Measuring and testing – Fluid pressure gauge – Mounting and connection
Patent
1997-04-08
2000-09-26
Oen, William
Measuring and testing
Fluid pressure gauge
Mounting and connection
G01L 700
Patent
active
061229768
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to pressure transducers or sensors for measurement of pressures from fluids of various kinds, both gases and liquids, and also to methods of producing pressure transducers or sensors and in particular mounting or attaching a sensor element in a transducer/sensor.
BACKGROUND OF THE INVENTION AND STANDPOINT OF THE ART
In developing the sensor element for a pressure sensor a very large number of technical parameters exist which must be considered. These parameters are of a thermal, electrical, mechanical or chemical nature. Each such group contains itself a multitude of technical parameters and further various properties interact between the groups as applied to a sensor element. Chemical characteristics influence surface coatings, which influence thermal and mechanical properties. The density and impermeability influence possible structural thicknesses what influences the mechanical characteristics, etc. A search ol the characteristics of various conceivable materials concludes usually that the following materials can possibly be used: metals of special types such as the alloys "Inconel" and "Hastalloy", semi-conductor materials, for example silicon, ceramic materials, for example aluminum oxide.
A very large work has been made in developing different types of sensor elements. In order to use the sensor element it must, however, be mounted in a housing, casing or similar device, to obtain a complete or finished pressure sensor, which is ready to be used after a simple connection to some volume, where a medium is present. However, the mounting or attachment method for forming a complete pressure sensor can often result in the fact that the high precision of the very sensor element is lost. It depends on the fact that, again, in the mounting process problems in regard of the materials used appear which are for example of the following kind. For metals, their high coefficients of thermal expansion result in thermal stresses, they are not impermeable to some gases, they are deformable. Semiconductor materials are sensitive to temperature and are easily attacked chemically, what can have the consequence that a system comprising oil capillaries must be used to conduct the pressure that is to be measured to a pressure sensitive surface. The attachment or securing of parts of ceramic materials is often performed, due to the difficulty of working these materials and their production at very high temperatures, must often by means of O-rings, which do not possess a sufficient chemical resistance or inertness.
The housing of the pressure sensor is nearly always made of metal and thus, to this metal the very sensor element must be attached or clamped. A suitable ceramic material for use in the construction of sensor elements is glass ceramics, since components or parts of this material can be produced and joined/bonded at temperatures which are rather low in this context. If the sensor element thus is to be bonded directly to metal, it is a critical problem to adapt the coefficient of thermal expansion of the metal to which the sensor element is to be mounted or clamped, further of the material in the very sensor element and also of the bonding or joining material used.
Sensor elements for pressure sensors based on ceramic materials and constructed as dilatation sensors or capacitive sensors can comprise various ceramic materials. Then, often ceramics based on aluminum oxide is used but also glass ceramics is used. In the production of sensor elements based on aluminum oxide the various surface coating processes and the procedures for burning/fusioning the various elements included in a sensor element to each other must be performed at a significantly higher temperature than for glass ceramics. To design, for sensor elements based on aluminum oxide, a sequential order for all these processes comprising surface coating procedures of various kinds and burning/fusion processes, which does not destroy the result of earlier coating processes and other processes in the sequence
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Hallberg Nils Gunno
Jonsson Staffan
Cecap AB
Oen William
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