Patent Description:
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.

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.

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.

There is an ongoing need for improved coupling between a pressure transmitter and a process fluid.

<CIT> describes a high-pressure sensor mounting configuration including a cylinder pressure sensor cavity. An internally threaded collet includes a second bearing surface that bears on a first bearing surface when the internally threaded collet is threaded onto a pressure port, causing a convex conical open end to bear on a concave conical mating surface of the pressure port.

<CIT> describes a pressure transmitter comprising a body including transmitter circuitry, and a sensor body including a pressure sensor. A flange is pressed against process seals, which are seated on the sensor body. Each seal comprises a ring having an outer diameter, an inner diameter <NUM>, and an arched region between them. The seals provide a metal-to-metal contact with a non-metallic seal to prevent process fluid leakage.

<CIT> describes an assembly for aligning and supporting an adapter flange for connecting fluid pressures to a sensor body. For transmitter body changes or at factory installation, a shoulder bolt and a guide stud are applied to keep a gap between a surface of a body and a surface of a flange in order to not seal the connection.

<CIT> describes a flange joint for pipes leading fluids under high pressures. Contact surfaces of two flanges form an angle to each other so that each surface forming a conical shape in its cross section. When securing bolts are tightened, the contact surfaces are being forced towards each other in order to form a seal.

<CIT> describes a flanged member for being part of a flanged joint for installation in a pressure equipment device. End surfaces of the flange and/or the pressure equipment are curved in a concave shape in the radial direction and having an area that essentially will be subjected to deforming forces when the joint is assembled together.

<CIT> describes a deformable V-shaped metallic seal gasket to be used in joining metallic sections of fluid pressure systems to facilitate metal-to-metal sealing.

A pressure transmitter for measuring a pressure of a process fluid in an industrial process is provided according to claims <NUM> and <NUM>.

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.

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.

<FIG> shows an exemplary pressure transmitter <NUM> having transmitter housing <NUM>, coupling flange or manifold <NUM> and sensor body <NUM> 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 <NUM> includes pressure sensor <NUM>, and transmitter housing <NUM> includes transmitter circuitry <NUM>. Sensor circuitry <NUM> is coupled to transmitter circuitry <NUM> through communication bus <NUM>. Transmitter circuitry <NUM> sends information related to pressure of the process fluid over a communication link such as a two wire process control loop <NUM> (or circuit). The transmitter <NUM> may optionally be wholly powered over the control loop <NUM> by a controller <NUM>. Other communication techniques may also be used including wireless techniques.

In this example embodiment of a transmitter, pressure sensor <NUM> measures a difference in pressure between pressure P1 in passageway <NUM> and pressure P2 in passageway <NUM> of flange <NUM>. Pressure P1 is coupled to sensor <NUM> through passageway <NUM>. Pressure P2 is coupled to sensor <NUM> through passageway <NUM>. Passageway <NUM> extends through coupling <NUM> and tube <NUM>. Passageway <NUM> extends through coupling <NUM> and tube <NUM>. Passageways <NUM> and <NUM> are filled with a relatively incompressible fluid such as oil. Couplings <NUM> and <NUM> are attached to sensor body <NUM> and provide a long flame-quenching path between the interior of the sensor body carrying sensor circuitry <NUM> and process fluid contained in passageways <NUM> and <NUM>.

Passageway <NUM> is positioned adjacent to opening <NUM> in sensor body <NUM>. Passageway <NUM> is positioned adjacent to opening <NUM> in sensor body <NUM>. Diaphragm <NUM> is positioned in opening <NUM> and is coupled to sensor body <NUM> adjacent to passageway <NUM>. Passageway <NUM> extends through coupling <NUM> and sensor body <NUM> to diaphragm <NUM>. Diaphragm <NUM> is coupled to sensor body <NUM> adjacent to passageway <NUM>. Passageway <NUM> extends through coupling <NUM> and sensor body <NUM> to diaphragm <NUM>.

In operation, flange <NUM> presses against seals <NUM> and <NUM> when transmitter <NUM> is bolted to flange <NUM> due to the applied mounting force N as shown in <FIG>. Seal <NUM> is seated on sensor body <NUM> adjacent to opening <NUM> and diaphragm <NUM>, and prevents process fluid leakage from passageway <NUM> and opening <NUM> past flange <NUM> to the outside environment. Similarly, seal <NUM> is coupled to sensor body <NUM> adjacent to opening <NUM> and diaphragm <NUM>, and prevents process fluid leakage from passageway <NUM> and opening <NUM> past flange <NUM> to the outside environment. As discussed below in greater detail, at least one of a pressure coupling face <NUM> of sensor body <NUM> or a flange face <NUM> of flange <NUM> (see <FIG>) is curved or otherwise protrudes in the direction of the mounting force.

<FIG> shows an exploded perspective view of transmitter <NUM> and flange <NUM> in accordance with one example embodiment. In the embodiment of <FIG>, the flange <NUM> is shown as having a two-dimensional curvature in which flange face <NUM> is curved along one axis of the flange <NUM>. <FIG> shows the flange <NUM> and transmitter <NUM> in a "unloaded" condition in which no mounting force is applied therebetween. However, when installed, the flange <NUM> is mounted to the sensor body <NUM> through mounting bolts <NUM> which extend through mounting holes <NUM> of flange <NUM> and are threadably received in bolt holes <NUM> of the sensor body <NUM>. This causes the mounting force N shown in <FIG> to be applied between faces <NUM> and <NUM>. Although <FIG> illustrates four mounting bolts, any number or configuration may be used. Further, other attachment techniques may be employed to mount the flange <NUM> to the sensor body <NUM> and thereby "load" flange <NUM> and sensor body <NUM>. The geometry of the flange face <NUM> will improve the distribution of the clamping force applied by the bolts <NUM> at the four corners of the flange <NUM>. The configuration serves as a spring element and adds to the bolt pre-loading. Once the loading force is applied, the flange face <NUM> and the pressure coupling face <NUM> will tend to conform to one another and form a substantially continuous surface such as illustrated in <FIG>. The interface may be substantially flat, or may have some other profile.

<FIG> is a perspective view of another example embodiment of flange <NUM> in which the curve of flange face <NUM> is three dimensional. In this example, the curvature has a spherical shape which is spread across the entire surface of flange face <NUM>. 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 <NUM>. As illustrated in <FIG>, the flange <NUM> is in an unloaded state. When a sufficiently larger load force (mounting force) is applied against the sensor body <NUM>, the interface between faces <NUM> and <NUM> will be substantially continuous as shown in <FIG>. In the configuration shown in <FIG>, the pressure coupling face <NUM> of pressure transmitter <NUM> may also be configured to have a curved profile. This may be separate from, or in addition to, the curvature of flange <NUM>.

<FIG> is a bottom perspective view of transmitter <NUM> showing such a configuration in which pressure coupling face <NUM> is curved. When the flange <NUM> is sufficiently loaded against face <NUM>, the faces <NUM> and <NUM> will conform and provide a continuous surface such as that shown in <FIG>. Note that if only face <NUM> is curved, the profile of the flange face <NUM> in a loaded condition will tend to also be curved and conform to face <NUM>. This is because flange <NUM> may be less stiff than sensor body <NUM>, such that face <NUM> will tend to maintain its original shape while face <NUM> will tend to bend to the profile of face <NUM>.

<FIG> is side plan and top plan views of another example. In <FIG>, a beveled seal <NUM> is positioned between the flange <NUM> and the sensor body <NUM>. The beveled seals <NUM> extend around openings <NUM> and <NUM>, shown in <FIG>. The seals <NUM> and <NUM> 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> are additional mounting holes <NUM> positioned near a central region of the flange <NUM>. In a similar approach shown in <FIG>, the seal or gasket <NUM> has an area which is variable about the openings <NUM> and <NUM>. This variation in area causes the loading force to be spread as desired. In another example, the gasket or seal <NUM> is uniform however a groove into which it is placed has a variable depth to achieve a desired load distribution.

<FIG> is a top plan view of another example in which a single gasket or seal <NUM> is used which is arranged to fit around the two openings <NUM> and <NUM> and is held in alignment by bolt holes <NUM>. In the above description, the gasket or seal <NUM> can comprise a traditional gasket material or can comprise a material which can be used to form a "confined gasket" such as PTFE.

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 <NUM> into a desired shape. In addition to machining, the flange <NUM> 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.

Claim 1:
A pressure transmitter (<NUM>) for measuring a pressure (P1; P2) of a process fluid in an industrial process, comprising:
a pressure sensor (<NUM>) having an output related to an applied pressure (P1; P2);
measurement circuitry (<NUM>; <NUM>) coupled to the pressure sensor (<NUM>) configured to provide a transmitter output related to the applied pressure (P1; P2);
a pressure coupling face (<NUM>) having an opening (<NUM>; <NUM>) therein arranged to transfer the applied pressure (P1; P2) to the pressure sensor (<NUM>); and
a pressure coupling flange (<NUM>) having a flange face (<NUM>) abutting the pressure coupling face (<NUM>) configured to convey the process fluid to the opening (<NUM>; <NUM>) of the pressure coupling face (<NUM>); and
wherein at least one of the pressure coupling face (<NUM>) and the flange face (<NUM>) is curved to protrude in a direction toward another of the pressure coupling face (<NUM>) and the flange face (<NUM>) such that, application of a mounting force (N) to mount the pressure coupling face (<NUM>) to the pressure coupling flange (<NUM>) causes the curved one of the pressure coupling face (<NUM>) and the flange face (<NUM>) to bend to conform to a shape of the other of the pressure coupling face (<NUM>) and the flange face (<NUM>).