Patent GB-526250-A (GB)
Title: Improvements in or relating to sound signal apparatus
IPC: G08B3/10
Filed: 1939-03-09
Abstract: 526,250. Electro-magnetically-actuated fog horns. WALLACE & TIERNAN PRODUCTS, Inc. March 9, 1939, No. 7645. Convention date, March 14, 1938. [Classes 13 and 118 (ii)] [Also in Group XXXVII] In electrically actuated fog horns, constancy of amplitude of vibration of the sounding diaphragm is maintained by (i) reversing at each blast the direction of current flow through the main and other electric contacts to prevent excessive pitting and (ii) adjusting the point of opening of the main contacts in response to a lesser movement of the diaphragm consequent on, say, reduction in the potential of the supply battery. The armature 46, Fig. 2, of the diaphragm actuating solenoid 30 is carried by the through bolt and hollow spindle 34 from the double diaphragm 35, 36, the spindle passing through a copper lining in the solenoid; on an extension 48 is mounted the lower of the two main contacts 50 the upper being supported by a stiff leaf spring 51. This follows the downward movement-of the armature until the end of the spring strikes an adjustable anvil 53, when the contacts open the circuit through the solenoid the main diaphragm 35, 36 returning the armature. The anvil is carried on a screw and has its edge in the form of a worm wheel engaged by a worm 55 which can be turned automatically or by hand by means of a screw driver at the end 57. The solenoid &c. are contained in a casing whose closing door carries a motor and switch gear for controlling the working. The motor 23, Fig. 5, which may be of the slow speed kind described in U.S.A. Specifications 1,985,357 and 2,181,841, drives a timing cam 67 and a reversing cam 68 ; the cam 67 has two risers 69 and the cam 68 one in a position corresponding to one of the risers 69. As the motor rotates the circuit to the solenoid is completed alternately by the risers 69 through the heavy current relay 24 ; the battery is arranged in two parts 65, 66 and according as the riser 71 on the cam 68 is active or not one or other part supplies to the horn, the change over reversing the current direction through the system, especially the contacts 50,70 and 77. The relay 24 may be dispensed with, the main circuit being broken at the contacts 70 worked by the cam 67. In modifications of this supply a single battery unit as 138, Fig. 10, is connected to the system by a reversing switch 129 with two sets of contacts and a double stepped riser 132 on the cam 127 ; in another form of this arrangement (Fig. 14 not shown) a timing and reversing cam are used with an electromagnetic relay-actuated switch for moving the reversing contacts. Using a two-part battery an electromagnetic relay 206, Fig. 13, closes the horn circuit at 212, and steps round a ratchet wheel 214 to control 'reversing contacts 209; in a modification (Fig. 15 not shown) using a single battery a timing cam closes the horn circuit and steps round the ratchet wheel. If the circuit resistance rises or for any other cause the amplitude of vibration of the main horn diaphragm falls off, the armature 46, Fig. 6, in its movement does not strike a pin 87 on a leaf spring 85 as hard as it would normally ; in consequence a circuit is maintained through contacts 90 from supply points 61 to an electromagnet 80, which drives the ratchet 83 and through a spindle turns the worm 55 to lower the anvil 53 thereby increasing the amplitude. Normally the leaf spring is raised to close contacts 91, closing a circuit through a hold-off magnet 93 and preventing working of the ratchet 83 &c. An iron block 98 and magnet 99 form loading for the leaf spring. The supply to the points 61 takes place only when the timing cam 67 closes the supply contacts 70, Fig. 5. In modifications :-(a) A dashpot is connected to the spring 85 normally holding the contacts 90 open. (b) The time during which contacts 107, Fig. 9, are closed determines the working of the ratchet 83 ; normally the relay 110 closes the short circuiting contacts 113 ; in a modification the contacts 108 are connected directly to the ratchet electromagnet. (c) The vibrating armature 46, Fig. 10, carries a coil 121 to generate current, rectified at 123 and working a hold-off relay 124 under normal conditions. The generator may be a soft iron bar 142, Fig. 11b, moving in a coil 143 carried by pairs of pole pieces 146, 147, 149 on the magnet 144. (d) An electromagnet 150 (Fig. 12 not shown) in the supply line to the main solenoid acts normally as a hold-off relay as 124 above, and is responsive to fall of current in the supply line. The light relays should be mounted outside the horn casing to avoid the effects of vibration.