Patent GB-1478023-A (GB)
Title: Velocity measuring apparatus
IPC: G01S15/50
Filed: 1974-05-31
Abstract: 1478023 Acoustic velocity measurement JUNGNER INSTRUMENT AB 31 May 1974 [1 June 1973] 24199/74 Heading G1G Apparatus for measuring a component of the velocity of a body such as a ship relative to a reflecting reference surface e.g., the sea bed or a reflecting layer of water comprises a transmitter mounted on the body the transmitter having at least one transmitting transducer coupled thereto for transmitting a coherent acoustic signal toward the reference surface from where the signal is reflected, at least one receiver mounted on the body, at least two spaced receiver transducers coupled to the receiver the receiver transducers having substantially rectangular sensing areas oriented such that the long sides thereof extend substantially at right angles to the component of velocity measurement, the positions of the spaced receiver transducers being such that they both lie in the path of the beam reflected from the reference surface such as to receive reflected signals which differ from one another inphase due in part to the distance in the direction of measurement between the two spaced receiver transducers and in part to the component of the velocity of the body in the direction of measurement, each of the reflected signals received by the receiver being modulated by reflection at the reference surface and thus representative of the instantaneous position of each of the receiver transducers relative the reference surface, and processing means coupled to the receiver and operative to compare the reflected signals with each other and to generate an output signal which is a function of the phase difference between the two signals this output signal being indicative of the component of the velocity of the body relative to the reference surface. The invention may utilize signals reflected from the ocean floor or other discontinuities in the body of water beneath the ship, and a suppression function may be used to eliminate unwanted reflections. A depth finder may also be included in the apparatus according to the invention, to enable such a suppression function to be used. The signals S1, S2 received in receivers M1, M2 in Fig. 2, being the reflected transmitted signal from transmitter S comprise'random fluctuations in time but represent a stationary spatial distribution, are substantially identical and are mutually phase shifted a time T Fig. 3, where T = <SP>L</SP>/ v  where L is distance separating transmitter S and receivers M1 and M2 and v is the velocity component of the ship along a line intersecting the receivers M1, M2. The received signals are fed respectively via amplifiers F1 and F2 to detectors D1 and D2, see also Fig. 19. Referring to Fig. 19, the detector Dl is directly connected via an amplifier 401 to a first input of a differential amplifier 403, while the detector D2 is connected via an amplifier 402 and a sampling delay circuit 404 to another input of the differential amplifier 403. The sampling delay circuit 404 comprises switches 414, 415 connected to a grounded capacitor 416. The otuput of differential amplifier 403 is connected via a comparison circuit 417 to two parallel branches of the circuit, one branch comprising a coupling switch 405, a grounded capacitor 406 and a resistor 407, and the other branch including a coupling switch 408, a capacitor 409 and a resistor 410. The two branches are connected to an integrating circuit 411 whose output is connected via an analogue frequency converter 412 to an indicating unit 1, and to a control unit 413 arranged to control, by pulses, the switches 405, 408, 414 and 415 (switching on and off) in a manner such that the signal arriving from the other detector D2 is electronically time shifted #e coinciding with the time shifting #m between the detectors Dl and D2. When the object moves with a certain constant speed v, there originates a balancing condition resulting in a certain frequency f on the output of the analogue frequency converter 412. This frequency is fed to the indicating unit 1 which is calibrated to directly show the speed v. The frequency signals also are supplied to the control circuit 413 which, in a known way is arranged to issue pulse series with fixed pulse repetition frequencies, pulse spacing, pulse length and delay. In relation to the frequencies f, as shown in Fig. 23 (not shown), there are four outputs S A , S B , S C , S D . These outputs are adapted to actuate the respective switches 414, 415, 405 and 408, which switches naturally need not be conventional contact means, but can comprise transistors or may be selected or arranged in another manner. The output signal provides an indication of the component of velocity which may be displayed as at I, along with, if provided, a depth reading R. In the embodiment of Fig. 4, and of Fig. 5 (not shown), the transmitting transducer may be dispensed with, either one or both receiver transducers operating as the transmitter in time division multiplex fashion. If the ship is drifting orthogonal velocity components v x  and v y  may be separately obtained by suitable spacing and shaping and orientation of the antenna elements, of which there may be a plurality. In another embodiment, Fig. 9 (not shown), for a drift angle up to 20 degrees from the longitudinal direction, two pairs of receiver antennas are provided, to make two deviating directional measurements. Another embodiment, Fig. 17, has two receiver antennas M1, M2, where M2 is split in two parts M2A, M2B. The component v x  is measured by adding the signals S2A and S2B in adder 217, producing signal S2 which is processed as above to yield velocity component v x . The difference signal, (S2A-S2B) = S3 is multiplied in unit 220 with the delayed signal S1 (t-#) and integrated by filter 222. The sign and magnitude of the output signal U T  is proportional to the sign and magnitude of the orthogonal velocity component v y . In another embodiment, Fig. 20 the ships velocity may be measured down to zero using a sensor comprising many elements which are successively connected to the receiver in a scanning fashion, the output from two sensors separated at distance L being measured at any instant.