Patent GB-616794-A (GB)
Title: Improvements in and relating to means for measuring the displacement of a vehicle relative to a fluid medium and the velocity of such displacement
IPC: G01P5/24
Filed: 1945-07-11
Abstract: 616,794. Measuring velocity etc.; utilizing sounds and like vibrations. HUGHES & SON, Ltd., H., SPROULE, D. O., and HUGHES, A. J. July 11, 1945, No. 17727. [Class 118 (ii)] [Also in Group XX] Apparatus for measuring relative velocity in a fluid medium comprises means for emitting a sound signal (sonic or supersonic) into a flow of said medium, means located in said medium fixedly at a distance from the emitting means for receiving said sound signals, means for measuring the time taken by the signal in travelling from the emitting means to the receiving means and means for comparing the measured time with the time taken by the signal to travel the same distance in the medium at rest. The invention as applied to a ship comprises a hull a, Fig. 10, moving in a fluid medium (i.e. water) in the direction of the arrow d carrying a transmitter b<SP>1</SP>, receivers c<SP>1</SP>, f, responsive to relative movement between hull and water in the fore-and-aft direction and receivers f<SP>1</SP>, f<SP>2</SP> responsive to transverse movement, both pairs of receivers being equally spaced about the transmitter. A triggering circuit g sets the time bases h, h<SP>1</SP> connected to the double beam cathode-ray tubes m, m<SP>1</SP> in operation shortly before the thermionic driver j causes the transmitter bl to emit a sound impulse and the electrical pulses due to signals received by f<SP>1</SP>, c<SP>1</SP> and f<SP>1</SP>, f<SP>2</SP> are applied to the cathoderay tubes through the thermionic amplifiers k, n, and kl, n<SP>1</SP>. The indication on the screen of m is shown in Fig. 5 (a similar trace appears on the screen of m<SP>1</SP>) in which the " pips " y<SP>1</SP>, z<SP>1</SP> represent the instant of transmission of the sound pulse, y<SP>2</SP> that of the reception of this pulse by c<SP>1</SP>, z<SP>2</SP> its reception by f and x a direct function of the velocity V. This distance may be measured by means of a sliding scale which is set with its zero on y<SP>2</SP> or the time-base h may be arranged to start at the instant y<SP>2</SP> is received, thus making full use of the cathoderay tube scale which may be adjusted to represent the maximum speed of the ship. The following equation applies, V=vt 3 /(2t 2 - - t3), where V is the velocity of the hull, v the velocity of the sound in the medium (water), t 2 the time between the transmission of a sound pulse from bl and its reception by f and t 3 the difference between t 2 and the time between the transmission of the same pulse and its reception by c<SP>1</SP>. A similar equation applies in connection with receivers f<SP>1</SP>, f<SP>2</SP>, V in this case being the transverse component of the motion of the hull (i.e. side drift, &c.). In a modification described with reference to Fig. 7 (not shown), the space x in Fig. 5 is converted into a constant current of that duration by an electronic timer and the velocity V is read directly on an ammeter calibrated in knots whilst an integrating watt-hour-meter shows the distance travelled. In a further modification, Fig. 11 (not shown), the sound signal emitted by the transmitter is supplied by a modulator driven by a c.w. oscillator, the received signal being used to operate the modulator so that the frequency of this modulation depends on the velocity of the hull. This velocity is read directly on a frequency meter and the distance travelled is read directly on an integrator. An arrangement in which the integration constant corresponding to still water conditions is balanced out by the use of a reference oscillator of constant frequency is described with reference to Figs. 12 and 13 (not shown).