Patent GB-1380271-A (GB)
Title: Sonar apparatus
IPC: G01S7/527
Filed: 1970-12-24
Abstract: 1380271 Echo-sounders SMITHS INDUSTRIES Ltd 22 Dec 1971 [24 Dec 1970] 61305/70 Heading H4D Sonar apparatus comprises a transducer 11 receiving echo signals and storage means 14 having a number of separate storage elements for receiving successive samples of the received echoes, the storage means having N storage locations, the echo signals being sampled at a frequency F and being written into the store during a period longer than N/F and the store retaining samples only of the last N samples obtained during the period, a chart recorder being provided to display the echo signal information and providing a triggering signal to cause read out of the stored signals. In Fig. 1, transducer 11 also transmits the acoustic signals and is fed from generator 12 which is triggered by recorder 16. Received signals are fed to pre-amplifier 13. The pre-amplifier input signals include transmitter breakthrough TP, fish echoes FE, and sea bed echo SE, the amplified values (i) of which are shown in Fig. 2. Signals (i) are fed to storage means 14. The remaining circuitry ensures that device 14 only records fish echoes within a predetermined range of the sea bed and that the recorded signals are fed to recorder 16 at a lower rate then that of storing to give an expanded scale on chart 17. Threshold gate 20 only passes signals from the transmitter and sea bed echo to circuit 21 which gives corresponding output pulses DT, DS, Fig. 2. Pulse generator 24 feeds a pulse SP to gate 22, SP closing gate 22 to pulse DT and any short range echoes. The output from gate 22, i.e. pulse DS, triggers mono-stable 23 giving pulse SQ. SQ is differentiated at device 25 and the pulses derived from its leading and trailing edges clipped and inverted respectively at device 26, producing pulse WT. A slope gate 28 passes only those signals from amplifier 13 having rise times above a threshold. i.e. pulses TP, SE and sea-bed echo SR. These signals produce corresponding pulses WP, WE, WR at the output of gate 28, the pulses resetting, and pulse WT setting, a bi-stable 27. From Fig. 2, it can be seen that waveforms WT, WE of signals (v), (vi) produce a pulse WC at the output of bi-stable 27. By comparison of pulse WC and signals (i) it is seen that pulse WC triggers embrace fish echoes FE received within a certain range of the sea-bed and also the start of echo SE. The pulse WC is therefore fed to storage means 14 which then stores echoes FE and the start of echo SE. A pulse RP is provided by variable delay 30, fed from recorder 16, the delay allowing adjustment of the recording position on chart 17. The pulse RP triggers monostable 33 giving a pulse RC fed to store 14. The pulse RC results in read out of the stored signals (X), Fig. 2, to amplifier 15 and recorder 16. Pulse RC can be much longer than pulse WC so that recording is in a time expanded form and hence an enlarged scale on chart 17. Fig. 3, illustrates an embodiment of storage means 14. Signals (i) are fed via rectifier 40 and current supply circuit 41 to gate 42. When pulse WC, i.e. signal (vii), arrives the gate is opened and oscillator 44 activated. The oscillator steps capacitor selector 45 via OR gate 46 so that each capacitor 43 has a voltage applied equal to the value of signal (i) at the capacitor's time of selection. The selector operates cyclically, so that the capacitors are selected several times during pulse WC. At the end of pulse WC gate 42 closes and oscillator 44 stops. The pulse (ix) from mono-stable 33 eventually arrives, opening gate 47 and activating oscillator 48. Selector 48 therefore feeds out the voltages from capacitors 43 to 49 to low pass filter 50, feeding amplifier 15. The refquency of oscillator 48 is normally such that each capacitor voltage is passed only once to amplifier 15 but the frequency may be increased so that the voltages are read out cyclically several times. Fig. 4 shows another embodiment of store 14. In this case, analogue to digital converter 51, shift registers 53 and digital to analogue converter 55 replace the capacitors. Fig. 5 shows a further embodiment of the store. In this case, the frequency of oscillator 60 is modulated according to the echo signal amplitude and its output is differentiated by device 61 which supplies pulse of one polarity to monostable 62. The output of the monostable consists of a pulse train, the mark-to-space ratio of which depends upon the echo signal amplitude. The pulse train is stored in shift register 63 and read out via filter 50. An alternative simplified embodiment to that of Fig. 1 (Fig. 6, not shown), enables echoes received within a period timed from the transmitter pulse, as opposed to the sea-bed echo, to be stored and recorded. In this case, the storage process is controlled and initiated by the recorder (16<SP>1</SP>) via a mono-stable (23<SP>1</SP>), of time period corresponding to the required wrting period and coupled to pulse generator (12<SP>1</SP>). The feeding of the stored signals to the recorder (16<SP>1</SP>) is also controlled by the recorder itself via mono-stable (33<SP>1</SP>) having a greater time period than monostable (23<SP>1</SP>) to give an enlarged recording scale. (For Figures 4 and 5 see next page.)