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: 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 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: 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: An electronic token for use with a prepayment commodity meter such as an electricity meter comprises a key-like device 10 having a head 12 containing an electronic circuit and a body portion 14 for insertion into a keyway in a receptable 40 in the meter. The body portion 14 has grooves 24 which serve to guide the body portion into the keyway, and which contain electrical contacts 28, 30 connected within the device 10 to the electronic circuit. Between the body portion 14 and the head 12, the device 10 is provided with a locating recess 27, which engages a projection 78 in the receptacle 40 when the body portion is fully inserted into the keyway. The receptacle 40 incorporates a combined shutter 98 and spring 102, which serve to close the keyway in the absence of the device 10, and to urge the body portion 12 to one side of the keyway during insertion, such that the recess 27 engages the projection 78 and the contacts 28, 30 engage contacts 68, 72 in the receptacle.

Abstract: An optical transducer system for producing an optical output signal representative of the rotational speed of a rotary member, particularly a shaft of a gas turbine engine, comprises a conventional inductive speed probe positioned adjacent the shaft to sense the passing of the teeth of a toothed wheel secured to and rotatable with the shaft. The inductive sensor thus produces an AC output signal whose frequency is proportional to the rotational speed of the shaft, and this signal is used to excite electrostatically vibration of a cantilever beam micromachined in silicon. The vibrating beam is arranged in an optical path defined by one or more optical fibres, such that its vibrations modulate light directed along the optical path at a frequency which is again proportional to the rotational speed of the shaft.