Abstract:
A pressure transmitter for measuring a pressure of a process fluid in an industrial process, includes a pressure sensor having an output related to an applied pressure. Measurement circuitry coupled to the pressure sensor is configured to provide a transmitter output related to sensed pressure. A pressure coupling face having an opening therein is arranged to transfer the applied pressure to the pressure sensor. A pressure coupling flange having a flange face abutting the pressure coupling face is configured to convey the process fluid to the opening of the pressure coupling face. Features are provided to control distribution of a leading force across the pressure coupling face and the flange face.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates to industrial process pressure transmitters. More specifically, the present invention relates to coupling of the pressure transmitter to a process fluid of an industrial process. 
         [0002]    Industrial process control systems are used to monitor and control industrial processes used to produce or transfer fluids or the like. In such systems, it is typically important to measure “process variables” such as temperatures, pressures, flow rates, and others. Process control transmitters are used to measure such process variables and transmit information related to the measured process variable back to a central location such as a central control room. 
         [0003]    One type of process variable transmitter is a pressure transmitter which measures pressure of a process fluid and provides an output related to the measured pressure. This output may be a pressure, a flow rate, a level of process fluid, or other process variable. The transmitter is configured to transmit information related to the measured pressure back to a central control room. The transmission is typically over a two wire process control loop, however, other communication techniques may be used including wireless techniques. 
         [0004]    The pressure transmitter must be coupled to a process fluid through a process coupling. For example, the process fluid can comprise a component used in an industrial process such as natural gas, oil, etc. Some of these materials may be under extremely high pressures. These high pressures can lead to leakage between the pressure transmitter and the industrial process through the “flange” or fitting which is used to couple to the pressure transmitter to the process. 
         [0005]    There is an ongoing need for improved coupling between a pressure transmitter and a process fluid. 
       SUMMARY 
       [0006]    A pressure transmitter for measuring a pressure of a process fluid in an industrial process, includes a pressure sensor having an output related to an applied pressure. Measurement circuitry coupled to the pressure sensor is configured to provide a transmitter output related to sensed pressure. A pressure coupling face having an opening therein is arranged to transfer the applied pressure to the pressure sensor. A pressure coupling flange having a flange face abutting the pressure coupling face is configured to convey the process fluid to the opening of the pressure coupling face. Features are provided to control distribution of a leading force across the pressure coupling face and the flange face. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  is a cross-sectional view of a transmitter and flange in accordance with the present invention. 
           [0008]      FIG. 2  is a exploded perspective view of the transmitter and flange of  FIG. 1 . 
           [0009]      FIG. 3  is a perspective view of a flange in accordance with another example embodiment. 
           [0010]      FIG. 4  is a bottom perspective view of a pressure coupling face of the transmitter in accordance with another example embodiment. 
           [0011]      FIG. 5  is a side plan view of an example embodiment showing a gasket or seal in accordance with the present invention. 
           [0012]      FIG. 6  is a top plan view of a flange showing a gasket or seal having a variable area. 
           [0013]      FIG. 7  is a top plan view of a gasket or seal formed of a single piece. 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    As discussed in the Background section, there is an ongoing need for an improved coupling between a pressure transmitter and the process fluid. Under some conditions, the coupling between the pressure transmitter and the process fluid is insufficient for the operating conditions which can result in leakage of the process fluid. In a pressure transmitter, a typical arrangement for coupling the transmitter to the fluid utilizes a flange into which piping is threaded. The piping couples to the process fluid for example to a process pipe. The flange provides a substantially flat interface onto which the pressure transmitter is bolted. However, it has been discovered that in a typical installation, the bolting force is spread in an inconsistent manner across the flange face. This can allow, under certain conditions, process fluid to leak between the interface of the flange with the pressure transmitter. 
         [0015]    The present invention addresses this leakage of process fluid by providing a flange and/or transmitter configuration which is curved or otherwise protrudes in an outwardly manner, i.e., in the direction of a mounting force. As the mounting force is applied between the flange and the transmitter, the protrusion causes the flange/transmitter interface to bend in a manner which more evenly spreads the mounting force across a wider area. By more evenly spreading the mounting force across a wider area, an improved seal is provided between the flange and the process transmitter. This improved seal reduces the potential for leakage between the pressure transmitter and the flange. 
         [0016]      FIG. 1  shows an exemplary pressure transmitter  10  having transmitter housing  12 , coupling flange or manifold  13  and sensor body  14  in accordance with the present invention. Although the present invention is shown with a Coplanar™ flange, the invention may be used with any type of flange, manifold, or other coupling adapted to receive process fluid. Sensor body  14  includes pressure sensor  16 , and transmitter housing  12  includes transmitter circuitry  20 . Sensor circuitry  18  is coupled to transmitter circuitry  20  through communication bus  22 . Transmitter circuitry  20  sends information related to pressure of the process fluid over a communication link such as a two wire process control loop  23  (or circuit). The transmitter  10  may optionally be wholly powered over the control loop  23  by a controller  25 . Other communication techniques may also be used including wireless techniques. 
         [0017]    In this example embodiment of a transmitter, pressure sensor  16  measures a difference in pressure between pressure P 1  in passageway  24  and pressure P 2  in passageway  26  of flange  13 . Pressure P 1  is coupled to sensor  16  through passageway  32 . Pressure P 2  is coupled to sensor  16  through passageway  34 . Passageway  32  extends through coupling  36  and tube  40 . Passageway  34  extends through coupling  38  and tube  42 . Passageways  32  and  34  are filled with a relatively incompressible fluid such as oil. Couplings  36  and  38  are attached to sensor body  14  and provide a long flame-quenching path between the interior of the sensor body carrying sensor circuitry  18  and process fluid contained in passageways  24  and  26 . 
         [0018]    Passageway  24  is positioned adjacent to opening  28  in sensor body  14 . Passageway  26  is positioned adjacent to opening  30  in sensor body  14 . Diaphragm  46  is positioned in opening  28  and is coupled to sensor body  14  adjacent to passageway  24 . Passageway  32  extends through coupling  36  and sensor body  14  to diaphragm  46 . Diaphragm  50  is coupled to sensor body  14  adjacent to passageway  26 . Passageway  34  extends through coupling  38  and sensor body  14  to diaphragm  50 . 
         [0019]    In operation, flange  13  presses against seals  48  and  52  when transmitter  10  is bolted to flange  13  due to the applied mounting force N as shown in  FIG. 1 . Seal  48  is seated on sensor body  14  adjacent to opening  24  and diaphragm  46 , and prevents process fluid leakage from passageway  24  and opening  28  past flange  13  to the outside environment. Similarly, seal  52  is coupled to sensor body  14  adjacent to opening  26  and diaphragm  50 , and prevents process fluid leakage from passageway  26  and opening  30  past flange  13  to the outside environment. As discussed below in greater detail, at least one of a pressure coupling face  60  of sensor body  14  or a flange face  62  of flange  13  (see  FIGS. 2-4 ) is curved or otherwise protrudes in the direction of the mounting force. 
         [0020]      FIG. 2  shows an exploded perspective view of transmitter  10  and flange  13  in accordance with one example embodiment. In the embodiment of  FIG. 2 , the flange  13  is shown as having a two-dimensional curvature in which flange face  62  is curved along one axis of the flange  13 .  FIG. 2  shows the flange  13  and transmitter  10  in a “unloaded” condition in which no mounting force is applied therebetween. However, when installed, the flange  13  is mounted to the sensor body  14  through mounting bolts  82  which extend through mounting holes  80  of flange  13  and are threadably received in bolt holes  84  of the sensor body  14 . This causes the mounting force N shown in  FIG. 1  to be applied between faces  60  and  62 . Although  FIG. 2  illustrates four mounting bolts, any number or configuration may be used. Further, other attachment techniques may be employed to mount the flange  13  to the sensor body  14  and thereby “load” flange  13  and sensor body  14 . The geometry of the flange face  62  will improve the distribution of the clamping force applied by the bolts  82  at the four corners of the flange  13 . The configuration serves as a spring element and adds to the bolt pre-loading. Once the loading force is applied, the flange face  62  and the pressure coupling face  60  will tend to conform to one another and form a substantially continuous surface such as illustrated in  FIG. 1 . The interface may be substantially flat, or may have some other profile. 
         [0021]      FIG. 3  is a perspective view of another example embodiment of flange  13  in which the curve of flange face  62  is three dimensional. In this example, the curvature has a spherical shape which is spread across the entire surface of flange face  62 . This configuration also serves to more uniformly distribute the clamping force. However, in this configuration, the mounting force is more evenly distributed along both axes of the flange face  62 . As illustrated in  FIG. 3 , the flange  13  is in an unloaded state. When a sufficiently larger load force (mounting force) is applied against the sensor body  14 , the interface between faces  60  and  62  will be substantially continuous as shown in  FIG. 1 . In the configuration shown in  FIG. 2 , the pressure coupling face  60  of pressure transmitter  10  may also be configured to have a curved profile. This may be separate from, or in addition to, the curvature of flange  13 . 
         [0022]      FIG. 4  is a bottom perspective view of transmitter  10  showing such a configuration in which pressure coupling face  60  is curved. When the flange  13  is sufficiently loaded against face  60 , the faces  60  and  62  will conform and provide a continuous surface such as that shown in  FIG. 2 . Note that if only face  60  is curved, the profile of the flange face  62  in a loaded condition will tend to also be curved and conform to face  60 . This is because flange  13  may be less stiff than sensor body  14 , such that face  60  will tend to maintain its original shape while face  62  will tend to bend to the profile of face  60 . 
         [0023]      FIG. 5  is side plan and top plan views of another example embodiment of the present invention. In  FIG. 5 , a beveled seal  100  is positioned between the flange  13  and the sensor body  14 . The beveled seals  100  extend around openings  24  and  26 , shown in  FIG. 6 . The seals  24  and  26  can be a conventional seal or can comprise, for example, a “confined gasket” in which materials such as PTFE is held in a groove. Also shown in  FIG. 6  are additional mounting holes  81  positioned near a central region of the flange  13 . In a similar approach shown in  FIG. 6 , the seal or gasket  100  has an area which is variable about the openings  24  and  26 . This variation in area causes the loading force to be spread as desired. In another example embodiment, the gasket or seal  100  is uniform however a groove into which it is placed has a variable depth to achieve a desired load distribution. 
         [0024]      FIG. 7  is a top plan view of another example embodiment in which a single gasket or seal  102  is used which is arranged to fit around the two openings  24  and  26  and is held in alignment by bolt holes  81 . In the above description, the gasket or seal  100  can comprise a traditional gasket material or can comprise a material which can be used to form a “confined gasket” such as PTFE. 
         [0025]    Although either or both of the flange or sensor body may be made to have a curved profile, in some configurations it may be preferable that one or the other component be curved. For example, a small modification to the flange can be used to retrofit with existing transmitter bodies. On the other hand, in some configurations, it may be easier to machine the sensor body  14  into a desired shape. In addition to machining, the flange  13  or the transmitter body may also be cast in a manner to have a desired profile. Although gentle curved profiles are shown, the present invention may use any desired profile, and the profile may not be uniform across the surface of a particular face. This can be arranged to more evenly distribute the mounting force between the flange and the pressure transmitter. Although bolts are shown as applying the loading (mounting) force, any mounting technique may be employed. Further, although four bolts are shown at the four corners of the flange and the transmitter body, any number of bolts or mounting apparatus may be used and arranged as desired. In some configurations, this may also eliminate the need for additional center line bolts which are located near the center of the flange and provide assist in more evenly distributing the coupling force. As used herein, “flange” refers to any component used in coupling a pressure transmitter to a process fluid and is not limited to the particular flange configurations shown herein. Further, although two pressure couplings are illustrated, the present invention may be used with any number of pressure couplings for a pressure transmitter. 
         [0026]    Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.