Devices of this type are known in the shape of numerous variants, a. o. devices with temperature sensitive markings in the shape of bar codes, which make it possible to transfer a wide information concerning not only heating program and temperature conditions but also previously realized temperature related handling of packages with food.

The known devices have proved to work sufficiently with packages containing fluid food, where the read temperature on the surface of the package has proved to closely follow the temperature of the content of the package. Packages containing predominently solid food, however, are subjected to a considerable delay with respect to the determined temperature on the surface of the package, compared to the temperature within the food.

There are also other irregularities depending on the kind of food in the package.

The object of the invention is to achieve a device of the type introductorily mentioned, which works in an easy and a reliable way also with food consisting of. solely or mainly solid food.

This has been achieved, according to the invention, by the fact, that said marking is arranged readable on the surface of a block of polymeric material, which is thermally insulated with respect to the food, and which is arranged to be exposed to the same microwave radiation as the food.

Polymeric material of this kind is available in the market and is obtainable with a broad dielectric constant spectrum, which as is well known determines the degree of heating of the polymeric material by microwaves. This results in that it is possible to proceed by trial and error with different kinds of solid food products, which are heated by microwaves during measuring of the temperature in the food at the same time as a calibration is carried out of the heating of different tested polymeric blocks in dependence of the value of the dielectric constant of the different polymeric blocks, which are exposed to the same microwave radiation as the food but is kept insulated with respect of the food. In this way a correlation or correspondence is achieved between the temperature of the food and the temperature of the polymeric block, which then can be arranged indicated by a temperature depending marking on the surface of the polymeric block, which indication can be utilized for controlling the heating program of the oven.

Independently of this, a special, known marking may also be positioned on the surface of the block which marking consists of the usual bar code for identifying the kind and and price of the food, and so on.

It is especially advantageously if the polymeric material has such a composition that it simultaneously and closely follows the heating progress of the food.

The polymeric material may well be at least partly transparent and the marking may be composed of thermo-chromatic colour pigments embedded in the block, which pigments at changes of the temperature inside the block gradually change colour and/or colour intensity readable on the surface of the block.

A number of alternative blocks of polymeric material may be available as accessories to a microwave oven, which blocks have different dielectric constants that are matching different, standardized food products. One of the different blocks in dependence on kind of food product may be selected and placed at a predetermined place, suitably marked by a holder for the block on the food or, if it is provided with a surrounding package, on the package before the food or the package is introduced to a predetermined place in the oven. As an alternative such a holder may be positioned directly in the oven at a place where the block will be exposed for the same microwave radiation as the food placed in the oven. In this way alternative degrees of cooking of food may be possible, for instance more or less roasted.

Due to the fact that a polymeric block attached to a food product or a package must not be influenced by the temperature of the food, the polymeric block is suitably hinged to the package such that the block may be folded outwards from the package to a position distant from the surface of the food or package. As an alternative the polymeric block may be arranged to hang down freely from a protruding edge of a package enclosing the food.

The invention is described in more detail in the following with reference to the attached-drawings-,-which-schematically disclose-an---example-of-an---------- embodiment of the device according to the invention, and on which Figure 1 is a short side view of a package containing food, which package is designed as a plate, Figure 2 is a long side view of the same plate, Figure 3 is a plan view of the plate, and Figure 4 is a front view of a microwave oven shown with a food package placed in the oven.

The package shown in Figs. 1-3 in the shape of a long and narrow plate 1 has a cup-shaped part 2 with a plane, upper, protruding brim 3. The package is sealed by a membrane 4 and contains a predominantly solid food product 9 marked with dashed lines. In the middle of the long side of the plate there is a small block or plate 5 of polymeric material freely hanging down attached by an adhesive tape 6 that is pressed against the upper side of the brim 3. A bar code 8 is printed with black colour on a self-adhering label 7 attached to the outwards directed side of the polymeric block 5.

A part of the label is also provided with a marking 15 consisting of thermo- chromatic colour that changes at a predetermined temperature. Said part may alternatively be transparent and the marking 15 placed directly on the surface of the block beneath said transparent part. Also the bar code may of course be printed directly on the surface of the block 5, in which case the label is superfluous. The polymeric block 5 may for practical reasons be turned towards the under side of the brim 3 before the heating of the package and turned to the position shown on the drawing in connection with the introduction of the package into the oven. As shown in Fig. 4 the package 1 may be provided with a holder 16 in which a block 5 may be placed.

Such a holder may of course be positioned in the oven 10 at a place where a block 5 placed in the holder is exposed to the same microwave radiation as the food in the package 1 (not shown).

At small-scale application of the invention polymeric blocks provided with adhesive tapes may be obtainable with accompanying bar codes for different applications, or with separate, transparent and self-adhering labels with bar codes to be attached on polymeric blocks.

In order to heat a package in the shape of the shown plate 1, it is placed in a microwave oven 10 with the marking 15 placed in front of a reader 11, which at reading the marking delivers control signals via a line 12 to a control circuit 13, which in a manner known per se is arranged to control the heating system 14 of the oven in dependence of the red information, which also may include the bar code 8. If the package inserted into the oven has a deep-freeze temperature also the polymeric block will have this temperature so that the heating time will be automatically extended.

If the the package has a refrigerator temperature the heating time will be shorter, and the heating time will be further shortened if the package has been kept in room temperature so that the food in the package and the polymeric block have assumed a temperature close to the room temperature.

The invention is of course not limited to the embodiment shown and described by way of example but can be modified in different ways within the scope of the invention defined by the patent claims. Accordingly, in more uncomplicated applications it is possible to use a marking designed as a restricted area of the polymeric block, which only indicates that a certain temperature is reached, at which the oven is shut off. In this case the reader is a device for IR-reading.