Patent US5838615A successfully refreshed from Google Patents.
US4864192A
Expired / Lapsed
US
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CRT magnetic field compensation
Assignee: General Electric Co
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Filing: 1987-11-09
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Granted: 1989-09-05
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Expires: 2007-11-09
Abstract
Abstract As CRT display is housed in a magnetic shield to reduce the image distortions caused by the external magnetic field produced by an NMR scanner. To further improve image quality, three sets of compensating coils are positioned around the CRT display and inside the shield to produce magnetic fields which offset the effects of the residual external magnetic field components that penetrate the shield or enter through the window in the shield used to view the CRT screen.
Inventors
- 👤 Randall H. Buchwald
- 👤 Gary L. Mrotek
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-09 22:45
CPC Classifications
H; H04; H04N; H04N9/00; H04N9/12; H04N9/16; H04N9/29; H01; H01J; H01J29/00; H01J29/003; H01J29/86; H01J29/867; H01J2229/00; H01J2229/0007; H01J2229/003
Claims Analysis
Total Claims: 4
Claim 1
Independent Claim
230 words
In a display which employs an electron beam for producing an image and which is subjected to an external magnetic field, the improvement comprising: a first pair of coils, each disposed along an opposing side of the display, said first pair of coils being supplied with direct current to produce a net compensating magnetic field which extends horizontally across the path of the electron beam that forms the image and which deflects the electron beam; a second pair of coils, one disposed along the top side and the other disposed along the bottom side of the display, said second pair of coils being supplied with direct current to produce a net compensating magnetic field which extends vertically across the path of the electron beam and which deflects the electron beam; and third coil which encircles the path of the image forming electron beam and which is supplied with direct current to produce a net compensating magnetic filed which extends in the general direction of the electron beam of the electron beam and which alters the velocity of the electron beam; a current adjusting means associated with each pair of coils to adjustable control the current flowing through the associated pair of coils; wherein the magnitudes of the dc currents supplied to said coils are adjustable to enable distortions in the image due to the external magnetic field to be reduced.
Claim 2
Dependent Claim
230 words
In a display which employs an electron beam for producing an image and which is subjected to an external magnetic field, the improvement comprising: a first pair of coils, each disposed along an opposing side of the display, said first pair of coils being supplied with direct current to produce a net compensating magnetic field which extends horizontally across the path of the electron beam that forms the image and which deflects the electron beam; a second pair of coils, one disposed along the top side and the other disposed along the bottom side of the display, said second pair of coils being supplied with direct current to produce a net compensating magnetic field which extends vertically across the path of the electron beam and which deflects the electron beam; and third coil which encircles the path of the image forming electron beam and which is supplied with direct current to produce a net compensating magnetic filed which extends in the general direction of the electron beam of the electron beam and which alters the velocity of the electron beam; a current adjusting means associated with each pair of coils to adjustable control the current flowing through the associated pair of coils; wherein the magnitudes of the dc currents supplied to said coils are adjustable to enable distortions in the image due to the external magnetic field to be reduced.
Claim 3
Dependent Claim
41 words
The improvement as recited in claim 1 in which a shield formed of ferromagnetic material is disposed around the display and said coils, and an opening is formed in the shield through which the image may be viewed by an operator.
Claim 4
Dependent Claim
16 words
The improvement as recited in claim 1 in which the display is a cathode ray tube.
References Cited (Backward Citations)
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USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1992-09-04 | 1993-03-06 | 1993-09-05 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1996-09-04 | 1997-03-06 | 1997-09-05 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2000-09-04 | 2001-03-06 | 2001-09-05 | $7700.00 | Window Closed / Lapsed |