Patent GB-150749-A (GB)
Title: Improvements in or relating to the locating of a submerged cable
IPC: G01S1/02
Filed: 1919-02-06
Abstract: 150,749. Drysdale, C. V. Feb. 6, 1919. Navigable channels, systems of indicating; marine bell signalling.-Relates to the locating of a submerged cable or cables through which alternating currents are passed so that a ship provided with receivers may follow the track of the cable, .and consists mainly in the use of low infrasonic frequencies, for example 10 to 15 per second, in the cable and tuned alternating current relays in the receiving circuit, instead of or in addition to high sonic frequencies, for example 200 to 1000 per second, and telephone receivers. A submarine bell may be provided at the end of the cable to enable the ship to pick up this point from a considerable distance by means of a directional hydrophone. The receiving coils on the ship are preferably two in number and arranged at an inclination to each other substantially vertically, either above decks as at 1, 2, Fig. 1, or around the ships as at 1, 2, Fig. 3. These coils are connected up to an apparatus Fig. 4 comprising alternating current relays 7, auxiliary relays 8, a pointer indicator 11, and red and green steering lamps 9, 10. If desired, a third relay circuit for a white lamp is adapted to be connected to both receiving coils in series for picking up the submerged cable from a longer distance than can be done with either coil separately. The connexions of the devices of this apparatus are such that when the ship is at the centre of the cable track and both receiving coils are affected to the same intensity, the vibrating contact makers of the alternating current relays produce intermittent currents of equal average strength which maintain the pointer of the indicator 11 in the central position; whereas when the receiving coils are unequally affected, the pointer moves to one side or the other. A suitable form of pointer indicator, Figs. 5 and 7, comprises two coils 13, 13<1> at right angles to each other about an astatic combination 14 to the spindle 15 of which is attached the pointer 16 moving over a dial 17 beneath a glass cover 18. In a modification, Fig. 8, the coils 13, 13<1> are replaced by electromagnets 22 with pole pieces 21 shaped to embrace a circular recess containing the magnetic needle 19 surrounded by a silver ring 20 for damping its movements and provided with a pointer 16. Alternatively, a moving coil instrument may be - used comprising two coils at right angles as in a power-factor indicator, but in a permanent magnet field. In order to maintain the low irequency correct within half of one per cent., a small magneto generator is coupled to the shaft of the alternating current generator, and its E.M.F. is balanced against a battery by a potentiometer when the speed is correct. A small polarised relay is coupled between the magneto and the battery and controls the governor of the engine, or a rheostat in the exciting circuit of a motor, driving the alternator. When high and low frequencies are both to be used, the two alternators are connected in series and the low frequency one is shunted with a condenser and an interrupter so that when the condenser is in circuit the high frequency current can pass through but when the condenser is cut off the high frequency current is choked by the high inductance of the low frequency alternator, which inductance may be increased by a choking coil if desired.