Abstract:
A process fluid pressure measurement system includes a process fluid pressure transmitter coupled to a coplanar manifold. The coplanar manifold includes a first bore coupleable to a source of process fluid, and a vent passageway connected to the first bore and terminating in a vent hole. The coplanar manifold includes at least one port configured to receive a valve stem. Directly engaging the valve stem with the coplanar manifold selectively vents the coplanar manifold. Aspects of the present invention also include a coplanar manifold for coupling fluid to a process fluid pressure transmitter, and a method of venting such a coplanar manifold.

Description:
BACKGROUND OF THE INVENTION 
   The term “process variable” generally refers to a physical or chemical state of matter or conversion of energy. Examples of process variables include pressure, temperature, flow, conductivity, pH, and other properties. The term “process measurement” refers to the acquisition of information that establishes the magnitude of process quantities. Pressure is considered a basic process variable in that it is used for the measurement of flow (the difference of two pressures), level (head or back pressure), and even temperature (fluid pressure in a thermal system). 
   An industrial process transmitter generally includes a transducer or sensor that responds to a measured variable with a sensing element that converts the variable to a standardized transmission signal, e.g., an electrical or optical signal where air pressure, that is a function of the measured value. Industrial process pressure transmitters are used to measure pressure within industrial processes such as slurries, liquids, vapors and gasses in chemical, pulp, petroleum, gas, pharmaceutical, food, and other fluid processing plants. Industrial process fluid transmitters are often placed near the process fluids, or in field applications. Often, these field applications are subject to harsh and varying environmental conditions that provide challenges for designers of such transmitters. 
   Process fluid pressure transmitters are generally coupled to the process by virtue of a manifold. The manifold routes the process fluid from one or more process fluid inlets to one or more process fluid outputs, which process fluid outputs are arranged, or otherwise configured in a standardized manner to match, or otherwise cooperate with, the location of process fluid inputs on pressure sensor modules of process pressure transmitters. 
   One particular type of manifold is known as a coplanar style manifold. Such manifolds are available from Rosemount, Inc. of Eden Prairie, Minn. under the trade designation Model 305 and Model 306 manifolds. Each of the models 305 and 306 manifolds can be ordered in a variety of configurations. Generally, a manifold will have at least one valve that provides pressure transmitter isolation. This isolation can allow the process pressure transmitter to be removed and repaired and/or replaced while the valve maintains isolation from the process. Coplanar manifolds can also be provided with two, three and five valve configurations. All such coplanar manifolds generally provide a plug for drain/vent capabilities. Coplanar manifolds can allow a number of process fluid pressures to be coupled to a process fluid pressure transmitter through a single, unitary manifold. Such a configuration can reduce installation costs and technician time, as well as provide an extremely robust process fluid connection. 
   Any interface between two surfaces which contacts process fluid, and extends to an outer surface that is in contact with the ambient environment may create a source of process fluid leaks. In order to remedy process fluid leaks, a field technician or other skilled worker may be required to diagnose and repair the problem. Providing a process pressure transmitter manifold that is less susceptible to leaks would benefit the process measurement and control industry. 
   SUMMARY 
   A process fluid pressure measurement system includes a process fluid pressure transmitter coupled to a coplanar manifold. The coplanar manifold includes a first bore coupleable to a source of process fluid, and a vent passageway connected to the first bore and terminating in a vent hole. The manifold includes at least one port configured to receive a valve stem. Directly engaging the valve stem with the coplanar manifold selectively vents the manifold. Aspects of the present invention also include a coplanar manifold for coupling fluid to a process fluid pressure transmitter, and a method of venting such a coplanar manifold. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a diagrammatic view of a process fluid pressure transmitter coupled to a coplanar manifold in accordance with the prior art. 
       FIG. 2  is a cross sectional view of a valve stem/seat assembly engaged with a coplanar manifold in accordance with the prior art. 
       FIG. 3  is a cross sectional view of a valve seat engaged with a coplanar manifold in accordance with an embodiment of the present invention. 
       FIG. 4  is a diagrammatic view of a valve seat engaged with a coplanar manifold in accordance with another embodiment of the present invention. 
       FIG. 5  is a diagrammatic view of a valve seat engaged with a coplanar manifold in accordance with yet another embodiment of the present invention. 
       FIG. 6  is a diagrammatic view of a process fluid pressure measurement system in accordance with an embodiment of the present invention. 
       FIG. 7  is a bottom plan view of plurality of valve seats directly engaged with a coplanar manifold in accordance with an embodiment of present invention. 
       FIG. 8  is a diagrammatic view of a valve seat engaged with a coplanar manifold in accordance with an embodiment of the present invention. 
   

   DETAILED DESCRIPTION 
     FIG. 1  is a diagrammatic view of a process fluid pressure transmitter  10  coupled to coplanar manifold  12  in accordance with the prior art. Process fluid pressure transmitter  10  generally includes an electronics compartment  14  coupled to a sensor compartment  16 , which sensor compartment  16  is further coupled to an isolator assembly  18  that is finally coupled to coplanar manifold  12 . Manifold  12  generally includes a pair of process fluid inlets  20 ,  22 .  FIG. 1  illustrates manifold  12  having a plurality of vent assemblies  24 ,  26 . Each of assemblies  24 ,  26  generally threads into an internally threaded bore within manifold  12 . Such internally threaded bores are typically specified as ¼ NPT. 
     FIG. 2  is a cross sectional view of vent assembly  24  threaded into coplanar manifold  12 . As illustrated, vent assembly  24  includes valve seat  40  that includes externally threaded region  42 , which region  42  is adapted to engage internally threaded portion  44  of coplanar manifold  12 . Region  42  of valve seat  40  includes an internal bore  46  in fluid communication with internal bore  48  of coplanar manifold  12 . Valve seat  40  also includes an internally threaded region  50  that is adapted to receive valve stem  52 . Valve stem  52  includes external thread  54  that is configured to engage internal thread  50  of valve seat  40 . Accordingly, rotation of valve stem  52  within valve seat  40  translates valve stem  52  axially in the direction of arrow  56 . Valve stem  52  includes seal  58  disposed on a distal end of stem  52 . Accordingly, as valve stem  52  is suitably rotated within valve seat  40 , seal  58  is brought into contact with edge  60  of internal bore  46 . As valve stem  52  is rotated in an opposite direction, seal  58  moves away from edge  60  and allows internal bore  46  to fluidly communicate with vent hole  62 . 
   The prior art valve stem/seal assembly described above with respect to  FIG. 2  is somewhat limited. Specifically, the threaded joint between valve seat  40  and coplanar flange  12  provides a leak potential whereby process fluid could escape. Further, valve seat  40 , itself, adds to the cost of the entire assembly. Further still, since valve seat  40  is threaded into flange  12 , the orientation of vent hole  62  is randomly located relative to the transmitter assembly. This is undesirable because the actual location of the vented process fluid cannot be specified, or otherwise determined, with certainty. 
   Embodiments of the present invention generally facilitate venting a coplanar process fluid pressure manifold using a valve stem coupled directly to the coplanar manifold.  FIG. 3  is a cross sectional view of valve stem  52  coupled to coplanar manifold  100  in accordance with an embodiment of the present invention. Coplanar manifold  100  includes an internal bore  102  that is fluidically coupled to the process fluid. Bore  102  is fluidically coupled to vent passageway  106 , which ultimately leads to vent hole  108 . The portion of passageway  106  proximate vent hole  108  may include internal threads in order to allow a threaded plug therein, in case a user wishes to use a different form of venting, or no venting at all. Corner  104  is preferably shaped to engage seal  58  of stem  52 . As illustrated in  FIG. 3 , bore  102  and vent passageway  106  are generally arranged at right angles relative to each other with corner  104  interposed therebetween. However, this is merely one arrangement which is configured to facilitate allowing seal  58  to selectively block fluidic communication between bore  102  and vent passageway  106 . Additionally, since vent passageway  106  is machined, or otherwise created, directly into manifold  100 , the location and/or orientation of vent hole  108  relative to manifold  100  is completely determined. Various configurations of vent passageway  106  and internal passageway  102  can be implemented in accordance with various embodiments of the present invention. For example, vent passageway  106  and internal bore  102  need not be at right angles with respect to each other, and rotation of valve stem  52  need not translate valve stem  52  axially along the center line of internal bore  102 . 
     FIG. 4  is a diagrammatic view of a valve seat engaged with a coplanar manifold in accordance with another embodiment of the present invention.  FIG. 4  bears many similarities to  FIG. 3 , and like components are numbered similarly. The main difference between the embodiments illustrated in  FIGS. 3 and 4 , is that in  FIG. 4 , vent hole  108  has directional adapter  109  engaged therein. Adapter  109  is configured to engage internal threads of vent hole  108  to be affixed thereto. Adapter  109  includes a passageway that fluidly couples to vent passageway  106  and changes the direction of fluid exiting vent hole  108  from the axis of vent passageway  106 . In the embodiment illustrated in  FIG. 4 , adapter  109  generates a substantially right angle turn in the vented fluids, however, other configurations can also be practiced in accordance with embodiments of the present invention. Adapter  109  is also somewhat rotatable within vent hole  108  to allow the direction of venting to be configurable. Preferably, but not necessarily, adapter  109  includes a portion that extends in the new direction. For example, in  FIG. 4 , adapter  109  includes portion  107  extending in a direction that is substantially perpendicular to the axis of vent passageway  108 . However, it is also contemplated that adapter  109  could merely include a vent hole directing vent fluid in a different direction than that of the axis of vent passageway  106 . 
     FIG. 5  is a diagrammatic view of valve stem  52  being arranged such that rotation of valve stem  52  about axis  110  generates movement of stem  52  along axis  110 , which axial movement generally drives seal  58  between passageway  112  and vent passageway  114 . 
   Coplanar manifold  120  includes valve stem receiving portion  122  that is configured to receive valve stem  52  in such a way that valve stem  52  directly obstructs fluidic communication between internal passageway  112  and vent passageway  114 . Valve stem  52  can be any suitable size, including that configured to directly engage an internal port of coplanar manifold  120  having straight (non-tapered) internal threads. 
     FIG. 6  is a diagrammatic view of a process fluid pressure measurement system  200  in accordance with an embodiment of the present invention. System  200  includes process fluid pressure transmitter  210 , which generally includes electronics compartment  214  coupled to sensor compartment  216 , which sensor compartment  216  is further coupled to isolator assembly  218  that is finally coupled to coplanar manifold  212 . Process fluid inlets  220 ,  224  couple to a source of process fluid, and convey the process fluid into coplanar manifold  212 . Coplanar manifold  212  is configured to directly receive valve stems  52 , for purposes of selectively venting process fluid. Coplanar manifold  212  is coupled to isolator assembly  218  of process fluid pressure transmitter  210 . 
   Isolator assembly  218  responds to process fluid pressure by generating a similar pressure within an isolation fluid, such as silicone oil, that is presented to a pressure sensor within sensor compartment  216 . The pressure sensor can include any suitable transducing element that changes, such as deflects, in response to isolation fluid pressure. The transducer preferably includes an element that has an electrical property that changes with deflection. For example, the pressure sensor may include a conductive sensing diaphragm that has a capacitance that changes with deflection. 
   The pressure sensor is coupled to suitable electronics within electronics compartment  214 . The electronics are configured to measure the changing electrical characteristic of the pressure sensor, to arrive at a pressure calculation. Moreover, the electronics preferably include controller electronics to transmit, or otherwise convey, digital information indicative of the pressure over a process communication loop, such as a Highway Addressable Remote Transducer (HART) loop or a FOUNDATION™ Fieldbus loop. 
     FIG. 7  is a bottom plan view of coplanar manifold  212  in accordance with an embodiment of the present invention. Coplanar manifold  212  includes a plurality of mounting holes  124  to allow manifold  212  to be mounted. As illustrated in  FIG. 6 , valve stem  52  engages directly with manifold  212  thereby obviating the necessity of a valve seat. The absence of the valve seat provides a number of advantages for embodiments of the present invention. Specifically, the cost of manufacturing a valve seat itself is eliminated. Moreover, any potential leak source of process fluid between a valve seat/manifold interface is also removed. Finally, since the vent passageway and vent hole are machined directly into the manifold, the location where the vented process fluid escapes is completely determined. 
     FIG. 8  is a diagrammatic view of a valve seat engaged with a coplanar manifold in accordance with an embodiment of the present invention. Valve stem  300  engages directly with coplanar manifold  302 . Preferably, such direct engagement is via external threads  304  cooperating with non-tapered internal threads  306  of coplanar manifold  302 . Valve stem  300  includes seal  58  disposed at the distal end of valve stem  300 . Seal  58  is configured to bear against corner  104  of coplanar manifold  302  to selectively interrupt fluid communication between passageway  102  of manifold  302  and vent passageway  308  disposed within valve stem  300 . Providing a valve stem with a vent passageway disposed therein allows for a simpler design within coplanar manifold  302 . However, like embodiments described above, valve stem  300  still directly engages manifold  302 . While valve stem  300  is illustrated as being substantially one piece, it is contemplated that certain portions, such as seal  58 , may be constructed of different materials than the rest of valve stem  300 . 
   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.