Patent GB-1327236-A (GB)
Title: Multiple coating apparatus
Inventor: KRITZ JACOB A
IPC: G01S15/50
Filed: 1970-12-04
Abstract: 1327236 Sonar navigation SPERRY RAND CORP 4 Dec 1970 [4 Dec 1969] 57605/70 Heading H4D A Janus type sonar system producing pulse trains indicative of the velocity of a vessel along two axes has means for producing first and second signals representing the distance moved along said two axes in a measuring time interval, and means for storing said distance signals. A ship-borne system, Fig. 1, includes transducers 2-5, 8-11 mounted to transmit and receive signals along the fore-aft and portstarboard axes. The measuring time is generated by unit 19 (Fig. 2, not shown) in which the positive pulses in the differentiated output of a square-wave oscillator (38) triggers two series connected monostables (40, 43) and also resets a bi-stable (41) which is set by the output of the second monostable (43). Thus the bi-stable (41) produces a long output pulse followed by two successive pulses, one from each monostable, the first being an UPDATE pulse from gate (42) when an UPDATE signal from spectrum evaluator 15 is present and the second being a DISCHARGE pulse for capacitors in the distance computers 14, 16 and evaluator 15. In order to ignore invalid reflections from inhomogenities in the sea, the spectral content of the signals is examined. The signals from the two transducers in each axis are mixed and the two resulting sum frequency signals mixed. The difference frequency thereof is converted to a square wave, differentiated and fed to a clocked bi-stable through a gate enabled during the measuring time interval. On receiving a sync. pulse derived from the transmitted signals, the bi-stable output changes state and enables a gate which passes sync. pulses to a counter which on detecting fifty pulses resets the bi-stable. The bi-stable output is thus equal in length to a predetermined number of transmitter cycles and during this time opens a F.E.T. gate allowing a capacitor to charge. At the end of the measuring time interval the voltage on this capacitor indicates the spectral content of the received signals. If this voltage is above a threshold corresponding to the distance travelled during the previous measuring time interval, a comparator produces a signal inhibiting the use of the distance measured during the present measuring time interval. Distance measurement, Fig. 4.-Signals from the receiving transducers on one axis are applied directly to a mixer 52 and with one delayed by 90 degrees to a mixer 56. The difference frequency signals from mixer 56 are converted to squarewaves and applied to a sampler 60 which determines the polarity of this signal at the occurrence of a positive pulse from the differentiated squared output of the mixer 52. The frequency and polarity of the sampler 60 output indicates the velocity and direction of movement along the relevant axis. Separator 61 passes pulses to AND gates 64, 65 in response to positive and negative sampler 60 outputs respectively. Gates 64, 65 are enabled during the measuring time interval and each pulse from the sampler passes to one of two bi-stables 66, 67 which produces pulses of a width equal to a predetermined number of transmitter cycles, as described above in the spectrum evaluator 15. Bi-stable 66 output opens a F.E.T. gate 73 which charges capacitor 75 to a positive potential, the charging current being determined by temperature compensator 18, Fig. 1. Thus the voltage on the capacitor at the end of the measuring time interval is proportional to the distance travelled therein and is independent of the sea temperature and transmitter frequency. Bi-stable 67 opens gate 74, charging the capacitor to a negative voltage. At the end of the measuring time interval gate 79 is opened by an UPDATE pulse from generator 19 transferring the distance measurement to capacitor 80 and at the end of the UPDATE pulse, the DISCHARGE pulse discharges capacitor 75 through gate 78. Right angle triangle computer, Fig. 6.-The D.C. voltage from the two distance computers 14, 16 are fed to choppers 98, 99 driven in quadrature by oscillator 100. The chopper outputs are added and the fundamental frequency extracted providing a signal whose maximum amplitude is proportional to the resultant distance travelled during the measurement time interval. This signal is converted to a squarewave, differentiated and applied to reset a bi-stable 110, which is set by the inverted, squared and differentiated chopper oscillator 100 output driving the fore-aft axis chopper 98. The duty cycle of the flip-flop output is a linear measure of the drift angle The resultant signal is also split into positive and negative halfcycles and applied to the distance summer 36 and spectrum evaluator 15. In the summer Fig. 7 bi-stable 120 operates switches 121, 122 in a push-pull arrangement so that e.g. capacitor 116  charges up from source 114 controlled by the amplitude of the pulses from the right angled triangle computer 34. When the charge on the capacitor reaches a predetermined reference level comparator 118 sets bi-stable 120 which then opens gate 121 discharging capacitor 116 and allowing capacitor 117 to charge from the other computer 34 output. Each switching of the bi-stable increments a solenoid counter which may be calibrated in metres, yards, nautical miles &c.