CA1120984A - Heater for controllably heating liquid and method therefor - Google Patents
Heater for controllably heating liquid and method thereforInfo
- Publication number
- CA1120984A CA1120984A CA000325502A CA325502A CA1120984A CA 1120984 A CA1120984 A CA 1120984A CA 000325502 A CA000325502 A CA 000325502A CA 325502 A CA325502 A CA 325502A CA 1120984 A CA1120984 A CA 1120984A
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- CA
- Canada
- Prior art keywords
- pad
- temperature
- container
- heated
- heating
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B1/00—Details of electric heating devices
- H05B1/02—Automatic switching arrangements specially adapted to apparatus ; Control of heating devices
- H05B1/0227—Applications
- H05B1/023—Industrial applications
- H05B1/025—For medical applications
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61L—METHODS OR APPARATUS FOR STERILISING MATERIALS OR OBJECTS IN GENERAL; DISINFECTION, STERILISATION OR DEODORISATION OF AIR; CHEMICAL ASPECTS OF BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES; MATERIALS FOR BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES
- A61L2/00—Methods or apparatus for disinfecting or sterilising materials or objects other than foodstuffs or contact lenses; Accessories therefor
- A61L2/16—Methods or apparatus for disinfecting or sterilising materials or objects other than foodstuffs or contact lenses; Accessories therefor using chemical substances
- A61L2/18—Liquid substances or solutions comprising solids or dissolved gases
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61L—METHODS OR APPARATUS FOR STERILISING MATERIALS OR OBJECTS IN GENERAL; DISINFECTION, STERILISATION OR DEODORISATION OF AIR; CHEMICAL ASPECTS OF BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES; MATERIALS FOR BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES
- A61L2/00—Methods or apparatus for disinfecting or sterilising materials or objects other than foodstuffs or contact lenses; Accessories therefor
- A61L2/24—Apparatus using programmed or automatic operation
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B3/00—Ohmic-resistance heating
- H05B3/68—Heating arrangements specially adapted for cooking plates or analogous hot-plates
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B2203/00—Aspects relating to Ohmic resistive heating covered by group H05B3/00
- H05B2203/021—Heaters specially adapted for heating liquids
Landscapes
- Health & Medical Sciences (AREA)
- Animal Behavior & Ethology (AREA)
- Public Health (AREA)
- Veterinary Medicine (AREA)
- Epidemiology (AREA)
- Life Sciences & Earth Sciences (AREA)
- General Health & Medical Sciences (AREA)
- Chemical & Material Sciences (AREA)
- General Chemical & Material Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Apparatus For Disinfection Or Sterilisation (AREA)
- Control Of Resistance Heating (AREA)
- Cookers (AREA)
- Resistance Heating (AREA)
- Surface Heating Bodies (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A heater for controllably heating liquid in a container includes a substantially flat, elongated pad which is electrically non-conductive and is adapted to receive the liquid bearing container on one of its sur-faces. An electrical heating device is embedded in the pad and is adapted to heat the end portions of the pad but not a central portion thereby defining heated and non-heated sections, respectively. A first thermostat, associated with the heating device, is in the non-heated section and is adapted to monitor the temperature if the container at its interface with the pad and limit the temperature to which the container can rise during heating. A second thermostat, associated with the heating device, is in the heated section and is adapted to monitor the temperature of the heated section and limit the temperature to which the heated section may rise during heating.
The method includes placing a container with a prescribed amount of liquid on a surface of an electrically non-conductive heating pad having a controllable electrical heating device embedded therein. Heat is applied to the container from the end portions of the pad only, which constitute the heated section thereof, a centrally located portion of said pad being a non-heated section.
The maximum temperature to which the interface of the container and the pad can rise during heating is limited to a first predetermined temperature; the maximum temperature to which the heated section can rise during heating is limited to a second predetermined temperature, the second predetermined temperature being higher than the first predetermined temperature. In this way, the liquid in the container is controllably heated to the desired temperature which is approximately that of the first predetermined temperature.
A heater for controllably heating liquid in a container includes a substantially flat, elongated pad which is electrically non-conductive and is adapted to receive the liquid bearing container on one of its sur-faces. An electrical heating device is embedded in the pad and is adapted to heat the end portions of the pad but not a central portion thereby defining heated and non-heated sections, respectively. A first thermostat, associated with the heating device, is in the non-heated section and is adapted to monitor the temperature if the container at its interface with the pad and limit the temperature to which the container can rise during heating. A second thermostat, associated with the heating device, is in the heated section and is adapted to monitor the temperature of the heated section and limit the temperature to which the heated section may rise during heating.
The method includes placing a container with a prescribed amount of liquid on a surface of an electrically non-conductive heating pad having a controllable electrical heating device embedded therein. Heat is applied to the container from the end portions of the pad only, which constitute the heated section thereof, a centrally located portion of said pad being a non-heated section.
The maximum temperature to which the interface of the container and the pad can rise during heating is limited to a first predetermined temperature; the maximum temperature to which the heated section can rise during heating is limited to a second predetermined temperature, the second predetermined temperature being higher than the first predetermined temperature. In this way, the liquid in the container is controllably heated to the desired temperature which is approximately that of the first predetermined temperature.
Description
The present invention relates to a heater and method for controllably heating liquid in a container, and, more particularly, concerns a heater and a method especially useul in the heating of sterilization and disinfectant solutions which, when heated, become significantly more effective.
Surgical instruments, equipment and accessories which are not disposable require sterilization and/or disinfection before they are usedO One convenient expedient for such sterilization/disinfection is the use of CIDEX* Sterilizing and Disinfection Solution which is manufac-ture~ by Arbrook, Inc., Arlington, Texas. For example, CIDEX* activated dialdehyde solution is prepared and the instruments are placed in a tray for complete emersion in the solution for a desired period of time. Shorter periods of time in the solution will provide disin~ection, while longer periods will provide sterilization of the instruments. The CIDEX* solutions, besides providing the sterilization/disinfection features, are effective at room temperature and safe as well. It has been found9 however, that heating certain types of CIDEX* solution will significantly increase its ability to kill microorganisms which contaminate the instruments and which must be-destroyed to assure a thoroughly sterilized instrument.
One aim of using a heated CIDEX* solution instead of a room-temperature CIDEX* solution, where appropriate, * Registered Trade Mark . ~
38~
is to use the same or similar e~uipment for holding the solution, regardless of its type. For instance, one convenient carrier for a sterllization/disinfection solution is a plastic tray, such as polycarbonate, which may hold up to two gallons (7.57 1.) of the solution.
A specific tray, known as the CX27 tray, manufactured by Arbrook, IncO, Arlington, Texas, is made o~ plastic and has an elongated, rectangular box shape, the top of tJhich is open for placement of the sterilizing solution and the instruments therein. This type of tray is most compatible with the sterilizing solutions which are normally effective at room temperature. However, when this type of tray is heated to increase the temperature for the heated solutions, some problems may arise.
Notably, when the tray is placed on a heating device, the sur~ace temperature of which is fairly consistent throughout, the tray may warp due to its high coefficient of thermal expansion during heating causing it to "high center" when in contact with such a surface. This, accordingly, distorts the temperature of the solution at various places in the tray. Additionally, the temperature of the heating device cannot be excessively high inasmuch as this could cause distortion or melting of the plastic.
Furthermore, the plastic material comprising the tray is a heat insulator which increases the time for warming up the solution in the tray. Since it is a desideratum to use this type o~ tray with both room temperature and heated sterilizing solutions, a heating device has been sought which would provide the necessary compatibility.
Besides over~oming the aforementioned problems, other criteria which the proposed heater must meet include a relatively rapid heat-up time with the ability to reach its ultimate temperature with a minimu~ of overshoot. The final temperature must be held to a tight range to prevent any breakdown of the sterilization/
disinfection solution due to excessive temperatures, ~2~ ARK 39 while maintaining a temperature high enough to insure the increased kill rate of microorganisms. The heater of the present invention satisfactorily solves the prob-lems as described above while meeting the criteria es-tablished for its effective performance.
SUMMARY OF THE INVENTION
One aspect of the present invention is a method of controllably heating liquid in a container. This method comprises placing a contalner having a prescribed amount of liquid therein on a surface of an electrically non-conduc-tive heating pad having a controllable electrical heating means embedded therein. Heat is applied to the container from the end portions of the pad only which constitute the heated section thereof, a centrally located portion of the pad being a non-heated section~ This method further contemplates limiting the maximum temper-ature to which the interface of the container and the pad can rise during heating to a first predetermined temperature, and also limiting the maximum temperature to which the heated section can rise during heating to a second predetermined temperature. ~he second predeter-mined temperature is higher than the first predetermined temperature so that the liquid in the container is controllably heated to the desired temperature which is approximately that of the first predetermined temperature.
The heat limiting steps of the present invention preferably include monitoring the temperature of the container at its interface with the pad in the non-heated section and temporarily removing the applied heat at each instance when the interface temperature reaches the first predetermined temperature. Regarding the heated section, the heat limiting step preferably includes monitoring the temperature of the heated section of the pad and temporarily removing the applied heat at each instance when the heated section temperature ~ ARK 39 reaches the second predetermined temperature. Heat is removed from the container by interrupting the electrical current to the heating de~ice when either the first or the second predetermined temperature is reached.
Another aspect of the present invention is a heater for controllably heating the liquid in a container.
This heater includes a substantially flat, elongated pad which is electrically non-conductive and is adapted to receive the liquid bearing container on one of its surfacesO An electrical heating means is embedded in the pad and is adapted to heat the end portions of said pad but not a central portion, thereby defining heated and non-heated sections, respectively. First temperature sensing means, associated with the heating means, is in the non-heated section and is adapted to monitor the temperature of the container at its interface with the pad and limit the temperature to which the container can rise during heating. Second temperature sensing means, associated with the heating means, is in the heated section and is adapted to monitor the temperature of the heated section and limit the temper-ature to which the heated section can rise during heating, so that liquid in the container is controllably heated to the desired temperature.
In the preferred embodiment of the heater of the present invention, the pad is flexible and is made of silicone rubber. The electrical heating means includes a plurality of electrical resistance heating elements embedded in the pad and lying in a substantially flat plane in the elongate cross-section of the pad. These elements are substantially equally spaced apart from one another and form a pattern to cover the entire cross-section, except for a centrally located portion in the pad. The patterned portion defines a heated section and the centrally located portion (without the heating ~lements) defines a non-heated section.
A flrst thermostat is electrically connected to the resistance elements and is located in the non-heated section. In addition to monitoring the temperature of the container at its interface with the pad, this first 5 thermostat is adapted to interrupt electrical current to the resistance elements when a predetermined temperature of the container interface is reached during heating, this predetermined temperature being the nominal temperature required to heat the liquid in the 10 container. A second thermostat is electrically connected to the resistance elements and is embedded in the pad in its patterned portion. This second thermostat, besides monitoring the temperature of the heated section, is adapted to interrupt electrical current to the 15 resistance elements when a predetermined temperature of the heated section is reached during heating. This predetermined temperature of the heated section is the maximum temperature which the heated section is not to exceed.
This type heater controllably heats the liquid in the container to the desired temperature which is approximately that of the first predetermined temperature.
This heater allows the heated section to reach a certain level before the current is interrupted; thic accordingly 25 imparts heat to the container on the pad. Inasmuch as the predetermined temperature of the heated section is higher than the predetermined ultimate temperature of the container~ the container will eventually, but controllably and progressively, reach the level which 30 is desired.
A further aspect of the present invention is a combination of the heater substantiall~ as described above and a support member which includes a support surface onto which the pad is positioned, and further 35 including restraining means for preventing the pad and the container ~which is placed on top of the heater pad) ~2~913~
from sliding off the support member during use. It is contemplated that the preferable support member will also include a plurality of support legs and an outer wall to serve as load beariny points for the support surface. This preferable support member is fabricated from plastic as an integral, unitary structure.
From the structural standpoint, the heater of the present inventlon is notably different from prior heating devices which may be employed in heating liquid in a con-tainer. For instance, the centrally located non-heated section of the instant heater which includes as isolated thermostat therein are features which, inter alia, cannot be found in prior heating devices exemplified by U.S. Patent Nos. 3,98~,098, 3,790,753, and 3,5~1,753. Accordingly, the specific feat~res of the present heater and the method of controlLably heating liquid in a container reflect an improvement in heating devices, especially for the adaptions which the present invention is capable.
According to a still further aspect of the present invention there is provided a heater for controllably heating liquid in a container comprising: a substantially flat, elongated pad, said pad being electrically non-conduc-tive and adapted to receive said liquid bearing container on one surface thereof, a plurality of electrical resistance heating elements embedded in said pad, said elements lying in a substantially flat plane in the elongate cross-section of said pad and forming a pattern to cover said cross-section along the ends and the side edges of the pad except for a centrally located portion of said pad which is substantially equally spaced inwardly from said end and side edges respec-tively to define a heated and a non heated portion of said pad; first temperature sensing means electrically connected to said resistance elements and located at the container bearing surface of the pad in sai.d non-heated centrally located portion o the pad to monitor the -temperatu~e of said container at its interface with said pad and limit the temperature to which said container can rise during heating, and second temperature sensillg means electrically connected to said resistance elements and embedded i.n said pad in the portion of the pad conta:ininy said heating ele-ments, said second sensin~ means adapted to monitor the temperature of said heated section and limit -the tempera-ture to which said heated section may rise duriny heating, whereby said liquid in said container is controllably heated to the desired temperature.
According to a sti.11 further aspect of the present invention there is provided a method of controllably heating liquid in a container comprising: placing a container having a prescribed amount of liquid therein on a surface of an electrically non-conductive heating pad having a controllable electrical heating means embeclded therein, applying heat to said container from the end portions of said pad only which constitute the heated section thereof, a centrally located portion of said pad being a non-heated section; limiting the maximum temperature to which the in-terface of said container and said pad can rise during heating to a first predetermined temperature; and limiting the maximum te~perature to which said heated section can rise duriny heating to a second predetermined temperature, said second predetermined tempe-rature being higher than the first predetermined -temperature, whereby the liquid in the con-tainer is controllably heated to the desired temperature which is approximately that of the first predetermined temperature.
- 6a -8~
BRIEF DESCRIPTION OF THE DRAWINGS
FIGURE 1 is a perspective view of the preferred heater of the present invention positioned on a support member with a liquid bearing container being heated on one of its surfaces, FIGURE 2 is a perspective view of the preferred heater of the present invention, FIGURE 3 is a cross-sectional view taken along line 3 3 of Figure 2, FIGURE 4 is a cross-sectional view taken along line 4-4 of Figure 2, FIGURE 5 ia a schematic diagram of the electrical components and connections of the heater pad-FIGURE 6 is a pl.an view of the support member Eorsupporting the heater, as illustrated in ~igure l; and - 6b -~' ~ igure 7 is an enlarged cross-sectional view taken along line 7-7 of Figure 6.
DETAILED DESCRIPTION
While this invention is satisfied by embodiments in many different forms there is shown in the drawings and will herein be described in detail a preferred embodiment of the invention, with the understanding that the present disclosure is to be considered as exemplary of the principles of the invention and is not intended to limit the invention to the embodiment illustrated.
The scope of the invention will be pointed out in the appended claims.
Adverting to the drawings, particularly to Figure 1, there is illustrated the preferred heater 10 of the present invention positioned on a supportive base 11.
On the top surface of heater 10 a~d within the upper rim of base 11 is positioned a container 12 which carries liquid L therein. This liquid is controllably heated by the contact of the bottom surface of the container 12 with the upper surface of heater 10~ The controlled heat rise of liquid L is especially suitable for sterilization~disinfection solutions which prepare surgical instxuments S for the surgical operation.
Heater 10 is conveniently connected to an electrical current source by means of a cord 14.
Referring now to Figures 2 4, heater 10 is illustra-ted in detail. The heater is comprised of a substantially flat~ elongated pad 15. ~ad 15 is preferably made of a flexible materiall such as an elastomer and, particularly, silicone rubber, the elastomer material imparting an electrically non-conductive nature to the pad itself.
One of the advanta~es of such a fle~ible pad is its ability to conform to the bottom surface of the liquid bearing container 12 during the heating process. In many instances, container 12 is also plastic, and as a 3~
result of its high coefficient of thermal expansion, has a tendency to warp when heat is applied to it. The flexible nature of pad 15 allows it to conform to the bottom of container 12 if any dimensional defle~ion occurs; additionally, more consisent heat application is achieved by this type of heater inasmuch as more consistent surface-to-surface contact is assured. The electrically non-conductive suface of pad 15 not only provides a slower and more consistent application of heat to the container, but also minimizes the possibility of electrical shorting which may occur in metallic heating devices.
Embedded within pad 15 is an electrical heating device which is comprised of a plurality of electrical resistance heating elements 16. While many different resistance element constructions are feasible, one approach is to spiral one or more fine nickel alloy wires around a glass cord. Depending upon the wattage distribution desired, resistance elements 16 are laid out in a sub5tantially flat plane to form a pattern for such distribution. In this instance, resistance elements 16 lie across the elongate cross-section of pad 15 and are substantially equally spaced apart from one another, in order to produce more uniformity of heat produced. Moreover, the advantage of employing a plurality of electrical resistance elements is that it confines failure, if any, to one element, rather than the entire unit; this in turn prevents a hot spot from developing which wou~d distort the application of heat.
It is noted, especially as seen in Figure 3, that resistance elements are substantially uniformly distri-buted over the entire cross-section except for a centrally located portion, i.e~, the end portions of pad 15 are patterned with resistance elements 16, whereas the central portion intermediate the end 3~ K 39 portions doe~ not inclu~e any resistance elements~ The patterned portion of pad 15 defines a heated section 18, which includes both end portions of the pad, while the centrally located portion defines a non-heated section 19. In order to assure that non-heated section 19 is remote ~rom the influence of resistance elements 16, the wires forming the resistance elements are placed as close as possible to the edge of pad 15 in the central portion o~ the pad. ~esistance elements are connected to electrically conductive pins ox wires 20 which exit from pad 15 through cord 14 for connection to the electrlcal source. ~ suitable connector 21 embodies cord 14 and provides for the internal connection between wires 20 and resistance elements 16.
Also embedded within pad 15 is a thermostat 22, Thermostat 22 is positioned within the patterned, heated section 1~ of the pad and is electrically connected to resistance elements 16 (not shown in Figure 3 for sake of clarity, but schematically diagramed in Figure 5).
It is the purpose of thermostat 22 to directly monitor the temperature of heated section 18 during use of the pad. Only one thermostat is required in heated section 1~, since the pattern of resistance elements 16 will establish a temperature substantially equal in both end portions of the padO Thermostat 22 is selected for operation at a specific temperature. When that temperature of heated section 18 is reached, thermostat 22 operatively responds to interrupt the electrical current to resistance elements 16. This effectively limits the maximum temperature to which heated section 1~ can rise during heating; of course, there may be a slight overshoot of the maximum ox control tempera~ure of thermostat 22 due to the thermal momentum provided by the heating elements. However, once the initial overshoot has been passed and thermal momentum diminished, a quality thermostat can control the temperature to within a few degrees of its programmed temperature.
Accordingly, the surface temperature o~ pad 15 is effectively controlled so that an excessive amount of heat cannot be applied to the container during the heating operation.
Another thermostat 24 is electrically connected to resistance elements 16, but this one is located in non-heated section 19, a remote distance from resistance elements 16. Thermostat 24 is positioned in non-heated section 19 so that its temperature controlling surface 25 is preferably substantially flush with the surface of pad 15 onto which container 12 is to be placed so that it may contact thermostat 24 during heating. It is the purpose of thermostat 24 to monitor the temperature of container 12 at its interface with pad 15. When the contxol temperature of thermostat 24 is reached, it operatively responds to interrupt the electrical current to resistance elements 16. This control temperature limits the maximum temperature to which the container can xise during the heating opexation and is the nominal temperature required to heat the liquid in container 12 to the desired temperature. Once again, there may be an initial over-shoot of the thermostatically controlled temperature due to thermal momemtum, but this is effectively controlled to within a few degrees thereafter~
The fabrication of heater pad 15 includes plural resistance elements 16, thermostats 22 and 24 and electri-cal connector 21. Silicone rubber is preferably coated over the aforementioned items to produce a homogeneous, rubbery, electrically non~conductive jacket. Resistance elements 16 and th~rmostat 22 are completely embedded within pad 15, whereas thermostat 24 is covered with an electrically non-conductive potting compound 26 to protect its electrical connections. This type of heater pad, with the specific structural configuration and arrangement may be manufactured according to procedures employed by Watlow Electric Manufacturiny Company, St. Louis, Missouri.
Figure 5 schematically illustrates that thermostaks 22 and 24 are connected in series to resistance elements 16. With this arrangement, when the control temperature of either thermostat is reached during heating, the electrical current between the electrical source and resistance elements 16 is interrupted. This interruption occurs at each instance when a control temperature is attainea and lasts until the overshoot has been passed and the temperature drops down once again to the control temperature. In this regard, the thermostats 22 and 24 will cyclically apply and interrupt electrical current in order to maintain the control temperature within a very tight range of tolerance.
Turning now to Figures 6 and 7, support base 12 is illustrated in detail. Base 11 acts as a supportive member for heater 10, and to that end, includes a support surface 30 onto which the heater is positioned during use. The support surface is substantially flat and is preferably rectangularly shaped so as to conform to the shape of pad 15 of the heater. Surrounding support surface 30, and as part of support base 11, is a rim 31. This rim serves to confine or restrain the heater which rests on support surface 30; in this regard, the heater is prevented from sliding off the support surface during use. ~im 31 is also sufficiently high enough to extend a short distance higher than the heater pad. Thus, when container 12 is placed on the heater pad, rim 31 also sexves as a restraining device to prevent the container from moving off the heater pad or the support base (this is best seen by referring to Figure 1).
As rim 31 tapers away from support surface 30, it forms an outer wall 32. Both outer wall and support legs 34 serve as load bearing points for the support surface with the liquid bearing container thereon.
Support legs 34 are, in this instance, circularly shaped indentations at six places in support surface 30. These indentations may be readily formed in the support base during fabrication. It is noted that each support leg 34 includes a hole 35 therethrough.
Holes 35 are preferably included in the support legs, and other places throughout the support base if desired, to act as drain holes to allow solution spills to drain away from the heater pad. To accommodate the type of heater pad as described above, a notch 36 is provided in wall 32 in order to allow cable 14 to extend from the heater; a center hole 38 is provided in support surface 30 to allow the centrally located thermostat 24 sufficient clearance when the pad flatly rests on support surface 30 While support base 11 may be fabricated from many different materials, for ease of manufacture and for minimal expense, it is preferably made from plastic, such as polycarbonate. In this regard, the entire support base may be molded as a unitary struc~ure so that the support surface, rim, support legs and outer wall are all integrally joined.
As mentioned earlier, a typical container for use in sterilization/disinfection procedures may hold up to two gallons (7.57 1.~ of solution. To hold such amount of solution, container 12, in the embodiment being described, has a rectangularly shaped bottom surface approximately 6 x 24 inches (15.2 x 60.g cm.).
Accordingly, pad 15 of the heater is formed slightly larger in order to provide sufficient surface coverage.
The thickness of heater pad 15, in ~is instance, is approximately .25 inch (0~64 cm~). With a heater pad this slze, support base 11 has slightly larger dimensions in order to accommodate the heater pad. The thickness of the molded support base 11 is approximately 1~8 inch (0.32 cm.). It is appreciated that the dimensions of the heater, support base, container and the amount of liquid to be heated are merely exemplary of the embodiment being described, and that many varia-tions in size and shape are within the purview of this invention.
In operation, a container having a prescribed amount of liquid therein, such as two gallons (7.57 1.), is placed on the upper surface of the heating pad essentially as described above. Preferably, the heating pad is positioned on the support base not only for support, but to assure that the heat from the pad is properly transmitted to the container on top of the pad; if the heating pad merely rests on a table or other large mass item, it may act as a heat sink and draw much o the heat away from the container. The electrical current is provided to the heat resistance elements which ~hen start to heat up the pad and transmit heat to the container and the liquid therein. Thermostat 22 in the heated section of the pad is selected, in any exemplary instance, to operati~ely function at 200F (93C), while the thermostat 24 in the non-heated section of the pad is selected to activate at 100F ~38C). Because thermostat 22 is directly in the heated section, the 200 temperature level will be reached therein before the 100 temperature level at the interface of the container and the pad which thermostat 24 detects.
Accordingly, the maximum temperature of the heated section of the paa will be reached before the maximum interface temperature of the container and the pad. At that point, thermostat 22 will limit the surface temperature of the heater pad so as not to exceed the 200F level (except for tolerance overshoots), and thereby constantly maintain the heat at that level.
This is accomplished by cyclically and temporarily interrupting the electrical current to the heating elements within a tight range about the desired temper-ature~ Inasmuch as the heater pad temperature is normally greater than the temperature to which the container must be heated, the container will eventually and progressively heat to its desired temperature, in this case and as an example, 100F. At that instant, thermostat 2~ in the non-heated section, uneffected by any extraneous heat from the heating elements due to its remote position in the heater pad, accurately senses and controls the temperature at the interface of the container and pad. This thermostat 24 acts similarly to thermostat 22 to maintain the container temperature at the operative temperature of the thermostat. Thus, the liquid in the container is controllably heated to the desired temperature. It is understood that the control temperatures of the thermostats may be selected according to many factors including type of liquid to be heated, size and shape of the heater, base support and container, and materials;
also the time frame for heating the liquid also plays a part in determining the control temperature of the respective thermostats.
Thus, there has been provided a method and heater for controllably heating liquid in a container in which heat is applied at a controlled temperature and from specific portions of a heating pad so that the temperature of the container being heated can be monitored accurately without the distorting influence of the heating elements themselves on the temperature reading of the container. This, in turn, provides better correlation between the desired temperature of the container and the actual temperature attained.
Surgical instruments, equipment and accessories which are not disposable require sterilization and/or disinfection before they are usedO One convenient expedient for such sterilization/disinfection is the use of CIDEX* Sterilizing and Disinfection Solution which is manufac-ture~ by Arbrook, Inc., Arlington, Texas. For example, CIDEX* activated dialdehyde solution is prepared and the instruments are placed in a tray for complete emersion in the solution for a desired period of time. Shorter periods of time in the solution will provide disin~ection, while longer periods will provide sterilization of the instruments. The CIDEX* solutions, besides providing the sterilization/disinfection features, are effective at room temperature and safe as well. It has been found9 however, that heating certain types of CIDEX* solution will significantly increase its ability to kill microorganisms which contaminate the instruments and which must be-destroyed to assure a thoroughly sterilized instrument.
One aim of using a heated CIDEX* solution instead of a room-temperature CIDEX* solution, where appropriate, * Registered Trade Mark . ~
38~
is to use the same or similar e~uipment for holding the solution, regardless of its type. For instance, one convenient carrier for a sterllization/disinfection solution is a plastic tray, such as polycarbonate, which may hold up to two gallons (7.57 1.) of the solution.
A specific tray, known as the CX27 tray, manufactured by Arbrook, IncO, Arlington, Texas, is made o~ plastic and has an elongated, rectangular box shape, the top of tJhich is open for placement of the sterilizing solution and the instruments therein. This type of tray is most compatible with the sterilizing solutions which are normally effective at room temperature. However, when this type of tray is heated to increase the temperature for the heated solutions, some problems may arise.
Notably, when the tray is placed on a heating device, the sur~ace temperature of which is fairly consistent throughout, the tray may warp due to its high coefficient of thermal expansion during heating causing it to "high center" when in contact with such a surface. This, accordingly, distorts the temperature of the solution at various places in the tray. Additionally, the temperature of the heating device cannot be excessively high inasmuch as this could cause distortion or melting of the plastic.
Furthermore, the plastic material comprising the tray is a heat insulator which increases the time for warming up the solution in the tray. Since it is a desideratum to use this type o~ tray with both room temperature and heated sterilizing solutions, a heating device has been sought which would provide the necessary compatibility.
Besides over~oming the aforementioned problems, other criteria which the proposed heater must meet include a relatively rapid heat-up time with the ability to reach its ultimate temperature with a minimu~ of overshoot. The final temperature must be held to a tight range to prevent any breakdown of the sterilization/
disinfection solution due to excessive temperatures, ~2~ ARK 39 while maintaining a temperature high enough to insure the increased kill rate of microorganisms. The heater of the present invention satisfactorily solves the prob-lems as described above while meeting the criteria es-tablished for its effective performance.
SUMMARY OF THE INVENTION
One aspect of the present invention is a method of controllably heating liquid in a container. This method comprises placing a contalner having a prescribed amount of liquid therein on a surface of an electrically non-conduc-tive heating pad having a controllable electrical heating means embedded therein. Heat is applied to the container from the end portions of the pad only which constitute the heated section thereof, a centrally located portion of the pad being a non-heated section~ This method further contemplates limiting the maximum temper-ature to which the interface of the container and the pad can rise during heating to a first predetermined temperature, and also limiting the maximum temperature to which the heated section can rise during heating to a second predetermined temperature. ~he second predeter-mined temperature is higher than the first predetermined temperature so that the liquid in the container is controllably heated to the desired temperature which is approximately that of the first predetermined temperature.
The heat limiting steps of the present invention preferably include monitoring the temperature of the container at its interface with the pad in the non-heated section and temporarily removing the applied heat at each instance when the interface temperature reaches the first predetermined temperature. Regarding the heated section, the heat limiting step preferably includes monitoring the temperature of the heated section of the pad and temporarily removing the applied heat at each instance when the heated section temperature ~ ARK 39 reaches the second predetermined temperature. Heat is removed from the container by interrupting the electrical current to the heating de~ice when either the first or the second predetermined temperature is reached.
Another aspect of the present invention is a heater for controllably heating the liquid in a container.
This heater includes a substantially flat, elongated pad which is electrically non-conductive and is adapted to receive the liquid bearing container on one of its surfacesO An electrical heating means is embedded in the pad and is adapted to heat the end portions of said pad but not a central portion, thereby defining heated and non-heated sections, respectively. First temperature sensing means, associated with the heating means, is in the non-heated section and is adapted to monitor the temperature of the container at its interface with the pad and limit the temperature to which the container can rise during heating. Second temperature sensing means, associated with the heating means, is in the heated section and is adapted to monitor the temperature of the heated section and limit the temper-ature to which the heated section can rise during heating, so that liquid in the container is controllably heated to the desired temperature.
In the preferred embodiment of the heater of the present invention, the pad is flexible and is made of silicone rubber. The electrical heating means includes a plurality of electrical resistance heating elements embedded in the pad and lying in a substantially flat plane in the elongate cross-section of the pad. These elements are substantially equally spaced apart from one another and form a pattern to cover the entire cross-section, except for a centrally located portion in the pad. The patterned portion defines a heated section and the centrally located portion (without the heating ~lements) defines a non-heated section.
A flrst thermostat is electrically connected to the resistance elements and is located in the non-heated section. In addition to monitoring the temperature of the container at its interface with the pad, this first 5 thermostat is adapted to interrupt electrical current to the resistance elements when a predetermined temperature of the container interface is reached during heating, this predetermined temperature being the nominal temperature required to heat the liquid in the 10 container. A second thermostat is electrically connected to the resistance elements and is embedded in the pad in its patterned portion. This second thermostat, besides monitoring the temperature of the heated section, is adapted to interrupt electrical current to the 15 resistance elements when a predetermined temperature of the heated section is reached during heating. This predetermined temperature of the heated section is the maximum temperature which the heated section is not to exceed.
This type heater controllably heats the liquid in the container to the desired temperature which is approximately that of the first predetermined temperature.
This heater allows the heated section to reach a certain level before the current is interrupted; thic accordingly 25 imparts heat to the container on the pad. Inasmuch as the predetermined temperature of the heated section is higher than the predetermined ultimate temperature of the container~ the container will eventually, but controllably and progressively, reach the level which 30 is desired.
A further aspect of the present invention is a combination of the heater substantiall~ as described above and a support member which includes a support surface onto which the pad is positioned, and further 35 including restraining means for preventing the pad and the container ~which is placed on top of the heater pad) ~2~913~
from sliding off the support member during use. It is contemplated that the preferable support member will also include a plurality of support legs and an outer wall to serve as load beariny points for the support surface. This preferable support member is fabricated from plastic as an integral, unitary structure.
From the structural standpoint, the heater of the present inventlon is notably different from prior heating devices which may be employed in heating liquid in a con-tainer. For instance, the centrally located non-heated section of the instant heater which includes as isolated thermostat therein are features which, inter alia, cannot be found in prior heating devices exemplified by U.S. Patent Nos. 3,98~,098, 3,790,753, and 3,5~1,753. Accordingly, the specific feat~res of the present heater and the method of controlLably heating liquid in a container reflect an improvement in heating devices, especially for the adaptions which the present invention is capable.
According to a still further aspect of the present invention there is provided a heater for controllably heating liquid in a container comprising: a substantially flat, elongated pad, said pad being electrically non-conduc-tive and adapted to receive said liquid bearing container on one surface thereof, a plurality of electrical resistance heating elements embedded in said pad, said elements lying in a substantially flat plane in the elongate cross-section of said pad and forming a pattern to cover said cross-section along the ends and the side edges of the pad except for a centrally located portion of said pad which is substantially equally spaced inwardly from said end and side edges respec-tively to define a heated and a non heated portion of said pad; first temperature sensing means electrically connected to said resistance elements and located at the container bearing surface of the pad in sai.d non-heated centrally located portion o the pad to monitor the -temperatu~e of said container at its interface with said pad and limit the temperature to which said container can rise during heating, and second temperature sensillg means electrically connected to said resistance elements and embedded i.n said pad in the portion of the pad conta:ininy said heating ele-ments, said second sensin~ means adapted to monitor the temperature of said heated section and limit -the tempera-ture to which said heated section may rise duriny heating, whereby said liquid in said container is controllably heated to the desired temperature.
According to a sti.11 further aspect of the present invention there is provided a method of controllably heating liquid in a container comprising: placing a container having a prescribed amount of liquid therein on a surface of an electrically non-conductive heating pad having a controllable electrical heating means embeclded therein, applying heat to said container from the end portions of said pad only which constitute the heated section thereof, a centrally located portion of said pad being a non-heated section; limiting the maximum temperature to which the in-terface of said container and said pad can rise during heating to a first predetermined temperature; and limiting the maximum te~perature to which said heated section can rise duriny heating to a second predetermined temperature, said second predetermined tempe-rature being higher than the first predetermined -temperature, whereby the liquid in the con-tainer is controllably heated to the desired temperature which is approximately that of the first predetermined temperature.
- 6a -8~
BRIEF DESCRIPTION OF THE DRAWINGS
FIGURE 1 is a perspective view of the preferred heater of the present invention positioned on a support member with a liquid bearing container being heated on one of its surfaces, FIGURE 2 is a perspective view of the preferred heater of the present invention, FIGURE 3 is a cross-sectional view taken along line 3 3 of Figure 2, FIGURE 4 is a cross-sectional view taken along line 4-4 of Figure 2, FIGURE 5 ia a schematic diagram of the electrical components and connections of the heater pad-FIGURE 6 is a pl.an view of the support member Eorsupporting the heater, as illustrated in ~igure l; and - 6b -~' ~ igure 7 is an enlarged cross-sectional view taken along line 7-7 of Figure 6.
DETAILED DESCRIPTION
While this invention is satisfied by embodiments in many different forms there is shown in the drawings and will herein be described in detail a preferred embodiment of the invention, with the understanding that the present disclosure is to be considered as exemplary of the principles of the invention and is not intended to limit the invention to the embodiment illustrated.
The scope of the invention will be pointed out in the appended claims.
Adverting to the drawings, particularly to Figure 1, there is illustrated the preferred heater 10 of the present invention positioned on a supportive base 11.
On the top surface of heater 10 a~d within the upper rim of base 11 is positioned a container 12 which carries liquid L therein. This liquid is controllably heated by the contact of the bottom surface of the container 12 with the upper surface of heater 10~ The controlled heat rise of liquid L is especially suitable for sterilization~disinfection solutions which prepare surgical instxuments S for the surgical operation.
Heater 10 is conveniently connected to an electrical current source by means of a cord 14.
Referring now to Figures 2 4, heater 10 is illustra-ted in detail. The heater is comprised of a substantially flat~ elongated pad 15. ~ad 15 is preferably made of a flexible materiall such as an elastomer and, particularly, silicone rubber, the elastomer material imparting an electrically non-conductive nature to the pad itself.
One of the advanta~es of such a fle~ible pad is its ability to conform to the bottom surface of the liquid bearing container 12 during the heating process. In many instances, container 12 is also plastic, and as a 3~
result of its high coefficient of thermal expansion, has a tendency to warp when heat is applied to it. The flexible nature of pad 15 allows it to conform to the bottom of container 12 if any dimensional defle~ion occurs; additionally, more consisent heat application is achieved by this type of heater inasmuch as more consistent surface-to-surface contact is assured. The electrically non-conductive suface of pad 15 not only provides a slower and more consistent application of heat to the container, but also minimizes the possibility of electrical shorting which may occur in metallic heating devices.
Embedded within pad 15 is an electrical heating device which is comprised of a plurality of electrical resistance heating elements 16. While many different resistance element constructions are feasible, one approach is to spiral one or more fine nickel alloy wires around a glass cord. Depending upon the wattage distribution desired, resistance elements 16 are laid out in a sub5tantially flat plane to form a pattern for such distribution. In this instance, resistance elements 16 lie across the elongate cross-section of pad 15 and are substantially equally spaced apart from one another, in order to produce more uniformity of heat produced. Moreover, the advantage of employing a plurality of electrical resistance elements is that it confines failure, if any, to one element, rather than the entire unit; this in turn prevents a hot spot from developing which wou~d distort the application of heat.
It is noted, especially as seen in Figure 3, that resistance elements are substantially uniformly distri-buted over the entire cross-section except for a centrally located portion, i.e~, the end portions of pad 15 are patterned with resistance elements 16, whereas the central portion intermediate the end 3~ K 39 portions doe~ not inclu~e any resistance elements~ The patterned portion of pad 15 defines a heated section 18, which includes both end portions of the pad, while the centrally located portion defines a non-heated section 19. In order to assure that non-heated section 19 is remote ~rom the influence of resistance elements 16, the wires forming the resistance elements are placed as close as possible to the edge of pad 15 in the central portion o~ the pad. ~esistance elements are connected to electrically conductive pins ox wires 20 which exit from pad 15 through cord 14 for connection to the electrlcal source. ~ suitable connector 21 embodies cord 14 and provides for the internal connection between wires 20 and resistance elements 16.
Also embedded within pad 15 is a thermostat 22, Thermostat 22 is positioned within the patterned, heated section 1~ of the pad and is electrically connected to resistance elements 16 (not shown in Figure 3 for sake of clarity, but schematically diagramed in Figure 5).
It is the purpose of thermostat 22 to directly monitor the temperature of heated section 18 during use of the pad. Only one thermostat is required in heated section 1~, since the pattern of resistance elements 16 will establish a temperature substantially equal in both end portions of the padO Thermostat 22 is selected for operation at a specific temperature. When that temperature of heated section 18 is reached, thermostat 22 operatively responds to interrupt the electrical current to resistance elements 16. This effectively limits the maximum temperature to which heated section 1~ can rise during heating; of course, there may be a slight overshoot of the maximum ox control tempera~ure of thermostat 22 due to the thermal momentum provided by the heating elements. However, once the initial overshoot has been passed and thermal momentum diminished, a quality thermostat can control the temperature to within a few degrees of its programmed temperature.
Accordingly, the surface temperature o~ pad 15 is effectively controlled so that an excessive amount of heat cannot be applied to the container during the heating operation.
Another thermostat 24 is electrically connected to resistance elements 16, but this one is located in non-heated section 19, a remote distance from resistance elements 16. Thermostat 24 is positioned in non-heated section 19 so that its temperature controlling surface 25 is preferably substantially flush with the surface of pad 15 onto which container 12 is to be placed so that it may contact thermostat 24 during heating. It is the purpose of thermostat 24 to monitor the temperature of container 12 at its interface with pad 15. When the contxol temperature of thermostat 24 is reached, it operatively responds to interrupt the electrical current to resistance elements 16. This control temperature limits the maximum temperature to which the container can xise during the heating opexation and is the nominal temperature required to heat the liquid in container 12 to the desired temperature. Once again, there may be an initial over-shoot of the thermostatically controlled temperature due to thermal momemtum, but this is effectively controlled to within a few degrees thereafter~
The fabrication of heater pad 15 includes plural resistance elements 16, thermostats 22 and 24 and electri-cal connector 21. Silicone rubber is preferably coated over the aforementioned items to produce a homogeneous, rubbery, electrically non~conductive jacket. Resistance elements 16 and th~rmostat 22 are completely embedded within pad 15, whereas thermostat 24 is covered with an electrically non-conductive potting compound 26 to protect its electrical connections. This type of heater pad, with the specific structural configuration and arrangement may be manufactured according to procedures employed by Watlow Electric Manufacturiny Company, St. Louis, Missouri.
Figure 5 schematically illustrates that thermostaks 22 and 24 are connected in series to resistance elements 16. With this arrangement, when the control temperature of either thermostat is reached during heating, the electrical current between the electrical source and resistance elements 16 is interrupted. This interruption occurs at each instance when a control temperature is attainea and lasts until the overshoot has been passed and the temperature drops down once again to the control temperature. In this regard, the thermostats 22 and 24 will cyclically apply and interrupt electrical current in order to maintain the control temperature within a very tight range of tolerance.
Turning now to Figures 6 and 7, support base 12 is illustrated in detail. Base 11 acts as a supportive member for heater 10, and to that end, includes a support surface 30 onto which the heater is positioned during use. The support surface is substantially flat and is preferably rectangularly shaped so as to conform to the shape of pad 15 of the heater. Surrounding support surface 30, and as part of support base 11, is a rim 31. This rim serves to confine or restrain the heater which rests on support surface 30; in this regard, the heater is prevented from sliding off the support surface during use. ~im 31 is also sufficiently high enough to extend a short distance higher than the heater pad. Thus, when container 12 is placed on the heater pad, rim 31 also sexves as a restraining device to prevent the container from moving off the heater pad or the support base (this is best seen by referring to Figure 1).
As rim 31 tapers away from support surface 30, it forms an outer wall 32. Both outer wall and support legs 34 serve as load bearing points for the support surface with the liquid bearing container thereon.
Support legs 34 are, in this instance, circularly shaped indentations at six places in support surface 30. These indentations may be readily formed in the support base during fabrication. It is noted that each support leg 34 includes a hole 35 therethrough.
Holes 35 are preferably included in the support legs, and other places throughout the support base if desired, to act as drain holes to allow solution spills to drain away from the heater pad. To accommodate the type of heater pad as described above, a notch 36 is provided in wall 32 in order to allow cable 14 to extend from the heater; a center hole 38 is provided in support surface 30 to allow the centrally located thermostat 24 sufficient clearance when the pad flatly rests on support surface 30 While support base 11 may be fabricated from many different materials, for ease of manufacture and for minimal expense, it is preferably made from plastic, such as polycarbonate. In this regard, the entire support base may be molded as a unitary struc~ure so that the support surface, rim, support legs and outer wall are all integrally joined.
As mentioned earlier, a typical container for use in sterilization/disinfection procedures may hold up to two gallons (7.57 1.~ of solution. To hold such amount of solution, container 12, in the embodiment being described, has a rectangularly shaped bottom surface approximately 6 x 24 inches (15.2 x 60.g cm.).
Accordingly, pad 15 of the heater is formed slightly larger in order to provide sufficient surface coverage.
The thickness of heater pad 15, in ~is instance, is approximately .25 inch (0~64 cm~). With a heater pad this slze, support base 11 has slightly larger dimensions in order to accommodate the heater pad. The thickness of the molded support base 11 is approximately 1~8 inch (0.32 cm.). It is appreciated that the dimensions of the heater, support base, container and the amount of liquid to be heated are merely exemplary of the embodiment being described, and that many varia-tions in size and shape are within the purview of this invention.
In operation, a container having a prescribed amount of liquid therein, such as two gallons (7.57 1.), is placed on the upper surface of the heating pad essentially as described above. Preferably, the heating pad is positioned on the support base not only for support, but to assure that the heat from the pad is properly transmitted to the container on top of the pad; if the heating pad merely rests on a table or other large mass item, it may act as a heat sink and draw much o the heat away from the container. The electrical current is provided to the heat resistance elements which ~hen start to heat up the pad and transmit heat to the container and the liquid therein. Thermostat 22 in the heated section of the pad is selected, in any exemplary instance, to operati~ely function at 200F (93C), while the thermostat 24 in the non-heated section of the pad is selected to activate at 100F ~38C). Because thermostat 22 is directly in the heated section, the 200 temperature level will be reached therein before the 100 temperature level at the interface of the container and the pad which thermostat 24 detects.
Accordingly, the maximum temperature of the heated section of the paa will be reached before the maximum interface temperature of the container and the pad. At that point, thermostat 22 will limit the surface temperature of the heater pad so as not to exceed the 200F level (except for tolerance overshoots), and thereby constantly maintain the heat at that level.
This is accomplished by cyclically and temporarily interrupting the electrical current to the heating elements within a tight range about the desired temper-ature~ Inasmuch as the heater pad temperature is normally greater than the temperature to which the container must be heated, the container will eventually and progressively heat to its desired temperature, in this case and as an example, 100F. At that instant, thermostat 2~ in the non-heated section, uneffected by any extraneous heat from the heating elements due to its remote position in the heater pad, accurately senses and controls the temperature at the interface of the container and pad. This thermostat 24 acts similarly to thermostat 22 to maintain the container temperature at the operative temperature of the thermostat. Thus, the liquid in the container is controllably heated to the desired temperature. It is understood that the control temperatures of the thermostats may be selected according to many factors including type of liquid to be heated, size and shape of the heater, base support and container, and materials;
also the time frame for heating the liquid also plays a part in determining the control temperature of the respective thermostats.
Thus, there has been provided a method and heater for controllably heating liquid in a container in which heat is applied at a controlled temperature and from specific portions of a heating pad so that the temperature of the container being heated can be monitored accurately without the distorting influence of the heating elements themselves on the temperature reading of the container. This, in turn, provides better correlation between the desired temperature of the container and the actual temperature attained.
Claims (11)
1. A heater for controllably heating liquid in a container comprising: a substantially flat, elongated pad, said pad being electrically non-conductive and adapted to receive said liquid bearing container on one surface thereof, a plurality of electrical resistance heating elements embedded in said pad, said elements lying in a substantially flat plane in the elongate cross-section of said pad and forming a pattern to cover said cross-section along the ends and the side edges of the pad except for a centrally located portion of said pad which is substantially equally spaced inwardly from said end and side edges respectively to define a heated and a non heated portion of said pad, first temperature sensing means electrically connected to said resistance elements and located at the container bearing surface of the pad in said non-heated centrally located portion of the pad to monitor the temperature of said container at its interface with said pad and limit the temperature to which said container can rise during heating; and second temperature sensing means electrically connected to said resistance elements and embedded in said pad in the portion of the pad containing said heating elements, said second sensing means adapted to monitor the temperature of said heated section and limit the temperature to which said heated section may rise during heating, whereby said liquid in said container is controllably heated to the desired temperature.
2. A heater as defined in claim 1 wherein said first temperature sensing means is a first thermostat adapted to interrupt electrical current to said resistance elements when a predetermined temperature of said container interface is reached during heating, said predetermined temperature being the nominal temperature required to heat said liquid in the container.
3. A heater as defined in claim 1 wherein said second temperature sensing means is a second thermostat adapted to interrupt electrical current to said resistance elements when a predetermined temperature of said heated section is reached during heating, said predetermined temperature being the maximum temperature which said heated section is not to exceed.
4. A heater as defined in claim 1 wherein said pad is flexible.
5. A heater as defined in claim 3 wherein said first thermostat is operatively responsive at a temperature less than the operatively responsive temperature of said second thermo-stat.
6. A heater as defined in claim 4 wherein said flexible pad is made of silicone rubber.
7. In combination with the heater of claim 1, a support member having a support surface onto which said pad is positioned, and restraining means for preventing said pad and said container from sliding off said support member.
8. A method of controllably heating liquid in a container comprising: placing a container having a prescribed amount of liquid therein on a surface of an electrically non-conductive heating pad having a controllable electrical heating means embedded therein, applying heat to said container from the end portions of said pad only which constitute the heated section thereof, a centrally located portion of said pad being a non-heated section, limiting the maximum temperature to which the interface of said container and said pad can rise during heating to a first predetermined temperature, and limiting -the maximum temperature to which said heated section can rise during heating to a second predetermined temperature, said second predetermined temperature being higher than the first predetermined temperature, whereby the liquid in the container is controllably heated to the desired temperature which is approximately that of the first predetermined temperature.
9. A method as defined in claim 8 wherein the limiting of said interface temperature includes monitoring the temperature of said container at its interface with said pad in said non-heated section and temporarily removing said applied heat at each instance when said interface temperature reaches said firs-t-predetermined temperature.
10. A method as defined in claim 9 wherein the limiting of said heated section temperature includes monitoring the temperature of the heated section of said pad and temporarily removing said applied heat at each instance when said heated section temperature reaches said second predetermined temperature.
11. A method as defined in claim 10 wherein said heat is removed from said container by interrupting electrical current to said heating means when either said first or said:
second predetermined temperature is reached.
second predetermined temperature is reached.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US89683778A | 1978-04-17 | 1978-04-17 | |
| US896,837 | 1992-06-11 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1120984A true CA1120984A (en) | 1982-03-30 |
Family
ID=25406930
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000325502A Expired CA1120984A (en) | 1978-04-17 | 1979-04-12 | Heater for controllably heating liquid and method therefor |
Country Status (10)
| Country | Link |
|---|---|
| AT (1) | AT362522B (en) |
| BE (1) | BE875650A (en) |
| CA (1) | CA1120984A (en) |
| CH (1) | CH640094A5 (en) |
| DE (1) | DE2914754A1 (en) |
| FR (1) | FR2423946A1 (en) |
| GB (1) | GB2019177B (en) |
| NL (1) | NL7902998A (en) |
| SE (1) | SE7903227L (en) |
| ZA (1) | ZA791799B (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| SE8505911L (en) * | 1985-12-13 | 1987-06-14 | Kanthal Ab | Foil elements |
| ITMO20090033A1 (en) * | 2009-02-10 | 2010-08-11 | Balboni Inox Srl | THERMAL STERILIZATION TANK, PARTICULARLY FOR WORKING TOOLS FOR FOOD AND SIMILAR USE |
Family Cites Families (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3231718A (en) * | 1962-02-05 | 1966-01-25 | Akay Corp | Automatic electric food warmer tray |
| US3334414A (en) * | 1962-10-12 | 1967-08-08 | Corning Glass Works | Method of making an electrically heated immersible warming unit |
| US3591753A (en) * | 1969-12-08 | 1971-07-06 | Kem Ind Inc | Planar electrical food warmer |
| US3890486A (en) * | 1973-05-01 | 1975-06-17 | Equipment Dev Corp | Aquarium-tank heating control |
| FR2258594B1 (en) * | 1974-01-23 | 1977-09-23 | Scholtes Ets Eugen | |
| US3982098A (en) * | 1974-12-23 | 1976-09-21 | Trostler Richard M | Heater and control system |
| US4063068A (en) * | 1976-08-12 | 1977-12-13 | Minnesota Mining And Manufacturing Company | Food heating and cooking receptacle |
-
1979
- 1979-04-11 GB GB7912777A patent/GB2019177B/en not_active Expired
- 1979-04-11 DE DE19792914754 patent/DE2914754A1/en not_active Withdrawn
- 1979-04-11 SE SE7903227A patent/SE7903227L/en not_active Application Discontinuation
- 1979-04-12 CA CA000325502A patent/CA1120984A/en not_active Expired
- 1979-04-13 FR FR7909470A patent/FR2423946A1/en not_active Withdrawn
- 1979-04-13 AT AT280879A patent/AT362522B/en not_active IP Right Cessation
- 1979-04-17 NL NL7902998A patent/NL7902998A/en not_active Application Discontinuation
- 1979-04-17 BE BE0/194667A patent/BE875650A/en unknown
- 1979-04-17 ZA ZA791799A patent/ZA791799B/en unknown
- 1979-04-17 CH CH360479A patent/CH640094A5/en not_active IP Right Cessation
Also Published As
| Publication number | Publication date |
|---|---|
| FR2423946A1 (en) | 1979-11-16 |
| ZA791799B (en) | 1980-11-26 |
| ATA280879A (en) | 1980-10-15 |
| GB2019177A (en) | 1979-10-24 |
| BE875650A (en) | 1979-10-17 |
| SE7903227L (en) | 1979-10-18 |
| DE2914754A1 (en) | 1979-10-18 |
| CH640094A5 (en) | 1983-12-15 |
| AT362522B (en) | 1981-05-25 |
| NL7902998A (en) | 1979-10-19 |
| GB2019177B (en) | 1982-08-04 |
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