Patent GB-174354-A (GB)
Title: Improved method of and apparatus for depth sounding
IPC: G01S1/72
Filed: 1922-01-19
Abstract: 174,354. Blondel, A. Jan. 21, 1921, [Convention date]. Addition to 161,988. Determining distances acoustically; subaqueous audible siqnals; detecting subaqueous sounds. - Relates to apparatus for finding the depth of the sea or the distance of an iceberg or the like by timing the echo of a subaqueous sound and comprises oscillographic means for observing the impacts of the initial sound and the echo. In the form shown in Fig. 1, the arm 101 is rotated through gearing by a motor k and wipes a succession of contacts on a sector 102, closing a succession of circuits through explosive devices of which one is shown at r. These circuits have in common the secondary coil 103 of a transformer, the primary 104 of which is shortcircuited periodically on the battery q when a conducting segment m revolving with the shaft x, y is wiped bv the brushes n. Consequently a series of explosions take place, the number of revolutions between each two explosions being determined by the wiper 101 while the phase of the revolution at which the explosions occur is determined by the brushes n, which can be rotated about the shaft x, y by turning the disc p by hand. Revolving on the shaft x, y is a mirror a, which reflects on to a flat or cylindrical screen b a spot of light from the mirror a' of a galvanometer, the axes of rotation of these mirrors being at right angles. The brushes n are set so as to bring upon the line z, z<1> first the movement of the spot of light clue to the sound of the explosion reaching the microphone c, and then the movement due to the echo. The angular difference between the two settings of the brushes a is proportional to the depth to be measured. Alternatively, the speed of the shaft may be such that both movements can be seen on the screen b for the same setting, the distance between the two being measured with a scale. In order to moderate the effect of the initial explosion on the galvanometer, the latter may be shunted at the required moment by a short-circuit or by the resistance f<1> brought into circuit by a revolving sector m<1> co-operating with brushes n<1>. Instead of moving the brushes n, use may be made of a third mirror which can be rotated through a measured angle about a shaft parallel to x, y until the movement of the spot of light occurs on the line z, z'. In a modification (not shown) the galvanometer and lamp j are mounted upon and revolve with the shaft x, y, and the beam of light is thrown by an oblique mirror revolving with the system on to a screen at right angles to x, y. The spot of light then traces a circular path broken at points corresponding to the explosion and echo. In a further modification the galvanometer mirror a<1>, Fig. 4, is mounted at the end of the shaft, x, y, and reflects a beam from the lamp j through a cylindrical lens v on to an annular reflector a, and thence on to a disc-shaped screen b. The screen may be luminously graduated with a phosphorescent or optically projected scale. The galvanometer is connected to the microphone circuit by brushes 106, with or without the interposition of a transformer and amplifier. As in Fig. 1, the brushes n<2>, Fig. 4, serve to shunt the galvanometer at the moment of the explosion, and the brushes n to explode a charge selected bv the wiper 101, the wiper being in this case variably geared down from the shaft x, y: In order that the lamp j may be eflective during only one revolution after an explosion, a drum 20 bearing insulated conducting strips co-operates with brushes 21 to close a circuit for cutting off the light as required and the galvanometer may be similarly cut out, or may he given a large current to remove the spot of light from the screen. The width of the strips can be changed at the same time as the gear ratio of the shafts x, y, x2, y3, in order to adapt the apparatus for depth measurements of different orders. In a further modification, two galvanometers are used, one being momentarily shortcircuited by brushes so as to record the echo but not the explosion, while the other is permanently shunted so as to give a substantial deflection for the initial sound only. Two corresponding mirrors mounted on the revolving shaft are angularly adjusted so as to bring the two galvanometer readings into coincidence. The relative angular displacement of these mirrors gives the depth which is to be found. In modifications described in connection with the use of a bell instead of explosions (see below), the stator of the motor k may be rotated by hand, its angular displacement being measured in lieu of the displacement of the brushes n : or the mirror a of Fig. 1 may be on a separate shaft driven by differential gearing, the positions of which corresponding to the initial sound and the echo are measured for the same purpose. Subaqueous bell. A bell for use instead of the explosive charges referred to above is shown in Fig. 6. A disc A is struck by a striker B which is raised by a stem C passing through a watertight joint D in a water-tight casing. A stud on the stem C engages cams on a wheel F, which thus actuates the striker. The wheel F is turned by a motor strictly synchronous with the motor k which turns the shaft x, y in Figs. 1, 3, 6. Alternatively use may be made of a synchronized bell actuated pneumatically or by direct-acting electromagnets. Oscillographs. The galvanometer or oscillograph in Figs. 1, 4 may be a telephone receiver with a mirror secured to its diaphragm: or it may comprise a permanent magnet 30, Fig. 7, of the telephone type with pole-pieces 31, in combination with a flat spring 33 supported in slots in the end pieces 32 so as to be capable of torsional movement and bearing a coil 34 and a small mirror. Specifications 6549/00, [Class 97, Philosophical instruments], 22940/14 and 182,873 are referred to. The Specification, as open to inspection under Sect. 91 (3) (a) comprises a further modification, shown in Fig. 3 (Cancelled) in which telephones are used instead of galvanometers. The subaqueous microphone c affects a telphone T1, which is shunted or short-circuited by the brushes n<1> at the moment of the explosion. The echo heard in the telephone T1 is compared with the sound caused in the telephone T2 by the battery c when the brushes n<2> wipes the contact m<2> on the disc l<2>, or by a bell and microphone controlled by the brushes n<2>. The sounds in the two telephones are made to coincide by moving the disc p<2> bearing the brushes n<2>, the angular setting of which then gives the required depth. Specification 161,988 is referred to. This subject-matter does not appear in the Specification as accepted.