Patent GB-407819-A (GB)
Title: Improvements in and relating to velocity measuring apparatus
IPC: G01P5/04
Filed: 1933-02-25
Abstract: 407,819. Measuring the velocity of solids relative to fluids. BRITISH THOMSON - HOUSTON CO., Ltd., Crown House, Aldwych, London.-(Assignees of Heinz, W. B. ; 314, 5th Street, Scotia, New York, U.S.A.) Feb. 25, 1933, No. 5813. Convention date, Feb. 25, 1932. [Class 97 (iii).] The velocity of a body, e.g. an aircraft, relative to a fluid, e.g. air, is determined by an element suspended in the fluid and attached to the body so as to be movable in a plane at an angle to the direction of relative motion, the element thereby vibrating at a frequency proportional to the velocity of the body relative to the fluid and independent of variations in the density of the fluid. The relative velocity is indicated by means, preferably electro-responsive, associated with the movable element and influenced by its frequency of vibration. In the form shown the movable element comprises a cylinder 18 arranged in the throat of a Venturi tube 10 carried by an aircraft and is pivoted at 19 to the lower part of a magnet 16 on the Venturi tube for transverse oscillation as shown by the arrow 20. An armature 17 integral with the cylinder 18 extends between the poles N, S of the magnet and is biassed towards the central position by compression springs 21. Vibration of the cylinder 18 causes an alternating magnetic flux in the armature 17 and gives rise to an alternating voltage in the coil 23 surrounding the armature. An electro-responsive device such as that described in Specification 377,458, [Group XXXVI], may be used for indicating the frequency of the alternating voltage in the coil 23. A transformer 25, having two legs 29, 30 joined by a bridge 31 which does not become magnetically saturated and a bridge 32 which becomes saturated within the range of speeds to be indicated, has the voltage generated in coil 23 applied to a primary winding 26 round the bridge 31. A secondary winding 27 round the bridge 32 and a secondary winding 28 in an air gap between the legs 29, 30 are connected in series with their voltages opposed. Leads 33 connect the coils 27, 28 and a high resistance 34 to a full wave rectifier 35. A direct current milli-voltmeter 36 which may be graduated in speed units is connected to the rectifier 35. Resistance 34 and a resistance 37 connected across the millivoltmeter 36 have slightly negative temperature coefficients to compensate for errors arising in the circuit due to temperature variations. The magnitude of the voltage generated in the coil 23 is proportional to the speed of the aircraft and the density of the air. A milli-voltmeter 41 connected through a rectifier 38 to the coil 23 may thus be used to indicate whether or not an aircraft is flying sufficiently fast to sustain itself safely in the air. In a modification the armature 17 is arranged to oscillate in a plane at right angles to a line joining the poles of a magnet and to vary the flux through a coil surrounding the magnet. In a further modification the armature carries contacts adapted to oscillate between fixed contacts. The contacts may be arranged either to cause a pulsating unidirectional current to flow through the primary winding 26, or to cause a condenser to alternately charge and discharge through the winding 26, or to cause a condenser to discharge through an ammeter.