Patent GB-1434744-A (GB)
Title: Sonar display
IPC: G01S15/12
Filed: 1973-08-06
Abstract: 1434744 Cathode-ray tube circuits; sonar WESTINGHOUSE CANADA Ltd 6 Aug 1973 [9 Aug 1972] 37167/73 Headings H4T and H4D Plan position indicator display, Fig. 1.- A P.P.I. display for a sonar system has sine and cosine signals for the circular deflection provided by read-only memories 13, 14 which are driven from master clock 11 via counter 12 to determine the circular sweep period and have their outputs multiplied at 17, 18 by pulses from a variable clock 15 also driven by the master clock but adjusted manually at 16 in accordance with ambient temperature, salinity, &c. of the water. The output from clock 15 is increased progressively during successive sweep periods with the effect that the display is built up from a series of concentric circular sweeps of diameters increasing in proportion to the velocity of sound in water. The outputs from multipliers 17, 18 control the cathode-ray tube X- and Y-deflection inputs 25, 26 by way of counters 19, 20 and D/A convertors 23, 24. A range control 27 controls dividers 21, 22 to permit variation of the maximum range of the display. Cursor generator, Fig. 1.-A line adjustable in angle and length to permit its end to be located on an echo under consideration is produced under control of a manually adjustable ball-tab unit 28 which supplies counts to range and angle registers 29, 30. Range and angle counters 31, 32 are driven from the master clock 11 and when coincidence of count occurs between the counters and registers, comparator circuits operate range and angle read-outs 35, 37. The angle register also controls a sine/ cosine read-only memory 38 whose outputs control sine and cosine multipliers 39, 40 receiving the output from the range counter 31. The resulting signals are applied through counters 41, 42 to the range dividers 21, 22 and the D/A converters 23, 24 and are effective as X and Y sawtooth signals to draw the cursor on the display. A drive from master clock 11 to dividers 21, 23 causes multiplexing of the divider inputs whereby each circular sweep is followed by a cursor sweep (Fig. 5, not shown). Range and angle read-out displays.-These take the form of seven-segment alpha-numeric displays, four for range and three for angle. Converters are provided to get from digital counts to decimal codes suitable for driving the alpha-numeric displays (Figs. 3 and 4, not shown).  Control of display heading, Fig. 2.-The sonar receiving staves are sequentially and repetitively interrogated to cause rotation of the receiving lobe of sensitivity. The interrogation is controlled by a beam selector 54 which is driven by a counter 49 triggered by master clock 11 (see Fig. 1) in synchronism with counter 12 which controls the display sweep. Counter 49 however may operate out of phase with counter 11 under control of unit 51 which receives an input by way of a TRUE/RELATIVE switch 48. In the RELATIVE position, the switch signal is derived from counter 12 through terminal 43 and a zero detector. The counters 12 and 49 then step in phase and the display is oriented with zero degrees at the top, i.e. in correspondence with the heading of the ship on which the sonar is fitted. However in the TRUE position the switch input is derived from a digital compass and comparator 52. In this mode the counters step out of phase and the display is oriented with compass north at the top. Coarse and fine display of echo azimuth, Fig. 6a.-In the specific example described the echo signal extends over 30 degrees (coarse video signal). A more accurate azimuth display (fine video signal) is obtained by operating the beam selector 54 in a phase comparison mode (not described in detail) under the control of a second counter 50 which is also reset by control 51 but receives a controlling signal from the cursor angle register 30 by way of terminal 53.