RU2054738C1 - Electromagnetic screen for devices with cathode-ray tubes - Google Patents

Abstract

FIELD: television equipment. SUBSTANCE: electromagnetic screen for devices with cathode-ray tubes has optically transparent dielectric plate one side of which carries antireflection and continuous current carrying coats. Its other side has two coats in the form of lattice of conductive material and antireflection coat as well as mount of conductive material. Its upper part houses brackets, screening turn and cable. Lattices under antireflection coat are oriented transverse to each other, are connected over perimeter to mount in upper part to which brackets are joined with one side. Brackets have protrusions for attachment. Lattices are coupled to central conductor of cable and to grounding wire. Screening turn is formed by outer screening braiding of cable. EFFECT: expanded application field. 3 dwg

Description

 The invention relates to electromagnetic field technology and optics and can be applied both in everyday life and in production for personal computers (PCs), industrial TV installations and for television receivers.

 Known devices mounted on the screen of a cathode ray tube: a plate filter electroluminescent index device for reproducing an image (US patent N 414304, publ. 02/06/1979, t. 980, N 1), consisting of a filter that enhances the contrast of the image, with an optical strip, corresponding to the spectral emission characteristics of the screen; a filter for a kinescope of an information display device (French application N 2404978, publ. 07/01/1979, N 22), consisting of a filtering pad on the screen, made in the form of a black matte fabric.

 A transparent screen overlay (UK application N 2148675), an optical filter (US patent N 4575767), etc. are also known.

 These devices do not allow shielding in a wide range of frequencies and cannot fully protect against the influence of monitor radiation on the health of the operator, which does not allow them to be used for a full working day.

 Also known is a protective device for shielding electromagnetic fields, consisting of a transparent substrate and a metal grid or a transparent substrate and a deposited conductive layer (see Donald R.Zh. Whitet. Electromagnetic compatibility of electronic devices / Translation edited by A.I. Sapgir. M. Soviet Radio, 1978, p. 42), selected for the prototype.

 This device does not allow uniform filtering in a wide range of frequencies, that is, the screening effect decreases with increasing frequency, weakly protects from a magnetic field. Using this device does not fully protect the operator from ionizing radiation.

 The aim of the invention is to increase the shielding and filtering effects in a wide range of frequencies of the electromagnetic field and from static electricity.

 To achieve the goal, in the known device consisting of an optically transparent plate coated with antireflection and continuous conductive coatings, two coatings are introduced on the other side of the plate in the form of lattices of conductive material and an antireflection coating, a frame of conductive material, brackets, a shielding coil and cable, this, under the antireflection coating, the gratings are oriented transversely to each other, connected along the perimeter with a frame in the upper part, to which brackets are attached on one side, having on each other on the other side, a protrusion for fastening, and are also connected to the central core cable and ground, and the shielding coil is formed by an outer shielding cable sheath closed in a ring.

 In FIG. 1 shows an electromagnetic screen; in FIG. 2 shows the operation of the screen.

 The electromagnetic screen contains two gratings 1 made of a conductive material, an antireflective coating 1a, a frame 2 of a conductive magnetic material, brackets 3 with a protrusion 4 for mounting, a shielding coil 5, a cable 6 and a conductive coating with an antireflective coating 7 on an optically transparent plate 7a.

 The electromagnetic screen operates as follows.

 Electromagnetic radiation from monitor 8 in a wide frequency range (9 electromagnetic field with a frequency of up to 50 kHz from horizontal scanning; 10 from soft x-ray radiation from infrared; 11 electrostatic field; 14 ultra-low frequency field of 50-60 Hz from vertical scanning) gets onto the grating from a conductive material, while optical radiation 10 passes through a continuous layer, attenuating due to the metallized coating 7 and polarization effects when two crossed gratings pass 1. For an electromagnetic field 9, 14 sieves ki are a screen, because when the gratings are spaced apart, they can be represented by a polarizer and an analyzer, when crossed, the initial field does not pass.

 The magnetic field from the horizontal and vertical scans, the beam deflection system of the cathode ray tube is neutralized using shielding coils, one of which is made in the form of a dielectric plate frame made of conductive magnetic material. The coil closes the magnetic field coming from the tube, and the magnetic field coming from the disconnecting system of the tube is neutralized by a shielding coil made of a shielding braid of the grounding cable. This loop is worn over the monitor cover. The action of the shielding coil is based on the fact that the magnetic flux excites a current in it, which in turn creates a magnetic field, the direction of which is opposite to the direction of the initial field, and reduces it.

 The plate frame in the upper part is attached to brackets having a protrusion for mounting to the monitor, the protrusion enters the ventilation holes in the upper part of the monitor casing. They have a L-shaped shape, which provides a reliable fixation of the screen.

 The electrical connection of the gratings of the coating and the frame with the cable allows you to short-circuit the arising currents to the earth bus of the device (the cable is connected by the central core to the "earth" of the device). In this case, the cable shielding braid, closed in a ring, forms a shielding coil covering the monitor casing in the region of the tube deflecting system. According to the theory of shielding, the currents induced in such a turn are directed against the field exciting them and quench it.

 X-ray radiation 10 is absorbed by the material of the dielectric substrate plate, and the degree of absorption depends on the density of the material, attenuation also occurs due to metallized layers. The metallized layer provides the necessary shielding efficiency due to reflection, while the attenuation reaches the following values: electric field more than 150 dB; magnetic field 10-30 dB, and at frequencies: 1 MHz 74-95 dB; 10 MHz 52-72 dB; 50 MHz 28-46 dB.

 A corresponding graph is shown in FIG. 3, where the frequency (kHz) of the electromagnetic field and its attenuation (dB) are plotted on the axes.

 Thus, the use of a combination of a conductive coating and crossed gratings of conductive material makes it possible to reduce the operator exposure level by approximately 70-90 dB and maintain its operability.

Claims (1)

 ELECTROMAGNETIC SCREEN FOR INSTRUMENTS WITH ELECTRON BEAM TUBE, containing an optically transparent dielectric plate coated with antireflective and continuous conductive coatings on one side, characterized in that two additional coatings are introduced in the form of a lattice of conductive material and an antireflective coating located on the other side optically transparent dielectric plate, frame of conductive material, brackets, shielding coil and cable, while under the antireflection coating The ki are oriented across each other and are electrically connected around the perimeter with a frame, to the upper part of which brackets are attached on one side, having a protrusion on the other side for fastening and are electrically connected to the central core cable and ground, and the shielding coil is formed by an outer shielding cable braid in the ring .

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