Patent Publication Number: US-2005139010-A1

Title: Positive and negative pressure sensor

Description:
FIELD OF THE INVENTION  
      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 continuation-in-part of a prior application filed on Dec. 30, 2003, having Ser. No. 10/748,817, which is incorporated herein by reference in its entirety.  
     SUMMARY OF THE INVENTION  
      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.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      For a more complete understanding of the invention, reference is hereby made to the drawings, in which:  
       FIG. 1  is a side elevational view, in section, of the present invention as a positive and negative pressure sensor; and  
       FIG. 2  is an exploded plan view of the embodiment shown in  FIG. 1 . 
    
    
      In the figures, like reference characters designate identical or corresponding components and units throughout the several views.  
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
      The pressure sensors of this invention have elements disclosed in a prior, commonly owned application by the same inventors and filed on Dec. 30, 2003, having Ser. No. 10/748,817, which has been incorporated herein above by reference in its entirety.  
      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  15  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 may 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.