DOMESTIC PEF COOKING DEVICE AND METHOD FOR OPERATING SAME

Abstract

A household PEF cooking appliance includes a cooking product container fillable with liquid and cooking product and including, on its inner faces, a plurality of mutually insulated electrodes. An excitation device supplies at least two of the plurality of electrodes with pulsed electric signals, and a resistance measuring device applies a measuring signal to at least two of the plurality of the electrodes in order to measure an associated current signal and to determine a resistance value of a content of the cooking product container. A control device operates the excitation device and the resistance measuring device separately and operates the excitation device based on the resistance value.

Claims

1-13. (canceled)

14. A household PEF cooking appliance, comprising: a cooking product container fillable with liquid and cooking product and including a plurality of mutually insulated electrodes on an inner face of the cooking product container; an excitation device configured to supply at least two of the plurality of electrodes with pulsed electric signals; a resistance measuring device configured to apply a measuring signal to at least two of the plurality of the electrodes in order to measure an associated current signal and to determine a resistance value of a content of the cooking product container; and a control device configured to operate the excitation device and the resistance measuring device separately and to operate the excitation device based on the resistance value.

15. The household PEF cooking appliance of claim 14, wherein the excitation device and the resistance measuring device are connected to a same one of the plurality of the electrodes, said control device configured to operate the excitation device and the resistance measuring device at different times.

16. The household PEF cooking appliance of claim 14, wherein the excitation device includes a voltage source, a first pair of switches, with one of the first pair of switches configured to connect the voltage source to one of the at least two of the plurality of electrodes via a first voltage connection, and a second pair of switches, with one of the second pair of switches configured to connect the voltage source to another one of the at least two of the plurality of electrodes via the first voltage connection, wherein another one of the first pair of switches is configured to connect the voltage source to the other one of the at least two of the plurality of electrodes via a second voltage connection and another one of the second pair of switches is configured to connect the voltage source to the one of the at least two of the plurality of electrodes via the second voltage connection, and further comprising a third pair of switches, with one of the third pair of switches configured to connect the resistance measuring device to one of the at least two of the plurality of electrodes and with another one of the third pair of switches configured to connect the resistance measuring device to another one of the at least two of the plurality of electrodes, said control device configured to switch the first, second and third pairs of switches such that, when the switches of the third pair of switches are closed, the switches of the first and second pairs are opened, and vice versa.

17. The household PEF cooking appliance of claim 14, wherein a pair of the plurality of electrodes is an operating electrode pair connected to the excitation device, and another pair of the plurality of electrodes is an measuring electrode pair which is connected to the resistance measuring device and isolated from the operating electrode pair.

18. The household PEF cooking appliance of claim 17, wherein the control device is configured to operate the excitation device and the resistance measuring device at a same time.

19. The household PEF cooking appliance of claim 17, wherein the control device is configured to operate the excitation device and the resistance measuring device at different times.

20. The household PEF cooking appliance of claim 17, wherein the excitation device includes a voltage source, a first pair switches, with one of the first pair of switches configured to connect the voltage source to one of the operating electrode pair via a first voltage connection, and a second pair of switches, with one of the second pair of switches configured to connect the voltage source to another one of the operating electrode pair via the first voltage connection, wherein another one of the first pair of switches is configured to connect the voltage source to the other one of the operating electrode pair via a second voltage connection and another one of the second pair of switches is configured to connect the voltage source to the one of the operating electrode pair via the second voltage connection, and further comprising a third pair of switches, with one of the third pair of switches configured to connect the resistance measuring device to one of the measuring electrode pair and with another one of the third pair of switches configured to connect the resistance measuring device to another one of the measuring electrode pair.

21. The household PEF cooking appliance of claim 17, wherein the measuring electrode pair is arranged on at least a same wall of the cooking product container as the operating electrode pair.

22. The household PEF cooking appliance of claim 17, wherein the measuring electrode pair is arranged on a wall of the cooking product container which wall differs from walls on which the operating electrode pair is arranged.

23. The household PEF cooking appliance of claim 17, wherein the measuring electrode pair is configured to protrude into the cooking product container on a bottom side.

24. The household PEF cooking appliance of claim 14, further comprising a series resistor connected to one of the at least two of the plurality of electrodes, said excitation device configured to supply electric signals to the plurality of electrodes via the series resistor.

25. A method for operating a household PEF cooking appliance, said method comprising: applying with a resistance measuring device a measuring signal to at least two electrodes of a cooking product container in order to measure an associated current signal; during operation, determining with the resistance measuring device a resistance value of a content of the cooking product container; and triggering a first safety-relevant action when the resistance value falls below a predetermined first threshold value.

26. The method of claim 25, further comprising triggering a second safety-relevant action when the resistance value falls below a predetermined second threshold value which is lower than the predetermined first threshold value.

27. The method of claim 25, further comprising: supplying with an excitation device the at least two electrodes as an operating electrode pair with pulsed electric signals; during operation of the excitation device, monitoring whether an electrode voltage applied to the operating electrode pair has dropped by a predetermined amount due to voltage pulses output by the excitation device; and measuring the resistance value by the resistance measuring device, when the electrode voltage applied to the operating electrode pair has dropped by the predetermined amount.

Description

[0074] The above-described properties, features and advantages of this invention and the manner in which they are achieved will become clearer and more clearly understood in connection with the following schematic description of an exemplary embodiment which is described in more detail in connection with the drawings.

[0075] FIG. 1 shows a circuit diagram of a PEF cooking appliance;

[0076] FIG. 2 shows a circuit diagram of a PEF cooking appliance according to a first exemplary embodiment according to the invention;

[0077] FIG. 3 shows a circuit diagram of a PEF cooking appliance according to a second exemplary embodiment according to the invention;

[0078] FIG. 4 shows a first cooking product container according to the invention;

[0079] FIG. 5 shows a second cooking product container according to the invention;

[0080] FIG. 6 shows a third cooking product container according to the invention; and

[0081] FIG. 7 shows a fourth cooking product container according to the invention.

[0082] FIG. 1 shows a circuit diagram of a PEF cooking appliance 101. The PEF cooking appliance 101 has a cooking product container 102 which is able to be filled with liquid F and cooking product G (not illustrated separately) and which has a first electrode 103 and a second electrode 104 on opposing sides. The electrodes 103, 104 are exposed on the inner face of the cooking product container 102 and as a result come into contact with the contents F, G of the cooking product container 102.

[0083] The PEF cooking appliance 101 also has a voltage generator 105 as an energy source for supplying a pulsed electrical PEF signal to the two electrodes 103, 104. The voltage generator 105 here by way of example has, for example, a controllable DC voltage source 106 with an (optionally intrinsic) internal resistance Ri and a back-up capacitor Cs electrically connected in parallel thereto, which ensures the highest possible pulse currents.

[0084] The voltage generator 105 is able to be connected by a first voltage connection 107 via a first switch S1a of a first pair of switches S1a, S1b to the first electrode 103 via a series resistor Rv for suppressing current peaks, and via a second switch S2b of a second pair of switches S2a, S2b to the second electrode 104. The voltage generator 105 is also able to be connected by a second voltage connection 108 via a second switch S1b of the first pair of switches S1a, S1b to the second electrode 104, and via a first switch S2a of the second pair of switches S2a, S2b via the series resistor Rv to the first electrode 103. The four switches S1a, S1b, S2a, S2b serve for the pulse shaping of the PEF signals and to this end are alternately opened and closed in pairs, i.e. here by way of example either the switches S1a and S1b or the switches S2a and S2b are closed. Due to the short pulse duration the switches S1a, S1b, S2a, S2b are preferably electronic switches, for example IGBTs, but are not limited thereto. The switches S1a, S1b, S2a, S2b and the voltage source 106 are controlled by means of a control device 109 as indicated by the dotted arrows.

[0085] The excitation device 105, S1a, S1b, S2a, S2b comprises here both the voltage generator 105 and the switches S1a, S1b, S2a, S2b.

[0086] Generally the cooking product container 102 is not completely filled. The capacitance of the capacitor formed by the electrodes 103, 104 and the contents of the cooking product container 102 is thus composed of the capacitance Cf of the part filled with the liquid (for example water) and the capacitance Ca of the part filled only with air, which corresponds to a parallel circuit of the two capacitances Ca and Cf. The ohmic resistance between the two electrodes 103, 104 is similarly composed of the ohmic resistance Rf of the part filled with water and the ohmic resistance Ra of the part only filled with air, which corresponds to a parallel circuit of the two resistances Ra, Rf.

[0087] A measurement of the voltage applied to the series resistor Rv permits the calculation of the electrical current flowing through the cooking product container 102. Together with the electrode voltage which is applied to the cooking product container 102 or the electrodes 103, 104 thereof and which is able to be determined from the voltage level of the PEF pulses and the resistance value of the series resistor Rv, the impedance of the contents F, G of the cooking product container 102 is able to be concluded in a manner known in principle.

[0088] In this case, an estimation or measurement of the impedance which is as accurate as possible is expedient, since the operational reliability is able to be increased thereby. There are substantially two reasons for determining the operational reliability: (1) when metal is located in the cooking product container 102, a short circuit could be triggered thereby. (2) If the impedance is accurately known, this is able to be taken into consideration during the shaping of the PEF pulses, for example relative to the voltage level and/or pulse duration thereof. Due to the high pulse voltages, high pulse currents and relatively short pulse durations (which in practice cause unpredictable settling times) in household PEF cooking appliances 101, however, a reliable and at the same time cost-effective determination of the impedance from the evaluation of the voltage signals on the series resistor Rv and on the cooking product container 102 is practically impossible or only possible with significant effort in terms of circuit technology.

[0089] FIG. 2 shows a circuit diagram of a PEF cooking appliance 1 which is designed for improved determination of the impedance of the contents F, G. The PEF cooking appliance 1 represents a modification of the PEF cooking appliance 101. In this case, and as in FIG. 3 described below, the capacitor 102 is shown with the contents F, G as a simplified equivalent circuit with a capacitance Cf and an ohmic resistance Rf, since typically Ca<<Cf and Ra>>Rf.

[0090] In addition to the PEF cooking appliance 101 the PEF cooking appliance 1 has a resistance measuring device 2 which is designed to apply a measuring signal to the two electrodes 103, 104 for determining the impedance of the contents F, G. In the present case, the resistance measuring device 2 is able to be connected via a first switch S3a of a third pair of switches S3a, S3b via the series resistor Rv to the first electrode 103, and via a second switch S3b of the third pair of switches S3a, S3b to the second electrode 104. The resistance measuring device 2 has here by way of example a shunt 3, a signal generator 4 for generating the measuring signals and an evaluation device 5 for determining the impedance.

[0091] The control device 6 may communicate with the evaluation device 5 and is additionally configured for the operation of the resistance measuring device 2 and the switches S3a and S3b (which may also be regarded as components of the resistance measuring device 2). The control device 6 is also configured to operate the excitation device 105, S1a, S1b, S2a, S2b on the basis of the determined impedance. In particular, the control device 6 operates the switches S3a, S3b of the third pair S3a, S3b such that when they are closed or switched to a conductive state, the switches of the first and second pair S1a, S1b, S2a, S2b are opened. If conversely PEF pulses are applied to the electrodes 103, 104, the switches S3a, S3b are opened or switched to a blocking state.

[0092] If the switches S3a, S3b are closed, the signal generator 4 may generate a measuring signal for the impedance measurement, the voltage thereof being known very accurately, for example relative to the frequency, shape and/or voltage value thereof. Since the resistance value of the series resistor Rv is also very accurately known, the electrode voltage applied to the electrodes 103 and 014 is able to be derived with a high degree of accuracy. By measuring the voltage on the shunt resistor or shunt 3, additionally the electrical current, which flows in the circuit formed during the impedance measurement, is able to be accurately determined, for example by means of the evaluation device 5. With the knowledge of the electrode voltage and the current, by means of the evaluation device 5 the impedance value of the contents F, G of the cooking product container 102 is able to be determined and the capacitance Cf thereof and the ohmic resistance Rf estimated in a manner known in principle.

[0093] The household PEF cooking appliance 1 is able to be operated such that, during an operation, the resistance measuring device 2 determines the impedance of the cooking product container 2 or the contents F, G thereof and the control device 6 triggers at least one safety-relevant action when the impedance value falls below a predetermined threshold value. This is able to be configured such that when the impedance value falls below a predetermined first threshold value, at least one first safety-relevant action (for example a limit of the voltage level of the PEF pulses, optionally with the output of a message to a user) is triggered and when the impedance value falls below a predetermined second threshold value which is lower than the first threshold value, at least one second safety-relevant action is triggered, for example the excitation device 105, S1a, S1b, S2a, S2b is not operated and a corresponding message is output to a user.

[0094] The control device 6 may also be configured, for example programmed, such that during an operation of the excitation device 105, S1a, S1b, S2a, S2b or a PEF cooking phase it is monitored whether an electrode voltage applied to the operating electrode pair 103, 104 has dropped within a predetermined time period by a predetermined amount due to the PEF voltage pulse output by the excitation device 105, S1a, S1b, S2a, S2b and, if this is the case, the impedance value is measured by means of the resistance measuring device 2. This is able to be implemented such that a discharge speed of the electrode voltage is monitored and, when this discharge speed is greater than a predetermined threshold value, the impedance measurement is carried out. In this case, the effect is taken into consideration that this drop is due to the discharge of the capacitance of the cooking product container 102 through the internal ohmic resistance of the cooking product container. If, for example, metal is located in the cooking product container 102, the capacitor provided by the cooking product container 102 may be more rapidly discharged than without metal. This monitoring may additionally or alternatively take place, for example, for carrying out an impedance measurement before the start of a PEF cooking phase and/or after the end thereof.

[0095] The only drawback of this PEF cooking appliance 1 is that in practical use the switches S3a and S3b in the open state have to separate the high voltage of the PEF signals reliably from the resistance measuring device 2. This requires relatively expensive switches S3a and S3b. In cooking appliances in the industrial or professional field, costs for a circuit/electronics play only a relatively minor role.

[0096] FIG. 3 shows a circuit diagram of a PEF cooking appliance 11 which eliminates the drawback of the PEF cooking appliance 1. The PEF cooking appliance 1 now uses a cooking product container 12 which has separate electrodes for applying the PEF signals (“operating electrodes” 15, 18, 103, 104) and electrodes for applying the measuring signals (“measuring electrodes” 17, 19) as explained in more detail in the following FIG. 4 to FIG. 7. The switches S3a and S3b in this case connect the resistance measuring device 2 directly to the measuring electrodes 17, 19, whilst the operating electrodes 15, 18, 103, 104, similar to the PEF cooking appliance 1, are connected via the switch pairs S1a and S1b or S2a and S2b and via the series resistor Rv to the excitation device 105, S1a, S1b, S2a, S2b. As a result, the use of relatively expensive switches S3a and S3b may be dispensed with. Additionally, the advantage is achieved that a resistance measurement is able to be selectively carried out at the same time or alternately with the imposition of the PEF signals.

[0097] When using separate measuring electrodes 17, 19 it may arise that the electrical current flowing through the contents F, G of the cooking product container 12 differs from a current which would be generated when applying the measuring signal to the operating electrodes 15, 18, 103, 104, for example due to a different size and/or position of the measuring electrodes 17, 19, in comparison with the operating electrodes 15, 18, 103, 104. Thus the impedance determined by the resistance measuring device 2 would deviate from the impedance present during a PEF operation, as indicated by the measured capacitance Cm and the measured resistance Rm. However, the impedance determined by the resistance measuring device 2 still correlates with the impedance present during PEF operation. This deviation may be resolved by the impedance determined via the measuring electrodes 17, 19 being converted into the impedance present during the PEF operation. This may be converted, for example, by using characteristic curves—which are, for example, calculated or empirically determined—and which are stored for example in the evaluation device 15 or in the control device 6. To this end, a set of characteristic curves, with a plurality thereof, may also be used, wherein the individual characteristic curves are able to be assigned, for example, to different filling levels, cooking products, etc.

[0098] FIG. 4 shows a cooking product container 12 in a first version 12a. The cooking product container 12a has by way of example a rectangular basic shape with four side walls 13a, 13b, 13c, 13d and a bottom 14 and is filled here with liquid F (for example water) and cooking product G (not shown). Here operating electrodes 15 of an operating electrode pair which are electrically isolated from one another when the cooking product container 12a is empty are attached to the left-hand side wall 13a and the right-hand side wall 13b on the inner face over a large surface area. No operating electrodes are attached to the front side wall 13c and the rear side wall 13d but they could be attached in principle.

[0099] Each of the two operating electrodes 15 has—here by way of example on a corner—a recess 16 in which a measuring electrode 17 is located on the inner face, spaced apart and electrically isolated from the respective operating electrode 15.

[0100] If the cooking product container 12a is inserted into the PEF cooking appliance 11, one of the two operating electrodes 15 corresponds in terms of connection technology and function to the first electrode 103 and the other of the two operating electrodes 15 corresponds in terms of connection technology and function to the second electrode 103. The measuring electrodes 17 are connected to the switches S3a or S3b.

[0101] The control device 6 may be designed to be functionally analogous to the control device 6 described in FIG. 2.

[0102] FIG. 5 shows a cooking product container 12 in a second version 12b. The cooking product container 12b has a basic shape which is the same as that of the cooking product container 12a, wherein both measuring electrodes 17 are now arranged, however, on the same (here the right-hand) side wall 13b so as to be spaced apart in respective recesses 16 of the operating electrode 18. The measuring electrode pair 17, 17 is thus arranged on the same side wall 13b of the cooking product container 12 as the operating electrode 18. The left-hand operating electrode may correspond to the first operating electrode 103 of the cooking product container 102 (alternatively the second operating electrode 104).

[0103] FIG. 6 shows a cooking product container 12 in a third version 12c. The cooking product container 12c has a basic shape which is the same as that of the cooking product container 12a, wherein both measuring electrodes 17 are now attached, however, to the side walls 13c or 13d on the inner face. The measuring electrode pair 17, 17 is thus arranged on those side walls 13c, 13d of the cooking product container 12c which differ from the side walls 13a, 13b on which the operating electrode pair 103, 104 is arranged. As a result, the operating electrodes may correspond to the operating electrodes 103 and 104 of the cooking product container 102. This provides the advantage that no recesses have to be incorporated in the operating electrodes 103, 104.

[0104] FIG. 7 shows a cooking product container 12 in a fourth version 12d. The cooking product container 12d also has a basic shape which is the same as that of the cooking product container 12a, wherein both measuring electrodes 19 now protrude, however, into the cooking product container 12d on the bottom side. As a result, the operating electrodes may correspond to the operating electrodes 103 and 104 of the cooking product container 102. This also provides the advantage that no recesses have to be incorporated in the operating electrodes 103, 104. The measuring electrodes 19 are also able to be provided and mounted in a particularly simple manner.

[0105] However, in principle, mixed forms of the cooking product container 12 are also possible, for example a variant in which a measuring electrode 17 located on the same side wall 13a or 13b becomes an operating electrode 15, and the other measuring electrode 17 or 19 is located on a wall 13c, 13d or 14 of the cooking product container 12 on which none of the operating electrodes 103 and 104 are arranged, etc.

[0106] Naturally, the present invention is not limited to the exemplary embodiment shown.

[0107] Thus circuit variants with only two switches or more than four switches are also possible. A plurality of operating electrode pairs may also be present, to which, for example, PEF-signals may be supplied independently of one another.

[0108] Generally, “a”, “one”, etc. is able to be understood to mean a singular or a plurality, in particular in the sense of “at least one” or “one or more”, etc. provided this is not explicitly excluded, for example by the expression “exactly one”, etc.

LIST OF REFERENCE NUMERALS

[0109] 1 PEF cooking appliance [0110] 2 Resistance measuring device [0111] 3 Shunt [0112] 4 Signal generator [0113] 5 Evaluation device [0114] 6 Control device [0115] 11 PEF cooking appliance [0116] 12 Cooking product container [0117] 12a-12d Cooking product container [0118] 13a-13d Side walls of cooking product container [0119] 14 Bottom of cooking product container [0120] 15 Operating electrode [0121] 16 Recess [0122] 17 Measuring electrode [0123] 18 Operating electrode [0124] 19 Measuring electrode [0125] 101 PEF cooking appliance [0126] 102 Cooking product container [0127] 103 First electrode [0128] 104 Second electrode [0129] 105 Voltage generator [0130] 106 Voltage source [0131] 107 First voltage connection of voltage generator [0132] 108 Second voltage connection of voltage generator [0133] 109 Control device [0134] Ca Capacitance of part of cooking product container filled with air [0135] Cf Capacitance of part of cooking product container filled with liquid [0136] Cm Measuring capacitance [0137] Cs Back-up capacitor [0138] F Liquid [0139] G Cooking product [0140] Ra Ohmic resistance of cooking product container filled with air [0141] Rf Ohmic resistance of cooking product container filled with liquid [0142] Ri Internal resistance [0143] Rm Measuring resistance [0144] Rv Series resistor [0145] S1a First switch of a first pair of switches [0146] S1b Second switch of a first pair of switches [0147] S2a First switch of a second pair of switches [0148] S2b Second switch of a second pair of switches [0149] S3a First switch of a third pair of switches [0150] S3b Second switch of a third pair of switches