EP0944293A1 - Method for determining the simmering and boiling points of a foodstuff in a cooking vessel - Google Patents

Abstract

The method has a hotplate (1) fitted with a sensor (10) e.g. a microphone, to monitor the sound generated by the bubbles. By analysing (11) the relative amplitudes of the noise at different frequencies, the control system can differentiate between simmering and boiling. The bubbles generated at the bottom of the cooking vessel generate different frequencies of noise to those bursting at the surface of the liquid when boiling. A feedback control turns down the heating setting at the onset of boiling. The control system (12) monitors low frequency noise below 1000 Hz and high frequency noise above 1000 Hz. Filter circuits separate the two levels of noise. When the amplitude of the low frequency noise increases while that of the high frequency noise decreases, boiling starts and the control system reduces the heating. For the converse, indicating going off the boil, the heating is increased.

Description

The invention relates to a method for determining the boiling point and Cooking point of a liquid taken up in a cooking vessel or a mixture of liquid and cookware for regulation of a cooking process in one on one with at least one Controllable heating device equipped hotplate Cooking vessel, wherein when the filled cooking vessel is heated caused by the formation and bursting of steam bubbles Noise with the help of at least one vibration-sensitive Sensors are detected.

The heating devices operated, for example, with electrical energy conventional hobs are usually done manually adjustable, timed circuit breakers controlled. There is no feedback of the actually existing Temperature of the cooking zones or the food. The user is forced to continuously adjust the setting manually so that even cooking is achieved. Among other things when cooking vegetables or pasta it is relatively difficult to cook without overcooking. Therefore, it is often necessary the food only simmering at a temperature below to keep the cooking point.

A procedure based on the procedure is desirable of a user or cook. Experience has shown that the user knows the characteristic that announces the upcoming cooking point Noise when the first boiling bubbles appear at the bottom of the cooking vessel. The familiar, hissing sound that So-called bubble boiling is caused by locally exceeding the temperature-dependent Vapor pressure at the bottom of the pot, resulting in local small boiling delays caused by bladder germs. Short Time later the noise changes when you transition to one bubbly boiling, so when the bubbles tear off the bottom of the pot, rise and burst at the surface of the liquid. At the The transition from bubble boiling to bubbly cooking changes Amplitude and spectral composition of the noise.

For this purpose, from the unpublished DE 196 38 355.2 a method is known in which in the range of the temperature control point recorded noise frequency spectrum a limited, upper frequency range and one of them at least partially deviating, limited lower frequency range in one evaluation section each is transferred. The amplitudes of these two frequency ranges are evaluated. The two evaluation results are related to each other. When there is a change this ratio is due to the decrease in amplitude strength of the lower frequency range and / or the increase in Amplitude strength of the upper frequency range the heat input lowered and when the ratio formation changes due to Increase in the amplitude strength of the lower frequency range and / or decrease in the amplitude strength of the upper frequency range the heat supply increased. The process is fragile against irregular noise, their frequencies lie in the noise frequency spectrum to be evaluated.

The present invention is therefore based on the problem of a Finding a process that is independent of cooking the cooking location, the type of food, the amount of food, the cooking vessel, the hotplate and disturbing ambient noises, the onset of boiling or cooking is precisely recognized and measurement signals are generated, which is reliably an actuator for controlling a hotplate heater can influence.

The solution to the problem is achieved in that the cooking process resulting noise into a lower, low-frequency and dividing an upper, high frequency range, wherein in each area either for the entire bandwidth or for multiple frequencies and / or smaller frequency ranges from the Frequency spectrum the amplitudes are measured. Each from the Amplitudes of the lower and the upper frequency range become one Average formed. The two calculated averages will be regularly compared with each other, being in the bladder boiling phase the mean of the lower frequency range below the mean of the upper frequency range while it is behaves the other way round in the bubbling boiling phase. In the heating phase is after the time at which the mean of the lower frequency range is the mean of the upper frequency range exceeds the energy supply for the heating device interrupted or throttled while in the cooling phase after the time when the average of the upper frequency range exceeds the average of the lower frequency range, the energy supply is resumed or increased.

To eliminate interference, use at least one Vibration sensitive sensor every time the controllable is switched off Heater over at least a period of at least a second recorded ambient noise, its frequencies in the frequency ranges necessary for boiling and boiling point detection lie. The frequencies of the ambient noise are determined from those necessary for the boiling and cooking point determination Filtered out frequency ranges. The amplitudes of the frequencies that are filtered out are used for averaging the lower and upper frequency ranges are not taken into account.

This procedure is based on the physical processes during the Boiling and cooking process adapted and takes advantage of the fact that every phase of the cooking process - depending on the watery food - a typical sound can be assigned. From approx. 90 ° C, based on Normal pressure, a typical boiling noise forms, the a high frequency hiss and a significant increase in Total volume is recognizable from approx. 96 ° C. At the transition to bubbling cooking become the previous sound by the Bursting of the steam bubbles rising to the surface low-frequency vibrations superimposed. The bursting of the Steam bubbles also cause the cooking vessel to vibrate at low frequencies on. The physical process described here is extensive regardless of the cooking location, the type of watery food, on the shape, size, type and cleaning status of the cooking vessel and from the hotplate. The latter can e.g. a halogen heating element, have a heating coil or a gas burner as a heating device.

The lies within the division of the two frequency ranges lower frequency range below 1000 Hz, while the upper Frequency range lies above. On the one hand, the lower one Range between 100 and 1000 Hz and the other upper range between 1000 and 5000 Hz. The ranges to be measured however, do not have to adjoin one another.

Furthermore, the amplitudes can be within a frequency range from 3 to 10 frequencies or frequency intervals can be measured. The frequencies or frequency intervals to be measured are chosen so that at least the typical for the design of the hob Spurious vibrations can be avoided. A frequency interval is usually a fraction of an octave.

To have a negative impact on the boiling and boiling point determination due to interference vibrations that are not typical of the design, a "learning phase" precedes the process. The learning phase begins each time the heater is switched on. Part of the period before the first boiling sound lies, the or the vibration-sensitive sensors one or more short periods of time the current ambient noise on. The sound level of the disturbing noise frequencies, those necessary for the determination of boiling and boiling points Frequency ranges are used in the evaluation not considered.

To record the noises generated by heating the food, including noise, one or more Sensors on the device carrying the cooking vessel Cooking area can be arranged. The sensor or sensors are as Microphones and / or accelerometers formed. The the The device carrying the cooking vessel is, for example, a glass ceramic plate, a gas burner rack or an electric hot plate. Depending on the device, the sensor or sensors are in, under or arranged on it. The sensors are preferably outside or mounted on the edge of the heatable cooking zone.

Figur 1

Kochstelle mit Gargefäß und schematischer Beschaltung.

Figur 2

Schallspektrums-Diagramm mit Störgeräuschen für einen mittelgroßen Edelstahltopf mit einer einlitrigen Wasserbefüllung.

Further details of the invention result from the exemplary embodiment described below and shown schematically.

Figure 1

Cooking area with cooking vessel and schematic wiring.

Figure 2

Sound spectrum diagram with noise for a medium-sized stainless steel pot with a single liter water filling.

Figure 1 shows a glass ceramic electric hob (1) with a Radiant heater (2) and its connections to a power source. There is a cooking vessel (7) on the hob (1). Below the hob (1) is next to the cooking zone at a distance of approx. 35 mm A microphone capsule (10) is arranged from the outer edge of the radiator (2). The microphone capsule (10) is on an assembly (11) for the signal processing and evaluation connected. In this The signal levels are proportional to the sound pressure preamplified fed to a frequency analysis unit. The frequency resolution is, for example, a 1/12 octave.

The in the different heating phases for multiple frequencies and / or frequency intervals or the respective frequency range measured over a fixed period of time, for example 1 sec Levels are digitized - if necessary using an A / D converter - recorded separately for the lower and upper frequency range and averaged. This results in relation to the lower frequency range a so-called lower level and related to the upper frequency range a so-called upper level. Both levels are during monitored the heating of the food. The heating process will divided into three warming phases. The first phase is the so-called warm water phase, the upper limit temperature of 70 ° c is defined. The second phase is the so-called Simmer phase, in the food is hotter than 90 ° C, but the boiling temperature has not yet reached. The third phase is the so-called cooking phase. In it has the food to be cooked or the food to be cooked Liquid reaches the boiling or boiling temperature.

The lower and upper levels are in the hot water phase for itself under a common limit level. In contrast this results in total noise levels in the two hotter phases, which exceed twice the limit value, where the overall level is generally somewhat higher in the simmer phase is. Furthermore, the lower level is lower in the simmer phase than the upper level. In the cooking phase it is the other way round.

The ratios of the lower and upper level values as well as the total level values to the limit level value and its multiples in addition to comparing the lower and upper level values in the three warming phases were used for plausibility checks become.

To determine the respective lower and upper level the individual measured values of filtering through two bandpasses with the corner frequencies 100/1000 Hz and 1/5 kHz.

To suppress individual, relatively short disturbances In addition to the temporal averaging of the individual measured values, extraneous noise is generated an additional averaging and evaluation of several Time intervals carried out. Only if, for example, over 5 up to 10 time intervals the conditions for recognizing the transition from bubble boiling to bubbly cooking - including, if necessary the plausibility check above the double limit value - remain unchanged, a signal for a control unit (12) generated to control the heating power of the heating device (2). The analog signals are evaluated and processed digitally with the help of a microcontroller, a signal processor or another programmable logic module.

The switching or control information is in the control unit (12) compared with the power selection on the control element (3) and corresponding to a circuit breaker or regulator (4) for energizing supplied to the heating device (2).

A sound spectrum diagram is shown in FIG. It sets a sound spectrum for a bubble boiling and Cooking noise from a liter of water in a medium-sized, stainless steel pot not covered with a lid.

The ordinate in the diagram shows the sound pressure level in "dB" plotted against the frequency in "Hz". There are two different curves (21) and (31) shown. The dashed Curve (21) shows the total noise level during bubble boiling. The solid curve (31) gives the level curve at bubbling boiling again. Both for the lower frequency range from 100-1000 Hz as well as for the upper range of 1000-5000 Hz are the range averages for the simmering and cooking phases through the straight line sections running parallel to the abscissa (23, 24) and (33, 34).

The diagram clearly shows that in the so-called simmer phase the average sound pressure level (24) in the upper frequency range is about 12 dB higher than the average sound pressure level (23) in the lower frequency range. In contrast lies in the Cooking phase the average sound pressure level (33) in the upper frequency range about 5 dB lower than in the lower one. It can also be seen that here the overall noise level in the simmer phase which is the cooking phase.

In Figure 2 are approximately at the frequencies 120 Hz, 250 Hz and 1050 Hz the noise (41), (43) and (42) dash-dotted drawn. The noise (41) and (42) are by a Coffee grinder generated. This is the higher frequency noise (42) generated by the mill motor, while the low-frequency, broadband noise (41) caused by the striking mechanism becomes. The noise (43) represents the noise of one flinging washing machine. All three listed as examples Kitchen noises have a lasting impact on frequency evaluation, since they take too long to be evaluated of several short time intervals not as background noise would be recognized. You deceive in the simmer phase Sound level spectrum that corresponds to the cooking phase. Hence would the heater without suppressing this noise turned down too early.

By detecting the noise just after switching on the heating device or the hotplate, i.e. before the simmer phase, their frequencies can be taken into account in the evaluation become. Depending on the level of evaluation electronics there is also the possibility of being in the vicinity of the hotplate more often - e.g. on different days - recorded noise save for a long period of time and keep them within this Period should also be taken into account with every cooking process, if the respective noise measurement was negative. In In this case, for example, one can only be in the simmer phase switched on coffee grinder recognizing the transition from the Do not irritate the boiling phase. Of course you can the information collected about the noise in the evaluation unit also be deleted when this noise is over stay away for a long period of time.

Reference symbol list: Figure 1:

1

Glass ceramic electric hob

2nd

Radiant heater, heater

3rd

Control element

4th

Circuit breaker or regulator

7

Cooking vessel, pot

10th

Microphone capsule, microphone

11

Module for signal processing and -evaluation

12th

Control unit

Figure 2:

21

Sound level spectrum for the simmer phase

23

mean sound pressure level of the simmer phase in lower frequency range (100-1000 Hz)

24th

mean sound pressure level of the simmer phase in upper frequency range (1000-5000 Hz)

31

Sound level spectrum for the cooking phase

33

average sound pressure level during the cooking phase lower frequency range (100-1000 Hz)

34

average sound pressure level during the cooking phase upper frequency range (1000-5000 Hz)

41-43

Noise

Claims (8)

Method for determining the boiling and boiling point of a liquid taken up in a cooking vessel or a mixture of liquid and cooking goods for the regulation of a cooking process in a cooking vessel standing on a hotplate equipped with an at least controllable heating device, wherein the noises caused by the formation and bursting of steam bubbles when the filled cooking vessel heats up are detected with the aid of at least one vibration-sensitive sensor arranged outside the cooking vessel, the amplitudes being measured at a plurality of frequencies and / or smaller frequency intervals from the frequency spectrum of the noise, allocated to a lower, low-frequency and an upper, high-frequency range, or in the case of a frequency band from the frequency spectrum of the noise, divided into a lower and an upper frequency range, the amplitudes are measured, where an average is formed from the amplitudes of the lower and the upper frequency range, wherein the two calculated mean values are regularly compared with one another and in the phase of the bubble boiling the mean value of the lower frequency range is below the mean value of the upper frequency range, while the reverse is true in the bubbling boiling phase, wherein in the heating phase after the time at which the mean value of the lower frequency range exceeds the mean value of the upper frequency range, the energy supply for the heating device is interrupted or throttled, while in the cooling phase after the time when the mean value of the upper frequency range exceeds the lower frequency range, the energy supply is resumed or increased,
characterized, that with at least one vibration-sensitive sensor (10) each time the controllable heating device is switched on for at least a period of at least one second, ambient noises whose frequencies are in the frequency ranges necessary for boiling and boiling point detection are detected, that the frequencies of the ambient noise are filtered out of the frequency ranges necessary for the boiling and boiling point determination and that the filtered frequencies are not taken into account when averaging the lower and upper frequency ranges. A method according to claim 1, characterized in that filtered frequencies are stored and interference frequencies, that come back at different times automatically the interference frequencies determined when the heating device is switched on to be added. Method according to claim 1, characterized in that an interference frequency component of more than 30% of the lower or upper Frequency range the boiling and boiling point determination including the heater turned off or at least the latter is partially turned down. Method according to at least one of the preceding claims, characterized in that for detecting the environmental and Noise used for a period of 6 to 12 seconds becomes. A method according to claim 1, characterized in that the lower frequency range is below 1000 Hz, while the upper frequency range is above. Method according to at least one of the preceding claims, characterized in that within a frequency range the amplitudes of 3 to 10 frequencies or frequency intervals be measured. Method according to claim 1, characterized in that the one or more sensors (10) on the one carrying the cooking vessel (7) Device of the hotplate (1) are arranged. Method according to claim 1, characterized in that the one or more sensors (10) as microphones and / or accelerometers are trained.

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