DE974968C - Device for generating an additional magnetic field in an electron beam tube - Google Patents

Description

The invention relates to a device for generating an additional magnetic field in a cathode ray tube, in particular how it is used for panoramic imaging in a radar system, and it aims to provide means for image adjustment, e.g. B. to decenter the image to create.

In a cathode ray tube for panoramic imaging, one set usually becomes revolving Coils provided for magnetic deflection,

to which sawtooth-shaped deflection currents are applied for drawing up a screen image on the tube. The image adjustment can take place, for example, with the aid of a fixed coil system, by means of which an additional magnetic field that determines the image setting is generated. As well as the rotating as well as the fixed coil system are usually very close Arranged on the hollow cone of the cathode ray tube so as not to run the risk of the deflected Electrons strike the neck of the hollow cone. These coil systems are necessary in this way also arranged in close proximity to each other.

It is also already known that the additional magnetic field can be increased by permanent magnets with a high coercive force generate whose flow is closed by a ring made of magnetically soft material.

According to the invention, the additional magnetic field is generated by one or more ring-shaped, i.e. H. a more or less large part of a closed ring

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ges forming permanent magnetic body (s) produced, which consists of a nearly non-conductive permanent magnetic material, which consists of essentially non-cubic crystals of polyoxides of iron, at least one of the metals barium, strontium and lead and optionally calcium, but does not contain any nickel or cobalt and has a ratio of the remanent induction B _r to the coercive field strength rHc at most = 4. The invention is explained in more detail in the drawing using an exemplary embodiment shown in FIG. 1 and a special design for a magnet body according to the invention shown in FIGS. 2 and 3.

In Fig. 1, 1 denotes a cathode ray tube with an electron acceleration and density modulation system 2, which is indicated by way of illustration, and a deflection coil system 3 which is arranged near the beginning of the hollow cone of the tube 1 and which is rotated with the aid of a motor, not shown. In order to be able to set the panorama image designed in this way on the screen 4 of the electron beam tube 1, a magnetic body 5 is provided which generates a diametrically directed additional magnetic field H and, as indicated in the side view of FIG , ferromagnetic material with attached two bodies 7 and 8 magnetized in the direction NS of their smallest dimension of permanent magnetic material. The magnetization of the bodies 7 and 8 is much easier than if the magnetic body 5 were made entirely of permanent magnetic material.

If, in a device of the type specified, the image setting is carried out with the aid of an in the vicinity of the deflection coils 3 arranged permanent magnets made of conductive material, so that Field of these coils 3 cause eddy currents in this magnet, whereby the deflection field is distorted and in particular the ramp-down time of the sawtooth increases. This makes this disadvantage avoided that an almost non-conductive, permanently magnetic material is assumed.

However, according to the knowledge on which the invention is based, it is not sufficient that the permanent magnetic material is non-conductive, but it is also necessary that the ratio of the remanent induction to the coercive field strength of the permanent magnetic material remains less than 4. Materials (which also usually have a high conductivity) is the ratio between the remanent induction B _r and the coercive field strength bHq z. B. equal to 12, so that the hysteresis loop, which is described around a certain setting of the field strength and the induction of this material, will have a slope which is considerably smaller than the ratio B _r : bHc, whereby this hysteresis loop have a fairly large area can. However, the lower this ratio becomes, the more this area has to shrink, since the inclination of the hysteresis loop then approaches the mentioned ratio more and more. With a ratio that is less than 4, the hysteresis losses generally turn out to be practically negligible. This also has the advantage that the magnetic resistance which the field of the coils 3 finds is practically the same in every position of these coils. A permanent magnetic material that comes close to these conditions is, for. B. the well-known material marketed under the name »Vectolite«, which has a ratio of B _r : bHc = 1.8, but still has a relatively low specific resistance of 225 Ω.

The material used according to the invention for the stated purpose, on the other hand, has a specific ohmic resistance of more than ίο ⁵ Ω at a ratio B _r = bHc of a maximum of = 4. In addition, a fairly large maximum value of BH is found, as a result of which the required volume of permanent magnetic material to generate a given field can remain relatively small. In order to be able to change the strength of the generated magnetic field, two magnetic bodies according to FIG. 2, which consist of the highly permeable rings 6 and 6 'and the permanent magnetic bodies 7 and 8 or 7' and 8 ', can be arranged one behind the other as shown in 3 is shown, these bodies being rotatable about the axis 10 with respect to one another. The deflection that the electron beam then experiences is due approximately to the vector composition of the magnetic fields H and H ' generated by the bodies 7 and 8 or the bodies 7' and 8 'and can thus be varied within wide limits.

The invention is also applicable to image adjustment or image correction in a cathode ray tube usable for television purposes, but in this case the need to use the deflection coils and the to arrange permanent magnetic bodies close together, usually not so compelling.

Claims (2)

PATENT CLAIMS: I. Device for generating an additional magnetic field in a cathode ray tube with at least one deflection coil for the magnetic deflection of the electron beam with the aid of one or more ring-shaped permanent magnetic bodies which generate or generate a diametrically directed additional magnetic field, characterized in that at least one of the Near the deflection coils arranged body made of almost non-conductive, permanently magnetic, essentially non-cubic crystals of polyoxides of iron and at least one of the metals barium, strontium, lead and optionally calcium, but not nickel or cobalt-containing material with a ratio of remanent induction B _r to the coercive field strength bHc maximum = 4. 2. Device according to claim 1, characterized in that that two bodies made of the aforementioned permanent magnetic material on one for the eddy currents of the coils almost non-conductive, ferromagnetic ring, e.g. B. made of ferrite or sheet iron, attached diametrically opposite are. 3 · Device according to claim ι or 2, characterized characterized in that two annular magnetic bodies arranged one behind the other in the beam direction are provided from the mentioned permanent magnetic material, which are arranged rotatably against one another are. Considered publications:
ίο United States Patent No. 2,544,898; Swiss Patent No. 185 511; French Patent No. 818,639; Archiv für Elektrotechnik, 1948, pp. 260 to 266; R. M. Bozorth, Ferromagnetism, 1951, p. 421; The Iron Age, May 1946, pp. 66 and 68; Philips' Technische Rundschau, December 1946, pp. 353 and 357; Electronics, December 1947, p. 189, and January 1948, P. 122/123; Denki Kagaku, 1937, No. 5, pp. 411 to 419; Soller, Starr and Valley, Cathode Ray Tube Displays, 1948, p. 414. 1 sheet of drawings © 109 5 »8 6.61