Patent GB-656804-A (GB)
Title: Improvements in or relating to display arrangements for cathode ray tubes
Inventor: CLEAVER RICHARD FRANCIS
IPC: H01J29/70
Filed: 1948-09-17
Abstract: 656,804. Cathode-ray oscillographs. STANDARD TELEPHONES & CABLES, Ltd. Sept. 17, 1948, No. 24413. [Class 37] [Also in Groups XL (a) and XL (c)] Means are provided for adjusting the angle of the deflection axes of a cathode - ray tube, thereby permitting the employment of a scale marked on the inside of the end of the tube. As shown in Fig. 1 the tube is provided with a pair of deflecting plates 1, 2 for producing deflections along the axis X<SP>1</SP>OX<SP>2</SP>, Fig. 2. These plates are connected to earth through equal resistances 5, 6. A pair of auxiliary deflecting plates 7, 8 are connected to the plates 2, 1 through equal resistances 9, 10 and to earth through equal resistances 11, 12. The plates 7, 8 produce deflections along the line x<SP>1</SP>Ox<SP>2</SP> perpendicular to X<SP>1</SP>OX<SP>2</SP> so that the deflection axis is rotated through an angle # to Z<SP>1</SP>OZ<SP>2</SP>. By making the resistance 11 adjustable the angle # may be varied as desired. The plates 7, 8 may be located at any convenient point along the beam. In a modification, Fig. 3, two similar potentiometers 13, 14 are connected between the plates 1, 2 and their movable contacts are connected to the auxiliary plates 7, 8, either directly or through a buffer amplifier 15. The movable contacts are coupled so that they can be simultaneously adjusted equally in opposite directions from the centre. Where the tube has two pairs of deflecting plates at right angles for producing two independent deflections along perpendicular axes, the second pair of plates may be provided with a second pair of auxiliary plates and potentiometers and buffer amplifier, the auxiliary plates being separated from the main deflection plates at some other part of the electron beam so that the two sets do not interfere. The direction of each deflection plate may thus be independently adjusted so that each may be brought into coincidence with the corresponding axis of the scale. If the tube shown in Fig. 1 has the usual two pairs of deflecting plates the second, or Y-axis pair, can take the place of the auxiliary plates 7, 8, the effect being to turn both deflection axes simultaneously about the origin in opposite directions. The two pairs of auxiliary plates 20, 21, Fig. 4 (a) may be arranged in a group just beyond the Y-plates 19, or the pair 20 may be placed between the last anode 17 of the electron gun and the X-plates 18, the plates 21 being just beyond the Y-plates 19, as shown in Fig. 4 (b). In both cases they may be mounted on the electron gun deflection plate assembly. The auxiliary plates 20, 21 may be mounted or deposited as metallic films on the inner surface of the envelope, with external connections fused through the glass, as shown in Fig. 4 (c). The auxiliary plates may alternatively be placed in various positions outside the tube, as shown in Fig. 4 (d, e, f). Analogous arrangements may be made where the deflecting elements are coils instead of plates. Another method employs a locally produced axial magnetic field. The undeflected beam OC, Fig. 5, is directed along the axis of the cathode-ray tube and is unaffected by a uniform magnetic field H parallel to the axis. If the beam is deflected through an angle # to OB the field H at any point X can be resolved into rectangular components H sin # and H cos #, and the beam is deflected at right angles to the plane of the diagram so that the deflection axis is rotated from ACB to A<SP>1</SP>CB<SP>1</SP>, Fig. 6. The field H may be produced by a coil 22, Fig. 7, whose length and winding depth are small compared with its diameter, placed coaxially with the tube 23 and surrounding the outer face of the tube. A magnetic screen 24 surrounds the tube. The coil 22 is supplied with D.C. from a battery 25 supplying a potentiometer 26, or it may be supplied with A.C. if a cyclically varying shift of the display is required. The coil 22 is wound in a metal former 27, Fig. 9, and is fixed behind the panel 28 by screws 29 passing through large clearing holes to permit the coil to be adjusted so that its axis coincides with that of the tube. The coil 22 may alternatively surround the central portion of the tube. The scale may be marked on the inner face of the bulb by firing precious metals or metallic compounds into the glass surface. Specification 619,974, [Group XL (c)], is referred to.