Patent GB-336572-A (GB)
Title: Improvements in or relating to electric signalling systems
IPC: H04M11/04
Filed: 1929-07-12
Abstract: 336,572. Automatic Telephone Manufacturing Co., Ltd., and Burns, G. A. July 12, 1929. Fire and like alarm systems and apparatus.- In an electric signalling system having a number of stations connected in series in a loop circuit and each arranged to transmit a code characteristic of the station by momentary interruptions of the loop, in the event of the loop being opened due to a break in the line the signalling circuits are automatically modified by the operation of a relay which is mechanically locked in operated position until the loop circuit is again completed. The invention is described with reference to an alarm arrangement in which two loops LP1 and LP2 extend to a central station, each loop including a number of public call boxes preferably of the type whereby, if two or more boxes are pulled simultaneously, proper signals are transmitted in succession. Normally relays 1L, 2L and 1T of loop LP1 are operated and also corresponding relays 3L, 4L and 2T of loop LP2. Signalling under normal conditions. When the handle is pulled at a call box, the loop is opened for an interval and then groups of impulses are transmitted by the intermittent opening of the loop. If a box in loop LP1 is operated, relays 1L and 2L are de-energized for a period and a circuit is closed for one winding of relay 2H through contacts c1, a1, 2l1, 2lb3, the relay closing contact 2h2 to complete a circuit for its locking winding. Contact 2h3 is closed whereby lamp LS2 indicates the loop which is calling. Contact 2h1 completes circuits through relays A, I, and a delay device SR. Relay A at contact a1 opens the initial energizing circuit of relays 1H, 2H, at contact a2 completes a locking circuit actuation of relay B, which in turn operates relay C. Relay I operates in accordance with the action of relay 2L which corresponds to the transmission of the impulses at the call box, and actuates contact i<5> controlling the circuit of a puncher P and gong G, whereby an audible signal is given and the code is recorded on a moving tape. Conditions due to break or earth in loop circuit. When a break occurs due to a fault, relays 1L, 2L release and relay 2H operates, completing a circuit for the mechanical delay device SR. This device may comprise an electromagnetically controlled pawl and ratchet mechanism operating in conjunction with two slow relays, the first of which completes a circuit for the second, and the second opening the circuit of the first. The device actuates contact openings Sr1, Sr2. Sprins Sr1 completes a circuit for a latching relay 2LB which looks its contacts by a mechanical latch. Spring Sr2 opens the circuit of relay I. Relay 2LB at contact 2lb1 completes the circuit of a further latching relay IE and at contacts 2lb3, 2lb4 opens the initial and locking circuits of relay 2H. This relay releases, opening the circuits of delay device SR, relays A, Band C, so that the circuits of relays 2LB and 1E are opened but their contacts are held operated by mechanical latching arrangements. Relay IE upon operating, at contact 1e3 connects the right-hand side of battery B1 to earth and at contacts 1e7 separates the two sides of the loop circuit connecting the earthed battery B3 to the right-hand side of the loop. Contact 1e4 completes a circuit for lamp LBL indcating a break in the loop, and operates relay 1P whereby through contact 1p2 common break lamp CLB and a bell BLL are caused to give a visual and audible signal. The attendant at the central station operates the key K1 associated with the lamp LBL to prepare a point in the circuit of the lamp LCL, which is lighted when the fault is cleared. Relay 1E also through contact 1e2 completes a circuit for relay 1H which completes circuits for relays A, I and the device SR. Through spring Sr1 and contact 1h5 latching relay 1LB is energized, opening the circuit of relay 1H which releases relays A, B, C and the device SR. The arrangement is such that due to the fault in the loop circuit relays 18, 1LB and 2LB are operated and remain in operated position without involving any consumption of current. If an earth fault, develops relay 18 is operated to complete at 1f1 a circuit for lamp 1EF and bell 1BL. Signalling during the existence of a fault in the loop circuit. In the case of a break in the line if the call-box which is pulled is in the left-hand side of the loop circuit, at first a momentary earth at the call-box completes a circuit through battery B1 and relay 1L, the battery through contact 1l1 closing a circuit for release coil 1LBR, whereby the latch associated with contacts of relay 1LB is lifted to release the contacts. Relays 1H, A, I, and delay device SR are thereby caused to operate. Relay 1L operates in accordance with the impulses transmitted at the call-box and repeats the impulses to relay I which operates the puncher P and gong G. At the end of the sending period relay 1L de-energizes, operating relay SR to effect the re-operation of latching relay 1LB, and release of relays A, B and C. If the callbox which is operated is in the right-hand side of the loop circuit release coil 2LBR is operated to release contacts of relay 2LB, and connect up the circuit of switching relay 2H for the preparation of a circuit for impulsing relay I. If the line break fault is repaired, the re-establishment of the loop circuit completes a circuit through the loop including relays 1L and 2L whereby release coils 1LBR and 2LBR are energized and the contacts of relays 1LB and 2LB are released. A circuit is then completed for slow relay D which through d1 completes a circuit for release coil 1ER, to release contacts of relay 1E. Lamp LCL is then lighted and the attendant restores key K1. If a box is pulled when an earth fault exists relay 2L or 1L is de-energized and signals are transmitted in the usual manner. Telephone communication. When it is desired to speak from a call-box to the central station, a telephone key is operated at the call box, bring- ing into the loop circuit a resistance which lowers the current so that marginal relay IT releases. A circuit is then closed through the upper winding of relay 1AT which locks up through springs TK1 and at contact 1at2 completes alarm circuits through bell TB and lamp. TBL. The attendant at the central station operates a telephone key tb connect the telephone apparatus to the calling loop through condensers m1, m2. Springs TK1 of the telephone are operated to open relay 1AT and disconnect the alarm circuits and springs TK2 open the circuit through relay 1F to improve speech transmission. Release of the telephone key restores conditions to normal.