Measuring and testing – Fluid pressure gauge – Diaphragm
Patent
1986-08-18
1988-02-23
Woodiel, Donald O.
Measuring and testing
Fluid pressure gauge
Diaphragm
73 493, 338 4, 338 42, G01L 708, G01L 906
Patent
active
047262338
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a pressure pick-off for generating electrical signals of the type of the main claim. Semiconductor pressure pick-off device with integrated piezoresistive resistor bridge are known in which the sensor elements are mounted in the edge area of a membrane made from a silicon semiconductor by means of spark erosion, etching or other method and which closes a reference pressure chamber against the medium being under pressure (U.S. Pat. No. 4,079,508). The reference pressure chamber is closed under a vacuum for measuring of absolute pressures. In such and similar pressure pick-off devices which have a reference pressure chamber being filled with precious gas or being under a vacuum for pressure measuring the signals which are transmitted from the sensor elements or from a pressure switch are falsified as soon as the reference pressure chamber becomes leaky. A leakage in the reference pressure chamber in such pressure pick-off devices can only be recognized by an aftermeasuring during the maintenance of the sensors. The subject solution tries to monitor the tightness of the reference pressure chamber during the use of the pressure pick-off with connected evaluation circuit.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an electric pressure pick-off which avoids the disadvantages of the prior art.
In keeping with this object, one feature of the invention resides in a pressure pick-off which comprises means forming a reference pressure chamber which is oxygen-free, at least one pressure dependent deformable membrane closing the reference pressure chamber from a medium under pressure and supporting at least one electric sensor element, and a conductor located in the reference pressure chamber and connectable with a measuring current circuit, the conductor being formed so that during a leakage in the reference pressure chamber it is oxidixed by penetrated oxygen so that it is electrically interrupted.
The inventive pressure pick-off is advantageous in that with the connected evaluation circuit the reference pressure chamber can be tested any time for an air collapse. The conductor which oxidizes during penetration of oxygen into the reference pressure chamber represents a type of a safety element which interrupts the measuring current of the sensor elements or a particular monitoring circuit. It is considered to be a further advantage that with such a monitoring of the reference pressure chamber one can use pressure pick-off devices in safety relevant parts, for example, for a tire pressure monitoring of motor vehicles. Moreover, the suggested solution is not only usable for semiconductor sensors but also for all pressure pick-off systems which operate with a reference pressure chamber.
It is particularly advantageous if the conductor, which is interrupted by oxidation, is mounted on a substrate which also supports the sensor elements. Thereby, the substrate is shaped in known manner as a pressure dependent deformable membrane in the area of the sensor elements. It is particularly advantageous for the electrical connection of the conductors if the same are connected with an electrically conducting area of the reference pressure chamber which is applied to a reference potential, on the one hand, and with an electrically insulated throughput through the reference pressure chamber, on the other hand. In the simplest manner the reference potential is applied to an annular conductor of a printed circuit board which is soldered with the edge of a capsule which closes the reference=pressure chamber toward the outside.
BRIEF DESCRIPTION OF THE DRAWING
The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with t
REFERENCES:
patent: 4023562 (1977-05-01), Hynecek et al.
patent: 4276533 (1981-06-01), Tominaga et al.
patent: 4314225 (1982-02-01), Tomiaaga et al.
patent: 4661759 (1987-04-01), Klein
Eckardt Dieter
Gerhard Hettich
Robert & Bosch GmbH
Striker Michael J.
Woodiel Donald O.
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