CN1031297A - Deflection Line Diagram Magnetic Shunt - Google Patents

Abstract

A device used to weaken the radiation of the magnetic field distributed in mesh in front of the screen of a cathode ray device. In such a cathode ray device a deflection yoke with axially distributed copper wire segments relative to the central axis and along the circular axis generates a harmful unwanted magnetic field in front of the screen. The present invention provides a magnetic shunt arranged between the deflection yoke and the screen. This magnetic shunt is made of magnetically permeable material. Its structure and position depend on the coil. It can be selected in front of said coil There is the best maximum elimination of the mesh-like distribution of magnetic field at the position, so that the best comprehensive reduction of the induced magnetic field can be obtained through the action of this magnetic shunt.

Description

The present invention relates to a display device, and more particularly to a device capable of reducing external harmful magnetic radiation reaching the front of a cathode ray tube display screen.

A cathode ray tube usually has an auxiliary coil, that is, a deflection coil, to provide a changing magnetic field to deflect electrons for raster scanning. In addition to deflecting the electron beam in the cathode ray tube to realize the display of the cathode ray tube, this magnetic field also spreads out of the tube and even reaches the front of the screen. This external magnetic field is not beneficial, and it is often necessary to try to reduce the magnetic field of this part of the deflection coil.

Field weakening of deflection yokes has been disclosed in the prior art, for example by placing Helmholtz coils in front of the saddle deflection yoke, or radially away from or adjacent to the coil. These coils are coupled to deflection yokes in which an electromotive force is induced to produce a magnetic field which helps to cancel the magnetic field of the wire tubes in front of the screen. However, this solution to the problem is costly and cumbersome.

Another solution is to shield around the cathode ray tube to attenuate the magnetic radiation due to eddy currents induced in the shield. But this solution to the problem is also costly and only slightly reduces the magnetic field in front of the screen.

Therefore, there is a need for a device that can reduce the unwanted magnetic field in front of the screen of a cathode ray tube to a permissible level, which device should be cheap and compact.

The present invention is used in a cathode ray device with a cathode ray tube. The cathode ray tube has a screen for viewing; there is a charged particle beam that shoots from the back to the screen and is parallel to the central axis of the tube, but the charged particle beam can be deflected by magnetic force. Axial; there is also a deflection coil, which generates a magnetic component from a copper wire segment parallel to the axis and a magnetic component formed by a copper wire segment arranged along a circumference, forming a reticularly distributed magnetic field in front of the coil. Due to the measure of configuring a magnetic shunt between the coil and the screen, this measure weakens the magnetic field distributed in a grid in front of the coil. The magnetic shunt is made of magnetically permeable material, and its shape and position should be selected according to the deflection coil, so that the magnetic field distributed in the net shape in front of the coil is the least.

The invention can be made of flat rings or the like from less expensive linear ferrite materials. Therefore, the cost is very low. And the tested embodiments have shown that, after being used in a cathode ray tube, the harmful radiation in front of the cathode ray tube screen can be greatly weakened.

The above and other objects and advantages of the present invention will be further illustrated in the following discussion of the preferred embodiments of the present invention with reference to the accompanying drawings.

Figure 1 shows the relevant parts of a tube assembly incorporating a complete deflection yoke.

Fig. 2 is a schematic diagram of one more turn of the upper and lower deflection yokes of the electron tube assembly shown in Fig. 1 equipped with a complete deflection yoke.

FIG. 3 is a graph showing the distribution of magnetic field strength along the z-axis of the typical deflection yoke shown in FIG. 1. FIG.

Fig. 4 is a view similar to Fig. 1 after adding a ring 50 to the electron tube assembly shown in Fig. 1 according to a preferred embodiment of the present invention.

Fig. 5 is a view similar to Fig. 2 after adding a ring 50 according to a preferred embodiment of the present invention.

Figure 6 is a graph showing the effective and actual μ values for the rings given in Figures 4 and 5 compared.

FIG. 7 is a set of curves showing the effect of the ring 50 on the reticulated magnetic field A on the same coordinate axes as in FIG. 3 .

FIG. 8 is a set of graphs showing the effect of ring 50 on the magnetic field at the end of the coil shown in FIG. 3 .

Fig. 9 is an enlarged view of the part to the right of 2.5 cm of the curve shown in Fig. 7 .

Figure 10 is a graph similar to that shown in Figure 9, except that the distance of the ring 50 from the deflection yoke is slightly different.

FIG. 11 is a graph similar to FIG. 9 except that the range of the inner diameter of the ring 50 is slightly different from that of FIG. 9 .

FIG. 12 is a graph similar to FIG. 9 except that the distance of the ring 50 from the end of the deflection yoke is different from that of FIGS. 9 and 10 .

FIG. 13 is a view of another embodiment, which has a lip portion 62. As shown in FIG.

Figure 14 shows a diagram of yet another embodiment, the ring is divided into two parts.

Figure 15 shows an embodiment produced by injection molding of a material, such as ferric oxide particles injected into a nylon material.

Figure 16 is a partial cross-sectional view of yet another embodiment of a ring fabricated from metal laminate sheets having a typical μ value.

Figure 17 shows yet another embodiment having a hexagonal shape.

Figure 1 shows the relevant portion of a complete deflection yoke assembly 10 comprising a cathode ray tube 12 having a display screen 14 at its front end and upper and lower horizontal deflection coils 16,18. As is well known, deflection yokes 16, 18 generate therebetween a varying magnetic field which acts within cathode ray tube 12 to deflect the electron beam within the tube to scan horizontally across the entire surface of screen 14.

FIG. 2 is a schematic diagram of one turn of the upper and lower deflection yokes 16, 18 shown in FIG. Coil 20 is a single turn of deflection yoke 16 and coil 22 is a single turn of deflection yoke 18 . A current i flows through each coil as shown to generate a varying magnetic field acting on the horizontally deflected electron beams. The useful parts of the coils 20, 22 are the axial parts 24, 26, 28, 30 which generate the main deflection magnetic field.

Circumferentially distributed portions of the coil (coil end portions) 32, 34, 36, 38 serve only to complete the loop of the coils 20, 22. In other words, it is not necessary for the operation of the deflection yokes 16,18. The stray distributed magnetic field in front of the screen 14 (FIG. 1) is mainly produced by the circumferentially distributed parts 32, 34, 36, 38 of the coils. This stray distributed magnetic field is harmful and should be weakened. In fact, the stray distributed magnetic field is the vector sum of the main magnetic field of the deflection coil and the magnetic field at the end of the coil. Due to the larger magnetic field component at the end of the coil, this vector sum will coincide with the polarity of the magnetic field at the end of the coil, and both decay at the same rate with distance.

Figure 2 shows the x, y and z axes with their origin in the plane of the circumferentially distributed coil sections 34, 38 and positioned at the center of the plane. The z-axis coincides with the central axis of cathode ray tube 12 (FIG. 1). Note that the upper and lower halves 20, 22 are symmetrical with respect to the x-z plane and the y-z plane.

As is well known, in practice the upper and lower coils are interconnected so as to generate a dipole field along the z-axis. According to the known coil shape and current, the magnetic field B can be given by the following formula:

where J is the current, R is the direction, and R is the distance to point p on the z-axis.

After the typical line deflection coil shown in Figure 1 is shielded with a high magnetic permeability material such as ferrite, the distribution curve A of its magnetic field B is shown in Figure 3. The actual magnetic field B is a directional magnetic field, and the curve shown in Figure 3 only shows the magnitude of this magnetic field along the z-axis, that is, the intensity. The unit of the abscissa is cm, and the unit of the ordinate is Gauss. This curve represents the magnetic field generated by a typical deflection yoke with current flowing through it, which is capable of deflecting a 20kV electron beam by an angle of 40°.

Curves A and BC in FIG. 3 respectively represent the total magnetic field, the partial magnetic field generated by the axial coil and the partial magnetic field generated by the end coil. Curve A represents the magnitude of the vector sum of the magnetic fields represented by curves B and C, respectively. In a typical uncompensated deflection yoke, the magnetic field is in the range of about 1000 to 2000 nanoTesla at a distance of 55 cm from the front end of the deflection yoke. Admittedly, this is not a very large magnetic field, however, according to the present invention, this field can be reduced to an even smaller extent. In the preferred embodiment described below, practical tests have determined that the reduction can be as low as 200 nanotesla at 55 cm.

Fig. 4 shows that according to a preferred embodiment of the present invention, a metal ring 50 made of linear ferrite and acting as a magnetic shunt is installed on the electron tube assembly 10 with a complete deflection yoke shown in Fig. 1 .

Fig. 5 shows the corresponding shape and the position of the ferrite ring 50 after the ferrite ring 50 is arranged in front of the coils 20, 22 shown in Fig. 2 .

As mentioned above, the ring 50 is made of linear ferrite. Linear ferrite is a well-known material commonly used in the production of transformers and deflection yokes. According to a preferred embodiment, the ring 50 has a relatively high magnetic permeability [mu] and a high volume resistivity [rho], such as above 1 megohm per cubic centimeter. Such a high value of ρ keeps eddy currents at a minimum. Otherwise, more energy would be required to excite the deflection yoke due to the effect of the load on the deflection yoke. In some embodiments of the invention, eddy currents are kept low and this loading effect is avoided in preferred embodiments if fabricated with metal tabs outside of the usual [mu] values. The cross-sectional area of the ring 50 is large enough to avoid saturation.

Referring to FIG. 6, there is shown the effective μ or μe versus the actual μ or μa for a loop which is the loop 50 placed in front of the coils 20, 22 shown in FIG. It can be seen that when μa is small, μe increases sharply with the increase of μa, and then reaches a certain point. After this point, although μa continues to increase, μe does not increase and remains constant. A value of 1000 represents a point, such as the value of μ corresponding to point 52, which corresponds to a typical sized ring made of a linear ferrite material as described herein. If the value of μ is selected as 10, it will be in the slope region 53 of the curve shown in Figure 6. Such a material will be very sensitive to changes in manufacturing tolerances, operating temperatures and other factors. Due to the complexization of these factors, the Its characteristics are extremely unstable. By selecting the magnetic permeability to be in the flat portion, ie, the horizontal curvature of the curve shown in Fig. 6, the above-mentioned detrimental characteristic changes can be avoided. However, considering the cost of the material, the material with low magnetic permeability should be selected as much as possible under the premise that the required stability can be guaranteed.

Fig. 7 is according to the preferred embodiment of the present invention, on the same coordinate axis as Fig. 3, represents a set of curves of the effect of a flat ring on the network magnetic field A as shown in Fig. 3, for example this flat ring is in Fig. 4 The Ring 50. Curve A in FIG. 7 is the same as curve A in FIG. 3 . Curve D in FIG. 7 shows the magnetic field distribution due to the magnetization of the ring 50 . Curve E represents the combined effect of curves A and D.

Fig. 8 shows a set of curves to help us better understand the effect of the magnetic field component D of the end coil on the total magnetic field A. This set of curves includes curve D representing the magnetic field component of the end coil and two other curves to aid in understanding. Curve C is the same as curve C in FIG. 3 . Curve F is a curve representing the total magnetic field distribution resulting from the combination of curves D and C. Note that the abscissa in Figure 8 is the same as that in Figures 3 and 7, and the scale on the ordinate (vertical magnetic field) is enlarged for better clarity.

As mentioned above, the curve D represents the theoretical magnetic field distribution when the ring exists alone. An intrinsic magnetic field is generated due to the magnetizing force of the end coil magnetic field. The presence of the ring weakens the magnetic field of this end coil. The degree of attenuation is controlled by varying variables such as the size of the ring, the gap between the ring and the deflection yoke, as discussed in more detail below. It should also be pointed out that the net-like redundant magnetic field located in the area in front of the CRT screen is jointly formed by the end coil magnetic field and the main deflection magnetic field. The task of the present invention is to try to weaken this stray magnetic field. In the case of ideal weakening, the rectified final object coil magnetic field F is equal in magnitude and opposite to the main deflection magnetic field, and its vector sum is zero. In fact, it is impossible for the measurable stray magnetic field in front of the cathode ray tube screen to decay to zero. But applying the above method of the present invention, this unwanted magnetic field can be reduced to a very small level.

The part to the right of 2.5 cm on the abscissa of Figure 7 is shown in Figure 9 . In order to observe the change of the curve in this area more clearly, the scale of the ordinate is enlarged than that in Figure 7. In order to highlight the changes of curves A and E, only curves A and E in FIG. 7 are drawn in FIG. 9 , and curve D is not drawn. Pay attention to observe that the curve E is very close to the horizontal axis representing that the magnetic field is zero near 9.5cm.

Curve E is a curve after compensation of a cathode ray tube deflection coil with a typical structure. The compensation method is to dispose of a ring 50 made of iron and oxygen at 0.4 cm from the end of the coil. The inner diameter of the ring is 4 cm, thick 0.2 cm, wide 1cm, magnetic permeability 1000-3000, resistivity ρ≥1MΩ/cm ³ . The width of the ring here refers to the radial width obtained by subtracting the inner diameter from the outer diameter.

Figures 10-12 are curves similar to the one shown in Figure 9, but with a slightly different ring structure than that shown in Figure 9 . In Fig. 10, all parameters of the ring are the same as in Fig. 9 except the distance of the ring from the end of the deflection coil. The curves shown in Figure 10 are for a distance of 0.3 cm from the ring to the end of the deflection yoke. It can be seen that after compensation, the curve E' is a little farther from the horizontal axis, such as at 9.5cm.

Figure 11 shows that other parameters are the same as those in Figure 9, except that the inner radius of the ring is not 4cm, but 5cm. It can be seen that the compensation is severely under-compensated, and the curve E″ falls below the horizontal axis at 9.8 cm, which is caused by a much larger value at this point than the curve E on the horizontal axis.

The curve shown in Figure 12 is the same as Figure 9 in other dimensions, except that the distance from the ring to the deflection coil is increased from 0.4cm to 0.6cm. It can be seen that after a slight reduction in compensation, the curve E'" intersects the horizontal axis at 9.5 cm. This means that the optimum compensation is achieved.

The effect of ring width variation on compensation is not shown in the graph. In general, shortening the width of the ring will make the compensation weaker, while increasing the width of the ring will make the compensation stronger.

Therefore, it can be seen from the above-mentioned Figures 9-12 how to change these dimensional parameters in the preferred embodiment of the present invention so that the characteristics of the ring can better offset the magnetic field component produced by the deflection yoke winding on the z-axis in front of the screen to achieve compensation the goal of. Through knowledge of these effects. With the method of the invention it is possible to obtain orthotics with optimum counteracting action.

In the actual test, the M34JDJ00×01 series electron tube assembly equipped with a complete deflection coil and the ferrite ring made of ordinary linear ferrite are used. The ring’s μ=1000-3000, ρ>1MΩ /cm ³ , inner diameter 4 3/8 inches, width 3/8 inches, thickness 1/8 inches. When the ring is placed against the circumferential distribution part of the deflection coil of the electron tube assembly, the distance is as long as the insulation with the deflection coil can be ensured. At this time, the ring can produce a good compensation effect.

It must be pointed out that other configurations of the invention can also be applied, such as a ring 60 with a lip 62 as shown in FIG. 13 . This lip 60 acts to enhance the cancellation of unwanted magnetic fields. However, since the machining of the structure shown in FIG. 13 is more complicated, the cost is higher than that of the ring 50 .

Another alternative ring is made of two parts, as shown in Figure 14.

In addition, using the injection molding process, for example, injecting iron oxide particles into nylon, the ring with the cross-sectional structure shown in Figure 15 can be made. This structure provides an effective compensating magnetic field with orthopedic properties. But it also costs a bit more than the simple flat ferrite ring described above.

Figure 17 shows a hexagonal ring used in conjunction with a hexagonal deflection coil in another embodiment.

Finally, it should be pointed out that the rings in the above embodiments can be made of metal laminated plates with conventional μ values to form rings with the cross-sectional shape shown in FIG. 16 .

The present invention has been discussed in terms of preferred and other varied embodiments herein, and it should be noted that those skilled in the art can easily modify and change the present invention without departing from the spirit of the present invention as set forth herein. and range. All such changes and modifications are intended to come within the scope of the appended claims.

Claims (3)

1. A device for reducing the mesh-like distributed magnetic field in front of the screen of a cathode ray device, comprising: means for producing a beam of charged particles projecting from behind the screen onto said screen parallel to the central axis but magnetically deflected from said axis; and A deflection yoke having, with respect to said axis, a magnetic component produced by copper wire segments parallel to the axis and a magnetic component produced by copper wire segments arranged along a circumference, and creating a mesh in front of said coil distributed magnetic field; It is characterized by: magnetic shunt means disposed between said coil and said screen; Said magnetic shunt device is made of magnetically permeable material, and its structure and position will be selected according to said coil, so that said net-like distributed magnetic field before said coil is reduced. 2. The apparatus of claim 1 wherein said magnetic shunt means is a ring of magnetically permeable material substantially coaxial with said central axis. 3. The device according to claim 1, characterized in that said magnetic shunt device is a linear ferrite product having magnetic properties such that the effective μ substance depends on its structure and position The above changes very little when the actual μ changes.

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