Thermistor heating device

Abstract

 A thermistor heating device, particularly for heating tablets emanating insecticide substances and/or an evaporating deodorant; the device comprises a ceramic container (10) for a thermistor (15) having a bottom face provided with metal-plated surfaces (16, 17) for electrical contacts (18, 19), positione on the face furtherest away from a heat emanating radiant plate (24); insulating layers (23) are interposed between the thermistor (15) and the above-mentioned metallic plate (21).

Description

[0001] The present invention refers to a thermistor heating device, particularly for heating tablets emanating evaporating insecticide substances and/or deodorants.

[0002] Heating devices for the already-mentioned use, amongst which can be included devices using a thermistor element seated in a special ceramic case closed by a metallic heat-emanating plate are generally known. In the known devices, both of the opposite upper and lower faces of the thermistor that are bound to contact the metal strips connecting to an external source of electrical energy, are conveniently metal-plated to guarantee that electric contact is adequate. Layers of insulated material are then interposed between the metal-plated surface for the upper contact strip and the metallic heat-emanating plate so as to adequately insulate the latter from the heating thermistor. Such positioning of the metal-plated surfaces and of the contacting strips however present some drawbacks in that it does not guarantee that the heat-emanating plate is adequately insulated against electricity, with high risk for the user. In fact, though insulating sheets are placed between the upper contact strip and the metal plate, these sheets cannot be unduly thick for otherwise heat effectiveness and its conduction to the radiating plate would be reduced. To excessively reduce the thickness of the insulating layers or sheets in order to improve the conduction of heat would seriously risk insufficient electrical insulation. It is often necessary, therefore, to compromise between the two opposed exigencies to the detriment of the device's safeness.

[0003] The object of this invention is to provide a thermistor heating device of the type mentioned above, that is capable of satisfying as much as possible the two stated exigencies, that is to say, to guarantee contemporaneously the conduction of a high degree of heat from the thermistor to the metallic radiating plate, and an increased electric insulation whose safeness is far superior to other known devices.

[0004] Another object of the present invention is to provide a thermistor heating device, of the type mentioned, in which the electric contacts are kept notably spaced apart from the metallic surface of the radiating plate which, in this manner, is not subjected to direct voltage even if it can accidentally come into contact with the hands of the utilizer when the apparatus or the heating device is under tension.

[0005] A further object of the present invention is to provide a thermistor heating device, as defined above, that can be easily assembled and that offers the maximum safety.

[0006] According to the invention, therefore, a thermistor heating device has been provided comprising a ceramic case member having a seat for the thermistor closed by a metallic radiating plate, and contact strips protruding from openings through the above-mentioned case member, each of said strips being kept in contact with a corresponding metal-plated portion of the thermistor surface, characterised by the fact that said metal-plated surfaces of the thermistor for the contact strips positioned on a same side of the thermistor facing towards the ceramic case, and by th fact that there is at least on layer of insulating material interposed between said thermistor and the above-mentioned metallic plate.

[0007] The thermistor heating device according to this invention will be described in greater detail hereunder, with reference to the examples of the accompanying drawings, in which:

Fig. 1 shows a top view of the device;

Fig. 2 shows an under view of the device;

Fig. 3 shows a side view;

Fig. 4 shows a sectional view along the line 4-4 of figure 2.

[0008] As shown, the heating device according to the invention comprises a case member 10, in ceramic material, having a bottom wall 11 and lateral walls 12 defining a cavity or seating 14 for a thermistor 15. The thermistor 15, on the side facing towards the bottom wall 11 of the ceramic case 10 has two superficial areas 16 and 17 duly metal-plated, positioned at suitable distance one from the other against which are made to rest respective electric contact strips 18 and 19 to connect the device with an external source of electric power.

[0009] In particular, as shown in the detail of figure 4, each contact strip 18 and 19 comprises an internal part 20 defining a C-shaped spring means suitable to fit between the bottom wall 11 of the ceramic case 10 and the bottom surface of the thermistor 15, and a stem portion 21 protruding from a corresponding opening 22 in the bottom wall 11 of the ceramic case 10.

[0010] The device is completed by one or more sheets 23 of electrically insulating material, for example, in micarta and/or nylon, placed above the seating 14 for the thermistor that adequately insulate the metallic radiating plate 24, on which is normally placed a tablet 25 comprising an insecticidal substance or deodorant for evaporation. The radiating plate 24 also serves to assemble the various parts of the device; in this respect plate 24 comprises four lateral legs 26 which are positioned in contact with and in respective seats outside two parallel walls 12 of the ceramic case 10 and whose extremities 26a are folded and pressed externally against the bottom wall 11 of the ceramic case 10.

[0011] From what has been said and shown in the attached drawings, it is therefore evident that the innovation consists in the particular disposition of the metallic surfaces 16 and 17 on a same face of the thermistor, and in the disposition of the contact strips on the same side allowing an extremely simple assemblage of the entire device. Furthermore, the particular disposition of the contact strips and of the respective metal-plated surfaces of the thermistor allows for maximum security in that between the metallic radiating plate 24, on the one side, and the electric contacts 18, 19, on the opposite side, are placed not only the insulating sheets 23, but also the entire thickness of the thermistore's body 15, that can reach and exceed 4 mm, obtaining in this manner insulation tension values that can exceed 5.000 volts at 3 micro A, unthinkable and unattainable in the traditional devices in which both faces of the thermistor are metal-plated. Consequently, even in cases of perforation or of total destruction of the insulating layers 23, the radiating plate 24 will never be subjected directly to high voltage in that said voltage will be reduced in proportion to the thickness of the thermistor body.

Claims

1. Thermistor heating device comprising a ceramic case member having bottom and side walls (11, 12) defining a seat (14) for a thermistor (15) closed by a metallic heat-radiating plate (24), and contact strips (19) protruding from openings (22) through the above-mentioned case member (10), one end (20) of said contact with a corresponding metal-plated surface (16, 17) of the thermistor (15), characterised by the fact that said metal-plated surfaces (16, 17) of the thermistor (15), are positioned on a same side of the thermistor (15) facing towards the bottom wall (11) of the ceramic case (10) and by the fact that at least one layer (23) of insulating material is interposed between the thermistor (15) and the above-mentioned metallic plate (24).

2. A device according to claim 1, characterised by the fact that the contact strips (14) are protruding from corresponding openings (22) in the bottom wall (11) of the ceramic case (10).

3. A device according to previous claims characterised by the fact that the ends of the contact ends (20) of the said contact strips (19) are in the form of a C-shaped spring, said contac spring (20) being disposed between the ceramic case (10) and the thermistor (15).

Drawing