Patent GB-278051-A (GB)
Title: Conversion of modulated electric current into a series of telegraphic impulses, particularly applicable to phototelegraphy
IPC: H04N1/41
Filed: 1926-04-01
Abstract: 278,051. McFarlane, M. L. D. April 1, 1926, Copying-telegraphs. - Current variations produced by the action of light on a light-sensitive element in the circuit are supplied to relay means set to respond to particular values of current intensity in order to produce in a plurality of output circuits one or more currents suitable for recording the variations. The current of varying intensity may be a direct current or a pulsating or intermittent current obtained by the use of a commutator, buzzer or valve oscillator. In one arrangement, Fig. 2, light transmitted or reflected from successive elemental areas of the picture or the like, mounted on a rotatable and axiallymovable drum A, is incident on a photo-electric cell G, and the varying direct current in the circuit of the cell, after thermionic amplification, is supplied to the relay device e.g. to the operating windings, arranged in series as shown, or in parallel, of five relays 8 each responsive to a predetermined minimum intensity of current. Transformer amplification may be employed for a pulsating or intermittent current. The current to which each relay 8 responds may be predetermined by adjustment of a series resistance 8R in its biasing circuit or of the tension of a spring controlling the armature, and the setting of each relay may be indicated by a corresponding lamp, a switch being provided for temporarily connecting these lamp to the output circuits a - - e. Each of the circuits a - - e may control a punch magnet in a machine for producing a tape perforated according to a standard five-unit code. The five relays 8 may be replaced by a single vibrating relay V, Fig. 7, or by a solenoid 10, Fig. 11. In the arrangement of Fig. 7 current is supplied to the biasing winding v<2> through an interrupter 9 and adjustable resistance and the amplified current of varying intensity supplied to the operating winding v<1> produces corresponding variations in the durations of contact of the relay armature with the marking contact M. The resulting currents of varying duration in the output circuit L are supplied to a, five-segment commutator C, Fig. 10, of which each segment is connected to one of the circuits a - - e. The commutator makes one revolution per elemental area of picture explored. In the arrangement of Fig. 11 the core 11 of the solenoid moves an arm 12 over five contacts 13<a> - - 13e in the circuits a - e e respectively the strength of input current corresponding to a particular output circuit being pre-determined by adjustment of a returning spring 14. In a further modification the amplified current is supplied, as shown in Fig. 12, to five thermionic valves T<1> - - T<5> having their grids arranged in parallel and subjected to successively increasing biasing potentials and having their plates connected in the circuits a - - e. The commutator C, Fig. 10, may also be used for connecting the circuits a - - e directly to line L for recording the impulses or reproducing the picture at the receiving station. The commutator segments may be of successively increasing length in order that the durations of the line currents may have a logarithmic relation corresponding to the logarithmic relation between the intensity of received light and the density in the original photographic negative or print. Specifications 195,577 and 197,402 are referred to.