EP2271175B1 - Method and device of thermal monitoring of inductive heatable cooking vessel - Google Patents

Method and device of thermal monitoring of inductive heatable cooking vessel Download PDF

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Publication number
EP2271175B1
EP2271175B1 EP10178369A EP10178369A EP2271175B1 EP 2271175 B1 EP2271175 B1 EP 2271175B1 EP 10178369 A EP10178369 A EP 10178369A EP 10178369 A EP10178369 A EP 10178369A EP 2271175 B1 EP2271175 B1 EP 2271175B1
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Prior art keywords
frequency
cooking
temperature
cooking vessel
predetermined
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EP10178369A
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German (de)
French (fr)
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EP2271175A2 (en
EP2271175A3 (en
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Martin Andersson
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Electrolux Home Products Corp NV
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Electrolux Home Products Corp NV
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    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B6/00—Heating by electric, magnetic or electromagnetic fields
    • H05B6/02—Induction heating
    • H05B6/06—Control, e.g. of temperature, of power
    • H05B6/062—Control, e.g. of temperature, of power for cooking plates or the like
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B2213/00—Aspects relating both to resistive heating and to induction heating, covered by H05B3/00 and H05B6/00
    • H05B2213/07—Heating plates with temperature control means

Definitions

  • the invention relates to a method and a device for thermal monitoring of an inductively heated cooking vessel.
  • Induction cooking surfaces have glass ceramic surfaces for receiving the cooking vessels and arranged below induction coils for their heating.
  • the induction coils an alternating current in the frequency range of about 15 kHz to 80 kHz, in particular about 20 kHz to 60 kHz supplied.
  • the resulting alternating fields generate eddy currents in ferromagnetic bottoms of the cooking vessels, which lead to heat generation.
  • Their monitoring is done by sensor systems that are complex and / or sluggish.
  • US 3,781,506 relates to an induction cooking device equipped to measure and adjust the temperature of the cookware. Described are a temperature control circuit and a non-contact method for measuring the temperature of an inductively heated object based on the detection of electrical parameters of the power circuit, which supplies the induction heating coil with energy.
  • US 5,477,035 relates to a heating temperature control method in high-frequency induction heating apparatus and apparatus for high-frequency induction heating temperature control, and more particularly to a control method and apparatus capable of accurately controlling a heating temperature of an object to be heated when a high-frequency induction heating coil is used to heat the object by high frequency induction.
  • EP 0 806 887 A1 relates to a method for detecting the boiling point of food in a set up on a hob container with the help of at least one cooktop associated temperature sensor, in which the time course of the temperature of the at least one temperature sensor is tracked and a turning point is detected in this temperature profile as a cooking point.
  • DE 101 22 427 A1 relates to a method for limiting and / or controlling the surface temperature of a heated via a power source, provided with a temperature limiter cooktop, in particular a hob with a glass ceramic cooking surface, wherein the switching temperature of the temperature limiter is changed according to a predetermined switching temperature-time profile during the cooking process.
  • DE 199 06 115 C1 relates to a method for detecting the emptying of dishes in hobs with a glass ceramic cooking surface having at least one cooking zone, which is associated with a radiator, the power supply is set via control and regulating bodies, and in which the temperature or a derived therefrom size as Signal (temperature signal) is recorded operationally and limited by means of a protective temperature limiter with adjustable switch-off temperature.
  • the invention has for its object to provide a method and apparatus for thermal monitoring of an inductively heated cooking vessel, which operate simple and low in inertia.
  • the thermal monitoring of the inductively heated cooking vessel is carried out by monitoring the frequency (f) of the inductive Heating causing AC (I).
  • T there is the monitoring, in particular absolute, temperatures (T) by assigning predetermined frequencies (f) and / or frequency ratios (f / f-start) to predetermined temperatures (T) or vice versa.
  • the monitoring is preferably carried out on the boiling of a food in the cooking vessel and / or on the empty cooking of the cooking vessel or the dry cooking of the food therein therein as a monitoring the frequency-time curve (f (t)) to predetermined sudden changes or to predetermined changes or absolute values of the first derivative (f '(t)) of the frequency-time curve (f (t)).
  • the alternating current (I) or the corresponding power (P) is reduced to a predetermined value if, during this monitoring, one or more changes have been determined which coincide with one or more predetermined changes.
  • the alternating current (I) or the corresponding power (P) is switched off if, during this monitoring, one or more changes have been determined which coincide with one or more predetermined changes.
  • the predetermined sudden change (s) of the frequency-time curve (f (t)) are in particular in or immediately after the transition from the falling frequency curve (f (t)) into the constant frequency curve (f (f). t)) and / or from the constant frequency curve (f (t)) in the falling frequency curve f (t).
  • the assignment of the frequencies (f) and / or frequency ratios (f / fstart) to the temperatures (T) preferably takes place as a function of predetermined properties, in particular material properties, of the cooking vessel, which are predetermined in particular for use or queried by the user, for example Specification of a selection list.
  • the assignment of the frequencies (f) and / or frequency ratios (f / fstart) to the temperatures (T) can also take place as a function of predetermined powers (P).
  • this also means a method for monitoring and / or controlling the cooking process in an inductively heated cooking vessel In which temperatures and / or temperature changes are detected and evaluated during cooking as frequencies and / or frequency changes of an alternating current causing the inductive heating in order to signal and / or influence the temperature of the cooking vessel.
  • the third means comprise first memory means with which predetermined sudden changes of frequency-time courses (f (t)) or predetermined changes of first derivatives (f '(t)) of frequency-time courses (f (t)) can be stored; representing as reference data in particular a boiling or boiling of a food in the cooking vessel or an empty cooking of the cooking vessel or a dry cooking of the food therein.
  • the third means also have second storage means with which predetermined frequency-temperature curves (f (T)) or frequency-ratio temperature curves (f / f-start (T)) can be stored, in particular per cooking vessel characteristic or power.
  • input means are assigned to the third means with which the user can select desired temperatures and / or programs, in particular cooking programs containing temperatures, and / or services and / or cooking vessels or their properties can enter.
  • the third means in particular have computing means with which the frequencies determined with the second means and the data stored with the first and / or second storage means and the data input with the input means can be offset to AC currents or corresponding powers which are the temperature of the cooking vessel influence according to the entered and / or stored data.
  • the influencing of the temperature may consist in the predetermined reduction in determined boiling and / or determined emptying or dry cooking and / or in their adjustment or maintenance according to user data entered.
  • An inventive cooking appliance has at least one of the above-described devices.
  • the power of the cooking vessel receiving the cooking zone is regulated. For this it is necessary to measure the temperature in the cooking vessel. Normally, the user has to manually change the power level on the duty-controlled cooking zones in order to obtain a certain temperature in the cooking vessel.
  • the following describes a method and a device for measuring temperatures T or temperature changes in the bottom of a cooking vessel or cooking appliance 8 standing on an induction cooking zone K and for using the information for controlling the power P of the induction cooking zone K, so that automatic cooking functions become possible ,
  • the resonant circuit of the induction heating system consists of an inverter 5 and an induction coil 6, which is arranged under a cooking appliance or cookware 8 supporting surface 9, for example, a glass ceramic plate.
  • the bottom of the harness 8 is ferromagnetic. In it, heat is generated by eddy currents induced by the magnetic field of the induction coil 6.
  • This impedance Z is influenced by the temperature T in the dish bottom, in particular due to changes in the electromagnetic properties of the bottom material. In turn, it influences the oscillation frequency f of the inverter 5, which is finally used to measure the temperature T in the bottom of the dish.
  • the coil current I is measured by means of a current transformer 7. Its basic appearance shows Fig. 2 ,
  • the oscillation frequency f (20 to 60 kHz) is modulated with the rectified mains power supply.
  • This signal leads to a frequency measuring circuit 3, which analyzes the signal and determines the oscillation frequency f.
  • the size of the mains voltage supply is measured by a voltage measurement circuit 10 and the information is passed to a control logic 2.
  • the control logic contains control algorithms A and ensures filtering of the signal if it is noisy.
  • Algorithm A calculates the appropriate power P for the cooking zone K to ensure the desired functionality, based on the information about the frequency f, the power supply U, and the user settings N entered by user interface (FIG. Fig. 3 ).
  • the operating frequency of the induction inverter 5 moves in particular in the range between 20 and 60 kHz, depending on the power level.
  • the frequency f ie, the inverse of the period of a cycle
  • the frequency f also varies over the rectified sinusoidal period (ie, over a period of 10 ms) by about 10%. Therefore, the frequency is measured when the mains voltage has its maximum.
  • a timer with a delay time of 5 ms which is triggered at the zero crossing of the mains voltage, triggers the frequency measurement after the delay time has elapsed.
  • Fig. 2 is the triggering of the timer with ZT and the triggering of the frequency measurement with FM, the time delay signal with ZV.
  • the signal of the current transformer 7 is sampled with an A / D converter and stored in a memory (500 samples in an interval of 666 ns gives 25-75 samples per period). From this, the period of the oscillations (6-20, depending on the frequency) is calculated, and in turn the center frequency. Effects of the frequency by changes in the mains power supply (by the mains power supply 4) can be achieved by measuring the voltage (by the voltage measuring device 10) and offsetting be corrected with empirically determined values or formulas. The corrected and / or uncorrected frequency is then used in the algorithms to signal temperatures.
  • a calibration curve f (T) is to be recorded. This is done by measuring the temperature T in the dish bottom (by means of separate temperature sensors) and registering the temperature T and the frequency f at a fixed power setting P. The measurement data can then be adjusted to an accepted accuracy using a curve fitting method, such as polynomial fitting. At the end of this section you get a relationship f (T) for a particular harness. However, since the frequency f depends on the power level P, all this has to be repeated for the other power levels to be used to finally have a relation f (T, P) stored in the control logic as a calibration curve (for a particular harness).
  • Fig. 4 shows a family of decreasing f (T) calibration curves for powers P1, P2, P3 and P4.
  • control logic associates the measured frequency f with a temperature T for a particular power level P. This then makes it possible to perform the desired functions according to the algorithms stored in the control logic perform.
  • This method requires identification of the harness 8 used.
  • the value f-rel for 250 ° C is about 0.83 for a broad index of pans that can be recommended to the user using this method.
  • the control algorithm A monitors the change of the frequency characteristic f (t) over the time t ( Fig. 5 ).
  • the first derivative f '(t) changes from a negative value to approximately zero, the bottom of the pot has reached a constant temperature, so that the time t, to which the food boils or boils, can be derived.
  • the power P or the current I in the induction coil 6 is reduced to a predetermined value. Notwithstanding this shows Fig.
  • a drop in frequency f occurs when, for example, water has escaped from the pot. This can be recognized as a sudden fall or a sudden change in the first derivative f '(t) or as a specific value of the first derivative f' (t), corresponding to a temperature rise in an empty pot.
  • the temperature T does not rise so fast.
  • the stable frequency level during boiling (cooking) as a reference level used to calibrate for 100 ° C.
  • the frequency drops and the power of the cooking zone is turned off at a certain relative value f1 with respect to 100 ° C. Notwithstanding this shows Fig.
  • a frequency curve f (t) can be assigned, which changes in the region of the boiling point its previously approximately linearly sloping course in a thereafter approximately constant course and in the range of empty or dry cooking its previously approximately constant course in a thereafter approximately linearly sloping course.
  • the temperature control could then be carried out, for example, as a thermostat function.
  • the power of the cooking zone can be set to two different levels P-high and P-low (for example P1 and P2), which are connected to two calibration curves f (T, P-high) and f (T, P-low).
  • the frequency f is then measured continuously and the temperature T derived from the calibration curves, depending on which power level is used. If the calculated temperature T-meas is greater than the set temperature T-set, the Cooking zone fed the lower power P-low. If T-meas is less than T-set, the cooking zone receives the higher power P-high ( Fig. 7 ). In this way, the pan or pot is kept at a significantly constant temperature level.
  • temperatures and / or temperature conditions and / or temperature changes and / or temperature profiles and / or their first derivatives can be assigned to frequencies and / or frequency ratios and / or frequency changes and / or their first derivatives and / vice versa.

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  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Cookers (AREA)
  • Induction Heating Cooking Devices (AREA)
  • Frying-Pans Or Fryers (AREA)
  • Control Of High-Frequency Heating Circuits (AREA)

Description

Die Erfindung betrifft ein Verfahren und eine Vorrichtung zur thermischen Überwachung eines induktiv erwärmbaren Gargefäßes.The invention relates to a method and a device for thermal monitoring of an inductively heated cooking vessel.

Induktionskochflächen besitzen Glaskeramikflächen zur Aufnahme der Gargefäße und darunter angeordnete Induktionsspulen zu deren Erhitzung. Den Induktionsspulen wird ein Wechselstrom im Frequenzbereich von ca. 15 kHz bis 80 KHz, insbesondere ca. 20 kHz bis 60 kHz zugeführt. Die hierdurch entstehenden Wechselfelder erzeugen in ferromagnetischen Böden der Gargefäße Wirbelströme, die zu Wärmeentwicklung führen. Deren Überwachung erfolgt durch Sensorsysteme, die aufwendig und/oder träge sind.Induction cooking surfaces have glass ceramic surfaces for receiving the cooking vessels and arranged below induction coils for their heating. The induction coils an alternating current in the frequency range of about 15 kHz to 80 kHz, in particular about 20 kHz to 60 kHz supplied. The resulting alternating fields generate eddy currents in ferromagnetic bottoms of the cooking vessels, which lead to heat generation. Their monitoring is done by sensor systems that are complex and / or sluggish.

US 3,781,506 betrifft eine Induktionskochvorrichtung, die ausgestattet ist, um die Temperatur des Kochgeschirrs zu messen und einzustellen. Beschrieben sind ein Temperaturkontrollschaltkreis und eine kontaktlose Methode zum Messen der Temperatur eines induktiv erhitzten Objekts basierend auf dem Erkennen von elektrischen Parametern des Leistungsschaltkreises, der die Induktionsheizspule mit Energie versorgt. US 3,781,506 relates to an induction cooking device equipped to measure and adjust the temperature of the cookware. Described are a temperature control circuit and a non-contact method for measuring the temperature of an inductively heated object based on the detection of electrical parameters of the power circuit, which supplies the induction heating coil with energy.

US 5,477,035 betrifft eine Heiztemperaturregelmethode bei Hochfrequenzinduktionsheizgeräten und eine Vorrichtung zur Hochfrequenzinduktionsheizungstemperaturregelung, insbesondere eine Regelmethode und eine Vorrichtung, die dafür geeignet ist, eine Heiztemperatur bei einem zu heizenden Objekt genau zu regeln, wenn eine Hochfrequenzinduktionsheizspule verwendet wird, um mittels Hochfrequenzinduktion das Objekt zu heizen. US 5,477,035 relates to a heating temperature control method in high-frequency induction heating apparatus and apparatus for high-frequency induction heating temperature control, and more particularly to a control method and apparatus capable of accurately controlling a heating temperature of an object to be heated when a high-frequency induction heating coil is used to heat the object by high frequency induction.

EP 0 806 887 A1 betrifft ein Verfahren zum Erkennen des Kochpunktes von Kochgut in einem auf einem Kochfeld aufgestellten Behälter mit Hilfe von wenigstens einem dem Kochfeld zugeordneten Temperaturfühler, bei dem der zeitliche Verlauf der Temperatur des wenigstens einen Temperaturfühlers verfolgt wird und als Kochpunkt ein Wendepunkt in diesem Temperaturverlauf erkannt wird. EP 0 806 887 A1 relates to a method for detecting the boiling point of food in a set up on a hob container with the help of at least one cooktop associated temperature sensor, in which the time course of the temperature of the at least one temperature sensor is tracked and a turning point is detected in this temperature profile as a cooking point.

DE 101 22 427 A1 betrifft ein Verfahren zur Begrenzung und/oder Steuerung der Oberflächentemperatur eines über eine Energiequelle beheizten, mit einem Temperaturbegrenzer versehenen Kochfelds, insbesondere eines Kochfelds mit einer Glaskeramikkochfläche, wobei die Schalttemperatur des Temperaturbegrenzers entsprechend einem vorgegebenen Schalttemperatur-Zeit-Profil während des Kochvorgangs verändert wird. DE 101 22 427 A1 relates to a method for limiting and / or controlling the surface temperature of a heated via a power source, provided with a temperature limiter cooktop, in particular a hob with a glass ceramic cooking surface, wherein the switching temperature of the temperature limiter is changed according to a predetermined switching temperature-time profile during the cooking process.

DE 199 06 115 C1 betrifft ein Verfahren zum Erkennen des Leerkochens von Geschirr bei Kochfeldern mit einer Glaskeramik-Kochfläche, die mindestens eine Kochzone aufweist, welcher ein Heizkörper zugeordnet ist, dessen Energiezufuhr über Regel- und Steuerorgane eingestellt wird, und in welcher die Temperatur oder eine davon abgeleitete Größe als Signal (Temperatursignal) betrieblich erfasst und mittels eines Schutztemperaturbegrenzers mit einstellbarer Abschalttemperatur begrenzt wird. DE 199 06 115 C1 relates to a method for detecting the emptying of dishes in hobs with a glass ceramic cooking surface having at least one cooking zone, which is associated with a radiator, the power supply is set via control and regulating bodies, and in which the temperature or a derived therefrom size as Signal (temperature signal) is recorded operationally and limited by means of a protective temperature limiter with adjustable switch-off temperature.

Der Erfindung liegt die Aufgabe zugrunde, ein Verfahren und eine Vorrichtung zur thermischen Überwachung eines induktiv erwärmbaren Gargefäßes zu schaffen, die einfach und trägheitsarm arbeiten.The invention has for its object to provide a method and apparatus for thermal monitoring of an inductively heated cooking vessel, which operate simple and low in inertia.

Erfindungsgemäß wird diese Aufgabe durch die Merkmale der Ansprüche 1 und 11 gelöst. Vorteilhafte Ausbildungen ergeben sich aus den Unteransprüchen.According to the invention, this object is solved by the features of claims 1 and 11. Advantageous embodiments will become apparent from the dependent claims.

Verfahrensseitig erfolgt die thermische Überwachung des induktiv erwärmbaren Gargefäßes durch Überwachung der Frequenz (f) des die induktive Erwärmung bewirkenden Wechselstroms (I).On the process side, the thermal monitoring of the inductively heated cooking vessel is carried out by monitoring the frequency (f) of the inductive Heating causing AC (I).

Die Vorteile sind folgende:

  • Die erfindungsgemäße thermische Überwachung (beispielsweise auf Überhitzungen) ist trägheitsarm. Während es gemäß dem Stand der Technik geschehen kann, dass eine Überhitzung des Gargefäßes oder sogar Feuer auftritt, bevor die Kochzone durch eine zu langsame Überwachungslösung abgeschaltet wird, reagiert die erfindungsgemäße Lösung viel schneller, d. h., sie liefert eine schnellere Antwort.
  • Die Temperatur wird erfindungsgemäß direkt im Boden des Gargefäßes nahe dem Gargut gemessen und ermittelt, während nach dem Stand der Technik eine Messung andernorts erfolgt und die Temperatur geschätzt wird.
  • Es ist kein separater Übertragungskanal für Messdaten vom Gargefäß zur Kochmulde erforderlich.
  • Es ist auch kein separater Sensor oder andere gesonderte Hardware erforderlich, da sie normalerweise schon in der Leistungskarte des Wechselrichters implementiert ist, d. h., die zusätzlichen Kosten sind sehr gering.
The advantages are the following:
  • The inventive thermal monitoring (for example, overheating) is low in inertia. While it can happen according to the prior art that overheating of the cooking vessel or even fire occurs before the cooking zone is switched off by a monitoring solution that is too slow, the solution according to the invention reacts much faster, ie it provides a faster response.
  • The temperature is inventively measured and determined directly in the bottom of the cooking vessel near the food to be cooked, while according to the prior art, a measurement is carried out elsewhere and the temperature is estimated.
  • There is no need for a separate transmission channel for measuring data from the cooking vessel to the hob.
  • There is also no need for a separate sensor or other separate hardware as it is normally already implemented in the power card of the inverter, ie, the extra cost is very low.

Es erfolgt die Überwachung auf sprunghafte Änderungen des Temperatur-Zeit-Verlaufs (T(t)) als Überwachung auf sprunghafte Änderungen des Frequenz-Zeit-Verlaufes (f(t)).There is monitoring for sudden changes in the temperature-time curve (T (t)) as monitoring for sudden changes in the frequency-time curve (f (t)).

Es erfolgt die Überwachung auf, insbesondere absolute, Temperaturen (T) durch Zuordnung vorbestimmter Frequenzen (f) und/oder Frequenzverhältnisse (f/f-start) zu vorbestimmten Temperaturen (T) oder umgekehrt.There is the monitoring, in particular absolute, temperatures (T) by assigning predetermined frequencies (f) and / or frequency ratios (f / f-start) to predetermined temperatures (T) or vice versa.

Entsprechend erfolgt bevorzugt die Überwachung auf das Sieden eines im Gargefäß befindlichen Gargutes und/oder auf das Leerkochen des Gargefäßes bzw. das Trockenkochen des darin befindlichen Gargutes als Überwachung des Frequenz-Zeit-Verlaufes (f(t)) auf vorbestimmte sprunghafte Änderungen oder auf vorbestimmte Änderungen oder Absolutwerte der ersten Ableitung (f'(t)) des Frequenz-Zeit-Verlaufes (f(t)).Accordingly, the monitoring is preferably carried out on the boiling of a food in the cooking vessel and / or on the empty cooking of the cooking vessel or the dry cooking of the food therein therein as a monitoring the frequency-time curve (f (t)) to predetermined sudden changes or to predetermined changes or absolute values of the first derivative (f '(t)) of the frequency-time curve (f (t)).

Die Überwachung auf das Sieden erfolgt insbesondere als Überwachung

  • auf eine vorbestimmte sprunghafte Änderung des Frequenz-Zeit-Verlaufes (f(t)) aus Richtung einer im wesentlichen linear abfallenden Frequenz (f) in Richtung einer im wesentlichen konstanten Frequenz (f) und/oder
  • auf eine vorbestimmte Änderung der ersten Ableitung (f'(t)) des Frequenz-Zeit-Verlaufes (f(t)) aus Richtung eines negativen Wertes in Richtung eines Wertes von etwa Null und/oder
  • auf einen vorbestimmten Wert der ersten Ableitung (f'(t)) des Frequenz-Zeit-Verlaufes (f(t)).
The monitoring of the boiling takes place in particular as a monitoring
  • to a predetermined abrupt change of the frequency-time curve (f (t)) from the direction of a substantially linearly decreasing frequency (f) in the direction of a substantially constant frequency (f) and / or
  • to a predetermined change of the first derivative (f '(t)) of the frequency-time curve (f (t)) from the direction of a negative value in the direction of a value of approximately zero and / or
  • to a predetermined value of the first derivative (f '(t)) of the frequency-time history (f (t)).

Der Wechselstrom (I) bzw. die entsprechende Leistung (P) wird insbesondere auf einen vorbestimmten Wert reduziert, wenn bei dieser Überwachung eine oder mehrere Änderungen ermittelt wurden, die mit einer oder mehreren vorbestimmten Änderungen übereinstimmen.In particular, the alternating current (I) or the corresponding power (P) is reduced to a predetermined value if, during this monitoring, one or more changes have been determined which coincide with one or more predetermined changes.

Die Überwachung auf das Leer- bzw. Trockenkochen erfolgt insbesondere als Überwachung

  • auf eine vorbestimmte sprunghafte Änderung des Frequenz-Zeit-Verlaufes (f(t)) aus Richtung einer im wesentlichen konstanten Frequenz (f) in Richtung einer im wesentlichen linear abfallenden Frequenz (f) und/oder
  • auf eine vorbestimmte Änderung der ersten Ableitung (f'(t)) des Frequenz-Zeit-Verlaufes (f(t)) aus Richtung eines Wertes von etwa Null in Richtung eines negativen Wertes und/oder
  • auf einen vorbestimmten Wert der ersten Ableitung (f'(t)) des Frequenz-Zeit-Verlaufes (f(t)).
The monitoring of the empty or dry cooking takes place in particular as a monitoring
  • to a predetermined abrupt change of the frequency-time curve (f (t)) from the direction of a substantially constant frequency (f) in the direction of a substantially linearly decreasing frequency (f) and / or
  • to a predetermined change of the first derivative (f '(t)) of the frequency-time curve (f (t)) from the direction of a value of approximately zero towards a negative value and / or
  • to a predetermined value of the first derivative (f '(t)) of the frequency-time history (f (t)).

Der Wechselstrom (I) bzw. die entsprechende Leistung (P) wird insbesondere abgeschaltet, wenn bei dieser Überwachung eine oder mehrere Änderungen ermittelt wurden, die mit einer oder mehreren vorbestimmten Änderungen übereinstimmen.In particular, the alternating current (I) or the corresponding power (P) is switched off if, during this monitoring, one or more changes have been determined which coincide with one or more predetermined changes.

Die vorbestimmte(n) sprunghafte(n) Änderung(en) des Frequenz-Zeit-Verlaufes (f(t)) liegen insbesondere im oder unmittelbar nach dem Übergang aus dem abfallenden Frequenzverlauf (f(t)) in den konstanten Frequenzverlauf (f(t)) und/oder aus dem konstanten Frequenzverlauf (f(t)) in den abfallenden Frequenzverlauf f(t).The predetermined sudden change (s) of the frequency-time curve (f (t)) are in particular in or immediately after the transition from the falling frequency curve (f (t)) into the constant frequency curve (f (f). t)) and / or from the constant frequency curve (f (t)) in the falling frequency curve f (t).

Die Zuordnung der Frequenzen (f) und/oder Frequenzverhältnisse (f/fstart) zu den Temperaturen (T) erfolgt vorzugsweise in Abhängigkeit von vorbestimmten Eigenschaften, insbesondere Materialeigenschaften, des Gargefäßes, die insbesondere für die Nutzung vorgegeben oder vom Nutzer abgefragt werden, beispielsweise durch Vorgabe einer Auswahlliste. Die Zuordnung der Frequenzen (f) und/oder Frequenzverhältnisse (f/fstart) zu den Temperaturen (T) kann aber auch in Abhängigkeit von vorbestimmten Leistungen (P) erfolgen.The assignment of the frequencies (f) and / or frequency ratios (f / fstart) to the temperatures (T) preferably takes place as a function of predetermined properties, in particular material properties, of the cooking vessel, which are predetermined in particular for use or queried by the user, for example Specification of a selection list. However, the assignment of the frequencies (f) and / or frequency ratios (f / fstart) to the temperatures (T) can also take place as a function of predetermined powers (P).

Die Temperatur des Gargefäßes wird insbesondere auf einen gewünschten Wert eingestellt bzw. auf einem gewünschten Wert gehalten, indem

  • die Frequenz (f) (kontinuierlich) überwacht wird,
  • der Frequenz (f) und/oder dem Frequenzverhältnis (f/f-start) in Abhängigkeit von der aktuell zugeordneten Leistung (P) und dem aktuell zugeordneten Gargefäß (kontinuierlich) eine Temperatur (T) zugeordnet wird,
  • die Abweichung zwischen der zugeordneten und der gewünschten Temperatur (T) (kontinuierlich) ermittelt wird und
  • entsprechend der Abweichung eine der zuordenbaren Leistungen ausgewählt wird.
The temperature of the cooking vessel is in particular set to a desired value or maintained at a desired value by
  • the frequency (f) is monitored (continuously),
  • the frequency (f) and / or the frequency ratio (f / f-start) depending on the currently assigned power (P) and the currently associated cooking vessel (continuously) is assigned a temperature (T),
  • the deviation between the assigned and the desired temperature (T) (continuously) is determined and
  • one of the assignable services is selected according to the deviation.

Insgesamt steht damit auch ein Verfahren zur Überwachung und/oder Steuerung des Garprozesses in einem induktiv erwärmbaren Gargefäß zur Verfügung, bei dem während des Garens Temperaturen und/oder Temperaturänderungen als Frequenzen und/oder Frequenzänderungen eines die induktive Erwärmung bewirkenden Wechselstroms erfasst und ausgewertet werden, um die Temperatur des Gargefäßes zu signalisieren und/oder zu beeinflussen.Overall, this also means a method for monitoring and / or controlling the cooking process in an inductively heated cooking vessel In which temperatures and / or temperature changes are detected and evaluated during cooking as frequencies and / or frequency changes of an alternating current causing the inductive heating in order to signal and / or influence the temperature of the cooking vessel.

Die erfindungsgemäße Vorrichtung zur thermischen Überwachung eines induktiv erwärmbaren Gargefäßes und zur Durchführung des vorbeschriebenen Verfahrens besitzt

  • erste Mittel zur Bereitstellung eines die induktive Erwärmung bewirkenden Wechselstroms,
  • zweite Mittel zur Ermittlung der vom Gargefäß beeinflussten Frequenz des Wechselstroms und
  • dritte Mittel zur Signalisierung oder Steuerung der Temperatur des Gargefäßes in Abhängigkeit von der Frequenz des Wechselstroms.
The inventive device for thermal monitoring of an inductively heated cooking vessel and to carry out the method described above has
  • first means for providing an inductive heating causing AC current,
  • second means for determining the cooking vessel influenced frequency of the alternating current and
  • third means for signaling or controlling the temperature of the cooking vessel in dependence on the frequency of the alternating current.

Die dritten Mittel weisen erste Speichermittel auf, mit denen vorbestimmte sprunghafte Änderungen von Frequenz-Zeitverläufen (f(t)) oder vorbestimmte Änderungen erster Ableitungen (f'(t)) von Frequenz-Zeit-Verläufen (f(t)) speicherbar sind, die als Referenzdaten insbesondere ein Sieden bzw. Aufkochen eines im Gargefäß befindlichen Gargutes oder ein Leerkochen des Gargefäßes bzw. ein Trockenkochen des darin befindlichen Gargutes repräsentieren.The third means comprise first memory means with which predetermined sudden changes of frequency-time courses (f (t)) or predetermined changes of first derivatives (f '(t)) of frequency-time courses (f (t)) can be stored; representing as reference data in particular a boiling or boiling of a food in the cooking vessel or an empty cooking of the cooking vessel or a dry cooking of the food therein.

Die dritten Mittel weisen auch zweite Speichermittel auf, mit denen vorbestimmte Frequenz-Temperatur-Verläufe (f(T)) oder Frequenzverhältnis-Temperaturverläufe (f/f-start(T)) speicherbar sind, insbesondere je Gargefäßeigenschaft oder Leistung.The third means also have second storage means with which predetermined frequency-temperature curves (f (T)) or frequency-ratio temperature curves (f / f-start (T)) can be stored, in particular per cooking vessel characteristic or power.

Den dritten Mitteln sind insbesondere Eingabemittel zugeordnet, mit denen der Nutzer gewünschte Temperaturen und/oder Programme, insbesondere Temperaturen enthaltende Garprogramme, und/oder Leistungen und/oder Gargefäße bzw. deren Eigenschaften eingeben kann.In particular, input means are assigned to the third means with which the user can select desired temperatures and / or programs, in particular cooking programs containing temperatures, and / or services and / or cooking vessels or their properties can enter.

Schließlich weisen die dritten Mittel insbesondere Rechenmittel auf, mit denen die mit den zweiten Mitteln ermittelten Frequenzen und die mit den ersten und/oder zweiten Speichermitteln gespeicherten und die mit den Eingabemitteln eingegebenen Daten zu Wechselströmen bzw. entsprechenden Leistungen verrechenbar sind, die die Temperatur des Gargefäßes entsprechend der eingegebenen und/oder gespeicherten Daten beeinflussen.Finally, the third means in particular have computing means with which the frequencies determined with the second means and the data stored with the first and / or second storage means and the data input with the input means can be offset to AC currents or corresponding powers which are the temperature of the cooking vessel influence according to the entered and / or stored data.

Die Beeinflussung der Temperatur kann in deren vorbestimmter Verringerung bei ermitteltem Sieden und/oder ermitteltem Leer- bzw. Trockenkochen und/oder in deren Einstellung bzw. Aufrechterhaltung entsprechend eingegebener Nutzerdaten bestehen.The influencing of the temperature may consist in the predetermined reduction in determined boiling and / or determined emptying or dry cooking and / or in their adjustment or maintenance according to user data entered.

Ein erfindungsgemäßes Kochgerät weist wenigstens eine der vorbeschriebenen Vorrichtungen auf.An inventive cooking appliance has at least one of the above-described devices.

Die Erfindung wird nachstehend anhand eines Ausführungsbeispiels näher erläutert. In den zugehörigen Zeichnungen zeigen:

  • Fig. 1 das Blockschaltbild einer Vorrichtung zur Überwachung und/oder Steuerung der Temperatur in einem induktiv erwärmbaren Boden eines Gargefäßes, beispielsweise einer Pfanne, einer Friteuse oder eines Topfes,
  • Fig. 2 einen die induktive Erwärmung bewirkenden Wechselstrom und dessen Messung,
  • Fig. 3 ein Prinzip der Regelung,
  • Fig. 4 Frequenz-Temperatur-Kurven für unterschiedliche Leistungen,
  • Fig. 5 prinzipielle zeitliche Verläufe der Temperatur, der Frequenz und der ersten Ableitung der Frequenz beim Sieden eines im Gargefäß befindlichen Gargutes,
  • Fig. 6 prinzipielle zeitliche Verläufe der Temperatur, der Frequenz und der ersten Ableitung der Frequenz beim Leerkochen des Gargefäßes bzw. beim Trockenkochen eines im Gargefäß befindlichen Gargutes.
  • Fig. 7 ein Prinzip der Temperaturregelung einer Bratpfanne und dgl.
The invention will be explained in more detail below with reference to an embodiment. In the accompanying drawings show:
  • Fig. 1 2 is a block diagram of a device for monitoring and / or controlling the temperature in an inductively heatable bottom of a cooking vessel, for example a pan, a fryer or a pot,
  • Fig. 2 an inductive heating causing AC and its measurement,
  • Fig. 3 a principle of regulation,
  • Fig. 4 Frequency-temperature curves for different outputs,
  • Fig. 5 principle temporal courses of the temperature, the frequency and the first derivative of the frequency during boiling of a food in the cooking vessel,
  • Fig. 6 principle temporal courses of the temperature, the frequency and the first derivative of the frequency when emptying the cooking vessel or during dry cooking a food in the cooking vessel.
  • Fig. 7 a principle of temperature control of a frying pan and the like.

Um in einem Gargefäß oder einem Gargerät eine gewünschte Temperatur einzustellen, wird die Leistung der das Gargefäß aufnehmenden Kochzone geregelt. Hierfür ist es erforderlich, die Temperatur in dem Gargefäß zu messen. Normalerweise hat der Nutzer an leistungsgeregelten Kochzonen manuell das Leistungsniveau zu ändern, um im Gargefäß eine bestimmte Temperatur zu erhalten.To set a desired temperature in a cooking vessel or a cooking appliance, the power of the cooking vessel receiving the cooking zone is regulated. For this it is necessary to measure the temperature in the cooking vessel. Normally, the user has to manually change the power level on the duty-controlled cooking zones in order to obtain a certain temperature in the cooking vessel.

Im folgenden werden ein Verfahren und eine Vorrichtung beschrieben, um im Boden eines auf einer Induktionskochzone K stehenden Gargefäßes oder Gargerätes 8 Temperaturen T bzw. Temperaturänderungen zu messen und die Informationen zur Regelung der Leistung P der Induktionskochzone K zu nutzen, so dass automatische Kochfunktionen möglich werden.The following describes a method and a device for measuring temperatures T or temperature changes in the bottom of a cooking vessel or cooking appliance 8 standing on an induction cooking zone K and for using the information for controlling the power P of the induction cooking zone K, so that automatic cooking functions become possible ,

Der Schwingkreis des Induktionsheizsystems gemäß Fig. 1 besteht aus einem Wechselrichter 5 und einer Induktionsspule 6, die unter einer ein Kochgerät bzw. Kochgeschirr 8 tragenden Oberfläche 9, beispielsweise einer Glaskeramikplatte, angeordnet ist. Der Boden des Geschirrs 8 ist ferromagnetisch ausgebildet. In ihm wird durch Wirbelströme, die durch das Magnetfeld der Induktionsspule 6 induziert werden, Wärme erzeugt. Der Oszillationsstrom (Größe und Frequenz) durch die Induktionsspule unterliegt dem Einfluss verschiedener Elemente des Schwingkreises, deren eines die Impedanz (Z=R+jωL) des Systems Induktionsspule 6/Geschirr 8 ist. Diese Impedanz Z wird beeinflusst durch die Temperatur T im Geschirrboden, insbesondere aufgrund von Änderungen der elektromagnetischen Eigenschaften des Bodenmaterials. Sie beeinflusst wiederum die Schwingungsfrequenz f des Wechselrichters 5, was schließlich zur Messung der Temperatur T im Geschirrboden genutzt wird.The resonant circuit of the induction heating system according to Fig. 1 consists of an inverter 5 and an induction coil 6, which is arranged under a cooking appliance or cookware 8 supporting surface 9, for example, a glass ceramic plate. The bottom of the harness 8 is ferromagnetic. In it, heat is generated by eddy currents induced by the magnetic field of the induction coil 6. The oscillation current (magnitude and frequency) through the induction coil is influenced by various elements of the oscillation circuit, one of which is the impedance (Z = R + jωL) of the induction coil 6 / harness 8 system. This impedance Z is influenced by the temperature T in the dish bottom, in particular due to changes in the electromagnetic properties of the bottom material. In turn, it influences the oscillation frequency f of the inverter 5, which is finally used to measure the temperature T in the bottom of the dish.

Der Spulenstrom I wird mittels eines Stromwandlers 7 gemessen. Sein prinzipielles Aussehen zeigt Fig. 2. Die Schwingungsfrequenz f (20 bis 60 kHz) wird mit der gleichgerichteten Netzstromversorgung moduliert. Dieses Signal führt an eine Frequenzmess-Schaltung 3, die das Signal analysiert und die Schwingungsfrequenz f ermittelt. Die Größe der Netzspannungsversorgung wird durch eine Spannungsmessungsschaltung 10 gemessen und die Information an eine Steuerlogik 2 geführt. Die Steuerlogik enthält Regelalgorithmen A und sichert eine Filterung des Signals, falls dieses rauscht. Der Algorithmus A berechnet die geeignete Leistung P für die Kochzone K, um die gewünschte Funktonalität zu sichern, basierend auf den Informationen über die Frequenz f, die Spannungsversorgung U und die mittels Nutzerschnittstelle eingegebenen Nutzereinstellungen N (Fig. 3).The coil current I is measured by means of a current transformer 7. Its basic appearance shows Fig. 2 , The oscillation frequency f (20 to 60 kHz) is modulated with the rectified mains power supply. This signal leads to a frequency measuring circuit 3, which analyzes the signal and determines the oscillation frequency f. The size of the mains voltage supply is measured by a voltage measurement circuit 10 and the information is passed to a control logic 2. The control logic contains control algorithms A and ensures filtering of the signal if it is noisy. Algorithm A calculates the appropriate power P for the cooking zone K to ensure the desired functionality, based on the information about the frequency f, the power supply U, and the user settings N entered by user interface (FIG. Fig. 3 ).

Die Betriebsfrequenz des Induktions-Wechselrichters 5 bewegt sich insbesondere im Bereich zwischen 20 und 60 kHz, abhängig vom Leistungsniveau. Die Frequenz f (d. h., die Umkehrung der Periodendauer eines Zyklus) variiert auch über die gleichgerichtete Sinuskurvenperiode (d. h., über eine Periode von 10 ms) mit etwa 10 %. Deshalb wird die Frequenz gemessen, wenn die Netzspannung ihr Maximum hat. Eine Zeitschaltung mit einer Verzögerungszeit von 5 ms, die im Nulldurchgang der Netzspannung ausgelöst wird, löst nach Ablauf der Verzögerungszeit die Frequenzmessung aus. In Fig. 2 ist die Auslösung der Zeitschaltung mit ZT und die Auslösung der Frequenzmessung mit FM gekennzeichnet, das Zeitverzögerungssignal mit ZV. Das Signal des Stromwandlers 7 wird mit einem A/D-Wandler abgetastet und in einem Speicher gespeichert (500 Abtastungen in einem Intervall von 666 ns ergeben 25-75 Abtastungen je Periode). Davon wird die Periodenzeit der Schwingungen (6-20, abhängig von der Frequenz) errechnet und davon wiederum die Mittenfrequenz. Beeinflussungen der Frequenz durch Änderungen in der Netzstromversorgung (durch die Netzstromversorgungseinrichtung 4) können durch Messung der Spannung (durch die Spannungsmesseinrichtung 10) und Verrechnung mit empirisch ermittelten Werten oder Formeln korrigiert werden. Die korrigierte und/oder unkorrigierte Frequenz wird dann in den Algorithmen benutzt, um Temperaturen zu signalisieren.The operating frequency of the induction inverter 5 moves in particular in the range between 20 and 60 kHz, depending on the power level. The frequency f (ie, the inverse of the period of a cycle) also varies over the rectified sinusoidal period (ie, over a period of 10 ms) by about 10%. Therefore, the frequency is measured when the mains voltage has its maximum. A timer with a delay time of 5 ms, which is triggered at the zero crossing of the mains voltage, triggers the frequency measurement after the delay time has elapsed. In Fig. 2 is the triggering of the timer with ZT and the triggering of the frequency measurement with FM, the time delay signal with ZV. The signal of the current transformer 7 is sampled with an A / D converter and stored in a memory (500 samples in an interval of 666 ns gives 25-75 samples per period). From this, the period of the oscillations (6-20, depending on the frequency) is calculated, and in turn the center frequency. Effects of the frequency by changes in the mains power supply (by the mains power supply 4) can be achieved by measuring the voltage (by the voltage measuring device 10) and offsetting be corrected with empirically determined values or formulas. The corrected and / or uncorrected frequency is then used in the algorithms to signal temperatures.

Um die Beziehung zwischen der Frequenz f und der Temperatur T zu erhalten, ist eine Kalibrierungskurve f(T) aufzunehmen bzw. zu registrieren. Dies erfolgt durch Messung der Temperatur T im Geschirrboden (mittels separater Temperatursensoren) und gleichzeitige Registrierung der Temperatur T und der Frequenz f bei einer festen Leistungseinstellung P. Die Messdaten lassen sich dann mit einer Kurvenanpassungsmethode, beispielsweise einer Polynomanpassung, an eine akzeptierte Genauigkeit anpassen. Am Ende dieses Abschnitts erhält man eine Beziehung f(T) für ein bestimmtes Geschirr. Da jedoch die Frequenz f vom Leistungsniveau P abhängt, ist all dies für die anderen zu nutzenden Leistungsniveaus zu wiederholen, um schließlich eine Beziehung f(T, P) zu haben, die in der Steuerlogik als Kalibrierungskurve (für ein bestimmtes Geschirr) gespeichert wird. Fig. 4 zeigt eine Schar abfallender f(T)-Kalibrierungskurven für Leistungen P1, P2, P3 und P4.In order to obtain the relationship between the frequency f and the temperature T, a calibration curve f (T) is to be recorded. This is done by measuring the temperature T in the dish bottom (by means of separate temperature sensors) and registering the temperature T and the frequency f at a fixed power setting P. The measurement data can then be adjusted to an accepted accuracy using a curve fitting method, such as polynomial fitting. At the end of this section you get a relationship f (T) for a particular harness. However, since the frequency f depends on the power level P, all this has to be repeated for the other power levels to be used to finally have a relation f (T, P) stored in the control logic as a calibration curve (for a particular harness). Fig. 4 shows a family of decreasing f (T) calibration curves for powers P1, P2, P3 and P4.

Wenn dieses Geschirr (Pfanne, Topf, Friteuse und dgl.) später benutzt wird, verbindet die Steuerlogik die gemessene Frequenz f mit einer Temperatur T für ein bestimmtes Leistungsniveau P. Dies macht es dann möglich, die gewünschten Funktionen entsprechend der in der Steuerlogik gespeicherten Algorithmen durchzuführen.When this harness (pan, pot, fryer and the like) is later used, the control logic associates the measured frequency f with a temperature T for a particular power level P. This then makes it possible to perform the desired functions according to the algorithms stored in the control logic perform.

Dieses Verfahren erfordert eine Identifikation des benutzen Geschirrs 8.This method requires identification of the harness 8 used.

Es gibt Unterschiede zwischen verschiedenen Pfannen/Töpfen in bezug auf das f(T, P)-Verhalten, wobei sowohl das relative Niveau als auch der Anstieg bzw. die erste Ableitung f(t) bei einer bestimmten Temperatur variieren kann.There are differences between different pans / pots with respect to the f (T, P) behavior, where both the relative level and the slope or the first derivative f (t) may vary at a particular temperature.

Unter der Annahme, dass sich die Pfanne zu Beginn auf Raumtemperatur T-start befindet, der eine Startfrequenz f-start zugeordnet ist, wird der Messwert als relative Frequenz f-rel=f/f-start ausgedrückt, so dass sich die Abweichungen zwischen unterschiedlichen Pfannen aufgrund des relativen Frequenzniveaus vermeiden lassen. In jedem Fall liegt so beispielsweise der Wert f-rel für 250 °C bei ungefähr 0,83 für ein breites Register von Pfannen, die dem Nutzer bei Benutzung dieser Methode empfohlen werden kann.Assuming that the pan is initially at room temperature T-start, which is assigned a start frequency f-start, the Measured value expressed as relative frequency f-rel = f / f-start, so that the deviations between different pans due to the relative frequency level can be avoided. In any case, for example, the value f-rel for 250 ° C is about 0.83 for a broad index of pans that can be recommended to the user using this method.

Im Folgenden werden die Steuer- bzw. Regelalgorithmen A beschrieben.In the following, the control algorithms A will be described.

Um ein Sieden bzw. Aufkochen zu erkennen, ist es nicht notwendig, den absoluten Wert der Temperatur T zu kennen, d. h., eine Beziehung zwischen der Frequenz f und der Temperatur T zu haben. Der Steuer- bzw. Regelalgorithmus A überwacht die Änderung des Frequenzverlaufs f(t) über der Zeit t (Fig. 5). Wenn sich die erste Ableitung f'(t) von einem negativen Wert her zu etwa Null hin verändert, hat der Topfboden eine konstante Temperatur erreicht, so dass sich daraus die Zeit t, zu der das Gargut siedet bzw. aufkocht, ableiten lässt. In diesem Fall wird die Leistung P bzw. der Strom I in der Induktionsspule 6 auf einen vorbestimmten Wert reduziert. Unbeschadet dessen zeigt Fig. 5, dass einem Temperaturverlauf T(t), der im Bereich des Siedepunktes seinen zuvor etwa linear ansteigenden in einen danach etwa konstant bleibenden Verlauf ändert, ein Frequenzverlauf f(t), der im Bereich des Siedepunktes seinen zuvor etwa linear abfallenden in einen danach etwa konstant bleibenden Verlauf ändert, zuordenbar ist und umgekehrt.In order to recognize boiling, it is not necessary to know the absolute value of the temperature T, that is, to have a relationship between the frequency f and the temperature T. The control algorithm A monitors the change of the frequency characteristic f (t) over the time t ( Fig. 5 ). When the first derivative f '(t) changes from a negative value to approximately zero, the bottom of the pot has reached a constant temperature, so that the time t, to which the food boils or boils, can be derived. In this case, the power P or the current I in the induction coil 6 is reduced to a predetermined value. Notwithstanding this shows Fig. 5 in that a temperature profile T (t), which in the region of the boiling point changes its previously approximately linearly rising course to a course which remains approximately constant, has a frequency curve f (t) which in the region of the boiling point is approximately linear before it decreases linearly in one direction changes, is assignable and vice versa.

Während des Leer- bzw. Trockenkochens (Fig. 6) tritt ein Abfall der Frequenz f auf, wenn beispielsweise Wasser aus dem Topf entwichen ist. Dies kann als plötzlicher Abfall bzw. eine plötzliche Änderung der ersten Ableitung f'(t) oder als bestimmter Wert der ersten Ableitung f'(t) erkannt werden, entsprechend einem Temperaturanstieg in einem leeren Topf. Für langsame Trockenkochprozesse (Gargut mit geringem oder mittleren Wassergehalt) steigt die Temperatur T nicht so schnell. Dann kann das stabile Frequenzniveau während des Siedens (Kochens) als Referenzniveau genutzt werden, um eine Kalibrierung bzgl. 100 °C vorzunehmen. Wenn das Wasser entwichen ist, fällt die Frequenz, und die Leistung der Kochzone wird bei einem bestimmten relativen Wert f1 in bezug auf 100 °C abgeschaltet. Unbeschadet dessen zeigt Fig. 6, dass einem Temperaturverlauf T(t), der im Bereich des Siedepunktes seinen Verlauf aus einem zuvor etwa linear ansteigenden in einen danach etwa konstanten Verlauf und im Bereich des Leer- bzw. Trockenkochens seinen zuvor konstanten Verlauf in einen danach etwa linear ansteigenden Verlauf ändert, ein Frequenzverlauf f(t) zuordenbar ist, der im Bereich des Siedepunktes seinen zuvor etwa linear abfallenden Verlauf in einen danach etwa konstanten Verlauf und im Bereich des leer- bzw. Trockenkochens seinen zuvor etwa konstanten Verlauf in einen danach etwa linear abfallenden Verlauf ändert. Sowohl im T(t)-Verlauf als auch im f(t)-Verlauf ist das schnelle Leer- bzw. Trockenkochen mit B1 und das langsame Leer- bzw. Trockenkochen mit B2 gekennzeichnet. Im f'(t)-Verlauf gibt S die Spannweite f'(t) an, die mit dem Erhitzen eines leeren Topfes korrespondiert.During the empty or dry cooking ( Fig. 6 ), a drop in frequency f occurs when, for example, water has escaped from the pot. This can be recognized as a sudden fall or a sudden change in the first derivative f '(t) or as a specific value of the first derivative f' (t), corresponding to a temperature rise in an empty pot. For slow Trockenkochprozesse (food with low or medium water content), the temperature T does not rise so fast. Then, the stable frequency level during boiling (cooking) as a reference level used to calibrate for 100 ° C. When the water has escaped, the frequency drops and the power of the cooking zone is turned off at a certain relative value f1 with respect to 100 ° C. Notwithstanding this shows Fig. 6 in that a course of temperature T (t) which changes its course in the region of the boiling point from a previously approximately linearly ascending course to an approximately constant course and in the area of empty or dry cooking changes its previously constant course into an approximately linearly ascending course thereafter, a frequency curve f (t) can be assigned, which changes in the region of the boiling point its previously approximately linearly sloping course in a thereafter approximately constant course and in the range of empty or dry cooking its previously approximately constant course in a thereafter approximately linearly sloping course. Both in the T (t) run and in the f (t) run, the fast empty or dry cooking is labeled B1 and the slow empty or dry cooking is labeled B2. In the f '(t) run, S indicates the span f' (t) corresponding to the heating of an empty pot.

Beim Regeln der Temperatur einer Pfanne oder eines Topfes auf konstante Temperatur entsprechend einer Nutzereinstellung N (insbesondere genutzt für Bratpfannen, Braten und Frittieren in Öl) wird eine Anzahl von Leistungsniveaus benutzt. Gemäß dem zuvor Beschriebenen sind hierfür Kalibrierungskurven f(T, P) nach Fig. 4 für die zur Nutzung vorgesehenen Leistungsniveaus heranzuziehen.In controlling the temperature of a ladle or pot to a constant temperature corresponding to a user setting N (particularly used for frying pans, frying and frying in oil), a number of performance levels are used. According to what has been described above, calibration curves f (T, P) are after Fig. 4 for the levels of use envisaged for use.

Die Temperaturregelung könnte dann beispielsweise als Thermostatfunktion durchgeführt werden. Die Leistung der Kochzone kann auf zwei unterschiedliche Niveaus P-high und P-low gesetzt werden (beispielsweise P1 und P2), die mit zwei Kalibrierungskurven f(T, P-high) und f(T, P-low) verbunden sind. Die Frequenz f wird dann kontinuierlich gemessen und die Temperatur T aus den Kalibrierungskurven abgeleitet, abhängig davon, welches Leistungsniveau genutzt wird. Wenn die berechnete Temperatur T-meas größer ist als die eingestellte Temperatur T-set, wird der Kochzone die niedrigere Leistung P-low zugeführt. Ist T-meas kleiner als T-set, erhält die Kochzone die höhere Leistung P-high (Fig. 7). Auf diese Weise wird die Pfanne oder der Topf auf einem deutlich konstanten Temperaturniveau gehalten.The temperature control could then be carried out, for example, as a thermostat function. The power of the cooking zone can be set to two different levels P-high and P-low (for example P1 and P2), which are connected to two calibration curves f (T, P-high) and f (T, P-low). The frequency f is then measured continuously and the temperature T derived from the calibration curves, depending on which power level is used. If the calculated temperature T-meas is greater than the set temperature T-set, the Cooking zone fed the lower power P-low. If T-meas is less than T-set, the cooking zone receives the higher power P-high ( Fig. 7 ). In this way, the pan or pot is kept at a significantly constant temperature level.

Insgesamt lassen sich zu Frequenzen und/oder Frequenzverhältnissen und/oder Frequenzänderungen und/oder Frequenzverläufen und/oder deren ersten Ableitungen Temperaturen und/oder Temperaturverhältnisse und/oder Temperaturänderungen und/oder Temperaturverläufe und/oder deren erste Ableitungen zuordnen und/umgekehrt.Overall, temperatures and / or temperature conditions and / or temperature changes and / or temperature profiles and / or their first derivatives can be assigned to frequencies and / or frequency ratios and / or frequency changes and / or their first derivatives and / vice versa.

Dem Nutzer stehen so auf erfindungsgemäße Weise Geräteeigenschaften zur Verfügung, die sowohl die Funktionalität als auch die Sicherheit positiv beeinflussen. Diese Merkmale sind allgemein:

  • Siedeerkennung:
    • Die Leistung wird trägheitsarm auf ein vorbestimmtes Niveau reduziert oder abgeschaltet, wenn der Inhalt des Gargefäßes siedet bzw.
    • aufkocht. Die schnelle Siedeerkennung arbeitet auch als Überkochschutz.
  • Leer- bzw. Trockenkocherkennung:
    • Die Leistung wird trägheitsarm abgeschaltet, wenn das Wasser aus dem Gargefäß entwichen und/oder die Temperatur des Gargefäßes zu hoch ist. Feuer und Gefäßschäden werden vermieden.
  • Temperaturregelung:
    • Die Temperatur wird trägheitsarm auf einem einmal eingestellten konstanten Temperaturniveau gehalten, ohne dass der Nutzer nach der ersten Einstellung manuell eingreifen muss. Dies lässt sich insbesondere nutzen, um
      • eine stabile Temperatur für das Braten zu erhalten,
      • eine stabile Temperatur während des Frittierens in Öl (bei beispielsweise etwa 180 °C) zu erhalten, was auch als Überhitzungsschutz wirkt, und
      • die Temperatur auf niedrigeren Niveaus zu begrenzen, um ein Anbrennen und Ankleben am Gefäßboden zu vermeiden.
The user is thus in the manner of the invention device properties available that positively affect both the functionality and safety. These features are general:
  • Siedeerkennung:
    • The power is reduced inertially to a predetermined level or switched off when the contents of the cooking vessel boils or
    • boils. The quick boiling detection also works as overcooker protection.
  • Empty or dry cooker detection:
    • The power is turned off inertially when the water escaped from the cooking vessel and / or the temperature of the cooking vessel is too high. Fire and vessel damage are avoided.
  • Temperature control:
    • The temperature is kept low in inertia at a set constant temperature level, without the user having to intervene manually after the first setting. This can be used in particular to
      • to get a stable temperature for frying,
      • a stable temperature during deep-frying in oil (for example, about 180 ° C), which also acts as overheating protection, and
      • limit the temperature to lower levels to avoid burning and sticking to the bottom of the vessel.

Claims (14)

  1. Method for thermal monitoring of an inductively heatable cooking vessel by monitoring the frequency (f), which is influenced by the cooking vessel, of the alternating current (I) effecting inductive heating,
    a) in which monitoring of temperatures (T) is effected by assignment of predetermined frequencies (f) or frequency ratios (f/f start) to predetermined temperatures (T) or vice versa,
    characterised in that
    b) monitoring of rapid changes of the temperature-time curve (T(t)) is effected as monitoring of rapid changes of the frequency-time curve (f(t)) and
    c) the frequency (f) is measured when the mains voltage has its maximum.
  2. Method according to claim 1, in which
    a) monitoring of boiling or simmering of a cooking material located in the cooking vessel or of boiling dry of the cooking vessel or cooking dry of the cooking material located therein is effected as monitoring of predetermined rapid changes of the frequency-time curve (f(t)) or of predetermined changes or absolute values of the first derivation (f'(t)) of the frequency-time curve (f(t)).
  3. Method according to claim 2, in which
    a) monitoring of boiling or simmering is effected as monitoring of a predetermined rapid change of the frequency-time curve (f(t)) from the direction of a linearly falling frequency (f) in the direction of a constant frequency (f) or of a predetermined change of the first derivation (f'(t)) of the frequency-time curve (f(t)) from the direction of a negative value in the direction of a value of zero or of a predetermined value of the first derivation (f'(t)) of the frequency-time curve (f(t)), or in which
    b) monitoring of boiling dry or cooking dry is effected as monitoring of a predetermined rapid change of the frequency-time curve (f(t)) from the direction of a constant frequency (f) in the direction of a linearly falling frequency (f) or of a predetermined change of the first derivation (f'(t)) of the frequency-time curve (f(t)) from the direction of a value of zero in the direction of a negative value or of a predetermined value of the first derivation (f'(t)) of the frequency-time curve (f(t)).
  4. Method according to claim 2 or claim 3, in which the predetermined rapid change(s) of the frequency-time curve (f(t)) lie in or directly after the transition from the falling frequency curve (f(t)) to the constant frequency curve (f(t)) or from the constant frequency curve (f(t)) to the falling frequency curve f(t).
  5. Method according to one of claims 2 to 4, in which the alternating current (I) or the corresponding power (P) is reduced to a predetermined value, in particular switched off, when during monitoring, one or more changes have been established which concur with one or more predetermined changes.
  6. Method according to one of the preceding claims, in which the assignment of the frequencies (f) or frequency ratios (f/f start) to the temperatures (T) is effected as a function of predetermined properties, in particular material properties, of the cooking vessel which are preset in particular for the use or retrieved by the user, or in which the assignment of the frequencies (f) or frequency ratios (f/f start) to the temperatures (T) is effected as a function of predetermined powers (P).
  7. Method according to one of the preceding claims, in which assuming that the cooking vessel at the start is at room temperature (T start), to which is assigned a starting frequency (f start), the measured value is expressed as a relative frequency (f rel) as a quotient (f/f start) of the frequency (f) and of the starting frequency (f start), wherein in particular the deviations between different cooking vessels can be avoided due to the relative frequency level, wherein in particular the value of the relative frequency (f rel) for 250°C is approximately 0.83 for a broad register of cooking vessels which may be recommended to the user when using this method, or wherein in particular the properties of the cooking vessel are preset for the use or retrieved by the user.
  8. Method according to one of the preceding claims, in which the temperature of the cooking vessel is set to a required value or kept at a required value, in that
    - the frequency (f) is monitored continuously,
    - a temperature (T) is assigned continuously to the frequency (f) or to the frequency ratio (f/f start) as a function of the currently assigned power (P) and the currently assigned cooking vessel,
    - the deviation between the assigned and the required temperature (T) is established continuously and
    - according to the deviation, one of the assignable powers is selected.
  9. Method according to one of the preceding claims having at least one of the following further features:
    - the temperature is measured and established directly in the base of the cooking vessel close to the cooking material,
    - a separate transmission channel for measured data from the cooking vessel to the cooking hob is not provided,
    - the method is used to monitor or control the cooking process in an inductively heatable cooking vessel, in which during cooking, temperatures or temperature changes are recorded and evaluated as frequencies or frequency changes of an alternating current effecting inductive heating to signal or to influence the temperature of the cooking vessel,
    - the coil current (I) is measured by means of a current transformer 7, wherein the oscillating frequency (f) of typically 20 to 60 kHz is modulated by the rectified mains power supply and this signal leads to a frequency measuring circuit (3) which analyses the signal and establishes the oscillating frequency (f),
    - the operating frequency of the induction inverter 5 is moved in particular in the range between 20 and 60 kHz, depending on the power level and the frequency f (that is, the reversal of the period length of a cycle) also varies over the rectified sine curve period,
    - for slow cooking-dry processes (cooking material with low or average water content), the temperature (T) does not increase so rapidly and the stable frequency level during boiling (simmering) is used as a reference level to carry out calibration with respect to 100°C, and when the water has escaped, the frequency drops and the power of the cooking zone is switched off at a certain relative value (f1) with respect to 100°C,
    - during regulation of the temperature of a pan or of a pot at constant temperature corresponding to a user setting N (in particular used for frying pans, frying and deep-frying in oil), a number of power levels are used and calibration curves f(T, P) for the power levels provided for use are thus consulted.
  10. Method according to one of the preceding claims having at least one of the following further features:
    - temperatures or temperature ratios or temperature changes or temperature curves or their first derivations are assigned to frequencies or frequency ratios or frequency changes or frequency curves or their first derivations or vice versa
    - boiling detection: the power is reduced or switched off in low-inertia manner to a predetermined level when the content of the cooking vessel boils or simmers. Rapid boiling detection also operates as protection against boiling over.
    - boiling dry or cooking dry detection: the power is switched off in low-inertia manner when the water has escaped from the cooking vessel or the temperature of the cooking vessel is too high. Fire and vessel damage are avoided.
  11. Device for thermal monitoring of an inductively heatable cooking vessel and for implementing the method according to one of claims 1 to 10, having
    a) first means (4, 5) for providing an alternating current (I) effecting inductive heating,
    b) second means (3) for establishing the frequency (f), which is influenced by the cooking vessel (8), of the alternating current (I) and
    c) third means (2) for signalling or controlling the temperature (T) of the cooking vessel (8) as a function of the frequency (f) of the alternating current (I), characterised in that
    d) the third means (2) have first storage means, with which predetermined rapid changes of frequency-time curves (f(t)) or predetermined changes of first derivations (f'(t)) of frequency-time curves (f(t)) can be stored which as reference data represent in particular boiling or simmering of a cooking material located in the cooking vessel (8) or boiling dry of the cooking vessel (8) or cooking dry of the cooking material located therein, and in that
    e) the third means (2) have second storage means, with which predetermined frequency-temperature curves (f(T)) or frequency ratio-temperature curves (f/f start(T)) can be stored, in particular per cooking vessel property or power.
  12. Device according to claim 11, in which input means (1), with which the user may input required temperatures (T) or programs, in particular cooking programs containing temperatures (T), or powers (P) or cooking vessels (8) or their properties, are assigned to the third means (2).
  13. Device according to claim 11 or claim 12, in which the third means (2) have computing means, with which the frequencies (f) established using the second means (3) and the data stored using the first and second storage means and the data input using the input means (1) can be converted to alternating currents (I) or corresponding powers (P) which influence the temperature (T) of the cooking vessel (8) according to the input or stored data, wherein in particular the influencing of temperature (T) consists in its predetermined reduction on established boiling or established boiling dry or cooking dry or in its setting or maintenance of correspondingly input user data.
  14. cooking appliance having at least one device according to one of claims 11 to 13.
EP10178369A 2002-11-15 2003-10-24 Method and device of thermal monitoring of inductive heatable cooking vessel Expired - Lifetime EP2271175B1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE2002153198 DE10253198B4 (en) 2002-11-15 2002-11-15 Method and device for thermal monitoring of an inductively heated cooking vessel
EP03024314.1A EP1420613B1 (en) 2002-11-15 2003-10-24 Method and device of thermal monitoring of inductive heatable cooking vessel

Related Parent Applications (2)

Application Number Title Priority Date Filing Date
EP03024314.1 Division 2003-10-24
EP03024314.1A Division-Into EP1420613B1 (en) 2002-11-15 2003-10-24 Method and device of thermal monitoring of inductive heatable cooking vessel

Publications (3)

Publication Number Publication Date
EP2271175A2 EP2271175A2 (en) 2011-01-05
EP2271175A3 EP2271175A3 (en) 2011-01-19
EP2271175B1 true EP2271175B1 (en) 2012-12-26

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EP10178369A Expired - Lifetime EP2271175B1 (en) 2002-11-15 2003-10-24 Method and device of thermal monitoring of inductive heatable cooking vessel
EP03024314.1A Expired - Lifetime EP1420613B1 (en) 2002-11-15 2003-10-24 Method and device of thermal monitoring of inductive heatable cooking vessel

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DE (2) DE10253198B4 (en)
DK (1) DK2271175T3 (en)
ES (1) ES2401740T3 (en)

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Also Published As

Publication number Publication date
EP2271175A2 (en) 2011-01-05
EP1420613A3 (en) 2006-03-22
EP1420613A2 (en) 2004-05-19
ES2401740T3 (en) 2013-04-24
DE10253198B4 (en) 2007-07-05
DE10262141B4 (en) 2009-10-15
DK2271175T3 (en) 2013-04-02
DE10253198A1 (en) 2004-06-24
EP2271175A3 (en) 2011-01-19
EP1420613B1 (en) 2016-07-13

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