Patent GB-685113-A (GB)
Title: Improvements in and relating to turn-sensitive devices
Inventor: LIVERSIDGE JOSEPH HORACE
IPC: G01P9/04
Filed: 1949-02-07
Abstract: 685,113. Turn-sensitive devices. METROPOLITAN-VICKERS ELECTRICAL CO., Ltd. Feb. 27, 1950 [Feb. 7, 1949], No. 3355/49. Class 97 (iii). [Also in Group XXXVIII] In a turn-sensitive device of the vibrating reed type, the reed is supported at one end by pressure-responsive means so arranged that when the reed is subjected to an angular velocity about its longitudinal axis, the resulting precessional torque is substantially wholly resisted by the pressure-responsive means, which latter are arranged to provide an electrical output representative of the angular velocity. The device shown comprises a reed 1, Fig. 1 of magnetic material which is electromagnetically maintained in vibration in the plane of the diagram at its natural frequency. The reed is provided with a shouldered end 3 having a shrink fit in a hole in a plate 2 whereon the reed is thus rigidly mounted. The plate 2 rests on three piezo-electric quartz crystals 5, 6, 7, Fig. 2, located at the angles of an isosceles triangle, pressure being maintained on the crystals by a wire 8 secured within a bore in the reed 1 and having a screw-threaded end 10 carrying lock-nuts 11 engaging a plate 4 to adjust the tension of the wire. The crystals are received within recesses in the plate 4 or in the plate 2 so as to be positively located. Rotation of the device about axis R, Fig. 1, creates a torque about axis P, Fig. 2, with resulting differential pressure on the crystals 5, 6 which are connected by appropriate electric circuit arrangements to a device indicating the rate of turn. The driving system comprises a pair of laminated magnetic cores having limbs 15, 18 and 23, 24 separated from the reed by air gaps, the upper limbs carrying coils 16, 19. The pole faces are narrow in the direction parallel to the length of the reed and are of considerable axial length so as to minimize movement of the flux axis. The casing 12 and cover 2a are preferably of steel for magnetic shielding. The upper faces of the crystals 5, 6, 7 are electrically connected by the plate 2, the connection being shown at 2<SP>1</SP>, Fig. 3. The lower faces of the crystals 5, 6 are connected by conductors 30, 31 to a phase-discriminating rectifier 50 with or without one or more stages of amplification, the output of which operates the indicating device. The device 50 may be of the kind described in Specification 592,208, [Group XXXVIII]. The lower faces of crystals 5, 6 are also connected by a resistor 34, the centre point of which is connected to earth and through a resistor 33 to the cathode of valve 32, the grid of which is connected to the lower face of crystal 7. Connected across the resistor 33 are a condenser 38 and the primary 37 of a transformer, the secondary of which is connected at its ends to the control grids of valves 40, 41, the cathodes of which are connected through bias voltages 42, 43 to a centre tapping on the secondary and to earth. The anodes of the valves 40, 41 are connected through the windings 16, 19 of the driving electromagnet to a source of anode current also supplying the anode of the valve 32. The valves 40, 41 are biased to conduct alternately, so that the windings 16, 19 are energized alternately so as to prevent frequency doubling. The anodes of the valves 40, 41 are also connected through condensers 45, 46 to the ends of the centre-tapped primary 44 of a transformer the secondary output of which may be connected, if necessary with further amplification, for energization of the device 50. A resistor 49 may be connected across the crystal 7 and a resistor 48 may connect the centretapping of the resistor 34 to plate 2. A highpass filter may be connected between the crystals 5, 6 and the input to the device 50 to avoid effects due to mechanical vibration. Reference has been directed by the Comptrollerto Specification 601,051.