US4996461A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Closed loop bucking field system
Assignee: Raytheon Co
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Filing: 1989-09-07
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Granted: 1991-02-26
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Expires: 2009-09-07
Abstract
Abstract A system for improving the operation of a cathode ray tube (CRT) is disclosed whereby interference caused by external magnetic fields is mitigated. The system comprises a CRT having a CRT magnetic shield housing and at least one electromagnetic field sensor disposed adjacent to the inner surface of the CRT housing. Sensors form to generate a reference magnetic field and to generate a sensor output signal in response to the detection of both the reference field and an external field as sensed within the housing. A bucking field coil drive circuit is provided in electrical communication with the field sensor, the drive circuit being operative to generate a bucking field coil drive signal responsive to the field sensor output signal. A bucking field coil is disposed circumferentially about the CRT and is driven by the bucking field coil drive signal. The bucking field coil generates a bucking electromagnetic field in opposition to the sensed external magnetic field, thereby opposing and reducing the degrading effects of the external magnetic field on the CRT display.
Inventors
- 👤 Robert Bentley
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-09 22:15
CPC Classifications
H; H04; H04N; H04N9/00; H04N9/12; H04N9/16; H04N9/29; H01; H01J; H01J29/00; H01J29/003; H01J2229/00; H01J2229/0007; H01J2229/003; H01J2229/0038
Claims Analysis
Total Claims: 20
Claim 1
Independent Claim
167 words
A system for improving the operation of a cathode ray tube (CRT) by reducing interference caused by external electromagnetic fields comprising: a CRT having a CRT magnetic shield housing at least one electromagnetic field sensor disposed adjacent to an inner surface of the CRT magnetic shield, said sensor being formed to generate a reference electromagnetic field and to generate a sensor output signal in response to detection of both the reference field and an external field as sensed within the shield; a bucking field coil drive circuit in electrical communication with said field sensor, the bucking field drive circuit being operative to generate a bucking field drive signal responsive to said field sensor output signal; and a bucking field coil disposed circumferentially about said CRT and driven by said bucking field coil drive signal to generate a bucking electromagnetic field in opposition to the sensed external magnetic field, to oppose and reduce the degrading effects of the sensed external magnetic field on the operation of the CRT.
Claim 2
Independent Claim
167 words
A system for improving the operation of a cathode ray tube (CRT) by reducing interference caused by external electromagnetic fields comprising: a CRT having a CRT magnetic shield housing at least one electromagnetic field sensor disposed adjacent to an inner surface of the CRT magnetic shield, said sensor being formed to generate a reference electromagnetic field and to generate a sensor output signal in response to detection of both the reference field and an external field as sensed within the shield; a bucking field coil drive circuit in electrical communication with said field sensor, the bucking field drive circuit being operative to generate a bucking field drive signal responsive to said field sensor output signal; and a bucking field coil disposed circumferentially about said CRT and driven by said bucking field coil drive signal to generate a bucking electromagnetic field in opposition to the sensed external magnetic field, to oppose and reduce the degrading effects of the sensed external magnetic field on the operation of the CRT.
Claim 3
Dependent Claim
20 words
The system as recited in claim 1 further comprising a plurality of said sensors disposed about the CRT inner surface.
Claim 4
Dependent Claim
31 words
The system as recited in claim 1 wherein said sensor comprises an "E" core, said "E" core having an open end disposed in abutting contact with the CRT shield inner surface.
Claim 5
Dependent Claim
43 words
The system as recited in claim 3 wherein said sensor further comprises a sensor drive coil disposed about a center leg of the "E" core and first and second detector coils disposed about first and second outer legs of the "E" core, respectively.
Claim 6
Dependent Claim
27 words
The system as recited in claim 4 wherein said first and second detector coils are disposed in electrical series connection and both wound in the same direction.
Claim 7
Dependent Claim
29 words
The system as recited in claim 5 further comprising a sensor drive signal circuit operative to generate a sensor drive signal having signal portions of alternating polarity signal portions.
Claim 8
Dependent Claim
28 words
The sytem as recited in claim 1 wherein said sensor output signal, in the absence of a sensed external field, comprises a first spiked signal of alternating polarity.
Claim 9
Dependent Claim
46 words
The system as recited in claim 7 wherein, in the presence of a sensed external field, said sensor output signal comprises a second spiked signal of alternating polarity, the amplitude of said spiked signal varying in response to the strength of the sensed external magnetic field.
Claim 10
Dependent Claim
43 words
The system as recited in claim 8 wherein the external magnetic field is additive with respect to the amplitude of a spiked signal portion having a first polarity and subtractive with respect to the amplitude of spiked signal portions having a second polarity.
Claim 11
Dependent Claim
23 words
The system as recited in claim 8 wherein the amplitude of the alternating polarity spiked signal corresponds to detection of the reference field.
Claim 12
Dependent Claim
52 words
The system as recited in claim 1 wherein the bucking field drive circuit is operative to segregate a first portion of the sensor output signal attributable to detection of the external field and to regulate the amplitude of said bucking field drive signal in response to said sensor output signal first portion.
Claim 13
Dependent Claim
28 words
The system as recited in claim 1 further comprising a plurality of field sensors exposed at spaced locations adjacent the inner surface of the CRT magnetic shield housing.
Claim 14
Dependent Claim
172 words
Sensor apparatus for sensing an electromagnetic field within a ferromagnetic body comprising: an "E" core sensor body having an open end disposed in abutting contact with the ferromagnetic body, the "E" core having a center leg and first and second outer legs; a sensor drive coil disposed about the "E" core center leg; and first and second detector coils disposed about the "E" core first and second outer legs, respectively, said first and second detector coils being disposed in electrical series connection; said sensor drive coil being operative to receive a sensor drive signal and generate a reference field in response thereto; said first and second detector coils being operative to generate a minimum output signal in response to a generation of said reference field, when no external field is present and to generate a sensor output signal in response to the generation of said reference field when an external field is present, said sensor output signal being useful to generate a bucking electromagnetic field in response to the external magnetic field.
Claim 15
Dependent Claim
172 words
Sensor apparatus for sensing an electromagnetic field within a ferromagnetic body comprising: an "E" core sensor body having an open end disposed in abutting contact with the ferromagnetic body, the "E" core having a center leg and first and second outer legs; a sensor drive coil disposed about the "E" core center leg; and first and second detector coils disposed about the "E" core first and second outer legs, respectively, said first and second detector coils being disposed in electrical series connection; said sensor drive coil being operative to receive a sensor drive signal and generate a reference field in response thereto; said first and second detector coils being operative to generate a minimum output signal in response to a generation of said reference field, when no external field is present and to generate a sensor output signal in response to the generation of said reference field when an external field is present, said sensor output signal being useful to generate a bucking electromagnetic field in response to the external magnetic field.
Claim 16
Dependent Claim
20 words
The sensor as recited in claim 14 wherein said first and second detector coils are wound in the same direction.
Claim 17
Dependent Claim
38 words
The system as recited in claim 14 wherein said sensor drive signal comprises an alternating polarity signal, the amplitude of said alternating polarity signal being sufficient to a magnetic path within the ferromagnetic body adjacent the sensor body.
Claim 18
Dependent Claim
26 words
The system as recited in claim 16 wherein said sensor output signal, when no external field is present, comprises a first spiked signal of alternating polarity.
Claim 19
Dependent Claim
45 words
The sensor as recited in claim 17 wherein said sensor output signal, in the presence of an external field, comprises a second spiked signal of alternating polarity, the amplitude of said spiked signal varying in response to the strength of the sensed external magnetic field.
Claim 20
Dependent Claim
39 words
The sensor as recited in claim 18 wherein the second spiked signal comprises a first polarity portion and a second polarity portion, said external field being additive with respect to only one of said first and second polarity portions.
References Cited (Backward Citations)
US3757154A
Cited
US3867668A
Cited
JPS5247321A
Cited
JPS55104187A
Cited
US4560900A
Cited
US4380716A
Cited
FR2555385A1
Cited
US4556821A
Cited
US4922153A
Cited
US4851737A
Cited
US4899082A
Cited
US4864192A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1994-02-25 | 1994-08-27 | 1995-02-26 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1998-02-25 | 1998-08-27 | 1999-02-26 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2002-02-25 | 2002-08-27 | 2003-02-26 | $7700.00 | Window Closed / Lapsed |