Control apparatus for heating, defrosting and/or cooking foods with microwave energy

A control apparatus for heating, defrosting and/or cooking foods to be heat-treated by exposure to microwave energy at a given location inside a closed cooking chamber includes a microwave generator beaming microwave energy into the cooking chamber, and a sensor detecting the state of the food and controlling the energy beamed into the cooking chamber. The sensor is disposed in the cooking chamber filled with microwave energy between the microwave generator and the given location for food exposed to microwave energy, for detecting a value for microwave energy potential and controlling the output of the microwave generator.

Referring now in detail to the single FIGURE of the drawing, it is seen 
that microwave energy is supplied through a rotating antenna MA to a 
cooking chamber GR of the microwave oven, into which food GG which is to 
be heat-treated has been introduced. The rotating antenna MA receives the 
microwave energy from a waveguide HL which in turn receives the microwave 
energy from a microwave generator MG, a magnetron. An output control unit 
LS which is provided for the control of the magnetron, conventionally 
contains a high-voltage transformer as well as rectifier and condenser 
units. These units, as well as switching elements required for a safe 
microwave operation, need not be considered in detail herein. 
Through the use of an indicator/operating panel AE, set values regarding 
the output and length of time that the microwaves are to be beamed into 
the cooking chamber GR are entered into a logic control circuit AL which 
converts these input values for the control of the output control unit. 
The set values can be displayed on the indicator/operating panel AE. 
A microwave directional coupler RK is connected to the waveguide HL. A 
first output line A1 of the microwave directional coupler RK detects 
measurement values which correspond to the microwave energy moving through 
the waveguide HL from the microwave generator MG in the direction towards 
the cooking chamber GR, and a second output line A2 detects measurement 
values regarding oppositely moving microwave energy. The relationship 
between these microwave movements and thus the relationship between the 
measurement values detected by the output lines A1 and A2 of the 
directional coupler RK, gives a good indication of which respective 
microwave energy potential is present in the cooking chamber. This is due 
to the fact that not only is the microwave generator capable of 
introducing microwave energy into the wave guide HL, but the cooking 
chamber returns microwave energy to the wave guide HL in accordance with 
the microwave energy potential prevailing in the cooking chamber, which 
can be detected at the output line A2 by the microwave directional coupler 
RK. Since the microwave potential occurring in the cooking chamber when 
microwaves are beamed in depends on the ability of the food GG present in 
the cooking chamber GR to absorb microwaves, the food can be measured by 
means of this chain of relationships. The ability of the food to absorb 
microwaves and to transform them into heat depends on the type, mass 
(weight) and state of the food. If, for example, no food is present in the 
cooking chamber GR, no significant energy is absorbed in the cooking 
chamber GR and the returning microwave energy detected by the microwave 
directional coupler RK will increase to a very large degree in relation to 
the microwave energy supplied. However, during the implementation of 
cooking processes, the change in the state of the food, e.g. from the 
frozen to the defrosted state, becomes important for control measurements. 
The output lines A1 and A2 of the directional coupler RK are sent to a 
comparison circuit VS, which performs a comparison between the measured 
and supplied measured values and as a result sends a criterion to the 
logic control circuit AL. The output control unit LS of the microwave 
generator MG is controlled in dependence on this criterion and is 
readjusted in regard to the energy demand inside the cooking chamber GR 
and the values supplied. The values for the particular cooking processes 
can be supplied to the logic control circuit AL through the 
indicator/operating panel AE or permanently set values can be stored in 
the logic control circuit AL for performing standard cooking processes. 
The continuation of the individual process steps can be controlled and 
modifications of these steps may be made by superimposition of the values 
detected by the microwave directional coupler RK, which represent the 
actual cooked state of the food. 
In place of the directional coupler RK in the vicinity of the wave guide 
HL, a corresponding sensor for detecting the microwave potential may be 
disposed in the cooking chamber itself between a given location for the 
food GG and the microwave generator MG. However, it must be taken into 
consideration that different intensities of microwave energy build up in 
the cooking chamber GR. In the present exemplary embodiment these 
microwave intensities are additionally spatially changed through the 
rotating antenna MA for an even heat-treatment of the food. These 
circumstances must be considered from a circuit point of view, during 
detection by measurement of the microwave energy potential in the cooking 
chamber GR as well as by means of a corresponding disposition of the 
sensor and by evening out the results of measurement over time. 
In the illustrated exemplary embodiment, the microwave energy supplied by 
the microwave generator is used for heat-treatment of the food GG as well 
as for measuring purposes. This combination is suggested, but by no means 
is a prerequisite for the detection performed through measurement. On the 
contrary, it is also possible to supply microwave energy to the cooking 
chamber for measurement purposes only. This microwave energy may be 
relatively weak and may be beamed out only in the time slots required for 
measuring purposes. There is a further possibility of the microwave 
frequency for measuring purposes varying from the microwave frequency for 
performing the cooking process. This has advantages for measurement 
purposes due to the fact that the different wave lengths of the microwaves 
have different penetration depths into the food. In this connection it is 
also possible to use solid state microwave energy generators because the 
required outputs may be relatively small, as already stated. 
However, it is also possible to use microwave techniques only for the 
purpose of measuring the state of the food and to perform the 
heat-treatment in connection with or exclusively by means of thermal 
heating elements.