FTFT D OF THF TNVENTTON

The present invention relates in general to pressure sensor technology and, more particularly, to low cost pressure sensors for either disposable or high volume applications of pressure sensors for gas and liquid based pressure sensing of either positive or negative pressure changes. This is a contϊnuation-in-part of a prior application filed on December 30, 2003, having Serial No. 10/748,817, which is incorporated herein by reference in its entirety. ςTTMMAKY OP THP TNVRNTTON The present invention provides improvements in low cost, effective meso-pressure sensors that are capable of measuring both positive and negative pressure", depending upon the atmosphere to which it is exposed. The sensor includes a sealed chamber defining part and can be made from inexpensive, injection molded plastics and plastic films that are readily available from many commercial sources. A first perforated rigid film having a conductive surface is mounted on one side in communication with the chamber in the sealed chamber defining part and on a first insulator mounted on the other side. A non-perforated flexible diaphragm having a conductive surface is mounted in communication with the first insulator. A second insulator is mounted on the non- perforated diaphragm to separate it from a second perforated rigid film. Finally, a sensor chamber defining part is mounted on the other side of the second flexible diaphragm to provide an opening for communication with a sensing atmosphere. Appropriate electrical connections contacting the first and the second films and the non-perforated flexible diaphragm are used to measure the capacitance between the diaphragms as a function of the pressure in the sensor chamber introduced through the opening and causing the non-perforated diaphragm to move with respect to one of the perforated flexible diaphragms. BRTFP DESOR TPTTON OF THF. DK AWTNGS

For a more, complete understanding of the invention, reference is hereby made to the drawings, in which: FIGURE 1 is a side elevational view, in section, of the present invention as a positive and negative pressure sensor; and FIGURE 2 is an exploded plan view of the embodiment shown in FIGURE 1. In the figures, like reference characters designate identical or corresponding components and units throughout the several views. DFTAH FD DESCRIPTION OF TTTF. PREFERRED EMBODTMFNT

The pressure sensors of this invention have elements disclosed in a prior, commonly, owned application by the same inventors and filed on December 30, 2003, having Serial No. 10/748,817, which has been incorporated herein above by reference in its entire ty. Referring to the figures, Fig. 1 illustrates a pressure sensor 10 generally that has an upper chamber forming element 11 defining closed chamber 13 and a lower chamber forming element 15, to define an open chamber 17, having port 19. The chamber defining elements 11 and 17 may be made from plastic or other nonconductive materials and may be molded or fabricated. Neither part 11 or 17 has any metallization or other patterning. An upper or first perforated film 21 is mounted on the closed chamber forming element 11 and has first insulator or spacer 23 on its other side. Film 21 may be a plastic film with metallization or a dielectric film. Film 21 is perforated and may remain rigid during operation. A lower or second perforated film 27 is mounted on the lower chamber forming element IS and on the other side, of spacer 25. Film 27 may be a plastic film, either with metallization or formed from dielectric film and communicates with sealed cavity or closed chamber 13. Spacer 25 is also preferably made from plastic and contains no metallization. A flexible, non-perforated middle diaphragm 29 is mounted between spacers 23 and 25. Non-perforated diaphragm 29 makes capacitive bridge differential cooperating with either film 21 or 27, depending on whether the pressure in chamber 17 has increasing or decreasing pressure. Non-perforated diaphragm will move toward film 21 with increased pressure in chamber 17 and toward film 27 when pressure in chamber 17 decreases. Fig. 2 is an exploded view of the parts of Fig. 1, shown in plan view. Upper chamber forming element 11 includes cavity 13 and holes 31 which are open for electrical contact. Film 21 includes hole 31 for electrical contact, and has holes or perforations 33 and includes a contact point 35. Spacer 23 also has a hole 31 for electrical contact. Film 27 is also perforated with holes 33 and has contact point 35 for contact. Finally, lower chamber defining element 15 provides pressure access via port 19 and includes cavity 17. Holes 33 in films 21 and 27 are shown in Fig. 2 as being equally spaced from the center of the films: This is only shown to illustrate the existence of the holes 33. Holes 33 can .be place anywhere on films 21 and 27, such as, for example, closer to the periphery of the films 21 and 27, or in a pattern where some or all holes are in a different orientation with respect to rest of the holes. The placement of holes on film 21 does not have to be the same as on film 27. The number of holes may be as few as one and as many as desired. Any pattern ma}' be used. The function of the holes is to permit pressure changes to be communicated to the device to permit diaphragm 29 to change the capacitive relationship with either film 21 or 27, or both. As can be appreciated, the device of Figs. 1 and 2 provides for diaphragm deflection of the non— perforated diaphragm 29 toward either of the two perforated films and the addition of this diaphragm permits the device to have much more versatility than prior designs. The sensing atmosphere may be any fluid, including gases such as the atmosphere, gas pumps, chemical and electrolytic reactions, and the like or including liquids such as reactors, test devices, pumps and the like. While particular embodiments' of the present invention have been illustrated and described, they are merely exemplary and a person skilled in the art may make variations and modifications to the embodiments described herein without departing from the spirit and scope of the present invention. All such equivalent variations and modifications are intended to be included within the scope of this invention, and it is not intended to limit the invention, except as defined by the following claims.