Measuring and testing – Fluid pressure gauge – With protective separator
Patent
1996-10-16
1998-12-08
Felber, Joseph L.
Measuring and testing
Fluid pressure gauge
With protective separator
73727, G01L 700
Patent
active
058472827
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a piezoresistive pressure sensor or pressure pickup.
Piezoresistive pressure cells are used in millions of numbers in a very wide range of applications.
Particularly when measuring the pressure of aggressive media, the measuring cells cannot be directly exposed to the aggressive medium. To this end, they are preferably installed in a pressure chamber which is filled with oil and accommodated in a housing. The pressure of the aggressive medium which is to be measured is transmitted via the diaphragm into the inner pressure chamber, holding the measuring cell, in the housing.
FIGS. 4 to 6 herein show a conventional piezoresistive pressure pickup in an assembly for measuring pressure in aggressive media. In this case it is an absolute pressure pickup, which is explained below.
The piezoresistive pressure pickup assembly shown in FIGS. 4 and 5 comprises a housing 1 and a connection housing 3, also referred to below as housing front part, on which an external screw thread 5 is arranged. The housing 1 further comprises a transmission diaphragm housing 7. The transmission diaphragm housing 7 has a hexagonal wrench face 9, comparable to a hexagonal screw or nut. The abovementioned transmission diaphragm housing 7 adjoins the connection housing 3 in the axial direction and is welded to the latter along the weld seam 10.
It can be seen from FIG. 4 that the transmission diaphragm housing 7 accommodates a piezoresistive pressure measuring cell 13 in an oil-filled pressure chamber 15, the chamber 15 being separated by means of a flexible transmission diaphragm 17 from a fluid pressure chamber 19 which is provided in the connection housing 3 and in which possibly the aggressive medium whose pressure is to be measured is present due to a pressure through-bore 20 made in the connection housing 3.
The oil-filled measuring cell pressure chamber 15 of the assembly is sealed at the opposite end to the transmission diaphragm 17 running transversely to the axial direction of the entire housing by a so-called glass bushing 21 which has a stepped shoulder and is also referred to below as the backplate. Guided through the glass bushing 21 are electrical contact conductors or contact pins 23, with which contact is made electrically on the inside directly or, for example, via a ribbon conductor 25 which may be a component such as a film or mounted on a printed circuit board, comprising a flexible conductor, by the pressure measuring cell 13 lying on the inside in the measuring cell compression chamber 15 in the transmission diaphragm housing 7. The use of a film 25 of this kind with flexible conductor tracks is depicted in the installed state in FIG. 4 and in an enlarged detail illustration in FIG. 5. FIG. 6 shows that the electrical connections can be made by means of gold or aluminum wires 25' from the measuring cell to the contact conductors or pins 23.
The electrical connections extending to the outwardly projecting contact pins 23, i.e. to the contact pins 23 projecting downward through the glass bushing 21, are not shown in the exemplary embodiment according to FIGS. 4 to 6 which is known from the prior art.
In order to reduce the total volume of oil in the inner pressure chamber, if required a displacement element 27, preferably made of ceramic and preferably having the density of the oil medium, may be fitted as well. As a result, temperature-dependent changes in volume of the oil medium are minimized.
In this known pressure pickup assembly, the measuring cell 13 is installed in the transmission diaphragm housing 7 (optionally resting on the glass bushing 21) in such a way that the glass bushing 21 with the measuring cell is placed on the transmission diaphragm housing 7, without welding, in the lower end opening region thereof in order then to place the entire arrangement in a so-called oil pot. The oil pot is first evacuated and then filled with oil. The oil can then enter the pressure chamber 15 holding the pressure measuring cell 13. When the inner chamber has been fi
REFERENCES:
patent: 5115676 (1992-05-01), Lee
patent: 5583294 (1996-12-01), Karas
Felber Joseph L.
Keller AG Fur Druckmesstechnik
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