Patent GB-1159831-A (GB)
Title: An Analogue-Digital Computer for Radar Apparatus having a "True Motion" P.P.I Display
Inventor: MASTROPIETRO GUISEPPE
IPC: G01S7/24
Filed: 1966-07-21
Abstract: 1,159,831. Computer for true motion PPI display. SELENIA - INDUSTRIE ELETTRONICHE ASSOCIATE S.p.A. 21 July, 1966 [21 July, 1965], No. 32832/66. Heading G4G. [Also in Division H4] General construction.-In a calculator for true motion radar PPI presentation of the movements of a craft, enabling correction for currents of the supporting fluid and displacement of the origin, operative to return the trace to a diametrically opposite point of the display when the course line reaches the display limit, and to maintain the datum line of motion of the craft intersecting the centre of the display after the trace return, a train of pulses from a velocity measuring device representing the craft speed are connected over LOG terminal (Fig. 1) together with the ouput of a multivibrator J simulating log pulses, to an input of a sequence control circuit A, whose output is combined with the output of a further sequence control circuit A<SP>1</SP> and also to a scalechanging frequency divider X and the input of monostable multivibrator D. A monostable multivibrator MD controlled by a preset potentiometer ID introduces signals representing the vectorial speed of drift due to currents in the supporting fluid. The output of X energizes an input of monostable multivibrator C an output of which energizes -an input of sequence control circuit A. A further output C3 of C energizes input p1 of bi-stable multivibrator P whose output p2 excites input a1 of buffer-gate circuit Q whose imput q2 is energized by pulse generator W. Output c4 of C energizes a sawtooth generator E whose output excites a buffer G to energize a sawtooth comparator circuit H, whose output h2 is applied to a squaring circuit N exciting input p3 of bi-stable multivibrator P. Output q3 of Q energizes the input r2 of electronic commutator switch R. Outputs d2, d3 of monostable multivibrator are connected to inputs i3, r3 and i3<SP>1</SP>, r3 of electronic switches I, R, while the inputs i1, i2 of I are derived from outputs l1, m1 of sine cosine potentiometers L, M respectively; adjustable in accordance with the motional directions of the craft relative to the fluid, and those of the fluid. The output i4 of I also energizes the input h3 of comparator circuit H. Inputs r4, r5 of R are derived from the potentiometers L, M to indicate the signs of the respective trig functions. Outputs r6, r7 of R are respectively connected to frequency dividers S, S<SP>1</SP> which energize inputs t6, t7 of reset circuit T having also input t1 from potentiometer L and t2 from potentiometer Y. Outputs (6<SP>1</SP>, t7<SP>1</SP> of T energize multivibrators U, U<SP>1</SP> generating forward and reverse pulses for stopping motor Z adjusting potentiometer Y, whose output controls the off centre display of the PPI. For resolution and analogue to digital conversion, input c4 representing the modulatus of a vector craft velocity to be resolved along N-S and E-W co-ordinates is connected to input e1 of sawtooth generator E whose output e2 is applied to input h1 of comparator H and input h<SP>1</SP>1 of comparator H1. The remaining comparator inputs l1 and l2 are fed from sin # and cos # signals where # is the vectorial angle from potentiometer L, and the output h2 of H is connected to the input p2 of bi-stable multivibrator P whose input p1 is energized from C4. Output P3 energizes input q2 of gate circuit Q whose other input #1 is connected to the output of pulse generator W, while the output of the gate energizes electronic switch R. Similarly the output h<SP>1</SP>2 of H is connected to input p<SP>1</SP>2 of bi-stable multivibrator p<SP>1</SP> whose input p<SP>1</SP>1 is energized from C4; and output p<SP>1</SP>3 similarly energizes input q<SP>1</SP>2 of gate circuit Q<SP>1</SP> whose output operates electronic switch R<SP>1</SP> (Fig. 2). Operation.-Pulsation of input C4 activates sawtooth generator E to produce waveform e2 (Fig. 8) and simultaneously switches bi-stable units P, P<SP>1</SP> whose output pulses activate gates Q, Q<SP>1</SP> to pass pulses from W to outputs q3, q<SP>1</SP>3. Meanwhile comparators H, H<SP>1</SP> receive the sawtooth waveforms, and also signals representing sin #, cos #. At equality, pulses from h2, h<SP>1</SP>2 return bi-stable units P, P<SP>1</SP> to block gates Q, Q<SP>1</SP>, so that the numbers of pulses appearing at outputs q3, q<SP>1</SP>3 (Fig. 8) represent | V |sin # and | V | cos # where [ V | is the modulus of the velocity. As applied to a ship the signals representing the modulus of the velocity are obtained from a log, and its direction from a gyrocompass, while the modulus of the drift velocity and its angle are manually set in. Further N-S direction, (sin #) the velocity pulses of frequency proportional to ship speed pass through sequence control circuit A to release multivibrator C controlling sawtooth generator E and separator G to provide two identical sawtooth signals for the sin # and cos # channels, while potentiometer L provides a D.C. signal proportional to K sin #. For the E-W direction (cos #), resolution is effected by duplication (not shown) of the circuit elements shown asterisked in Fig. 1. Electronic switch I feeds this signal to the comparator H also receiving a sawtooth signal, and its output produces a release pulse delayed relatively to the corresponding velocity pulse, in proportion to sin #, and after squaring it changes over multivibrator P already switched coincidentally with multivibrator C by the corresponding velocity pulse, whereby a rectangular pulse of duration proportional to sin # releases gate Q to pass a group of pulses from oscillator W of number proportional to sin #, so that the total number of pulses over a period of time is proportional to | V | sin # = n when # = #/2. A similar arrangement produces a total number of pulses proportional to | V cos #. Similarly, pulses are produced at the output of Q and interleaved with the pulses representing | V | sin # thereat to represent the correspondingly resolved drift velocity | V<SP>1</SP> | sin #<SP>1</SP>. A stable multivibrator MD provides pulses of period manually variable proportionally to drift velocity V<SP>1</SP> by potentiometer ID with a switch (not shown) disabling the correction circuit, and the pulses are mixed in sequence by sequence control circuits A, A<SP>1</SP> comprising (Fig. 3, not shown) a diod-FET-transistor-capacitor circuit wherein velocity pulses operate in turn to trigger multivibrator C initiating operation of a resolver circuit; pulses arriving during a resolver cycle being stored until the commencement of the next cycle. Circuits A, A<SP>1</SP> operate similarly in response to the log and pulse generator J and to the multivibrator MD. A reverse connected series diode and resistance electronic switch I (Fig. 4, not shown) supplies a signal proportional to # to dimensioning circuit H when multivibrator C has been switched by a log velocity pulse, and a signal proportional to sin # when it has been switched by a drift velocity pulse; multivibrator D then being switched. Integration and conversion.-Groups of pulses at terminal q3 of unit Q at frequency representing | V |sin # and | V<SP>1</SP> | sin # are applied to circuit R (Fig. 5, not shown) comprising two chains of series opposed diodes and a Schmitt trigger circuit receiving logic signals, representing the signs of sin # and sin #<SP>1</SP>, from microswitches linked to the sliders of potentiometers L, M, and routing the pulse groups to output r6 for positive sign and r7 for negative sign, to energize frequency dividers S, S<SP>1</SP> introducing factor n representing the pulse number corresponding to sin # = unity. Switch unit T operates to direct the pulse trains to outputs t<SP>1</SP>6, t<SP>1</SP>7 for positive or negative signs, to energize multivibrators U, U<SP>1</SP> controlling a reversible stopping motor Z and potentiometer Y developing a voltage signal representing t1 {  t0  (V sin # + V<SP>1</SP> sin #<SP>1</SP>) dt which is applied to the off-centre deflection circuits of the PPI display. Frequency divider X divides the input pulses by a factor which enables scale change to be effected without recalibration of the N-S or E-W amplifying circuits or displacement of the display centre. A similar duplicate circuit (not shown) also provides voltage proportional to  #<SP>t</SP> t0  (V cos #+V<SP>1</SP> cos #<SP>1</SP>) dt   where V = instantaneous ship speed V<SP>1</SP>= instantaneous drift speed # = instantaneous ship's course #<SP>1</SP> = instantaneous drift course t 0  = time of commencement of integration. Zero potentiometer voltage designates sweep origin at the centre of the display. Sweep origin reset.-In the circuit (Fig. 6) automatically returning sweep origin from a limit of the display to a diametrically opposed limit, with the bow-stem line of the ship intersecting the display centre; and thereafter becoming inoperative; the appropriate potentiometer signal representing # (V sin #+V<SP>1</SP> sin #<SP>1</SP>) dt is applied to the base of Q 4  whose emitter is coupled over RR to polarized relay K1 and direct to contact K4.8 of relay K4; RR being normally shunted by delay switch S1 and also connected to polarized relay K2. Normallyopen contact K1.1 is connected to positive source and its operated contact to normally open contact K3.1 of delay relay K3 shunted by indicator lamp I1, and to the operated contact K22 of relay K2, whose moving contact is connected to positive source. The moving contact of K31 is connected to operated contacts K1.2 and K2.2 of relays K1, K2 and the operated contact K3.2 of K3 is connected to the winding of relay K4 and also to the winding of relay K7. The operated contact S2.2 is also connected thereto while the moving contact S2.1 is connected to positive source. The moving contact K4.1 of relay K4 is connected to the normal contact K7.2 of relay K7 whose moving contact is conn