Patent GB-190429532-A (GB)
Title: Improvements in Electrical Signalling Apparatus.
Inventor: HOLMES FRANKLIN SAWYER
Filed: 1904-12-31
Granted: 1905-05-04
Abstract: 29,532. Holmes, F. S. March 19, [date appliedfor under Patents Act, A.D. 1901]. Alarms, burglar and like.-Relates to automatic electric fire and burglar alarm systems in which signals are continuously received at a central station, such as a telephone exchange, indicating that the circuit has not been disturbed, and comprises arrangements and apparatus at the central station for closing an alarm circuit when the predetermined interval between the signals is not equalled or is exceeded. Apparatus for sending such signals is described in Specification No. 29,531, A.D. 1904. In addition to the usual telephone apparatus at the substation A, a branch wire 91 leads to ground G' through signal sending mechanism C<a>, C<c>. The telephone currents pass through the differential relay R<d> without affecting it, but the signal currents pass through one coil only to battery B and ground G', thus closing the relay circuit from the battery B', relay contacts 20, 21, wire 2, lamp L<2>, switch So, and the magnet M<c> to the battery B. So long as the signals are received at the normal rate, the magnet M<c> rotates the ratchet-wheel m' at such a rate that neither of the pins 12, 13 engages the arm 14, continuously rotated by clockwork. The pins 12, 13, Fig. 5, are respectively in contact with rings 61, 63, insulated from each other and having contact-brushes 60, 62 which keep the pins 12, 13 in circuit with wires 34, 20 respectively. The arm 14 is provided with spring wings 80, 81, Fig. 5, to prolong the contact with the pins 12,13. When the time interval between the signal impulses is not equalled, the arm 14 overtakes the pin 13 and closes a circuit from the battery B' through the resistance R', lamp L', wire 15, arm 14, contact 13, annunciator drop D<c>, and the wire 24 back to the battery. The annunciator drop closes a circuit from the battery B<2>, wire 26, wire 27, armature contacts 28, 29, wire 30, and the bell 34 to the battery. Thus, the lamp L', drop D<c>, and bell 34 show that the protection circuit has been disturbed. When the signal impulses arrive at more than the normal rate, the pin 12 overtakes the arm 14 and closes a circuit from the battery B', resistance R', lamp L', arm 14, pin 12, annunciator D<a>, and the wire 38 back to the battery. The annunciator closes a local circuit through the bell 44 so that the lamp L', drop D<a>, and bell 44 give the alarm. The normally open switch 51 serves to test and set the apparatus. Fig. 6 shows the yielding connection between the armature m of the electromagnet M‹ and the pawl m<1>. The armature m and arm o, carrying the pawl m<1>, are both mounted on the rock-shaft R and are connected by the spring r, the screws r<1>, o' serving for adjusting the relative position of the parts m, o. In the practical arrangement of the apparatus, one side of the switchboard carries the annunciators, lamps, and switches, and the other side the ratchet and alarm-giving mechanism. In order to be able to remove any defective mechanism, the connections between the apparatus on the two sides of the board are made by pins 6, 8, 16, 35, 21, Fig. 1, and sockets 5, 9, 17, 36, 22. Fig. 8 shows the construction of one such pin and socket, the spring y<3> bearing against the pin 6 when inserted in the socket 5.