Abstract:
An apparatus for holding a sensor for sensing the contents of a vessel is provided. The apparatus has an extended position where the sensor is exposed to the contents and a retracted position for cleaning the sensor. The apparatus includes a process connection configured to connect the apparatus to the wall of the vessel. The process connection defines an aperture including a first rim, a second rim angularly displaced from the first rim, and a sidewall extending between the first rim and the second rim. The sidewall is angularly displaced from the first rim by no less than 135 degrees.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application claims priority from U.S. Provisional Patent Application No. 60/190,845, entitled “A Mounting System and Retractable Sensor Holder for Analytical Sensors,” filed Mar. 20, 2000, the disclosure of which is incorporated herein by reference for all purposes. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a retractable sensor holder for immersion-type and flow-type measuring systems, and in particular to a retractable sensor holder that provides an effective cleaning and/or sterilization path for wetted parts of the sensor and sensor holder, while providing substantially flush mounting with the vessel wall. 
     BACKGROUND OF THE INVENTION 
     The pharmaceutical and biotechnology markets employ sensitive processes that require analytical sensors to be mounted in sterile environments. Typically, these environments are closed vessels, wherein fermentation and cell growth cycles can last from a few days to several months. The analytical sensors, for example pH sensors, are sensitive devices that can be affected by the conditions experienced inside the vessels, and must be maintained correctly to ensure adequate performance. Fouling from proteins will cause drift and biomass penetrating the electrode reference system will over time cause some offsets. Harsh cleaning cycles that would otherwise destroy pH electrodes require users to manually remove them prior to commencing with vessel cleaning. 
     Conformance to specific industry standards is often required to ensure the proper cleaning and sterilization of the vessels and the sensors. For example, ASME Bioprocessing standard 1997 &amp; 3-A recommendations (“the 3A Standards”), which are incorporated herein by reference for all purposes, have been developed by/for producers of meat, milk and eggs and are still the standards by which most food and beverage producers gage their equipment for suitability. Meat, milk and eggs are considered to be “worst case” for bacterial growth. If equipment follows the standards for these products, then producers properly using the equipment can be assured that the equipment will not add to their bacterial problems. Producers of other foods with less bacterial risk may thus choose how much of the standards to employ based upon what they feel they need. However, some users may ask for even further requirements, such as better surface finishes, etc. 
     In general, the 3A Standards assume that equipment will meet sanitation requirements by at least one of two methods (even though some users will demand both): “mechanical cleaning” (often called by users as “clean-in-place” or “CIP”), and “removable for cleaning.” In the latter case, equipment must be easily removable (i.e., require no tools to remove) so that an operator or quality assurance or regulatory inspector can routinely pull out sensors, inspect them for cleanliness, and clean them if necessary, before re-inserting them into the process. In the case of mechanical cleaning, the idea is that procedures carried out within the process itself can clean the installed sensors—with no need to pull them out. In general, this method requires such things as very smooth surface finishes and no acute angle corners (e.g., angles no less than 135 degrees) where material can build up or where flowing cleaning fluids cannot carry buildup away. Further, using the mechanical cleaning method, the equipment must be able to withstand the process and protect the integrity of the sealed, cleaned process system. For example, it is routine after a food or fermentation batch to clean the system before starting a new batch of similar or different product. To this end, a typical method might be to follow a product batch with hot water, then a caustic solution, then hot water, then a steam-sterilization, and then let the sealed system cool down (which creates a vacuum situation). 
     Regardless of which method is employed, under the 3A Standards anytime a “seal” is exposed to the process it must be an O-ring (i.e., not a flat gasket) that is acceptable for contact with food and it must be removable/replaceable by the operator each time the sensor is removed/replaced. Furthermore, all other materials of construction must be acceptable for contact with food, normally stainless steel (300 series or better) or TEFLON™. FDA approved food contact materials are listed in Title 21 of the United States Code of Federal Regulations (“21 CFR”), which is incorporated herein by reference for all purposes. Additionally, ASME BPE1997, which is also incorporated herein by reference for all purposes, sets out requirements for easy to clean tank and process connections. It is also noted that there are alternative sanitary standards being developed which seek not to assume cleanliness based upon theoretical design guidelines like the 3A Standards, but rather to actually test equipment with introduction of bacteria and media, cleaning, retesting, etc. 
     FIG. 1 shows a typical prior art 25 mm process connection or weld spud  1 . The historical approach to meeting the various sanitary requirements has become known as the 25 mm side port coupling or 25 mm weld spud, and is commonly used today for pH and dissolved oxygen sensors. The 25 mm weld spud  1  is generally tubularly shaped. In this approach, a “stationary” sensor (not shown) is mounted to a tank wall  2  via the 25 mm weld spud  1 . The sensor is held in place within the 25 mm weld spud  1  by a thread coupling  4 . The sensor is outfitted with an O-ring that forms a fluid tight seal between the sensor and the inside of the 25 mm weld spud  1 . With the sensor mounted in the 25 mm weld spud  1 , the sensor will typically be steam sterilized at the same time as the inside of the tank. When maintenance is required, the sensor can be removed from the port by disengaging the quick disconnect fitting or unscrewing the coupling nut, respectively. After the sensor is removed, it can then be cleaned and recalibrated or replaced, if necessary. Once maintenance is completed, the sensor is returned to the 25 mm weld spud  1 . The entire tank then undergoes sterilization to ensure that no foreign organisms were inadvertently introduced during the sensor maintenance. However, this approach has some obvious limitations, including: (1) maintenance can only be carried out while the vessel is empty; (2) sensors must be handled and maintained manually; and (3) after maintenance the entire tank needs to be re-sterilized. Moreover, because the generally tubular 25 mm weld spud  1  extends away from the inside of the tank, the interior  3  of the 25 mm weld spud  1  cannot be adequately reached by steam for sterilization and for cleaning. 
     In order to provide more flexibility to users, the concept of “retractable” sensor holders emerged some years ago. The idea was to be able to retract the sensor from the vessel and isolate it from the tank without having to interrupt the process. Maintenance could then be carried out on the sensor while the process continued to run. The object has been to design retractable holders that would fit onto the existing process connections. To this end, many unsuccessful attempts have been made to use the de facto standard 25 mm weld spud in conjunction with sanitary retractable holders. These too have not been successful primarily because not all wetted parts can be adequately reached by steam for sterilization. For example, FIG. 2 shows a typical prior art retractable holder  12  in a retracted, cleaning position. 
     The retractable holder  12  includes a stationary portion  5  and a movable portion  6  which holds a sensor  14 . The stationary portion  5  is connected to a vessel  16  (such as, for example, a tank) by a 25 mm weld spud  18 . In the retracted position, a front cap  20  provides a substantially flush mount with the inside surface  26  of the vessel  16 , and isolates the inside of the retractable holder  12  and the sensor  14  from the inside of the vessel  16 . A cleaner inlet  22  and a cleaner outlet  24  are provided in the retractable holder  12  to introduce cleaning and/or sterilization agents to clean the sensor  14  and the interior of the retractable holder  12 . A pair of O-rings  8 ,  10  are placed between the stationary portion  5  and the movable portion  6  to provide a fluid tight seal. The design provides a substantially flush, cleanable mount with the inside surface  26  of the vessel  16  that facilitates vessel cleaning. However, the cleaning of the sensor  14  and the interior of the holder  12  is still problematic. First, the area between the two O-rings  8 ,  10  cannot be effectively reached during the cleaning process. Also, the diameters of analytical sensors, for example pH electrode sensors, can typically be 12 mm and the inside diameter of the port adapter is only 25 mm. During cleaning, all internal surfaces and seals must be adequately contacted by cleaning agent with sufficient velocity. But channel  28  (the space between the stationary part and the moving part of the retractable holder  12 ) is impracticably narrow. The cleaning agent takes the path of least resistance and flows between the inlet  22  and the outlet  24  with insufficient velocity of the cleaner in the channel  28 . The end result is poor cleaning of the sensor  14  and the area immediately behind the front cap  20 . During sterilization, for example with steam, the same problems are evident. Steam sterilization is typically performed at 120-130° C. for approximately one hour. With steam, the situation is further complicated because steam condensate can become trapped in the area immediately behind the front cap  20 , making it difficult to raise the chamber temperature to the required level for effective sterilization. 
     Alternative designs have been attempted to solve some of the foregoing problems, for example the INTRAC® brand 777-SL Retractable Housing from Mettler-Toledo Process Analytical, Inc. of Wilmington, Mass. This retractable housing has a similar design based on 25 mm port couplings and O-rings, but it differs in that the sensor shaft is retracted further back into the chamber and it has multiple inlets and outlets for cleaning and sterilization agents. However, information from independent tests show that while drainability of steam condensate was better, the interior chamber of the retractable holder could still not be effectively sterilized or cleaned. Moreover, this retractable holder does not provide a flush in-vessel surface with the inside surface of the vessel to facilitate vessel cleaning. 
     Another alternative design is to use a retractable holder which requires a process connection that is much wider than the defacto standard 25 mm port connection, for example, the Endress+Hauser type CPA465-F retractable holder (“CPA465-F”). The CPA465-F provides enough room for all internal surfaces of the chamber and the process wetted sensor shaft to be adequately reached for cleaning and sterilization. The wider body process connection allows steam and cleaning agents to reach all the way down to the sensor and the back of the probe seal. Up to this point the CPA465-F has been available with industry standard process connections including the 2 inch TRI-CLAMP™, APV™ and VARIVENT™ quick disconnect type fittings (see Endress+Hauser Technical literature TI 146 C/24/ae). These process connections are most ideally suited to pipeline type installation. The manufacturers of the APV™ and VARIVENT™ fittings have also developed sanitary design flow through chambers for use with their process connections. However, most applications require the sensor to be mounted onto a vessel wall (typically fermenters and reactor vessels). In order to mount the CPA465-F to a vessel wall using the TRI-CLAMP™, APV™ or VARIVENT™ process connections, a nozzle would have to be welded to the side of the vessel at an angle. This is not considered preferred practice for sanitary applications as such nozzles cannot be cleaned easily and disturb the laminar flow often required for ideal mixing within the vessels. A flush mount construction approach is preferred. 
     Thus, there is a need for a retractable holder and process connection that has an effective cleaning and/or sterilization path for wetted parts of the sensor and retractable holder while also being capable of a substantially flush mounting with the interior wall of a vessel for cleaning and/or sterilization of the interior surface of the vessel. 
     SUMMARY OF THE INVENTION 
     In one embodiment, the present invention provides an apparatus for holding a sensor for sensing the contents of a vessel that has a wall. The apparatus has an extended position where the sensor is exposed to the contents of the vessel and a retracted position for cleaning and/or sterilization of the sensor. The apparatus includes a process connection configured to connect the apparatus to the wall of the vessel. The process connection defines an aperture including a first rim, a second rim angularly displaced from the first rim, and a sidewall extending between the first rim and the second rim. The sidewall is angularly displaced from the first rim by no less than 135 degrees. 
     In an alternative embodiment, the present invention provides a process connection for connecting a sensor holder to an opening in a wall of a vessel. The process connection includes a connector configured to be coupled to the sensor holder and further configured to be coupled to the wall of the vessel. The connector defines an aperture including a first rim, a second rim angularly displaced from the first rim, and a sidewall extending between the first rim and the second rim. The sidewall is angularly displaced from the first rim by no less than 135 degrees. 
     The retractable holder and process connection of the present invention incorporate the advantages of the wide body retractable holder with the benefits of a substantially flush mount process connection. In addition, it improves calibration accuracy via improved flow through the “cleaning” chamber, which also sometimes functions as a calibration chamber. The more complete ingress of calibration fluids (buffers), as well as proper rinsing out of other fluids (buffers of different pH value) prior to calibration improves calibration. Further it facilitates better rinse out/blow out of fluids prior to re-introducing the sensor to the process. This results in a retractable holder that provides repeatable and effective cleaning and/or sterilization of the sensor and the holder, while also providing for effective cleaning and/or sterilization of the vessel. 
     The retractable holder and process connection of the present invention addresses the requirements for sanitary operation. It has a retractable design that can be moved between an extended measuring position and a retracted, cleaning position either manually or automatically. It provides a steam sterilizable chamber containing the sensor when the retractable holder is in the retracted, cleaning position. It provides a substantially flush process connection with the interior of the vessel providing a cleanable process connection on the interior of the vessel. 
     The holder enables a sensor, for example a pH, ORP, Conductivity, Turbidity or Dissolved oxygen sensor, to be manually or automatically retracted from a sanitary vessel, to be serviced (cleaned/buffered) or replaced. The new or serviced sensor can then be effectively steam sterilized and be re-inserted into the vessel without contaminating the vessel. The process connection is optimally designed to facilitate its ease of cleaning and sterilization so that the process wetted components of the holder can be effectively cleaned and steamed in place while the vessel is undergoing clean-in-place and sterilization-in-place cycles. 
     These features, among others, make the present invention a viable solution for users who are looking for a product that allows sensors to be inserted (manually or automatically) into a sterile environment (without contamination occurring), while providing a process connection that is also easily cleaned and sterilized from the tank side. No hard to clean nozzles are needed that will disturb the laminar flow profile within tank. The flush connection ensures that the full stroke of the holder is available for insertion into the tank away from possible skin effects that may cause un-homogeneous samples. 
     Additional objects, advantages and novel features of the invention are set forth in the description that follows, and will become apparent to those skilled in the art upon reviewing the drawings and the following description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a typical prior art 25 mm weld spud; 
     FIG. 2 shows a typical prior art retractable holder in a retracted, cleaning position; 
     FIG. 3 shows an exploded cross sectional view of a retractable holder and a process connection according to the present invention in a retracted, cleaning position; 
     FIG. 4 shows an enlarged view of a tapered flare of an aperture of the process connection of FIG. 3; and 
     FIG. 5 shows an assembled cross sectional view of the retractable holder and the process connection of FIG. 3 in an extended, measuring position. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 shows a typical prior art 25 mm weld spud  1  which is discussed above in connection with the background of the invention; and FIG. 2 shows a typical prior art retractable holder  12  in a retracted, cleaning position which is discussed above in connection with the background of the invention. FIG. 3 shows an exploded cross sectional view of a retractable holder  30  and a process connection  32  according to the present invention in a retracted, cleaning position; and FIG. 4 shows an enlarged view of a tapered flare  104  of an aperture  102  of the process connection  32  of FIG.  3 . FIG. 5 shows an assembled cross sectional view of the retractable holder  30  and the process connection  32  of FIG. 3 in an extended, measuring position. Throughout the figures, like parts are identified by like reference numerals. 
     As shown in FIGS. 3 and 5, the retractable holder  30  of the present invention includes a cylindrical outer pipe  34 , and an inner pipe  36  which is mounted for axial displacement in the outer pipe  34  and which is simultaneously intended to receive a measuring sensor at a sensor chamber  38 . The outer pipe  34  sealingly engages the inner pipe  36  (as discussed further below) in a manner to form multiple chambers: a sterilization chamber  40 , a separation chamber  42 , and a rear pneumatic chamber  44 . 
     The sterilization chamber  40  surrounds the sensor chamber  38 . When the retractable holder  30  is in the extended, measuring position (see FIG.  5 ), the sensor chamber  38  protrudes through the vessel wall  39  into an interior space  41  of the vessel to expose the sensor to the contents of the vessel. When the retractable holder  30  is in the retracted, cleaning position (see FIG. 3) the sensor chamber  38  and the sterilization chamber  40  are separated and isolated from the interior of the vessel. During transition of the inner pipe  36  between the extended and cleaning positions, the interior of the sterilization chamber  40  may be momentarily exposed to the interior of the vessel. 
     A primary form seal  50  sealingly engages between a front cap  51  of the inner pipe  36  and the outer pipe  34  separating the interior of the sterilization chamber  40  from the interior of the vessel when the retractable holder  30  is in the retracted, cleaning position (see FIGS.  3  and  5 ). A rear form seal  52  sealingly separates the sterilization chamber  40  from the separation chamber  42  regardless of whether the retractable holder  30  is in the retracted or extended positions. The retractable holder  30  includes a sterilization chamber inlet  54  and a sterilization chamber outlet  56  which can be used for fluid communication with the interior of the sterilization chamber  40 . 
     The separation chamber  42  separates the sterilization chamber from the pneumatic chamber  44 . The pneumatic chamber  44  includes a first pressure agent connection  46  and a second pressure agent connection  48 . The inner pipe  36  includes a piston-like wider portion  58  which is rigidly connected to the inner pipe  36  and is disposed in the interior of the pneumatic chamber  44  between the first pressure agent connection  46  and the second pressure agent connection  48 . By introducing a pressure agent into the first and/or second pressure agent connections  46 ,  48 , the inner pipe  36  can be subjected to the action of the pressure agent for movement of the inner pipe  36  between the extended, measuring position and the retracted, cleaning position. The outer and inner pipes  34  and  36 , thereby, form sort of a piston-and-cylinder unit ensuring the axial relative movement of the inner pipe  36 , together with the sensor chamber  38 , relative to the outer pipe  34 . The stroke of the inner pipe  36  in the retractable holder  30  can be designed to be controlled by stops or sensors in the separation chamber  42  and/or the pneumatic chamber  44 , or by any other suitable manner. 
     The process connection  32  includes a mounting flange  62 , a process O-ring  64  and a weld spud  66 . The retractable holder  30  includes a mounting flange  60  with one or more fastening locations. The mounting flange  62  is configured to attach to the mounting flange  60  of the retractable holder  30 , such that, when tightly attached, the primary form seal  50  forms a fluid tight seal between the mounting flange  62  and the retractable holder  30 . Each of four holes  70  in the mounting flange  60  are aligned with a respective threaded cavity  72  in the mounting flange  62  and four bolts  71  for attaching the mounting flange  62  to the mounting flange  60 . Alternative fastening arrangements for the retractable holder  30  and the mounting flange  62  should be readily apparent to those skilled in the art, one example being threaded studs. 
     The weld spud  66  is configured to be mounted to the wall of the vessel. The mounting flange  62  is also designed to attach to the weld spud  66 , such that, when tightly attached, the process O-ring seal  64  forms a fluid tight seal between the mounting flange  62  and the weld spud  66 . The process O-ring  64  is attached to the mounting flange  62  in a depression  78  (see FIG.  3 ). Each of four holes  74  in the mounting flange  62  are aligned with a respective threaded cavity  76  in the weld spud  66  and four bolts  80  for attaching the mounting flange  62  to the weld spud  66 . Alternative fastening arrangements for the mounting flange  62  and the weld spud  66  should be readily apparent to those skilled in the art, one example being threaded studs. The fluid tight seal between the retractable holder  30  and the mounting flange  62 , and the fluid tight seal between the mounting flange  62  and the weld spud  66 , results in a fluid tight seal between the weld spud  66  and the retractable holder  30 . 
     The process connection  32  is designed to have the prescribed angles, sealing methods and surface finishes to provide what is referred to in the art as “mechanical cleaning” or “clean-in-place.” To this end, the process connection  32  defines the aperture  102  which runs through the mounting flange  62  and the weld spud  66  (see FIG.  3 ). In the exemplary embodiment described herein, the aperture  102  includes the tapered flare  104  having a first rim  106 , a second rim  108  that intersects the first rim  106  and is angularly displaced from the first rim  106  by a taper angle  114 , and a sidewall  110  that extends between the first rim  106  and the second rim  108 , with the sidewall  110  being angularly displaced from the first rim  106  by a flare angle  112  (see FIGS.  3  and  4 ). When the retractable holder  30  is in the extended, measuring position (see FIG.  5 ), the measuring sensor extends beyond the first rim  106  into the vessel. When the retractable holder  30  is in the retracted, cleaning position the measuring sensor is separated and isolated from the interior of the vessel and does not extend beyond the first rim  106 . 
     FIG. 4 shows an enlarged view of the tapered flare  104  of the process connection  32 . In the exemplary embodiment described herein, it should be appreciated that the taper angle  114  dictates a roughly equivalent mounting angle  116  at which the retractable holder  30 , when installed, is oriented with respect to the vessel wall (see also FIG.  3 ). To comply with the clean-in-place requirements and recommended installation methods for ph electrodes regarding the mounting angle  116 , the taper angle  114  is ideally in the range of 5 to 15 degrees, preferably 5 degrees. Further, to meet the clean-in-place requirements regarding prohibitions against acute angles, the flare angle  112  is preferably no less than 135 degrees. To this end, the sidewall  110  is preferably straight (as shown). However, it is noted that the tapered flare  104  as described herein is merely exemplary and in alternative embodiments the tapered flare  104  may include other suitable taper and/or flare angles, may include a suitable concave sidewall or a suitable convex sidewall, or may be configured in any number of other suitable ways to meet the clean-in-place requirements. 
     Referring to FIGS. 3 and 5, the weld spud  66  also includes a depth stop  118 . The depth stop  118  helps properly position the weld spud  66  for welding to the tank in accordance with the clean-in-place requirements. For example, a typical installation requires cutting a round hole into a tank wall, then setting the weld spud  66  into the hole for welding. The diameter of the cut hole is slightly smaller than the diameter of the stop  118  but large enough to allow the weld spud  66  to rest on depth stop  118 , so that the weld spud  66  does not fall through the hole but penetrates the hole at an appropriate depth. Accordingly, it should be appreciated that the exact position of the depth stop  118  on the weld spud  66  assumes a standard minimum tank wall thickness. For alternate wall thicknesses, the depth stop  118  may be offset as necessary to ensure flushness of the weld spud  66  with the inside the of the vessel. Additionally, installation may require “weld-bead clean-up;” i.e., grinding and polishing of the weld seam along the inside of the tank, in order to meet the clean-in-place requirements. In any event, it is noted that although the depth stop  118  is preferably a ridge or lip around the weld spud  66 , in alternative embodiments the depth stop  118  need not completely surround the weld spud  66 . 
     The retractable holder  30  is designed so that, when the retractable holder  30  is in the retracted, cleaning position, the process wetted moving parts in the sterilization chamber  40  are in complete contact with the fluid introduced through the sterilization chamber inlet  54  and expelled through the sterilization chamber outlet  56 . The fluid introduced through the sterilization chamber inlet  54 , which may be for cleaning, sterilization, or other purposes, is normally introduced at a high velocity. The cleaning solution impacts the rear face of the front cap  51  in the area of the sensor chamber  38  and then travels axially through the sterilization chamber  40  to the sterilization chamber outlet  56 . 
     The process connection  32  is much shorter than the typical 25 mm port coupling type. This allows the sterilization chamber inlet  54  to be positioned for direct cleaning and/or sterilization of the area directly behind the primary form seal  50  and near the sensor tip in the sensor chamber  38 . The cleaning or sterilization agent then moves upwards in a swirling action to exit at the sterilization chamber outlet  56  in a Z-type cleaning path. The measuring probe chamber  38  is in an open lantern design to minimize heat transfer during steam sterilization cycles. 
     The process connection  32  enables the retractable holder  30  to be attached to a vessel such that, when the retractable holder  30  is in the retracted, cleaning position, the front face  100  of the front cap  51  remains “substantially flush;” i.e., substantially in the same plane as the first rim  106  of the tapered flare  104  or spaced apart from the first rim  106  by a distance not greater than about {fraction (3/16)} inches. Additionally, the depth stop  118  preferably provides that the second rim  108  of the tapered flair  104  remains “substantially flush” with the interior of the tank wall; i.e., substantially in the same plane as the interior of the tank wall or penetrating the tank wall by a distance of no more than about {fraction (1/32)} inches. However, it should be appreciated that the distances for the substantially flush mounting of the front face  100  of the front cap  51  with respect to the first rim  106  of the tapered flare  104  and for the substantially flush mounting of the weld spud  66  with respect to the tank wall are merely exemplary, and in alternative embodiments these may be any suitable distances that will not significantly disturb the laminar flow typically required for ideal mixing within these types of vessels in accordance with the clean-in-place requirements. 
     The foregoing description of the invention is illustrative only, and is not intended to limit the scope of the invention to the precise terms set forth. Although the invention has been described in detail with reference to certain illustrative embodiments, variations and modifications exist within the scope and spirit of the invention as described and defined in the following claims.