Device for detecting a vessel put in the heating zone of a cooking or heating apparatus.

There have been several attempts to create pan detection systems that turn on a cooking appliance only at presence of a pot in the heating zone. Systems are known with optical sensors and partially with brightness comparison (DE-A 35 33 997 and 33 27 622) and with inductive sensors (DE-A 37 11 589 and 37 33 108). In all these systems, the placement of the sensor in the heated zone was problematic. Sensors that can withstand the high temperatures that are usually not sensitive enough to separate commercial from noise can, in particular, because the pots have a very different behavior on the touch panel.

Invention object is to provide a device in which the arrangement of the sensor in the heating zone is straightforward and allows for a wide variety of operating conditions, a clear recognition of an established pot. This object is achieved by the claim. 1

The dependence of the detection of the signal change avoids the adjustment of a certain absolute value for the switching point, so that changing basic conditions, eg. As may be accounted for by the influence of temperature changes in characteristics of the sensor. The dependence of the rate of change enables the response speed of the pan detection for than the rate of change of the underlying assets. This apparatus allows the detection of pots which cause such a low sensor signal changes, that it is not greater, or even smaller than the change in sensor characteristics. Since these characteristics but much slower to change than to be recognized pot formation, a clear distinction is possible.

Thus, a large area has been opened to possible sensors that were previously virtually unusable. In practice, inductive sensors could be used with poor results because they temperaturabgeschirmt and thus had to be too far removed from the actual hob. According to the invention, they can be largely arranged directly at the heating, z. B. at the edge or in the middle of the heating zone and especially just below the actual cooking surface, closer to this. As eg jet heaters. Be particularly advantageous a high temperature resistant material has been found for an inductive sensor as a material that has not previously been considered for such purposes can be used, namely an electrically insulating oxidized heat conductor, such as a chromium-nickel alloy of type Ni Cr 7030. This material, although is known as a heat conductor, regarded as useless, mainly because this has to be dispensed with for reasons temperature to a ferromagnetic coil core due to its high resistance value for induction coils. In the area of ​​the induction coil temperatures up to 1300 K (about 1000 degrees Celsius) occur during conventional coil materials only bear a fraction of these temperatures.

According to the invention, the evaluation means can operate in analog and determine the rate of change by differentiating the output sensor signal. Particularly advantageous, however, the evaluation work digitally, the starting point is a comparison of the counted over a certain gate time pulses a sensor oscillator frequency with a reference number that is kept away respectively by a certain threshold of the sensor dependent pulse number. The comparative figure is adapted in each case in a predetermined time sequence to the actual value of the frequency-dependent sensor number, so that in all operating conditions, the threshold has a specific or possibly also dependent on the absolute value of the sensor signal magnitude. It is, in each case depending on the detection (pot present / absent) changes the sign of the threshold. If the difference between the sensor-dependent value and the comparison value is too large, the readjustment may take place on the threshold, to exploit and weak values ​​to yes, slowly, be accelerated by shortening the readjustment time. This can be achieved through a directly dependent on the size of each difference value Nachregelgeschwindigkeit. In digital form, a simple, yet very good adaptation can thereby generate that after initial readjustment of constant adjustment speed this occurs abruptly when up to a predetermined time, the adjustment is completed.

In order to achieve particularly a micro-controller suitable, that is, a manner of a computer numerically operating, programmable component, as it is frequently used in control systems. He could at the same time the functions of an adjustable power control device, a temperature-dependent regulator and / or other control functions, such as for a parboiling boost, for the temperature limitation etc. with included, so that normally except control sensors only one encoder for manual setting and a performance a switching device (relay, triac or. the like.) are required to realize the entire control system of the cooking device.

The device is possible with various sensor systems, so even with capacitive, optical or similar probes. For some types of sensors, such as inductive, certain cooking vessel materials are not detected. Therefore, the device should have a jumper or a switch-off device which allows independent of the pan detection operation of the cooking appliance. They can be time controlled so that is switched back to automatic pan detection after a certain time.

In one the analog signals processing means, the operational flow described previously could also be used. There is a difference (beat) would be used between the sensor rate and a correspondingly readjusted comparison frequency instead of the pulse count and the difference of these values. The device can also be realized as a user-specific integrated circuit (ASIC).

The invention provides other than the ease of further benefits, especially increased security, because preventing a hotplate continues to operate at idle after removing the cooking appliance. The inductive, of a ferromagnetic material in the cooking vessel dependent version has the added security advantage that it does not respond, for example, when parking a plastic container on the hotplate, which would be possible with optical devices.

These and other features of preferred embodiments of the invention will become apparent from the claims and from the description and drawings, and the individual features to be realized in each case alone or together in the form of subcombinations in an embodiment of the invention and in other fields and can darsstellen advantageous and patentable embodiments, is claimed for which protection. Embodiments of the invention are shown in the drawings and are explained in more detail below. Show it:<dl id="dl0001"><dt>Fig. 1 and 2</dt><dd> by a cooking appliance with a glass ceramic plate and a radiant heater and each a schematic partial section</dd><dt>Fig. 3</dt><dd> a schematic block diagram of a pan detection device, in which the individual blocks are provided with explanatory function icons.</dd></dl>

FIG. 1 shows part of a cooking utensil 11 with arranged under a glass ceramic plate 12 radiant heater 13. It includes a sheet carrying tray 14 is a heat-resistant insulation 15 with a circumferential and abgestütztem on the glass ceramic plate 12 edge 16 and an annular recess 17, at the bottom for example, as Heizwinde trained Strahlheizwiderstände 18 spirally a central zone 19 are arranged surrounding. Several radiant heater 13 are pressed resiliently against the underside of a glass ceramic plate 12 and form individual heating zones 20. They are also suitable for heating or other purposes.

The central zone 19 is formed by an upwardly projecting portion of the isolation 15th In it, a recess 21 is provided in which a sensor coil is the 22nd The recess is closed at the top by a disc 23 of an insulating material 15 with respect to the firmer, temperature-resistant insulating material which is supported on the underside of the glass ceramic plate 12th Therefore, the coil 22 is located in a shielded against direct Wärmestahlung from the radiators her room. The electrically insulating disc 23 ensures that contact between them with live parts, since glass ceramic becomes conductive at operating temperatures. It also protects the edges of the central zone from damage.

It can be seen that the coil is thus closely below the glass ceramic plate and closer to these than the heating resistors 18 and also at a central location.

FIG. 2 differs only in that on Figure 1, as there the insulation 15 of the radiant heater 13 has a Bowl or bowl shape without upstanding central zone. The sensor coil 22 extends completely around the beam radiator around and is arranged in a recess provided in the upper part of the edge 16 of the insulation from the outside circumferential groove 24th Intermediate glass ceramic plate 12 and the edge 16 a washer 23 is inserted, the mechanical and electrical protection function has. The groove could also be an angular edge recess, that is, be without interposition of a portion of the insulator 15 between the coil and disc.

Here too, the coil is protected from direct exposure to the radiation heating. Nevertheless, there occur considerable temperatures. For this reason, the coil is made of a material including its insulation about 1300 K (ca. 1000 ° C) is constant. It is preferably a chromium-nickel alloy of type Ni Cr 7030. It is electrically isolated by oxidation of their outer surface. However, this material has a relatively high electrical resistance. Therefore, it can only have a few circumferential turns in particular, in an embodiment of FIG. 2. the package quality is therefore low also because of the absence of a ferromagnetic coil core. After allowing this material but the application directly in the region of the heating zone, possibly even closer to the heating resistors or between them and the glass ceramic plate.

The coil 22 is the sensor means for detecting a set up in the heating zone cooking vessel 25, which also includes roasting, heating or other receptacles to be heated objects are to be understood. The sensor responds to such cooking vessels, provided they are made of a material changing its inductance (ferromagnetic material) or containing.

Based on Fig. 3, the pan detection system will be explained. The sensor coil 22 produces a change in the induction of its environment that is created by putting up a cooking vessel 25, an output signal in the form of a change in inductance. It is part of an oscillating circuit, whose other parts, for example, a capacity, is included in a signal input element 26th Subsequently, the signal is converted into a signal traveling 27 into a rectangular signal, that is a rectangular frequency is produced from the sinusoidal oscillation frequency, the easier is suitable for digital processing. In the following frequency measuring means 28, the number of pulses of the square wave signal and thus a resonant frequency is determined and stored number representative of a certain time by a timer 29 predetermined gate time.

This from the Sensorfreque dependent nz pulse number is a subtraction means 30 fed, where it is compared with a corresponding reference number that comes from a comparison number memory, where it is, as described later formed. Once per gate time difference corresponding one of the resulting signal is sent to a logic circuit 32, namely, including the sign of the difference. The combinational logic 32 also includes a memory for a set distance or threshold at below which an output signal is supplied to switch 33, possibly via a later Illustrated regulating or control device 34. In practice, depending on the current operating status (cooking vessel yes / no or a cooking appliance / subtracted from) a threshold value corresponding to the number added to the difference or so respectively at the zero crossing a corresponding enable signal is produced.

This takes place respectively in the rhythm of the gate time, may be the fraction of a second.

The comparable figure that is stored in the memory 31, is the respective actual value, ie the corresponding sensor rate number adapted or tracked. With the aim to obtain a particular desired spacing or a nominal difference. For this purpose, each contact (gate time interval) added or subtracted (depending on the sign +/- in memory of the logic gate 32), a certain amount at a change of process value and thus the difference value through a matching device 35 of the comparative number in memory 31st The comparable figure is thus adjusted in the direction of the actual value, ie tracked, namely until the difference setpoint is reached. Thereby an equal threshold is always achieved independent of the absolute size of each present signal.

If this adaptation, the slower is in any case than the corresponding actual value, which should trigger a circuit, be too slow to have reached the differential setpoint in a predetermined time, which is determined in a timer 36, then a comparison -Sprungeinrichtung 37 the comparison value by leaps and bounds set to inch difference value. A resetting means 38 sets the timer 36 again beginning when the target differential has been reached before the time elapses.

With the exception of the switching means 33 and the regulating or control unit 34, the circuit described means belong to the evaluation means 40, as symbolized in figure 3 by the dashed frame. Here in the embodiment most digital. You can be part of a microcontroller 41 or microcomputer including the regulating or control unit 34th In it, the individual devices and elements described in Figure 3 for explanation are not physically, but replaced by suitable programming to perform the functions described. This also applies to the function of the regulating or control unit 34, which also turning on / off functions also as power setting, temperature, or monitoring and control, etc. executes. It also receives an output of the evaluation means 40, optionally signals of a code generator 42, which for example may be a by a knob-operated Binargeber, and / or of a temperature-measuring and / or switching device 44. The switching means 43 switch strong current side voltage the financial network 45 contain the heating resistors 18 and may be a mechanical relay or equivalent electronic components.

The device operates according to the following procedure: If the cooking apparatus is ready for operation, but its heating is not turned on, the oscillating circuit, the sensor coil 22 contained in operation. It produces its particular frequency, which results in that the frequency-measuring and storing device detects a certain number of pulses during the gating time. The corresponding comparative figure from the comparable figure memory 31 is away by a predetermined difference value.

will change by placing a cooking vessel, the inductance of up to a mHz operated at a relatively high frequency of for example 100 kHz resonant circuits, as also the actual number, which is determined by the frequency measuring means during the gate time, and the difference formation 30 is fed changes. If this exceeds the threshold, then made in the combination logic 32 in the manner previously described, a zero crossing, and a positive output signal, there is generated, for example, the heating switches via the regulating-control unit 34 and the switching means 33 eighteenth

The adaptation device 35 a gradual, relatively slow adjustment of the reference value to the current actual value is now done per clock. a highly ferromagnetic pot has been used, for example, has caused a large inductance, so the desired distance is not reached under certain circumstances within a predetermined, set by the timer 36 times, so that over the jump device 37 an abrupt adjustment is made by the comparison value is set the predetermined distance from the customs value. Thus, even after a relatively short time, the evaluation is again in a position to speak on lesser Induktivitätänderungen, for example, after taking down a highly ferromagnetic pot on setting up a little ferromagnetic pot.

By heat and other environmental influences, the Induktivitätseigenschaften the sensor coil 22 vary greatly. In particular, the high temperature resistant track material has a strong positive resistance characteristic, which leads to a significant drift of the inductance without spatial variation of cooker / heating zones assignment. However, since these substantial in absolute values ​​changes occur in a temporal order, which differ significantly from the placement or removal of a pot, can here the adjustment of the reference value on the adjustment device 35 of this change easily follow and adjust the respective threshold distance again without that there is an activation of the evaluation unit. So you will only respond to changes that occur faster than the adaptation, so that over the Anpassgeschwindigkeit the sensitivity of the device can be predetermined.

When taking down a pot happens again the same, except that in this case the difference another sign indicates, so that the combinational logic provides a correspondingly poled output and stores. From this polarity and the direction of the adjustment depends.

The evaluation means contain a temporary shutdown 50, which was by the user, for example, a push button 51, is pressed. With it the user can set the evaluation for one of a timer 53 predetermined time in their effect on the switching means 33 out of operation, for example, if he wants to cook with a glass ceramic dishes. In the schematic diagram, it is indicated that this the output of the logic gate 32 is suppressed. This disabling means, however, could also be realized in other ways, for example by switching off the entire evaluation, by starkstrom sided bypassing the switch 33 or the like .. But it is important that (53 timer) annulled the bridging serving off the pan detection again after a certain time is to return to the automatic pan detection, thus putting the beneficial function and safety action again. The manual influence can also be effected by a conventional on / off switch that is automatically reset after the given time. Since the automatic pan detection can lead not only to increased operational security, but also to significant energy savings, it is very suitable not only for domestic cookers, but also for the commercial kitchen. There the usual today passing through the cooking is avoided throughout the day and achieved the same result without any delay to the cooking in conjunction with a low-capacity heating. An additional advantage is the lower heat generation and thus improved working conditions for the kitchen staff.