Abstract:
A Pressure Sensing Apparatus is disclosed. Also disclosed is an apparatus that provides increased pressure sensitivity without added cost and complexity in the electronic detector circuitry. The apparatus further is less sensitive to gravity, vibrations or other external influences. It is a still further object that the apparatus be available with a curved bellow head, formed with either concave or convex reflective surfaces. Other versions of the apparatus may have a deflectable focusing diaphragm that permits pressure detection responsive to the curvature of a diaphragm in response to pressure differentials across the diaphragm.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is a continuation application of application Ser. No. 10/638,586, filed Aug. 11, 2003, which is a continuation-in-part of application Ser. No. 09/357,056, filed Jul. 19, 1999 and issued as U.S. Pat. No. 6,604,427 on Aug. 12, 2003. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     This invention relates generally to pressure sensors and, more specifically, to a Pressure Sensing Apparatus.  
         [0004]     2. Description of Related Art  
         [0005]     The bellows-type pressure sensor is widely used in high sensitivity applications. Essentially, what is involved is a very small bellow that is configured to reflect light onto a detector. When the bellow stretches or contracts in response to a pressure change, the detector will sense a corresponding change in the light intensity.  
         [0006]      FIG. 1  is a perspective view of a prior art bellow assembly  10 . As can be seen, from its outer dimensions, the bellow assembly  10  comprises a stem  12  from which extends the bellow section  14  which terminates in the head  16 . The bellow section  14  is formed somewhat like an accordion, such that the bellow assembly  10  can stretch and shrink in response to changes in external forces. If we now turn to  FIG. 2 , we can examine the details of how this bellow assembly  10  functions to detect pressure.  
         [0007]      FIG. 2  is a partial cutaway side view of the bellow assembly  10  of  FIG. 1 . Again we can see that the bellow section  14  extends from the stem  12  and terminates in the head  16 . In this current embodiment the head  16  comprises a reflector  18  formed on its inner surface. Within the bellow section  14  is conventionally located a light detector  20  mounted on a stand  22 . Also found within the bellow section  14  is a light emitter  24 . The light emitter is configured to transmit light to the reflector  18  where it is in turn reflected towards the light detector  20 . In a conventional bellow assembly pressure detector  10 , the light detector  20  is sensitive enough to detect a change in light intensity in response to a change in bellow length  26 . It should be noticed that in this conventional design, the reflector  18  has always been substantially flat. As such, the reflective light does not converge in any sort of focal point but instead essentially reflects outward in a Gaussean distribution and is spread into a wide area at the depth of the receiver  20 ; when the reflector moves towards the receiver  20 , reflected areas become smaller (in effect focusing the signal). If one imagines that the bellow assembly  10  has an internal pressure P 1  (which may be effectively zero) and the bellow assembly  10  is located within another volume at a unknown pressure P x , as P x  is changed, the bellow length  26  will also change to some length determined by the pressure difference and the physical properties of the bellow. It is this bellow length change  26  that is detected by the detector  20  and converted into an electrical signal for display to the user.  FIG. 3  depicts further information about this prior art device.  
         [0008]      FIG. 3  is a partial cutaway side view of a conventional bellow-type pressure sensor  30  of the present invention. As can be seen, bellow assembly  10  is typically located within a chamber  28 . If we imagine that the bellow assembly  10  is isolated from the chamber  28  and that the chamber  28  includes a sensor tube  32  for sensing an external pressure, we can appreciate that when the sensor tube  32  is placed in a location such that the pressure P x  changes from some reference pressure, and the bellows  10  later extend or contract while the internal pressure P 1  seeks to reach equilibrium with the sensed or unknown pressure P x . If we now turn to  FIGS. 4A through 4C  we can discuss the operation of the prior device more fully.  
         [0009]      FIG. 4A  is a depiction of the signal path of the bellow assembly  10  of  FIGS. 1, 2  and  3 . In this simplified drawing, the reflector  18  is shown at a distance Lx 1  from the detector  20 . We will assume at this point that Lx 1  defines the at rest condition of the bellow  10 . As can be seen, the transmitted light  34  from the transmitter (not shown) strikes the reflector  18  and is reflected back as reflected light  36 . As discussed above, it should be understood that substantially all of the transmitted light  34  is returned along the identical path of its arrival  36 . Some light however, will scatter as a result of surface irregularities on the reflector  18  and it is this light that is most likely received by the detector  20  (and therefore may contribute to the dynamic range). If we turn to  FIG. 4B  we can see that when the sensed pressure changes, the distance between the reflector  18  and the detector  20  changes to L x2 .  
         [0010]      FIG. 4B  is a depiction of the device of  FIG. 4A  after a pressure change has occurred. It should be casually apparent that the reflected light  36  is not substantially changed by the change in the location of the reflector  18 . In fact, in order to sense this changed distance, detector  20  must be extremely sensitive (and therefore expensive). Even still, this design will provide a fairly responsive and sensitive pressure detector having a dynamic range in the area of 2 dB. If we now turn to  FIG. 4C  we can see yet another limitation of the prior sensor.  
         [0011]      FIG. 4C  is a depiction of the device of  FIGS. 4A and 4B  when the device is experiencing off-axis deflection. As can well be imagined, the bellow  10  in order to be sensitive, is formed from very thin-walled material. As such, it is affected by external forces including vibrations, gravity and other acceleration and it is common for these external forces to result in an off-axis deflection θy. As can be seen here, while the transmitted light  34  has not changed, when a theoretical deflection θy is caused in the bellow  10 , the reflected light  36  tends to be directed away from the detector  20 . As such, where the sensor is experiencing vibrations they might actually be sensed as pressure changes but in fact this is not necessarily the case. This, again, adds expense because the detector must be isolated for many external acceleration-type forces.  
         [0012]     What is needed therefore, is an improved pressure sensor that will increase responsiveness of the detector while reducing the need for an extremely sensitive detector. It would further be desirable if the improved sensor was less sensitive to off-axis deflection.  
       SUMMARY OF THE INVENTION  
       [0013]     In light of the aforementioned problems associated with the prior devices, it is an object of the present invention to provide a Pressure Sensing Apparatus. It is an object that the improved apparatus provide increased pressure sensitivity without added cost and complexity in the electronic detector circuitry. It is a further object that the apparatus be less sensitive to gravity, vibrations or other external influences. It is a still further object that the apparatus be available with either concave or convex reflective surfaces, or a lens. It is a further object that the signal strength be increased. Other versions of the apparatus should have a deflectable focusing diaphragm that permits pressure detection responsive to the curvature of the diaphragm in response to pressure differentials across the diaphragm. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]     The objects and features of the present invention, which are believed to be novel, are set forth with particularity in the appended claims. The present invention, both as to its organization and manner of operation, together with further objects and advantages, may best be understood by reference to the following description, taken in connection with the accompanying drawings, of which:  
         [0015]      FIG. 1  is a perspective view of a prior art bellow assembly;  
         [0016]      FIG. 2  is a partial cutaway side view of the bellow assembly of  FIG. 1 ;  
         [0017]      FIG. 3  is a partial cutaway side view of a conventional bellow-type pressure sensor;  
         [0018]      FIG. 4A  is a depiction of the signal path of the bellow assembly of  FIGS. 1, 2  and  3 ;  
         [0019]      FIG. 4B  is a depiction of the device of  FIG. 4A  after a pressure change has occurred;  
         [0020]      FIG. 4C  is a depiction of the device of  FIGS. 4A and 4B  when the device is experiencing off-axis deflection;  
         [0021]      FIG. 5  is a preferred embodiment of the improved bellow type pressure sensor of the present invention;  
         [0022]      FIG. 6A  is a depiction of the light path of the device of  FIG. 5 ;  
         [0023]      FIG. 6B  depicts the light path of the device of  FIG. 6A  in response to a pressure change;  
         [0024]      FIG. 6C  is a depiction of the light path of the device of  FIGS. 6A and 6B  when the device is experiencing off-axis deflection;  
         [0025]      FIG. 7  is an alternate embodiment of the pressure sensor of the present invention having an alternate reflector and a unitary source/detector unit;  
         [0026]      FIG. 8  is yet another alternate embodiment of the pressure sensor of the present invention having a lens unit captured within the head of the bellow assembly;  
         [0027]      FIG. 9  is cutaway side view of an alternate pressure sensor;  
         [0028]      FIG. 10  is a cutaway side view of the sensor of  FIG. 9  in a heightened pressure condition;  
         [0029]      FIG. 11  is a cutaway side view of the sensor of  FIGS. 9 and 10  in a reduced pressure condition;  
         [0030]      FIGS. 12A and 12B  are side perspective views of a pair of alternate diaphragms for use in the sensor of  FIGS. 9-11 ;  
         [0031]      FIGS. 13A and 13B  are top and cutaway side views, respectively, of another alternate diaphragm for use in the sensor of  FIGS. 9-11 ; and  
         [0032]      FIG. 14  is a cutaway side view of yet another alternate diaphragm for use in a sensor of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0033]     The following description is provided to enable any person skilled in the art to make and use the invention and sets forth the best modes contemplated by the inventor of carrying out his invention, Various modifications, however, will remain readily apparent to those skilled in the art, since the generic principles of the present invention have been defined herein specifically to provide an Improved Bellow-Type Pressure Sensing Apparatus.  
         [0034]     The present invention can best be understood by initial consideration of  FIG. 5 . If we now turn to  FIG. 5  we can examine the improved bellow-type pressure sensor  40  of the present invention.  
         [0035]      FIG. 5  is a preferred embodiment of the improved bellow type pressure sensor  40  of the present invention. As can be seen (and just as with the prior art sensor), the sensor  40  comprises a stem  12  and a detector  20 . Unlike the prior unit, however, this bellow assembly  41  comprises a curved head  38 , which further forms a curved reflector  42  (known alternatively as focusing means for focusing the transmitted signals).  
         [0036]      FIG. 6A  is a depiction of the light path of the device of  FIG. 5 . As can be appreciated and as depicted by  FIG. 6A , the curved reflector  42  causes transmitted light  34  to be reflected  39  into a focal point  44 . If we imagine that the focal point  44  is the resting focal point (i.e. when the length of the detector  20  is Lx 1 ) the detector  20  being located in substantially the same location as the resting focal point  44 , by design.  
         [0037]      FIG. 6B  depicts the light path of the device of  FIG. 6A  in response to a pressure change. If, as depicted in  FIG. 6B , a pressure change causes the reflector  42  to now move to a distance L x2  from the detector  20 . it should be understood that the new focal point  46  is in a different location than the resting focal point  44 . Since substantially all of the reflected light  39  is passing through the focal point  46 , the detector  20  will experience a drastic change in detected light. In fact, the detected light, under certain conditions and designs, could drop to nearly zero intensity. As can be imagined, in such a design, the sensitivity of detector  20  need not be as good as with the prior designs, while still able to achieve substantial benefit in the area of dynamic range. In fact, theoretical response analysis indicates that a bellow assembly  41  having a curved reflector  42  will have many times the intensity response of the prior unit (to at least 20 dB).  
         [0038]      FIG. 6C  is a depiction of the light path of the device of  FIGS. 6A and 6B  when the device is experiencing off-axis deflection. Furthermore, and as depicted in  FIG. 6C , this improved bellow assembly  41  will be much less sensitive to external acceleration and/or other forces. As can be seen, when the reflector  42  experiences off-axis deflection θy just as described above in connection with  FIG. 4C , the focal point  44  will be expected to reside in substantially the identical location, so long as the center of mass is made to be close to the focal point, which is a simple design task. As such, the improved bellow-type pressure sensor  40  will be affected much less by bumping or other jarring. If we now turn to  FIG. 7  we can see yet another preferred embodiment of the pressure sensor of the present invention  50 .  
         [0039]      FIG. 7  is an alternate embodiment of the pressure sensor of the present invention  50  having an alternate reflector and a unitary source/detector unit  38 . As can be seen, the alternate bellows assembly  52  of this design comprises the alternate curved reflector  43  which is, in fact, convex (on its inner surface), in this case, furthermore, the light source and light detector are located in the chamber  28  rather than within the bellow assembly  52 . In fact, in this embodiment the detector and source are also found in a single unit  48  attached to the wall of the chamber  28 . In this form, the sensor tube  32  is actually in fluid communication with the bellow assembly  52 . This design enables the electronics to be external to the bellow, and perhaps be easier to repair. It should be understood, however, that the general operational parameters are likely to be identical to the design discussed above in connection with  FIGS. 5 and 6 .  
         [0040]      FIG. 8  is yet another alternate embodiment  47  of the pressure sensor of the present invention having a lens unit (also called a focusing means) captured within the head of the bellow assembly. In this embodiment, the curved head is replaced with a lens unit  45 . While the aforementioned benefits in regard to off-axis stability are not achieved, there are substantial improvements in responsiveness over the prior devices.  
         [0041]      FIG. 9  is cutaway side view of an alternate pressure sensor  60 . This pressure sensor  60  incorporates the convenience, cost-effectiveness and durability of a diaphragm into the previously-described novel an nonobvious device. This sensor  60  comprises a housing  62  which contains a detector chamber  64  and a process chamber  66 . The two chambers  64  and  66  are sealed and separated from one another by a diaphragm  70 . In this version, there is a blister  72  (a raised curved portion) located in the center of the diaphragm  70 . The blister  72  preferably has a polished concave reflective surface  74 A that will efficiently reflect light rays transmitted by the emitter  24  such that they can then be detected by the detector  20 .  
         [0042]     It should be apparent that the pressure Px in the process chamber  66  (obtained via the port  68  leading to the process/sensed pressure area  69 ) will change with the pressure being sensed. In contrast, the pressure P 1  in the detector chamber  64  will remain relatively constant since the detector chamber  64  is sealed, at some reference pressure, which may effectively be zero, or subject to some known reference. Now turning to  FIG. 10 , we can begin to discuss how this device functions.  
         [0043]      FIG. 10  is a cutaway side view of the sensor  60  of  FIG. 9  in a heightened pressure condition, i.e. when pressure Px is greater than P 1 . Under these conditions, the resilient diaphragm  70  (and the blister  72  attached thereto) will deflect away from the process chamber  66  and towards the detector chamber  64 . This depicted deflection will depend upon the difference in the pressures Px and P 1 , and will also cause the blister (and its reflective surface) to deflect in a stable straight line.  
         [0044]     In this deflected state, light rays  36  being reflected off of the blister  72  will strike the detector  20  in a different location than when the diaphragm is in a non-deflected condition—in fact, the focal point (see above in previous drawing figures) will move to an imaginary point below the surface of the detector  20 . Because the focal point for the reflected light rays has moved, the strength of the detected light will be reduced; this change in strength can be converted into a sensed pressure change. If we turn to  FIG. 11 , we can see what occurs when pressure drops.  
         [0045]      FIG. 11  is a cutaway side view of the sensor  60  of  FIGS. 9 and 10  in a reduced pressure condition. Here, Px is less than P 1 —the result is that the diaphragm  70  deflects away from the detector chamber  64  and towards the process chamber  66 . Since the blister  72  has moved away from the detector  20 , the focal point of the light rays  36 , has moved to a point somewhere above the surface of the detector  20 . Again, the detected light strength will be reduced which can be converted into a sensed pressure.  FIGS. 12A and 12B  depict different versions of the diaphragm  70 .  
         [0046]      FIGS. 12A and 12B  are side perspective views of a pair of alternate diaphragms  70 A and  70 B for use in the sensor of  FIGS. 9-11 . Diaphragm  70 A incorporates a small blister  72 A, i.e. one in which the diameter of the blister  72 A is smaller than the width of the planar ring  76 A. In this version, the shape of the blister  72 A will remain essentially unchanged for pressure changes—the diaphragm  70 A will deflect in the area of the planar ring  76 A, causing the blister  72 A to move closer to, or further away from the detector (see  FIG. 11 ).  
         [0047]     Diaphragm  70 B incorporates a large blister  72 B, i.e. one in which the diameter of the blister  72 B is larger than the width of the planar ring  76 B. In this version, the deflection of the diaphragm  70 B will manifest itself in both the planar ring  76 B and the blister  72 B. As the planar ring  76 B deflects, the blister  72 B will move closer to, or further from the detector. As the blister  72 B deflects, it will actually change its shape, and therefore the radius of its curvature. The changing of shape of the blister  72 B actually changes the focal point of the reflected light rays—this will amplify the change in the detected light due to pressure changes. In fact, in one non-depicted embodiment, the entire diaphragm  70 B acts as a large blister. This means that the planar ring  76 B does not exist, and the entire diaphragm  70 B can deflect to create a large blister by the curvature of the diaphragm. If we turn to  FIGS. 13A and 13B , we can examine another design.  
         [0048]      FIGS. 13A and 13B  are top and cutaway side views, respectively, of another alternate diaphragm  70 C for use in the sensor of  FIGS. 9-11 . This diaphragm  70 C incorporates a substantially flat planar ring  76 C with a focusing reflector  72 C. The focusing reflector is a reflective device that is designed very similar to a “Fresnel” lens, however, it is opaque and reflective, rather than a translucent lens. The “Fresnel” design is embodied in a plurality of concentric rings  77 , with each of the rings  77  defining a reflecting surface  74 B. Just as with a Fresnel lens, the reflecting surfaces  74 B are each at specific angles relative to one another (i.e. angles offset from perpendicular to the surface of the plane of the diaphragm) so that this substantially flat reflector will actually focus incident light to a point without the need for a concave shape. Furthermore, the Fresnel-type design can be expected to allow for more predictable, stable deflection from the diaphragm in response to pressure changes, since there is no blister causing a stiffening of the diaphragm  70 C. As with the large blister, the Fresnel focusing reflector  72 C will change its focal point as the focusing reflector is deflected (since the angles of the reflecting surfaces  74 B will change as the diaphragm  70 C deflects). Finally, turning to  FIG. 14 , we can examine yet another diaphragm  70 D for use with the present invention.  
         [0049]      FIG. 14  is a cutaway side view of yet another alternate diaphragm  70 D for use in a sensor of the present invention. This diaphragm  70 D is formed from a translucent and/or transparent base material  80 , and incorporates a Fresnel lens as the focusing means  82 . Here, the light rays  36  can pass through the diaphragm  70 D from the emitter  24  to the detector  20 . As the light passes through the substantially flat Fresnel lens, the light rays will be focused to a point on the surface of the detector (when the device is at rest); when the diaphragm  70 D deflects due to pressure changes, the lens  82  will change its focal properties, while at the same time the lens  82  will move either closer to, or further from the detector  20 —again, this will cause a change in the detected light strength which can be converted into a sensed pressure.  
         [0050]     Those skilled in the art will appreciate that various adaptations and modifications of the just-described preferred embodiment can be configured without departing from the scope and spirit of the invention. Therefore, it is to be understood that, within the scope of the appended claims, the invention may be practiced other than as specifically described herein.