Measuring and testing – Fluid pressure gauge – Photoelectric
Patent
1993-08-03
1995-06-20
Chilcot, Jr., Richard E.
Measuring and testing
Fluid pressure gauge
Photoelectric
25023119, 128675, G01L 900, G01D 534, A61B 50215
Patent
active
054252733
DESCRIPTION:
BRIEF SUMMARY
SUBJECT OF THE INVENTION
The present invention relates to a pressure sensor using optical fibers for transmission by light beams and extends to detection or measurement devices fitted with such a sensor.
DESCRIPTION OF THE PRIOR ART
Optical fiber pressure sensors may be classed in two categories, namely extrinsic and intrinsic sensors.
In extrinsic sensors, the optical fiber is passive and is only employed to transmit light from one point to another. In intrinsic sensors, the optical fiber is active and is employed for physical magnitude (pressure, temperature, pH, etc.) quantification.
U.S. Pat. No. 4,691,709 (Cohen) describes the pressure sensor capable of measuring blood speed and static pressure. This sensor is based on light energy losses resulting from the contact of an elastic foam with the optical fiber. The losses increase as a function of the widening of the contact zone.
This mode of operation is to be described as intrinsic since the basic characteristic of the optical fiber, total reflection, is altered in contact with the foam.
This sensor also makes use of the extrinsic mode of operation since it employs a reflecting membrane disposed at the end of the optical fiber and whose radius of curvature varies as a function of pressure.
However, if it is desired to mass produce this sensor, the positioning of this membrane in the sensor gives rise to technological problems whose cost implications are not negligible.
Patent Application JP-A-62,294,928 (Idemitsu Kosan Co. LTD) describes an optical attenuator measuring pressure on the basis of the variation in the transmission of the system.
The attenuator consists of a dispersion of colorant in an elastomer. The spatial distribution of the particles of colorants is modified by the pressure exerted on the elastomer such that a variation in the transmission of the system results therefrom.
This extrinsic sensor is for the most part based on a transfer function defined by the Behr-Lambert [sic] law, which amounts to saying that this function is of the exp(--ax) type in which a is the attenuation coefficient and x is the optical path covered by the light beam.
However, in mass production, such a sensor cannot guarantee a reproducible distribution of the colorant in the elastomer and consequently a reproducible configuration of the sensor cannot be obtained.
Furthermore, such a transmission sensor does not provide a sufficiently high signal
oise ratio and is difficult to transpose to a blood pressure measurement because of the necessary bulk.
Pressure sensors making use of optical fibers, and whose general operation is based on the displacement of mirrors fixed to membranes or to pistons subjected to pressure forces, are also known. [Scheggi (Institut di Ricerca Sulle Onde Electromagnetische [sic] CNR-Firenze, Italy) and Matsumoto (J. Med. Eng. and Tech. 2, 239 (5) Sept. 1978)].
The displacement of the mirrors modifies the distribution of the light intensity in the optical fiber and thus makes it possible to measure the pressure exerted on the membrane or on the piston.
Patent Application EP-A-0178806 (Sperry Corporation) describes a pressure sensor of the intrinsic type using a 2.times.2 coupler in which the energy ratio of the output channels is influenced by the variation in the refractive index as a function of pressure.
Pressure sensors employing bifurcated optical fibers in which one end is connected to a membrane are known.
Instead of relying on the displacement of a membrane, Patent Application JP-A-56,7034 (Tokyo Shibaura Denki K. K.) describes a sensor using the radius of curvature of the reflecting membrane. The radius of curvature of the membrane varies in this case as a function of pressure.
U.S. Pat. No. 3,273,447 (Frank) describes an optical fiber terminated by a bulb made of material which is elastic to deformation and which can be covered with a reflecting layer.
This bulb has an aspheric shape and has been prestressed as a function of the pressure to be measured and as a function of the elastic characteristics of the material. As a f
REFERENCES:
patent: 3273447 (1966-09-01), Frank
patent: 4599908 (1986-07-01), Sheridan et al.
patent: 4691709 (1987-09-01), Cohen
patent: 5173432 (1992-12-01), Lefkowitz et al.
patent: 5293780 (1994-03-01), Chadwick et al.
Patent Abstracts of Japan, vol. 12, No. 188 (P-711) (3035).
Chilcot Jr. Richard E.
Cosurvey Optics
Felber Joseph L.
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