GB1269566A - Improvements in and relating to determining the direction of sound waves - Google Patents

Abstract

1,269,566. Acoustic direction finders; monostable circuits. FREID. KRUPP G.m.b.H. 11 July, 1969 [12 July, 1968], No. 34988/69. Headings H3P and H4D. An arrangement for determining the direction of incidence of sound waves within a relatively broad angular region comprises an array of transducers whose outputs are combined to form a plurality of relatively narrow beam patterns covering different adjacent sectors of the region, a device for periodically scanning received signals of all the sectors, a cathode ray oscilloscope (CRO) for displaying the scanned signals and having its electron beam rotated in synchronism with the scanning, and a device for determining the incidence direction within any sector from the phase or travel time difference between received signals in two beam patterns associated with that sector. In the Fig. 1a embodiment 48 transducers W in a cylindrical array are coupled in groups to delay networks N1a, N1b to form 96 beams each 15 degrees wide and associated in pairs to cover 48 sectors each 7À5 degrees wide. Thus transducer group W1 to W8 forms beam R1a (Fig. 1b), and group W41 to W48 forms beam R1b, together covering sector R1 (Fig. 1c); groups W2 to W9 and W42 to W1 cover an adjacent sector, and so on. Considering sector R1, a voltage proportional to the phase difference between signals received in the two associated beams R1a, R1b, is provided at the output of phase meter P1 and a summation voltage for the two beams is provided at A1 output. Similarly, phase voltages and summation voltages are provided for the other sectors at P2- P48 and A2-A48 and these voltages are sampled by scanning switches SP, SA. K produces a sawtooth voltage with a period equal to the dwell time of scanning switch SP on a sector. When the sawtooth amplitude reaches the sampled phase voltage, coincidence circuit C provides an output pulse for opening gate G to apply the sampled summation voltage to the CRO to intensity modulate the CRO beam, which has a circular trace with a period 48 times the sawtooth period. Thus the summation voltage modulates the beam at an angular position corresponding to the direction of sound wave incidence. In sonar applications the CRO circular trace is expanded with echo time, to give a PP1 display. In the Fig. 2a embodiment the arrival time difference # of sound waves in the two beams associated with a particular sector is obtained by applying the two beam output signals from delay networks N1a, N1b to circuits 120, 121, 122, 123, 124, 125 (in one of 24 measuring channels L1-L24) which provide needle pulses corresponding to the positive-going zero crossings of the signals, the needle pulses being fed one directly and one via a fixed delay circuit 126, 127, 128 to " set " and " reset " a bi-stable 129 whose output voltage is integrated at 131. The D.C. integrated voltage is a function of both # and the sound wave frequency #. To eliminate the # dependence, the needle pulses from one beam trigger monostable 130 whose integrated output is subtracted at 133 from the integrator 131 output, the difference voltage being amplified at 134 and fed back as an error signal to vary the monostable 130 " on-time " duration so as to reduce the error. The output of amplifier 134 then represents #. Two offset beams R1 and R2 (Fig. 2b) are synthesized from the two beams R1a, R1b, by delaying the outputs of networks N1a, N1b at 107, 108 and combining delayed and undelayed signals in adders 109, 110, the addition signals being fed via gates 113, 114 to intensity modulate the CRO beam. These gates are opened at the correct times in the circular trace of the CRO beam, under the control of a timer (one of Z1 to Z24) comprising a monostable 106 which is " set " by a scanning pulse from one of 24 outputs on 48-stage shift register 102 and which " resets " after a delay determined by the amplifier 134 voltage representing #.