Position measuring device

In a position measuring device enabling the calculating of the magnitudes proportional to the coordinates X and Y of a vessel which can move on the water in relation to two axes of orthogonal coordinates IX and IY, comprising a sound wave emitter placed at a point 0 situated, at the bottom of the water, at least three detectors D1, D2, D3 on the bottom of the vessel and arranged at the apexes of a triangle, IX being parallel to D2 D1 and the plane of the axes IX, IY being the plane of the triangle D1, D2, D3, the distance between the detectors D1, D2 being 2a, the distance between the detectors D2, D3 being 2b, the distance between the point 0 and the detector D1 being d.sub.1, the distance between the point 0 and the detector D2 being d.sub.2, the distance between the point 0 and the detector D3 being d.sub.3 ;

• Means for calculating the depth of water H below the vessel;
• Means for calculating the difference in the travel time .DELTA.t.sub.21 of the sound waves between 0 and D2 on the one hand and 0 and D1 on the other hand;
• Means for calculating the difference in the travel time .DELTA.t.sub.32 of the sound waves between 0 and D3 on the one hand and 0 and D2 on the other hand;
• the improvement comprising:
• First means (18, 19) supplying, on the basis of the difference in travel time .DELTA.t.sub.21, by multiplication by a coefficient depending on the propagation speed c of sound waves in water, a signal xo equal to the difference between d.sub.2 and d.sub.1 and, on the basis of the difference in travel time .DELTA.t.sub.32 by multiplication by a coefficient depending on c, a signal yo equal to the difference between d.sub.3 and d.sub.2 ;
• Second means (20, 20') supplying, by algebraic multiplications and additions of the signals xo and d.sub.1, a signal equal to kx, x being the distance of the point 0 in relation to the mid plane of D1 D2;
• Third means (30, 30') supplying, by algebraic multiplications and additions of the signals xo, yo and d.sub.1, a signal ky, y being equal to the distance of 0 in relation to the mid plane of D2 D3;
• Fourth means (40) supplying, on the basis of kx, the signal kX;
• Fifth means (50) supplying, on the basis of the signals kx, ky, the signal kY;
• Sixth means (60, 60') supplying, by algebraic multiplications and additions of the signals kx, ky and H, a signal equal to k.sup.2 d.sub.1.sup.2 which, after application to a square root extractor (70, 70' ), is applied to the second and third means (20, 20') (30, 30').