KR920005005B1 - Magnetic shunt for deflection yokes - Google Patents

Abstract

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Description

Cathode ray tube display

1 shows an appropriate portion of an integrated air coco yoke tube component.

2 is a simplified illustration of one winding from each of the upper and lower horizontal coils of the integrated yoke tube component shown in FIG.

3 shows magnetic field strength in the Z-axis direction for a typical deflection coil as shown in FIG.

4 is a view in which the ring 50 according to the preferred embodiment of the present invention is added to the drawing of FIG.

5 is a view in which the ring 50 according to the preferred embodiment of the present invention is added to the drawing of FIG.

FIG. 6 shows the same series of axial curves as in FIG. 3 showing the effect on field A of ring 50. FIG.

FIG. 7 shows a series of curves showing the effect of the ring 50 on the end winding field shown in FIG.

FIG. 8 is an enlarged view of the portion of the curve shown in FIG. 6 past approximately 2.5 centimeters.

FIG. 9 is a view similar to FIG. 8 with the ring 50 at a slightly different distance from the yoke.

FIG. 10 is a view similar to FIG. 8 with the inner diameter radius of the ring 50 slightly different from that in FIG.

FIG. 11 is a view similar to FIG. 8, wherein the distance of the ring 50 from the end of the yoke is different from that of FIGS. 8 and 9;

12 shows a CRT with a yoke with ferrite cores and associated fields.

13 shows the system of FIG. 12 with a compensation ring.

FIG. 14 is a plan view of the core, coil and ring of FIG. 13 showing magnetization currents and fields. FIG.

Fig. 15 is a front view showing the magnetizing current and the field.

FIG. 16 shows a preferred embodiment of a ring for color tubes in which the ring is divided into two parts.

FIG. 17 shows a split ring showing the classifier field across the base of the tube.

18 is a cross-sectional view of another embodiment portion of a ring made of conventional μ metal sheeting.

19 shows another embodiment in the shape of a hexagon.

FIG. 20 shows an embodiment of the invention, which is a plan view of a CRT, choke coil, and ring.

21 is an electrical wiring diagram of the present invention.

FIG. 22 shows one winding of the upper and lower horizontal deflection coils to which a wire tube is connected.

23 is a spring end view of a ring showing a pair of loops.

FIG. 24 shows a ring with a pair of spherically located holes passing through the ring through which the loop passes before returning to the driver terminal 4; FIG.

FIG. 25 shows how the loop passes through the hole in the ring of FIG.

* Explanation of symbols for main parts of the drawings

10: integrated yoke tube component (ITC) 12: CRT

14 screen 16,18: horizontal deflection coil

50: ferrite ring 68: ferrite coil

TECHNICAL FIELD The present invention relates to a display device, and more particularly, to an apparatus for reducing unwanted magnetic radiation to the cathode ray tube display device without affecting the intended deflection field in the core of the yoke.

Cathode ray tubes (CRT) generally have associated coils or yokes and provide a variable magnetic field for electron beam deflection, for example for raster scanning. The magnetic field for beam deflection not only appears in the CRT but also extends out of the CRT to extend beyond the display. Since such external magnetic fields are not useful, there have been many attempts to reduce this portion of the York magnetic field. A particularly unwanted frequency range is 1K to 3500K Hertz (VLF).

Philips A. Seino Srütermann described the field emitted by the horizontal deflection system in his text, "The Radiation Field of the Magnetic Deflection System and its Compensation Act," submitted to the minutes of the SID Information Labeling Society meeting in 1987. In this paper, the radiated field of the horizontal magnetic circuit of the yoke in the midrange is explained that the mathematical center is similar to the vertically oriented dipole on the long axis slightly ahead of the yoke.

The paper proposes a means for reducing such radiation. In some cases, Helmholtz coils are placed on the saddle-shape deflected yoke “top” and “above” and in other cases below the yoke. This coil is combined with a deflection coil, which induces an EMF, weighting the magnetic field to offset the unwanted radiated magnetic field. However, this is a relatively expensive and not easy solution. A similar upper and lower coil configuration is disclosed in Nokia's Patent Application No. 861,458 of April 4, 1986.

Another proposed solution is to place a shield around the CRT to reduce magnetic radiation from the eddy currents induced in the shield, which is not only an expensive solution but also a small amount of magnetic field reduction in front of the screen. It is only.

Thus, there is a need for a means to provide a low cost and simple solution and to reduce the extra magnetic field to an acceptable level in front of the cathode ray tube display.

According to the pending application No. 07 / 265,115, filed Oct. 31, 1988, filed on Aug. 13, 1987, filed with the application of No. 07/084/949, a method for reducing magnetic radiation dispersed around a coil The apparatus for use utilizes a ring disposed between the coil and the screen, the ring being made of a magnetically permeable material having a configuration and location selected to minimize the magnetic field distributed at the front of the coil.

While the foregoing is applicable in many cases, physical constraints such as the shape of the coil tube, the presence of wedges for coil alignment, and the like, can prevent the ring from satisfactorily engaging the coil.

The present invention has a viewing screen, has a charged particle beam directed from the rear to the screen and aligned to the central axis of the tube but which can be deflected magnetically from the axis, generating magnetic components from the wire segments wired axially. It applies to a cathode ray device comprising a cathode ray tube ("CRT") with a deflection coil that generates magnetic components from wire segments aligned on the periphery with respect to the axis to increase the magnetic field distributed around the coil. The apparatus for reducing the magnetic radiation distributed around all of the coils uses a ring disposed around the tube, where the ring is made of a magnetically permeable material. According to the present invention, a pair of coupling wires are wound around the ring and engaged with the coil to have a negligible effect inside the tube and to support the induction of the magnetic field in the ring to reduce the magnetic field around the CRT.

The invention is embodied in the form of a relatively inexpensive linear ferrite material composed of a cheaply provided shape such as a flat ring. This makes it a relatively cheap solution. In addition, the examples examined demonstrate a significant reduction in unwanted radiation in front of the CRTs to which the present invention has been applied.

Various objects, features, advantages, and the like of the present invention will become apparent from the specific description of the preferred embodiments of the present invention as described in the accompanying drawings.

1 shows a suitable portion of an integrated yoke tube component (“ITC”) 10 that includes a front screen 14 and a CRT 12 having upper and lower horizontal deflection coils 16 and 18. The deflection coils 16, 18 are coils in the CRT 12 to deflect the electron beam within the tube 12 for horizontal sweeping across the surface of the screen 14, as is known in the art. Generate a variable magnetic field in between.

2 simplifies one winding from each of the upper and lower deflection coils 16, 18 of FIG. Thus, tube 20 is a single loop from coil 16 and loop 22 is a single loop from coil 18. As shown, current i flows through each coil to generate the variable magnetic field described above to horizontally horizontally electron beam.

In FIG. 2, the X, Y, and Z axes are shown as having an origin in the plane of the circumferential coil portions 34, 38 and centered between the portions. The X axis coincides with the central axis of the CRT (Figure 1). Note that the upper half and lower half 20, 22 are symmetric about the x-z plane and the y-z plane.

필드는 다음과 같이 주어진다.In practical operation, the upper and lower loops 20, 22 are interconnected to generate a dipole field on the Z axis, as is known. From known coil shapes and currents

The field is given by

는 전류,

는 방향, R은 Z축상의 대상점 P까지의 거리이다. 상기 식은 제3도 및 제7도 내지 12도의 필드 분포를 계산하는데 이용된다.here

Is the current,

Direction, R is the distance to the target point P on the Z-axis. The equation is used to calculate the field distributions in FIGS. 3 and 7-12.

필드 분포의 플롯이, 제3도에 도시되어 있다. 실제

필드는 방향 필드이며, 제3도에 도시된 필드 Z축을 따르는 자기장의 크기 또는 세기만을 도시하고 있다. 수평축 상에 표시된 단위는 센티미터인 반면, 수직축의 단위는 가우스이다. 곡선은 20킬로볼트 전자빔을 약 40도 각도로 편향시키는 필드를 발생시키도록 흐르는 전류를 가지는 통상적인 코일을 나타낸다.As shown in Figure 1, the calculated core of an air core horizontal deflection coil without any high permeability material such as a ferrite shield

A plot of the field distribution is shown in FIG. real

The field is a directional field and only shows the magnitude or intensity of the magnetic field along the field Z axis shown in FIG. The unit indicated on the horizontal axis is centimeters, while the unit on the vertical axis is Gaussian. The curve shows a conventional coil with current flowing to generate a field that deflects a 20 kilovolt electron beam at an angle of about 40 degrees.

Curves A, B and C in FIG. 3 represent the entire field, the partial field from the axial wiper and the partial field from the distal winding, respectively. Curve A is the magnitude of the vector sum of the fields represented by curves B and C. For a typical uncompensated yoke, the field at 55 centimeters in front of the yoke may be in the range of approximately 1,000 to 2,000 nano Tesla. Obviously, this is not a very large magnetic field. By the way, according to the present invention, the field can be taken in a smaller amount. Experimentally, when using the following preferred examples, a decrease of less than 200 nanotesera at 55 centimeters is observed.

4 shows the ITC 10 of FIG. 1 with the addition of a ring 52 of linear ferrite acting as a magnetic classifier, according to the invention of the applicant's application number 07 / 265,115.

FIG. 5 shows the loops 20 and 22 of FIG. 2 with the ferrite ring 50 disposed in front of it to show the relative shape and position of the ring 50.

Ring 50 is linear ferrite, as described above. Linear ferrites are known materials commonly used in the manufacture of transformers and yokes. According to a preferred embodiment the ring 50 has a relatively high magnetic permeability (μ is greater than 2,500). It also has a high volume resistivity, for example 1 Meg Ohm per cubic centimeter. High resistance values minimize eddy currents. Otherwise, more energy is required to drive the yoke due to the loading effect on the yoke. Although the embodiment has the above loading effect, for example in a conventional μ thin plate, and can be constructed according to the present invention, it is considered preferable to keep the eddy current low and to avoid the above loading effect in the preferred embodiment. The cross section of the ring 50 is large enough to avoid saturation.

FIG. 6 is a series of axial series of curves identical to FIG. 3, showing the effect on field A shown in FIG. 3 of a flat ring, such as ring 50 of FIG. 4, according to a preferred embodiment of the present invention. . Curve A in FIG. 6 is the same as curve A in FIG. In FIG. 6 curve D represents the field contribution from the magnetization effect of ring 50 and curve E represents the curve resulting from combining curves A and D. FIG.

To better understand the effect of field D on the total magnetic field A, a series of curves are shown in FIG. 7, including curve D and the end winding magnetic field component C. FIG. Curve C is the same as curve C shown in FIG. Curve F is a curve representing the field resulting from the combination of curves D and C. In Fig. 7, the horizontal axis is the same in Figs. 3 and 7 but the vertical unit is enlarged for clarity.

As mentioned above, curve D is an imaginary field of the ring only, an intrinsic field created by the magnetization of the end winding field. Note that the ring attenuates the end winding field. The degree of attenuation, as will be described in detail below, is controlled by variables such as ring area, ring yoke spacing, and the like. It is an object of the present invention to reduce this. At optimal attenuation, the modified end winding field F is the same size as the main deflection field but in the opposite direction, making the vector sum zero. As a practical matter, the extra field measurable in front of the CRT screen can be reduced to zero. However, applying the principles of the applicant's prior invention as described herein, the field can be reduced to a very small level.

The portion of FIG. 6 that is approximately 2.5 centimeters to the right is shown in FIG. In order to clearly show the pattern of the curve in this area, the unit has been enlarged in the vertical direction compared to FIG. Curves A and E are shown in FIG. Curve D is not shown in the figure to make curves A and E clearer. Curve E is very close to the zero field size at approximately 9.5 centimeters.

Compensated curve E has a susceptibility of 1,000 to 3,000, a high volume resistivity, a ring of ferrite (50 cm inside, 4 cm wide, 2 cm thick, 1 cm wide, 46 cm from the end of the yoke). For a typical CRT-yoke configuration with The width of the ring as used herein refers to the length extending radially from the inner diameter to the outer diameter.

9-11 are plots similar to those shown in FIG. 8 for a ring configuration that is slightly different from the configuration that makes the curve of FIG. Therefore, in FIG. 9 all parameters relating to the ring are the same as those corresponding to FIG. 8 except for the distance of the ring from the end of the yoke. The curves in FIG. 9 correspond to a configuration that is 3 centimeters in size. If curve E 'is slightly above the horizontal axis, for example 9.5 centimeters and slightly below curve E in Figure 8, it is evaluated to exhibit over-compensation.

The curve of FIG. 10 is for a configuration whose size is the same as that of FIG. 8 but with an inner diameter radius of 5 centimeters instead of 4 centimeters. It can be seen that if curve E "is below the horizontal axis, significantly less compensation is provided.

FIG. 11 is for the same configuration as in FIG. 8 but with a ring distance of 6 centimeters instead of 4 centimeters from the end of the yoke. It can be seen that a slightly smaller compensation has been provided, with the curve E " crossing the horizontal axis of 9.5 centimeters. This is believed to represent the optimal compensation.

Although the curves do not show the effect of varying the width of the ring on the compensating effect, in general, decreasing the width reduces the compensating effect and increasing the width also increases the effect.

Therefore, how changes in the various size parameters of the ring from previous Figures 8-11 will affect the performance of the ring compensating by canceling the magnetic field component on the X axis at the front of the screen due to the yoke winding and the magnetic field component. You will know if you give it. By understanding these effects, the person practicing the present invention can provide the adjustments that are deemed desirable to optimize the offset effects. In the arrangement described above, the CRT tube has an air core horizontal deflection coil without any high permeability shield around the neck of the tube. The direction of the horizontal deflection field, which moves the beam toward the right edge of the screen when viewed from the front, is indicated by arrow 70 in FIG. In a typical commercial form of yoke, the horizontal deflection coil has a ferrite shield (ferrite core) 68 around the horizontal deflection coil as shown in FIG. There is also a vertical deflection coil around the horizontal deflection coil and below the ferrite core (not shown). The radiated field generated by the horizontal coil with end loops 32, 34, 36, 38 extending beyond the ferrite core is located in front of the loop closest to the screen, as shown by arrow 70a in FIG. It is a centered dipole. The ferrite core reverses the polarity of the emitted field. As shown and described in FIG. 13, the ferrite ring 50 is mounted in front of the horizontal deflection coil near the radiation center of the horizontal coil.

The method of compensating field radiation without deflecting the noticeable effect of the ring has been described in conjunction with FIGS. 14 and 15. 14 is a plan view sketch of the coil 16, core 68, ring 50 showing the deflection current, magnetization current and resulting field in the deflection coil. FIG. 15 is a front view of FIG. The counterclockwise current of the horizontal deflection coil shown in the plan view is denoted by (71). The generated magnetic field is represented by OH, pointing from the center towards the viewer and corresponds to (12) in FIG. Ferrite 68 is coupled with the deflection coil and generates a more powerful equivalent ignited magnetization current M ₁ , represented by thick line 72. Combined current 72 circulates in the opposite direction (clockwise in FIG. 14) from the current along adjacent surfaces of the coil and core flowing in the same direction. The result is a magnetic field X ₁ at the center of the core (with the direction into the ground) and O ₁ at the front of the ring (with the direction out of the ground). Field X ₁ combines with field OH to generate the radiated field O ₁ or 70a of FIG. 12, which is the vector sum of O _H and X ₁ . The emitted field O ₁ is a dipole field and is the main component of the magnetic emission. The exposed end winding radiates a minority quadrupole field, represented by Xe. The symbols " X " and " O " coincide with the signal conventions set previously, where X means the field is towards the ground and O means the field is towards the observer. The sum of X ₁ and Xe is the whole radiated field when no ring is present.

When the ferrite ring is placed in front of the yoke as shown in FIGS. 13 and 14, the ring will be magnetized as described below. The magnetization current M ₂ in the yoke shield causes an equivalent magnetization current M ₂ in the counterclockwise direction. The field created is up inside the ring (O ₂ ) and down outside the ring (X ₂ ). The polarity of the field is also indicated in FIG. 15 by "N" (north) at the top of the ring and "S" (south) at the bottom of the ring. The front end windings (top, bottom) of the horizontal coil induce an equivalent magnetization current M clockwise in the ring. The field X ₃ made is face down inside the ring and up outside the ring (O ₃ ). The polarity of this field is also indicated by the letters "N" (north) and "S" (south) in FIG. From the distribution and polarity of the induced magnetization current end field, it is concluded that the radiated field X ₁ of the yoke shield initiates dipole magnetization O ₂ against the radiating dipole in the ring. Similarly, the quadrupole component of the radiated field by the exposed end windings of the horizontal deflection coils induces quadrupole magnetization that cancels the radiating quadrupole in the ring. Variables such as ring thickness, inner diameter, outer diameter, permeability, oak-ring distance, etc. can be used to adjust for optimal performance. The lower limit of the ring size is determined by the given CRT and yoke combination. In practice, the ring tends to stick as close to the front of the yoke as possible without adversely affecting the deflection field in the bore of the tube, which reduces the size of the ring and reduces the cost. The most closely located yoke has a lowest permeability of about 1,000. The higher the permeability, the greater the distance of the ring from the yoke.

Despite efforts to eliminate the interference between the ring and the main deflection field, it has been found that the presence of a solid ring shifts the center of deflection of the vertical deflection field slightly back towards the electron gun. This is not noticeable in monochromatic systems but causes a detectable deviation of about ^10-6 meters in color systems. This problem is solved by the split ring configuration of FIG. Here, the portion of the induced dipole field, as shown in FIG. 17, typically guided by the ring, is forced to enter the bore, joins the vertical deflection yoke field, reinforces the vertical deflection field, and forwards the center of deflection forward. Move it. In fact, it is known that a 2mm air cap can compensate for a deviation of ^10-6 meters.

In a typical typical experiment with ITC with serial number M34JDJ00X1 manufactured by Matsushita Co., Ltd., the ferrite ring of a routine linear ferrite has a volume resistivity of approximately 1,000 to 3,000 μ and a volume resistivity of more than 1 megohm per CC, 4 Having an inner size of 3/8 ", a width of 3/8", and a thickness of 1/8 ". The ring is separated by only the space due to insulation of the yoke wire so that the periphery wire portion of the yoke provided with the ITC ( When located relative to the screen (closest to the distal end), the ring is known to produce a good offsetting effect.

The embodiment may be made with a conventional μ thin plate, shield ring with a cross section as shown in FIG.

FIG. 19 shows a hexagon shaped ring showing another embodiment for use with a hexagon shaped yoke, for example.

As mentioned above, the compensation effect of the ring depends on the width of the ring, the different size, the size of the material and the like. As taught herein, these sizes and sizes of materials and distances from the end windings of the coils can be overcome by a pair of coupling wire loops around the ring 50 as shown in FIGS. 20-22. 20 is a plan view of the yoke, coil, tube and ring. 21 is an electrical wiring diagram showing terminals. Terminal 1 is coupled to one end of the driver and terminal 4 is returned to the driver. The upper coil represents the upper saddle yoke and the lower coil represents the lower saddle yoke. 22 illustrates the upper saddle yoke 220 and the lower saddle yoke 221. The first loop 210 begins at the terminal 1 of the rear terminal bundle and passes clockwise around the ring 50a and ends at the terminal 2. The upper and lower saddle yokes are coupled to terminal 2 at one end and end at terminal 3. The second loop 211 extends from the terminal 3 and passes through the ring 50a attention on the opposite side of the ring (opposite in diameter in the horizontal plane) in the clockwise direction and ends at the terminal 4. The distal sketch of the ring with the loop viewed from the screen is shown in FIG. The loop is connected to the yoke in such a way that the direction of the current in the loop matches the direction of the current in the bundle of the front end windings of the deflection coil. In FIGS. 20 and 22 the directions of arrows 215 and 216 coincide.

According to another embodiment of the present invention, the correction for the quadrupole effect can be made by the arrangement of loops passing around the ring through spherically located holes in the ring as shown in FIGS. 24 and 25.

It was found that the ring could be of any shape size, size, or material discussed herein, and the number of loop windings could be selected depending on the coupling needed to achieve the desired emission reduction.

Although the present invention has been described with reference to the preferred embodiments and various other embodiments, those skilled in the art will be skilled in the art without departing from the spirit and scope of the invention described herein. It will be appreciated that various modifications and changes can be made by the following embodiments. All such changes, modifications, and implementations are intended to be included within the scope of the appended claims.

Claims (15)

A cathode ray tube display with a viewing screen, comprising: means for generating a charged particle beam directed from the rear toward the screen and aligned with the tube's central axis but magnetically deflectable from the axis, and the first and second halves Magnetic components from the ferrite cores around the deflection coils and the wire segments that have magnetic components from the wire segments that are axially aligned with respect to the axis, thereby increasing the desired deflection field and the mathematical center being slightly A cathode ray tube display having a deflection coil yoke that increases unwanted distributed magnetic field radiation outside of a display device representing a vertical dipole field lying on the front major axis, the front of the screen and all surrounding display devices. The distributed magnetic field radiation with minimal effect in the tube The device for reducing while forming a substantially ring shaped device made of a magnetically permeable material substantially centered on the central axis disposed between the end winding of the coil and the screen, wherein the ring is the end winding of the coil. Located in close proximity to the deflection coil and electrically coupled to the deflection coil, inducing a magnetic field that reacts to the magnetic field at the front of the ring to the ring, with a negligible effect inside the tube, And at least one pair of coupling wire loops around the ring for reducing the distributed magnetic field around all of the exterior of the display device. The cathode ray tube display of claim 1, wherein the loop is connected in series with the deflection coil yoke. The cathode ray tube display device of claim 2, wherein the loop passes around the ring on the opposite horizontal side and is generally in the horizontal plane when the ring is on the CRT. 4. The method of claim 3, wherein the first half of the deflection yoke is connected in parallel to a second half that is an upper half, and the first half of the pair is coupled to one end of the parallel yoke half and A cathode ray tube display connected to a loop at an opposite end of the deflection yoke half. The cathode ray tube display device of claim 1, wherein the ring has a hole and the wire loop passes through the hole. 6. The cathode ray tube display of claim 5, wherein the aperture is paired with a pair of apertures located at spherical points around the ring. The cathode ray tube display device of claim 1, wherein the ring-shaped device is a ferrite ring that has a permeability of 1,000 or more and is away from the yoke by a distance determined to reduce the distant distance while minimizing the effect in the tube. The cathode ray tube display device of claim 1, wherein the coil is a saddle yoke and the ring shaped device is away from the yoke so that no part is below the yoke and all parts are in front of the yoke toward the screen. The cathode ray tube display device of claim 1, wherein the ring shaped device comprises a plurality of ferrite sections forming a ring. The cathode ray tube display device of claim 1, wherein the ring-shaped device has a pair of semi-circular ferrite sections separated by a gap of a pair of non-ferrite materials. 4. A cathode ray tube display device according to claim 3, wherein the ring-shaped device has a pair of sections with non-ferrite gaps between sections in a vertical plane with at least one loop around each section about its midpoint. . 11. The cathode ray tube display device according to claim 10, wherein the size of the non-ferrite gap between the sections is determined to correct a misalignment. 5. The cathode ray tube display of claim 4, wherein the plurality of sections are spaced apart to control misalignment. A cathode ray tube with three beams, a three-color fluorescent screen whose emitted color is in accordance with the angle of approach of the cathode beam, and a magnetically deformed coil around the thin neck of the tube arranged such that the beam scans the screen toward the screen. In a display device with colored cathode rays, the horizontal coil has an extending end winding, the horizontal coil increasing the unwanted magnetic field radiation outside the display which represents a vertical dipole field where the mathematical center is on the long axis slightly forward of the yoke. And a device for reducing the magnetic field radiation in front of the screen and all around the display device with minimal influence in the central axis and the tube, the magnetically permeable material being separated by a pair of gaps forming a ring. A pair of generally semicircular bodies of Disposed between the cleansing, the gap is along a plane of vertical deflection, the ring is disposed near the end winding of the horizontal coil, and the gap size controls the misalignment of the three beams on the tri-color phosphor Color cathode ray tube, characterized in that it comprises at least one joining wire loop around each semicircular body in electrical series with said deflection coil having said loop generally crossing about its midpoint in a horizontal plane. Display. A cathode ray tube display with an observation screen, comprising: means for generating a charged particle beam directed from the rear toward the screen and aligned on a central axis but capable of being magnetically deflected from the axis, and having an on-axis with first and second halves. A magnetic component from the wire segment aligned with the magnetic component from a wire segment aligned on the periphery with respect to the axis, thereby increasing the desired deflection field and unwanted distributed magnetic field radiation outside the display A cathode ray tube display device having a coil yoke, the apparatus for reducing the distributed magnetic field radiation in front of the screen and all around the display device with minimal effect in the tube, between the yoke and the screen. Made of a magnetically permeable material substantially centered on the central axis disposed In fact a ring-shaped device and a magnetic field electrically coupled to the deflection coil and reacting to the magnetic field at the front of the ring to the ring, with a negligible effect inside the tube, And at least one pair of coupling wire loops around the ring for reducing the dispersed magnetic field around all of the exterior of the display device.

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