Patent GB-190429531-A (GB)
Title: Improvements in Electrical Signalling Apparatus.
Inventor: HOLMES FRANKLIN SAWYER
Filed: 1904-12-31
Granted: 1905-06-29
Abstract: 29,531. Holmes, F. S. March 25, [date applied for under Patents Act, A.D. 1901]. Alarms, burglar and like.-Relates to automatic electric burglar and fire-alarm systems in which signals are continuously received at a central station, such as a telephone exchange, indicating that no disturbance of the protection circuits has occurred, and comprises arrangements and apparatus for sending varying signals of abnormal frequency when any of the protection circuits is disturbed. Means are also provided for testing the local protection circuits when desired, and for automatically winding up the actuating-motor by the signal impulses. Fig. 1 shows the general arrangement of circuits. The line-wires 12, 13, leading from an ordinary telephone outfit at the protected station, pass through a differential relay DR at the central station so that the relay is not affected by telephone currents. The signal - sending mechanism is connected by a wire 19 to the line-wire 13; when the wire 19 is earthed through the signal mechanism, current passes along the wire 13, through one coil of the relay DR, and the battery 8 to ground G<1>, thus closing the local circuit 17, 18 of the signal-receiving mechanism, which may be that described in Specification No. 29,532, A.D. 1904. The signal-sending mechanism comprises a toothed wheel 38 having, say, six groups of six teeth each, and a rotary drum 40, carrying two contacts 39 and three series of eight contacts 47, 48, 49, each of varying length. The wheel 38 rotates once a minute and the drum 40 once in eight minutes, and the arrangement is such that signals are sent only when the contacts 27, 28 are closed by the wheel 38 simultaneously with the closing of one of the pairs of contacts 30, 31 ; 41, 42 ; 43, 44 ; 45, 46 by the contacts on the drum 40. The length of the contacts 47, 48, 49 respectively is such that two, three, or four groups of contacts on the wheel 38 can pass while the circuit is closed by the drum 40, thus giving different signals according to the contacts closed. Under normal conditions, signals are sent once in four minutes over the following circuits :-from ground G<1>, battery 8, line-wire 13, wire 19, fuse F, magnet coil 23, switch 1, wire 27<1>, contacts 27, 28, contacts 30, 31, wire 32, magnet coil 34, and the wires 35, 36 to ground G. The circuits containing the three pairs of contacts 41, 42 ; 43, 44 ; 45, 46 lead to the contacts of the relays AR, FWR, FR respectively. The contacts of these relays are normally open, but are closed by a disturbance in their respective protection circuits, so that signals of abnormal frequency are sent to line. If, for example, the thermostat in the wire 102 should break the battery circuit through the wires 102, 103, relay FR, and the wires 104, 105, the relay armature is released and closes its contact so that signal currents of abnormal frequency pass over the following circuit :-from ground G<1>, battery 8, line-wire 13, wire 19, magnet coil 23, switch 1, contacts 27, 28, wire 29, contacts 45, 46, wire 52, switch 5, wire 61, contacts of the relay FR, wire 62, switch 2, wires 58, 33, and the magnet coil 34 to ground as before. In the same way, the disturbance of the circuits controlling the relays FR, FWR sends currents to line through contacts 41, 42 and 43, 44. The energizing of the magnet M rotates the ratchet-wheel 65 and winds up the spring 64, which imparts motion to the shaft 63 driving the wheel 38 and drum 40. To prevent overwinding, a contact-arm 71 is fixed to the shaft 63 and engages with the pin 72 on the ratchetwheel when the spring is fully wound up, thus closing a shunt round the magnet coil 34 as follows :-wires 33, 90, shaft 63, arm 71, pin 72, contact-ring 78, brush 82, resistance R, wire 35. This prevents the actuation of the magnet armature and consequent rotation of the ratchet-wheel. The switches 1, 2, 3, 4, 5 are connected together so that they can be simultaneously swung over for making the connections for testing the various circuits, suitable local means being described for this purpose or for merely throwing the protection circuits out of action. When the latter occurs, the spring 64 unwinds, and it is thus necessary to provide means for winding this spring immediately the switches are thrown over to 'protection.' To this end, the arm 71 is provided with a hook arm 75, Fig. 10, to engage the end of a spring 73 on the pin 77 carried by the ratchet-wheel. In this way, if the circuit of the magnet M is broken at the contacts 27, 28, a connection is made from ground G', battery 8, wire 19, magnet coil 23, switch 1, wire 68, contacts 87, 86 of a dash-pot DP, wire 85, brush 81, contact-ring 79, spring 73, arm 75, arm 71, wires 90, 33, and the magnet coil 34 to ground as before. Fig. 5 shows the yielding connection between the armature 60 of the magnet M and the pawl 143 of the ratchet mechanism The armature 60 and the arm 133 carrying the pawl 143 are carried by a rock-shaft 131, to which is also attached the arm 134. A spring 142, coiled round the shaft 131, bears against both arms 133, 134, pressing these apart. Adjustment is obtained by screws 136, 140.