Patent GB-674357-A (GB)
Title: Improvements in or relating to alarm systems
IPC: G08B27/00
Filed: 1950-02-09
Abstract: 674,357. Automatic exchange systems. PICKING, A. S. H., ROONEY, I. H., and SLAUGHTER, J. F. Jan. 31, 1951 [Feb. 9, 1950], No. 3391/50. Class 40 (iv). [Also in Group XXXVIII] In an alarm system in which apparatus at a telephone subscriber's substation automatically actuates the dial of the subset to set up a call and sends a warning signal, a selector switch connects in circuit for each digit one of a number of rotating digit switches each corresponding to a different digit, the digit switches controlling an electromagnet which inserts a rotating finger into the appropriate holes in the dial. In operation, the motor 11, Figs. 1, 2, drives a shaft 9 carrying the finger 16 and steps through a single-tooth gear 28 the moving disc 30 of the selector switch 4. A cam 37 on the disc 30 rotates a lever 35 to release the cradle switch, and a wiper contact 33 engages the first of a group of seven contacts 34 on the fixed disc 31 of the switch 4. According to the required first digit this connects up one of the digit switches, each comprising a fixed brush 26 and a ring 25 on a drum 14 secured to the shaft 9. Part of each ring 25 is made of conducting material and the remainder is cut away or made of non-conducting material so that the electromagnet 19 inserts the finger 16 into the hole in the dial chosen by the particular digit switch which also releases the electromagnet when the finger reaches the dial stop. The tip of the finger is resiliently mounted to prevent the stop being damaged. During the next revolution of the shaft 9 the wiper contact 33 is positioned between the first two contacts 34, thus providing the interdigital pause. Similarly the remaining six digits are dialled and the call is completed. After a short interval the wiper contact 33 steps across a group of three contacts 43, each of which is connected to one of ten brushes 42 associated with ten rings 40 on a drum 41 on the shaft 9. The rings 40 each have one to ten conducting projections, so that a buzzer 44 connected to all the rings and positioned near the microphone of the handset transmits three groups of sound pulses characteristic of the substation concerned. Alternatively the characterizing pulses may be inductively injected.into the telephone line. A further warning device 51, e.g. a wire record player, may be controlled by contacts 48, 49; 45, 46, on the moving and fixed discs 30, 31, respectively. After the disc 30 has completed half a revolution the lever 35 depresses the rest 36. During the second halfrevolution the operations described above may be repeated to set up a call to a second substation. In an alternative construction, Fig. 4, the digit switches comprise a row of fixed brushes 61 ... 70 co-operating with a series of concentric brass strips of varying length on a disc 58 connected to the main shaft 54. The selector switch is formed by a disc 87 loosely mounted on the shaft 54 and stepped from the shaft through a cam-ratchet-pawl-drive 81, 82, 83, respectively, the disc being provided with a number of connected projecting contacts 89 ... 96 wiping across two sets of fixed contacts 97 ... 104, 105 ... 112. Cams 123, 124 on the disc 87 operate the telephone rest through a lever 120. The operation is similar to that described above, but after one complete revolution of the disc 87 a nut 115 on a threaded sleeve 114 secured to the disc 87 actuates a switch 118 to stop the motor.