Patent GB-352032-A (GB)
Title: Improvements in or relating to electromagnetic vibratory devices for use in signalling systems
IPC: H04L5/06
Filed: 1930-04-03
Abstract: 352,032. Distant control systems. ASSOCIATED TELEPHONE & TELEGRAPH CO., 1033, West Van Buren Street, Chicago, U.S.A. April 3, 1930, No. 10614. Convention date, April 8, 1929. [Class 40 (i).] An electromagnetic device for use in signalling systems comprises an electromagnet adapted to cause the vibration of a tuned reed of magnetic material whereby current is generated in the circuit of a similar electromagnet similarly located with respect to the reed but having its field substantially at right-angles to that of the first electromagnet. In the construction shown in Figs. 2, 3 and 4, two brass cups 1, 2, detachably connected together, contain, respectively, magnet coils 16, 15 arranged so that their magnetic fields are at right-angles to each other. The tuned reed 11 is mounted adjustably on a brass block 10 by means of a clamp 12. The device is provided with a base 8 having spring contacts for making connections to an external circuit. Fig. 5 illustrates a signalling system in which the device is employed. Two oscillators 50, 60, operating at different frequencies, produce signals which are amplified and are separated by filters 80, 90. The output circuits of these filters operate relays 82, 92, which control other relays 85, 95, adapted to provide controlling circuits. A current flowing in the plate circuit of the valve 53 flows through the winding of magnet 15, which attracts the reed 11, thereby reducing the magnetic flux through magnet 16. The e.m.f. induced in the winding of the magnet 16 is stepped up by the transformer windings 51, 52 and varies the potential on the grid of the valve 53. This change of potential decreases the plate current through the magnet 15, allowing the reed to fall back and cause an increase in the flux through magnet 16 whereby the plate current through the magnet 15 is increased to attract again the reed 11. The reed continues to vibrate at its natural frequency and controls the oscillations generated in the circuit through the plate of valve 53. The current through this plate induces a current in the secondary winding 55 of a transformer, this winding being connected in series with a key 56 and the primary winding 57 of a second transformer. When the key is closed a current of the frequency generated by the oscillator passes through the grid of an amplifying valve 70. This valve is associated in a similar manner with an oscillator 60 operating at a different frequency from that of the oscillator 50. The currents of these oscillators are amplified and superimposed on a line leading to an amplifying valve 77, the plate circuit of which contains transformer primary windings 86, 96. The secondary windings are in the grid circuits of valves 88, 98, the plate circuits of which lead to electromagnetic devices with reeds 11 tuned, respectively to the frequencies of the reeds 11 of the oscillators 50, 60. With the closure of key 56 the oscillator 50 operates to cause the vibration of the reed 11 associated with the valve 88, whereby the potential on the grid of valve 83 is varied, causing a change of plate current which acts to operate relay 82. Similarly if key 66 is closed relay 92 operates. Relay 82 at contacts 84 closes a circuit for relay 85 and relay 92 also acts to close a circuit for relay 95. The relays 85, 95 when these contacts are associated as indicated permit the use of four control circuits. In a similar manner light control circuits may be obtained by the use of three oscillators and corresponding filters. The Specification as open to inspection under Sect. 91 (3) (a) comprises also a modification of the electromagnetic device wherein one of the magnets, e.g. magnet 16, is dispensed with, and a fixed plate is provided which is used with the tuned reed 11 to form a variable condenser. The reed 11 is in the grid circuit of a valve, the plate circuit of which contains the magnet 15, and the primary winding of an output transformer. The secondary winding may be connected to devices tuned to respond to the transmitted oscillations. This subject-matter does not appear in the Specification as accepted.