Patent GB-431395-A (GB)
Title: Improvements in and relating to electric signalling systems
IPC: H04L12/10
Filed: 1934-01-05
Abstract: 431,395. Code and type printing telegraphy. HILL, A. P., and EXCHANGE TELEGRAPH CO., Ltd., 64, Cannon Street, London. Jan. 5, 1934, No. 432. [Classes 40 (iii) and 40 (v)] Gas-filled valves, for use as telegraph relays and the like, are turned on alternately by discharge of the grid-potential or by impulses applied through a transformer. Relay circuits using gas-filled valves. In the idle state the contacts 35<a>, 36a, Fig. 2, remain closed so that the grids of the gas-filled valves 31, 32 are negative and no impulse passes out of the transformer 17. When one of the contacts is opened the associated valve is caused to strike, and an impulse, positive if one contact is opened and negative if the other, passes to line A, B through transformer 17. When the contact is closed again the valve current is extinguished by the action of the condenser 22 or by breaking the anode circuit. In the arrangement shown in Fig. 3, the point 99 is connected to the negative of a battery (not shown) while the positive of the battery can be connected alternately, through relays or through a telegraph transmitter of the kind described in Specification 12215/84, [Class 40], to either of the points 97, 98. When this is done the corresponding valve 64 or 65 is caused to strike by the impulse passed on by the transformer 84 or 95, and when the connection is interrupted a reverse impulse sufficient to extinguish the valve is produced. When one of the valves is in action a D.C. impulse of corresponding polarity is sent out through the line 79 with earth return. The electrostatic transformer screens 87, 91 prevent the grids 82, 89 from being accidentally impulsed by sudden changes in the potentials of the cathodes. In a singlevalve apparatus, Fig. 4 (not shown), the circuits shown in the lower half of Fig. 3 are discarded. Step-by-step keyboard transmitter. Fig. 2 shows a transmitter, suitable for use with a receiver such as that described in Specification 14430 /02, [Class 40], in which alternate positive and negative brief impulses are continuously sent to line through transformer 17 by the valves 31, 32 under the control of contacts 35a, 36<a>, until one of the keys 46 of a keyboard takes effect, whereupon a long printing impulse of one or other polarity is sent to line through contact 42 by battery 62. When no key is being depressed the shaft 39 is driven by motor 40 through a friction clutch 41 which, when stop-wheel 43 is free, applies a positive drive by means of a pawl. Contacts 35a, 36a are opened alternately by star-wheels 49, 50 on shaft 39. When a key such as 46 is depressed, rotation continues until a corresponding stud 44 on the drum 44a is reached, whereupon the shaft is arrested in a definite position by energization of the magnet 52 which causes a stop pawl 51 to engage the stop wheel 43. This wheel acts to disengage the positive drive so that the clutch 41 slips, and also to close the contact 42 so that a long D.C. printing impulse, whose polarity is determined by the position of the commutator shaft 54, is sent to the line A, B. The shaft 39 is arrested in such a position that both contacts 35a, 36a are closed so that both valves are quiescent.