Patent GB-482054-A (GB)
Title: Improvements in or relating to the measurement of rotational velocity
IPC: G01P3/66
Filed: 1936-11-19
Abstract: 482,054. Electric signalling systems. SUBMARINE SIGNAL CO. (LONDON), Ltd. (Submarine Signal Co.) Nov. 19, 1936, No. 31739. [Class 40 (i)] [Also in Group XIX] The angular velocity of a rotating shaft is measured by rotating an indicator at a speed proportional thereto and indicating the angle through which the indicator moves during a very short predetermined time interval. Different forms of timing devices comprising electric switches and retardation lines are described wherein an electric impulse created at the zero position of the rotating indicator acts to make available after a definite time lag a second electric impulse which may effect the lighting of a neon tube, for example, or the passage of the electron beam on to the fluorescent screen of a cathode-ray tube having a rotating field. Fig. 1 shows a propeller shaft 1, whose speed is to be measured, rotating a translucent scale 7 through a generator 4 and motor 5 When the zero mark on the scale 7 is opposite a neon tube 35, a cam 12 on the scale spindle 6 opens the contacts 14, 15 to de-energize a magnet 16 and permit a spring 18 to pull a stop 11 away from an arm 10, which now rotates under the influence of a constant speed motor 8 Before it has rotated a complete revolution, the contacts 14, 15, are closed and the stop 11 restored so that the arm 10 engages it and energizes the circuit shown to cause a discharge to take place in the neon tube 35, which thus shows the distance moved through by the scale 7 in the predetermined time interval. In a modification, Fig. 4, designed to give a much greater number of indications in a given time, a photo-electric cell 38 is energized by a light source 39 once in each revolution of the apertured disc 36, thereby producing an impulse which is impressed on a vacuum tube 42 to cause a current impulse to flow through a retardation line 47 so proportioned that, after a predetermined interval, the impulse reaches the input circuit of a vacuum tube 49 and by overcoming the negative bias on the grid it causes a current impulse to flow in the primary of a transformer 33. The high-voltage impulse thereby induced in the secondary of the transformer effects the illumination of the neon tube 35 and momentarily illuminates the rotating scale 7, the marks on which may be projected by a lens 83 upon a screen 82. Fig. 5 shows a modification wherein the retardation line 53 is left open-circuited so that the impulse is reflected back over the line and the anode-cathode circuit of the vacuum tube 42 is connected across the primary of the transformer 51, the secondary of which is connected across opposite corners of a bridge circuit having two arms formed by inductances 52, 52<1>, a third arm formed by the retardation line 53 and the fourth arm by the impedance 54 matched to the impedance of line 53. The photo-cell 38, vacuum tube 49 and neon tube 35 are connected as shown. In another modification eliminating the photo-electric cell, a commutator initiates the impulse when the scale 7 reaches its zero position, and the opposite terminals of the retardation line bridge circuit are connected across a resistance to the input of a " Thyratron " (Registered Trade Mark) having the discharge tube transformer in its anode - cathode circuit. In place of the retardation line a further modification makes use of the time required for a condenser to charge or discharge. Fig. 8 shows a cathode-ray tube indicator 71. The shaft 1 whose speed is to be measured is geared to an alternating current generator 67 and a commutator 68, and the current is conducted through a phase-splitting arrangement including a condenser 69 and resistance 70 to the two sets of control plates of the cathode-ray tube 71, the potential thus applied to the control plates producing an electrostatic field tending to rotate the cathode-ray beam in accordance with the angular velocity of the shaft 1. Brushes 58, 59 are short-circuited by a commutator bar to produce an electric impulse which is impressed on a retardation line 53. After reflection and amplification the impulse produces a potential in the secondary of transformer 72 which is connected to the grid and the cathode of the tube 71, and the deflected electron beam is now permitted to pass to the fluorescent screen 74, which is calibrated directly in terms of the speed of the shaft 1.