Patent GB-472728-A (GB)
Title: Improvements in or relating to telegraph transmitters
IPC: H04L17/14
Filed: 1936-10-30
Abstract: 472,728. Photo - electric telegraph transmitters ; thermionic relay circuits. CREED & CO., Ltd. Oct. 30, 1936, No. 29558. Convention date, Nov. 4, 1935. [Classes 40 (iii) and 40 (v)] In a photo-electric telegraph transmitter for multiple-unit code signals and using a tape with transverse rows of perforations or opaque marks start and stop impulses are transmitted independently of the tape and each row is scanned while the tape is moving continuously through the distance between successive rows of perforations or marks. Construction of transmitter, Figs. 2 and 5. The photo-electric cell 61 is mounted in a fixed cylinder 59 having a longitudinal slot 65 in its upper portion covered by a plate 66 having slits 67 arranged in an inclined row, the lefthand slit 60 being for a stop signal, the blank 68 for a start (spacing) signal and the remainder for a six unit code. Cylinder 59 is surrounded by a rotary drum 52 having slots 50, 53 registering in succession with the slits 60, 67, the drum 52 being nested within a further rotary drum 54 having rows of perforations 55 and tape feed pins 56 adapted to register with the perforations in the tape. The optical system comprising lamp 82, condenser lenses 83, 84 and cylindrical lens 85 is mounted in a tube 12 hinged to turn down about pivot 76 for inserting the tape. The axis of the cylindrical lens 85 is in the same vertical plane as the inclined row of slits 67 and the lower end of tube 12 carries a resilient gate 88 having two slots registering with the two groups of three slits 67 and separated by a guide for the pins 56 on the drum 54. The drums are driven by motor 17 through worm wheel 21 and a slipping clutch 26, 28, a projection on part 28 fixed to shaft 22 being normally held by the armature of magnet 33. Shaft 22 which carries drum 52 is geared to shaft 41 of the perforated drum 54 so that drum 52 performs one revolution while drum 54 rotates from one row of perforations to the next, the perforations of a row being thus scanned in turn. To obtain a well-defined impulse, only the centre portion of a perforation 55 is used as shown in Fig. 17 where 95 represents the width of a slot 53 which equals the length of slit 67 and makes the exposure while the tape is travelling a distance 97. Modifications. In the arrangement shown in Figs. 7 and 11, the tube carrying the lamp 171 and lens 173 are fixed horizontally and the light beam is deflected through cylindrical lens 175 by mirror 174. The lamp holder is mounted on plates 166, 167 sliding in vertical and horizontal guides for purposes of adjustment. The perforated scanning and tape feeding cylinder 54, Fig. 5, is dispensed with, and the oblique row of slits 67 is replaced by a plate 151 with a continuous oblique slot over which the tape is moved by a separate pin cylinder driven at suitable speed by gearing from shaft 106 which is driven by slipping clutch mechanism as before. The scanning is performed by slotted cylinder 112 similar to 52 and secured to permit longitudinal and rotary adjustment on shaft 106. The photo-electric cell 143 is mounted close to the upper portion of the scanning cylinder 112 in a detachable end plate 142 of a casing 141 enclosing the cylinder. The tape is guided in a groove 187, Fig. 11, and after the tape has been inserted, the U-shaped assembly 181, 182, 188 having slotted arms 183 is pulled forward against spring action so that blocks 185 are pressed by spring 193 on top of the tape in the guide and, hold it with sufficient freedom of movement, against the feed cylinder 122. The oblique slot in plate 151 may be made by coating one or both sides of a glass plate with opaque material which is removed to furnish the slot. Alternatively, similar slots may be formed in spaced opaque plates. The use of spaced slots for the light beam gives greater difference in the light intensity for perforated and non-perforated portions of the translucent tape ordinarily used. In a further modification, Fig. 14 (not shown), the plate 151 is replaced by a cylinder with an inclined slot and disposed within scanning cylinder 112 around cell 143. Thermionic relay circuits, Fig. 15. The operating potentials are derived from potentiometer 204 and are such that the first valve 206 is biassed negatively but not to cut-off so that its anode current over resistance 217 biasses the second valve 219 to cut-off. In the case of a perforated tape transmitter, when the transmitter is in the stop position, photo-electric cell is activated by light through one of the " stop " holes 58, Fig. 5, with the result that cell current biasses valve 206 to cut-off, whereupon valve 219 passes anode current and relay 227 transmits a stop (marking) signal. When the transmitter is started, the blank space 57, Fig. 5, cuts off the light and the valves reverse their condition to send the start (spacing) signal. Code signals follow in a similar manner, perforations in the tape causing marking signals to be transmitted. In the case of a printed translucent tape transmitter, the light conditions are reversed and the first valve Fig. 16 (not shown), is biassed to cut-off and actuation of the cell reduces the negative bias. The "stop" " holes 58, Fig. 5, are replaced by blank space and " start " holes are provided in space 57. Thus, in the stop position, the first valve is cut-off and the second valve passes marking current and in the start position, light activates the cell, which reduces negative bias to start the first valve and cut-off the second valve. The printed spots on the tape cause the transmission of marking signals and it will be seen that the character of the start, stop and code impulses is the same for perforated and printed tape.