorbing layers
• CPC Class Codes: H04N 5/65 Holding-devices for protective discs or for picture masks

Abstract

The present disclosure describes a shielding assembly which finds particular application in the suppression of electromagnetic emissions from the face of a CRT mounted in a metal chassis. The assembly effects an emissions seal with two electrical terminations. A filter window with two contiguous but non-coextensive glass plates which provide a ledge around the window periphery is provided. An O-ring disposed on said ledge and wrapped with a sleeve of the fine metallic mesh laminated between the glass plates is compressed against a metallic bezel for a first termination. An EMI/RFI shielding gasket assembly is interposed between the bezel and the chassis to provide a second termination. '"'"'

Claims

1. A shielding assembly for suppressing electromagnetic emissions from the face of a cathode ray tube mounted in a metallic chassis comprising:

a filter window positioned in proximity to the face of said cathode ray tube, said filter window being comprised of a pair of contigous glass plates having metallic mesh interposed therebetween, said pair of glass plates including an inner plate situated closest to said face of said cathode ray tube and an outer plate, the corresponding dimensions of said outer plate being smaller than those of said inner plate, whereby a ledge is formed around the periphery of said window, said metallic mesh protruding from said plates as a sleeve along said ledge,

a resilient member disposed on said ledge and encircling said filter window, said sleeve being wrapped upon said resilient member,

a metallic bezel, clamping means disposed on said bezel for retaining said filter window therein, said resilient member being positioned adjacent the inner surface of said bezel, said clamping means including a movable member having an arcuate section at one extremity thereof, an adjacent planar section having a slot-like aperture therein for accommodating a screw, and a section orthogonal to said planar section at the opposite extremity thereof, said last mentioned section having a tail-like medial projection,

said bezel having a tapped hole for receiving said screw and an oversized locating hole to accommodate said projection, said locating hole having a depth greater than the length of said projection, whereby the portion of the orthogonal section adjacent said projection abuts the inner surface of said bezel as said screw is torqued, said arcuate section contacting the surface of said inner glass plate whereby a pressure is applied normal to the glass surface, thereby compressing said resilient member against said bezel and effecting a first electrical termination.

2. A shielding assembly as defined in claim 1 further including means for mounting said bezel on said chassis, an emissions shielding gasket interposed between said mounted bezel and said chassis to provide a second electrical termination, thereby perfecting an emissions seal.

3. A shielding assembly as defined in claim 2 further characterized in that said emissions shielding gasket comprises a double-action, elongated, articulated structure of spring-like material having a substantially planar carrier enclosed thereby, said structure includes an arcuate section having opposed extremities bent toward each other to form a respective pair of spaced-apart, coplanar sections, means for mounting said gasket on the outer surface of said chassis encircling the opening thereof through which said cathode ray tube is mounted, the mounting of said bezel on said chassis causing the bezel to wipe against and to compress said arcuate section of said gasket, thereby establishing electrical contact between said bezel and said chassis.

4. A shielding assembly as defined in claim 3 wherein said resilient member is an O-ring formed of insulative material.

5. A shielding assembly as defined in claim 4 characterized in that said sleeve is wrapped around said O-ring in a single-turn configuration.

6. A shielding assembly as defined in claim 5 wherein said mesh is of copper and contains approximately 100 openings per linear inch.

7. A shielding assembly as defined in claim 6 characterized in that said glass plates are curved with a like radius of curvature.

8. A shielding assembly as defined in claim 7 further including a standoff of predetermined thickness interposed between said planar section of said movable member of said clamping means and said bezel in accordance with the thickness of said filter window.

9. A shielding assembly as defined in claim 8 further characterized in that the surfaces of the arcuate section of the movable member of said clamping means are coated with a soft plastic material.