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EP0739508A1 - Dispositif de commande de temperature de fonctionnement dans une zone de cuisson - Google Patents

Dispositif de commande de temperature de fonctionnement dans une zone de cuisson

Info

Publication number
EP0739508A1
EP0739508A1 EP95901363A EP95901363A EP0739508A1 EP 0739508 A1 EP0739508 A1 EP 0739508A1 EP 95901363 A EP95901363 A EP 95901363A EP 95901363 A EP95901363 A EP 95901363A EP 0739508 A1 EP0739508 A1 EP 0739508A1
Authority
EP
European Patent Office
Prior art keywords
temperature
cooking zone
energy
thermal load
supply
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP95901363A
Other languages
German (de)
English (en)
Inventor
Johan Axelson
Jan E. Dahl
Daniel Schneider
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Electrolux AB
Original Assignee
Electrolux AB
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Electrolux AB filed Critical Electrolux AB
Publication of EP0739508A1 publication Critical patent/EP0739508A1/fr
Withdrawn legal-status Critical Current

Links

Classifications

    • 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
    • H05B3/00—Ohmic-resistance heating
    • H05B3/68—Heating arrangements specially adapted for cooking plates or analogous hot-plates
    • H05B3/74—Non-metallic plates, e.g. vitroceramic, ceramic or glassceramic hobs, also including power or control circuits
    • H05B3/746—Protection, e.g. overheat cutoff, hot plate indicator
    • G—PHYSICS
    • G05—CONTROLLING; REGULATING
    • G05D—SYSTEMS FOR CONTROLLING OR REGULATING NON-ELECTRIC VARIABLES
    • G05D23/00—Control of temperature
    • G05D23/19—Control of temperature characterised by the use of electric means
    • G05D23/1917—Control of temperature characterised by the use of electric means using digital means
    • G—PHYSICS
    • G05—CONTROLLING; REGULATING
    • G05D—SYSTEMS FOR CONTROLLING OR REGULATING NON-ELECTRIC VARIABLES
    • G05D23/00—Control of temperature
    • G05D23/19—Control of temperature characterised by the use of electric means
    • G05D23/20—Control of temperature characterised by the use of electric means with sensing elements having variation of electric or magnetic properties with change of temperature

Definitions

  • the present invention relates to an apparatus for controlling the operating temperature of a cooking zone heated from below by energy supplied in pulses by detecting and classifying into neighbouring ranges the thermal load on its surface, and comprising means for determining the average temperature of at least part of the cooking zone.
  • the concept "pot detection” covers the determination whether a cooking vessel present on a cooking zone fulfils the criteria needed in order for it to represent an acceptable load, viz. its material, the flatness of its bottom, even whether the vessel covers a sufficient area of the heated cooking zone or whether water has boiled away entirely.
  • This is obtained by means of an apparatus according to the invention which is particular in that at least one measurement value contributing to a representation of the momentary thermal load condition is extracted from the function of temperature over time during transient heating and/or cooling phases, of which at least one value is stored representing the limit between neighbouring operational ranges, that the measurement value is compared to the stored value, and that a control signal is generated which represents the particular range of the applied thermal load, which control signal controls the supply of energy.
  • the thermal load is determined by means of the step response of the load to a known input energy step function. In this way all the problems of interpreting parameters related to non-thermal detection of the physical presence of a cooking vessel are eliminated.
  • An advantageous simplification of the evaluation is obtained by synchronizing the evaluation to the pulses of energy according to claim 3.
  • the rate of change of the temperature over time is compared to a predetermined value which is in itself a function of the desired operating temperature of the cooking zone which is set by the user.
  • SUBSTITUTESHEET The basis for the measurement of a thermal load is the stability of temperature. This is obtained and optimized by the measures of claim 4 by which means the hysteresis is kept to a minimum.
  • a further simplification is obtained by performing the measurements and evaluation during a phase where no energy is supplied to the thermal load.
  • the determination may be based on a differential decrease of temperature which corresponds to only two points of the curve of decrease or on a monitoring of the curve, in which case the rate of decrease in optional points may be determined.
  • an advantageous operation is obtained when a time delay is introduced from the time of determining the too small load and to the actual switching off of the energy because a further measurement may indicate that there is a load after all, the user was simply slow in putting a pot on the cooking zone. In case a second measurement indicates no change in the potentially dangerous no-load situation the control circuits switches off, and the cooking zone control will have to be reset.
  • the measurement of a temperature representative of the thermal load is performed when a sufficient degree of equilibrium of temperature based on the heat loss (thermal load) has been obtained, that is as late in a period of no energy supply as is possible. In this way, in particular influences from supply voltage fluctuations are avoided, which is important because the influence of such fluctuations follow a square law.
  • a cooking zone controlled by means of an apparatus according to claim 8 will have an advantageous fast heating because the energy supply is uninterrupted until the intended operating temperature is reached.
  • SUBSTITUTESHEET is defined in claim 9 which enables a more precise determination of the degree of overlap between a cooking vessel and the cooking zone.
  • an advantagous embodiment is defined which enables evaluation to take place even if the changes in operating conditions are vague or even conflicting from measuring area to another, such as would be the case if a cooking vessel is moved about or briefly removed and replaced on the cooking zone.
  • a further advantageous embodiment is defined which provides a greater flexibility in use, in that the calibration phase permits a personalization of the set of pots in use, thereby allowing the limit between acceptable and non- acceptable operating ranges to be determined with greater precision.
  • Fig. 1 shows the basic concept of the present invention in connection with a schematic diagram
  • Fig. 2 shows the experimental determination of temperature over time following the switching on of a heating element, in the cases “no pot”, “unsuitable pot”, and “normal pot”,
  • Fig. 3 shows a first embodiment of the invention according to the general schematic of Fig. 1, utilizing the different types of measurement results of Fig. 2,
  • Fig. 4 shows the first derivative over time of the measurements of Fig. 2,
  • Fig. 5 shows a preferred embodiment of the invention according to the general schematic of Fig. 1, utilizing the different results of Fig. 4,
  • Fig. 6 shows the classification of the representation of the thermal load on a two-dimensional graph of "maximum of temperature function derivative" over “limit temperature obtained", using the supplied power as a parameter,
  • FIG. 7 shows a further preferred embodiment of the invention utilizing the classification of Fig. 6,
  • Fig. 8 schematically shows an advantageous distribution of temperature sensors in order to obtain information relating to quality of pot and its degree of off-axis placement
  • Fig. 9 shows the function of the cooking zone temperature in a stable situation where the temperature is controlled by a thermostat, and indicates two different measures representing characteristic features which are influenced by the quality of pot or its degree of off-axis placement.
  • Fig. 1 shows schematically in a signal flow and functional block diagram the principal features of an apparatus according to the invention.
  • Heating elements 1 for a glass ceramic cooking zone 3 are connected by means of a switch 5 to the electrical supply 7 which may supply electric energy at predetermined rates which is indicated by the arrow. There may also be variations due to voltage fluctuations in the mains supply.
  • At least one continuous temperature sensor 9 is provided which may be of a conventional construction and which may be integrated with the cooking zone 3, placed directly below the cooking zone, supported in the volume V between the heating elements and the cooking zone or connected to a heat conductive support which follows the temperature or the average temperature of the volume it occupies.
  • the temperature sensor gives a signal S9 at its output dependent on the temperature th(t) which is a function of time t.
  • the output signal S9 of the sensor 9 is an input to the evaluation circuit 11. According to the invention it is determined whether the cooking zone 3 is loaded thermically in a permitted or non-permitted manner. Permitted or "acceptable” is the placement of a cooking pot or other utensil on the cooking zone, and
  • a transent phase is initiated as shown schematically by the switch 5.
  • the cooking zone 3 acts as a heat sink until the heat supplied by the heating elements 1 equals the heat transported to the surroundings by radiation and conduction.
  • the switching on phase may be described by means of a function of the type (1- exp(-at/tau) ) .
  • the cooking zone 3 acts as a heat source, and its temperature decreases according to a function of the type exp(bt/tau) .
  • a control signal S5 from the switch controlling the supply of energy to the heating elements 1 starts the evaluation circuit 11.
  • the evaluation occurs during the transient phases during which certain representations related to the signal S9 which are to be described further in the following are determined before the transient conditions have settled. Such determinations may occur by extrapolation of the temperature functions determined from the starting conditions or by determining characterizing representations which are essentially independent of an end condition which is approached but not reached.
  • the temperature function in the above mentioned transient phases is not only dependent on the load determined by the user but also by the instantaneous power delivered by the heating elements 1.
  • the evaluation in the evaluation circuit 11 occurs, as is shown in Fig.
  • SUBSTITUTESHEET 1 by using the power P as another input, e.g. by using the applied voltage SP fed to the heating elements 1.
  • characteristic values X(th(t)) of the temperature function appear and are fed to a comparator 13.
  • characteristic values Xo(th(t)) are stored and function as limit values for determining the allowability of the load on the cooking zone 3.
  • the instantaneous determined values X are compared to the stored values Xo, and dependent on the result a signal S13 is obtained at its output indicating the allowability which may be used as a control signal.
  • Fig. 2 the temperature function th(t) of the heating zone 3 is shown, whereby the function oT corresponds to "no pot", the function sT corresponds to "unsuitable pot", i.e. in the present case a pot with a concave bottom, and the function nT corresponds to a normal pot with an essentially flat bottom. It will be seen that the increase in temperature over time is slower in the case of oT as compared to sT or nT.
  • Fig. 3 it is quite possible to use the results of Fig. 2 in an evaluation circuit which uses a dividing circuit 16 to introduce a correction relating to the nominal power P fed to the heating element of the signal S9 from the temperature sensing element 9.
  • the signal derived by correction from S9 may be stored as thN(t) in the store 11a.
  • a comparator unit 13 it is compared to a previously stored function
  • SUBSTITUTESHEET th ⁇ (t) taken from a similar store 15 and produces the output signal S13 which is then used as a control signal for the power supply to the cooking zone.
  • the law governing the temperature drop is exponential
  • one descriptor could be the first derivative at the start of the temperature drop.
  • the exponential function is only an approximation, in particular because it is not a first order system. This may be realized in view of the different thermal time constants present in the system, such as for the heating element, the ceramic plate on which the cooking zone is defined and the pot, and may be seen from the time function given in Fig. 2 as oT.
  • Fig. 4 the first derivative function of the time functions oT, St, and nT are shown, indicated by the apostrophy. It may be seen that the maxima of the respective functions very clearly give the desired discrimination between various thermal load conditions.
  • Fig. 5 is given a schematic diagram of an apparatus which will perform an analysis of the signal according to the observations discussed in relation to Fig. 4.
  • a zero in the second derivative function indicates a maximum, and at this moment the switch K connects the first derivative signal from the differentiator 19 to the comparator 13 in which this value is compared to a previously stored value taken from the store 15.
  • a value above the value G on Fig. 4 indicates the presence of a pot.
  • the output S13 will be the control signal for the power supply.
  • Several similar signal processing means may be used to obtain reliable
  • This realization may be used in a circuit which is represented schematically in Fig. 7 in order to obtain a precise indication of the thermal load and to control precisely the temperature of the cooking zone.
  • the output signal S9 of the temperature sensor 9 of Fig. 1 is taken to the unit 19 which determines the first time derivative and to the unit 21 which determines the second time derivative.
  • a null-detector 23 determines the time of of obtaining a null of the second derivative, and the maximum of the
  • SUBSTITUTESHEET first derivative which this corresponds to is transferred by means of the switch Ql as the signal S19 to the comparator unit 13.
  • a null of the second derivative corresponding to the first minimum of the first derivative is irrelevant for the present purpose, while the minimum value of the first derivative after the maximum is relevant for determining the end of the transient switched-off state.
  • circuit elements 25, Q3 and Q5 are employed in order to eliminate the influence of the first minimum.
  • the signal S25 represents the temperature thoo at the minimum of the first derivative after the maximum, and so the end temperature reached at the end of the switched-off phase.
  • value pairs corresponding to the limit curves Fl and F2 are stored.
  • the determination which is described above is preferably performed digitally, the signals from the temperature sensors being converted in A/D converters.
  • the apparatus herein described is independent on the temperature sensor in use, however precision is increased by a more continuous function of temperature over time when several temperature sensors are distributed in proximity to the cooking zone. Such temperature sensors may combined, optionally via suitable weighting, into one signal which has been discussed as S9.
  • FIG. 8 A particularly suitable arrangement of temperature sensors is shown schematically on Fig. 8. Three temperature sensors 9a, 9b, 9c are disposed along the outer perimeter but excentrically, and these will give
  • SUBSTITUTESHEET rise to a number of curves corresponding to a large number of excentricities of an acceptable pot, which is hence a further parameter relating to the type of load which may be determined according to the invention.
  • Fig. 1 lends itself directly to the control of the temperature of the cooking zone.
  • the transient switched-off phase begins, and when the minimum acceptable temperature Pu has been reached, a phase of power supply begins again. This enables a simpler way of determining the thermal load, i.e. the quality of a pot and its placement.

Landscapes

  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Automation & Control Theory (AREA)
  • Chemical & Material Sciences (AREA)
  • Ceramic Engineering (AREA)
  • Cookers (AREA)

Abstract

La détection d'un récipient, la détermination de son type et celle d'une anomalie peuvent s'obtenir par le traitement approprié de signaux et par des statistiques concernant des mesures de rayonnement thermique provenant de la surface supérieure d'une zone de cuisson éventuellement constituée de vitrocéramique. Ces mesures sont converties en indicateurs de charge thermique appliquée en fonction de la durée aux éléments radiants et classés selon des limites mémorisées, éventuellement déterminées pendant des cycles d'étalonnage. La puissance fournie aux éléments chauffants sert de facteur de correction.
EP95901363A 1993-12-06 1994-12-05 Dispositif de commande de temperature de fonctionnement dans une zone de cuisson Withdrawn EP0739508A1 (fr)

Applications Claiming Priority (5)

Application Number Priority Date Filing Date Title
CH3636/93 1993-12-06
CH363693 1993-12-06
DK578/94 1994-05-20
DK57894 1994-05-20
PCT/DK1994/000456 WO1995016230A1 (fr) 1993-12-06 1994-12-05 Dispositif de commande de temperature de fonctionnement dans une zone de cuisson

Publications (1)

Publication Number Publication Date
EP0739508A1 true EP0739508A1 (fr) 1996-10-30

Family

ID=25693495

Family Applications (1)

Application Number Title Priority Date Filing Date
EP95901363A Withdrawn EP0739508A1 (fr) 1993-12-06 1994-12-05 Dispositif de commande de temperature de fonctionnement dans une zone de cuisson

Country Status (3)

Country Link
EP (1) EP0739508A1 (fr)
AU (1) AU1064195A (fr)
WO (1) WO1995016230A1 (fr)

Families Citing this family (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
AU7561396A (en) * 1995-11-21 1997-06-11 Aktiebolaget Electrolux A cooking surface with controls
DE19544652A1 (de) * 1995-11-30 1997-06-05 Ako Werke Gmbh & Co Leistungs-Regeleinrichtung für eine Strahlungsbeheizung
DE29702813U1 (de) 1997-01-10 1997-05-22 E.G.O. Elektro-Gerätebau Gmbh, 75038 Oberderdingen Kontaktwärmeübertragendes Kochsystem mit einer Elektro-Kochplatte
EP0853444B1 (fr) * 1997-01-10 2005-11-23 E.G.O. ELEKTRO-GERÄTEBAU GmbH Système à cuire avec une plaque de cuisson électrique, transférant la chaleur par conduction
DE19851029C2 (de) * 1998-11-05 2000-12-21 Schott Glas Verfahren zum Anpassen des Grenzwertes der Betriebstemperatur einer Glas-/Glaskeramikkochfläche und Vorrichtung zur Durchführung des Verfahrens
GB0313831D0 (en) * 2003-06-16 2003-07-23 Ceramaspeed Ltd Apparatus and method for detecting abnormal temperature rise associated with a cooking arrangement
DE10329840A1 (de) * 2003-06-27 2005-01-20 E.G.O. Elektro-Gerätebau GmbH Verfahren und Vorrichtung zur Erkennung von Erwärmungsvorgängen
DE102006057885A1 (de) 2006-12-01 2008-06-05 E.G.O. Elektro-Gerätebau GmbH Verfahren zum Erzeugen, Verarbeiten und Auswerten eines mit der Temperatur korrelierten Signals und entsprechende Vorrichtung
ES2392612B1 (es) * 2011-03-31 2013-10-22 BSH Electrodomésticos España S.A. Dispositivo electrodoméstico.
DE102013209720A1 (de) * 2013-05-24 2014-11-27 E.G.O. Elektro-Gerätebau GmbH Verfahren zum Ermitteln eines Stroms und Induktionsheizeinrichtung
US20230389135A1 (en) * 2022-05-25 2023-11-30 Haier Us Appliance Solutions, Inc. Cooktop appliance and method for detecting cookware removal

Family Cites Families (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2067880B (en) * 1980-01-14 1985-01-03 Johnson Matthey Co Ltd Glass ceramic hob including temperature sensor
US4740664A (en) * 1987-01-05 1988-04-26 General Electric Company Temperature limiting arrangement for a glass-ceramic cooktop appliance
DE3801225A1 (de) * 1988-01-18 1989-07-27 Wolfgang Fliecker Ueberhitzungsschutz fuer elektroherdkochplatten durch sensoren- oder dektorenueberwachung
FR2652172B1 (fr) * 1989-09-15 1996-06-28 Europ Equip Menager Dispositif et procede de regulation d'appareil de cuisson.

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See references of WO9516230A1 *

Also Published As

Publication number Publication date
WO1995016230A1 (fr) 1995-06-15
AU1064195A (en) 1995-06-27

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