EP0116861B2 - Electric radiant heating element for heating cooking or hot plates, especially glass ceramic plates - Google Patents

Electric radiant heating element for heating cooking or hot plates, especially glass ceramic plates Download PDF

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Publication number
EP0116861B2
EP0116861B2 EP84100541A EP84100541A EP0116861B2 EP 0116861 B2 EP0116861 B2 EP 0116861B2 EP 84100541 A EP84100541 A EP 84100541A EP 84100541 A EP84100541 A EP 84100541A EP 0116861 B2 EP0116861 B2 EP 0116861B2
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EP
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Prior art keywords
temperature sensor
heating
radiant heater
temperature
heater according
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EP84100541A
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German (de)
French (fr)
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EP0116861B1 (en
EP0116861A1 (en
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Gerhard Gössler
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EGO Elektro Geratebau GmbH
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EGO Elektro Gerate Blanc und Fischer GmbH
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    • HELECTRICITY
    • H05ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05BELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B1/00Details of electric heating devices
    • H05B1/02Automatic switching arrangements specially adapted to apparatus ; Control of heating devices
    • H05B1/0202Switches
    • H05B1/0216Switches actuated by the expansion of a solid element, e.g. wire or rod
    • HELECTRICITY
    • H05ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05BELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B3/00Ohmic-resistance heating
    • H05B3/68Heating arrangements specially adapted for cooking plates or analogous hot-plates
    • H05B3/74Non-metallic plates, e.g. vitroceramic, ceramic or glassceramic hobs, also including power or control circuits
    • H05B3/748Resistive heating elements, i.e. heating elements exposed to the air, e.g. coil wire heater

Definitions

  • the invention relates to an electric radiant heater for heating glass ceramic hot plates, in particular.
  • Such a radiant heater has become known from US-A-3 710 076. It describes an electric hotplate with an insulating web running between two heating fields up to the glass ceramic plate, on which the rod-shaped temperature sensor, which is flattened on one side, lies in a channel and is pressed by the web onto the underside of the glass ceramic plate. It should sense the temperature of the glass ceramic and thus also the temperature of the cooking vessel on it. Particular emphasis is placed on the sufficient physical pressure of the temperature sensor on the glass ceramic plate and on preventing the temperature from being exceeded.
  • US-A 3 710 076 thus describes an electric radiant heater for heating glass ceramic hot plates or hot plates, with heating elements arranged at a distance from the plate in a heating zone and a temperature controller with a rod-shaped element which projects above the heating zone and extends above the level of the heating elements
  • Temperature sensor which is at least partially shielded from direct radiation coming from the heating elements by a web of insulating material on which it is arranged, and which rises considerably above the level of the heating elements, the web being arranged at a distance from the plate, as a result of which Temperature sensor (20, 20a) has a temporarily effective thermal shield.
  • US-A-4,350,875 describes a radiant heater with two or more separately switchable heating zones and its task is to avoid that the temperature sensor is influenced by the second, in addition to the first switchable heating zone, because otherwise it would affect the radiant heater if both Heating zone are switched on, would switch off at too low a temperature.
  • This is achieved by permanently shielding the part of the temperature sensor that protrudes beyond the outer activation heating zone.
  • the part of the temperature sensor protruding beyond the outer switch-on heating zone is arranged in an insulating block, which rests with its side parts on the underside of the glass ceramic plate and accommodates the temperature sensor arranged at a distance from the glass ceramic plate in a narrow slot facing the glass ceramic plate. Even if both heating zones are switched on together, the influence of the outer sensor section is permanently suppressed.
  • EP-A-37 638 shows a temperature sensor which is arranged on the bottom of the radiant heating dish and is shielded from the heating by means of shielding webs. This largely point-shaped electrical sensor should be heated up more quickly than the glass ceramic hotplate, so that it can trigger an early shutdown.
  • the object of the invention is to increase the power throughput in an electric radiant heater, which in itself is determined by the limitation of the surface temperature of the glass ceramic plate, in particular when it is being brought to a boil, without permanent damage to the hotplate or hotplate.
  • the temporarily effective shielding which prevents the temperature sensor from reaching the full temperature immediately in the heating or heating phase, enables a higher temperature level to be reached in this heating phase, which is then reduced to a steady state during further operation. It has been found that, in practice, the surface temperatures permitted for continuous operation can be exceeded temporarily without significant damage to the glass ceramic. This only occurs if the Maximum temperatures.
  • the invention can produce a parboil with a peak of about 880 K (610 ° C) at a permanent limit temperature set to 810 K (540 ° C), which subsides again within a few minutes. A parboil of 50 to 100 K above the permanent limitation temperature is advantageous.
  • a temperature controller When we speak of a temperature controller here, it is in most cases a fixed temperature monitor, which is particularly advantageously equipped with a rod-shaped temperature sensor, which consists of a quartz sleeve and a metal rod located therein.
  • a temperature controller should also be understood to mean adjustable temperature controllers which have a maximum setting adjusted to a maximum temperature. and regulators of other types, for example with pipes filled with expansion fluid or electrical resistance sensors.
  • the temperature sensor is at least partially shielded from direct radiation coming from the heating elements, it is exposed to the radiation coming from the plate essentially over its entire length.
  • the temperature sensor can be partially surrounded by thermal insulating material, preferably it is over part of its circumference and / or its length, preferably in its lower Peripheral portion, in contact with thermal insulation material. This insulating material is heated up more slowly by the heating elements, so that the temperature sensor heats up with a time delay.
  • This material shields the temperature sensor, which is advantageously embedded up to half of it, against the direct radiation of the heating elements lying laterally below it, but presents it with the projected surface of the plate seen from above, so that it responds particularly well to retroreflective heat.
  • the division of the heating elements into, for example, approximately semicircular heating zones has no significant disadvantages compared to the conventional spiral arrangement and hardly leads to a noticeable shadow in the area of the insulating web from above.
  • the temperature sensor protrudes over a large part of its length over the heating elements. Shortening or relocating to an edge area is usually out of the question because the temperature sensor should, if possible, sense the entire heating zone in order, for example, to react correctly even when the pan is displaced relative to the heating element.
  • the thermal sensitivity of the temperature sensor can advantageously be provided in a part in which thermal shielding is possible, for example in an unheated middle area. This part with increased sensitivity then experiences a time delay which has a corresponding effect on the overall control behavior. Nevertheless, the influence of the other controller sections is retained, albeit to a lesser extent.
  • the temperature sensor in particular its outer shell, consists of a material with low thermal conductivity. This not only promotes the effect in the case of response sensitivities which differ over the longitudinal direction, but also prevents temperature compensation around the circumference of the temperature sensor, which could have a negative effect on the delay in the response of the controller.
  • the radiant heater 11 shown in FIGS. 1 and 2 is arranged below a glass ceramic plate 12, the surface 13 of which forms a cooking surface.
  • the radiant heater 11 has a carrier shell 14 made of sheet metal, into which insulation is inserted.
  • the insulation is two-layered, the bottom layer 15 can be made of a very good thermal insulating material with no demands on the mechanical strength, while the upper insulation 16 consists of a mechanically somewhat stronger material, because its edge 17 by not shown on the carrier shell 14 acting spring elements is pressed onto the glass ceramic plate and heating elements 18 and a temperature sensor 20 are arranged on it.
  • the thermal insulating material, in particular for the upper insulating body 16, consists of a ceramic fiber, preferably of aluminum silicate, which is pressed to achieve sufficient strength. Such material is offered under the trade name "Fiberfrax".
  • the insulating body 16 has a shell shape surrounded by the edge 17 with a cavity 19, on the bottom of which the heating elements 18 are arranged such that they form an essentially circular heating zone 21, which however consists of two semicircular sections 22, 23.
  • the heating elements 18 are filaments made of electrical resistance wire, which are guided essentially parallel to one another and thus form two semicircles which essentially fill the surface uniformly and which change from one section to the other at a transition point 24.
  • the heating elements 18 are at a substantial distance from the glass ceramic plate.
  • a web 25 of the insulating body 16 extends longitudinally on a diameter line between the sections 22, 23 and rises considerably above the level of the heating elements and thus lies much closer to the glass ceramic plate 12 than the latter. 2, which can be seen in particular from FIG.
  • the temperature controller 30 is switched on with the snap switch 31 contained in it into the circuit of the heating elements, which in this case are designed as a continuous heating resistor, and controls them by switching them on and off.
  • the temperature controller is a temperature controller that is permanently adjusted to a limiting temperature and could also be referred to as a temperature monitor.
  • the temperature sensor consists of an expansion sleeve 33 made of quartz material and an expansion rod 43 located therein, attached to the sleeve at the end of the temperature sensor, with a larger coefficient of thermal expansion than the sleeve.
  • the heating elements heat up relatively quickly and heat the underside of the glass ceramic plate by radiation, which on the one hand passes this on through its radiation permeability and on the other hand through heat conduction to a cooking vessel (not shown) placed thereon.
  • the temperature sensor is not heated up as quickly as the surface of the glass ceramic plate, so that its expansion remains somewhat behind the temperature rise on the glass ceramic plate. This is due on the one hand to the fact that the temperature sensor is shielded from direct radiation, and on the other hand to its close proximity to the insulating material of the web 25, which only heats up after a long time.
  • the temperature sensor is largely heated by the reflection from the glass ceramic plate, the delay effect being increased by a cold cooking vessel placed on it.
  • the delay also occurs when the plate is idling without a cooking vessel.
  • the heating elements are only switched off for the first time at a temperature which is on the surface 13 of the glass ceramic plate 12 somewhat above the temperature for which the controller itself is adjusted.
  • the heating element 18a in this case is wound as a double spiral, i.e. as a spiral consisting of two resistance wire coils running parallel to one another, leaving an unheated zone 32 in the middle, the diameter of which corresponds to about a quarter to a third of the diameter of the entire heating zone 21a.
  • the temperature sensor 20a of the temperature controller 30a therefore protrudes in the area of the annular heating zone over the heating elements 18a, but lies in the area of the unheated middle zone 32 on a web 25a which, with the exception of its length, is of the same design as in FIGS. 1 and 2. Only in In this area there is a temporary thermal shield.
  • the thermal sensitivity of the temperature sensor is increased in this area, in that the expansion rod 43 in this area consists of a material with a higher thermal expansion coefficient than in the other areas of the temperature sensor 20a.
  • This can be done, for example, by welding a piece of rod made of a material with a different coefficient of thermal expansion.
  • Such material is commercially available and, for example, a combination of materials sold by Vacuumschmelze GmbH, Hanau, under the trade name "Vacodil” could be used, where Vacodil 74 has a specific thermal expansion of 31 x 10 ⁇ 6 / K has, while with Vacodil 36 this factor is 9.2 x 10 ⁇ 6 / K.
  • the controller does not act sluggishly and with a greater control amplitude than previous controllers without application of the invention due to the temporary shielding in the later stationary state.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Ceramic Engineering (AREA)
  • Electric Stoves And Ranges (AREA)
  • Resistance Heating (AREA)

Abstract

1. Electric radiant heater for heating cooking or hotplates (12), particularly glass ceramic plates, with heating elements (18, 18a) arranged in a heating zone (21) at a distance from plate (12) and a temperature regulator (30, 30a) with a rod-like temperature sensor (20, 20a) projecting over the heating zone (21) and passing above the plane of heating elements (18) and which is at least partly shielded against the direct radiation from heating elements (18, 18a) by an insulating material web (25) on which it is arranged, characterized in that the temperature sensor (20, 20a) provided with a temporarily acting thermal shielding is spaced from plate (12) and is exposed to the radiation from plate (12) essentially over its entire length.

Description

Die Erfindung betrifft einen elektrischen Strahlheizkörper zur Beheizung von Glaskeramik-Koch- und Wärmeplatten, insbesondere.The invention relates to an electric radiant heater for heating glass ceramic hot plates, in particular.

Ein derartiger Strahlheizkörper ist aus der US-A-3 710 076 bekanntgeworden. Sie beschreibt eine Elektrokochplatte mit einem zwischen zwei Heizfeldern bis zur Glaskeramikplatte durchlaufenden Isoliersteg, auf dem in einer Rinne der einseitig abgeflachte, stabförmige Temperaturfühler liegt und von dem Steg an die Unterseite der Glaskeramikplatte angepreßt wird. Er soll die Temperatur der Glaskeramik und damit auch die Temperatur des darauf stehenden Kochgefäßes abfühlen. Besonderer Wert ist auf die ausreichende physikalische Anpressung des Temperaturfühlers an die Glaskeramikplatte und auf das Verhindern des Überschießens der Temperatur gelegt.Such a radiant heater has become known from US-A-3 710 076. It describes an electric hotplate with an insulating web running between two heating fields up to the glass ceramic plate, on which the rod-shaped temperature sensor, which is flattened on one side, lies in a channel and is pressed by the web onto the underside of the glass ceramic plate. It should sense the temperature of the glass ceramic and thus also the temperature of the cooking vessel on it. Particular emphasis is placed on the sufficient physical pressure of the temperature sensor on the glass ceramic plate and on preventing the temperature from being exceeded.

Die US-A 3 710 076 beschreibt also einen elektrischen Strahlheizkörper zur Beheizung von Glaskeramik-Koch- oder Wärmeplatten, mit in Abstand von der Platte in einer Heizzone angeordneten Heizelementen und einem Temperaturregler mit einem über die Heizzone ragenden, oberhalb der Ebene der Heizelemente verlaufenden stabförmigen Temperaturfühler, der zumindest teilweise gegen von den Heizelementen kommende direkte Strahlung durch einen Steg aus Isoliermaterial abgeschirmt ist, auf dem er angeordnet ist, und der sich erheblich über die Ebene der Heizelemente erhebt wobei der der Steg in Abstand von der Platte angeordnet ist, wodurch der Temperaturfühler (20, 20a) eine temporär wirksame thermische Abschirmung aufweist.US-A 3 710 076 thus describes an electric radiant heater for heating glass ceramic hot plates or hot plates, with heating elements arranged at a distance from the plate in a heating zone and a temperature controller with a rod-shaped element which projects above the heating zone and extends above the level of the heating elements Temperature sensor, which is at least partially shielded from direct radiation coming from the heating elements by a web of insulating material on which it is arranged, and which rises considerably above the level of the heating elements, the web being arranged at a distance from the plate, as a result of which Temperature sensor (20, 20a) has a temporarily effective thermal shield.

In der Praxis hat sich gezeigt, daß diese Art der Temperaturabfühlung bei strahlungsbeheizten Glaskeramikplatten zu keinen guten Resultaten führt, unter anderem deswegen, weil ein derartiger Fühler zu geringe Leistung freigibt.In practice it has been shown that this type of temperature sensing does not lead to good results with radiation-heated glass ceramic plates, among other things because such a sensor releases too little power.

Die US-A- 4 350 875 beschreibt einen Strahlheizkörper mit zwei oder mehreren getrennt schaltbaren Heizzonen, und ihre Aufgabe ist, zu vermeiden, daß der Temperaturfühler von der zweiten, zusätzlich zur ersten einschaltbaren Heizzone beeinflußt wird, weil er sonst den Strahlheizkörper, wenn beide Heizzone angeschaltet sind, bei einer zu niedrigen Temperatur abschalten würde. Dies wird durch eine dauerhafte Abschirmung des Teils des Temperaturfühlers bewirkt, der über die äußere Zuschaltheizzone ragt. Dazu ist der über die äußere Zuschaltheizzone ragende Teil des Temperaturfühlers in einem Isolierblock angeordnet, der an der Unterseite der Glaskeramikplatte mit seinen Seitenteilen anliegt und den mit Abstand von der Glaskeramikplatte angeordneten Temperaturfühler in einem schmalen, zur Glaskeramikplatte weisenden Schlitz aufnimmt. Auch bei einer möglichen gemeinsamen Einschaltung beider Heizzonen wird der Einfluß des äußeren Fühlerabschnitts dauerhaft unterdrückt.US-A-4,350,875 describes a radiant heater with two or more separately switchable heating zones and its task is to avoid that the temperature sensor is influenced by the second, in addition to the first switchable heating zone, because otherwise it would affect the radiant heater if both Heating zone are switched on, would switch off at too low a temperature. This is achieved by permanently shielding the part of the temperature sensor that protrudes beyond the outer activation heating zone. For this purpose, the part of the temperature sensor protruding beyond the outer switch-on heating zone is arranged in an insulating block, which rests with its side parts on the underside of the glass ceramic plate and accommodates the temperature sensor arranged at a distance from the glass ceramic plate in a narrow slot facing the glass ceramic plate. Even if both heating zones are switched on together, the influence of the outer sensor section is permanently suppressed.

In der EP-A-37 638 ist ein Temperaturfühler gezeigt, der auf dem Boden der Strahlungs-Heizschale angeordnet ist und durch Abschirmstege gegen die Heizung abgeschirmt ist. Dieser weitgehend punktförmige elektrische Fühler soll schneller aufgeheizt werden als die Glaskeramikkochplatte, so daß er eine frühzeitige Abschaltung auslösen kann.EP-A-37 638 shows a temperature sensor which is arranged on the bottom of the radiant heating dish and is shielded from the heating by means of shielding webs. This largely point-shaped electrical sensor should be heated up more quickly than the glass ceramic hotplate, so that it can trigger an early shutdown.

Aufgabe der Erfindung ist es dagegen, bei einem elektrischen Strahlheizkörper den Leistungsdurchsatz, der an sich durch die Begrenzung der Oberflächentemperatur der Glaskeramikplatte bestimmt ist, insbesondere beim Ankochen zu erhöhen, ohne daß es zu einer dauernden Schädigung der Koch- oder Wärmeplatte kommt.The object of the invention, however, is to increase the power throughput in an electric radiant heater, which in itself is determined by the limitation of the surface temperature of the glass ceramic plate, in particular when it is being brought to a boil, without permanent damage to the hotplate or hotplate.

Die temporär wirksame Abschirmung, die also in der Anheiz- bzw. Ankochphase den Temperaturfühler daran hindert, sofort auf volle Temperatur zu kommen, ermöglicht es, in dieser Ankochphase ein höheres Temperaturniveau zu erreichen, das dann jedoch beim weiteren Betrieb auf einen Beharrungszustand abgesenkt wird. Es ist festgestellt worden, daß man in der Praxis ohne wesentliche Schädigung der Glaskeramik die für den Dauerbetrieb zulässigen Oberflächentemperaturen tempörar überschreiten kann. Diese tritt erst bei länger andauernden Überschreitungen der Maximaltemperaturen ein. So kann beispielsweise durch die Erfindung bei einer auf 810 K (540 °C) eingestellten Dauerbegrenzungstemperatur ein Ankochstoß mit einer Spitze von etwa 880 K (610 °C) erzeugt werden, der innerhalb einiger Minuten wieder abklingt. Eine Ankochspitze von 50 bis 100 K über der Dauerbegrenzungstemperatur ist vorteilhaft. Er könnte so abklingen, daß er in einer Zeit von zwei bis fünf Minuten nach dem Erreichen der Spitzentemperatur etwa die Hälfte des über die Dauertemperatur überschießenden Temperaturbetrages erreicht hat, während er nach einer Zeit von etwa zehn bis fünfzehn Minuten asymptotisch in die Dauerbegrenzungstemperatur übergeht. Dabei ist zu beachten, daß die Regelschwingungen des meist durch Ein- und Ausschalten regelnden Temperaturreglers diese Kurve überlagern, so daß sie einen sägezahnartigen Verlauf hat. Die dadurch mögliche Temperaturspitze im Ankochbereich führt zu einem wesentlich erhöhten Leistungsdurchsatz, weil dieser in der vierten Potenz von der Temperatur abhängt.The temporarily effective shielding, which prevents the temperature sensor from reaching the full temperature immediately in the heating or heating phase, enables a higher temperature level to be reached in this heating phase, which is then reduced to a steady state during further operation. It has been found that, in practice, the surface temperatures permitted for continuous operation can be exceeded temporarily without significant damage to the glass ceramic. This only occurs if the Maximum temperatures. For example, the invention can produce a parboil with a peak of about 880 K (610 ° C) at a permanent limit temperature set to 810 K (540 ° C), which subsides again within a few minutes. A parboil of 50 to 100 K above the permanent limitation temperature is advantageous. It could decay so that within two to five minutes after the peak temperature had been reached it would have reached about half the temperature that exceeded the permanent temperature, while after about ten to fifteen minutes it would asymptotically switch to the permanent limit temperature. It should be noted that the control vibrations of the temperature controller, which usually regulates by switching on and off, overlap this curve so that it has a sawtooth-like course. The possible temperature peak in the parboil area leads to a significantly increased throughput, because the fourth power depends on the temperature.

In den meisten Fällen bringt dies schon bei der üblichen Leistungsausstattung der Strahlheizkörper eine wesentliche Verkürzung der Ankochzeit, weil bisher wegen der Glaskeramik-Oberflächentemperaturen die an sich vorhandene Leistung bereits frühzeitig abgeregelt werden mußte. Es ist jedoch nun auch möglich, höhere Leistungen vorzusehen, so daß auch die reine Aufheizungszeit bis zum Erreichen der Maximaltemperatur noch kürzer wird.In most cases, this already leads to a significant reduction in the boil-up time with the conventional power equipment of the radiant heaters, because previously the output per se had to be curtailed early because of the glass ceramic surface temperatures. However, it is now also possible to provide higher outputs, so that the heating-up time is even shorter until the maximum temperature is reached.

Wenn hier von einem Temperaturregler gesprochen wird, so handelt es sich in den meisten Fällen um einen fest eingestellten Temperaturwächter, der besonders vorteilhaft mit einem stabförmigen Temperaturfühler ausgerüstet ist, der aus einer Quarzguthülse und einem darin liegenden Metallstab besteht. Unter dem Begriff "Temperaturregler" sollen in diesem Zusammenhang aber auch einstellbare Temperaturregler verstanden werden, die eine auf eine Maximaltemperatur einjustierte Maximaleinstellung haben. und um Regler anderer Bauarten, beispielsweise mit durch Ausdehnungsflüssigkeit gefüllten Rohren oder elektrischen Widerstandsfühlern. Der Temperaturfühler ist zwar zumindest teilweise gegen von den Heizelementen kommende direkte Strahlung abgeschirmt, aber der von der Platte her kommenden Strahlung im wesentlichen über seine ganze Länge ausgesetzt. Auf diese Weise wird zwar der Einfluß der schnell ihrer Temperatur erreichenden Heizelemente verzögert, die gute Ankopplung an die Platte und ihre Rückwirkung auf den Fühler wird jedoch beibehalten, so daß die Regelcharakteristik, insbesondere die Regelamplitude, nicht negativ beeinflußt wird. Der Temperaturfühler kann teilweise von thermischem Isoliermaterial umgeben sein, vorzugsweise ist er über einen Teil seines Umfanges und/oder seiner Länge, vorzugsweise in seinem unteren Umfangsabschnitt, in Kontakt mit thermischem Isoliermaterial. Dieses Isoliermaterial wird von den Heizelementen langsamer aufgeheizt, so daß dadurch eine zeitlich verzögerte Aufheizung des Temperaturfühlers erfolgt. Dieses Material schirmt den vorteilhaft etwa bis zur Hälfte in ihn eingebetteten Temperaturfühler gegen die direkte Strahlung der seitlich unterhalb von ihm liegenden Heizelemente ab, präsentiert ihn aber mit der von oben gesehenen projezierten Fläche der Platte, so daß er auf Rückstrahlungswärme besonders gut anspricht. Die Aufteilung der Heizelemente in zwei beispielsweise etwa halbkreisförmige Heizzonen hat gegenüber der üblichen spiralförmigen Anordnung keine wesentlichen Nachteile und führt auch kaum zu einem von oben merklichen Schatten im Bereich des Isoliersteges.When we speak of a temperature controller here, it is in most cases a fixed temperature monitor, which is particularly advantageously equipped with a rod-shaped temperature sensor, which consists of a quartz sleeve and a metal rod located therein. In this context, the term “temperature controller” should also be understood to mean adjustable temperature controllers which have a maximum setting adjusted to a maximum temperature. and regulators of other types, for example with pipes filled with expansion fluid or electrical resistance sensors. Although the temperature sensor is at least partially shielded from direct radiation coming from the heating elements, it is exposed to the radiation coming from the plate essentially over its entire length. In this way, the influence of the heating elements quickly reaching their temperature is delayed, but the good coupling to the plate and its reaction on the sensor is retained, so that the control characteristic, in particular the control amplitude, is not adversely affected. The temperature sensor can be partially surrounded by thermal insulating material, preferably it is over part of its circumference and / or its length, preferably in its lower Peripheral portion, in contact with thermal insulation material. This insulating material is heated up more slowly by the heating elements, so that the temperature sensor heats up with a time delay. This material shields the temperature sensor, which is advantageously embedded up to half of it, against the direct radiation of the heating elements lying laterally below it, but presents it with the projected surface of the plate seen from above, so that it responds particularly well to retroreflective heat. The division of the heating elements into, for example, approximately semicircular heating zones has no significant disadvantages compared to the conventional spiral arrangement and hardly leads to a noticeable shadow in the area of the insulating web from above.

Insbesondere in Fällen, in denen sich eine Trennung der Heizzone nicht anbietet, ragt der Temperaturfühler über einen großen Teil seiner Länge über die Heizelemente hinweg. Eine Verkürzung oder Verlegung in einen Randbereich kommt meist nicht in Frage, weil der Temperaturfühler möglichst die ganze Heizzone abfühlen soll, um beispielsweise auch bei gegenüber dem Heizelement verschobenem Topf noch richtig zu reagieren. In diesem Falle kann vorteilhaft die thermische Ansprechempfindlichkeit des Temperaturfühlers in einem Teil vorgesehen sein, in dem eine thermische Abschirmung möglich ist, beispielsweise in einem unbeheizten Mittelbereich. Dieser Teil mit erhöhter Ansprechempfindlichkeit erfährt dann eine zeitliche Verzögerung, die sich auf das gesamte Regelverhalten entsprechend auswirkt. Trotzdem bleibt der Einfluß der übrigen Reglerabschnitte, wenn auch in geringerem Maße, erhalten. Dies kann beispielsweise durch die Verwendung von Materialien mit über die Länge unterschiedlichem Ausdehnungskoeffizienten bei einem Stab-Ausdehnungsfühler geschehen, wobei im Bereich hoher Ansprechempfindlichkeit entweder das Teil mit insgesamt höherer Ausdehnung einen gegenüber den übrigen Bereichen erhöhten Ausdehnungskoeffizienten hat oder das Teil mit geringerer Ausdehnung mit einen Abschnitt mit besonders geringem Ausdehnungskoeffizienten. Wenn mit einem mit Ausdehnungsflüssigkeit gefüllten Temperaturfühler gearbeitet wird, könnte an der abgeschirmten Stelle ein größeres Volumen pro Längeneinheit verwendet werden oder ein besonderer, an den gleichen Regler angeschlossener Fühler eingefügt werden.Especially in cases where there is no obvious separation of the heating zone, the temperature sensor protrudes over a large part of its length over the heating elements. Shortening or relocating to an edge area is usually out of the question because the temperature sensor should, if possible, sense the entire heating zone in order, for example, to react correctly even when the pan is displaced relative to the heating element. In this case, the thermal sensitivity of the temperature sensor can advantageously be provided in a part in which thermal shielding is possible, for example in an unheated middle area. This part with increased sensitivity then experiences a time delay which has a corresponding effect on the overall control behavior. Nevertheless, the influence of the other controller sections is retained, albeit to a lesser extent. This can be done, for example, by using materials with expansion coefficients that differ over their length in a rod expansion sensor, whereby in the area of high sensitivity either the part with overall higher expansion has an expansion coefficient that is higher than the other areas or the part with less expansion with one section with a particularly low coefficient of expansion. If you are working with a temperature sensor filled with expansion fluid, a larger volume per unit length could be used at the shielded point or a special sensor connected to the same controller could be inserted.

In jedem Falle ist es zweckmäßig, wenn der Temperaturfühler, insbesondere seine Außenhülle, aus einem Material mit geringer Wärmeleitfähigkeit besteht. Dies fördert nicht nur die Wirkung bei über die Längsrichtung unterschiedlichen Ansprechempfindlichkeiten, sondern verhindert auch einen Temperaturausgleich um den Umfang des Temperaturfühlers herum, der sich für die zeitliche Verzögerung des Ansprechens des Reglers negativ auswirken könnte.In any case, it is expedient if the temperature sensor, in particular its outer shell, consists of a material with low thermal conductivity. This not only promotes the effect in the case of response sensitivities which differ over the longitudinal direction, but also prevents temperature compensation around the circumference of the temperature sensor, which could have a negative effect on the delay in the response of the controller.

Merkmale von bevorzugten Weiterbildungen der Erfindung gehen aus den Unteransprüchen und der Beschreibung im Zusammenhang mit den Zeichnungen hervor, wobei die einzelnen Merkmale jeweils für sich allein oder zu mehreren in Form von Unterkombinationen bei einer Ausführungsform der Erfindung verwirklicht sein können. Ausführungsbeispiele der Erfindung sind in der Zeichnung dargestellt und werden im folgenden näher erläutert. Es zeigen:

  • Fig. 1 eine Draufsicht auf einen elektrischen Strahlheizkörper,
  • Fig. 2 einen Schnitt nach der Linie II in Fig. 1,
  • Fig. 3 eine Draufsicht auf eine weitere Ausführungsform und
  • Fig. 4 einen Teilschnitt nach der Linie IV in Fig. 3.
Features of preferred developments of the invention emerge from the subclaims and the description in conjunction with the drawings, the individual features being able to be implemented individually or in groups in the form of subcombinations in one embodiment of the invention. Embodiments of the invention are shown in the drawing and are explained in more detail below. Show it:
  • 1 is a plan view of an electric radiant heater,
  • 2 shows a section along the line II in FIG. 1,
  • Fig. 3 is a plan view of a further embodiment and
  • 4 shows a partial section along the line IV in FIG. 3.

Der in den Figuren 1 und 2 dargestellte Strahlheizkörper 11 ist unterhalb einer Glaskeramikplatte 12 angeordnet, deren Oberfläche 13 eine Kochfläche bildet.The radiant heater 11 shown in FIGS. 1 and 2 is arranged below a glass ceramic plate 12, the surface 13 of which forms a cooking surface.

Der Strahlheizkörper 11 besitzt eine aus Blech bestehende Trägerschale 14, in die eine Isolierung eingelegt ist. Die Isolierung ist zweischichtig, wobei die unterste Schicht 15 aus einem sehr gut thermisch isolierenden Material ohne Ansprüche an die mechanische Festigkeit bestehen kann, während die obere Isolierung 16 aus einem mechanisch etwas festeren Material besteht, weil ihr Rand 17 durch nicht dargestellte, auf die Trägerschale 14 einwirkende Federelemente an die Glaskeramikplatte angedrückt wird und Heizelemente 18 sowie ein Temperaturfühler 20 auf ihr angeordnet sind. Das thermische Isoliermaterial, insbesondere für den oberen Isolierkörper 16, besteht aus einer keramischen Faser, vorzugsweise aus Aluminiumsilikat, die zur Erzielung ausreichender Festigkeit verpreßt ist. Derartiges Material wird unter dem Handelsnamen "Fiberfrax" angeboten.The radiant heater 11 has a carrier shell 14 made of sheet metal, into which insulation is inserted. The insulation is two-layered, the bottom layer 15 can be made of a very good thermal insulating material with no demands on the mechanical strength, while the upper insulation 16 consists of a mechanically somewhat stronger material, because its edge 17 by not shown on the carrier shell 14 acting spring elements is pressed onto the glass ceramic plate and heating elements 18 and a temperature sensor 20 are arranged on it. The thermal insulating material, in particular for the upper insulating body 16, consists of a ceramic fiber, preferably of aluminum silicate, which is pressed to achieve sufficient strength. Such material is offered under the trade name "Fiberfrax".

Der Isolierkörper 16 hat eine von dem Rand 17 umgebene Schalenform mit einem Hohlraum 19, an dessen Boden die Heizelemente 18 so angeordnet sind, daß sie eine im wesentlichen kreisförmige Heizzone 21 bilden, die jedoch aus zwei halbkreisförmigen Abschnitten 22, 23 besteht. Die Heizelemente 18 sind Wendeln aus elektrischem Widerstandsdraht, die im wesentlichen parallel zueinander geführt sind und so zwei im wesentlichen die Fläche gleichmäßig ausfüllende Halbkreise bilden, die an einer Übergangsstelle 24 von einem Abschnitt zum anderen überwechseln. Die Heizelemente 18 haben einen wesentlichen Abstand von der Glaskeramikplatte. Zwischen den Abschnitten 22, 23 ragt längs auf einer Durchmesserlinie ein Steg 25 des Isolierkörpers 16 hindurch, der sich erheblich über die Ebene der Heizelemente erhebt und somit wesentlich dichter an der Glaskeramikplatte 12 liegt als diese. Der insbesondere aus Fig. 2 zu erkennende, im wesentlichen rechtwinklig begrenzte Steg 25 hat in seiner Oberseite eine halbkreisförmige Rinne 26, in der der Temperaturfühler 20 liegt. Er ist also etwa zur Hälfte seines Umfangs in das Isoliermaterial eingebettet, und die seitlich vorspringenden Kanten 27 des Steges decken den Temperaturfühler gegen von den nächstliegenden Heizelementen kommende Strahlung weitgehend ab. Der Temperaturfühler ragt in einer Durchmesserlinie über den gesamten kreisförmigen Strahlungsheizkörper hinweg, und der zugehörige Schalterkopf 28 des Temperaturreglers 30 liegt außerhalb der Trägerschale 14, in die ein Anschlußstück 29 mit den elektrischen Anschlüssen für die Heizelemente eingefügt ist. Der Temperaturregler ist mit dem in ihm enthaltenen Schnappschalter 31 in den Stromkreis der in diesem Falle als ein durchgehender Heizwiderstand ausgebildeten Heizelemente eingeschaltet und regelt diese durch Ein- und Ausschalten. Es handelt sich um einen fest auf eine Begrenzungstemperatur einregulierten Temperaturregler, der auch als Temperaturwächter bezeichnet werden könnte. Der Temperaturfühler besteht aus einer Ausdehnungshülse 33 aus Quarzgut und einer darin liegenden, am Ende des Temperaturfühlers an der Hülse befestigten Ausdehnungsstab 43 mit größerem thermischen Ausdehnungskoeffizienten als die Hülse.The insulating body 16 has a shell shape surrounded by the edge 17 with a cavity 19, on the bottom of which the heating elements 18 are arranged such that they form an essentially circular heating zone 21, which however consists of two semicircular sections 22, 23. The heating elements 18 are filaments made of electrical resistance wire, which are guided essentially parallel to one another and thus form two semicircles which essentially fill the surface uniformly and which change from one section to the other at a transition point 24. The heating elements 18 are at a substantial distance from the glass ceramic plate. A web 25 of the insulating body 16 extends longitudinally on a diameter line between the sections 22, 23 and rises considerably above the level of the heating elements and thus lies much closer to the glass ceramic plate 12 than the latter. 2, which can be seen in particular from FIG. 2 and is essentially rectangular, has in its upper side a semicircular channel 26 in which the temperature sensor 20 is located. So he is about half of its circumference is embedded in the insulating material, and the laterally projecting edges 27 of the web largely cover the temperature sensor against radiation coming from the closest heating elements. The temperature sensor protrudes in a diameter line over the entire circular radiant heater, and the associated switch head 28 of the temperature controller 30 lies outside the carrier shell 14, into which a connector 29 with the electrical connections for the heating elements is inserted. The temperature controller is switched on with the snap switch 31 contained in it into the circuit of the heating elements, which in this case are designed as a continuous heating resistor, and controls them by switching them on and off. It is a temperature controller that is permanently adjusted to a limiting temperature and could also be referred to as a temperature monitor. The temperature sensor consists of an expansion sleeve 33 made of quartz material and an expansion rod 43 located therein, attached to the sleeve at the end of the temperature sensor, with a larger coefficient of thermal expansion than the sleeve.

Beim Einschalten des Strahlungsheizkörpers kommen die Heizelemente relativ schnell auf Temperatur und beheizen durch Strahlung die Unterseite der Glaskeramikplatte, die dies einerseits durch ihre Strahlungsdurchlässigkeit und andererseits durch Wärmeleitung an ein darauf gestelltes, nicht dargestelltes Kochgefäß weitergibt. Dabei wird anfänglich der Temperaturfühler infolge seiner Abschirmung nicht so schnell aufgeheizt wie die Oberfläche der Glaskeramikplatte, so daß seine Ausdehnung hinter dem Hochlaufen der Temperatur an die Glaskeramikplatte etwas zurückbleibt. Dies liegt einerseits daran, daß der Temperaturfühler gegen die direkte Strahlung abgeschirmt ist, andererseits an seiner engen Nachbarschaft mit dem Isoliermaterial des Steges 25, das sich erst nach längerer Zeit aufheizt. Zu Anfang wird also der Temperaturfühler weitgehend von der Rückstrahlung von der Glaskeramikplatte her beheizt, wobei die Verzögerungswirkung durch ein darauf gestelltes kaltes Kochgefäß noch erhöht wird. Es ist aber festgestellt worden, daß die Verzögerung auch beim Leerlauf der Platte ohne Kochgefäß eintritt. Dadurch erfolgt die erste Abschaltung der Heizelemente erst bei einer Temperatur, die an der Oberfläche 13 der Glaskeramikplatte 12 um einiges über der Temperatur liegt, für die der Regler an sich einjustiert ist. Nach dem Absinken der Temperatur schaltet er daher auch schon früher als im Beharrungszustand wieder ein, so daß sich ein aus einer zickzackförmigen Linie bestehenden Kurve ergibt, die nach Art einer Exponetialkurve abfällt und nach einiger Zeit in der Größenordnung zwischen 10 und 30 Minuten gänzlich in ein horizontal verlaufendes zickzackförmiges Band übergeht, wenn man die Temperatur über der Zeit aufträgt.When the radiant heater is switched on, the heating elements heat up relatively quickly and heat the underside of the glass ceramic plate by radiation, which on the one hand passes this on through its radiation permeability and on the other hand through heat conduction to a cooking vessel (not shown) placed thereon. Initially, due to its shielding, the temperature sensor is not heated up as quickly as the surface of the glass ceramic plate, so that its expansion remains somewhat behind the temperature rise on the glass ceramic plate. This is due on the one hand to the fact that the temperature sensor is shielded from direct radiation, and on the other hand to its close proximity to the insulating material of the web 25, which only heats up after a long time. At the beginning, the temperature sensor is largely heated by the reflection from the glass ceramic plate, the delay effect being increased by a cold cooking vessel placed on it. However, it has been found that the delay also occurs when the plate is idling without a cooking vessel. As a result, the heating elements are only switched off for the first time at a temperature which is on the surface 13 of the glass ceramic plate 12 somewhat above the temperature for which the controller itself is adjusted. After the temperature has dropped, it therefore switches on again earlier than in the steady state, so that there is a curve consisting of a zigzag-shaped line, which declines in the manner of an exponetial curve and after a period of time in the order of magnitude between 10 and 30 minutes, completely on horizontally running zigzag band passes over when the temperature is plotted against time.

Es ist also zu erkennen, daß eine Ankochspitze erzeugt wird, die über eine Zeit in der Größenordnung zwischen 5 und 10 Minuten eine wesentliche Erhöhung des Leistungsdurchsatzes in der Glaskeramikplatte mit sich bringt. Für derartige kurze Zeiten kann Glaskeramik Überhitzungen in der Größenordnung unter 100 K so oft ertragen, daß trotzdem eine ausreichende Lebensdauer gewährleistet ist.It can thus be seen that a parboiling tip is produced which brings about a substantial increase in the power throughput in the glass ceramic plate over a period of the order of 5 to 10 minutes. For such short times, glass ceramics can withstand overheating in the order of magnitude below 100 K so often that an adequate service life is nevertheless guaranteed.

Bei der Ausführungsform nach Fig. 3 und 4 tragen gleiche Teile gleiche Bezugszeichen, die bei ähnlichen Teilen durch den Index "a" ergänzt sind. Wegen ihrer Beschreibung im einzelnen wird auf das Vorstehende Bezug genommen.In the embodiment according to FIGS. 3 and 4, the same parts have the same reference numerals, which are supplemented by the index "a" for similar parts. For the detailed description thereof, reference is made to the above.

Das Heizelement 18a ist in diesem Falle als Doppelspirale gewickelt, d.h. als Spirale aus zwei zueinander parallel laufenden Widerstandsdrahtwendeln, die in der Mitte eine unbeheizte Zone 32 freilassen, deren Durchmesser etwa einem Viertel bis einem Drittel des Durchmessers der gesamten Heizzone 21a entspricht. Der Temperaturfühler 20a des Temperaturreglers 30a ragt demnach im Bereich der ringförmigen Beheizungszone über die Heizelemente 18a hinweg, liegt jedoch im Bereich der unbeheizten Mittelzone 32 auf einem Steg 25a, der mit Ausnahme seiner Länge gleich ausgebildet ist wie in Fig. 1 und 2. Nur in diesem Bereich findet also eine temporäre thermische Abschirmung statt. Um diesen Bereich mit seiner thermischen Verzögerung jedoch für das Regelergebnis stärker zur Auswirkung zu bringen, ist in diesem Bereich die thermische Ansprechempfindlichkeit des Temperaturfühlers erhöht, indem der Ausdehnungsstab 43 in diesem Bereich aus einem Material mit höherem thermischem Ausdehnungskoeffizienten besteht als in den übrigen Bereichen des Temperaturfühlers 20a. Das kann beispielsweise durch das Einschweißen eines Stabstücks aus einem Material mit anderem thermischem Ausdehnungskoeffizienten erfolgen. Derartiges Material ist im Handel erhältlich, und es könnte beispielsweise eine Kombination von Materialien verwendet werden, die von der Firma Vacuumschmelze GmbH, Hanau, unter dem Handelsnamen "Vacodil" vertrieben wird, wobei Vacodil 74 eine spezifische thermische Ausdehnung von 31 x 10⁻⁶ / K hat, während dieser Faktor bei Vacodil 36 bei 9,2 x 10⁻⁶ /K liegt. Auf diese Weise wird der Einfluß dieser längenmäßig relativ geringen Zone überbetont, und es ist festgestellt worden, daß dies auf das übrige Regelverhalten keinen nachteiligen Einfluß hat. Vor allem ist bei allen Ausführungsformen zu bemerken, daß der Regler durch die temporäre Abschirmung im späteren stationären Zustand keinesfalls träger und mit größerer Regelamplitude arbeitet als bisherige Regler ohne Anwendung der Erfindung.The heating element 18a in this case is wound as a double spiral, i.e. as a spiral consisting of two resistance wire coils running parallel to one another, leaving an unheated zone 32 in the middle, the diameter of which corresponds to about a quarter to a third of the diameter of the entire heating zone 21a. The temperature sensor 20a of the temperature controller 30a therefore protrudes in the area of the annular heating zone over the heating elements 18a, but lies in the area of the unheated middle zone 32 on a web 25a which, with the exception of its length, is of the same design as in FIGS. 1 and 2. Only in In this area there is a temporary thermal shield. However, in order to make this area with its thermal delay more effective for the control result, the thermal sensitivity of the temperature sensor is increased in this area, in that the expansion rod 43 in this area consists of a material with a higher thermal expansion coefficient than in the other areas of the temperature sensor 20a. This can be done, for example, by welding a piece of rod made of a material with a different coefficient of thermal expansion. Such material is commercially available and, for example, a combination of materials sold by Vacuumschmelze GmbH, Hanau, under the trade name "Vacodil" could be used, where Vacodil 74 has a specific thermal expansion of 31 x 10⁻⁶ / K has, while with Vacodil 36 this factor is 9.2 x 10⁻⁶ / K. In this way, the influence of this lengthwise relatively small zone is overemphasized, and it has been found that this has no adverse influence on the rest of the control behavior. Above all, it should be noted in all embodiments that the controller does not act sluggishly and with a greater control amplitude than previous controllers without application of the invention due to the temporary shielding in the later stationary state.

Claims (9)

  1. Electric radiant heater for heating glass ceramic cooking or hotplates (12), with heating elements (18, 18a) arranged in a heating zone (21) at a distance from plate (12) and a temperature regulator (30, 30a) with a rod-like temperature sensor (20, 20a) projecting over the heating zone (21) and passing above the plane of heating elements (18) and which is at least partly shielded against the direct radiation from heating elements (18, 18a) by an insulating material web (25) on which it is arranged and which rises significantly over the plane of the heating elements, the temperature sensor (20, 20a) and the web (25) are spaced from plate (12) and the temperature sensor (20, 20a) is exposed to the radiation from plate (12) essentially over its entire length, so that the temperature sensor (20, 20a) receives a temporary thermal shielding and during the heating-up or preheating phase prevents the temperature sensor (20, 20a) from immediately reaching the full temperature and consequently in the heating-up or preheating phase allows a glass ceramic plate temperature value exceeding a permanent limit temperature.
  2. Radiant heater according to claim 1, characterized in that the temperature sensor (20, 20a) substantially centrally projects over the entire heating zone (21).
  3. Radiant heater according to claims 1 or 2, characterized in that the temperature sensor (20, 20a) is partly surrounded by thermal insulating material and is in contact with the thermal insulating material (16) over part of its circumference and/or length, advantageously in its lower circumferential portion.
  4. Radiant heater according to one of the preceding claims, characterized in that web (25, 25a) at least partly separates from one another two separate portions (22, 23) of heating zone (21a).
  5. Radiant heater according to claim 4, characterized in that the web (25, 25a) is made from a compressed, fibrous insulating material, such as aluminosilicate fibres.
  6. Radiant heater according to one of the preceding claims,
    characterized in that the temporary thermal shielding is provided on part of the length of the temperature sensor (20a) projecting over heating zone (21a) and that on said part (32) the thermal response sensitivity of temperature sensor (20a) is raised.
  7. Radiant heater according to one of the preceding claims,
    characterized in that the temperature sensor (20a) passing in unshielded manner in the vicinity of and over heating zone (21a) is constructed in a central, unheated area (32) for engaging on the web (25a) only provided in said unheated area (32).
  8. Radiant heater according to claims 6 or 7, characterized in that a temperature sensor (20a), which operates with a rod and a sleeve (33) having different thermal expansion coefficients, has in its shielded part larger differences in the thermal expansion coefficients.
  9. Radiant heater according to one of the preceding claims, characterized in that the temperature sensor (20, 20a), particularly its outer sleeve, is made from a material with low thermal conductivity.
EP84100541A 1983-01-26 1984-01-19 Electric radiant heating element for heating cooking or hot plates, especially glass ceramic plates Expired - Lifetime EP0116861B2 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AT84100541T ATE31463T1 (en) 1983-01-26 1984-01-19 ELECTRIC RADIANT RADIATOR FOR HEATING COOKING PLATES OR HOT PLATES, ESPECIALLY GLASS-CERAMIC PLATES.

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE3302489 1983-01-26
DE3302489A DE3302489A1 (en) 1983-01-26 1983-01-26 ELECTRIC RADIATOR HEATER FOR HEATING COOKING OR WARM PLATES, ESPECIALLY GLASS CERAMIC PLATES

Publications (3)

Publication Number Publication Date
EP0116861A1 EP0116861A1 (en) 1984-08-29
EP0116861B1 EP0116861B1 (en) 1987-12-16
EP0116861B2 true EP0116861B2 (en) 1994-03-02

Family

ID=6189220

Family Applications (1)

Application Number Title Priority Date Filing Date
EP84100541A Expired - Lifetime EP0116861B2 (en) 1983-01-26 1984-01-19 Electric radiant heating element for heating cooking or hot plates, especially glass ceramic plates

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EP (1) EP0116861B2 (en)
AT (1) ATE31463T1 (en)
DE (2) DE3302489A1 (en)

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DE3502497A1 (en) * 1985-01-25 1986-07-31 Grünzweig + Hartmann und Glasfaser AG, 6700 Ludwigshafen HEATING DEVICE, ESPECIALLY FOR A RADIATED HEATING COOKING PLATE, AND METHOD FOR THE PRODUCTION THEREOF
AT381784B (en) * 1985-02-27 1986-11-25 Electrovac DEVICE FOR REGULATING OR LIMITING THE TEMPERATURE OF RADIATION OR CONTACT HEATERS
DE3526783A1 (en) * 1985-07-26 1987-01-29 Ego Elektro Blanc & Fischer Radiant heating unit
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DE3817113A1 (en) * 1988-05-19 1989-11-30 Ego Elektro Blanc & Fischer Radiating heater
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Also Published As

Publication number Publication date
EP0116861B1 (en) 1987-12-16
DE3468159D1 (en) 1988-01-28
EP0116861A1 (en) 1984-08-29
DE3302489A1 (en) 1984-07-26
ATE31463T1 (en) 1988-01-15

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