Patent GB-141764-A (GB)
Title: Improvements in and relating to signalling apparatus
IPC: G01S15/74
Filed: 1918-09-07
Abstract: 141,764. British Thomson - Houston Co., (General Electric Co.). Sept. 7, 1918. Subaqueous sound signals; sound, controlling apparatus by.-Apparatus controlled by the receipt of sound waves is arranged so that, on receipt of a sound of sufficient duration, independently-produced sound signals of predetermined character are emitted. As described, the apparatus is provided in a water-tight casing 1 adapted to float or be submerged, and a number of such devices emitting characteristic signals may be arranged on the sea-bottom so that sound arriving from a passing vessel actuates the devices. An observer equipped with suitable listening apparatus can, by noting the characteristic signal given, estimate the approximate location of the vessel. The casing 1 is in the form of a truncated cone, so that cables &c. dragging along the sea-bottom pass over the apparatus. A normally de-energized oscillator of Fessenden type, having a fixed coil 9, a coil 10 carried by a stationary core 8, and a moving cylinder 3 secured to a diaphragm 2, is used to emit the predetermined signal. The diaphragm 2 also receives the sound waves controlling the apparatus, and transmits the vibrations to a reed or tuning-fork 12, one limb of which carries a microphone 13 in the input circuit of an amplifier 14. A coil 16 in the output circuit of the amplifier is supplied with current from a battery 15 and holds a magnet 18 carried by a wheel 17 in the axial position shown against the action of a spring 21 which tends to rotate the wheel 17. Adjustment is made so that receipt of vibrations by the microphone decreases the current through the coil, whereupon the wheel 17 is moved by the spring, and a contact 19 carried by the wheel bridges contacts 22. Circuit is thus closed through a solenoid 23, switch 31, and battery 23<A>. The core 24 of solenoid 23 is thus moved, against the action of a returning- spring 25, and, by means of a cord 26, a wheel 27 is rotated against the action of a spring 40 until a contact 28 carried by the wheel 27 bridges contacts 29. This closes a circuit through a solenoid 30 and battery 23A, whereupon the core of the solenoid 30 rises, breaking contact at tEe switch 31 and closing switches 32 - - 36. Switch 32 closes a circuit supplying current from battery 23<A> to coil 9 of the oscillator, switch 33 closes a circuit supplying current from battery 23A to a motor 37, switch 35 closes a circuit supplying current to slip-rings 38 on the motor shaft, and switch 34 closes circuit of a device 39 supplying alternating current to the coil 10 of the oscillator with a frequency depending on the motor speed. Switch 36 closes circuit supplying current to a solenoid 47, closing a switch 48. Closure of this switch supplies current from battery 15 to coil 16, so that the magnet 18, wheel 17, and contact 19 return to the position shown and remain there, irresponsive to further sounds actuating the microphone, for a period controlled by a dashpot 49 and sufficiently long to enable the predetermined sound signal to be given. Breaking circuit at the switch 31 de-energizes solenoid 23, and return movement of the wheel 27 takes place, the return movement being retarded by a flygovernor 43 or other device. This return movement breaks circuit at 29, de-energizing solenoid 30; but the return of its core and the switches 31 - - 36 is retarded by a dash-pot 46 for a period long emough to allow the predetermined signal to be given. The predetermined signal is controlled as follows. In series with switch 34 supplying alternating current to the coil 10 is a pair of contacts 41. The wheel 27 is of iusulating-material and carries conducting-segments 42 which successively bridge the contacts 41 during return movement of the wheel 27, so that alternating current is supplied to the coil 10 in an intermittent and characteristic manner determined by the disposition of the segments 42. Owing to the comparatively slow response of the apparatus as a whole, sound signals are not given when short sounds such as those due to an explosion are received; but when the cycle of movements described above has been started by a sound of sufficiently long duration, the apparatus remains irresponsive to further sounds received until the signals have been given and the device returns tc normal condition, whether these further sounds are due to continuation of the original disturb. ance or to the signals emitted by the apparatus.