EP0393506B1 - Electric cooker - Google Patents

Description

The invention relates to an electric cooker with several hot plates, at least one of which can be switched to increased heating power, in particular with glass ceramic cooktops, an electronic control circuit being provided for controlling the hot plates, the clock frequency of which can be switched to a lower value at higher heating powers.

The energy supply to the hot plates of electric cookers is usually clocked, i. H. at intervals. The hotplate is controlled at a constant clock frequency, with the pulse-pause ratio of each energy pulse being changed depending on the setting of the hotplate controller. With small powers, the pulse time is small within a pulse period, whereas the pulse pause is large, with large powers, however, the pulse time is long and the pulse pause is short. In order to avoid excessive interference in the network and surrounding radio reception systems, the provisions of the VDE for the operation of such devices stipulate that the clock frequency with a power input of 2000 watts in the 220V network must not be greater than 0.04167 Hz, with even higher powers of e.g. B. 2500 watts even a maximum of 0.025 Hz.

From DE-A 27 31 782 a control device for electric hot plates has already become known, which operates as a so-called "automatic boost". This means that the maximum output permitted for the hot plates is supplied for a certain warming-up time of the cooking material. For this function, the heating power can either be supplied without clocking or with a low clock frequency. A switch for high heating outputs is not provided.

Modern hot plates, but in particular glass ceramic cooktops, have a low heat storage capacity, which means that the hot plate or the cooktop still transfers the timing of the energy supply to the food to be cooked. However, such an effect is undesirable.

The object of the invention is therefore to design an electric cooker in such a way that it is operated at the maximum permissible frequency when supplying energy to the hot plates or the hob.

To solve this problem, it is therefore proposed that, in addition to the hotplate controllers, a switch is provided which is used to switch a hotplate to a heating power which is still higher than the maximum power and which at the same time switches the clock frequency in the control circuit to a lower value.

With hobs, it is now provided that, in addition to normal cooking, which is carried out with a maximum heating power of 2000 watts, a so-called roasting stage can be switched on, in which a heating power of 2500 watts constant can be supplied. The changeover switch proposed by the control switches to a lower frequency in accordance with the VDE regulations.

In the sense of the invention it is further possible that the control circuit outputs different clock frequencies at its outputs for controlling the individual hot plates, depending on the heating power set. This makes it possible to work with a higher clock frequency in accordance with the values permitted by the VDE, even in the range below the maximum heating output of 2000 watts and the possible clock frequency of 0.04167 at maximum, with lower heating outputs. This gives a more even cooking.

The control circuit for the cooker is preferably designed as a microprocessor, which also serves to generate the clock. In principle, however, it would also be possible in the sense of the invention to carry out the clock generation by means of a frequency divider with switchable outputs.

The invention will be explained briefly below with reference to the drawing.

Figur 1

einen Elektroherd in perspektivischer Darstellung;

Figur 2

die elektrische Steuerschaltung in einem solchen Herd.

Show it:

Figure 1

an electric stove in perspective;

Figure 2

the electrical control circuit in such a stove.

In an electric cooker 1 4 hot plates 2, 3, 4 and 5 are provided, which can be controlled by the hotplate controllers 6 - 9 in their heating power. A switch 10 is used to switch the hotplate 2 to an increased heating power of 2500 watts.

In FIG. 2, the electrical control circuit is designated 11, which contains a microprocessor 12, on the control inputs of which both the changeover switch 10 and the hotplate controller 6 - 9 are located. These hotplate controllers are shown schematically as switches that can be adjusted in several positions. The control signals for controlling the hot plates are taken from the outputs of the microprocessor. At the uppermost output of the microprocessor 12, a relay 13 is represented as a representative of the other outputs, which controls the heating power for the hotplate 2 by controlling the clock signals of the microprocessor. At the corresponding output of the microprocessor either a frequency f₁ for heating power up to 2000 watts or a frequency f₂ for a heating power of 2500 watts is given. At the other outputs of the microprocessor constant frequencies f 1 can be emitted for the other hot plates, provided that these hot plates are to be operated in the usual way. However, it is also possible to increase the cycle frequency in stages in the range of heating outputs below 2000 watts, assigned to the corresponding heating outputs, and to cycle each hotplate individually to the set heating output with different frequencies. In this way, the cooking plates are heated as evenly as possible within the prescribed maximum permissible clock frequencies.

Claims (3)

1. Electric cooker with several hot-plates, at least one of which can be switched to a higher heating power, in particular with glass ceramic cooking zones, an electronic control circuit (11 being provided which controls the hot-plates (2-5), and of which the pulse frequency can be switched with higher heating powers to a lower value,
   characterized in that,
   in addition to the cooker controls (6-9), a switch (10) is provided which serves to switch a hot-plate (2) to a heating power which is even greater than the maximum power and which simultaneously switches the pulse frequency in the control circuit (11) to a lower value.
2. Cooker according to Claim 1,
   characterized in that
   the control circuit delivers different pulse frequencies to its outputs for controlling the individual hot-plates (2-5), depending on the adjusted heating power.
3. Cooker according to Claim 1,
   characterized in that
   the control circuit has a microprocessor (12) for production of pulse frequency.

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