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
• • 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 cooking hearth, for example placed under an insulating plate, hearth for which it is desired to detect the presence of an electrically conductive container, for example placed on the insulating plate. This detection can be used to start the fireplace only when it is partially or completely covered by a container. This technique is commonly used for radiant or halogen fireplaces.
• a known hearth is described in European patent EP 0490289.
• This hearth comprises, in its insulating border, an inductive detection coil going around the hearth.
• This fireplace is designed to be placed under an insulating plate, for example a ceramic hob.
• an electrically conductive container for example placed on the insulating plate, covers this coil, the value of its inductance is modified and the container can thus be detected.
• the main disadvantage of this type of hearth is that the coil can only detect containers having a diameter at least equal to that of the coil. Indeed, it can be seen that the value of the inductance of such a coil does not change appreciably until the coil is almost covered by the container. A container with a diameter smaller than that of the coil cannot therefore be detected.
• Another disadvantage of this type of hearth is that it is necessary to provide a coil size for a hearth size.
• a container in a cooker or in a hob for domestic use, there are several fireplaces of different sizes, which requires multiplying the tools for producing the different coils and consequently increases the cost of producing such sets with several fireplaces .
• the detection of the presence of a container is used to start the hearth, it is understood that such a hearth cannot be started when the container is of a diameter slightly smaller than that of the hearth. More specifically, one can cite by way of example a hearth with a diameter of 220 mm, this hearth having in its border a coil detection. It can be seen that the coil does not detect the presence of a container with a diameter less than or equal to 180 mm.
• US Pat. No. 4,319,109 Another means used for detecting the presence of a container and knowing its diameter is described in US Pat. No. 4,319,109.
• the device describes a series of point sensors, for example inductive, placed radially on the hearth. Each sensor reacts when it is covered by a container. When the sensor (s) located near the center of the hearth are covered, the presence of a small container is detected and when the sensors farther from the center are covered, the presence of a larger container is detected.
• This device has the drawback of requiring a large number of sensors to know with precision the diameter of the container covering the hearth, which multiplies the electrical connections of these sensors and which complicates the processing of the various information items coming from the sensors.
• knowing the diameter of the container is interesting, because it allows for example, to start the hearth, depending on the diameter of the container, at a power lower than the maximum power of the hearth.
• the present invention aims to overcome the drawbacks described above by using an inductive sensor placed on a radial direction of the hearth, sensor sufficiently elongated to detect the presence and know the diameter of a container covering it.
• the cooking hearth comprising a bottom, a heating element disposed on the bottom and at least one inductive sensor capable of detecting the presence of an electrically conductive container, the inductive sensor comprising a coil comprising at least one turn, is characterized in that the turn is of elongated shape substantially in a radial direction of the hearth.
• FIG. 1 shows schematically an example of electrical conductor forming the detection coil, conductor substantially wound in a plane;
• - Figure 2 schematically shows another example of electrical conductor forming the detection coil, conductor wound around a rectangular mandrel;
• FIG. 3 shows a cooking hearth seen from above comprising an inductive sensor
• FIG. 4 shows a cooking hearth seen from above, smaller than the cooking hearth shown in Figure 3 and having an inductive sensor identical to that shown in Figure 3;
• FIG. 5 shows a top view, a cooking hearth with two concentric and separate heating circuits, comprising an inductive sensor
• FIG. 6 shows a top view of a cooking hearth with two separate heating circuits, this hearth being provided for heating containers of oblong or round shape;
• FIG. 7 shows a cooking hearth seen from above comprising two inductive sensors;
• FIG. 8 shows a cooking hearth seen from above comprising three inductive sensors.
• the principle of the invention is based on the use of an elongated inductive sensor.
• a preferred example of the form of winding of the electrical conductor forming a coil used to make the sensor is given in FIG. 1.
• the winding takes place in a plane, that of FIG. 1.
• an electrical conductor 2 is wound for example around a rectangle 3 whose long side is clearly larger than the short side. This first turn forms a first elongated turn.
• the conductor wraps around itself several times while maintaining sufficient electrical insulation, up to a second end 4, thus forming several elongated turns, this as many times as necessary to obtain a desired inductance value.
• a coil comprising 11 turns around the rectangle 3 having the dimensions given previously gives a no-load inductance value of the order of 10 ⁇ H.
• a first method consists in cutting, for example chemically, a metal and immobilizing it between two thin layers of electrical insulator, such as for example mica, to form a sensor.
• Mica has been proposed here for its good temperature resistance. Indeed, such a sensor can be subjected to maximum temperatures of the order of 500 ° C.
• electrically connect the sensor one can for example provide at each of the ends 1 and 4 a range of metal wider than the conductor electrical 2.
• the connection by means of electrical wiring wires electrically welded to the metal pads.
• the metal which constitutes the coil is chosen for example for its good temperature qualities so that the value of the inductance varies as little as possible with temperature.
• This method has the advantage of providing a very thin sensor, for example of the order of 100 ⁇ m which can subsequently be pressed against the insulating plate under which, for example, the cooking hearth is located.
• a second method for producing this sensor consists in producing, for example by molding in a support, a groove which extends according to the shape which one wishes to give to the electrical conductor 2. It then suffices to deposit in this groove an electric wire bare. The insulation between turns is here obtained by the distance separating two grooves.
• the support can for example be made of vermiculite.
• a third method for producing this sensor consists in carrying out a screen printing of conductive ink on a support.
• the reason for this screen printing is that described in FIG. 1.
• the support material must be sufficiently smooth and not very porous, such as, for example, magnesian cement, to allow screen printing.
• the shape of the coil, described in FIG. 1 makes it possible to press the sensor against the insulating plate.
• This has the advantage of a sensor as close as possible to the container to be detected. Which improves her sensitivity.
• Another advantage is that the sensor will follow the temperature of the container through the insulating plate.
• the resistance of an electrical conductor varies as a function of its temperature. It is possible to use this property to know the temperature of the container by measuring the resistance of the sensor.
• FIG. 2 Another example of the form of winding of the electrical conductor of a coil is given in FIG. 2.
• an insulated electrical conductor is wound on one or more layers around an elongated section mandrel. .
• the elongated section is for example a rectangle of length 60 mm and width 15 mm.
• Figure 2 is shown in strong lines an electrical conductor 2 wound on the mandrel mentioned above but not shown.
• four turns are shown on a single layer.
• the electrical conductor 2 extends beyond the two ends 1 and 4 of the winding.
• the two extensions 5, each beyond one of the ends 1 and 4 can be used for the electrical connection of the sensor.
• FIG 3 shows the mounting of a sensor in a radiant hearth. It is understood that the radiant hearth is given here only by way of example: one can use such a sensor for any type of hearth, such as for example a halogen hearth.
• the fireplace described in Figure 3 has a plate 10 in the form of a disc forming the bottom of the hearth. This plate 10 is usually made of thermal insulating material. The periphery of this plate 10 is raised by an edge 11, an edge also made of thermal insulating material. The upper part of this border 11 defines a plane which thereafter will preferably be in contact with the insulating plate which covers the hearth. On this plate 10 is disposed an electrical resistance 12 forming the heating element of the hearth.
• the hearth can also include, as is usual, a device 14 for temperature limiting in order to prevent the internal temperature of the hearth from exceeding an upper limit.
• This limiting device comprises for example a rod 15 of which an internal element expands with the increase in internal temperature of the hearth. When the expansion of this internal element reaches a given value, this causes the switching of a bimetallic switch located inside a cover 16 and, consequently, this makes it possible to cut off the electrical supply to the resistor 12.
• This switch can be mounted in series between the resistor 12 and one of the terminals of the electrical supply to the fireplace.
• the hearth also includes a mound 17 placed on the plate 10.
• This mound 17 has substantially a parallelepiped shape, one end 18 of which is preferably located in the vicinity of the edge 11.
• the end 19 opposite 18 is substantially located in the center of the hearth, so that the mound 17 extends substantially in a radial direction of the hearth.
• This mound 17 serves as a support for a sensor 20 on which it is positioned so that the direction, in which the turns of the sensor 20 are elongated, is substantially coincident with the radial direction of the focal point on which the mound 17 is positioned.
• L thickness of the mound 17 measured perpendicular to the plate 10 is substantially equal to that of the edge 11 so that the surface of the sensor 20 opposite the surface with which it is in contact with the mound 17 is substantially in the same raised plane of the edge 11, this so that the sensor 20 and the edge 11 are in contact with the insulating plate which preferably covers the hearth in a stove or a hob. It is possible to provide an imprint in the border in order to position the sensor 20.
• One end 21 of the sensor perpendicular to the radial direction is substantially positioned on the edge 11.
• the opposite end 22 is on a concentric circle 23 of the edge 1 1.
• the material of the mound 17 is advantageously the same as that of the edge 11.
• An additional function of the mound 17 is to serve as a support for the cane 15, this cane then being positioned between the mound 17 and the edge 11, for example in another radial direction than that on which the mound 17 extends.
• an electrically conductive container for example a metallic container
• it can, depending on its diameter, partially or completely cover the sensor 20.
• a container with a diameter greater than or equal to that of the hearth will completely cover the sensor 20.
• a container with a diameter between the diameter of the circle 23 and the diameter of the border will partially cover the sensor 20 and a container with a diameter less than the diameter of the circle 23 will not cover the sensor.
• Knowing the diameter of a container covering the hearth can for example allow the electrical power delivered to the resistor 12 to be modulated. It is therefore possible, for example, to reduce the power when the diameter of the container is less than the diameter of the border.
• Figure 4 shows the mounting of a sensor in a radiant hearth where we find all the elements of the hearth described in figure 3.
• the hearth described in figure 4 has a diameter smaller than that described in figure »-.
• the senor 20 is formed of one or more elongated turns, that is to say of sufficient length to detect a size of container in a range compatible with the dimensions of the hearth.
• the length of the sensor 20 is at least three times greater than its width. For example, it is undesirable that the hearth shown in Figure 3, whose diameter is 220 mm, can heat a container whose diameter would be less than 160 mm.
• the sensor 20 will automatically detect any metal container with a diameter greater than 160 mm and the power control of the hearth can be done according to the information provided by the sensor.
• FIG. 5 represents the mounting of a sensor in a radiant hearth comprising two separate heating circuits. These two circuits are concentric. One, 30, is in the center: it is limited at its periphery by a border 31. The other, 32, is concentric with the heating circuit 30 and is limited at its periphery by a border 33.
• This hearth also has tongues 13 for the electrical supply to the heating circuits and a device 14 for temperature limiting itself comprising a rod 15 and a cover 16.
• This hearth further comprises a mound 34 carrying a sensor 20. This mound is, as for the hearths shown in figures 3 and 4, oriented in a substantially radial direction of the hearth. One of its ends 19 is also located substantially in the center of the hearth.
• the other end 18 is, in FIG. 5, located substantially between the edges 31 and 33.
• the sensor 20 is positioned on the mound 34, one of its ends 21 being arranged in the vicinity of the end 18 of the mound 34.
• the sensor 20 is thus substantially positioned astride the border 31; it makes it possible to know whether a container partially or completely covers the heating circuits 30 and 32. This makes it possible to electrically supply one and / or the other of the heating circuits 30 and 32 depending on the size of the container placed on the hearth .
• FIG. 6 represents, as in FIG. 5, the mounting of a sensor in a radiant hearth comprising two separate heating circuits.
• the heating circuits are not concentric: one 40 is circular, limited by an edge 41, the other 42 is positioned on one side of the heating circuit 40 so that the periphery of the grouping of two circuits 40 and 42 have an oblong shape.
• This type of hearth finds its utility when one wishes to be able to heat on the same hearth a circular container or an elongated container such as for example a fishmonger.
• the sensor 20 is substantially positioned astride the edge 41 in its zone separating the heating circuits 40 and 42.
• FIGS. 7 and 8 The foci represented in FIGS. 7 and 8 are similar to that represented in FIG. 3.
• two sensors 20 which are diametrically opposite in FIG. 7, and 3 sensors placed at 120 ° in FIG. 8 are placed.
• a small circular mound 50 has been added to the center of the hearth.
• the advantage of these variants is to allow the measurement of the diameter of an off-center container. It is understood that these variants with two or three sensors can be transposed whatever the size of the hearth and whatever the number of heating circuits.

Landscapes

• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Ceramic Engineering (AREA)
• Measuring Temperature Or Quantity Of Heat (AREA)
• Electric Stoves And Ranges (AREA)
• Induction Heating Cooking Devices (AREA)
• Cookers (AREA)
• Geophysics And Detection Of Objects (AREA)
• Adornments (AREA)
• Seeds, Soups, And Other Foods (AREA)
• Food-Manufacturing Devices (AREA)

Applications Claiming Priority (3)

Publications (2)

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ID=9506663

Family Applications (1)

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Cited By (1)

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• 1997
  • 1997-05-07 FR FR9705623A patent/FR2763116B1/fr not_active Expired - Fee Related
• 1998
  • 1998-05-07 WO PCT/FR1998/000924 patent/WO1998051128A1/fr not_active Ceased
  • 1998-05-07 ES ES98924402T patent/ES2268778T3/es not_active Expired - Lifetime
  • 1998-05-07 EP EP98924402A patent/EP0929991B1/de not_active Expired - Lifetime
  • 1998-05-07 AT AT98924402T patent/ATE333203T1/de not_active IP Right Cessation
  • 1998-05-07 DE DE69835197T patent/DE69835197T2/de not_active Expired - Lifetime

Non-Patent Citations (1)

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