TEMPERATURE PROBE AND OVEN PROVIDED WITH SUCH PROBE

Abstract: Temperature probe which is intended to be inserted into a foodstuff to be heated and an oven for treatment of foodstuffs including a temperature probe. A temperature probe (10) which is intended to be inserted into a foodstuff (27) to be heated has the shape of a rod and supports, at its tip and at at least one additional position along its length, a temperature sensor (13, 14, 15) of the type the resistance of which varies with the temperature. The temperature probe is connected, via a wire (16), to a connector (20) of the telephone plug type which via a corresponding jack, disposed in an oven (28), is connected to a control device (32) for the control of the heating treatment in the oven. Three temperature sensors (13, 14, 15) are provided in the probe suitably interspaced with respect to one another and the connector (20) is provided with three contact areas (17, 18, 19). The three temperature sensors (13, 14, 15) are connected to form a triangle or to form a star, the three terminals (21, 22, 23; 24, 25, 26) of which being connected to each respective one of the contact areas (17, 18, 19) on the connector (20). The probe is used together with an oven (28) which is provided with a control device (32) of a design such that the treatment process in the oven is controlled in accordance with the lowest one of the temperatures sensed by the temperature sensors.

Description: Temperature probe and oven provided with such probe The present invention pertains to a temperature probe of the kind indicated in the preamble of the appending claim 1. According to another aspect, the invention also refers to an oven having a temperature probe and defined in the preamble of claim 3. In domestic ovens it is common to use a temperature probe in order to sense the temperature of the foodstuff to be treated in the oven for the purpose of improving the control of the course of treatment. The probe is inserted in a piece of meat or a poultry, for example, so that the temperature sensor, which is usually disposed at the tip of the probe, will be placed essentially in the center of the piece of meat or in the center of the fleshy part of the poultry. It is namely impor¬ tant for the result that the lowest temperature in the food- stuff is to control the treatment. In practice, often the tip of the probe does not end up at the point of lowest temperature but at the side of said point. As a result, meat and poultry needed to be cooked all trough will not have the proper treatment because the oven, controlled by the temperature probe, will be prematurely switched off. In the Japanese patent application No. 58-99623 a microwave oven is disclosed which is provided with a temperature probe. In the application it is noticed that if poultry is being treated in such oven its surface tends to become scorched while the interior of the poultry still has a condition close to raw. In order to remedy this drawback it is suggested to provide the temperature probe with an additional sensor which is disposed so that when the probe is inserted in the poultry the sensor at the tip of the probe is positioned in the center of the fleshy part of the poultry while the additional sensor is positioned adjacent to the surface of the poultry. Then, the treatment is controlled by means of the temperature values from the two sensors so that the interior of the poultry reaches the desired temperature at the same time as does the surface of the poultry. Further, it is established that from a theoretic point of view an even finer heating control can be achieved by the number of sensors being increased. In such case, however, the complexity of the control device and of the probe with ist connectors increases and for cost reasons the application with two sensors has been found rational. The known temperature probe is intended for use together with a microwave oven and then for the control of the energy supply for the purpose of the desired temperature to be reached simultaneously inside a piece of meat and at the surface of said piece of meat. The supply of energy is controlled in accordance with a predetermined program with the use of the temperature values from the two sensors. In an oven, heated in a traditional way, i.e. an oven provided with heating elements or a hot air fan, a temperature probe of a conventional design, will frequently end up at the wrong position inside a piece of meat, or the like, to be treated. Accordingly, it is of interest to make use of the technique described above of providing additional sensors in the probe in order to increase the chances that at least one of the sensors takes the position of lowest temperature in said piece of meat. Of course, as suggested in the publication referred to, it is possible to provide several sensors in the probe but for the reasons given above this will lead to a situation where the construction of the probe, of the connec¬ ting parts and of the control device for the energy supply will become complicated. A reasonable compromise between the desired degree of fine regulation and the cost leads to a probe having three sensors and being provided with a connector of the telephone plug type having three contact areas (sterophonic audio plug) . The object of the invention is to provide a temperature probe of the kind referred to above which makes possible for the sensed temperature, as far as possible, to equal the lowest temperature of a piece of meat, or the like, to be treated. Another object of the invention is to provide for controlled energy supply to an oven in accordance with the lowest tempera¬ ture thus measured. The objects indicated will be achieved by a temperature probe having the characterizing features in- dicated in claim 1 and by an oven having the characterizing features indicated in claim 3-10. The invention will now be described more in detail in connection with an embodiment with reference to the enclosed drawings, in which: Fig. 1 shows a temperature probe with associated connector, Fig. 2A and 2B show alternative interconnecting arrange¬ ments for three sensors, and Fig. 3, finally, schematically shows an oven with a tempera¬ ture probe connected thereto and with a con¬ trol device for the supply of energy. In Fig. 1 a temperature probe 10 is shown which is designed in accordance with the invention. In the conventional way, the probe comprises an elongate tubular part 11 one end of which being attached to a handle 12 whereas the opposite end is provided with a tip intended to facilitate the insertion of the probe into a foodstuff the temperature of which is to be monitored. A temperature sensor 13 is disposed at the tip and another two sensors 14,15 of the same type are provided along the tubular part 11. These sensors are resistors the resistance of which depends on temperature, referred to as thermistors. Each of the thermistors is disposed in the tubular part or housing so as to be electrically insulated from said part. In addition, each thermistor has two connecting terminals which by suitable conductors, not shown, in a cable 16 are connected to three contact areas 17,18,19 disposed on a connector 20 of the telephone plug type. In this case, where three thermistors are present, these can be connected in Y-connection as shown in Fig. 2A. The thermis¬ tors have been designated R lf R 2 and R 3 and are connected between the respective terminal 21,22,23 and a common point O. If there is a desire for a direct measurement of the resistance of the respective thermistor this can be performed by a measurement between the respective terminal and the common point 0. However, such a measurement would require an additio¬ nal conductive area on the connector which leads to a special design of said connector. The aim is to use, as far as pos¬ sible, standard components and the connector 20 shown in Fig. 1 is such a component in the shape of a telephone plug of a sterophonic design used in audio applications. The connector offers three contact areas only which means that with the thermistors connected in Y-connection, as shown in fig. 2A, measurement can only take place between the terminals 21-23, 21-22 and 22-23, respectively. The resistances measured are designated R,, R b AND R-. From the circuit diagram it appears that R, is determined by R, in series with R 3 while, correspon¬ dingly, R b is determined by R, in series with R 2 and R c is determined by R 2 in series with R 3 . With the designations given three mathematic formulas can be set up between R a , R b and R c , respectively, and the three resistance values R t , R 2 and R 3 and a certain amount of calculation leads to the following formulas for the three resistances R,, R 2 and R 3 as expressed in the three measured resistances R,, R b and R < .: R, = (R S +R b -R c ) R 2 = %(R b +R.-R R 3 = %(R a -R b +R c ) An alternative connection of the three thermistors is shown in Fig. 2B according to which the thermistors hav been connec¬ ted so as to form a triangle. Here, the resistances have been designated R 4 , R 5 and R^ whereas the corresponding terminals have been designated 24,25 and 26. The resistance values measu¬ red between the terminals 24-26, 24-25 and 25-26, respectively, have been designated R d , R. and R f . In this variant of connection the resistances R,, R 5 and R < ; and the measured resistances are so correlated that a much more difficult calculation work is required in determining the resistance of the respective thermistor than is the case in the connection according to Fig. 2A. In this case the simplest way is to use the known formulas for transfer from triangle connection to Y-connection in order first to transform the coupling to star shape and therafter to use the formulas presented in connection with Fig. 2A for determining the resistance of the respective thermistor and of the temperatures represented by said resistance values. In the first place, the temperature probe is intended to be used in a domestic oven and such an oven is shown schematically in Fig. 3. The tip of the probe has been inserted into a piece of meat 27 so that the three sensors will take somewhat different positions in the piece of meat, this in order for the point of lowest temperature in the piece of meat to be more easily determined. The distance between the sensors is chosen with this desire in mind and in the practical case the distance fc 5 can be in the range of 1-3 centimetres. The connector 20 is connected to an outlet of a corresponding design, here referred to as a telephone jack disposed in the inner wall of said oven. The oven, designated by 28, is in the conventional way provided with heating elements 29,30 disposed in the upper and lower 10 part, respectively, of the oven compartment, referred to by 31. In order to control the supply of heat from the two heating elements in the oven a control device 32 is provided which conveniently comprises a microprocessor for the necessary resistance calculations to be performed. The setting of 15 temperature and the choice of heating mode, such as bottom heat, top heat, both top heat and bottom heat, can be performed by means of suitable knobs 33. By carrying out the described measurements and then the calculations indicated the temperatu¬ res sensed by the thermistors can be determined. Then, in 20 accordance with the invention, the oven is controlled according to the lowest of said temperature values. This means that when the temperature set has been reached in the present piece of meat, one knows with greater certainty than before that in no point in said piece of meat a lower temperature is prevailing. 25 By the temperature probe described it will be possible to insert same into a piece of meat, a poultry or the like without the requirement for the tip of the probe to be disposed in the exactly correct position, namely in the center of the piece of meat or the fleshy part of the poultry, which position is 30 considered to be the latest one to reach the desired tempera¬ ture. In addition, by controlling the oven according to the lowest of the sensed temperatures, the desired temperature will always be achieved in every point of the piece of meat or the poultry with greater certainty than before.

Claims: C l a i m s 1. Temperature probe intended to be inserted into a foodstuff to be heated, the temperature probe (10) having the shape of a rod and supporting, at its tip and at at least one additional position, a temperature sensor (13,14,15) of a type the resistance of which varies with the temperature, the tempera¬ ture probe via a wire (16) being connected to a connector (20) of the telephone plug type which, via a corresponding jack disposed in an oven (28) provided for the heating treatment, is connectable to a control device (32) for the control of the heating process, characterized in that three temperature sensors (13,14,15) are provided to be supported by the probe (10) at positions suitably interspaced with respect to one another, the connector (20) having three contact areas (17,18,19) and the three temperature sensors (13,14,15) being connected to form a star or a triangle with the three terminals thus formed being connected to the respective contact area of the connector. 2. Temperature probe according to claim 1, characterized in that the space between the temperature sensors is in the range of 1-3 centimetres. 3. Oven for treatment of foodstuffs, comprising a temperature probe (10) intended to be inserted into a foodstuff (27) to be heated, the temperature probe having the shape of a rod and, at its tip and at least one additional position along its length, supporting a temperature sensor (13,14,15), the temperature probe (10) being connectable to a control device (32) for the control of the treatment process in the oven (28) , charac¬ terized in that as a total at least three temperature sensors (13,14,15) are provided in the probe (10) suitably interspaced with respct to one another, the control device (32) being arranged to control the treatment process based on the lowest one of the temperatures sensed by the sensors. 4. Oven according to claim 3, characterized in that the space between the temperature sensors is in the range of 1-3 centi- metres. 5. Oven according to claim 3, characterized in that the temperature sensors (13,14,15) are of the type the resistance of which varies with the temperature, the resistance of the sensors being in essentially the same range and, further, each sensor being connected to the control device (32) via a suitable connector (20) , said control device being arranged to V- 5 determine the resistace value that corresponds to the lowest temperature value by comparison of the sensed resistance values. 6. Oven according to claim 5, characterized in that three sensors (13,14,15) are provided and connected to form a star, 10 the three connecting points (21,22,23) formed by the free ends of the sensors being connected to its respective contact area (17,18,19) on a connector (20) of a standardized design of the telephone plug type. 7. Oven according to claim 5, characterized in that thee 15 sensors (13,14,15) are provided and connected to form a triangle, the three connecting points (24,25,26) being connec¬ ted to each respective contact area (17,18,19) on a connector (20) , said control device (32) being arranged to perform, by means of known transfer formulas, a transform of the triangle 20 connection to a star connection in order to determine the resistance values of the different sensors. 8. Oven according to claim 7, characterized in that the three connecting points (24,25,26) are connected to each respective contact area (17,18,19) of a connector (20) in a standardized 25 form of the telephone plug type. 9. Oven according to any of the preceding claims,charac¬ terized in that the control device (32) comprises a micropro¬ cessor. 10. Oven according to any of the preceding claims, charac- 30 terized in that the oven (28) is arranged to be heated by means of thermal energy.

Inventors: LJUNGGREN PER HENRIK, TIMGREN ROLAND HENRY, LJUNGGREN, PER, HENRIK, TIMGREN, ROLAND, HENRY
Applicants: ELECTROLUX AB, AKTIEBOLAGET ELECTROLUX
Application year: 1993
Main classification: G01K1
IPC codes: F24C7, G01K13