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Publication numberUS2433024 A
Publication typeGrant
Publication dateDec 23, 1947
Filing dateApr 27, 1945
Priority dateApr 27, 1945
Publication numberUS 2433024 A, US 2433024A, US-A-2433024, US2433024 A, US2433024A
InventorsJackson Burgess
Original AssigneeBurgess Battery Co
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Freezer alarm and means for energizing same
US 2433024 A
Abstract  available in
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Claims  available in
Description  (OCR text may contain errors)

Dec. 23, 1947. J. BURGESS FREEZER ALARM MEANS FOR ENERGIZING SAME 2 Sheets-Sheet 2 Filed April 27, 1945 (jar/755072,

Z X MM fi y Patented Dec. 23, 1947 FREEZER ALARM AND MEANS nnsnorzme SAME FOR Jaclrson Burgess, Glencoe, 111., assignor, by mesne assignments, to Burgess Battery Company, Freeport, 111., a corporation of Delaware Application April 27, 1945, Serial No. 590,621

This invention relates to alarms for freezers in which perishable goods such as food are preserved and stored in frozen condition for relatively longperiods of time, It relates in particular to an alarm which is responsive to the im- 14 Claims. (Cl. 177-311) proper operation of such a freezer. In the operation of freezers of. this type, one of the most important factors is the detection of a rise in temperature before spoilage of the contents occurs. Such rise in temperature may be due to the failure of the power supply or. of the refrigerating unit, the improper closing of a door or lid, or the inadvertent leaving open of a door or lid. Such freezers usually contain a relatively large amount of goods and if spoilage occurs, the loss may be serious. For that reason, it is desirable to have an alarm which is entirely reliable at all times. 2

In accordance with the present invention, an alarm is provided which is adapted to give a signal upon the occurrence of an undesired rise in temperature within the cabinet of a freezer of the class described. More broadly, an alarm is provided for the detection in any apparatus or location of a rise in temperature to a predetermined value which is below 32" F.

. It is an object of the invention to provide an alarm for freezers which is entirely dependable and adapted to become operative upon an undesired rise in temperature regardless of how long the alarm has remained inactive beforethe rise occurs. This is desirable because freezers frequently operate for long periods of time without the occurrence of an undesirable rise in temperature.

It is another object of the invention to provide an alarm which is independent of the source of power for the operation of the freezer, and will operate without fail regardless of the cause of the undesirable rise in temperature.

It is a further object of the invention to provide an alarm which may be used with a gas fired refrigerator or freezer in locations where electrical energy is not available.

It is a further object of the invention to provide an alarm of the character described which is simple and inexpensive.

It is a further object of the invention to provide means for operating an alarm of the character described which comprises a deferred action primary battery which is adapted .to become operative at any time upon the occurrence of a. rise in temperature to a predetermined point, and does not suffer change or deterioration with the passage of time.

Further objects and advantages will become apparent as the following description progresses, which is to be taken in connection with the accompanying drawings, in which:

Fig. 1 is a view, partly sectional and partly diagrammatic, of an alarm apparatus in accordance with the invention;

Fig. 2 is an enlarged sectional view of the energizing means for the alarm shown in Fig. 1;

Fig. 3 is a diagrammatic view of a modified circuit arrangement for the alarm apparatus of the invention; and

Fig. 4 is a sectional view of a modified form of energizing means for the alarm apparatus of the invention.

In Fig. 1, a portion of the freezer cabinet ill is shown having an opening II for the insertion and removal of the perishablegoods which are to be preserved and stored, which opening is adapted to be closed by a removable lid i2. Some freezers have separate compartments for freezing and storing the goods, and the alarm apparatus may be located in either of such compart ments. The details of the freezer construction are not a part of the invention and will not be.

described. A suitable support is provided, such as the shelf l3 attached to one of the cabinet walls as shown,fsuch support preferably being located at an upper portion of the cabinet in-' terior so as to interfere as little as possible with the storage of goods, and be fairly near to the opening Ii, whereby the apparatus will be readily responsive to the improper closing of opening II or the inadvertent failure to close said opening.

Upon the shelf I3 is supported an energizing unit i5 which is adapted to energize the alarm upon the occurrence of an undesirable rise in temperature within the interior of the cabinet ill. The-energizing unit I5 is connected by means of conductors l8, l1, l8, and I9 to a suitable audible alarm, such as the electrically operated bell 20, and a suitable visible alarm, such as the electrically operated flag 2|. The lower portion 22 of the shaft of the flagv 2| is composed of electromagnetic material, such as soft iron, and the upper portion 23 is composed of nonmagnetic material, such as brass. The lower portion is encircled by the energizing winding 24, which is connected to connectors I1 and 16, the arrangement being such that, upon energization of the winding" 24, a lifting force is applied to the shaft and the flag is raised, A projection 25 upon the shaft cooperates with one end of a latch member 26 which is pivotally mounted near its opposite end upon a stationary member 21 and is sup- 3 ported in a substantially horizontal position by a lug 28 proiecting forwardly (as seen in Fig. 1)

. the passage of air and moisture. The means comfrom stationary member 21. When the flag 2| is raised, projection 25 lifts and passes latch 24, and the latch then drops back upon lug 28. When winding 24 is de-energized and flag 2| descends, projection 25 engages latch 26 and the flag is held in an elevated position until the latch is disengaged manually from projection 25. The said elevated position of the flag 2| may be understood by the attendant as being thealarin position, or means (not shown) may be provided for hiding the flag from view when in its lower position and exposing it to view when in the elevated position. A switch- 29 is arranged in conductor l6 whereby the circuit may be opened if desired.

The alarmenergizing unit i is shown in detail in Fig. 2. It comprises a rectangular open top container 30 closed by a cover 8| which may be joined by crimping its edges to the top edges of the container, whereby the interior of the container is effectively enclosed against the inward and outward movement of air. Container 30 and cover 3| are preferably composed of a highly heat conductive material, such as metal.

Within the container 30 is a second open top container 32 which fits within the exterior container 30 along the sides and bottom and is of lesser height than is the exterior container 30,- as shown. The walls of container 32 are composed of an electrical insulating and electrolyte resisting material, such as phenol-formaldehyde resin, polystyrene resin, cellulose acetate, etc. The container 32 has a, number of transverse partitions 33 extending upwardly from the bottom to a height somewhat less than that of the container walls, as shown. The partition 33 may be integral parts of the container 32.

Within the compartments formed by the partitions 33 are arranged the cells of a deferred action electric battery. Each compartment contains a cell which is composed of cell elements which are in the form of flat plates which rest upon the bottom of the container 32 and are of a width substantially equal to the distance between the interior surfaces of the container walls and are of a height somewhat less than that of the partitions 33. as shown. The elements of each cell comprise, in succession, a cathode 34 which may be composed of carbon, a layer of depolarizing material 35which may be a compressed mixture composed of finely divided manganese dioxide and carbon, 9. layer 36 of electrical insulating and electrolyte resisting -bibulous material, such as porous blotting paper, and an anode 31 composed of magnesium. The elements of each cell are in firm pressure contact with each other. The anode 3'! of one cell is connected to the cathode 34 of the next cell by a conductor 38, which may be welded or soldered to anode 3! and connected to the cathode 34 by first spraying molten metal such as copper. or electroplating asimilar metal, upon the desired portion of the surface of the cathode and then soldering the conductor to the sprayed metal coating. The cells are thereby connected in series.

A terminal conductor 40 is connected to the cathode 34 of the first cell and a second terminal conductor 4| is connected to the anode 31 of the last cell. The conductors 40 and 4| pass through openings in the walls of inner and outer containers 3|] and 32. Means are provided for sealing the openings in the container walls against trical clearance between the parts.

prises a metal eyelet 42 which passes through the openings. The opening 44 in the metal container 30 is larger than the eyelet to provide an elec- Washers 46 and 46, which may be composed of phenol-formaldehyde resin, surround the end portions of the eyelets and are arranged between the flanges of the eyelet and the walls of containers 30 and 32. Preferably, a washer 41 of elastic material, such as the synthetic elastomer sold under the trademark neoprene, is arranged between washer 46 and the surface of outer container 30. The construction is the same for each of the conductors and 4| and said conductors pass through the interior of the eyelets 43. If the conductors do not fill the interior of the eyelets, the spaces may be filled with solder.

The conductors 40 and 4| are connected respectively to conductors 50 and 5| which pass through the wall of cabinet I!) and are electrically insulated therefrom by sleeves B2 and 53 andwashers 54 and 55, composed of a suitable electrical insulating material. The conductors 50 and 5| are, in turn, connected to the conductors l6 and I1 which lead to the alarm signals.

Extending across the interior of outer container 30 and spaced above the inner container 32 is a partition or shelf 56 in the form of a screen or perforated sheet of a material which is resistant to the battery activating composition and preferably has a. relatively high coefficient of heat conductivity, such as iron or steel. 7 The shelf 56 may be soldered, welded or otherwise attached to the walls of container 30. Also extending across the interior of container 30 and suitably attached as by an adhesive, to the top edges of the inner container 32, is a sheet or membrane 51, which is composed of a material adapted to be ruptured by an accumulation of the liquid activating composition, such as paper, regenerated cellulose, polymerized vinyl acetate, or a thin foil of metal, such as magnesium. The attachment between sheet 51 and the edges of container 32 is preferably such as to provide a seal against the passage of moisture from the portion of container 30 above sheet 51 to the portion below.

Upon the shelf 56 rests an envelope 58 composed of frangible material, such as glass, which is substantially filled with the electrolyte or activating composition 69 for the battery. The activating composition 59 is an aqueous solution of an electrolyte compound, such as zinc sulfate, in a concentration such that the solution has a melting point between the normal operating temperature of the interior of the cabinet l0 and 32 F. For most of the freezers intended for domestic use in homes the normal operating temperature is around 0 F., while some of those used in commercial locker establishments operate at a somewhat lower temperature, in the neighborhood of -10 F. For closer control, it is preferable to employ a solution which has a relatively sharp melting point, so that upon a temperature rise to its melting point, melting to the liquid condition occurs relatively rapidly. Such solutions are the 22.5% barium chloride (melting point 173 F.),

19.0% magnesium sulfate (melting oint 25 F.),

and 23.3% sodium chloride (melting point --6.0' F.)

While an eutectic mixture is a preferred form of electrolyte, other aqueous solutions may be used employing a suitable electrolyte compound in a concentration such that the melting point is between the normal operating temperature of the interior of the freezer cabinet and 32 F. Mixtures of electrolyte compounds may be employed to obtain the desired melting point, and the electrolyte compound may be supplemented by other substances which are well known as having the property of depressing the freezing point of water or aqueous solutions, such as alcohol, ethylene glycoi,orthelike.

In the use and operation of the alarm apparatus, the battery unit i is placed upon the shelf i9 and connected in the alarm circuit as described heretofore. The temperature of the battery unit becomes lowered to that of'the interior of the cabinet i0, which may be assumed to be approximately 0 F. During this time the activating liquid 59 becomes frozen to a solid mass and undergoes a considerable expansion in volume. When water freezes, it undergoes an increase in volume equal to approximately 10% of its liquid volume, and the aqueous solutions here involved undergo an expansion which is substantially of the same order. Such expansion causes a rupture of the frangible envelope 58, but freezing begins at the surfaces of the activating composition 59, and a shell of frozen composition is first formed about a liquid interior, and although rupture of the envelope may occur before all of the composition has frozen, the liquid will be retained by the frozen shell and will not escape from the upper compartment of the container 30. After freezing, the activating composition will remain in said upper compartment in a frozen condition until the interior of the cabinet in undergoes an undesirable rise in temperature. This may be caused by failure of the refrigerating unit or of the source of power for the latter, or simply by an improper closing of the lid I2 or the inadvertent failure to close said lid. In any event, upon the occurrence of a rise in temperature to the melting point of the activating composition 59, the latter composition melts and the resulting liquid escapes from they ruptured envelope 58 and passes through the foraminous shelf 56 and accumulates upon supporting sheet 51. The sheet .51 is constructed so as to be ruptured by the weight of the activating composition after suficient of such composition has accumulated upon it to render the battery satisfactorily operative. The time of rupture can be controlled conveniently by regulating the thickness of the sheet 51, or by providing a relatively thick sheet and providing score lines in it so that the sheet is weakened and rupture takes place at such lines after the proper amount of activating composition has accumulated upon the sheet.

Upon rupture of the sheet 51, the activating composition flows downwardly upon the several cells of the battery and is readily absorbed by the bibulous layers 36, and the said layers become the electrolyte spaces for the cells. The layers 35 of depolarizing material also become moistened by the activating composition and the'batterythereupon becomes operative and energizes the alarm signals 20 and 2|. The bell 20 rings until the circuit is broken, which may be accomplished by opening the switch 29 in conductor It. In the same way, flag 2| is raised to its upper position 6 and remains there until the latch 29 is manip lated manually to permit the lowering of the flag. After the alarm has operated, the used battery unit I5 is replaced with a new one.

The alarm apparatus described above is simple and inexpensive and yet is thoroughly dependable, regardless of the length of time which may pass before it is called into operation. The battery unit described performs satisfactorily at the relatively low temperature at which the alarm operates. The battery unit is of the deferred action type and, since it is enclosed by the container 30, moisture does not collectin the electrolyte spaces and cause dissipation of energy. It, therefore,.remains quite unaffected in its abil- .ity to deliver full energy when called upon to operate. In addition, operation of the alarm is independent of the source of power for the refrigerating unitand is not affected by the'failure of such power source.

The alarm apparatus of the present invention is quite sensitive to a rise in temperature. The container 30 is composed of a material having a high coefficient of heat conductivity, preferably metal, whereby'changes in the ambient tempera ture are conveyed promptly to the interior-of the container. The foraminous supporting shelf 56 is also composed of a highly heat conductive material and said changes in ambient temperature are conveyed rapidly to the frangible envelope 58 and thence to the activating composition 59. As a result, any rise in temperature is conveyed quickly to the activating composition and the apparatus is highly sensitive to the temperature conditions which it is desired to detect.

A modification of the alarm apparatus is shown in Fig. 3. In this modification, the conductors 65 and 66 lead from the battery unit contained in the' freezer cabinet, which may be similar to the unit l5 of'Figs. 1 and 2, and are adapted to energize a; relay 61. The alarms 68 and 89, which may be similar to the alarms 20 and 2| shown in Fig. l, are connected in parallel with each other and in series with the relay 6! and a source of electrical energy, which may be the battery 10. Upon energization of the relay by the battery unit within the freezer cabinet, said relay closes the series circuit and energizes the alarm signals 58 and 69. In this modification, the battery unit within the freezer cabinet is not called upon to furnish the energy to operate the alarm signals, but only to energize the relay, and a battery unit of smaller capacity may be used. A switch 1| may be inserted in series connection between the battery 10 and the signals 68 and 59 and in parallel relation with the relay 61. The switch Ii may be closed from time to time to determine whether the battery 10 has retained sufficient energy to operate the signals.

In the modification of the invention illustrated in Fig. 4. a battery unit 89 is provided, which may be similar to the portion of battery unit l5 consisting of the inner container 32 and the cells contained therein. The unit 99 rests upon the bottom of container 90, which has a hinged lid 9| member 95 whereby somewhat more than. half of said cradle extends beyond the end of shelf 92. The cradle member 95 has a partition 98 extending thereacross, said partition having an opening 9! in the bottom portion thereof. Partition 99 divides the cradle into a compartment 98 directly above shelf 92 and a second compartment 99 which projects beyond the end of shelf 92.

Within the compartment 98 is arranged a frangible envelope I99 containing a-quantity of activating composition l9i. Container 99, lld9l, shelf 92 and cradle member 95 are preferably composed of a highly heat conductive material. Conductors I92 and I93 are connected to the terminals of the battery unit 89 and extend through openings in the wall of container 99 and are adapted to be connected to an alarm circuit such as shown in Fig. 1 or Fig. 3.

In the use of the last modification, the battery unit 89 is first inserted in the container 99, the lid 9| being raised for this operation, and the shelf 92 also being raised upon the supporting hinge 93 if required for the passage of the battery unit 89. The parts 9| and 92 and the cradle 95 are then placed in the position shown in Fig. 4 and the frangible envelope I99, containing the activating composition in liquid form, is placed in compartment 99. In this position, the weight of the envelope I99 and activating composition l9l overbalances that of the portion of the cradle member 95 which projects beyond the end of shelf 92 and the cradle member remains in the position shown. The unit is then inserted into the freezer cabinet and connected to the alarm circuit. The activating composition becomes frozen as its temperature drops to that of the interior of the cabinet, and the frangible envelope I99 is fractured. Upon the occurrence of a rise in temperature to the melting point of the activating composition IN, the latter melts and fiows into compartment 98 and through the opening 91in partition 96 and into compartment 99. The arrangement is such that when substantially all of the activating composition has melted, or sufficient thereof to satisfactorily activate the battery unit 89, the weight of the portion of cradle member 95 which projects beyond the pivotal support 94 and its contents overbalances that of the remainder. Thereupon, the cradl member pivots clockwise (as viewed in Fig. 4) upon said support '94 and the activating composition is dumped into the battery unit 89 and serves to activate the latter and render it operative for producing the desired signal.

In the modification shown in Fig. 4, all of the parts of the signal energizing unit are contained in a closed container and moisture does not collect upon the interior thereof to cause frosting which might interfere with its proper operation. The pivoted cradle 95 will, therefore, function properly when called upon to do 50.

Further modifications of the alarm apparatus may be made. For example, the battery need not be of the type specifically described. The anodes may be composed of zinc, aluminum, or other suitable metal, the cathodes may be composed of copper, silver, or other suitable sub-stance, the depolarizing material may be silver chloride or other suitable material, and the activating composition may be different from those described heretofore. An example of a suitable batter is one of the Leclanche type having a zinc anode, a carbon cathode, a depolarizing element composed of a mixture of finely divided manganese dioxide and carbon or graphite and an activating composition composed of an aqueous solution of ammonium chloride and zinc chloride having the proper melting point. The form and mechanical features of the battery may be different from those of the plate type of battery illustrated and described, and a deferred action battery of any suitable form and containing parts of any suitable composition may be employed.

In the battery unit l5, the supporting sheet 51 may be omitted if desired. If this is done, an activating composition having a relatively sharp melting point should be used, such as one of the eutectic mixtures described heretofore, whereby the activating composition is introduced into the battery at a rapid rate when the alarm temperature is reached. Also, while it is preferred to provide the moisture proof seals at the openings in the containers for the passage of conductors 49 and 4|, they may be omitted if desired. Also,

the batter may consist of a single cell or a plurality of cells connected in parallel, instead of in series as shown.

The alarm signal may be of a type different from that described. For example, the energiz ing unit may actuate a solenoid valv which is adapted, upon actuation, to cause the operation of a compressed air signal, such as a whistle. Other forms of signal may be employed.

Only a few examples of the alarm apparatus of the invention are described herein, and it is understood that these are for illustrative purposes and that the invention is not limited thereto, and that other modifications are included within its scope as the latter is set forth in the accompanying claims. The invention is not limited to alarms for freezers but is adapted generally for the detection of an undesired rise in temperature to a predetermined value below 32 F.

What is claimed is:

1. Means for'energizin a work circuit upon rise of temperature to a predetermined value up to 32 F., comprising a substantially closed container, a deferred action battery in said container, a frangible envelope in said container, an aqueous activating composition in said frangible envelope and adapted to rupture said envelope upon freezing, said activating composition having a melting point of approximately said predetermined temperature, means in said container for retaining said activating composition following melting thereof after rupture of said frangible envelope, said retaining means being adapted to release said composition for passage to said battery upon accumulation of a quantity thereof by said retaining means.

2. Means for energizing a Work circuit upon rise of temperature to a predetermined value, comprising a deferred action battery, an aqueous activating composition for said battery having a melting point of approximately saidpredetermined temperature, means for retaining said activating composition outside of said battery, said means being adapted to be ruptured upon freezing of said activating composition.

3. Means for energizing a work circuit upon rise of temperature to a predetermined value, comprising a deferred action battery having positive and negative electrodes, an aqueous activating composition for said battery having a melting point of approximately said predetermined temperature, means for retaining said activating composition out of contact with said electrodes, said retaining means being adapted to be afing composition into contact with said electrodesupon subsequent melting of said activating composition.

4. Means for energizing an alarm signal for a deep freezer alarm, comprising a deferred action battery, an aqueous activating composition for said battery having a melting point of approximately between F. and 32 F., means for retaining said activating composition outside of said battery, said means being adapted to be ruptured upon freezing of said activating composition, and means for conducting said activating composition into said battery upon melting of said activating composition.

5. An energizing unit for an alarm signal for a freezer, comprising a deferred action battery, an aqueous activating composition for said battery having a melting point between approximately 32 F; and the normal operating temperature of the freezer, means for retaining said activating composition outside of said battery, said means being adapted to be ruptured upon freezing of said activating composition.

6. The energizing unit as claimed in claim 5, in which means are provided for delaying delivery of the melted activating composition to the battery until a substantial amount thereof has accumulated.

7. The energizing unit as claimed in claim 5, in which a separating member is arranged between the retaining means and the battery, said separating member being adapted to be ruptured by the accumulation of melted activating composition in contact therewith.

8. The energizing unit asclaimed in claim 5,

in which the retaining means for the activating.

composition is contained in a receptacle the walls of which are composed of a highly heat conductive material, such as metal.

9. The energizing unit as claimed in claim 5, in which an enclosure is provided for the energizing unit which is substantially sealed against the entrance of moisture.

10. A freezer alarm comprising, in combination, a freezer cabinet, an alarm signal outside of said cabinet, an electric supply circuit for said signal, a deferred action battery within said cabinet and operatively associated with said supply circuit, a frangible envelope in said cabinet, an aqueous activating composition for said battery in said envelope and adapted to fracture said envelope upon the expansion of said ac-- tivating composition occurring with freezin thereof, said composition having a melting point between 32 F. and the normal operating temperature of the interior of said cabinet.

11. A freezer alarm, comprising, incombination, a freezer cabinet, an alarm signal outside of said cabinet, a deferred action battery within said cabinet and electrically connected to said signal, an aqueous activating composition for said battery located within said cabinet and outside of said battery, said activating composition be- 10 ing in frozen condition and having a melting point between 32 F. and the normal operating temperature of the interior of said cabinet, a

retaining member for said activating composition, said retaining member being adapted to be ruptured by the accumulation of melted activating comp sition thereagainst and thereby release said activating composition for passage to said battery.

12. A freezer alarm,.comprising, in combination, a freezer cabinet, an alarm signal outside of said cabinet, a deferred action battery within said cabinet and electrically connected to said signal, an aqueous activating composition for said battery located within said cabinet and outside of said battery, said activating composition being in frozen condition and having a melting point between 32 F. and the normal operating temperature of the interior of said cabinet, retaining means for said activating composition adapted to be actuated by the weight of a predetermined quantity of melted activating composition for releasing said activating composition for passage to said battery.

13. A freezer alarm, comprising, in combination, a freezer cabinet, an alarm signal outside of said cabinet, a, deferred action battery within said cabinet and electrically connected to said signal, an aqueous activating composition for said battery located within said cabinet and outside of said battery, said activating composition being in frozen condition and having a melting point between 32 F. and the normal operating temperature of the interior of said cabinet, 9. retaining member for said activating composition, said retaining member being adapted to release said activating composition upon accumulation. of melted activating composition thereagainst.

14. A freezer alarm, comprising, in combination, a freezer cabinet, an alarm signal outside of said cabinet, a deferred action battery within said cabinet and electrically connected to said signal, an aqueous activating composition for said battery located within said cabinet and outside of said battery, said activating composition being in frozen condition and having a melting point between 32" F. and the normal operating temperature of the interior of said'cabinet, and means for delaying delivery of the melted activating composition to said battery until a suflicient quantity thereof has accumulated to render said battery operative.

JACKSON BURGESS.

REFERENCES crrnn The following references are of record in the file of this patent:

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Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US2561943 *Dec 13, 1945Jul 24, 1951Edison Inc Thomas AElectric battery
US2564495 *Feb 27, 1947Aug 14, 1951Burgess Battery CoDeferred action primary battery
US2594879 *Oct 9, 1948Apr 29, 1952Sylvania Electric ProdDeferred-action battery
US2691722 *Nov 8, 1949Oct 12, 1954Ohio Brass CoDragging equipment indicator and a normally nonactivated battery therefor
US2960558 *Oct 9, 1957Nov 15, 1960Union Carbide CorpDry cell
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US3052201 *Dec 11, 1948Sep 4, 1962Union Carbide CorpMounting for heavy duty battery
US3052744 *Oct 7, 1949Sep 4, 1962James W HenryGas displacement activator for deferred action type batteries
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US3095331 *Feb 10, 1960Jun 25, 1963Ever Ready CoGalvanic cells
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US3959787 *May 8, 1975May 25, 1976Lawrence Peska Associates, Inc.Refrigeration alarm
US5041816 *Jul 26, 1990Aug 20, 1991Morrissey Robert LFreezer alarm system with two sensor models
Classifications
U.S. Classification340/585, 340/693.1, 340/588, 62/130, 429/90, 429/113, 340/590
International ClassificationF25B49/00
Cooperative ClassificationF25B49/00
European ClassificationF25B49/00