Patent GB-1346106-A (GB)
Title: Method of and apparatus for measuring distances in water in accordance with the reflected sound beam method
IPC: G01S15/88
Filed: 1971-09-10
Abstract: 1346106 Echo sounding FRIED KRUPP GmbH 10 Sept 1971 [12 Sept 1970] 42343/71 Heading H4D A method for measuring distance comprises transmitting pulses of sound energy from equidistantly spaced transducers 4, Fig. 1, to a point 6 at an angle α inlined to the direction of the required distance 2. As the final distance calculation does not involve velocity it is stated that variations in the propagation velocity due to various layers S1, S2, S3 of the medium, e.g. sea water, have little effect. It can be shown that distance 2 = “ (sin 2#.t)/A, where # is the angle shown and A = sin #/C m , C m  being the mean wave propagation velocity. Transducers 4 are energized with constant phase difference of, e.g. 120 or 90 degrees and the frequency of the transmitted sound is adjusted so that # = 45 degrees. In this case distance 2 = “ t/A and A is given by 1/3af, a being the distance between individual transducers and f the sound frequency. The time t may be measured using a counter 8.1 controlled by a gate 8.2. At the start of transmission, a control signal 9 opens the gate and pulses from generator 11.1 at frequency f, are gated through, the counter having been reset by a pulse from control 18. A frequency divider 11.2 derives the frequency f and feeds output stage 11.3 giving a three phase (120 degree) or two phase (90 degree) output. The length of a transmission is controlled by the length of signal 12 which in turn is controlled by the value of the time i.e. distance measurement at the output of store 8.3 obtained when the reflection is received i.e. transmission length is distance dependent. The signals from 11.3 are fed via a transmit/receive switch 13.1 to a circuit 13.2. The signals may pass circuit 13.2 only when the transducers are disposed in the correct plane perpendicular to distance 2, this being determined by inclinometer 13.3. The received signal is passed to i.f. amplifier 14.1 the signal having been mixed with the output of oscillator 14.2 and then passed to demodulator 14.3. The signal is then applied to gate 8.2 via threshold type circuit 15 and stops the count. The output of store 8.3, for # = 45 degrees, will also correspond to a length 7, Fig. 1, and this length is added by summing network 17 to the position of the transducers when transmission began to define the reflection location. Various embodiments of transmitter 11 are described. In an alternative electromechanical recording system a stylus (20) (Fig. 3, not shown) is moved on a belt (21) around pulleys (24.1) and (24.2) by a motor (25), the speed of which is controlled by frequency f 1 . The stylus moves at an angle 90-γ to the paper feed, the angle being related to angle #. As the stylus passes a contact (31) a pulse is passed to transmitter (11) via delay (32) and transmission pulse length control (18). A signal (33) passes from delay (32) via amplifier (34) and back to the stylus to mark the position of the transducers. The received signal is again processed as in the system of Fig. 2 and is passed to amplifier (34) and then stylus (20) to mark the reflection point and hence give distance 2. The time between signals 33 and the received signal, indicative of distance may be used to determine the length of transmission. In both systems it can be shown that the use of a frequency f 1 , related to frequency f, effectively makes the scales (i.e. number of pulses or stylus movement corresponding to distance) independent of frequency f provided angle # is maintained at 45 degrees. A conventional chart recorder, in which the paper feed and stylus motion are at right angles, may be used. However in this case sound energy is transmitted alternately or simultaneously at equal angles α fore and aft of the vessel. The reflection location (6) (Fig. 4, not shown) is recorded twice as the vessel moves towards and beyond the location and by halving the time period t 2  - t 1  between both recordings (Fig. 4.2, not shown) the position of the reflection relative to the position of the vessel at e.g. time t 1 , may be obtained. The method of the invention may also be used for measuring water levels (Fig. 6, not shown).