GB1498146A - Indication device in plan position indication system - Google Patents

Abstract

1498146 Sonar displays FURUNO ELECTRIC CO Ltd 17 Sept 1975 [15 Nov 1974] 38262/75 Heading G1G [Also in Division H4] A P.P.I. system includes means (e.g. sonar) for transmitting and receiving signals over the whole range (360 degrees) of azimuth at a constant angle of elevation (tilt), the system including a c.r.t. with scanning means to provide a number of concentric circular scan lines, means for brightening one of the circular scan lines, and means for indicating a specific radius having an angle (measured from a reference diameter) equal to the tilt angle. The screen 2 of c.r.t. 1 is scanned with concentric circles, in synchronism with the rotating beam of a TR device 27, by means of sine and cosine generators 11, 12. These are driven from a clock source 15 which emits 1 degree pulses and feeds counters 13, 14. The counter 13 emits the count output in coded form and also produces a pulse at output 16 on completion of every count (360) and a pulse at output 17 halfway (180) through each count. The counter 14 emits on the completion of each count a coded output effective to increase the amplitude of the sine and cosine signals. A specific distance, set in the distancesetting unit 19, is compared with the output of counter 14 in a coincidence gate 18 which supplies a pulse to the beam modulating electrode 5 effective to illuminate the circle having radius corresponding to the set distance. The tilt angle # (e.g. # = 30 degrees) is set in tilt-setter 25 and the beam width α (e.g. α = 10 degrees) is set in a device 26 which has an output corresponding to the complement of half at beam-width (e.g. 90-10/2 = 85 degrees). Circuit 24 produces the difference between the outputs of circuits 25 and 26 (e.g. 85-30 = 55 degrees) and feeds a corresponding signal to coincidence gate 23. A reversible counter 22 is controlled through a flip-flop 21 by the outputs 16, 17 of counter 13 such that it counts from 0 to 180 during the first half of a 360 degree cycle and from 180 to 0 during the second half. The second input of the coincidence gate 23 is connected to the output of the reversible counter 22. Thus, during the first half-cycle, gate 23 emits a pulse at an angle 55 degrees (measured from a zero corresponding to radius OY') and causes circuit 28 to generate the (pre-set) angle α. The generator 28 is connected through OR gate 20 to the modulating electrode and is effective to produce on the screen an illuminated sector of width α (10 degrees) at a radius 35 which meakes an angle # (30 degrees) with the horizon reference diameter OX. At the start of the second half of the cycle, a signal corresponding to α is fed from a pre-set circuit 29 to the reversible counter 22 and subtracted from the content of the counter. Thus, during the reverse run of the counter, the count of 55 is reached earlier by 10 pulses at a radius 34', and the sector of width α between radii 33' and 34' is illuminated. The horizontal distance and depth of a chosen object 32 are given respectively by the distances s and d on the screen.