EP0982973B2 - Sensor for cooking vessel detection - Google Patents

Abstract

A sensor (30) has a single-wind loop that consists of a tube or thick wire and fits over the sensor near heater zones (18,19) and tightly under a glass ceramic plate. In the case of a two-circuit electric radiant element, the sensor loop is shaped in the heater zones with concise peripheral areas (37,38). An Independent claim is also included for a radiant element.

Description

The invention relates to an electric radiant heater with an active sensor for detecting the positioning of a cooking vessel on a heating plate covering the cooking plate, in particular a glass ceramic plate.

The automatic switching on and off a hotplate in direct dependence on setting up a cooking vessel is a long-pursued goal, but so far only incomplete, could be solved with great technical effort and not with the necessary reliability, which is why such systems in practice little are introduced.

The systems proposed for this purpose are based on a wide variety of principles, with the type and arrangement of the sensor usually being decisive. Thus, mechanical, capacitive, optical, resistive and inductive sensors have been proposed. In inductive sensors both coils have been proposed with several turns as well as with only one turn. These coils are either circular and concentric with the respective cooking zone or frame them in the case of non-circular shaped cooking zones. These coils are usually in the area of the edge insulation. (Please refer EP 490 289 B1 and EP 442 275 A2 )

The mentioned one-wind pot detection loop is from the DE 37 11 589 A1 known. It is a passive short-circuit loop, which is arranged between the heating elements and a glass ceramic plate. It is acted upon externally by a magnetic field transmitter arranged below the heating elements. By periodic short-circuiting and a corresponding Bedämpfungsmessung the evaluation circuit is applied. The introduction of such a system in practice fails because of the great effort and especially the required large height to accommodate the magnetic encoder.

The aforementioned multi-winding coils in the outer edge region (or in an unheated middle zone) pose thermal problems and, as has been recognized according to the invention and as will be explained later, are less suitable for sharp signal generation and detection.

From the DE 37 33 108 For example, a circuit arrangement g has become known for a pan detection system with a drip detection sensor which operates in the manner of a passive quadrupole. The type of transmitter and receiver antennas operating sensor is applied to the underside of the hot plate as a printed circuit and has a generally spiral arrangement.

The EP 0 469 189 A describes a control method for the heating elements of a cooker with a designed as an air coil with only a few turns sensor, on the arrangement and design of the rest, no information is provided.

From the DE 42 24 934 A a sensor arrangement for a pan detection system has become known, in which two capacitive, electrically conductive, temperature-resistant pan detection sensors are arranged on the outer edge of radiant heaters. These are discrete sensors that cover only a small area of the circumference of the radiant heater. Their effect and the switch-on behavior is therefore highly dependent on where the sensors are arranged on the circumference. The exact positioning of a cooking vessel, therefore, they can not detect beyond doubt.

TASK AND SOLUTION

The object of the invention is to provide a radiant heater with an active sensor that provides a simple and robust design as concise as possible signal to control the radiator.

This object is achieved by claim 1.

The sensor, which is part of an inductively, preferably by means of oscillating circuit detuning resonant circuit of a control, is arranged as a loop of electrically conductive material in the region of the heating zone and this at least partially arranged across. As a result, the signal is significantly more meaningful for the coverage of the heating zone and thus for the detection of a sensor circulating in the edge region of the radiator more concise. This is unusual in that it should be assumed that the associated cooking vessel size would be detected particularly accurately by a sensor arranged at the edge, because the signal size in the form of the relative frequency shift in the edge region is particularly large and then drops sharply (parabolically) towards the center. The problem here, however, that, as has been noted, such an edge coil can hardly distinguish between a relatively small pot, which is still to effect a switch, and a large, but shifted to the heating pot pot, which should cause no intervention. In addition, there was always a problem with the edge coils due to the fact that radiant heaters are usually arranged in a metal plate whose bottom and especially its edge strongly damped the resonant circuit. The field thus extends to a very narrow edge region, which provides an evaluable signal at all.

In general, in such radiant heaters must be taken into account that the bottom of the sheet metal plate causes a damping of the magnetic field, so that this can form relatively small-scale hose around the actual sensor conductor around.

Due to the arrangement of the sensor loop in the In the area of the heating zone as large as possible coverage of the sensor can be achieved in the area in which the pot is to effect a switch, and the lowest possible coverage in the area in which the heating element in question should be turned off. Therefore, even a small pot with proper centric arrangement brings a big signal, while a shifted pot provides only one of them clearly distinguishable small signal. The sensor loop should therefore have its effective diameter in the range of the minimum diameter, advantageously something above it, namely around the area of the magnetic field "hose". As a result of the distance to the outer edge there is no significant attenuation by this, which would simulate a pot, so to speak. As a result, it is also possible to make do with a sensor loop having only one turn, whereas in the past the arrangement of a coil with many turns was usually considered necessary in order to obtain a sufficiently large signal in the form of a frequency shift in the measuring resonant circuit.

The invention therefore advantageously allows the sensor loop in the immediate area of the heating zone, i. Immediately exposed to the radiant heat, because in such a coil with a winding with air gap in between an insulation is not necessary. It consists of a shape-stable, self-supporting and temperature-resistant conductive material, preferably of a tube or solid, strong wire. The material used is a material such as a high alloy steel, e.g. a FeCrNi alloy in question. The formation of non-ferromagnetic material is expedient because with a ferromagnetic material due to the high temperature occurring, the Curie point would be exceeded and the magnetic properties changing in this point would give rise to a signal completely different from the desired determination of a cooking vessel position is independent and therefore the result would be distorted.

The sensor loop and the controller can be advantageously designed for cooking vessel size detection. For this purpose, the sensor loop may have different effective ranges at a radial distance from each other, e.g. in different peripheral regions substantially in the circumferential direction extending loop portions which are interconnected by radial connecting portions. For example, a sensor loop with a circular or polygonal shape with omega-shaped bulges can result. This cloverleaf has been recognized as particularly effective.

Since, in the present conditions, the signal magnitude essentially corresponds to the degree of coverage of the sensor loop through a cooking vessel, the characteristic curve "frequency deviation / diametrical coverage by the cooking vessel" has, in contrast to the parabolic curve, a stage progression with a steep portion displaced more towards the interior of the heating zone, which can have two diameter stages in two-circuit radiators. In this way, the waveform can be more adapted to the ideal shape. This would be the radiator with only one heating zone, a flat waveform in the edge region, the steepest possible drop in the range of the diameter of a smallest possible pot, which should still lead to an intervention, and then a shallow, the lowest possible course to Heizzonenmitte out.

In a two-circuit radiator, in which depending on the size of the cooking vessel, either only one (central) or both heating zones are turned on, can be achieved by two effective ranges having only one sensor a very succinct signal waveform with two approximate levels, the differentiated Switching the two heating zones can be evaluated.

The robust, self-supporting sensor loop can be easily arranged in any radiator configurations. These usually have an outer edge made of insulating material and two-ring radiators possibly an intermediate wall. On this, the sensor loop can rest, for which recesses may be provided in order to establish a system of sensor and insulating edge on the plate or a certain, but only small distance thereto. Even with existing radiator designs, retrofitting with pan detection is possible.

It has been found that the form, type and arrangement of the sensor loop can significantly improve the previous SIGAL / Rauschverhältnis in previous sensors of this kind.

BRIEF DESCRIPTION OF THE DRAWING

Fig. 1

einen zentralen Schnitt durch einen Strahlungsheizkörper unter einer Glaskeramikplatte mit angedeuteten Kochgefäßen,

Fig. 2

eine Draufsicht auf den Strahlungsheizkörper nach Fig. 1,

Fig. 3

eine Diagramm über den Frequenzgang bei einem Zweikreisheizkörper,

Fig. 4

eine Draufsicht auf eine Variante eines Strahlungsheizkörpers,

Fig. 5-10

Draufsichten auf weitere Varianten in schematischer Darstellung und

Fig. 11

eine Frequenzgang-Diagramm eines Sensors für einen Einkreisheizkörper (Fig. 5 bis 7).

An embodiment of the invention is illustrated in the drawings and will be explained in more detail below. In the drawings show:

Fig. 1

a central section through a radiant heater under a glass ceramic plate with indicated cooking vessels,

Fig. 2

a plan view of the radiant heater after Fig. 1 .

Fig. 3

a diagram of the frequency response in a two-circuit radiator,

Fig. 4

a top view of a variant of a radiant heater,

Fig. 5-10

Top views of other variants in a schematic representation and

Fig. 11

a frequency response diagram of a sensor for a single-circuit heater ( Fig. 5 to 7 ).

DESCRIPTION OF DBR EMBODIMENTS

The Fig. 1 and 2 show an electric radiant heater 11, which is arranged under a glass ceramic plate 12 of an electric cooktop or other Strahlungskochgerätes. It has a flat sheet metal plate 13, the bottom 14 and edge 15 receive a bottom layer 16 and a rim 17 of electrically and thermally insulating and insulating heat-resistant insulating material. It is preferably a microporous, pressed from bulk material fumed silica airgel. The outer edge 17 is made separately because of improved mechanical strength and consists of a pressed or wet-formed and then dried ceramic fiber with binders, etc.

The sheet edge 15 is not quite up to the glass ceramic plate 12 zoom, but probably the insulating edge 17 which is pressed from below to the glass ceramic plate by the heater 11 is pressed by a pressure spring, not shown, upwards.

The radiant heater has two mutually concentric heating zones 18, 19, which are delimited from one another by an intermediate wall 20, but which does not reach up to the glass ceramic plate.

In both heating zones 18, 19 electrical heating elements 21 are arranged in the form of thin, wavy deformed bands which are arranged standing upright on the surface 22 of the insulator 16 and anchored in this formed with feet on its underside, due to the curl of the band have a spade shape. They cover the two heating zones 18, 19 uniformly, with the exception of an unheated central zone 59, in which an upwardly directed projection 43 of the insulating floor 16 is located.

Fig. 2 shows the arrangement of the heating elements in meandering ring tracks. They are connected via Heizelementanschlüsse 23 to a temperature monitor 24 and a separate connection block 25 so that the outer heating zone 19 of the constantly activated during operation of the radiator heating zone 18 can be switched on. The temperature monitor 24 has a rod-shaped sensor 26, which acts on a temperature monitor / contact to maintain a permissible maximum temperature on the glass ceramic underside and a hot-alarm contact for signaling the hot condition of the radiator in a temperature monitor head 27. The sensor 26 protrudes through the Isolierkörperrand 17 and through the intermediate wall 20 therethrough and extends in a plane above the heating elements 21, but mostly in an area free of heating elements lane 28th

The radiator has a sensor in the form of a loop 30, which is part of a control 31 for detecting the positioning of a cooking vessel on the radiator covering the cooking plate 12. The sensor loop 30 forms an inductance of a resonant circuit 32, which is excited at a relatively high frequency of, for example, 1 MHz to 5 MHz. When placing a cooking vessel, the damping of the sensor loop 30 and thus the frequency of the resonant circuit 32 changes. This is evaluated in the controller 31 and depending on mechanical or electronic switches 33, 33 a are controlled in the control, the heating zones 18, 19 for Switch on operation.

To set the respective released power, a power control unit 34 (often referred to as an energy regulator) is also provided, which can be adjusted via a knob 35 to a certain power. It can also be provided a temperature controller. Control or control is usually a cycling power release, i. to a suspension control or control. The power controller 34 may be thermo-mechanical, i. be designed as a bimetal switch or, preferably, as an electronic component that may optionally be integrated into the controller 31. To keep interference from the resonant circuit 32 as far as possible, the line between the actual sensor loop 30 and the other elements of the resonant circuit should be kept as short as possible. A shielding of the cables is possible. Possibly. The component 36 of the control, which contained the actual cooking vessel detection, could also be arranged separately from the rest of the radiator control, spatially close to the radiant heater 11.

The sensor loop 30 consists of a relatively thick round wire with a diameter between 1 and 4 millimeters, preferably about 2 millimeters, of a heat-resistant and non-magnetizable material. This can be, for example, a high-alloy steel such as an iron-chromium-nickel alloy. Suitable materials are e.g. a steel with the material no. 1.4876 or a Heizleitermaterial with the material no. 2.4869.

The sensor can be grounded on one side. To achieve a low grounding resistance (preferably less than 0.1 ohms), and the required for this very low resistance of the sensor, this can be made correspondingly thick. However, because of the skin effect, only its surface is effective for its function as a pot detection sensor with Hochfrequenzbeaufschlagung, so that they could also be designed as a tube. Because of the low ohmic resistance, this could then also be filled with copper or another highly conductive material, while the jacket material ensures temperature resistance and scaling resistance. Particularly advantageous is an embodiment with a highly electrically conductive galvanic coating, for example made of silver, or an embodiment of good conductive solid material with, for example, galvanic, scale-resistant coating. The very rigid design of the sensor loop 30 ensures that is not to be expected even at high thermal stresses with a drop to the heating elements 21.

Because of the shape of the sensor loop 30, reference is made to the drawings. In Fig. 2 the sensor loop forms a single-winding coil with outer circumferential sections 37 extending over the outer heating zone 19 but with a relatively large radial distance from the outer edge 17 and inner circumferential sections 38, again at a radial distance from the intermediate wall 20, above the heating zone 18.

These peripheral sections are in Fig. 2 Circular arc sections of different diameters, which are interconnected by connecting portions 39. Although these connecting portions extend substantially radially, but obliquely so that the sum of the angle of the outer and inner peripheral portions 37, 38 is greater than 360 °. The top view of the sensor loop 30 has the basic shape of a trilobal clover having a relatively large, nearly full-circle center region and three lateral "leaves" in the shape of a triangular sector or omega. Depending on the size and control requirements, more peripheral section sectors may be provided. On one of the peripheral portion sectors 40 are provided terminals 41 in the form of outwardly directed, mutually parallel portions of the loop material.

The entire sensor loop 30 with the described shape is flat and self-supporting and dimensionally stable due to the relatively strong material. It lies in the present example, on the one hand in the region of the terminals 41 in shallow depressions of the insulator outer edge 17 and is supported in the rest with their connecting portions 39 on the intermediate wall 20, which does not quite come up to the glass ceramic plate. As a result, the sensor loop is arranged adjacent or at a small distance from the underside of the glass ceramic plate 12 and with a safety distance above the heating elements 21. It can be seen that the sensor 26 of the temperature monitor as a result of the arrangement shown, the sensor loop underpasses only once, in the area an inner peripheral portion 38. In this area, it also runs in the lane 28 so that it could be placed slightly lower without risk of collision with the heating elements 21. It is also possible to bring out each one of the terminals 41 on one side of the temperature sensor 26, so that each crossing sensor / loop is avoided. Sensor and loop can then lie in the same plane. As a result, the height of the radiant heater determining space 42 between the heating elements 21 supporting floor 16 and the glass ceramic plate 12 is ideally used and the distances for the high voltage test can be maintained.

While Fig. 2 shows a dual-circuit heater with two concentric heating zones 18, 19 is in Fig. 4 a two-circuit radiator shown with a total oblong oval shape. This radiant heater 11 has the rest of the same basic structure a circular Hauptheizzone 18, to which one side, delimited by an intermediate wall 20, an additional heating zone 19 connects, which has a half or quarter moon shape. A temperature monitor 24 is provided obliquely at the main heating zone 18 and its sensor 26 protrudes radially only about to the middle, where it rests on a central projection 43 in the unheated central zone 59 of the Isolierkörperbodens 16.

The provided for this radiant heater sensor loop 30 is made of the same material as that of the FIGS. 1 and 2 , It has the shape of a quadrangle, which consists of rectilinear peripheral portions which form parallel outgoing connections 41 in the region of the longitudinal center line 44 of the radiator. The lying in the transverse line 45 of the Hauptheizzone 18 corners 46 of the rectangle lie in corresponding shallow depressions 47 of the insulating outer edge 17, but within the sheet shell rim 15. The peripheral portions 38 thus extend in the form of tendons with a significant distance from the outer edge over large surface sections of the radiator and thus have a lying in the region of the heating zone 18 effective diameter.

In the region of the intersection of the longitudinal center line 44 with the intermediate wall 20, ie at the opposite corner of the quadrant connections is connected with a strong bend to the outside depending on a connecting portion 39 which extends to outer corners 48, which, like the corners 46, on the Insulating body outer edge 17 rest in corresponding recesses. They are connected to each other by a straight section 37a in the exemplary embodiment, which crosses them substantially centrally to the additional heating zone 19 and extends transversely to the longitudinal center line 44. This section could also be rounded according to the crescent shape of the additional heating zone 19. The sensor loop 30 is thus located on a total of seven locations on the insulator, namely at the corners 46 and 48, at the terminals 41 and, with their inner corners 49 between the square legs 38 a and the connecting portions 39, on the intermediate wall 20. Your Basic form is about that of a stylized fish.

Of the in the FIGS. 5 to 10 schematically shown sensor loop shapes corresponds to the Fig. 9 about the post Fig. 2 but with straight peripheral portions 37, 38 instead of in Fig. 2 shown arcuate design. Here, too, the peripheral portions 39 are largely directed radially and not as strongly recapturing as in Fig. 2 , This embodiment has a because of the deviation from the theoretical ideal shape of the circle (or the cup shape) slightly lower expression of the signal levels than Fig. 2 , but is easier. manufacture.

The explanations after the FIGS. 5 to 7 are intended for Einkreisheizkörper, ie radiators, which have only one contiguous and always jointly operated heating zone 18. The sensor loop 30 in Fig. 5 has the shape of a square with supported on the edge 17 corners 46. The sensor 46 of the temperature monitor 24 projects substantially diagonally across the field defined by the sensor.

In Fig. 6 is an execution accordingly Fig. 5 but in which the sensor 26 of the temperature monitor 24 is flanked on both sides by straight sections of the sensor loop 30. Behind the free end of the temperature sensor 26, these are connected together. This makes it possible to guide the temperature sensor and the sensor loop in the same plane, which contributes to reducing the height with sufficient electrical distances.

Fig. 7 shows a particularly preferred embodiment of the sensor loop 30, which, at a distance from the edge 17 extending, almost a full circle forming peripheral portions 37 which are interrupted only by the parallel led out terminals 41 and cat ears outwardly directed corners 46a, for the necessary support on the outer edge 17 provide.

Fig. 8 shows a sensor loop 30 for a two-circuit heater, which lies in the region of the partition wall 20 between the main heating zone 18 and the surrounding additional heating zone 19. The substantially square design similar Fig. 5 The loop is much smaller and extends with the outer corners in the area of Zusatzheizzone, while the peripheral portions 38a sweep the outer of the Hauptheizzone 18.

Fig. 10 shows an embodiment of a two-circuit radiator, which forms a double loop in contrast to the other radiators, but which is connected in parallel. The shape is that of two nested squares, both of which are connected to the same terminals 41 and have circumferentially spaced peripheral portions only to increase their surface coverage, but electrically form a single loop. The inner of the two loops lies, as in Fig. 8 described on the intermediate wall 20, while the outer loop accordingly Fig. 5 with its corners on the outer edge 80 rests. The relative design solid, but elastic design of the sensor loop also makes it possible to set them safely, for example by snapping into recesses of the edge. A determination by plugging in the insulating material, eg by welded pins, is possible.

FUNCTION

The method according to which the pan detection works is based on the FIGS. 1 to 3 described.

When the radiant heater 11 is to be put into operation, the desired power level is set on the adjusting knob 35, and thus the control 31 including the cooking vessel recognition 36 is put into operation. This Kochgefäßerkennung works inductively, ie the resonant circuit 32 is energized at a relatively high frequency between 1 MHz and 5 MHz and the evaluation of pot detection described below in its result is constructed in a conventional manner. Because of details, this will be on the European Patent Application 0442 275 A2 Referenced.

Accordingly, an alternating electromagnetic field is generated around the wire of the sensor loop 30, whose properties determine the frequency of the resonant circuit.

Now, if a cooking vessel 51 is placed on the plate 12, this magnetic field is changed, i. E. the sensor loop is attenuated, whereby the frequency of the resonant circuit 32 changes. This frequency change is evaluated in the pot detection element 36 and, when a preset threshold value is reached, activates one or both of the switches 33, 33a, so that the heating elements 21 are then current-flowed and heated accordingly.

The diagram in Fig. 3 shows the relative frequency response df across the diameter, ie the frequency change df in percent of the maximum frequency change in the measurement as a function of the diameter coverage of the cooking plate and thus the sensor loop through a cooking vessel. Below the diagram, for illustrative purposes, the cross section of the radiator 11 is corresponding Fig. 1 indicated.

The diagram shows the following: using a conventional sensor coil arranged in the edge 17, the course of the frequency change across the diameter shown as a dotted line 52 would result. The signal value added over the circumference would be practically proportional to the coverage of the perimeter. An exactly centric attached large pot 51a (s. Fig. 1 ) would therefore give a good signal, but a slightly smaller pot despite exactly centric coverage no reasonably usable signal. If, for example, the switching threshold were now substantially less than 50% of the total signal magnitude set, so would the one hand, the signal noise, which is relatively large in such sensors and their arrangement, make a circuit unreliable and on the other could then an eccentric (shifted) pot (see double dashed line 51b in Fig. 2 ) already lead to an undesired activation.

In the Fig. 3 shown by a solid line has two stages, namely the upper stage 54, which corresponds to the large, both heating zones 18, 19 covering pot 51a and the activation of both heating zones 18, 19 and 19 cause a lower stage 55, for example, at 50% of Frequency difference df . In the region of this step, which corresponds to the diameter of the small pot 51, only the central main heating zone 18 should be switched on alone, while at the left end of the step 55, which indicates the minimum pot diameter for the central heating zone, the signal should drop rapidly.

It can be seen that the curve 56 generated by the sensor loop 30 approximates this theoretical ideal curve 53, while it generally has a largely linear course, that is, the signal magnitude is largely proportional to the covered diameter, but contains steps approximating the step shape of the ideal curve , This makes it possible to reliably distinguish large small pots with only one sensor and, above all, to distinguish between a displaced potted pot which is to effect a switch on and a small pail intended to set the central main heating zone in motion.

In the diagram Fig. 3 the switching points 57, 58 are shown. At point 57 (signal level S1), only the middle heating zone 18 should be switched on and remain switched on until the switching point 58 (switch 33 "ON"). At switching point 58 (signal size S2), the outer heating zone 19 is then switched on (both switches 33 and 33a "ON"). In other words, the switching point 58 symbolizes the smallest size of the large pot 51a, which is to work with both heating zones, while the switching point 57 indicates the smallest size of a pot 51, which should still lead to an intervention.

It can be seen above all that in the area of the switching points 57, 58, the slope of the signal curve 56 is relatively large, so that a reliable circuit is possible even under consideration of confounding factors. At the same time, it can be seen that this would not be possible with the curve 52 of a conventional sensor coil.

With respect to the sensor coil, the following happens: Fig. 1 shown cooking vessel 51 is a pot whose diameter corresponds to the central Hauptheizzone 18. It covers the area of the heating zone 18 and the corresponding area of the sensor loop 30, that is to say mainly the inner circumferential sections 38. This results in a signal level approximately in the area of the first step 55 in the diagram Fig. 3 lies. This signal thus lies between the signal values S1 and S2 indicated there, so that only the central main heating zone 18 is switched on.

When placing the larger pot 51 a, in addition to the inner peripheral portions 38 and the outer peripheral portions and the connecting portions 39 are covered, so that there is a stronger signal change. From Fig. 3 To be recognized gradeability is given by the location of the peripheral portions 37, 38, which result in their coverage a relatively sharp signal change, while in between the relatively flat curve sections corresponding to the stages 54, 55 of the ideal curve.

Incidentally, the cooking operation is either power-controlled or temperature-controlled without any influence from the pot detection and is monitored by the temperature monitor 24, which protects the glass-ceramic plate against overheating.

In the embodiment according to Fig. 4 the function is comparable, except that instead of the concentric arrangement, the juxtaposition of the heating zones and their coverage by a correspondingly round or elongated cooking vessel (oval roaster) either only the Hauptheizzone 18 or additionally the Zusatzheizzone 19 is turned on. Also there arises a certain degree of difficulty through the arrangement of the individual sections of the sensor loop. Above all, however, is given by the step signal waveform, the possibility to switch diameter-dependent.

At one in the FIGS. 5 to 7 shown Einkreisheizkörper with a heating zone 18 is the waveform as in Fig. 11 shown. There, the ideal curve contains only one stage 54 and there is the waveform 56 of the sensor coil 30 of the invention largely adapted to this ideal course, so that there is a steep waveform for switching on and off at the switching point 58 (smallest possible pot). In the curve 52 of a conventional sensor coil, the switching point would be in a range of small signal sizes, that no reliable circuit would be possible.

It is thus created by the invention, a radiant heater with a pan detection sensor, which is not only particularly simple, robust and retrofittable, but also provides a sharp and useable for the circuit in a wide range signal. Above all, this can create several effective areas for pot detection, so that pots of different diameters trigger different heaters. It is possible with a sensor, a true cooking vessel size detection. It would also be possible, albeit with a larger construction cost, to do this e.g. in two-circuit radiators, to achieve with two sensors according to the invention, resulting in both structural and above all functional advantages over an arrangement of two conventional sensors in the outer and intermediate edge.

By the arrangement in the area of the heating zone itself, there is a result provided over the diameter with changes useful to the circuit, which may roughly be called linearized, but advantageously those in the diagrams Fig. 3 and 11 has shown step or jump characteristic.

Claims (12)

1. Electric radiant heater (11) having an active sensor for detecting the positioning of a cooking vessel (51) on a hotplate (12), particularly a glass ceramic plate, covering the heater (11), the sensor being a part of an inductively operating resonant circuit (32), preferably operating by resonant circuit detuning, of a control means (31) and the sensor being positioned as a loop (30) of electrically conductive material in the vicinity of at least one heating zone (18, 19) heated by electric radiant heating elements (21) and so as to at least partly overlap the same, characterized in that the sensor loop (30) is shape-stable, self-supporting and thermally stable, and has only one turn.
2. Radiant heater according to claim 1, characterized in that the sensor loop (30) has a shape diverging from a concentricity with respect to the heating zone (18, 19).
3. Radiant heater according to one of the preceding claims, characterized in that, radially spaced from one another, the sensor loop (30) has different, substantially circumferentially directed loop sections (37, 38), which are optionally interconnected by several radially directed connecting sections (39).
4. Radiant heater according to one of the preceding claims, characterized in that the sensor loop (30) is made from solid, strong wire, which is in particular uninsulated.
5. Radiant heater according to one of the preceding claims, characterized in that the sensor loop (30) is constructed as a tube.
6. Radiant heater according to one of the preceding claims, characterized in that.the sensor loop (30) is made from a multilayer material, e.g. a tube of thermally stable, non-scaling material with a filling of a good conducting material, such as copper.
7. Radiant heater according to one of the preceding claims, characterized in that the sensor loop (30) has a thermally stable coating.
8. Radiant heater according to one of the preceding claims, characterized in that the coating is of electrically good conducting material.
9. Radiant heater according to one of the preceding claims, characterized in that the sensor loop (30) is supported on an outer edge (17) made from insulating material and/or on an intermediate edge (20) bounding different heating zones (18, 19) and preferably radial connecting sections (39) and/or outwardly directed bends (46, 48) of the sensor loop (30) form support sections.
10. Radiant heater according to one of the preceding claims, characterized in that the sensor loop (30) has a circular or polygonal shape with circumferential section sectors (40) in the form of omega-shaped convexities.
11. Radiant heater according to one of the preceding claims, characterized in that the sensor loop (30) is made from a non-magnetizable material, such as a high-alloyed steel, e.g. an iron-chromium-nickel alloy.
12. Radiant heater according to one of the preceding claims, characterized in that the sensor loop (30) is positioned just below the hotplate (12), optionally over a sensing device (26) of a thermostat (24) or in the same plane therewith with a significant spacing from the heating elements (21).

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