Abstract: A device for reading an elongate magnetic data carrier attached to or embedded in an article, having an active read head adapted to have a lateral extent greater than the width of the data carrier, preferably four times greater, such that the magnetic field produced by the read head results in a signal from the data carrier which has an amplitude which varies by less than 50% for head to data carrier spacings of from 0 to 60 microns. A wide read head can also make the reading of data more reproducible when reading narrow tracks using swipe readers, where precise alignment is difficult to achieve.

Abstract: An apparatus for reading permanently structured magnetic records having a first coercivity, comprising an oscillator having an inductive read head that is coupled to a circuit arrangement. At least one side of the read head sees an impedance that is larger than the impedance of the read head over the range of frequencies of interest, such that the read head provides an electrical signal in response to magnetic records having a second coercivity that is higher than the first coercivity (typically 2,000 to 5,000 oersteds). The electrical signal is derived from the voltage across the read head, which is preferably detected by a differential integrator that subtracts the voltages on either side of the read head to give a voltage difference, and integrates this difference over time.

Abstract: A record carrier has a secure first data storage device storing a plurality of different identification numbers in a sequence and a further data storage device storing a further number. The identification numbers are successive integers, and the further number is the least significant digit of one of the successive integers. The secure data storage device preferably includes permanently structured magnetic tape. The further number is derivable in a predetermined way from only one of the identification numbers, thus identifying uniquely which one of the identification numbers is characteristic of the record carrier.

Abstract: Apparatus for coupling power into a body of gas by induction to provide a gas discharge, comprises a source of a/c power (3) coupled to a circuit arrangement having an inductor comprising two coils (1, 2), each constituted by a respective elongate conductor, the conductors each having one end coupled to the circuit arrangement at opposite respective sides of the inductor, and having the other end at a floating potential. The mutual capacitance between the coils, together with the inductance of the inductor as a whole, constitute a balanced self-resonant circuit having a resonant frequency which is greater than 1 MHz and less than 100 MHz. This arrangement can reduce temperature variations in the resonant frequency and can reduce unwanted r.f. emissions.

Abstract: An electrochemical cell sensing circuit for an electrochemical cell having a working electrode, a counter electrode and a reference electrode in an electrolyte, which in use, when a gas to be analysed is introduced into the cell, generating a current between the counter electrode and the working electrode, and a potential at a position in the electrolyte is sensed by the reference electrode.

Abstract: Glow discharge apparatus comprises a light-transmissive body (101) defining a cavity (102) containing neon or xenon gas. The glow discharge is powered by one or more electrodes (103) external to the cavity. The apparatus also comprises a secondary light source (104) for illuminating the neon gas to provide electrons in the cavity, thereby assisting discharge initiation in intermittent use, for example when controlled by a pulse time modulation drive circuit (107).

Abstract: A method of identifying a data carrier such as a credit card, benefit card, access control card, identity card or stored value card, carrying data in the form of a plurality of rational number in a sequence, successive numbers having a marker between them, comprises a) measuring the distance from a fixed point on the data carrier to a given part of a marker, b) dividing this distance by the distance between corresponding give parts of successive markers, thereby obtaining a rational number, and c) subtracting this rational number from the number in the sequence adjacent the marker in a given direction, thereby obtaining a further rational number which is capable of identifying the data carrier uniquely.

Abstract: In order to overcome problems with residual d.c. offset, and input signals with arbitrary timing, a drive circuit for a ferroelectric liquid crystal device includes a counter arranged for counting between first and second predetermined values in response to an input signal. The counter is designed so as to count in a first direction in response to a positive edge of the input signal and in a second direction in response to a negative edge of the input signal. Gating and latching circuits are responsive to the counting of the counter and the direction of count so as to provide appropriate positive or negative output voltage pulses for driving a ferroelectric liquid crystal device. An output stage comprising a bridge circuit is coupled via a step up transformer to the display device.

Abstract: A drive circuit arrangement for a gas discharge lamp includes a) a self resonating inverting for providing a drive voltage across a load impedance, the inverter having a pair of field effect transistors which operate in anti-phase, b) a tank circuit for canceling the reactive component of the load impedance coupled to the inverter, c) a voltage division circuit which provides a given fraction of the drive voltage to the gates of the field effect transistors, and d) a phase shifting means comprising an inductance in series with the tank circuit for shifting the phase of the given fraction of the drive voltage. The voltage division circuit is provided with a voltage limiter which in operation provides a further phase shift to the given fraction of the drive voltage when the drive voltage exceeds a given threshold value, increasing the resonant frequency of the inverter and limiting the peak drive voltage.

Abstract: This invention relates to a composite image arrangement, comprising a pattern and a further pattern, substantially parallel to the first pattern, each comprising a plurality of visually contrasting regions, the patterns being in fixed positions relative one to the other on either side of a light transmissive lamina.

Abstract: In a computerized axial tomographic apparatus it is proposed to use, as radiation detectors, alkali halide scintillator crystals cooperating with photodiodes to measure the light output therefrom, or else photodiodes directly sensitive to the radiation passed through the patient. For advantageous operation, especially in regard to drift and rapidity of operation, it is proposed to use the photodiodes photovoltaically and in the so-called "current mode".