Patent GB-490015-A (GB)
Title: Alarm signalling arrangements in connection with telephone and like exchange systems
IPC: H04M11/04
Filed: 1937-02-05
Abstract: 490,015. Police and like alarm systems. STANDARD TELEPHONES & CABLES, Ltd. Feb. 5, 1937, No. 3482. Convention date, May 27, 1936. [Class 40 (i)] [Also in Group XXXIX] Police &c. alarms transmitted over a telephone system, test calls, and line faults cause the taking into use at the exchange of common apparatus which switches the call directly to the police &c. station, transmits the number of the subscriber's line followed by a code signal representing the type of call, and except in the case of line faults completes a talking circuit between the police station and the subscriber's station. The distinction between alarm and test calls is effected by transmitting two voicefrequencies from the common apparatus over a simplex circuit to the substation at which alternative tuned circuits are connected up causing the return of one or other frequency over the loop circuit to the exchange. The alarm is transmitted even if the line is in use for a call. Circuit arrangements. To set the alarm, switch CK is moved from position 1 in which relays P, Q lock over door and window contacts DC, WC, through position 2 in which check lamp CL lights, to position 3. Each line has at the exchange an adaptor circuit connected between the line and the line and cutoff relays, the adaptor circuits being connected over a call-finder LF with common apparatus, Figs. 2, 3. When any of the contacts DC, WC is opened, the release of relays P, Q operates relay R which disconnects the telephone set and completes a simplex circuit from transformer I over wires a, b causing the response of a differential relay D in the adaptor circuit. In the case of a test call, the closure of key TK operates relay O which in addition to energizing relay R changes the impedance of the tuned circuit K. If the line becomes broken or grounded on the a-wire, relay A normally energized over a choke RC releases, whilst if grounded on the b-wire relay D operates. In all these cases, the operation of D or the release of A energizes the finder starting relay S. If the line becomes permanently looped relay B operates connecting up a timing device TA and if the loop continues for a predetermined time, an alternative start relay W is energized. Magnet LFM is energized when switch S1 is in normal position, and when the calling circuit is found, relay T operates over wiper d or f. Relays Lb, Lx operate, and relays Ar, Br, Cr commence a self-interrupting cycle producing impulses which step switch S2 through a series of revolutions, switch S 1 being advanced one step for each revolution by ground on bank S2a. In the first position of S1, relay To operates over wiper S1c, and connects two voice-frequencies from transformer TR2 over a simplex circuit to the line to ground at transformer I. If the call is a police alarm, the impedance of tuned circuit K is high for one of the frequencies so that the other is transmitted back over transformer J, the line loop, and transformer TR3 to amplifier CT and thence through band-pass filters associated with tubes AT, BT, causing the operation of relay X. Similarly for a test call, the other frequency is returned and relay Y is operated. In the case of a line fault, both or neither of relays X, Y is operated. In position 2 of S1, marginal relay I t is also operated over wiper S1c and one of relays Ma, Mt, Mf is energized according to the nature of the call, and relay Dp also energizes to connect up the line d, c to the police station. In position 3 of S1, ground is connected over wiper S1a to conductor c and battery over wiper S1b to conductor d, and impulses corresponding to the tens digit of the calling line are transmitted by relay Cr under control of relay It over wiper g and a connection to bank S2b of S2. In position 4 of S1 the units digit, and in position 5 a code digit indicating the nature of the call and determined by connections A, T, F, to bank S2b, are similarly sent. The number and the code digit (letter " A," " T," or " F ") are recorded by a printer at the police station, and at the same time a local printer is operated over wiper S1d. In position 6 of S1, relay Ca operates to connect highvoltage battery over the simplex circuit to the line operating relays M, N which disconnect the alarm circuit, relay N remaining locked until the alarm is reset. In position 21 of S2 with S1 in position 6 relay Pr operates over wiper S2b and energizes Sr so that ringing current over relay Rt is connected to the police station and the stepping of S1 is suspended. When the station replies, relay Rt releases Pr and relay Pf operates and energizes Rc so that the ringing current is now applied to the calling line. When ringing-cut-off relay Rt again operates, it releases Sr to complete a talking circuit. Release is controlled from the police station and when relay Pf falls back, switch S1 continues to step on to normal, relay Lb being short-circuited in positions 9 and 10 to restore the circuits to normal. In the case of a call due to a fault, no talking connection is required, and in position 7 of S1, relay E in the adaptor circuit, Fig. 1, is operated over wipers e, S1a to operate alarm lamp AL and disconnect the common circuit. The substation alarm circuit may include a phonograph to transmit a stored message to the police station.