Abstract: An optical absolute pressure sensor constituted by a body made of a substance having photoelastic properties and provided with at least one internal duct extending parallel to the longitudinal direction of said body, the pressure inside said duct being substantially zero and the ends thereof being closed in sealed manner. The invention also applies to a method of making the sensor, to apparatus for implementing the method, and to a sensor constituting the product of the method.

Abstract: A single optical port in an electric meter is multiplexed between at least two internal systems by using a multiplexer circuit which has a set of data lines which can be connected to the optical port and to one of the internal systems. The multiplexer is controlled by means of a magnetic reed switch which is mounted within the cover of the meter, so no mechanical changes to the meter cover are required.

Abstract: A rotary displacement transducer comprises a shaft rotatably supported in a housing, and to which the rotary displacement to be sensed is applied. The shaft is axially fixed in the housing, and has a precision screw thread formed over part of its length. An internally threaded sleeve coaxially surrounds the shaft in threaded engagement with the precision screw thread, the sleeve carrying a collar having two diametrically opposed radial projections. The first projection carries a roller which engages in a slot in the housing to prevent the collar and sleeve rotating as the shaft is rotated, so that rotation of the shaft causes the sleeve and collar to move axially of the shaft by an amount dependent on the rotary displacement to be sensed. The axial movement of the collar is sensed by a linear displacement transducer of the LVDT type coupled to the other radial projection on the collar.

Abstract: When a hydrocarbon liquid is pumped (11) for retail delivery, it is degassed by means of a vortex device (13). A control valve (21) shuts off delivery if the gas content in the degassed liquid being delivered via a main duct (16) is too high. Unlike prior systems which sense gas content only in the liquid being delivered, the present invention senses the greater gas content in the recycled gas-enriched fraction from the vortex separator device (13). This is done by means of a venturi system (19) controlling a servo-valve (25) which in turn controls the control valve (21). By using a magnified image of the gas content, the system is made more sensitive and more reliable.

Abstract: An optical transducer system for use with an optical transducer of the kind which produces a wavelength multiplexed optical output signal comprises a broadband optical source, and a tunable filter in the form of a Fabry-Perot interferometer connected to receive a broadband optical signal from the source. The interferometer is repeatedly swept through its pass band by a control signal of triangular or sawtooth waveform, producing a swept wavelength optical output signal for application to the transducer. In one embodiment, the optical output signal from the transducer is compared with the output signal from the interferometer to decode it, while in another embodiment, a control loop maintains the output amplitude (intensity) of the broadband source substantially constant over the range of wavelengths used by the transducer, enabling a reference channel provided in the transducer to be used for decoding purposes.

Abstract: A solid state sensor, micromachined in silicon, comprises first and second beams which can be optically excited into resonant vibration. The first beam is arranged to be acted upon by a diaphragm, so that the tension in it, and therefore its resonant frequency, is affected by the pressure applied to the diaphragm. The second beam is provided for temperature correction purposes, and to this end is positioned close to the first beam but free at one end, so that it is insensitive to the pressure applied to the diaphragm, while being subject to the same temperature variations as the first beam. Additionally, the second beam is positioned sufficiently close to the first beam that it can be optically excited simultaneously with the first beam via a single optical fibre.

Abstract: The transmitter in a power line communications system applies to the power line encoded logical-one and logical-zero bit signals consisting of signals formed respectively of predetermined different sequences of frequencies. The receiver, coupled to the power line, includes a first homodyne, non-coherent, quadratic demodulator for demodulating the logical-one bits and a second for demodulating the logical-zero bits. The first demodulator produces, locally, and in first and second channels, respectively, a first reference signal that is a replica of the logical-one bit sequence of frequencies and a second reference signal that is the replica in quadrature. The second demodulator produces, locally, and in third and fourth channels, respectively, cooresponding third and fourth reference signals for the logical-zero bit sequence. Each of the four reference signals is applied to a corresponding analog multiplier for multiplication by the input signal in each channel.

Abstract: Solid state pressure sensors based upon aluminum gallium arsenide devices are disclosed. One embodiment uses a TEGFET as a hydrostatic pressure sensor. By adjustment of the gate voltage, it is possible to vary the operating conditions of the sensor, so as to adapt it dynamically to particular measurement conditions. Another hydrostatic pressure transducer, essentially made from aluminum gallium arsenide on a gallium arsenide substrate, comprises a layer sensitive to pressure and a layer sensitive to temperature: due to its homogeneous structure and its rigorous temperature compensation, this transducer offers both high accuracy and high sensitivity.

Abstract: A single vibrating tube transducer comprises a tube (4) held between two nodal masses (6) which are attached to the tube (2) close to their respective centers of gravity (16). Each nodel mass (6) has an extended portion (14) which is attached at its free end to the opposing nodal mass by an arrangement of metal ligaments (18). Vibrating means (19) and sensing means (20) drive and detect the tube motion respectively. The tube has discontinuities (28) adjacent to the vibrating means (19) and the sensing means (20), to ensure the desired mode of resonance is achieved. Acoustic baffles (30) prevent inaccuracies due to internal acoustic resonance in the transducer.

Abstract: A calibration circuit for a solid state electricity meter comprises a plurality of resistors formed on an integrated circuit. The resistors are connected by an on-chip array of electrically controlled switches, such as MOSFETs, to signal processing circuitry driving the meter. The resistors establish variable voltage divider networks which compensate the meter for phase, gain and offset errors distributed in the signal processing circuitry. The values of the variable voltage divider network may be established automatically during testing of the meter, by a digital computer, or semi-automatically, by a technician, to establish the "on" and "off" states of the various transistors of the array.

Abstract: A device for guiding a magnetic tape suitable for being wound helically around a cylindrical drum and for running past at least one magnetic head driven in rotation around the periphery of a slot provided in an equatorial plane of the drum, the device being of the type comprising elongate bearing means linked to the drum and defining at least two bearing points against which one of the edges (bottom edge or top edge) of the tape may bear, the device including link means linking the bearing means to the drum and suitable for modifying the inclination of the bearing means as a function of temperature said link means suitable under the effect of differential thermal expansion to cause the bearing means to rotate about a radial axis (extending transversely to the axis of the drum) passing through a point which is invariant in rotation, and whose position is fixed regardless of temperature.

Abstract: A triangle waveform generator for a pulse-width amplitude multiplier includes a digital-to-analog converter and a charge transfer network. Clocked signals applied to the converter, which includes a resistor chain for providing a set of different potentials, sequentially select ones of the potentials and supply two of them to the charge transfer network. The network weights each of the potentials received, then combines them at an output node. By employing appropriate clocking of the converter, a triangular waveform having a plurality of discrete steps results.

Abstract: A high accuracy power meter capable of measuring power supplied or consumed in multiple phases of a distribution system is fabricated as an integrated circuit. Voltage and current sensing transducers coupled to the power meter provide input signals having a potential proportional to the voltage and current in the distribution system. A low charge injection pulse width amplitude multiplier using a digitally-synthesized triangular wave is provided for each phase. Each multiplier receives the input signals and provides an output signal having a current proportional to the product of voltage and current in that phase of the distribution system.Charge from the multiplier output currents for all phases is accumulated in a capacitor connected across an autozeroing amplifier, which corrects for its own offset voltage. The amplifier output controls a switch connected between a reference potential and the capacitor.

Abstract: A transducer for measuring a parameter of a fluid, such as density or viscosity, comprises two generally parallel tines extending from a common yoke, forming a tuning fork adapted to be immersed in the fluid. The tines are excited to vibrate resonantly and in anti-phase by one or more piezo-electric exciting elements, which are housed in one or more cavities within the tines or the yoke. The vibrations are sensed by one or more similarly-housed piezo-electric sensing elements. The tines are shaped to enhance their sensitivity to the parameter to be measured: for example they are provided with re-entrant surfaces to enhance density sensitivity, or elongated in the direction in which they vibrate to enhance viscosity sensitivity.

Abstract: The method in suitable for authenticating electronic memory cards intended for authorizing the supply of goods or services after being processed by a card reader machine. The card memory includes at least three zones (Z.sub.1, Z.sub.2, Z.sub.3) comprising a first zone (Z.sub.1) which is readable from outside and which contains information (I) and a corresponding signature (S) obtained by means of secret data (D) recorded in the third zone (A.sub.3) which cannot be read from outside the card. The second zone (Z.sub.2) which can be read from outside the card contains the result of secret key and public key encoding all of the data contained in the first zone. This method provides effective protection against several types of fraud.

Abstract: An apparatus for detecting the presence of magnetic particles in a fluid is described. The apparatus uses a magnet which is mounted so that its field is transverse to the fluid flow, so that the magnetic field imparts a transverse velocity to any magnetic particles in the fluid. An ultrasound transducer mounted adjacent to the magnet. The ultrasound transducer is used to direct ultrasound energy into the moving fluid and to detect any particles having a velocity which is not in the direction of the main fluid flow, i.e., the velocity of a particle affected by the magnetic field will be detected by the ultrasound transducer as a result of the Doppler shift in the transmitted and reflected ultrasound frequency.

Abstract: A device for detecting the position of a recording/read head (20) for use with a magnetic tape, the head being fixed to the free end of an elongate support (14) fixed to a component (5) which is mounted to rotate in a slot (4) provided in an equatorial plane of a cylindrical drum (1) on whose outside surface the recording tape is wound helically. Said support is capable of bending in a direction (f) which is transverse to the direction of relative head-to-head tape displacement. The device is characterized in that it includes a position sensor comprising a variable electrical capacitance including a fixed plate (32) fixed to the drum (1) of the moving plate (24) fixed to said head support, together with measurement means (33, 34, 35.sub.i) which are sensitive to said capacitance and are suitable for providing a signal representative of the position of the head support (14) and thus of the head (20).

Abstract: A multi-rate commodity metering system comprises an electronic key containing an EEPROM, and a meter for metering the commodity and having a receptacle for receiving the key. The meter also contains a real-time clock. The key can operate as a prepayment device, a programming device and a meter-reading device. Thus the key is taken to the commodity suppliers premises, where, in return for a payment, a credit signal representative of the payment is stored in the key. At the same time, a new program for the meter, i.e. new times for switching between rates and new prices per unit of commodity for each rate, together with the date and time at which the new program is to come into operation, can also be stored in the key. Then, when the key is inserted in the receptacle in the meter, the payment signal and the new program are entered into the meter. Additionally, the current set of meter readings (i.e., the respective readings for each rate) are read into the key, along with the date and time.

Abstract: The system comprises memory cards and card readers. The card memories (MEM) include validation memory points V.sub.j and credit memory points C.sub.i,j. The addresses of the validation points V.sub.j and the addresses of the associated credit point C.sub.i,j are defined by a reference table (TRR) and a permutation table (TP) which make use of a data item (Z.sub.F) which is specific to the card.