Measuring and testing – Fluid pressure gauge – Diaphragm
Patent
1991-01-17
1993-10-05
Woodiel, Donald O.
Measuring and testing
Fluid pressure gauge
Diaphragm
73718, 3612834, G01L 912
Patent
active
052494691
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a pressure gauge comprising a hollow volume and a pressure sensing means mounted in this volume. The pressure sensor means has a conventional construction and comprises a substantially rigid, not flexible support plate and a flexible diaphragm attached to said support plate. Between said support plate and diaphragm is in this way formed a closed space which contains a reference pressure. The deflection of said diaphragm for different exterior pressures acting on said diaphragm is detected electrically by means of electrodes arranged on said diaphragm and/or support plate. Thus the support plate and membrane may be configured as a capacitor, the capacitance of which is sensed by means of suitable electronic circuits. The hollow volume in which the pressure sensor means is mounted has a free gas connection to the volume where the pressure is to be measured.
BACKGROUND OF THE INVENTION
Pressure sensor means of the type indicated above are described e.g. in the Swedish patent application 8700556-7 which is available to the public and has been filed by the applicant.
For pressure gauges of the kind mentioned above various problems are raised in relation to the attachment of said pressure sensor means to the interior surface of the surrounding hollow volume. Generally the desires for and demands on a pressure gauge having a high precision, intended both for measuring low pressures and pressures originating from corrosive gases, may be summarized in the following way.
1. The whole of said pressure sensor means should be freely hanging or standing in the measuring volume inside the hollow volume in such a way that the pressure being measured, besides acting on said diaphragm, also acts on the whole of said pressure sensor means. No forces should influence the mechanical construction, particularly the support plate, of the pressure sensor means, which is displaced due to the relation of the measured pressure to the reference pressure inside said pressure sensor means.
A mounting of this kind will among other things result in the fact that the values provided by said pressure sensor means are given an increased repeatability when the pressure sensor means is subjected to varying pressures.
2. The freely hanging or standing pressure means should be mounted in such a way that the means attaching the pressure sensor means to the inner surface of the surrounding hollow volume has a small sectional area compared to the large, substantially flat surfaces of the pressure sensor means.
Such an attachment of the pressure sensor means naturally has a relation to the desire mentioned under point 1. that no forces or as small forces as possible, besides the pressure to be measured, should influence the pressure sensor means. In addition a reduced temperature convection may in this way be obtained between the walls of the surrounding hollow volume and the pressure sensor means.
3. The attachment means by means of which the pressure sensor means is attached inside the hollow volume should be mechanically connected partly to the pressure sensor means, partly to the interior wall of the surrounding hollow volume in such a way that the connecting joints do not comprise any type of soldering or elastomer. Only weld joints and glass joints should be allowed to be used.
This requirement has a direct connection to the object of being able to use the pressure gauge for measurement of both very low pressures and for pressures generated by corrosive media.
4. The electric conductors connecting the electrodes of said pressure sensor means to the exterior of the surrounding hollow volume should not be subjected to the gases in the measuring volume. If the electric conductors were to pass through said measurement volume this would influence the capacitive measurement or totally disable this.
First it will be observed that the desire under point 3. for certain cases possibly could be obtained by means of a reconstruction of constructions known in the art, e.g. by a choice of
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Jonsson Staffan
Olsson Ray
Jonsson & Billquist Development AB
Woodiel Donald O.
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