Patent GB-417051-A (GB)
Title: Improvements in or relating to dynamometric apparatus
IPC: G01L3/12
Filed: 1933-03-21
Abstract: 417,051. Dynamometers ; speedmeters. FITZGERALD, A. S., 433, Warwick Road, Wynnewood, Pennsylvania, U.S.A. March 21, 1933, No. 8534. [Classes 106 (ii) and 106 (iii).] Comprises a method and means for measuring the torque of a shaft in which the amount of light impinging on photo-electric means is caused to vary in accordance with the angular torsion of rotating element and an indicating device is energized with the current derived from the photo-electric means. Two screens 4, 5 are mounted a suitable distance apart on a shaft 3 of a power transmission system 1, 2, 3. Each screen is provided with two circular bands of apertures, and the screens so fixed to the shaft that the outer ring of apertures on each screen are in alignment when no torque is being transmitted. The inner ring on the screen 4 is radially in alignment with the outer ring, but on the screen 5 the apertures are displaced relatively to the extent of half the spacing between two apertures. Light from a source 8 is directed in two beams parallel with the shaft and aligned with the inner and outer bands of apertures respectively. The beams after passing through the screen impinge on photoelectric cells 9, 10. These are connected in a bridge circuit 14, if necessary through amplifiers 11, 12 energized from an alternating current source 13. The bridge circuit includes three variable impedance devices 15, 16, 17 and a constant impedance 18. The saturating windings of saturable reactors 15, 16 are energized from the outputs of the amplifiers 11, 12 and if of usual form rectifiers 19, 20 may be included. Associated with the bridge circuit 14 is an electron tube regulating system 21 which supplies a saturating current to the saturating reactor 17 and automatically varies the current to maintain a bridge balance. The current which flows in the saturating reactor 17 is thus caused to bear a definite relation to the ratio of currents supplied to the saturating windings of the saturating reactors 15, 16 and is likewise related to the ratio of the light intensities impinging upon the cells 9, 10. The bridge circuit 14 and regulating system 21 is described in Specification 413,269. When the shaft 3 and screens 4, 5 are rotating under no load, if no relative angular displacement between screens 4, 5 takes place, the cell 9 is intermittently illuminated with a frequency proportional to the speed of the shaft. If load is applied and displacement occurs between screens 4 and 5, less illumination passes through the outer rings of apertures to the cell 9 and more light to the cell 10. The regulating system 21 includes a valve 28 the grid of which is excited with the potential across a capacitor 29 charged through a high resistor 37 by two valves 41, 42 reversely connected in parallel so that the capacitor 29 may be charged to either polarity by means of a transformer 34 provided with two secondary windings 43, 44 connected to the grids of valves 41, 42. The transformer 34 is energized across a diagonal of the bridge 14. The anode circuit of the valve 28 is energized from the secondary 31 of a transformer 30 and the circuit includes a current measuring instrument 33 and one coil of a electrodynamometer 35. Thus a current flows in the instrument 33 and in one coil of the instrument 35 which is a measure of the torque. In addition a valve system 38 is included comprising valves 39, 40, capacitors 45, 46 and resistors 47, 48. The grids of the electric valves 39, 40 are energized through a grid transformer 49 from the output of the amplifier 11. The function of this system is to furnish a direct current the magnitude of which is proportional to the frequency at which the transformer 49 is excited. The mean direct current which flows through the circuit 38 may be made proportional to the frequency. A direct current voltage for supplying the valves 39, 40 is obtained from a rectifier 50 energized from the secondary winding 32 of the transformer 30. Filtering means 51, 52, 53 may be included. The circuit connecting the rectifier 50 to the frequency indicating system 38 includes a current measuring instrument 54 and the second coil 54 of the electrodynamometer 35. The instrument 54 may be calibrated in revolutions per minute. The indication of the instrument 35 will be a function of the power transmitted and this can be calibrated in horse-power. A separate photo cell and a third range of apertures may be provided for exciting the transformer 49. Specifications 319,010, [Class 38 (ii)], and 342,681, [Group XXXVIII], also are referred to.