Abstract: Pulsed Field Magnetometry (PFM) method and apparatus to compensate for zero signal errors in a material characterisation process involving first constructing a synthesised zero signal expressed with a range of variable parameters. A measurement cycle is performed on a sample of material to be characterised the waveform data obtained in said measurement cycle is stored. The synthesised zero signal is then applied to the stored data while adjusting the values of the variable parameters, and the values are selected which best fit the synthesised zero signal to the stored data. The synthesised zero signal with the selected values is then removed from the stored data to obtain compensated material characterisation data.

Abstract: A method of magnetizing members of magnetizable material (210) including presenting a magnetizer head to a circular array of the members (210) mounted on a rotor plate (200) of an electrical machine. The magnetizer head includes a circular array of coils (142), each coil (142) being positioned adjacent a respective one of the members (210). A current is supplied to selected juxtaposed pairs of the coils (142) so as to set up a magnetic field. Flux of the field forms a closed loop through the pair of coils (142) and the adjacent pair of members (210), such that uncontrolled flux leakage from this loop is minimized and such that the pair of members (210) are at least partially magnetized.

Abstract: A method of magnetising members of magnetisable material (210) including presenting a magnetiser head to a circular array of the members (210) mounted on a rotor plate (200) of an electrical machine. The magnetiser head includes a circular a array of coils (142), each coil (142) being positioned adjacent a respective one of the members (210). A current is supplied to selected juxtaposed pairs of the coils (142) so as to set up a magnetic field. Flux of the field forms a closed loop through the pair of coils (142) and the adjacent pair of members (210), such that uncontrolled flux leakage from this loop is minimised and such that the pair of members (210) are at least partially magnetised. Current is then passed through a second selected juxtaposed pair of the coils (142) so as to at least partially magnetise the respective adjacent pair of members (210), the second pair of coils (142) and the adjacent members (210) overlapping the first pair by one coil (142) and one member (210) respectively.

Abstract: High-energy permanent magnetic materials are characterized by exposing the material to sequential pulsed fields of respectively different rates of change of magnetic field strength, sensing the total magnetic field strength, sensing the total magnetic field generated in the sample by the respective pulses including eddy currents induced therein, and eliminating eddy current components from the said fields, whereby the net magnetic fields relate to the magnetic characteristics of the sample. Preferably the pulsed field is capacitor-generated via a solenoid and the rate of change of the magnetic field strength is produced by holding the waveform constant and altering the pulse duration, for example by providing taps on the solenoid together with an inductor and a balancing resistor, to enable the ratio of resistance to inductance to be maintained substantially constant across the range of taps utilized.

Abstract: Apparatus for testing the response of a viewer to questions or problems displayed on a video screen comprises apparatus to modulate the video signal to display coded patches on the screen. The patches are coded by alternately raising and lowering the luminance signal of the video without destroying spacial variations of the signal in the patch. The coding is detected by a probe having a light guide pointer conducting light from the video screen to a photo-detector in the casing of the probe. The coded luminance variations are read by the probe and produce response indications such as sound or light signals which qualify the response. The apparatus is useful as a teaching aid.