EP1542507B1 - Vorrichtung zur Detektierung eines Kochgefässes auf einer Kochplatte - Google Patents

Vorrichtung zur Detektierung eines Kochgefässes auf einer Kochplatte Download PDF

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Publication number
EP1542507B1
EP1542507B1 EP20030028039 EP03028039A EP1542507B1 EP 1542507 B1 EP1542507 B1 EP 1542507B1 EP 20030028039 EP20030028039 EP 20030028039 EP 03028039 A EP03028039 A EP 03028039A EP 1542507 B1 EP1542507 B1 EP 1542507B1
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EP
European Patent Office
Prior art keywords
heating element
coil
impedance
current
cooking
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.)
Expired - Lifetime
Application number
EP20030028039
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English (en)
French (fr)
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EP1542507A1 (de
Inventor
Cristiano Pastore
Davide Parachini
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.)
Whirlpool Corp
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Whirlpool Corp
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Application filed by Whirlpool Corp filed Critical Whirlpool Corp
Priority to EP20030028039 priority Critical patent/EP1542507B1/de
Priority to ES03028039T priority patent/ES2280679T3/es
Priority to DE2003611835 priority patent/DE60311835T2/de
Publication of EP1542507A1 publication Critical patent/EP1542507A1/de
Application granted granted Critical
Publication of EP1542507B1 publication Critical patent/EP1542507B1/de
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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
    • 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
    • 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
    • H05B2213/05—Heating plates with pan detection means

Definitions

  • the present invention relates to a system for detecting the presence of a cooking utensil on a cooking hob comprising detection means whose impedance changes in relation to the presence or absence of said cooking utensil on the hob.
  • the system according to the invention is particularly useful for use with cooking utensils detection system on glass ceramic electric cooking hob.
  • the invention further relates to a temperature compensation method for inductive and cross-inductive pot-detection methods, used in glass-ceramic electric cooktops.
  • US 2001/00119262 A1 and US 6,424,145 B1 disclose non contact proximity sensor that operate as saturable core proximity sensor, a variable reluctance proximity sensor and an eddy current proximity sensor.
  • the known detection systems may be divided into two categories.
  • the conventional inductive systems as described in EP-A-0553425, and the cross-inductive systems, as described in EP-A-328092 or EP-A-1206164.
  • FIG 1 The electrical model of such known system is shown in figure 1, where an electronic circuit 8 is connected to a pickup coil 9 placed just beneath the cooktop (not shown), over the heater. Said electronic circuit detects variations of the pickup coil impedance.
  • the presence of a cooking utensil 10 (shown in figure 1 as an equivalent electrical loop circuit having impedance Lp and resistance Rp) modifies the coupling coefficients Kp of the equivalent transformer, thus causing output signal variation when the cooking utensil is placed on the cooktop.
  • the cross-inductive methods are based on the idea of injecting a radiofrequency signal into a first coil and detecting the signal induced into a second coil (receiving coil) placed in the vicinity of the cooktop surface. Detected voltage variations are related to the coupling strength variation caused by the presence or absence of the cooking utensil.
  • the above-mentioned EP-A-328092 describes the technique for a single hob where both the emitting coil and the receiving coil are different from the heating coil.
  • EP-A-1206164 describes a method for using the same heating coil also as electromagnetic field emitter and, for this reason, it is particularly well suited for detecting cooking utensils on a cooking hob with discrete distributed heating elements as described in EP-A-1 303168.
  • Both said known methods produce an output signal suffering from a strong variation induced by the variation of the magnetic characteristics of the heating element caused by temperature variations.
  • Said variation of the magnetic characteristics can be, in some cases, of the same order of magnitude of the variation induced by the presence/absence of the cooking utensil, therefore rendering the pan detection quite unreliable.
  • the Curie temperature being the temperature over which the magnetic permeability ( ⁇ r ) of the material abruptly falls from a typical value of some tenth to unity, as shown in the attached figure 2).
  • US-A-5900174 describes a method for rejecting the temperature-induced variation of the output signal by knowing the power control switching times. Said method has the disadvantage of being applicable only with ON/OFF power control methods (hence not being applicable to continuos or quasi-continuos power controls). In addition said known method is able to compensate only for the sharp variation caused by the Curie temperature crossing and not for the smooth variations or "drifts" experienced at temperatures below that temperature.
  • the system comprises an electronic circuit adapted to drive said detection means towards magnetic saturation. If the detection means of the system detect the impedance of a probing coil placed below the cooking surface or the complex cross-impedance between an emitting coil and a pick-up coil, the impedance, or cross-impedance, is preferably measured when the heating element alloy, or any ferromagnetic object affecting such measurement, is driven into magnetic saturation by means of a strong enough current injection.
  • the sampling of the voltage/current induced into the probing coil is preferably performed synchronously with the injection of a saturating current, which is preferably obtained by direct application of the mains voltage to the heating element.
  • the pan detection is carried out when the current flowing into the heating element is high enough to have a relative permeability lower than at room temperature.
  • the applicant started from the aforementioned physical behavior, in order to minimize or even cancel the thermal induced variations.
  • the method according to the invention consists in inducing magnetic saturation in the heater alloy by feeding it with a strong polarising current.
  • a suitable coupling network decouples the saturating current from the signal injected for pan detection purposes. The saturation grants that both at low and high temperature, the magnetic properties of the alloy are almost equal and the temperature-induced variation are limited to a negligible level.
  • a magnetic pan detection system according to the invention can be arranged in at least three embodiments.
  • the reference RF current 8 is fed into the injection coil 9, that is physically separated by both the heating element 17 and the receiving coil 10.
  • the loop 10 made by conductive material is placed above the injection coil 9 in order to pick up part of the generated magnetic field.
  • the induced voltage 11 is fed to the signal conditioning unit shown in figure 6. Said induced voltage is typically lower in presence of any metallic object 15 onto the cooking surface.
  • FIG 7 which represents a simplified model for a mutual inductive method, in which the injection coil is also the heating element
  • the reference AC current 8 is fed to the heating element 17 through a coupling filter 18.
  • Said heating element 17 is used also as injection coil 9, its structure having a suitable geometry that allows the generation of a magnetic field directed towards the cooking surface.
  • the aforementioned coupling filter (see figure 8) provides the necessary insulation between the high frequency reference signal and the biasing current.
  • a loop 10, similar to the loop of figure 5, made by conductive material is placed above the injection coil 9 in order to pick up part of the generated magnetic field.
  • the induced voltage 11 is fed to the signal conditioning unit (figure 6). Said induced voltage is lower in presence of any metallic object 15 onto the cooking surface.
  • the reference RF current 8 is fed into a loop 10 made by conductive material that is placed above the heating element 17.
  • a current is fed into the heating element 17 in order to saturate its alloy. Said action is straightforward when the heating element 17 is switched on, since the heating current flows through the heating element 17 saturating its alloy.
  • the saturating current must be supplied to the heating element just for the time needed for the measurement, being said power not used for cooking purposes but for saturation purpose only. In both cases, the pan detection signal must be sampled when the heater alloy is saturated enough.
  • the above embodiments can be applied to a single hob as well as to a cooktop made by a matrix of multiple heating elements.
  • FIG 10 it is shown the result of experimental results of a pan detection system according to the invention compared with a traditional system.
  • the pan detection signal of a known system changes by changing the power of a heating element, i.e. by changing its temperature, without any cooking utensil on the cooking hob.
  • the reference 25 it is shown the variation of the pan detection signal of the system according to the invention. It is evident how this last signal is surprisingly more stable than the signal of the known system.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Ceramic Engineering (AREA)
  • Cookers (AREA)
  • Induction Heating Cooking Devices (AREA)

Claims (11)

  1. System zur Detektierung des Vorhandenseins eines Kochgerätes (15) auf einem Kocheinsatz mit wenigstens einem elektrischen Heizelement (17) und Detektormitteln (9, 10, 17), deren Impedanz sich wegen des Vorhandenseins des Kochgerätes (15) auf dem Kocheinsatz ändert, gekennzeichnet durch eine elektronische Schaltung (16), welche zur Steuerung des Heizelementes (17) in die magnetische Sättigung dient.
  2. System nach Anspruch 1, in dem die Detektormittel (9, 10, 17) die Impedanz einer unter der Kochfläche angeordneten Fühlerspule (9, 10) oder die komplexe Kopplungsimpedanz zwischen einer Emitterspule (9) und einer Aufnahmespule (10) detektieren, dadurch gekennzeichnet, dass die Impedanz gemessen wird, wenn die Heizelementlegierung oder die Messung beeinflussende ferromagnetische Objekte mittels eines ausreichend starken Polarisierungsstroms in die magnetische Sättigung gesteuert werden.
  3. System nach Anspruch 2, dadurch gekennzeichnet, dass die Tastung der/des in der Fühlerspule (9, 10) induzierten Spannung/Stroms synchron mit der Einspeisung eines Sättigungsstroms durchgeführt wird.
  4. System nach Anspruch 3, dadurch gekennzeichnet, dass der Sättigungsstrom durch direktes Anlegen der Versorgungsspannung an das Heizelement (17) erzeugt wird.
  5. System nach Anspruch 4, dadurch gekennzeichnet, dass die Muldendetektierung lediglich dann durchgeführt wird, wenn der in das Heizelement (17) fließende Strom ausreichend groß genug zu dessen Sättigung ist.
  6. System nach den vorhergehenden Ansprüchen, dadurch gekennzeichnet, dass das elektrische Heizelement Teil der Detektormittel ist.
  7. Verfahren zur Detektierung des Vorhandenseins eines Kochgerätes (15) auf einem Kocheinsatz auf der Basis einer Änderung der Impedanz eines im Bereich des Heizelementes (17) angeordneten leitenden Elementes (15), dadurch gekennzeichnet, dass das Heizelement (17) mittels einer ausreichend großen Stromeinspeisung im Wesentlichen magnetisch gesättigt wird.
  8. Verfahren nach Anspruch 7, bei dem die Impedanz einer unter der Kochfläche angeordneten Fühlerspule (9, 10) oder die komplexe Kopplungsimpedanz zwischen einer Emitterspule (9) und einer Aufnahmespule (10) detektiert wird, dadurch gekennzeichnet, dass die Impedanz gemessen wird, wenn eine Heizelementlegierung oder die Messung beeinflussende ferromagnetische Objekte in die magnetische Sättigung gesteuert werden.
  9. Verfahren nach Anspruch 8, dadurch gekennzeichnet, dass die Tastung der/des in der Fühlerspule induzierten Spannung/Stroms synchron mit der Einspeisung eines Sättigungsstroms durchgeführt wird.
  10. Verfahren nach Anspruch 9, dadurch gekennzeichnet, dass der Sättigungsstrom durch direktes Anlegen der Versorgungsspannung an das Heizelement (17) erzeugt wird.
  11. Verfahren nach Anspruch 10, dadurch gekennzeichnet, dass die Muldendetektierung durchgeführt wird, wenn der in das Heizelement (17) fließende Strom ausreichend groß genug zu dessen Sättigung ist.
EP20030028039 2003-12-08 2003-12-08 Vorrichtung zur Detektierung eines Kochgefässes auf einer Kochplatte Expired - Lifetime EP1542507B1 (de)

Priority Applications (3)

Application Number Priority Date Filing Date Title
EP20030028039 EP1542507B1 (de) 2003-12-08 2003-12-08 Vorrichtung zur Detektierung eines Kochgefässes auf einer Kochplatte
ES03028039T ES2280679T3 (es) 2003-12-08 2003-12-08 Sistema para detectar la presencia de un utensilio de cocinar sobre un hornillo de coccion.
DE2003611835 DE60311835T2 (de) 2003-12-08 2003-12-08 Vorrichtung zur Detektierung eines Kochgefässes auf einer Kochplatte

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
EP20030028039 EP1542507B1 (de) 2003-12-08 2003-12-08 Vorrichtung zur Detektierung eines Kochgefässes auf einer Kochplatte

Publications (2)

Publication Number Publication Date
EP1542507A1 EP1542507A1 (de) 2005-06-15
EP1542507B1 true EP1542507B1 (de) 2007-02-14

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EP20030028039 Expired - Lifetime EP1542507B1 (de) 2003-12-08 2003-12-08 Vorrichtung zur Detektierung eines Kochgefässes auf einer Kochplatte

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EP (1) EP1542507B1 (de)
DE (1) DE60311835T2 (de)
ES (1) ES2280679T3 (de)

Family Cites Families (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5351004A (en) * 1991-10-15 1994-09-27 Eldec Corporation Saturable core proximity sensor including a flux director and a magnetic target element
IT1260456B (it) * 1992-01-28 1996-04-09 Whirlpool Italia Metodo e dispositivo per rilevare a presenza di un corpo per esempio una pentola su un piano di cottura in vetroceramica in corrispondenza di un elemento riscaldante associato a tale piano
GB2320626B (en) * 1996-12-19 2000-10-18 Ceramaspeed Ltd Cooking utensil detection method
US6424145B1 (en) * 2000-02-29 2002-07-23 Eldec Corporation Inductive proximity sensor for detecting ferromagnetic, non-permeable or magnet targets

Also Published As

Publication number Publication date
DE60311835D1 (de) 2007-03-29
ES2280679T3 (es) 2007-09-16
DE60311835T2 (de) 2007-07-12
EP1542507A1 (de) 2005-06-15

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