Patent GB-1001371-A (GB)
Title: Improvements in and relating to indicating devices for sonic or ultrasonic apparatus
Inventor: HASLETT ROY WILLIAM GEORGE
IPC: G01S1/72
Filed: 1961-03-30
Abstract: 1,001,371. Echo sounding. KELVIN & HUGHES Ltd. March 19, 1962 [March 30, 1961], No. 11838/61. Heading H4D. In sonic or ultrasonic apparatus, wherein sonic or ultrasonic waves are transmitted by an electro-acoustical transducer and the resulting echo signals are picked up by two further spaced apart transducers, the echo periods of both receiver transducers of echo signals caused by the same transmitted signal, are compared and the difference found therebetween used to determine the amplitude of a signal controlling a gate circuit such that the gate circuit is closed when the control signal amplitude is greater than a given amount, and is opened to pass echo signals from one of the transducers to a display and/or recording device, when the amplitude is less than the said amount. The invention is described as applied to fish detecting echo sounding apparatus wherein it is desired to distinguish between signals due to an object at H<SP>1</SP>, Fig. 2, within the trawl area LONM and signals due to an equidistant object at C<SP>1</SP>. The receiving transducers 20 and 21, Fig. 5, are symmetrically arranged 10 feet apart, athwartships of the vessel S, with the transmitting transducer 43 between them. In operation an ultrasonic pulse 10A, Fig. 4, is transmitted at intervals determined by contact 40 and the resulting echo signal is picked up by the two transducers 20 and 21. The relative time positions of the two resulting received echo pulses are determined by the position of the echo producing object and are described with reference to Fig. 4, for three such positions:- Fig. 4(B). The object slightly to one side of the vertical SP through the ship.-In this case the echo pulses are slightly out of time but overlap each other. The two received pulses are amplified and oppositely rectified at 23 and 27 to produce the positive and negative half pulses thereof respectively. The half pulses are then passed through filters 24 and 28 to remove the ultrasonic components and the resulting oppositely going pulse envelopes, Fig. 4(1) and Fig. 4(2), are passed through amplitude gates 25 and 29 to remove any noise. The two resulting pulses, Fig. 4(3) and Fig. 4(4) are added together and, due to their overlapping, produce the reduced amplitude waveform of Fig. 4(B5). This waveform is then passed to two opposed amplitude gates 32 and 35 so as to let through only those parts of the waveform having amplitudes greater than + or - 2V. The two resulting pulses B6 and B7 are added together after invertion of the former pulse, to produce waveform B8 which is then squared (B9) and applied to close a normally open gate 31, by means of the two negative going portions thereof, so as to only pass the echo signal output from transducer amplifier 26 to a CRT 44 and a recorder 47, for a short interval. Fig. 4(C). The object some way away from vertical SP.-In this case the echo signals do not overlap, giving a gate controlling signal as at C9 such that although the gate is opened for a longer period no echo signal is being received during this period and so no indication is made on the CRT or recorder. Fig. 4(A). The object on the vertical SP.- In this case the echo signals coincide and cancel out with the result that the gate 31 remains open, and the whole of the echo pulse signal from amplifier 26, is displayed. Therefore, the nearer the object to the vertical SP, the bigger will its trace be, no trace at all being given for objects further from the vertical than an amount determined by the cut-off levels of the amplitude gates 32 and 35. High frequency ripple in the pulse envelopes merely causes the indication to be in the form of a great number of very close dots. A variable delay 46 may be used to trigger the time base so as to scan a predetermined depth. The invention may also be applied to flaw detection in materials.