FIELD OF THE INVENTION

The invention relates to a heating tube, comprising a tube and two resistance wires for generating heat during operation of the heating tube.

The invention furthermore relates to a device for heating items, particularly food items, comprising an accommodation area for accommodating the items to be heated, and at least one heating tube for supplying heat to the accommodation area during operation of the device, and also to an electrical circuit comprising an electrical power source and at least one heating tube.

BACKGROUND OF THE INVENTION

In many types of devices, including many types of kitchen appliances such as cooking devices, there is a need for having one or more heating elements. A commonly known type of heating element is a heating tube comprising a tube and a resistance wire which is mounted in or on the tube. The resistance wire is made of an electrically conducting material such as a metal, whereas the tube is made of an electrically insulating material, which may be glass, ceramic or quartz, for example. The resistance wire may be spirally wound around the tube, but it is also possible for the resistance wire to be arranged inside the tube.

The resistance wire is adapted to be connected to an electrical power source. When an electrical current is flowing through the resistance wire, the resistance wire gets hot and emits infrared heat radiation. Depending on the resistive value of the resistance wire, a specific heating energy can be provided. In general, assuming a certain standard voltage, a lower resistive value involves a higher level of heating power.

Heating tubes are quite simple and cheap heating elements, on the basis of which heating tubes are suitable to be used in cooking devices such as grills. However, a major disadvantage associated with the use of heating tubes is that an adjustment of the heating power cannot be done in an easy and cheap way. The only way to control the power is using a plurality of heating tubes and perform appropriate switching actions such as to realize different arrangements of the heating tubes and/or different numbers of heating tubes which are switched on in order to vary a consumption of electrical current. For example, two identical heating tubes may be used, so that it is possible to realize three power levels, namely a maximum power level when the heating tubes are arranged in parallel and are both switched on, a 50 % power level when only one of the heating tubes is switched on, and a 25 % power level when the heating tubes are arranged in series. With reference to this example, more possibilities of varying the power level can be realized by using different heating tubes with different resistance values and/or by using a higher number of heating tubes. In any case, a minimum number of two heating tubes has to be used for obtaining some form of power control. Power control between 50 % and 100 % is not possible when two heating tubes with the same resistance value are used. As mentioned in the foregoing, a 50 % power level can be achieved by switching on only one of the two heating tubes, but doing so involves an uneven heat distribution.

SUMMARY OF THE INVENTION

There is a need for providing a radiation grill in which heating tubes are used in a side arrangement with respect to a grilling area for accommodating food items to be heated, instead of an arrangement in which the heating tubes are located right below the grilling area, and in which, as a consequence, it may happen that the heating tubes get spoiled by grease and/or other fluids dripping from the food items through a grid for supporting the food items, and that smoke is generated during operation. In particular, it is desirable to use two heating tubes in the grill, one heating tube at one side of the grilling area, and another heating tube at an opposite side of the grilling area, wherein the heating tubes may be arranged alongside opposite sides of a drip tray arranged right underneath the grilling area. In order to still realize efficient use of heat in this arrangement, it is a practical option to use a reflector with each of the heating tubes for directing the heat towards the grilling area.

However, in this option, it is only possible to use one heating tube per side in order to guarantee uniform heat distribution in the grilling area, so that it is not possible to have adequate power control, wherein it is even impossible to vary the power level between 50 % and 100 %, as explained in the foregoing.

It is an object of the invention to provide a solution to the problems associated with the prior art. In particular, it is an object of the invention to provide a way for controlling a power level between 50 % and 100 % in a radiation grill comprising two heating tubes in a side arrangement with respect to a grilling area as mentioned in the foregoing.

The object of the invention is achieved by providing a heating tube comprising a tube, a first resistance wire associated with the tube for generating heat during operation of the heating tube, and a second resistance wire associated with the tube for generating heat during operation of the heating tube, wherein both the first resistance wire and the second resistance wire have electrical connections arranged at their ends for electrically connecting the resistance wire in an electrical circuit, wherein at least one of the electrical connections of the first resistance wire and at least one of the electrical connections of the second resistance wire, respectively, are separate from each other, wherein the first resistance wire is arranged at one of an outer surface and an inner surface of the tube, and wherein the second resistance wire is arranged inside the tube.

According to the invention, a heating tube comprises two resistance wires which are both associated with a tube, and which are both suitable to be used for generation of heat. On the basis of having two resistance wires, more possibilities are obtained with respect to known situations when it comes to varying a power level of the heating tube, by varying a way in which the resistance wires are connected and/or varying the number of resistance wires which are switched on, among other things. Hence, the invention provides a possibility of still having a relatively simple and cheap heating element, wherein a desired extent of variability of a power level of the heating element is obtained on the basis of equipping the heating element with a first resistance wire and a second resistance wire. When the invention is applied, there is no need for turning to known options like having a variable resistance for achieving a desired power level control, so that costs can be saved.

It is noted that using two resistance wires in one heating element is known per se. For example, US 2007/012681 Al discloses a heating body including a tube and a heating member inserted into the tube. The heating member includes a first heating member having a relatively high thermal expansion coefficient and a second heating member having a relatively low thermal expansion coefficient. The first and second heating members are coiled predetermined times, wherein the first heating member is disposed at an outside of the second heating member. The first heating member is supported by the second heating member, thereby preventing the first and second heating members from contacting the tube while emitting heat.

A major difference between the heating element known from US 2007/012681 Al and the heating tube according to the invention resides in the fact that in the known heating element, the ends of the first and second heating members are combined for connection to an electrical circuit for powering the heating members, so that the first and second heating members are always switched on or off simultaneously, in a fixed mutual arrangement, wherein there is no possibility of controlling the emission of heat of the heating element other than between 0 % and 100 %. Furthermore, the first and second heating members are arranged very close together, wherein the first heating member is wound around the second heating member, and wherein the first and second heating members extend only at the inside of the tube, whereas according to the invention, the first resistance wire and the second resistance wire are associated with the tube in mutually different ways. Within the framework of the invention, it is also possible for both resistance wires to be arranged inside the tube, but in such case, the first resistance wire is associated with an inner surface of the tube, wherein the second resistance wire extends through the tube at a distance from the inner surface, for example, at a central position in the tube. Also, it is possible for the first resistance wire to be an outer resistance wire associated with an outer surface of the tube. In that case, the second resistance wire may extend through the tube at a distance from the inner surface of the tube, as mentioned, or may be arranged such as to be associated with the inner surface of the tube. In any case, one of the resistance wires is associated with a surface of the tube, wherein it is optional for the other of the resistance wires to be associated with a surface of the tube as well, depending on whether the first resistance wire is an outer resistance wire or an inner resistance wire.

According to the invention, at least one of the electrical connections arranged at the ends of the first resistance wire and at least one of the electrical connections arranged at the ends of the second resistance wire, respectively, are separate from each other. Hence, there is a possibility of connecting the resistance wires in a different way in an electrical circuit, which offers a possibility of switching on and off the resistance wires independently. For example, it may be so that the resistance wires are arranged in series, wherein one electrical connection of the first resistance wire is connected to one electrical connection of the second resistance wire, while another electrical connection of the first resistance wire is connected to an electrical connection of an electrical circuit, and another electrical connection of the second resistance wire is connected to another electrical connection of the electrical circuit. In this configuration, it is possible to operate only one of the resistance wires when there is also a connection to the electrical circuit at the position where the resistance wires are interconnected, so that the other of the resistance wires may be bypassed. For sake of completeness, it is noted that the electrical connections of the resistance wires may simple be free ends of the wires or other areas of the wires which are suitable for being contacted by another electrical component.

Within the framework of the invention, it is possible for the first resistance wire and the second resistance wire to have different electrical resistance. On the basis of a desired maximum power level and desired sublevels, a designer of the heating tube according to the invention may choose resistance values of the resistance wires as appropriate.

In the heating tube according to the invention, the resistance wires may be arranged in series. According to another option, the resistance wires may be arranged in parallel. It is a practical option for both the first resistance wire and the second resistance wire to be spirally wound. For example, in a practical embodiment of the heating tube according to the invention, the first resistance wire is spirally wound around the outer surface of the tube, and the second resistance wire is spirally wound against the inner surface of the tube.

It is noted that DE 20 2005 011 686 Ul discloses a heating tube, comprising a tube and two resistance wires for generating heat during operation of the heating tube.

However, in the known heating tube, both resistance wires are arranged inside the tube, and none of the resistance wires is arranged at the tube, wherein an insulating plate is applied inside the tube for supporting the resistance wires, and wherein the resistance wires are embedded in insulating material inside the tube. Hence, the known heating tube is of a more complex design than the heating tube according to the invention, comprising more components, and is more expensive as a consequence thereof. The invention furthermore relates to a device for heating items, particularly food items, wherein the device may be a radiation grill, for example. In any case, the device comprises an accommodation area for accommodating the items to be heated, and at least one heating tube according to the invention, i.e. a heating tube comprising a first resistance wire and a second resistance wire, for supplying heat to the accommodation area during operation of the device.

In a practical embodiment, the device is equipped with a power connection means adapted to be connected to an electrical power source. In order to have control of a level of heating power in the device, the device may furthermore be equipped with a switching means arranged between the power connection means and the heating tube, wherein the switching means is adapted to assume one of a position for disconnecting the heating tube from the power connection means, a position for connecting both resistance wires of the heating tube to the power connection means, and a position for connecting only one of the resistance wires of the heating tube to the power connection means. By means of the switch, different power levels can be obtained with only one heating tube, wherein the exact value of the levels depends on whether the resistance wires are arranged in series or in parallel, among other things.

Even more possibilities of power control can be obtained when using two heating tubes, wherein each heating tube is of the type according to the invention. This is very practical in a radiation grill, as it is possible to realize an effective heat supply to the accommodation area and an even heat distribution in the accommodation area when one of the heating tubes has a side arrangement with respect to the accommodation area at one side of the accommodation area, another of the heating tubes has a side arrangement with respect to the accommodation area at another side of the accommodation area, and both heating tubes are combined with a reflector for directing heat from the heating tube to the accommodation area. Combining a heating tube comprising two resistance wires with a reflector appears to work surprisingly well, due to the fact that both resistance wires can have an equally advantageous position with respect to the focal point of the reflector, namely when a mutual position of the resistance wires is such that central longitudinal axes of the resistance wires coincide. The two heating tubes may be arranged in parallel, and, assuming that a power connection means is present in the device as mentioned in the foregoing, it is possible to use only one switching means between the power connection means and the heating tubes, wherein the switching means may comprise a dual pole rotation switch, for example. In particular, the switching means can be adapted to assume one of a position for disconnecting the heating tubes from the power connection means, a position for connecting both resistance wires of the heating tubes to the power connection means, a position for connecting only one of the resistance wires of only one of the heating tubes to the power connection means and connecting both resistance wires of another of the heating tubes to the power connecting means, and a position for connecting only one of the resistance wires of the heating tubes to the power connection means. Including the condition in which the heating tubes are switched off, it is possible to have four heating conditions in this way, wherein it is furthermore possible to realize control of emitted heat energy in a range of 50 % to 100 %.

It is noted that a device for heating food items, comprising an accommodation area for acommodating the food items to be heated, and a heating tube comprising two resistance wires, is known from DE 201 19 500 Ul . However, in the known device, the heating tube is of the design in which both resistance wires are located inside the tube of the heating tube, wherein insulating material is applied inside the tube for embedding the resistance wires, and wherein the tube is sealed by means of an insulating plug, wherein the resistance wires are attached to connecting bolts extending through the insulating plug, and wherein the insulating plug is adapted to hold the connecting bolts in a parallel configuration. As is the case with the heating tube as known from DE 20 2005 011 686 Ul, the heating tube known from DE 201 19 500 Ul is of a more complex design than the heating tube according to the invention.

The invention furthermore relates to an electrical circuit comprising an electrical power source and at least one heating tube according to the invention. As has already been explained in the foregoing, various levels of emitted heat of the heating tube can be realized by using a switching means, which may be adapted to assume one of a position for disconnecting the heating tube from the power source, a position for connecting both resistance wires of the heating tube to the power source, and a position for connecting only one of the resistance wires of the heating tube to the power source. Furthermore, for realizing even further extended power control, two heating tubes which are arranged in parallel may be used in the electrical circuit.

The above-described and other aspects of the invention will be apparent from and elucidated with reference to the following detailed description of a heating tube comprising an outer resistance wire and an inner resistance wire, a radiation grill comprising two heating tubes as mentioned, and an electrical circuit of the grill, comprising a switch besides the two heating tubes.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be explained in greater detail with reference to the figures, in which equal or similar parts are indicated by the same reference signs, and in which:

figure 1 diagrammatically shows an embodiment of a heating tube according to the invention, comprising a tube, an outer resistance wire and an inner resistance wire;

figure 2 illustrates how the resistance wires may be spirally wound, wherein the outer resistance wire is wound around the tube, and wherein the inner resistance wire extends through the tube, along a longitudinal axis of the tube;

figure 3 diagrammatically shows components of an embodiment of a radiation grill according to the invention;

figure 4 shows an electrical circuit of the grill, comprising two heating tubes and a switch; and

figures 5 a, 5b and 5 c illustrate three different switching conditions of the electrical circuit.

DETAILED DESCRIPTION OF EMBODIMENTS

Figure 1 shows an embodiment of a heating tube 1 according to the invention, comprising a tube 10, an outer resistance wire 11 which is located at an outer surface 12 of the tube 10, and an inner resistance wire 13 which extends through the tube 10. The resistance wires 1 1, 13 are made of an electrically conducting material such as a metal, while the tube 10 is made of an electrically insulating material such as glass, ceramic or quartz. The tube 10 may have a circular inner circumference and a circular outer circumference, although this is not necessary within the framework of the invention.

Figure 2 illustrates how the outer resistance wire 11 can be spirally wound around the tube 10, and how at least a portion of the inner resistance wire 13 can also be spirally wound. In the shown example, the inner resistance wire 13 extends at a central position inside the tube 10, along a longitudinal axis of the tube 10. With the inner resistance wire 13 in this position, it is not necessary for the other resistance wire 11 to be an outer resistance wire, as it would also be possible for the other resistance wire 11 to be arranged at an inner surface 18 of the tube 10 and still be at a sufficient distance from the inner resistance wire 13 such as to be insulated from the inner resistance wire 13. Another practical embodiment of the heating tube 1 existing within the framework of the present invention involves the outer resistance wire 11 in the configuration as shown and the inner resistance wire 13 wound against the inner surface 18 of the tube 10. In any case, the construction of the heating tube 1 in which at least one of the resistance wires 11, 13 is arranged at the tube 10 requires a minimum of components, wherein embodiments are feasible which do not require an application of insulating material and/or insulating supports or the like inside the tube 10.

At each of its ends, the outer resistance wire 11 is connectable to another electrical component, which may be the inner resistance wire 13 at one of its ends, through an electrical connection (not shown). Similarly, at each of its ends, the inner resistance wire 13 is connectable to another electrical component, which may be the outer resistance wire 11 at one of its ends, through an electrical connection. In any case, it is true that the outer resistance wire 11 and the inner resistance wire 13 may be powered independently, so that different power levels may be realized in operating the heating tube 1 , as will be explained later. In particular, both resistance wires 11, 13 may be switched off, only one resistance wire 11, 13 may be switched on, or both resistance wires 11, 13 may be switched on, wherein the resistance wires 11, 13 may be arranged in series or in parallel.

Figure 3 shows components of an embodiment of a radiation grill 2 according to the invention. In the first place, for supporting food items (not shown) to be grilled, the grill 2 comprises a grid 21, which may be of any suitable design. In the following, it is assumed that the grid 21 has a rectangular circumference, which does not alter the fact that another shape of the circumference is possible, including a circular shape. At a position underneath the grid 21, a drip tray 22 is present, which serves for receiving grease and/or other fluids which may drip from the food items during operation of the grill 2. Preferably, the drip tray 22 is shaped and sized for covering an entire area underneath the grid 21, such as to be capable of receiving all fluids dripping from the grid 21. In that way, the drip tray 22 allows for easy cleaning of the grill 2 after use, wherein it is advantageous for the drip tray 22 to have a removable arrangement in the grill 2, in any suitable manner known per se.

For the purpose of supplying heat to the grid 21 and a grilling area 23 above the grid 21 for accommodating the food items, the grill 2 is equipped with at least two heating elements, which are heating tubes 1 as shown in figures 1 and 2 and as described in the foregoing. Figure 3 illustrates the fact that the heating tubes 1 are arranged in a side

configuration with respect to the grid 21. In particular, the heating tubes 1 are not arranged in an area underneath the grid 21, i.e. an area covered by the drip tray 22, in order to avoid a situation in which the heating tubes 1 may be contaminated with fluids, and to avoid generation of smoke during operation. In the shown example, the heating tubes 1 are arranged right beside the drip tray 22, wherein one heating tube 1 extends along one side of the drip tray 22, and wherein another heating tube 1 extends along an opposite side of the drip tray 22. In order to have an efficient supply of heat in this configuration, each heating tube 1 is combined with a reflector 24 which is arranged such as to reflect heat emitted by the heating tube 1 in the direction of the grid 21 and the grilling area 23 above the grid 21. In figure 3, for sake of illustration, the heat as reflected from each heating tube 1 in the direction as mentioned is indicated by means of a number of lines. The grill 2 may furthermore be equipped with physical barriers 25 such as glass plates for separating the heating tubes 1 from an area which is directly associated with food items, including the grid 21 and the drip tray 22, yet allowing for radiation of heat from the heating tubes 1 and the reflectors 24 to the grid 21 and the grilling area 23.

The heating tubes 1 may be of any suitable shape. In general, a straight shape of the heating tubes 1 may be practical, but it is also possible to have other shapes,

particularly a curved shape, within the framework of the present invention. For example, it may be desirable to have curved heating tubes 1 in case the heating tubes 1 are intended for application in a grill comprising a grid 21 and a drip tray 22 having a circular circumference, so that it is possible to put the heating tubes 1 in an arrangement for surrounding the drip tray 22. In such a case, as an alternative, it is also possible to have one heating tube 1 with an annular shape, or a combination of straight heating tubes 1 and curved heating tubes 1 , for example. In general, if a reflector 24 is used with a heating tube 1, it is practical for the reflector 24 to have a similar shape as the heating tube 1.

In the grill 2, it is desirable to have control of the heating power. Especially, it is desirable to control the heating power in a range of 50 % to 100 %. In the following, with reference to figures 4, 5a, 5b and 5c, it is explained how this can be realized with the two heating tubes 1 and only a single switch 26.

Figure 4 shows an electrical circuit 30 of the grill 2, comprising the two heating tubes 1 and the switch 26 as mentioned, which is a dual pole rotation switch in the shown example. The two heating tubes 1 are arranged in parallel. In each of the heating tubes 1, the outer resistance wire 11 and the inner resistance wire 13 are arranged in series. In figure 4, the resistance wires 11, 13 are diagrammatically depicted as blocks. Furthermore, in figure 4, the electrical connection of the outer resistance wire 11 at the position where the outer resistance wire 11 and the inner resistance wire 13 are connected to each other is indicated by means of reference numeral 14, whereas the other electrical connection of the outer resistance wire 1 1 is indicated by means of reference numeral 15, and the electrical connection of the inner resistance wire 13 at the position where the outer resistance wire 11 and the inner resistance wire 13 are connected to each other is indicated by means of reference numeral 16, whereas the other electrical connection of the inner resistance wire 13 is indicated by means of reference numeral 17. The electrical circuit 30 comprises a means 31 for establishing a connection to a power source such as the mains. In figure 4, this power connecting means is diagrammatically depicted as a block delimited by dashed lines.

In the shown example, the switch 26 is adapted to assume one of four positions. For sake of clarity, in the following explanation of the positions and the switching conditions associated with the positions, the heating tube which is depicted at the left hand side of figure 4 is referred to as first heating tube la, and the heating tube which is depicted at the right hand side of figure 4 is referred to as second heating tube lb. By way of example, it is assumed that in both heating tubes la, lb, the outer resistance wire 11 has a resistance of 48 Ohms and the inner resistance wire 11 has a resistance of 24 Ohms, and that during operation of the grill 2, a voltage of 230 V is applicable. In the first position of the switch 26, as shown most to the left in figure 4 for both arms of the switch 26, and indicated by means of the reference sign a, there is no connection between the heating tubes la, lb and the power connecting means 31, so that a switching condition is realized in which both heating tubes la, lb are switched off and no heat is emitted when the power connecting means 31 are connected to a power source.

In the second position of the switch 26, as indicated by means of the reference sign b in figure 4, both heating tubes la, lb are connected to the power connecting means 31, in such a way that both the outer resistance wire 11 and the inner resistance wire 13 are connected to the power connecting means 31, in each of the heating tubes la, lb. For sake of clarity, this switching condition is illustrated in figure 5 a, wherein it is noted that like in figure

4, the resistance wires 11, 13 are diagrammatically depicted as blocks in this figure. In this switching condition, a total heating power being two times the power associated with a connection in series of the 48 Ohms resistance and the 24 Ohms resistance is realized when the power connecting means 31 are connected to a power source.

In the third position of the switch 26, as indicated by means of the reference sign c in figure 4, both heating tubes la, lb are connected to the power connecting means 31, in such a way that only the outer resistance wire 11 of the first heating tube la is connected to the power connecting means 31 , and both the outer resistance wire 11 and the inner resistance wire 13 of the second heating tube lb are connected to the power connecting means 31. It is possible to only connect the outer resistance wire 11 to the power connecting means 31 by establishing a direct connection between the switch 26 and the outer resistance wire 11 at the position where the outer resistance wire 11 is connected to the inner resistance wire 13, thereby bypassing the inner resistance wire 13. For sake of clarity, the switching condition associated with the third position of the switch 26 is illustrated in figure 5b, wherein it is noted that like in figure 4, the resistance wires 11, 13 are diagrammatically depicted as blocks in this figure. In this switching condition, a total heating power being a sum of the power associated with the 48 Ohms resistance and the power associated with a connection in series of the 48 Ohms resistance and the 24 Ohms resistance is realized when the power connecting means 31 are connected to a power source.

In the fourth position of the switch 26, as shown most to the right in figure 4 for both arms of the switch 26, and as indicated by means of the reference sign d in figure 4, both heating tubes la, lb are connected to the power connecting means 31, in such a way that only the outer resistance wire 1 1 is connected to the power connecting means 31 , in each of the heating tubes la, lb. For sake of clarity, this switching condition is illustrated in figure 5c, wherein it is noted that like in figure 4, the resistance wires 11, 13 are diagrammatically depicted as blocks in this figure. In this switching condition, a total heating power being two times the power associated with the 48 Ohms resistance is realized when the power connecting means 31 are connected to a power source.

On the basis of the foregoing, the power levels associated with the second, third and fourth positions of the switch 26 are determined as follows. For sake of

completeness, it is noted that it is clear that the power level associated with the first position is

0 W = 0 %.

In the fourth position of the switch 26, the total heating power is the highest, namely two times the power associated with the 48 Ohm resistance. In general, the relation between power and resistance is as follows: P = V ² / R, wherein P represents the power, V represents the voltage and R represents the resistance. Hence, the power associated with the

48 Ohms resistance equals 230 ² / 48 = 1,102 W, and the heating power in the fourth position of the switch 26 is 2 * 1,102 = 2,204 W = 100 %.

In the third position of the switch 26, the total heating power is a sum of the power associated with the 48 Ohms resistance, i.e. 1,102 W, and the power associated with a connection in series of the 48 Ohms resistance and the 24 Ohms resistance. In the latter case, a total resistance of 48 + 24 = 72 Ohms is applicable, which yields a power of 230 ² / 72 = 735 W. Hence, the heating power in the third position of the switch 26 is 1,102 + 735 = 1,837 W = 1,837 / 2,204 * 100 % = 83 %.

In the second position of the switch 26, the total heating power is two times the power associated with a connection in series of the 48 Ohms resistance and the 24 Ohms resistance, i.e. two times 735 W = 1,470 W = 1,470 / 2,204 * 100 % = 67 %.

It follows from the foregoing that by means of the switch 26, the level of the heating power can be one of 0 %, 67 %, 83 % and 100 %, wherein 100 % equals 2,204 W in the shown example. Naturally, it is possible to have other switching conditions, for example a condition in which only the inner resistance wire 13 is connected to the power connecting means 31 in at least one of the heating tubes la, lb and/or to have other power levels by choosing other values of the resistance of the outer resistance wire 11 and the inner resistance wire 13, wherein the resistance values of the resistance wires 11, 13 may be different as is the case in the shown example, but may also be chosen such as to be equal. For example, if the resistance value of both resistance wires 11, 13 is 48 Ohms, and the switch 26 of the example is used for realizing the switching conditions as explained in the foregoing, the power level associated with the fourth position of the switch 26 is still 2,204 W, while the power level associated with the third position of the switch 26 is 1,653 W, and the power level associated with the second position of the switch 26 is 1,102 W, on the basis of which control of the power level involves the following levels: 100 %, 75 %, 50 %, and 0 %.

The power level can be controlled by applying two heating tubes la, lb as is the case in the grill 2 as described in the foregoing. That does not alter the fact that power control is also possible by applying only one heating tube 1. For example, assuming that the outer resistance wire 11 has the 48 Ohms resistance and the inner resistance wire 13 has the 24 Ohms resistance, the power level is 1,102 W when only the outer resistance wire 11 is used, the power level is 2,204 W when only the inner resistance wire 13 is used, and the power level is 735 W when the outer resistance wire 11 and the inner resistance wire 13 are used in series, which involves a power control at the following levels for one heating tube: 100 %, 50 %, 33 % and 0 %.

In any case, when the heating tube 1 according to the invention is applied, a possibility of having cheap and easy power control is realized. In practical cases, a switch 26 is used for allowing a user to set one of a number of possible switching conditions of an electrical circuit 30 comprising one or more heating tubes 1. When two heating tubes la, lb are used, a dual pole rotation switch 26 can be applied for having a possibility of setting a operational condition of each of the heating tubes la, lb without having a need of applying two switches 26.

It will be clear to a person skilled in the art that the scope of the invention is not limited to the examples discussed in the foregoing, but that several amendments and modifications thereof are possible without deviating from the scope of the invention as defined in the attached claims. While the invention has been illustrated and described in detail in the figures and the description, such illustration and description are to be considered illustrative or exemplary only, and not restrictive. The invention is not limited to the disclosed embodiments.

Variations to the disclosed embodiments can be understood and effected by a person skilled in the art in practicing the claimed invention, from a study of the figures, the description and the attached claims. In the claims, the word "comprising" does not exclude other steps or elements, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope of the invention.

The invention can be summarized as follows. A heating tube 1 comprises a tube 10, a first resistance wire 11 associated with the tube 10, and a second resistance wire 13 associated with the tube 10, wherein the first resistance wire 1 1 is arranged at one of an outer surface 12 and an inner surface 18 of the tube 10, and wherein the second resistance wire 13 is arranged inside the tube 10. Both the first resistance wire 11 and the second resistance wire 13 serve for generating heat during operation of the heating tube 1 and have electrical connections 14, 15, 16, 17 arranged at their ends, for electrically connecting the resistance wire 11, 13 in an electrical circuit 30. At least one of the electrical connections 14, 15 of the first resistance wire 11 and at least one of the electrical connections 16, 17 of the second resistance wire 13, respectively, are separate from each other, so that it is possible to realize different switching conditions, namely a switching condition in which none of the resistance wires 11, 13 is connected in an electrical circuit 30, a switching condition in which only one of the resistance wires 11, 13 is connected in an electrical circuit 30, or a switching condition in which both resistance wires 11, 13 are connected in an electrical circuit 30, wherein the resistance wires 11, 13 may be arranged in series or in parallel. On the basis of the different switching conditions, different levels of heating power are obtained, so that it is possible to control the heating power according to desire. By using at least two heating tubes la, lb, it is possible to base power control on different combinations of the possible power levels associated with a single heating tube 1.

Having two resistance wires 11, 13 in a heating tube 1 is a cheap and easy solution to the problem of needing to control a level of heating power. Furthermore, the heating tube 1 according to the invention is of a relatively cheap design, comprising a minimum of components, wherein the first resistance wire 1 1 is arranged at the outer surface 12 of the tube 10 or at the inner surface 18 of the tube 10, and wherein the second resistance wire 13 has a position inside the tube 10, at the inner surface 18 of the tube 10 or at a distance from the inner surface 18 of the tube 10, wherein the first option of the positioning of the second resistance wire 13 is especially applicable when the first resistance wire 11 is arranged at the outer surface 12 of the tube 10. In the heating tube 1 according to the invention, there is no need for applying insulating material inside the tube 10, and there is no need for having components inside the tube 10 for supporting and/or separating the resistance wires 11, 13, in view of the fact that the tube 10 may serve as a separation, or the fact that the tube 10 may offer enough space for a resistance wire 11 located at the inner surface 18 of the tube 10 and a resistance wire 13 extending through the tube 10, at a distance from the inner surface 18 of the tube 10, to be insulated from each other.