Measuring and testing – Fluid pressure gauge – Photoelectric
Patent
1991-07-11
1993-03-23
Woodiel, Donald O.
Measuring and testing
Fluid pressure gauge
Photoelectric
73862624, 128667, 128675, 25023119, G01D 530, G01L 708, G01L 900
Patent
active
051953757
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a miniaturized pressure sensor with a shell of an elastic material, an elastic diaphragm arranged over an opening situated in the surface of the shell, a light conductor arranged inside the shell, a silicon body arranged inside the shell and a reflecting surface arranged on the body such as to be opposite of the light conductor.
2. Description of the Related Art
A device of the kind mentioned above is known from Swedish patent specification 86 02836-2. There is still a need to further miniatures this known pressure transducer, but in attempting to do so problems occur which are directly related to the small dimensions.
The known pressure transducer is a so-called relative pressure transducer, which means that it measures the pressure difference between ambient pressure and a reference pressure. The reference pressure is in contact with the atmospheric pressure via an air duct inside the shell. This air duct has a constriction formed by a silicon body situated in the region of the diaphragm.
The problem with the known pressure transducer is that the resistance of the air duct to volume changes caused by the diaphragm moving is not sufficiently low, and for rapid pressure changes this leads to the occurrence of a certain excess pressure in the distal air volume nearest the diaphragm, this air volume being limited on one side by the constriction. This excess pressure falsifies the measuring result.
SUMMARY OF THE INVENTION
The present invention has the object of providing a miniaturized pressure sensor of the kind described above, which allows maintenance of atmospheric pressure in the distal air volume nearest the diaphragm in spite of the diaphragm moving quickly.
Another object of the invention is to achieve a pressure sensor of the kind described above, and which has reduced compliance. Compliance is herein defined as volume change per pressure change. In other words, a small deflection or movement of the diaphragm shall provide a small volume change. This can be accomplished by either reducing the deflection or the size of the diaphragm.
In accordance with the invention, the above-mentioned objects are achieved by a body comprising a thin, cantilevering, short beamlike structure of silicon arranged for actuation by the diaphragm, and by the reflecting surface being arranged at the free end of the cantilever part of the beam structure, and upstanding from it, such that the pressure changes acting on the diaphragm will move the beam structure and thereby the reflecting surface, which then will move in front of the end of the light conductor or optical fiber.
By making the beam structure short, in accordance with the invention, and thereby decreasing the deflection of the diaphragm for an applied pressure, an acceptable signal-to-noise ratio is retained, while at the same time the pressure sensor has great sensitivity to rapid pressure changes.
By reducing the opening over which the diaphragm is arranged, in accordance with the invention, and thereby the volume change per pressure change, there is obtained the advantage that the diaphragm will be stiffer and afford good protection for the sensor. However, there is an adhesion effect resulting in the tendency for the diaphragm to stick to the beam structure when the structure moves. This gives rise to an undesired hysteresis in the pressure measuring result.
In accordance with another embodiment of the invention, the adhesion effect associated with a reduced opening is avoided by the cantilevering beam structure having a hump on its back part situated under the diaphragm, this hump projecting into the opening in the shell surface of the sensor.
BRIEF DESCRIPTION OF THE DRAWINGS
Two embodiments of the invention will now be described in more detail with reference to the accompanying drawings, wherein
FIG. 1 illustrates a miniaturized pressure sensor according to the state of the art as appears in the above-mentioned Swedish patent,
FIG. 2 is a cross-sectional view of
REFERENCES:
patent: 3789667 (1974-02-01), Porter et al.
patent: 4543961 (1985-10-01), Brown
patent: 4548205 (1985-10-01), Armeniades et al.
patent: 4611600 (1986-09-01), Cohen
patent: 4711246 (1987-12-01), Alderson
patent: 4712566 (1987-12-01), Hok
patent: 4727730 (1988-03-01), Boiarski et al.
patent: 4936310 (1990-06-01), Engstrom et al.
patent: 4991590 (1991-02-01), Shi
patent: 5018529 (1991-05-01), Tenerz et al.
patent: 5085223 (1992-02-01), Lars et al.
"Silicon Microcavities Fabricated with a New Technique," Reprinted from Electronics Letters, May 22, 1986, vol. 22, No. 11, pp. 615-616.
Hok Bertil
Tenerz Lars
Radi Medical Systems AB
Woodiel Donald O.
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