CA1135321A - Tilted unitary degaussing coil arrangement - Google Patents
Tilted unitary degaussing coil arrangementInfo
- Publication number
- CA1135321A CA1135321A CA000345759A CA345759A CA1135321A CA 1135321 A CA1135321 A CA 1135321A CA 000345759 A CA000345759 A CA 000345759A CA 345759 A CA345759 A CA 345759A CA 1135321 A CA1135321 A CA 1135321A
- Authority
- CA
- Canada
- Prior art keywords
- envelope
- coil
- degaussing
- shield
- flared
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J29/00—Details of cathode-ray tubes or of electron-beam tubes of the types covered by group H01J31/00
- H01J29/003—Arrangements for eliminating unwanted electromagnetic effects, e.g. demagnetisation arrangements, shielding coils
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N9/00—Details of colour television systems
- H04N9/12—Picture reproducers
- H04N9/16—Picture reproducers using cathode ray tubes
- H04N9/29—Picture reproducers using cathode ray tubes using demagnetisation or compensation of external magnetic fields
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J2229/00—Details of cathode ray tubes or electron beam tubes
- H01J2229/0007—Elimination of unwanted or stray electromagnetic effects
- H01J2229/0046—Preventing or cancelling fields within the enclosure
- H01J2229/0053—Demagnetisation
Landscapes
- Engineering & Computer Science (AREA)
- Multimedia (AREA)
- Signal Processing (AREA)
- Physics & Mathematics (AREA)
- Electromagnetism (AREA)
- Video Image Reproduction Devices For Color Tv Systems (AREA)
- Testing, Inspecting, Measuring Of Stereoscopic Televisions And Televisions (AREA)
- Shielding Devices Or Components To Electric Or Magnetic Fields (AREA)
Abstract
RCA 73,479 ABSTRACT OF THE INVENTION
A single degaussing coil for a kinescope has a first portion located along a first side of the base of a generally pyramidal kinescope envelope or bulb. Second and third portions of the coil extend along portions of second and third sides of the base, and are joined by a fourth portion of the coil lying between the juncture of the neck and the bulb.
A single degaussing coil for a kinescope has a first portion located along a first side of the base of a generally pyramidal kinescope envelope or bulb. Second and third portions of the coil extend along portions of second and third sides of the base, and are joined by a fourth portion of the coil lying between the juncture of the neck and the bulb.
Description
~13-53Z~
RCA 73,479 This invention relates to an arrangement for degaussing color picture tubes having magnetic shields by use of a unitary degaussing coil in a tilted or skewed position.
Color television displays are often accomplished by means of shadow-mask picture tubes. In such tubes, a plurality of electron beams are directed from slightly different points of origin towards a screen coated with fluorescent phosphors. The phosphors are grouped in triads or groups of three, each member of which fluoreseces in a different primary color when illuminated by an electron beam. Each member of each triad is made responsive to a single one of the plurality of electron beams by means of a shadow-mask. The shadow-mask is a thin conductive shield with a multitude of perforations precisely located with respect to each triad of color phosphors. The shadow-mask ideally allows the phosphor of a particular color to be illuminated only by an electron beam originating at a particular location. Thus, ~5 with three electron beams originating in slightly different locations, each of the color phosphors of a trio is pure, i.e. t iS illuminated by only one electron beam, and gradations of color may be achieved by appropriate control of the source of electrons.
In the past, color television displays were sensitive to the influence of the earth's magnetic field.
The magnetic field passing through the kinescope deflects the electron beams away from their intended paths and changes the apparent source of the electron beams arriving at the shadow-mask in a manner dependent upon the orientation of the picture tube relative to the earth's magnetic field, thereby impairing color purity. Early attempts to correct this problem involved the use of field neutralizing coils, as described in United States Patent ~3~2~ .
1 -2- RCA 73,479 No. 2,921,226 issued January 12, 1960 to Vasilevskis. In the field neutralization arrangement, a direct current is passed through one or more coils arranged about the kinescope in such a manner as to balance to zero or neutralize the earth's field. This required adjustment by an expert, and required readjustment if the television was moved to a new location.
Another approach to correcting color purity problems resulting from the earth's magnetic field involves the use of magnetic shields. In such an arrangement, a hollow shield in the form of the frustum of a cone surrounds the region through which the electron beam travels before reaching the shadow-mask and screen.
The high permeability of the shield diverts extraneous magnetic fields away from the electron beam. It was found, however, that the permeable magnetic shield was capable of becoming magnetized and, when so magnetized, itself perturbed the color purity. Degaussing arrangements were then devised to demagnetize the shield and the shadow-mask. The degaussing is accomplished by passing an alternating current of initially large magnitude through one or more coils arranged about the shadow-mask and magnetic shield as described in United States Patent No. 2,962,621 issued November 29, 1960 to Fernald. The magnitude of the alternating current is then gradually reduced to zero and the magnetization of the shield and shadow-mask is reduced. A coil disposed along the periphery of the shadow-mask as illustrated by Fernald tends to produce a relatively small magnetic field near the center of the shadow-mask and screen. Thus, effective degaussing with such a coil requires currents which may be undesirably large.
In order to increase the magnetic flux through the magnetic shield and through the screen without excessive coil currents, arrangements such as those described by Norley in United States Patent No. 3,322,998 issued May 30, 1967 and by Matsushima et al., in United ~13~ -'CA 73,479 States Patent No. 3,872,347 issued March 18, 1975 were devised. In the Norley and Matsushima arrangements, a pair of coils are arranged symmetrically on the picture tube, with each coil having a portion lying along the periphery of the shadow-mask and a portion extending towards the neck of the tube. The two-coil arrangements produce a magnetic field the lines of which are transverse to or across the longitudinal axis of the tube. "`his "cross axial" degaussing field approach using a pair of coils provides effective degaussing. However, the two coils require additional labor for mounting as compared with a single coil, and their interconnection may give rise to incorrect wiring. Furthermore, the two-coil arrangement tends to require a greater length of conductor than the single-coil type, and may respond to the deflection yoke field with currents which perturb color purity.
It is desirable to have a degaussing arrangement using a unitary coil requiring a relatively short conductor length which provides degaussing performance substantially equivalent to that of the two-coil system, combined with the simplicity and short conductor length of the single-coil type.
In a preferred embodiment, the present invention includes a degaussing arrangement for a color television picture tube. The picture tube comprises an envelope having a flared portion with large and small ends, a faceplate portion adjacent the large end, and a neck portion coaxial with the flared portion and joined to the small end. The picture tube further comprises a shadow-mask enclosed within the envelope adjacent the faceplate portion and an electron gun assembly enclosed within the neck portion of the envelope. A flared magnetic shield is enclosed within the envelope and has large and small ends. The shield is 3~ adjacent a segment of the flared portion of the envelope.
he degaussing arrangement further comprises a single degaussing coil encircling the flared portion of the envelope, with the axis of the degaussing coil tilted relative to the axis of the flared envelope portion in such manner as to dispose a first segment of the circumference of the coil ~1353~ RCA 73,479 in a position overlying a region of the envelope adjacent a portion of the large end of the shield. A second segment of the circumference of the coil, diametrically is disposed oppositely to the first segment, in a position which is - contiguous with a region of the envelope adjacent a portion of the small end of the shield and which is located more remotely from the axis of the flared envelope portion than is the periphery of the opening at the small end of the shield. Means are also provided for supplying a variable alternating current solely to the single degaussing coil to effect degaussing of the shadow-mask and the magnetic shield.
- In the Drawings:
FIGURES la and lb illustrate in perspective views a picture tube with a degaussing arrangement embodying the invention;
FIGURES 2a and 2b illustrate in respective rear and side views the arrangement of FIGURE la and lb;
Z FIGURE 3 is a cross-sectional view of the picture -~
tube of the preceding FIGURES;
FIGURE 4billustrates magnetic field distributions associated with the invention and FIGUR~S 4a and 4c illustrate magnetic field distributions associated with the prior art;
and FIGURE 5 is a semipictorial diagram containing block, schematic and pictorial portions depicting the arrangement of the invention as used with a television receiver.
Referring to the drawings:
In FIGURES la and lb, a picture tube designated generally as 10 includes an envelope consisting of three distinct portions. A frusto-conical or pyramidal portion 12a of the envelope is joined at the small end of the frusto-35 conical section with a neck portion 12b of the envelope. A
flattened faceplate portion 12c closes the large end of frusto-conical portion 12a. A base 14 at the end of neck section 12b remote from the frusto-conical portion supports pins by which connections are made to the electron gun 40 assembly mounted within neck portion 12b. A high-voltage, : .
~35~Z~ RCA 73,479 anode or ultor connection button 16 is located on the surface of frusto-conical section 12a. ~ degaussing coil designated generally as 20 is located on the exterior surface of envelope 12. Coil 20 has a generally rounded triangular shape. One leg 20a of coil 20 is adjacent the periphery of the junction of faceplate 12c and frusto-conical section 12a of the envelope. i~dditional legs 2Ob and 20c of coil 20 form a vertex extending towards and around the junction of the neck and frustum portions of the envelope. A pair of leads 22 are taken from coil 20 for connection to a source, not shown, by means of which a current of variable amplitude is passed through coil 20 for degaussing.
FIGURES 2a and 2b illustrate in respective rear and side views the arrangement of FIGURES la and lb. The rear view of FIGURE 2a illustrates the somewhat rectangular outline of the large end of the frusto-conical section which is common in the picture tubes currently in use. r~he neck portion, however, is circular as seen in this rear view for ease in mounting deflection yokes and other neck components.
The top cross-sectional view of kinescope 10 in FIGURE 3 illustrates a phosphor screen 330 adjacent the inside of faceplate 12c of the envelope. A shadow-mask 332 is mounted near phosphor layer 330 by means of mounting brackets 334 and 336. ~lounting brackets 334 and 336 also support a hollow magnetic shield 338 formed of a magnetically permeable material. Shield 338 preferably has the general form of frusto-conical portion 12a of the envelope of picture tube 10. Both the large and small ends of shield 338 are open to allow the passage of one or more electron beams from an electron gun assembly 340 mounted within neck portion 12b to phosphor layer 330.
l`he direction of magnetic field distribution generated by a degaussing coil mounted concentric with the 35 picture tube is illustrated in cross-sectional view in FIGURE 4a. In a test of such an arrangement, the magnitude of the field available for degaussing at the center of screen 332 was 0.2 gauss with a coil producing a maximum of 20 gauss.
The coil also produced between 0.3 and 0.6 gauss at the 40 periphery of the opening at the small or entrance end of ~ 1 3S 3 Z~ RCA 73,479 magnetic shield 338.
By contrast, the inventive arrangement has as its core more of magnetic shield 338, and produces a magnetic field distribution somewhat as shown in FIGURE 4b. The center of the screen is at a region of greater field strength. Using a degaussing coil producing the same maximum field strength as that of FIGURE 4a, the degaussing field at the center of the screen was 0.5 gauss, which is almost double that of the prior art arrangement. The corresponding field strengths at the entrance end of magnetic shield 338 were 7.5 gauss at the side nearest the coil, l gauss at the side farthest from the coil and 4 gauss at the other two sides. Thus, the fields available for 16 degaussing the magnetic shield are much greater in the inven-tive arrangement than in the arrangement of FIGURE 4a when the coils have the same number of ampere-turns.
FIGURE 4c illustrates the magnetic field distribu-tion associated with two-coil arrangements such as those of Norley and ~latsushima. In the arrangement of FIGURE 4c, the combined effect of the pair of coils causes a substantial magnetic field flux transverse to the axis of the picture tube in the region of magnetic shield 338. At the faceplate and shadow-mask end of the tube, the magnetic field lines are parallel with the shadow-mask and tend to have a uniform strength through the center of the shadow-mask. The degaussing provided by the inventive arrangement is substan-tially equivalent to that provided by the two-coil arrange-ment of FIGURE 4c in that it provides degaussing for the internal magnetic shield as well as for the mask and frame assembly. The inventive degaussing arrangement is less costly by virtue of requiring less conductor length than either the single-coil arrangement of FIGURE 4a or the two-coil arrangements. The inventive arrangement is easier to assemble than the two-coil arrangements and cannot be wired incorrectly.
FIGURE 5 illustrates a circuit by which the degaussing coil may be energized with an alternating current having an initially large amplitude which decreases to a substantially zero amplitude. In FIGURE 5, a portion of a .
- ~35Q~Z~ ~CA 73,479 television receiver includes a plug 510 adapted to be connected to the alternating power mains. A switch 512 and fuse 514 couple the mains across primary winding 516a of a power transformer 516. A secondary winding 516b of trans-former 515 produces alterna~ing current which is utilized by a power supply illustrated as a block 518 for energlzing the remainder o~ the television receiver, illustrated as a block 520. The alternating-current mains are also coupled through a thermally-response resistor 530 to leads 222 of coil 220.
Thermally-responsive resistor 530 has a positive temperature characteristic, 50 that the resistance of the thermistor is low at room temperature and increases with increasing temperature.
At room temperature, the resistance of thermistor 530 is low. When switch 512 is closed in order to energize the television receiver, power is applied through transformer 516 to power supply 518 to energize the receiver. At the same time, an alternating voltage is applied across the series combination of thermistor 530 and coil 220. Because the resistance of thermistor 530 is initially low, a relative-ly large alternating current flows through coil 220. The current flow through thermistor 530 causes the thermistor to heat, and its resistance to rise. The increasing resistance decreases the current flow resulting from the applied voltage and partially compensates for the reduced power dissipated in the thermistor at the decreased current. The temperature of the thermistor continues to rise, resulting in a rapid reduction in the current to a small limiting value as the 30 resistance of the t~m~tor reaches a maximum. A circuit arrangement using temperature-responsive resistors is des-cribed in United States Patent 4,~24,427 issued to Belhomme on ~lay 17, 1977.
'hile the arrangement as described uses an 35 internal magnetic shield, those skilled in the art will recognize that the principles of the invention are equally applicable to a kinescope fitted with an external shield.
~.
'' ~:
RCA 73,479 This invention relates to an arrangement for degaussing color picture tubes having magnetic shields by use of a unitary degaussing coil in a tilted or skewed position.
Color television displays are often accomplished by means of shadow-mask picture tubes. In such tubes, a plurality of electron beams are directed from slightly different points of origin towards a screen coated with fluorescent phosphors. The phosphors are grouped in triads or groups of three, each member of which fluoreseces in a different primary color when illuminated by an electron beam. Each member of each triad is made responsive to a single one of the plurality of electron beams by means of a shadow-mask. The shadow-mask is a thin conductive shield with a multitude of perforations precisely located with respect to each triad of color phosphors. The shadow-mask ideally allows the phosphor of a particular color to be illuminated only by an electron beam originating at a particular location. Thus, ~5 with three electron beams originating in slightly different locations, each of the color phosphors of a trio is pure, i.e. t iS illuminated by only one electron beam, and gradations of color may be achieved by appropriate control of the source of electrons.
In the past, color television displays were sensitive to the influence of the earth's magnetic field.
The magnetic field passing through the kinescope deflects the electron beams away from their intended paths and changes the apparent source of the electron beams arriving at the shadow-mask in a manner dependent upon the orientation of the picture tube relative to the earth's magnetic field, thereby impairing color purity. Early attempts to correct this problem involved the use of field neutralizing coils, as described in United States Patent ~3~2~ .
1 -2- RCA 73,479 No. 2,921,226 issued January 12, 1960 to Vasilevskis. In the field neutralization arrangement, a direct current is passed through one or more coils arranged about the kinescope in such a manner as to balance to zero or neutralize the earth's field. This required adjustment by an expert, and required readjustment if the television was moved to a new location.
Another approach to correcting color purity problems resulting from the earth's magnetic field involves the use of magnetic shields. In such an arrangement, a hollow shield in the form of the frustum of a cone surrounds the region through which the electron beam travels before reaching the shadow-mask and screen.
The high permeability of the shield diverts extraneous magnetic fields away from the electron beam. It was found, however, that the permeable magnetic shield was capable of becoming magnetized and, when so magnetized, itself perturbed the color purity. Degaussing arrangements were then devised to demagnetize the shield and the shadow-mask. The degaussing is accomplished by passing an alternating current of initially large magnitude through one or more coils arranged about the shadow-mask and magnetic shield as described in United States Patent No. 2,962,621 issued November 29, 1960 to Fernald. The magnitude of the alternating current is then gradually reduced to zero and the magnetization of the shield and shadow-mask is reduced. A coil disposed along the periphery of the shadow-mask as illustrated by Fernald tends to produce a relatively small magnetic field near the center of the shadow-mask and screen. Thus, effective degaussing with such a coil requires currents which may be undesirably large.
In order to increase the magnetic flux through the magnetic shield and through the screen without excessive coil currents, arrangements such as those described by Norley in United States Patent No. 3,322,998 issued May 30, 1967 and by Matsushima et al., in United ~13~ -'CA 73,479 States Patent No. 3,872,347 issued March 18, 1975 were devised. In the Norley and Matsushima arrangements, a pair of coils are arranged symmetrically on the picture tube, with each coil having a portion lying along the periphery of the shadow-mask and a portion extending towards the neck of the tube. The two-coil arrangements produce a magnetic field the lines of which are transverse to or across the longitudinal axis of the tube. "`his "cross axial" degaussing field approach using a pair of coils provides effective degaussing. However, the two coils require additional labor for mounting as compared with a single coil, and their interconnection may give rise to incorrect wiring. Furthermore, the two-coil arrangement tends to require a greater length of conductor than the single-coil type, and may respond to the deflection yoke field with currents which perturb color purity.
It is desirable to have a degaussing arrangement using a unitary coil requiring a relatively short conductor length which provides degaussing performance substantially equivalent to that of the two-coil system, combined with the simplicity and short conductor length of the single-coil type.
In a preferred embodiment, the present invention includes a degaussing arrangement for a color television picture tube. The picture tube comprises an envelope having a flared portion with large and small ends, a faceplate portion adjacent the large end, and a neck portion coaxial with the flared portion and joined to the small end. The picture tube further comprises a shadow-mask enclosed within the envelope adjacent the faceplate portion and an electron gun assembly enclosed within the neck portion of the envelope. A flared magnetic shield is enclosed within the envelope and has large and small ends. The shield is 3~ adjacent a segment of the flared portion of the envelope.
he degaussing arrangement further comprises a single degaussing coil encircling the flared portion of the envelope, with the axis of the degaussing coil tilted relative to the axis of the flared envelope portion in such manner as to dispose a first segment of the circumference of the coil ~1353~ RCA 73,479 in a position overlying a region of the envelope adjacent a portion of the large end of the shield. A second segment of the circumference of the coil, diametrically is disposed oppositely to the first segment, in a position which is - contiguous with a region of the envelope adjacent a portion of the small end of the shield and which is located more remotely from the axis of the flared envelope portion than is the periphery of the opening at the small end of the shield. Means are also provided for supplying a variable alternating current solely to the single degaussing coil to effect degaussing of the shadow-mask and the magnetic shield.
- In the Drawings:
FIGURES la and lb illustrate in perspective views a picture tube with a degaussing arrangement embodying the invention;
FIGURES 2a and 2b illustrate in respective rear and side views the arrangement of FIGURE la and lb;
Z FIGURE 3 is a cross-sectional view of the picture -~
tube of the preceding FIGURES;
FIGURE 4billustrates magnetic field distributions associated with the invention and FIGUR~S 4a and 4c illustrate magnetic field distributions associated with the prior art;
and FIGURE 5 is a semipictorial diagram containing block, schematic and pictorial portions depicting the arrangement of the invention as used with a television receiver.
Referring to the drawings:
In FIGURES la and lb, a picture tube designated generally as 10 includes an envelope consisting of three distinct portions. A frusto-conical or pyramidal portion 12a of the envelope is joined at the small end of the frusto-35 conical section with a neck portion 12b of the envelope. A
flattened faceplate portion 12c closes the large end of frusto-conical portion 12a. A base 14 at the end of neck section 12b remote from the frusto-conical portion supports pins by which connections are made to the electron gun 40 assembly mounted within neck portion 12b. A high-voltage, : .
~35~Z~ RCA 73,479 anode or ultor connection button 16 is located on the surface of frusto-conical section 12a. ~ degaussing coil designated generally as 20 is located on the exterior surface of envelope 12. Coil 20 has a generally rounded triangular shape. One leg 20a of coil 20 is adjacent the periphery of the junction of faceplate 12c and frusto-conical section 12a of the envelope. i~dditional legs 2Ob and 20c of coil 20 form a vertex extending towards and around the junction of the neck and frustum portions of the envelope. A pair of leads 22 are taken from coil 20 for connection to a source, not shown, by means of which a current of variable amplitude is passed through coil 20 for degaussing.
FIGURES 2a and 2b illustrate in respective rear and side views the arrangement of FIGURES la and lb. The rear view of FIGURE 2a illustrates the somewhat rectangular outline of the large end of the frusto-conical section which is common in the picture tubes currently in use. r~he neck portion, however, is circular as seen in this rear view for ease in mounting deflection yokes and other neck components.
The top cross-sectional view of kinescope 10 in FIGURE 3 illustrates a phosphor screen 330 adjacent the inside of faceplate 12c of the envelope. A shadow-mask 332 is mounted near phosphor layer 330 by means of mounting brackets 334 and 336. ~lounting brackets 334 and 336 also support a hollow magnetic shield 338 formed of a magnetically permeable material. Shield 338 preferably has the general form of frusto-conical portion 12a of the envelope of picture tube 10. Both the large and small ends of shield 338 are open to allow the passage of one or more electron beams from an electron gun assembly 340 mounted within neck portion 12b to phosphor layer 330.
l`he direction of magnetic field distribution generated by a degaussing coil mounted concentric with the 35 picture tube is illustrated in cross-sectional view in FIGURE 4a. In a test of such an arrangement, the magnitude of the field available for degaussing at the center of screen 332 was 0.2 gauss with a coil producing a maximum of 20 gauss.
The coil also produced between 0.3 and 0.6 gauss at the 40 periphery of the opening at the small or entrance end of ~ 1 3S 3 Z~ RCA 73,479 magnetic shield 338.
By contrast, the inventive arrangement has as its core more of magnetic shield 338, and produces a magnetic field distribution somewhat as shown in FIGURE 4b. The center of the screen is at a region of greater field strength. Using a degaussing coil producing the same maximum field strength as that of FIGURE 4a, the degaussing field at the center of the screen was 0.5 gauss, which is almost double that of the prior art arrangement. The corresponding field strengths at the entrance end of magnetic shield 338 were 7.5 gauss at the side nearest the coil, l gauss at the side farthest from the coil and 4 gauss at the other two sides. Thus, the fields available for 16 degaussing the magnetic shield are much greater in the inven-tive arrangement than in the arrangement of FIGURE 4a when the coils have the same number of ampere-turns.
FIGURE 4c illustrates the magnetic field distribu-tion associated with two-coil arrangements such as those of Norley and ~latsushima. In the arrangement of FIGURE 4c, the combined effect of the pair of coils causes a substantial magnetic field flux transverse to the axis of the picture tube in the region of magnetic shield 338. At the faceplate and shadow-mask end of the tube, the magnetic field lines are parallel with the shadow-mask and tend to have a uniform strength through the center of the shadow-mask. The degaussing provided by the inventive arrangement is substan-tially equivalent to that provided by the two-coil arrange-ment of FIGURE 4c in that it provides degaussing for the internal magnetic shield as well as for the mask and frame assembly. The inventive degaussing arrangement is less costly by virtue of requiring less conductor length than either the single-coil arrangement of FIGURE 4a or the two-coil arrangements. The inventive arrangement is easier to assemble than the two-coil arrangements and cannot be wired incorrectly.
FIGURE 5 illustrates a circuit by which the degaussing coil may be energized with an alternating current having an initially large amplitude which decreases to a substantially zero amplitude. In FIGURE 5, a portion of a .
- ~35Q~Z~ ~CA 73,479 television receiver includes a plug 510 adapted to be connected to the alternating power mains. A switch 512 and fuse 514 couple the mains across primary winding 516a of a power transformer 516. A secondary winding 516b of trans-former 515 produces alterna~ing current which is utilized by a power supply illustrated as a block 518 for energlzing the remainder o~ the television receiver, illustrated as a block 520. The alternating-current mains are also coupled through a thermally-response resistor 530 to leads 222 of coil 220.
Thermally-responsive resistor 530 has a positive temperature characteristic, 50 that the resistance of the thermistor is low at room temperature and increases with increasing temperature.
At room temperature, the resistance of thermistor 530 is low. When switch 512 is closed in order to energize the television receiver, power is applied through transformer 516 to power supply 518 to energize the receiver. At the same time, an alternating voltage is applied across the series combination of thermistor 530 and coil 220. Because the resistance of thermistor 530 is initially low, a relative-ly large alternating current flows through coil 220. The current flow through thermistor 530 causes the thermistor to heat, and its resistance to rise. The increasing resistance decreases the current flow resulting from the applied voltage and partially compensates for the reduced power dissipated in the thermistor at the decreased current. The temperature of the thermistor continues to rise, resulting in a rapid reduction in the current to a small limiting value as the 30 resistance of the t~m~tor reaches a maximum. A circuit arrangement using temperature-responsive resistors is des-cribed in United States Patent 4,~24,427 issued to Belhomme on ~lay 17, 1977.
'hile the arrangement as described uses an 35 internal magnetic shield, those skilled in the art will recognize that the principles of the invention are equally applicable to a kinescope fitted with an external shield.
~.
'' ~:
Claims (4)
1. A degaussing arrangement for a color television picture tube, said picture tube comprising an envelope comprising a flared portion having large and small ends, a faceplate portion adjacent said large end, and a neck portion coaxial with said flared portion and joined to said small end, said picture tube further comprising a shadow-mask enclosed within said envelope adjacent said faceplate portion and an electron gun assembly enclosed within said neck portion of said envelope, said picture tube further comprising a flared magnetic shield enclosed within said envelope and having large and small ends, said shield being adjacent a segment of said flared portion of said envelope, said degaussing arrangement being characterized by a single degaussing coil encircling said flared portion of said envelope, with the axis of said degaussing coil tilted relative to the axis of said flared envelope portion in such manner as to dispose a first segment of the circumference of said coil in a position overlying a region of said envelope adjacent a portion of said large end of said shield, and as to dispose a second segment of the circumference of said coil, diametrically opposed to said first segment, in a position which is contiguous with a region of said envelope adjacent a portion of said small end of said shield and which is located more remotely from said axis of said flared envelope portion than is the periphery of the opening at said small end of said shield; and means for supplying a variable alternating current solely to said single degaussing coil to effect degaussing of said shadow-mask and said magnetic shield.
2. A degaussing arrangement in accordance with claim 1 characterized in that said first coil segment is disposed in a position overlying a region of said envelope adjacent an upper portion of said large end of said shield, and wherein said second coil segment is disposed in a position contiguous with a region of said envelope adajacent a lower portion of said small end of said shield.
RCA 73,479
RCA 73,479
3. A degaussing arrangement in accordance with claim 1 or 2, characterized in that said picture tube envelope flared portion is in the general form of the frustum of a cone, and said magnetic shield is in the general form of the frustum of a cone.
4. A degaussing arrangement in accordance with claim 1 or 2 characterized in that said picture tube envelope flared portion and said magnetic shield each have the general shape of a truncated pyramid, and said shadow-mask is generally rectangular.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US1281079A | 1979-02-16 | 1979-02-16 | |
| US012,810 | 1979-02-16 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1135321A true CA1135321A (en) | 1982-11-09 |
Family
ID=21756797
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000345759A Expired CA1135321A (en) | 1979-02-16 | 1980-02-15 | Tilted unitary degaussing coil arrangement |
Country Status (20)
| Country | Link |
|---|---|
| JP (1) | JPS55112087A (en) |
| KR (1) | KR900006295B1 (en) |
| AT (1) | AT381201B (en) |
| AU (1) | AU535877B2 (en) |
| BE (1) | BE881758A (en) |
| CA (1) | CA1135321A (en) |
| DE (1) | DE3005763C2 (en) |
| DK (1) | DK148868C (en) |
| ES (1) | ES8100551A1 (en) |
| FI (1) | FI70357C (en) |
| FR (1) | FR2449382B1 (en) |
| GB (1) | GB2046559B (en) |
| HK (1) | HK27284A (en) |
| IT (1) | IT1140569B (en) |
| MY (1) | MY8500294A (en) |
| NZ (1) | NZ192884A (en) |
| PL (1) | PL126142B1 (en) |
| SE (1) | SE441886B (en) |
| SU (1) | SU936835A3 (en) |
| ZA (1) | ZA80875B (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| IN167955B (en) * | 1986-03-27 | 1991-01-12 | Nokia Data Systems |
Family Cites Families (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2921226A (en) * | 1956-05-24 | 1960-01-12 | Philco Corp | Apparatus for color purity correction in color television receivers |
| US2962621A (en) * | 1958-10-10 | 1960-11-29 | Westinghouse Electric Corp | Color television apparatus |
| US3322998A (en) * | 1964-08-31 | 1967-05-30 | Rca Corp | Color purity correcting apparatus for colored television picture tubes |
| US3614519A (en) * | 1967-12-18 | 1971-10-19 | Zenith Radio Corp | Cathode-ray tube magnetic shield |
| US3872347A (en) * | 1972-04-14 | 1975-03-18 | Tokyo Shibaura Electric Co | Degaussing device for colour cathode ray tubes |
| NL167289C (en) * | 1973-09-13 | 1981-11-16 | Philips Nv | COLOR TELEVISION DEVICE EQUIPPED WITH A COLOR TELEVISION IMAGE TUBE AND DEMAGNETIZING DEVICE. |
| NL165020C (en) * | 1974-12-16 | 1981-02-16 | Philips Nv | COLOR TV RECEIVER CONTAINING A DEMAGNETIZER CIRCUIT AND COMPOSITE THERMISTOR ELEMENT FOR USE IN SUCH A CIRCUIT. |
| JP3016048B2 (en) * | 1991-12-04 | 2000-03-06 | 東洋自動機株式会社 | Temperature control method for impulse sealing device |
-
1980
- 1980-02-08 FI FI800394A patent/FI70357C/en not_active IP Right Cessation
- 1980-02-08 AU AU55357/80A patent/AU535877B2/en not_active Ceased
- 1980-02-08 SE SE8001035A patent/SE441886B/en not_active IP Right Cessation
- 1980-02-12 IT IT19868/80A patent/IT1140569B/en active
- 1980-02-12 GB GB8004693A patent/GB2046559B/en not_active Expired
- 1980-02-14 JP JP1771880A patent/JPS55112087A/en active Pending
- 1980-02-15 BE BE0/199427A patent/BE881758A/en not_active IP Right Cessation
- 1980-02-15 CA CA000345759A patent/CA1135321A/en not_active Expired
- 1980-02-15 DE DE3005763A patent/DE3005763C2/en not_active Expired
- 1980-02-15 SU SU802885001A patent/SU936835A3/en active
- 1980-02-15 PL PL1980222054A patent/PL126142B1/en unknown
- 1980-02-15 KR KR1019800000615A patent/KR900006295B1/en active
- 1980-02-15 NZ NZ192884A patent/NZ192884A/en unknown
- 1980-02-15 FR FR8003444A patent/FR2449382B1/en not_active Expired
- 1980-02-15 DK DK67780A patent/DK148868C/en not_active IP Right Cessation
- 1980-02-15 ES ES488650A patent/ES8100551A1/en not_active Expired
- 1980-02-18 AT AT0088580A patent/AT381201B/en not_active IP Right Cessation
- 1980-09-17 ZA ZA00800875A patent/ZA80875B/en unknown
-
1984
- 1984-03-22 HK HK272/84A patent/HK27284A/en not_active IP Right Cessation
-
1985
- 1985-12-30 MY MY294/85A patent/MY8500294A/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| HK27284A (en) | 1984-03-30 |
| NZ192884A (en) | 1983-11-18 |
| KR900006295B1 (en) | 1990-08-27 |
| DK148868B (en) | 1985-10-28 |
| PL126142B1 (en) | 1983-07-30 |
| FI800394A (en) | 1980-08-17 |
| FI70357C (en) | 1986-09-15 |
| AU5535780A (en) | 1980-08-21 |
| SU936835A3 (en) | 1982-06-15 |
| SE8001035L (en) | 1980-08-17 |
| PL222054A1 (en) | 1980-11-03 |
| ES488650A0 (en) | 1980-11-01 |
| SE441886B (en) | 1985-11-11 |
| JPS55112087A (en) | 1980-08-29 |
| BE881758A (en) | 1980-05-30 |
| FI70357B (en) | 1986-02-28 |
| DK67780A (en) | 1980-08-17 |
| IT1140569B (en) | 1986-10-01 |
| ES8100551A1 (en) | 1980-11-01 |
| DE3005763C2 (en) | 1984-11-15 |
| GB2046559B (en) | 1983-04-20 |
| FR2449382B1 (en) | 1985-11-22 |
| AT381201B (en) | 1986-09-10 |
| DK148868C (en) | 1986-04-21 |
| GB2046559A (en) | 1980-11-12 |
| IT8019868A0 (en) | 1980-02-12 |
| ATA88580A (en) | 1986-01-15 |
| FR2449382A1 (en) | 1980-09-12 |
| ZA80875B (en) | 1981-08-26 |
| DE3005763A1 (en) | 1980-08-28 |
| AU535877B2 (en) | 1984-04-12 |
| MY8500294A (en) | 1985-12-31 |
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Legal Events
| Date | Code | Title | Description |
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| MKEX | Expiry |