Chemical apparatus and process disinfecting – deodorizing – preser – Control element responsive to a sensed operating condition
Reexamination Certificate
2001-03-12
2004-08-10
Alexander, Lyle A. (Department: 1743)
Chemical apparatus and process disinfecting, deodorizing, preser
Control element responsive to a sensed operating condition
C422S068100, C436S165000
Reexamination Certificate
active
06773678
ABSTRACT:
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 & 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 sur
Cummings Donald D.
Hockemeyer Todd M.
Lucey R. Todd
Wickens Geoffrey W.
Alexander Lyle A.
Bose McKinney & Evans LLP
Endress + Hauser Conducta Gesellschaft fur Mess und Regelte
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