Patent GB-988798-A (GB)
Title: Improvements in or relating to marine echo sounding apparatus
Inventor: ELLIS GEOFFREY HAROLD
IPC: G01S1/72
Filed: 1962-09-07
Abstract: 988,798. Echo sounding apparatus. S. SMITH & SONS (ENGLAND) Ltd. Dec. 6, 1963 [Sept. 7, 1962], No. 34277/62. Heading H4D. Marine echo sounding apparatus designed to overcome loss of echoes due to aeration at the surface of the transducer, comprises a paper strip recorder display means 1, generating trigger pulses (waveform a, Fig. 2) synchronous with the start of each line scanning, a plurality of similar transducer means, 4a, 4b and 4c located at different points of the vessel and able to emit a pulse of acoustic energy on application thereto of an electric pulse, and to produce a pulse of electric energy upon receipt thereby of a pulse of acoustic energy, an electric amplifier 5 amplifying electric pulses applied thereto and feeding the amplified pulses to the display means for display thereby, switching means 3, having a plurality of operative conditions corresponding to the number of transducer means, and serving to connect in each operative position, one transducer means to the amplifier 5 and to a pulse generator 2 emitting pulses in response to the trigger pulses from the display means, and means, 7 to 11 inclusive, responsive to the absence of electrical output pulses at the amplifier output greater than a predetermined amplitude within a predetermined time after the production of a pulse by the display means to operate the switching means 3 to cause it to assume a different operative condition, successive operations of the switching means resulting in the sequential connection of each of the transducer means to the pulse generator and amplifier. The amplifier 5 receives both the pulse from pulse generator 2 and also the corresponding echoes from the particular transducer being used, including the large sea bed echo. The combined input is shown in waveform g, Fig. 2. The input signal is amplified and rectified (waveform b, Fig. 2) and fed to the display means 1 and to an amplitude gate 7 which only passes those signals having an amplitude greater than a level I, waveform b and so rejects the first echoes. The trigger pulses from the display means are fed to a multivibrator 8 and cause the start of a negative pulse output from the multivibrator (waveform d). The negative pulse is stopped by the sea bed echo output from the gate 7. The output of the multivibrator is passed to a Miller-integrator 9 to produce the wedgeshaped waveform e, which is then passed to a second amplitude gate 10 which emits a pulse, waveform f, when the output of the Miller integrator exceeds a level II, waveform e. This level is not exceeded however when a sea bed echo is present. When a sea bed echo is absent or faint due to aeration at the transducer the output of the multivibrator 8 remains negative, and the amplitude of the output of the Miller integrator rises above the level II. The resultant pulse from gate 10 actuates a stepping device 11 which in turn operates the switch 3 so that a different transducer is brought into use. The amplifier 5 is provided with automatic gain control, the reference level being that of the sea bed echo, or the echo of a target, preferably a sphere, suspended at a known position below the vessel. As an alternative to the multivibrator 8, the thyratron circuit of Fig. 3 may be used. Waveforms a and c are applied to the grid of the thyratron 20, together with the output of the stepping device 11. A capacitor 22 discharges through the thyratron and coil 23 every time the thyratron is fired. The coil drives a twoposition switch which produces in its two positions the two potentials of waveform d. The thyratron is first fired by the trigger pulse in waveform a and coil 23 drives the switch such that the negative excursion in the waveform d is produced. The thyratron is next fired by the sea bed echo such that the switch is returned to its initial position. Waveform d is thus produced. In the absence of a sea bed echo the stepping device 11 will produce an output, and this is then used to return the switch to its initial position.