GB1004681A - A method of and apparatus for the analogue measurement of the speed of rotation of a rotating body - Google Patents

Abstract

1,004,681. Measuring angular speed electrically. SIEMENS-SCHUCKERTWERKE A.G. June 4, 1962 [June 2, 1961], No.21568/62. Heading G1N. Apparatus for measuring the angular speed of a shaft comprises a disc rotating with the shaft in the field of a stationary magnet, whereby eddy currents are induced in the disc and measured by the secondary magnetic field they produce. In one embodiment (Figs. 1, 3), a metal disc 4 is driven by a shaft 5 to cut the field of a permanent magnet 1 whose magnetic circuit is completed by cores 6, 7 separated by a Hall plate generator 8. The change in flux, indicated by the change in output volts from generator 8, is indicative of the angular speed of the shaft 5. The basic flux produced by the magnet 1 is sensed by a further Hall plate generator 11 in separate shunt magnetic members 9,10, unaffected by the eddy current field, so that the difference between the outputs from generators 8,11 is indicative of shaft speed. Alternatively the second generator 11 may be subjected to an independent, controlled magnetic flux, or the output from generator 8 may be opposed by a preset voltage representing the output from generator 8 when shaft 5 is stationary. Automatic temperature compensation is achieved by a magnetic shunt whose permeability varies with temperature in a compensating manner, or by controlling the control current of the Hall plate generators appropriately. In another embodiment (Figs. 4, 5)the eddy currents induced in a rotating disc 15 by a magnet 12 produce auxiliary flux in perpendicularly located cores 18,19 separated by a Hall plate generator 20, whose output is indicative of the angular speed of disc 15 and shaft 16. The magnet 12 may be a permanent magnet or energized by windings 13, 14 carrying the control current of generator 20, which can be varied for different speed ranges. In a modification, a winding 21 on core 18 can be energized to neutralize the auxiliary flux, as shown by zero output from generator 20, the neutralizing current being a measurer of the angular velocity of disc 15. Further embodiments are shown utilising measurement of the auxiliary flux in balanced arrangements where the main flux is neutralized. The Hall plate generators may alternatively comprise magnetic resistive elements. The rotated disc may be shaped as a hollow cone, cylinder or sphere, and may be provided with special short-circuiting rings for the eddy currents. Specification 1,004,682 is referred to.