Electric heating – Heating devices – Combined with container – enclosure – or support for material...
Patent
1996-12-06
2000-06-27
Pelham, Jospeh
Electric heating
Heating devices
Combined with container, enclosure, or support for material...
219432, 219438, 993233, H05B 102, A47F 3156
Patent
active
06080968&
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to liquid heating vessels having electrical heating elements, and in particular in certain aspects to liquid heating vessels having a liquid receiving container and an electrical heating element secured in good thermal contact to the underside of the container. An example of such an arrangement is shown in GB-A-2042269.
Such types of vessel are popular in certain areas of the world, for example in continental Europe, for boiling water for making hot beverages such as tea and coffee. Typically, the liquid receiving container has a base portion at least which is made from a corrosion resistant metal such as stainless steel, which gives the interior of the vessel an attractive appearance and makes it easier to clean. The rest of the vessel may also be of this metal, but could possibly also be of for example a plastics material suitably joined to the base portion. The container conventionally has an external base plate made of a high thermal conductivity metal such as aluminium, to which the element is secured and through which heat is conducted into the container.
It has been common in such vessels to provide thermally sensitive overheat protection means in thermal contact with the element of the vessel which operates to interrupt or reduce the supply of electrical energy to the element in the event of the element overheating, as might happen if the vessel boils dry or if it is switched on without any liquid in it. Typically such overheat protection means comprises a thermally sensitive switch, mounted on the base plate of the vessel, which operates to open a set of contacts in the electrical supply to the element. The switch may, for example, comprise a bimetallic actuator, and be such as to reset automatically upon the container cooling down. Some vessels may also be provided with a one-shot device such as a thermal fuse arranged under the base, which senses a dangerous overheating of the vessel and must be replaced after it operates.
The problem with existing controls of this type is that the temperature of the container base, and thus indirectly the temperature of the element, is sensed effectively only at a single location on the base. Thus if, for example, the vessel is accidentally placed on a work surface so that its base slopes, it is possible that as the vessel boils dry one part of the bottom of the container may still be covered by water, but another be uncovered. This part of the base will therefore overheat first, and if the overheat protecting means is arranged under the part of the vessel base still covered with water, severe overheating of the element may occur locally, which is potentially very dangerous.
The invention from one aspect seeks to provide an improved vessel of the above type.
From a first aspect therefore, the invention provides a liquid heating vessel comprising: a liquid receiving container; an electrical heating element provided on or in thermal contact with the base of said container; a thermally sensitive overheat control arranged to operate in the event of said element overheating so as to interrupt or reduce the supply of electrical energy to the element; said thermally sensitive overheat control comprising at least two thermally responsive sensors arranged in good thermal contact with, and at spaced apart locations on, the base of the container or the element, said sensors individually being operable, in the event of said element overheating so as to interrupt or reduce the supply of electrical energy to the element.
Thus in accordance with the invention, at least two thermally responsive sensors are provided in close thermal contact with the base of the vessel container, which will allow the temperature of the base and element to be detected accurately at at least two spaced apart locations so that should the base or element overheat locally, at least one of the sensors may sense this quickly and operate to interrupt or reduce the power supply to the element, for example opening a set of electrical contacts remote from the sensor through su
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Pelham Jospeh
Strix Limited
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