Patent GB-684559-A (GB)
Title: Improvements in or relating to circuit-arrangements for use in automatic signalling apparatus, for example, in telephone systems
IPC: H04Q3/52
Filed: 1949-04-19
Abstract: 684,559. Automatic exchange switches. NAAMLOOZE VENNOOTSCHAP PHILIPS' GLOEILAMPENFABRIEKEN. April 19, 1949 [April 20, 1948], No. 10348/49. Class 40 (iv). A cathode-ray tube switch hunts for one of a desired group of outlets under the control of a deflection voltage generator producing step-wise variations in voltage until the'beam strikes the collecting electrode of a desired outlet whereupon the voltage across a resistance leading to an auxiliary electrode of the tube is varied to cause the generator to be stopped. As shown, the test switch is the tube system 1 having a cathode 2, deflection electrodes 3, 4, collecting electrodes 5 ... 9 each associated with a line, and a grid-like electrode 10 connected by a resistance 11 to positive battery. The electrodes 5 ... 9 are connected through the corresponding lines to a positive voltage source but if a line is busy the corresponding electrode is grounded. When the beam strikes the electrode of a busy line, e.g. 5, most of the electrons travel to electrode 10 and the potential of the lower end 12 of resistance 11 is lowered. The generator increases the deflecting voltage by another step and the beam moves to electrode 6. Similarly it moves to electrode 7 but as this is at a positive potential the current is divided between electrodes 7 and 10 and the potential of point 12 rises. The voltage controlling the generator is thereby disconnected and the beam remains on electrode 7. The step-wise voltage is produced by a second cathode-ray tube system 13 having a cathode 14, deflection plates 15, 16, and two collecting electrodes 17, 18, the former having apertures 19 so that the beam strikes the electrodes 17, 18 alternately. The electrode 18 is connected via resistance 20 to positive battery and directly to the deflection plate 15. This arrangement results in a plurality of positions of stable adjustment for the beam and under the action of a control voltage the beam may be moved from one position to the next, the voltage between the deflecting plates varying in steps. Connection of deflecting plates 3 and 15 causes the beams of systems 13 and 1 to move in synchronism. If desired, the two systems may be housed in a single tube having a common cathode and deflection system and only one beam, preferably flat. The source of the control voltage comprises two non-contact-making relays 21, 22, each comprising a cathode-ray tube having two collecting electrodes and two deflecting plates. In each of these tubes one of the collecting electrodes (23, 31) is of the secondary emission type and is fed with voltage from a potential divider. The collecting electrode 24 is connected to battery and as long as the beam is not directed on to electrode 23 the switching path 23-24 is open; If the beam is deflected on to electrode 23 secondary electrons travel towards the electrode 24 and the potential of electrode 23 rises to a value only slightly less. than that of electrode 24. The path is then closed. The collecting electrode 32 is connected to electrode 23 of relay 21 and upon incidence of the beam upon electrode 31 its potential rises to substantially that of 32. Detailed explanation of this action is contained in Specification 660,794, [Group XL (a)]. Deflection plates 25, 36 are connected to electrode 31 and point 12 respectively. Assuming the cathode-ray beam of switch 1 is initially at the extreme left-hand side and strikes the auxiliary electrode 10, point 12 is at a low potential and the beam of relay 22 strikes electrode 31, but the beam of 21 does not strike electrode 23. If the contact 37 is changed over the potential of electrode 32 is raised and that of 31 thereupon rises so that the beam of relay 21 is deflected on to electrode 23. Both switching paths are then closed and if 37 is then restored the variations in voltage of electrode 24 brought about by the control voltage generator 39 are passed to electrode 31 and then to deflecting plate 15. When the beam of system 1 reaches a collecting electrode corresponding to a free outlet the rise in the potential at point 12 deflects the beam of relay 22 away from electrode 31, the potential of which then decreases and opens the path of relay 21 also. The control voltage is no longer transmitted and the beams of systems 1 and 13 remain stationary. Relay 41 pulls up and grounds electrode 7, whereupon the potential at point 12 again falls and the beam of relay 22 strikes electrode 31 but without effect, as electrode 32 is at low potential. Changing over of contacts 37 then initiates a new search. Methods of restoring the system 13 to its initial position after scanning of all outlets has been completed is described in Specification 684,552.