GB887646A - Improvements in or relating to the measurement of velocities - Google Patents

Abstract

887,646. Echo sounding; radar. GENERAL PRECISION Inc. Jan. 31, 1958, No. 3299/58. Class 40(7). In an apparatus for determining the relative velocity of two objects, the first object, for example a ship, carries transmitting and receiving apparatus, a movable receiver and means for moving this receiver such that the difference frequency between the transmitted wave and the wave reflected from the second object, for example the sea bed, is reduced to zero. The radiated energy is of sonic or radio frequency and is pulsed or continuous. In a ship-borne apparatus, Fig. 2, pulses of energy are directed toward the sea bed and, after reflection, detected by the movable receiver 16. The Doppler frequency is obtained in a detector 17 and a signal proportional to this frequency fed to a servo-system 19 comprising an amplifier, motor, and generator. The motor drives the receiver 16 at such a speed that the Doppler frequency is reduced substantially to zero. The output of the generator, which is coupled to the motor, is indicative of the speed of the receiver, this speed being the speed of the ship since the receiver must be stationary relative to the sea bed when the Doppler frequency is zero. To correct for pitch or roll of the ship a circuit comprising a resistor R-3 and a cosine potentiometer R-2 is provided, the wiper of the potentiometer being adjusted in correspondence with the pitch or roll angles. In a second embodiment, Fig. 3 (not shown), a number of receivers are used, all being rotated about a common axis and having connections to a commutator such that only the receiver moving most nearly to the horizontal is put in circuit. The brush to the commutator is kept vertical by means of a gyro- and servo-system.