Patent GB-1356019-A (GB)
Title: Digital display echo-sounding
IPC: G01S15/18
Filed: 1971-06-10
Abstract: 1356019 Echo sounding; transistor saw-tooth generators ELECTROACUSTIC GmbH 10 June 1971 [13 June 1970] 27357/71 Headings H4D and H3T In an echo sounder incorporating digital display of depth, during a sounding period the transit times of those echoes having the amplitude of bottom echoes are compared with the transit time of the bottom echo of the previous sounding period and that one is evaluated which differs least therefrom. Trigger pulse generator synchronizes clock generator I, resets counter 2 to zero, transfers the content of intermediate store 3 to display store 4 and triggers a rising sawtooth in generator 11 which sets output T to "high". The first received echo passes threshold amplifier 8 to squarer 9 where it is quantized in length by gating with clock pulses from generator 1. The echo causes AND gate 10 to emit a pulse which transfers the contents of counter 2 to intermediate store 3 and retriggers the sawtooth waveform. This procedure is repeated for all echoes until time T 1  which represents the sounding depth from the previous sounding period, this being stored in store 4. At T 1 , comparator 12 detects that the counter 2 output now exceeds the store 4 content and output V rises. This causes the sawtooth waveform to reverse, i.e. to fall with the same slope as before. If no further echo is received before the sawtooth reaches zero, the last detected echo is nearest to T 1  and output T drops to zero blocking gate 10 to further echoes. If an echo is received while the sawtooth is still falling, it will be the nearest to T 1  and the sawtooth is immediately reset to zero blocking further echoes and the counter output is read into store 3 as before. At the next transmitter pulse the store 3 content is transferred to store 4 whose output is decoded and passed to a digital display. Threshold amplifier, Fig. 5.-Echoes pass to the non-inverting input of differential amplifier 35. The first echo produces a high output which is fed back to charge capacitor 36 until the inputs are equal. Subsequent echoes must therefore exceed the previous highest amplitude in order to be passed. The capacitor is discharged by a negative pulse applied at R coincident with the trigger pulse. Sawtooth generator, Fig. 3.-A Miller integrator formed from transistors 16-18 and feedback capacitor 19 produces a linear rising voltage at D when V is earthed thereby shorting the positive bias to earth. When V is disconnected resistors 20, 21 provide a positive bias at 22 which causes the output voltage to fall with the same slope as before. Pulses from M, coincident with the echo pulses reset the output D to zero. Output T remains high except when D is zero. Digital comparator (Fig. 4, not shown).- Comparator 12 compares the outputs of each stage in counter 2 and store 4 and produces a high output only when the former exceeds the latter. Each stage of the comparator provides an output having the form where Z k  = content of the Kth stage of the counter and S k  = complement of the content of the Kth stage of the store. This function is accomplished by four NAND gates and all the stages are connected in series. The carry input to the first stage (U o ) is set to zero.