Patent GB-452859-A (GB)
Title: Improvements in electric arrangements for controlling electric lamps of a lamp screen adapted to reproduce pictures
IPC: G09F13/28
Filed: 1934-11-26
Abstract: 452,859. Monogrammic signs. REKLAMAKTIEBOLAGET EPOK, 14, Drottninggatan, Stockholm, and TRIGGS, W. W., 57, Lincoln's Inn Fields, London. Nov. 26, 1934, No. 34017. Addition to 432,501, [Group XL]. [A Specification was laid open to inspection under Sect. 91 of the Acts, May 27, 1935.] [Class 118 (ii)] [See also Group XL] Relates to an electric arrangement as described in the parent Specification for controlling electric lamps of a lamp screen adapted to reproduce pictures employing a film and photo-electrically controlled grid-controlled gas discharge tubes, in which the projected film strip contains in successive separate areas or frames the pictures to be transmitted divided up into parts, which are projected successively on to a photo-cell screen, the photo-cells being switched over to the lamp groups, corresponding to the picture parts, of the lamp screen in accordance with the advance, picture frame by picture frame, of the film strip by means of a changeover device which operates synchronously with the film advancing means, so that a complete picture appears on the lamp screen. According to the invention, the use of the change-over device is avoided by feeding the gas discharge tubes with alternating current or with rectified alternating current, the phase and frequency of which corresponds to the advance, picture frame by picture frame, of the part-pictures on the film strip. Fig. 1 shows an arrangement in which photo-cells 1, 1a each control a pair of gas-discharge tubes 4, 4a and 5, 5a arranged in inverted relationship as shown and connected to lamps 8, 8a and 9, 9a, the lamps and discharge tubes being fed from a source of alternating current 10. Fig. 4 shows a modified arrangement in which the pairs of gas discharge tubes are not in inverted relationship and in which the source 10 supplies a rectified alternating current, one of its terminals being connected with the cathodes 7 of all the discharge tubes whilst its other terminal is connected with the contact member of a commutator 20 which divides the rectified A.C. into two trains of half waves and feeds them alternately to the groups of lamps 8, 9 and 8a, 9a respectively. If desired, the commutator 20 may control additional gridcontrolled gas discharge tubes connected respectively in the leads between the common terminal 14 and the terminals 15 and 16, Fig. 5 (not shown). Fig. 8 shows an arrangement whereby the photo-cells are illuminated in phase with the half-wave trains. With this arrangement, the part pictures a and b are projected alternately on to a photo-cell screen (not shown), by means of a rotating diaphragm 27 provided with slots 28, 29 so arranged that when the part-picture a is uncovered by the slot 28 the part-picture b is covered and when the latter is uncovered by the slot 29 the former is covered, the diaphragm being rotated at such a speed that each part-picture is covered, or uncovered, during the period of a half wave. In a preferred arrangement, two projectors are employed and a diaphragm as shown in Fig. 8 is provided so that while one projector is projecting part-pictures the other one is covered and vice versa. The travel of the film may be arranged within the interval between two consecutive operating half waves as described in Specification 438,219, [Group XL]. Fig. 10 shows a further modified arrangement in which each photo-cell 1, 1a is associated with a gridcontrolled double anode gas discharge tube 34, 35 the cathodes 7 of which are connected to the centre-tapping of the secondary 37 of the transformer 36 whilst the anodes 6, 6a are connected to lamps 8, 8a, 9, 9a which are in turn connected as shown to the ends of the secondary. Specification 411,835, [Group XL], also is referred to.