Abstract: An apparatus for determining the concentration of a conductive fluid present in a fluid filled bore hole is described. Such apparatus are known as water hold-up meters and are frequently used in oil, gas and water filled bore holes. In bore hole applications, data bandwidth between a down hole device and the surface can be limited, while determining water hold-up based on down hole measurements can be data intensive. A technique is proposed for calculating the water hold up that requires less data to be transmitted between the down hole device and the surface.

Abstract: An apparatus for determining the concentration of a conductive fluid present in a fluid filled bore hole is described. Such apparatus are known as water hold-up meters and are frequently used in oil, gas and water filled bore holes. In bore hole applications, data bandwidth between a down hole device and the surface can be limited, while determining water hold-up based on down hole measurements can be data intensive. A technique is proposed for calculating the water hold up that requires less data to be transmitted between the down hole device and the surface.

Abstract: Coins may be validated and denominated by comparing varying signals from coin sensors and checking whether a predetermined relationship between them is maintained, for example, as the coin moves past die sensors. In some implementations, each varying signal may represent the varying effect on a sensor as the coin moves relate to the sensor.

Abstract: A coin or banknote validator is calibrated to accept items of value by taking successive measurements of items and using them to update acceptability data which defines at least one acceptability criterion for testing. Each measurement is first checked against a suitability criterion, and is only used for updating the acceptability data if the suitability criterion is met. In this way, the acceptability data can be derived without storing all the individual measurements, while still rejecting those measurements which are statistically unsound. The suitability criteria is such that if a measurement differs from the current acceptability data by more than a predetermined amount, the criterion is not met. To avoid problems resulting from the first measurement being unsound, this first measurement is discarded if it does not lie within a predetermined range of the second measurement.

Abstract: Apparatus for validating items of value is described. The apparatus includes a measurement circuit including an inductor, the complex impedance of which varies in accordance with the interaction between a test item of value and a magnetic field within which the inductor is located. Circuitry is provided for extracting first and second periodic signals from the measurement circuit, and a circuit is provided for timing the interval between corresponding portions of the first and second periodic signals. A processing element then determines the value of a parameter related to at least one of the real and imaginary parts of said complex impedance, as a measure of the validity of said test item, from the outputs of the timing circuit.

Abstract: Improved input filtering apparatus for loudspeaker systems, and loudspeaker systems including such apparatus. The bass roll-off point of input filtering apparatus for loudspeakers is automatically adjusted to an optimum in accordance with the amplitude and spectral content of the audio signal being received at the time, thereby attenuating components in the signal liable to cause "bottoming" of the loudspeaker.