Schlumberger Industries

Stc, Inc

Jolyon P Willson

Philip J Parsons

David N Batchelder

Roger E Jones

Paul N Richards

Eric Metcalf

Adrian Vivian Lewis

Peter G Hale

Teresa M Roberts

Darran Kreit

Graham K Thornton

A water level measurement system for use with a pressurized power plant boiler comprises a tubular pressure vessel for attachment to one end of the boiler such that the water level in the pressure vessel is the same as in the boiler. The pressure vessel has a central rod-like conductor which together with the vessel forms a coaxial RF waveguide. A pair of spaced reference discontinuities are provided in the conductor above the maximum level of the water, so that an RF pulse injected into the waveguide is reflected successively by both discontinuities and the surface of the water. The level of the water can then be determined independently of changes in the dielectric constant of the vapor above it, from the ratio between the time intervals between the first and second reflected pulses and between the first and third reflected pulses. The conductor is mounted at the top of the pressure vessel by way of a pressure seal and a ceramic insulator.

Measurement of liquid level

In pressure sensor systems based upon a micromachined silicon pressure sensor comprising a resonantly vibratable beam supported on a diaphragm, the beam is excited into resonant vibration by directing an optical excitation signal at the beam resonant frequency, via an optical fibre 26, onto a part of the sensor other than the beam, preferably the diaphragm. To detect the vibrations, the underside of the beam 16 and the adjacent upper surface of the diaphragm 18 are together arranged to define a Fabry-Perot cavity, and a continuous optical detection signal is directed at this cavity, also via the optical fibre 26. The optical detection signal is thus modulated at the vibration frequency of the beam 16 by the cavity, and the modulated signal is reflected back into the optical fibre 26.

Sensor systems

A relative position transducer for determining the angular position of a first member angularly movable relative to a second member includes a coded track on the first member, a read head mounted on the second member, drive means for oscillating the read head to scan over and read a limited region of the coded track, and a microcomputer for interpreting the code read by the read head as the position. A first sensor detects when the read head is in a predetermined reference position and a second sensor detects the end points and direction of the read head scan. The sensor outputs are connected to the computer for correct interpretation of the read head output. An interplation is used to improve the accuracy of the position determination.

Relative position transducer for oscillating and scanning a read head

In an optically-excited micromachined silicon pressure sensor comprising a resonantly vibrating beam mounted on a diaphragm, vibration of the beam is sensed optically via the same optical fibre through which the optical excitation signal is applied to the sensor. The end of the fibre and the beam are arranged to define a cavity or gap whose width varies with vibration of the beam and which behaves as a Fabry-Perot cavity: thus light from the fibre is directed onto the beam and then reflected back to the fibre, the reflected light being modulated at the frequency of vibration of the beam. In order to overcome the difficulty of setting the gap or cavity width at an optimum value for light of a given wavelength, light of two different wavelengths is used to sense the vibrations, the wavelengths being selected such that the phase difference produced by the gap for one wavelength differs from that for the other wavelength by roughly 90.degree..

Optical sensing systems

In a micromachined silicon pressure sensor comprising a resonantly vibratable beam supported on a diaphragm, the beam is indirectly excited into resonant vibration by directing an optical excitation signal at the beam resonant frequency onto a part of the sensor other than the beam, preferably the diaphragm. Preferably, the optical excitation signal is of a wavelength to which the sensor is fairly transparent, and is directed through the beam and diaphragm to be absorbed by a suitable coating on the underside of the diaphragm. The optical excitation signal produces local heating, and the resulting expansions and contractions at the beam resonant frequency propagate through the sensor structure to excite the beam into resonant vibration. Another optical signal is used to detect the frequency of vibration of the beam, and a positive feedback loop maintains the frequency of the excitation signal equal to the detected beam vibration frequency. In a modification, the indirect excitation is achieved by forming resistors or piezoelectric devices in a part of the sensor other than the beam, so that the expansions and contractions mentioned above can be excited electrically rather than optically.

Sensors

A solid state sensor, micromachined in silicon, comprised 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.

Solid state sensor with dual resonant vibratable members

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.

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.

Wavelength multiplexed optical transducer with a swept wavelength

An optical sensor uses a torsion-mounted thin silicon paddle (1) with magnetically soft material on its back. A light beam falls on the front face and part of the beam is reflected to a photo-diode (4) whose output drives a current in a magnetizing coil (5). The magnetic field thus produced rotates the paddle out of the beam, which cuts off the light to the photo-diode. Thus the paddle oscillates with an amplitude which depends on the strain due to the torsion mounting. This modulates the light beam, and if they have different resonances several such sensors can share the same beam with a common read-out.

Optical sensor

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.

Optical transducer systems

An optical sensor device uses surface plasmon resonance to detect the presence of a specific material. A transparent body (12) is coated with a thin gold film (14) which film may be coated e.g. with an antibody material. The arrangement is illuminated with a divergent light beam and light internally reflected from the gold film is detected by a photodiode array (16). The dielectric conditions adjacent the gold film determine the position of the surface resonance angle, this being indicated by a dark area on the detector array.

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Andover, United Kingdom

Jolyon P Willson