GB893986A - Improvements relating to electrical impulsing devices - Google Patents

Abstract

893,986. Electric selective signalling systems. FERRANTI Ltd. Oct. 27, 1959 [Oct. 28, 1958], No. 34418/58. Class 40 (1). A device for producing pulses in dependence upon the rotation of a shaft comprises a crystal exhibiting the Hall effect in respect of three mutually perpendicular axes X, Y, Z, means for passing a polarizing current through the crystal in the X-direction, a magnetic device to apply a repetitive magnetic field to the crystal in the Y-direction, and output means for receiving the pulses thus produced along the Z-direction. A crystal 12 is polarized by a generator 13<SP>1</SP> passing a current through it in the X-direction, and is subjected to a magnetic field in the Y-direction produced by a magnet 16 rotating on a shaft 15. The Hall voltage is in phase with the polarizing current when the field has one sense and in counterphase when it has the other. Leads 17, passing via an A.C. amplifier 51 and a transformer 52, supply the Hall voltage to a conventional phase discriminator 53 using the output of generator 13<SP>1</SP> as a reference signal. In known manner the discriminator produces a D.C. voltage between terminals 61, 62, which is of one sense when the reference signals and input are in phase and of the other sense when they are not. The repetition frequency of the pulses is dependent upon the rotation of the magnet 16, and hence also upon its driving-shaft 15. In modifications the magnet 16 may be replaced by an arrangement of magnets whose field does not alternate, so producing signals of only one polarity. D.C. polarization of the crystal may be used. If A.C. polarization is used and the magnetic component is such that the applied fields are of like sense the discriminator would be replaced by a rectifier to produce a unidirectional pulse for each A.C. cycle. The device is described as for use in an electric meter.