Clad industrial process transmitter housing with chassis

An industrial process transmitter apparatus includes a housing chassis of a first metallic material and a housing skin of a second metallic material. The housing chassis includes a substantially cylindrical body portion, a first circumferentially extending support member located at or near a first end of the body portion of the housing chassis, and a second circumferentially extending support member located at or near a second end of the body portion of the housing chassis opposite the first end. The first circumferentially extending support member extends radially outward from the body portion, and the second circumferentially extending support member extends radially outward from the body portion. The housing skin is fitted over the housing chassis and is in physical contact with both the first and second circumferentially extending support members. The housing skin is spaced from the housing chassis in between the first and second circumferentially extending support members.

BACKGROUND

The present invention relates to industrial process transmitters, and more particularly to housing assemblies for industrial process transmitters and methods of making the same.

Industrial process transmitters are used to sense, measure, manage and control processes in industrial processing facilities. Typically, industrial process transmitters include a housing that is sealed and explosion-proof. The geometry of these housings, both internal and external, can be relatively complex. In the prior art, these housings were generally one-piece die-castings made from aluminum, which is a material well-suited for die casting. Additional machining was then performed on the die-casting, as desired, and the casting was painted. However, aluminum is a relatively reactive material, making it less desirable for certain applications were the housing is exposed to materials that are reactive, caustic, etc. Paints and similar coatings may be undesired or inadequate for protecting the aluminum material of the housing in certain applications. Other materials, like stainless steel, are not readily able to be die cast, but instead require a process like investment casting, which is a relatively complicated and expensive process as compared to die casting. Furthermore, casting processes tend to leave relatively rough surfaces (greater than about 125 Ra), which are undesirable for hygienic applications where rigorous cleaning or sterilization processes must be performed. Machining all surfaces of a casting to increase smoothness would be an undesirably time-consuming and expensive undertaking.

Thus, an alternative industrial process transmitter housing assembly is desired.

SUMMARY

An industrial process transmitter apparatus according to the present invention includes a housing chassis of a first metallic material and a housing skin of a second metallic material. The housing chassis includes a substantially cylindrical body portion, a first circumferentially extending support member located at or near a first end of the body portion of the housing chassis, and a second circumferentially extending support member located at or near a second end of the body portion of the housing chassis that is opposite the first end. The first circumferentially extending support member extends radially outward from the substantially cylindrical body portion, and the second circumferentially extending support member extends radially outward from the substantially cylindrical body portion. The housing skin is fitted over the housing chassis and is in physical contact with both the first and second circumferentially extending support members of the housing chassis. The housing skin is spaced from the housing chassis in between the first and second circumferentially extending support members.

DETAILED DESCRIPTION

In general, the present invention provides to an industrial process transmitter assembly (also called a field device assembly) having a stainless steel outer skin and an aluminum chassis (or core), and a method of making the same.FIG. 1is a schematic block diagram of one embodiment of an industrial process transmitter20that includes a sensor22, signal circuitry24, one or more feedthroughs26, and field terminal circuitry28. The industrial process transmitter assembly20is operably connected to a power supply30and to a control room32through a communication link34. Furthermore, the industrial process transmitter20is installed at a location to sense, measure, manage and/or control an industrial process36.

In one embodiment, the sensor22is a pressure sensor of a known configuration positioned in operative contact with the industrial process36. In alternative embodiments, the sensor22can be configured to sense or measure temperature, vibration, flow, or nearly any other parameter associated with the industrial process36. The sensor22can be positioned relative to the industrial process36in any manner suitable for the type of parameter desired to be sensed or measured. In further alternative embodiments, the sensor22could be replaced with an actuator or other device that manages, controls, or otherwise interacts with the industrial process36.

The signal circuitry24is operatively connected to the sensor22. Data signals from the sensor22are sent to the signal circuitry24, which can perform desired operations on or with those data signals. For instance, the signal circuitry24can store, filter, compress, convert, summarize, analyze, or otherwise process raw data from the sensor22as desired for particular applications. The signal circuitry is typically sealed off from the industrial process36and the environment inside the industrial process transmitter20in order to help prevent damage or malfunction.

The field terminal circuitry28is located within the industrial process transmitter assembly, and is typically sealed off from the industrial process36and also from the signal circuitry. The one or more feedthroughs26(seeFIG. 9) electrically connect the field terminal circuitry28to the signal circuitry24. In one embodiment, the feedthroughs26provide electromagnetic interference (EMI) filtering in a conventional manner. The field terminal circuitry28can store, filter, compress, convert, summarize, analyze, or otherwise process data or other signals from the signal circuitry24. The field terminal circuitry28is operatively connected to the control room32via the communication link34, enabling communication between the field terminal circuitry28and control room32. In this way, data or other signals can be sent from the field terminal circuitry28to the control room32, and commands or other signals can be sent from the control room32to the field terminal circuitry28. The communications link34can be a direct wired connection, an Internet connection, a local area network (LAN), wide area network (WAN), virtual private network (VPN), a wireless connection (e.g., a mesh network), or any other suitable communication. Furthermore, the field terminal circuitry28can receive power input from the power supply30, which can be a line voltage, an energy harvesting device, and energy storage device, or other type of power source. Power received by the field terminal circuitry28can be distributed for use by other components the industrial process transmitter assembly20.

It should be noted that the industrial process transmitter20can include additional components not specifically mentioned. For example, circuitry to provide additional functionality can be provided as desired for particular applications.

FIG. 2is a perspective view of an industrial process transmitter20that includes a housing body40, first and second covers42and44engaged at opposite ends of the housing body40, a conduit46extending from the housing body40and a neck48extending from the housing body40. In the illustrated embodiment, the housing body40has a substantially cylindrical shape. The conduit46and the neck48protrude from the housing body40in different directions. The neck48can at least partially contain a sensor22, and can be mounted to a desired location for operatively interacting with an industrial process. The neck48can be secured to the mounting location and provide structural support for the rest of the industrial process transmitter20. The conduit46can at least partially house field wiring that can electrically connect circuitry within the housing body40to external equipment. In a typical installation, the conduit46is connected to another suitable electrical conduit (not shown). The particular configuration of the conduit46and the neck48can vary as desired for particular applications, such as for the neck48to accommodate a particular type of sensor22and for the conduit46to connect to provide a type of external electrical connection.

FIG. 3is an exploded, cross-sectional perspective view of one embodiment of the housing body40that includes a chassis (or housing chassis)50and a skin (or housing skin)52, shown during assembly.FIG. 4is a cross-sectional perspective view of the housing body40ofFIG. 3, shown with the chassis50and the skin52assembled together. As shown inFIGS. 3 and 4, the chassis50includes a substantially cylindrical body54having a first end56and an opposite second end58. A first support member (or land)60is located at or near the first end56, and a second support member (or land)62is located at or near the second end58. The first and second support members60and62each extend circumferentially and protrude radially outward from the body54, and can each be integrally formed with the body54. A circumferentially-extending recess (or groove)64is defined in between the first and second support members60and62at an outer surface of the body54. First and second openings66and68are formed through the body54at the recess64. In the illustrated embodiment the first and second openings66and68have circularly shaped perimeters. An additional support member (or land)70is defined about the first and the second openings66and68(only the support member70about the second opening68is visible inFIGS. 3 and 4). Each additional support member70extends about a perimeter of the respective first or second opening66or68, and extends radially outward from the body54. An internal wall72extends across the body54to divide the chassis50into two compartments. In the illustrated embodiment, the wall72defines a shelf and is positioned between the first opening66and the second opening68, such that the first and second openings66and68open into different compartments within the chassis50. Furthermore, a thickened structure74is located along an interior surface of the body54so as to surround the first opening66.

The chassis50can be made out of aluminum, or another suitable material. As will be discussed in turn, the chassis50can be die cast and then machined to produce a desired configuration. Suitable machining processes can be used to define or shape the first and second openings66and68, outer surfaces of the support members60,62and70, and other features as desired.

In the illustrated embodiment, seal members76(e.g., O-rings) are provided recessed within outer surfaces of the first support member60and the second support member62of the chassis50. The seal members76are optional, and can be omitted from alternative embodiments. The function of the seal members76is discussed below.

It should be noted that the configuration of the chassis50can vary as desired for particular applications. For instance, the wall72can be omitted, or additional walls can be added in order to provide a desired number of internal compartments in the chassis50. Moreover, the number and location of the openings66and68can vary as desired for particular applications. In addition, further support members extending from the body54can be provided in further embodiments.

The skin52is configured as a generally cylindrical sleeve. As shown inFIG. 3, first and second openings78and80are formed in the skin52at locations substantially aligned relative to the first and second openings66and68in the chassis50. Perimeter edges of the first and second openings78and80rest on the additional support members70. In the illustrated embodiment, the first and second openings78and80have circularly shaped perimeters and have diameters larger than the respective first and second openings66and68in the chassis50. As shown inFIG. 4, first and second lips82and84are formed by opposite edges of the skin52, with the first lip82located at the first end56of the chassis50adjacent to the first support member60and the second lip84located at the second end58of the chassis50adjacent to the second support member62.

The skin52can be made of stainless steel, or another suitable material. In one embodiment, an exterior surface of the skin52has an arithmetic average surface roughness of approximately 32 Ra or smoother. A relatively smooth exterior surface formed of stainless steel is well suited for use in hygienic applications, such as for food and beverage industries, as well as in corrosive environments, such as on off-shore platforms.

When the chassis50and the skin52are assembled together, as shown inFIG. 4, the skin52rests upon at least portions of the first and second support members60and62and the additional support members70such that the skin52generally surrounds and covers the chassis50. In this way the skin52is in direct physical contact with at least portions of the first and second support members60and62of the chassis50. A void or cavity is formed between the recess64of the chassis50and the skin52, such that the skin52is spaced from the body54of the chassis50adjacent to the recess64. The first and second lips82and84help secure the skin52to the chassis50, in particular limiting or preventing endwise sliding between the skin52and the chassis50. The seal members76create fluidic seals between the chassis50and the skin52, to reduce a risk of fluid entering the void at the recess64. The presence of a fluid in the void between the skin52and the chassis50could undesirably promote corrosion, such as through a galvanic effect.

FIG. 5is a cross-sectional view of a portion of the industrial process transmitter20, showing a conduit46and a portion of the housing body40. The conduit46includes a body portion90, a cap portion92, an adapter ring94, and seal members96and98(e.g., O-rings). In the illustrated embodiment, the body portion90is generally cylindrical in shape and has a circumferentially-extending flange100. A central cavity of the body portion90allows wire or other components to pass through the conduit46into the housing body40. The cap portion92is secured at one end of the body portion90. Another end of the body portion90, opposite the cap portion92, is engaged to the chassis50of the housing body40at the opening66. In the illustrated embodiment, a threaded engagement is provided between the body portion90of the conduit46and the chassis50of the housing body40. The adapter ring94surrounds part of the body portion90and is positioned adjacent to the flange100, between the flange100and the skin52of the housing body40. The adapter ring94has a saddle shaped inner face102positioned against the skin52. Because the skin52is generally cylindrically shaped, the saddle shape of the inner face102allows the adapter ring94to closely mate with adjacent portions of the skin52. The seal member98creates a fluidic seal between the adapter ring94and the skin52. The seal member98is positioned in a recess in the adapter ring94in the illustrated embodiment. An outer face104of the adapter ring94is located opposite the inner face102and is generally planar. The flange100of the body portion90is positioned adjacent to the outer face104, and the seal member96creates a fluidic seal therebetween. The seal member96is positioned in a recess in the flange100in the illustrated embodiment. The seal members96and98help reduce a risk of fluid entering the housing body40through the openings66and78.

FIG. 6is an exploded perspective view of another portion of the industrial process transmitter20, showing the housing body40, a neck48, and an adapter ring110.FIG. 7is a perspective view of the portion of the industrial process transmitter20ofFIG. 6, shown assembled together.FIG. 8is a cross-sectional perspective view of the industrial process transmitter20, taken along line8-8ofFIG. 7. In the illustrated embodiment, the neck48has a generally cylindrical shape, with a distal end112and a proximal end114. The proximal end114of the neck48is threaded. A shoulder116is formed adjacent to the threads at the proximal end114. The neck48can be configured to contain portions of the sensor22. The particular configuration of the neck48can vary as desired for particular applications, such as to accommodate a particular type of sensor or other component. The neck48can be made of stainless steel.

In this embodiment, the adapter ring110defines a saddle shaped inner face118and an opposite outer face120configured to mate with the shoulder116of the neck48. The outer face120can have a substantially planar configuration. Because the skin52of the housing body40is generally cylindrically shaped, the saddle shape of the inner face118allows the adapter ring110to closely mate with adjacent portions of the skin52. The adapter ring110further defines a central opening through which the proximal end114of the neck48can pass. In the illustrated embodiment, an outer diameter of the adapter ring110is equal to an outer diameter of the neck48adjacent to the shoulder116. The adapter ring110can be made of stainless steel.

When assembled, the proximal end114of the neck48is threadably engaged to the chassis50of the housing body40at the opening68. A portion of the neck48passes through the adapter ring110. The adapter ring110is positioned in between the skin52of the housing body40and the shoulder116of the neck48, with the inner face118in contact with the skin52and the outer face120in contact with the neck48at the shoulder116. Weld joints122are formed between the skin52and the adapter ring110, and between the adapter ring and the neck48at the shoulder116. The weld joints122can form hermetic seals to reduce a risk of fluid entering the housing body40through the openings68and80. Furthermore, the saddle shape of the inner face118of the adapter ring110allows close mating with the cylindrical shape of the skin52, while presenting the substantially planar outer face120to allow rotation of the neck48to threadably engage the proximal end114with the chassis50without obstruction.

FIG. 9is a quarter-section perspective view of the industrial process transmitter20. As shown in the illustrated embodiment, electrical feedthroughs26are threadably engaged through the wall72to provide electrical connections between separate compartments defined by the chassis50. Any number of electrical feedthroughs26can be provided as desired for particular applications. The feedthroughs can be configured such that a sealed and explosion proof barrier exists between the compartments spanned by the feedthroughs26, while still providing electrical connections between compartments through the wall72. This allows circuitry in one compartment (e.g., the signal circuitry24) to be electrically connected to circuitry (e.g., the field terminal circuitry28) in another compartment.

FIG. 10is a cross-sectional perspective view of a portion of the industrial process transmitter20, shown with the housing body40engaged with one embodiment of a cover42. In the illustrated embodiment, the cover42is formed as a single, solid body. The cover includes a generally disc-shaped central portion126and a flange128. The cover42can be made of stainless steel. In the illustrated embodiment, the flange128is annularly shaped and extends from a circumference of the central portion126. Radially outwardly facing threads130are formed on the flange128for engagement with the chassis50. A shoulder132is formed on the flange128adjacent to the threads130. A seal member134(e.g., an O-ring) is positioned at the shoulder132of the cover42, such that when the cover42is fully secured to the housing body40the seal member132abuts both the shoulder132of the cover42and the lip82of the skin52of the housing body40. A fluidic seal is thereby created between the cover42and the housing body40, to reduce a risk of fluid entering the housing body40. It should be noted that the cover44shown inFIG. 2can be configured substantially identically to the cover42.

FIG. 11is a cross-sectional view of the industrial process transmitter20, taken along line11-11ofFIG. 2. As shown inFIG. 11, the industrial process transmitter20is fully assembled, with two of the covers42and44engaged at opposite ends of the housing body40, with the sensor22installed at the neck48, and with the signal circuitry24and the field terminal circuitry28positioned in separate compartments within the housing body40. The neck48opens to one compartment of the housing body40, while the conduit46opens to a separate compartment. During operation, fluid sometimes enters the housing body40through the conduit46due to the presence of fluid in a conduit connected to the conduit46. However, the wall72helps to isolate the signal circuitry24and the sensor22from fluid introduced to the housing body40through the conduit46.

FIG. 12is a cross-sectional view of a portion of an alternative embodiment a cover136. The cover136is configured to engage the housing body40in a similar manner to the covers42and44. However, as opposed to being a single solid body, the cover136includes a cover chassis138and a cover skin140. The cover chassis138includes a generally disc shaped central portion142and an annular flange144. A first support member (or land)146is formed at or near an outer diameter of the central portion142, and one or more additional support members (or lands)148are formed at radially inner locations on the central portion142. The support members146and148are generally positioned adjacent to corners of the cover chassis138, and any other location where support for the cover skin140is desired. Recesses (or grooves)150are defined adjacent to the support members146and148. The cover chassis138can be made of aluminum, or another suitable material.

The cover skin140has a lip152formed at a perimeter thereof. The cover skin140can be made of stainless steel, or another suitable material. In one embodiment, an exterior surface of the cover skin140has an arithmetic average surface roughness of approximately 32 Ra or smoother. A relatively smooth exterior surface formed of stainless steel is well suited for use in hygienic applications and corrosive environments.

When the cover chassis138and the cover skin140are assembled together, the cover skin140rests upon at least portions of the support members146and148such that the cover skin140generally covers and surrounds the cover chassis138. In this way the cover skin140is in direct physical contact with at least portions of the support members146and148of the cover chassis138. A void or cavity is formed between the recesses150of the cover chassis138and the cover skin140, such that the cover skin140is spaced from the central portion142of the cover chassis138adjacent to the recesses150. The lip152helps secure the cover skin140to the cover chassis138.

FIG. 13is a flow chart of one method of making the industrial process transmitter20, in an embodiment using the housing body40and the cover136. Fittings (e.g., the conduit46and the neck48) are cast (step200), the housing chassis50is cast (step202), and the cover chassis138is cast (step204). Steps200,202and204can be performed simultaneously or at different times, as desired. The housing chassis50and the cover chassis138can each be die cast from aluminum, or alternatively using another known casting process. Die casting is suitable for use with a material like aluminum, and facilitates casting the relatively complex three-dimensional shape of a typical housing chassis50, which will often include multiple internal compartments formed by the wall72, features like the thickened structure74, etc. The fittings can be cast using any suitable process. In some embodiments, fittings like the conduit46and the neck48are cast from stainless steel. It should be noted that in alternative embodiments, steps200,202and204could involve injection molding or machining instead of casting.

After the housing chassis50and the cover chassis138are cast in steps202and204, each is machined in steps206and208, respectively. Machining in steps206and208includes machining support members (e.g., support members60,62,70,146,148) on the housing chassis50and the cover chassis138to desired dimensions. The presence of support members helps to focus and ultimately limit the total amount of machining required to compensate for natural tolerance variations present from casting operations. Additional machining, such as to form threads, form receiving grooves for seals, remove excess material, etc., can be performed on the fittings, the housing chassis50and/or the cover chassis138as desired for particular applications. After machining, seals (e.g., seal members76,96and98) are positioned (step210).

The housing skin52and the cover skin140are made in steps212and214, respectively. The skins52and140can be made using a drawing process, or any other suitable process. Once the housing skin52has been made, one or more openings (e.g., the openings66and68) are created in the skin52, using a machining process or any other suitable process (step216). Steps212,214and216can each be performed, before, simultaneously with, or after any of the previously-described steps.

Next, the housing skin52is fit over the housing chassis50(step218) and the cover skin140is fit over the cover chassis138(step220). In one embodiment, conventional shrink-fitting techniques are utilized to fit the skins52and140to the chassis50and138, respectively, such that the skins52and140rest on the support members60,62,70,146,148tightly and firmly. Fitting performed in steps218and220includes providing a desired alignment of the housing skin52relative to the housing chassis50and of the cover skin140relative to the cover chassis138, such as to substantially align the opening78in the housing skin52with the opening66in the housing chassis50and to substantially align the opening80in the housing skin52with the opening68in the housing chassis50. Once positioned as desired, edges of the skins52and140are rolled to form the lips82,84and152(step222), to help secure the skins52and140to the chassis50and138, respectively.

In the illustrated embodiment, adapters (e.g., adapters104and110) are positioned relative to openings in the housing body40(e.g., the openings78and80) (step224), and the fittings are threaded into engagement with the housing body40through the adapters (step226).

After structural components of the industrial process transmitter20are assembled, electrical components can be installed. Circuitry (e.g., the field terminal circuitry28, the feedthroughs26, the signal circuitry24and the sensor22) is installed (step228). Any other internal components utilized for particular application can also be installed. Then seals134are installed (step230), and a thread compound of a known type (e.g., thread sealing tape, thread locking compound, or thread lubricant) is applied to the threads on the cover136and/or the housing body40(step232). The cover136is then engaged with the housing body40by threadably securing the cover chassis138to the housing chassis50such that the seals134provide a fluidic seal at the interface of the cover136and the housing body40(step234).

It should be noted that in alternative embodiments the method described above can include additional steps not specifically mentioned. Moreover, particular steps can be omitted, for instance, by substituting the covers42and44for the cover136.

A number of alternative embodiments of an industrial process transmitter are possible according to the present invention.FIG. 14is an exploded perspective view of an alternative embodiment of an industrial process transmitter20′ during assembly, andFIG. 15is a perspective view of the industrial process transmitter20′. In the illustrated embodiment, a housing chassis50′ is integrally formed with a neck48′. The neck48′ and the housing chassis50′ can be die cast together from aluminum as a unitary structure. In other respects, the housing chassis50′ and the neck48′ are similar to the housing chassis50and the neck48described above.

A housing skin52′ can be formed from a relatively flat sheet of stainless steel having an arithmetic average surface roughness of approximately 32 Ra or smoother, with a neck feature52N formed thereupon. The neck feature52N can be a generally cylindrical formation with a central opening that has a shape corresponding to that of the neck48′. The neck feature52N can be created using a drawing operation, or any other suitable technique. The housing skin52′ is then positioned about the housing chassis50′. The neck48′ is inserted at least partially into the neck feature52N, such that the neck feature52N generally surrounds and covers the neck48′. The housing skin52′ is wrapped around the housing chassis50′ with opposite first and second ends52X and52Y of the housing skin52′ positioned adjacent to one another. As shown inFIG. 15, a weld joint300is made between the adjacent first and second ends52X and52Y of the housing skin52′, forming a hermetic seal. The weld joint300can be made using tungsten inert gas (TIG) welding, laser welding, or any other suitable process. Opposite ends of the housing skin52′ are rolled to form lips82′ and84′, and a distal end of the neck feature52N is rolled to form a lip302. The lips82′,84′ and302each help to secure the housing skin52′ to the housing chassis50′.

FIG. 16is a cross-sectional view of another alternative embodiment of an industrial process transmitter20″. In the illustrated embodiment, a housing chassis50″ is provided about which a housing skin52″ is positioned. The housing chassis50″ and the housing skin52″ can be configured similar to the housing chassis50and the housing skin52described above. An opening68″ in the housing chassis50″ is threaded, and a generally cylindrical neck chassis48″ is threadably engaged to the opening68″. The neck chassis48″ can be made of aluminum or another suitable material. A neck skin400, which can be made of stainless steel having an arithmetic average surface roughness of approximately 32 Ra or smoother, is positioned about the neck chassis48″. A weld joint402is formed between the neck skin400and the housing skin52″, forming a hermetic seal. The weld joint402can be made using tungsten inert gas (TIG) welding, laser welding, or any other suitable process. A lip404is formed at a distal end of the neck skin400to help secure the neck skin400to the neck chassis48″.

It will be recognized that the present invention provides numerous advantages and benefits. For example, the use of an industrial process transmitter chassis made of a material like aluminum allows for relatively simple and inexpensive die casting techniques to be used with relatively little post-casting machining required due to the configuration of support members on the chassis. Moreover, the use of skins made of a material like stainless steel that covers the chassis allows for relatively good corrosion resistance and hygienic application performance, as well as helping to limit an overall mass of the industrial process transmitter. A skin and chassis industrial process transmitter housing assembly according to the present invention helps to reduce cost and complexity associated with solid stainless steel housings made using investment casting or extensive machining. Additional features and benefits will be appreciated be those of ordinary skill in the art in view of the present disclosure.