JPH0246085A - Cathode ray tube display device - Google Patents

Abstract

PURPOSE: To reduce the effect of a magnetic field of a low frequency in front by mutually slanting two coils so that each of axial directions of two coils may be on the axis of a CRT and magnetic yoke assembly and also that the axes may cross with each other at a point in the rear of a CRT screen. CONSTITUTION: A pair of coils 5 and 6 is arranged so that two axes of the coils 5 and 6 are not parallel and also exist on the same flat plane, and a pair of coils 5 and 6 is positioned farther from a screen 3 than its ideal position. Thereby, the magnetic field in front of the screen 3 is increased and the magnetic field at the back of the screen is reduced. In this way, the effect of a magnetic field of a low frequency in front of a CRT display device can be decreased.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention is directed to a cathode ray tube display device having means for reducing the stray magnetic field generated in front of the screen.

B. Conventional Technology Although there is no scientific proof that leakage magnetic fields from the front of cathode ray tube (CRT) display devices are harmful to humans, in some countries, magnetic fields between 1 kilohertz and 400 kilohertz There is a requirement that the leakage field in the range of magnetic fields (hereinafter referred to as low-frequency magnetic field) be reduced below a certain value. For that purpose, CR
In the field of T-display devices, much effort has been made in the past to accommodate this requirement. The most common solution to this problem is to provide one or more coils to provide a compensation field to offset the unwanted stray fields. Examples of this solution are Finnish Patent Application No. 86148, PCT Application WO37105
437 and WO371060054, European Patent Application No.220777 and European Patent Application No.235863, West German Patent Application No.3631023 and European Patent Application No.370782
No. 9, U.S. Pat. No. 4,634,930, U.S. Pat. No. 4,677,34
No. 4 and No. 4709220, and pages 119 to 122 of the June 1988 18M Technical Disclosure Bulletin. A second solution is to use magnetic shielding, as described in European Patent Application No. 88105077.7.

Although the problem of leakage magnetic fields seems to have been analyzed and well understood, the solution to this problem is not as simple as thought, although numerous attempts have been made. It's obvious when you look at it. Furthermore, whatever solution to this problem, the cost of CRT display devices should not be made unreasonably high.

C9 Problems to be Solved by the Invention It is an object of the present invention to provide a device which provides a simple structure and an effective solution for mitigating the effects of low frequency magnetic fields in front of a CRT display device. .

Means for solving the D0 problem As is clear from the above-mentioned known examples, the use of one coil is not very effective, and therefore the use of two or more coils is proposed. .

The problem lies in the fact that it was generally believed that two or more coils were necessary to obtain optimal compensation.The present invention proposes to appropriately select the orientation and arrangement of only two coils. This is based on the discovery by the inventor of the present application that effective compensation can be obtained by doing so.

A CRT display device according to the present invention includes a CRT display device having an electromagnetic yoke assembly for scanning an electron beam across the screen of the CRT, and a leakage magnetic field in front of the CRT screen generated by the electromagnetic yoke assembly. a pair of opposingly mounted compensation coils, and the pair of compensation coils are disposed adjacent the electromagnetic yoke assembly such that the axes of the coils are not parallel but coplanar. The compensation magnetic field is increased in front of the CRT screen, and the CRT
It is characterized in that it is oriented such that it is reduced on the back side of the T screen. In other words, the two coils are arranged such that their respective axial directions are on the axis of the CRT and the electromagnetic yoke assembly and intersect at a point behind the CRT screen.
The coils are said to be tilted with respect to each other.

E. EXAMPLE Referring to FIG. 1, a CRT is shown provided with an electromagnetic yoke assembly 2 for scanning an electron beam over the surface of a phosphor layer on the inner surface of a screen 3. As shown, a low frequency magnetic field S generated by the leakage field from the electromagnetic yoke assembly 2 is often found in front of the screen 3.

In practice, the leakage magnetic field S is perpendicular to the axis 4 of the CRT and C
It is approximately the same as the magnetic field generated by a magnetic dipole positioned transverse to axis 4 of the RT.

In theory, a canceling coil energized to generate equal magnetic dipoles in opposite directions and placed in the same position as the dipoles would effectively cancel the stray field S of the deflection yoke. I can do it.

However, in practice, the glass tube of the CRT precludes the installation of only one cancellation coil, as illustrated by the above-mentioned prior art. As attempted in the prior art, a pair of cancellation coils, one above and the other below, is equivalent to a vertically oriented dipole. However, a conical CRT tube, with the axes of the coils coinciding with each other and with the axes of the dipoles of the equivalent stray field, prevents the mounting of the canceling coils. Become. To overcome this difficult problem,
Traditionally, complex wiring has been proposed.

However, by arranging the pair of coils 5 and 6 so that their two axes are not parallel and on the same plane, the pair of coils 5 and 6 are placed in a position other than the ideal position. This coil arrangement of the present invention, which can be positioned away from the screen to obtain effective cancellation, increases the magnetic field in front of the screen 3 and reduces the field behind the screen. The canceling magnetic field is indicated by the reference numeral 7.

Coils 5 and 6 have their axes aligned with the axis 4 of the CRT.
It is tilted so that it crosses the

In the apparatus shown in Figure 1, at a distance of 0°3 meters from the CRT screen, the leakage magnetic field with a frequency range of 1 kilohertz to 400 kilohertz is 20 mT/S d
B/dt was able to decrease to a value smaller than 8Q nT ΔB.

The dimensions of the coil, the number of turns in the coil, the angle of inclination of the coil, the position of the coil and the magnitude of the current are
Depending on T, which can be determined by simple experiments, by tilting the coil according to the invention, optimal cancellation of the stray field can be obtained in a simple way. The invention provides that if more than one compensation coil is used,
Additional costs (and energy losses) can be avoided.

The present invention utilizes a color CFLT display and a monochrome CRT display.
Can be used for both displays.

FIGS. 2A and 2B are schematic diagrams illustrating a further improved embodiment of the present invention. This embodiment differs from the embodiment of FIG. 1 in that a pair of sense coils 9.10
This is the addition of . That is, sense coil 9.
Reference numeral 10 is arranged within the case of the CRT display device to detect leakage magnetic fields generated by the horizontal deflection coil of the yoke, etc., and generates a voltage proportional to the amount of change (time differential) of the detected magnetic field.

The voltage on the sense coil is then integrated by an integrator 14 in the circuit shown in FIG.
It is supplied as a driving current of 6.

The polarity of the current is then selected to cancel the stray magnetic field.

DETAILED DESCRIPTION OF THE F1 INVENTION As described above, the present invention provides a simple structure and effective solution for mitigating the effects of low frequency magnetic fields in front of a CRT display device.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an embodiment of a CRT display device equipped with a leakage magnetic field compensation coil according to the present invention, and FIGS. 2A and 2B are schematic diagrams showing another embodiment of the present invention. FIG. 3 is a schematic diagram of the driving circuit of the embodiment of FIGS. 2A and 2B. 1... CRT tube, 2... Electromagnetic yoke assembly, 3... CRT screen, 5.6... Coil,
7... Magnetic field for cancellation, D... Magnetic dipole, S...
...Leakage magnetic field. 1 applicant

Claims (1)

[Claims] a cathode ray tube display; an electromagnetic yoke device for scanning an electron beam across a screen of the cathode ray tube display; and a device in front of the screen for canceling leakage low frequency magnetic fields generated by the electromagnetic yoke device. In a cathode ray tube display device having a pair of compensation coils for generating a magnetic field, the pair of compensation coils are arranged at an angle with respect to each other such that their axes intersect at a position away from the screen. Characteristic cathode ray tube display device.