Patent GB-1190931-A (GB)
Title: Improvements in or relating to Radar Display Apparatus
Inventor: CROUCHMAN ERNEST LESLIE
IPC: G01S7/24
Filed: 1966-01-19
Abstract: 1,190,931. Radar. SMITHS INDUSTRIES Ltd. 19 April, 1967 [19 Jan., 1966], No. 2418/66. Heading H4D. In a true-motion radar display apparatus digital representations of direction of movement of the radar-carrying craft are utilized for direction of movement of the craft-representation on the display and for resetting that representation when it arrives at a predetermined movement limit and the resetting is provided in two stages in the first of which the craft-representation is moved, irrespective of craft movement direction, to a predetermined reference point in the display area and in the second of which the craft-representation is moved from the reference point to a further point in the display area such that the direction of movement of the craft-representation is then initially at least towards the reference point. In the embodiment the displacement of the time-base origin from the centre of a cathoderay tube P.P.I. screen in accordance with ship movement is effected by orthogonal coils 4, 5, Fig. 3, energized from integrations with respect to time effected in a control unit 7. Unit 10 supplies pulses at a repetition rate proportional to ship's speed from a log (e.g. one pulse emitted for each 10 yards travelled) and unit 11 is a manually operable pulse generator for providing for each 10 yards travelled) and u it 11 is a pulses in accordance with estimated speed when the log is not available. The pulses are fed to a resolver slaved to the master compass of the ship thereby supplying control unit 7 with two pulse signals dependent respectively on increments in easting and northing travelled. Drift correction is supplied by pulses from a generator 13 fed to the control unit via a resolver set in accordance with the compass direction of tide or wind (actual or estimated), the pulses being of a rate representing its speed (actual or estimated). Resetting of the ship-representing spot on the screen 3, Fig. 2, is to a position across the screen on which substantially the whole display area A is occupied in displaying the region ahead thereby reducing the frequency of resetting: when the spot along path P reaches point Q on the boundary circle D (the distance between circles B and D corresponding to minimum acceptable display range ahead of the ship) it is reset to a point R in two stages. In the first stage, from point Q to point C energization of each coil 4, 5, Fig. 3, is reduced to zero quickly and in the second stage, from point C to point R, the sense of the energizing currents thereto are reversed and increased until point R is reached. Detailed arrangements. Fig. 3.-The two resolvers are provided as one by time-sharing in unit 20. The pulses from switch 9 and generator 13 are applied to a temporary store 21 and each pulse stored is sent from that store to a programmer 23 to initiate a two-stage programme for supplying to control unit 7 digital representations in respect of heading angle by a digitizer 24 and of drift angle by a digitizer 25. Each digitizer includes a commutator disc 26 with nine separate tracks, the disc for digitizer 24 being driven by a compass repeater to adopt an angular setting in accordance with heading angle and that for digitizer 25 being set in accordance with drift angle. Sine and cosine digital signals are derived by respective brushsets 27, 28, each brush-set comprising eight brushes to give an eight-digit reflected binary code; brushes 29, 30 give signals dependent on sign. The programme initiated by a pulse on lead 22 begins with a signal to a lead 31 which is applied to a gating unit 32, to a binary registeraccumulator 33 of eight-digit capacity, and to a binary register-accumulator 34 of six-digit capacity. Gating unit 32 reads from digitizer 24 or 25 the sine representation, the particular digitizer to be read being dependent on which of leads 35, 36 is energized. The eight-digit sine representation is entered into a register 37 within which it is converted to straight binary code under the control of programmer 23. After further processing, each pulse on lead 48 represents an easting increment of five yards. In the second stage of the programme a signal is supplied via lead 51 to result in northing increments of five yards on lead 55. The two-stage programme is repeated for successive log or drift pulses sent to store 21. The pulses on leads 48, 55 are applied to respective motorstepping circuits 60, 61 controlling motors 62, 64 having shafts 63, 65 controlling the D.C. to coils 4, 5. Sealing of the motor shafts to correspond to different display ranges utilizes a switch 67. The signals on the wipers of potentiometers 80, 81 are supplied to a circuit 86 where they are utilized to detect when the ship's spot reaches circle D, Fig. 2: rapid pulses are then emitted on leads 90, 91 to step respective shafts 63, 65 back to zero displacement to return the ship's spot to centre C; thereafter pulses on leads 95, 96 cause movement to point R. A push-button, common to both motor-stepping circuits, provides for change to a relative motion display, and each such circuit includes a counter associated with a decoding matrix connected to stator windings of the motor, Fig. .4 (not shown). The resetting process may be initiated manually, and manual movement of the spot is provided for, Fig. 4 (not shown).