Patent GB-637383-A (GB)
Title: Apparatus for the automatic calling of pre-selected and pre-set telephone numbers
IPC: H04M11/04
Filed: 1947-03-07
Abstract: 637,383. Automatic exchange systems. RAVERA, M. March 7, 1947, No. 6505. [A Specification was laid open to inspection under Sect. 91 of the Acts, Sept. 15, 1947.] [Class 40 (iv)] A burglar or fire alarm for use with an automatic telephone system has speed-controlled rotating members and a Geneva mechanism which switch out the local substation and transmit a repeated series of dialling impulses followed by the switching into circuit of a microphone, a local alarm being operated if the telephone line to the exchange is rendered unusable. As shown, a disc cam 13, Fig. 1, operates impulsing contacts 15, the cam being rotated from a drive shaft 1 by gears 11, 12,19 and a pawl and ratchet 17, 18. A drive spring 6 and winding knob 3, Fig. 2, are mounted on the underside of a base-plate 2. A cam 23 is connected to the drive shaft by a Geneva mechanism, which comprises a control wheel 20 fitted with a pin 16, and a slotted wheel 47. A rounded tooth (not shown) on the slotted wheel moves into locking engagement with a cam portion of the control wheel when the drive spring is fully wound and the moving parts are in their starting position. Operation of the device is prevented by a spring-controlled bell-crank lever 38 which engages a shoulder 54 of a driven disc 41. Closing of the alarm contacts C, Fig. 3, energizes a relay 30 which operates change-over contacts 32, thereby short-circuiting the local substation apparatus AT and connecting the impulsing contacts 15 in series with the telephone line. A spring-controlled lever 34, which in the open position of the relay has an extension 56 abutting a tongue 33 on the relay armature, locks the relay in the closed position. The closed armature displaces the bell-crank lever and releases the drive, which commences to rotate the disc cam at a constant speed under control of a governor 14. An arm 26 on the drive shaft opens contacts 29 which connect a relay 42 in series with the impulsing contacts and telephone line. If the telephone line is intact the exchange battery operates relay 42 which opens contacts 44 and deflects a stop crank 45 away from a stop cam 55 on the control wheel. If, however, the telephone line is open or short-circuited then relay 42 remains inoperative, contacts 44 remain closed, and the stop crank locks the control wheel. The arm 26 also closes contacts 27 at this point, completing the circuit of the local alarm bell S. Providing the telephone line is in order, the drive spindle continues to rotate and the arm 26 releases the contacts 27, 29. The impulse contacts set up a continuous train of impulses which are interrupted periodically to form a selected series of digital impulses by contacts 9 operated by a shaped disc 7 fitted to the drive spindle. The required number is set up during one revolution of the drive spindle. The cam 23 operates change-over contacts 24 during alternate complete revolutions of the drive shaft, the contacts connecting a resistance R in parallel with the impulsing contacts to provide partially suppressed impulses which enable the nature of the call to be identified by the called party. At the completion of each revolution an arm 25 on the drive shaft opens contacts 28 which temporarily release the line at the completion of each effective dialling revolution when the resistance R is not in circuit. The sequence of dialling trains followed by identification impulses is repeated until the device is stopped by the rounded tooth engaging the cam portion of the control wheel. At this point contacts 48 are opened by a pin 22 on the slotted wheel and connect microphones M in series with the line. The relay 30 is released on re-winding when pin 16 on the control wheel moving in a reverse direction to normal engages a pawl 36 on the lever 34 and moves the latter out of engagement with the relay armature. The device is controlled by a master switch 4. The Specification as open to inspection under Sect. 91 includes a feature in which the linetesting circuit is omitted so that the local alarm bell is always operated. In this construction the contacts 27 may be operated by the relay 30 ; the arm 26, the contacts 29, the relay 42 and its contacts 44, and the lever 45 being omitted. In a further feature the microphone may be omitted, the line being freed on the completion of the last impulse train. Mention is also made of the suitability of the device, after modification, as an automatic call-redirection switch. This subject-matter does not appear in the Specification as accepted.