Method and system for determining process parameters Number:7,520,667 from the United States Patent and Trademark Office (PTO) owispatent

Title: Method and system for determining process parameters

Abstract: The present invention relates to a method and a system for determining a set of process parameters of a treatment unit in which unit a product is subjected to a temperature treatment, the method comprising: subjecting a product to an electromagnetic signal before, during and/or after a temperature treatment, wherein said electromagnetic signal is adapted to interact with said product dependent upon the dielectric constant distribution of said product, receiving an electromagnetic signal which has interacted with said product, analysing the received electromagnetic signal in comparison with the transmitted electromagnetic signal and thereby determining a response being dependent upon the dielectric constant distribution of said product and based thereupon determine the temperature (distribution) or water content of the product, and analysing said temperature distribution or temperature of the product or products and based thereupon determining a set of process parameters for a temperature treatment in a treatment unit.

Patent Number: 7,520,667 Issued on 04/21/2009 to Pahlsson,   et al.

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Inventors:	Pahlsson; Sten (Odakra, SE), Gunawardena; Ramesh M. (Solon, OH)
Assignee:	John Bean Technologies AB (Helsingborg, SE)
Appl. No.:	11/432,296
Filed:	May 11, 2006

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Current U.S. Class:	374/45 ; 374/117; 374/120
Current International Class:	G01N 25/00 (20060101); G01N 25/58 (20060101)
Field of Search:	374/4-6,120,121,45,57,135,137,30,117-119,100,15

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References Cited [Referenced By]

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2956281	October 1960	McMillan et al.
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4326163	April 1982	Brooke
4499357	February 1985	Kojima
4627442	December 1986	Land
4632127	December 1986	Sterzer
4679561	July 1987	Doss
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4876059	October 1989	Conroy
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5047713	September 1991	Kirino et al.
5115673	May 1992	Kline et al.
5363050	November 1994	Guo et al.
5369369	November 1994	Cutmore
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5588032	December 1996	Johnson et al.
5715819	February 1998	Svenson et al.
5800350	September 1998	Coppleson et al.
5886534	March 1999	Bakhtiari et al.
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6422741	July 2002	Murphy et al.
6536948	March 2003	Vivekanandan et al.
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Foreign Patent Documents

	4311103		Oct., 1994		DE
	29719600		Feb., 1998		DE
	0232802		Aug., 1987		EP
	0619485		Oct., 1994		EP
	0990887		Apr., 2000		EP
	2145245		Mar., 1985		GB
	2262807		Jun., 1993		GB
	449138		Apr., 1987		SE
	512315		Jul., 1998		SE
	WO 96/21153		Jul., 1996		WO
	WO 98/01069		Jan., 1998		WO
	WO 99/15883		Apr., 1999		WO
	WO 2004/029600		Apr., 2004		WO

Other References

Derwent Publications Ltd., London, GB; 1984-068151 & SU1019312 A (DAVY-1) DAVYDOV NV, May 23, 1984. cited by other . Derwent Publications Ltd., London, GB; AN 1986-129887, SU 1185269A, Oct. 15, 1985. cited by other . Derwent Publications Ltd., London, GB; AN 1994-180890 & SU944468A1 (ASRA), Jan. 15, 1993. cited by other . Shi, Y., et al., "Ultrasonic Thermal Imaging of Microwave Absorption," Proceedings of the IEEE International Ultrasonics Symposium 1:224-227, Honolulu, Hawaii, Oct. 5-8, 2003. cited by other.

Primary Examiner: Verbitsky; Gail
Attorney, Agent or Firm: Christensen O'Connor Johnson Kindness PLLC

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Claims

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The invention claimed is:

1. Method of determining a set of process parameters of a treatment unit in which unit a product is subjected to a temperature treatment, the method comprising: providing a product, subjecting said product to a temperature treatment in a treatment unit, subjecting said product to a transmitted electromagnetic signal before, during and/or after said temperature treatment, wherein said transmitted electromagnetic signal is adapted to interact with said product, the product having a dielectric constant distribution and wherein said transmitted electromagnetic signal interacts with said product dependent upon the dielectric constant distribution of said product, subjecting said product to a second signal providing a local change, in time and position, of the dielectric constant distribution of said product, providing an interference between the second signal and the transmitted electromagnetic signal as the transmitted electromagnetic signal interacts with the product being subjected to said local, in time and position, change of the dielectric constant distribution, receiving an electromagnetic signal which has interacted with said product, analysing the received electromagnetic signal in comparison with the transmitted electromagnetic signal to determine a response dependent upon the dielectric constant distribution of said product and based on said response determine the temperature distribution of said product or the temperature in a predetermined location of said product or a water content of the product, and analysing said temperature distribution, temperature or water content of said product or a plurality of said products and based thereupon determining a set of process parameters for a temperature treatment in a treatment unit.

2. Method according to claim 1, further comprising providing said determined process parameters to a treatment unit.

3. Method according to claim 1, further comprising receiving data representing the temperature distribution or temperature of a plurality of products and based on said received data determining said set of process parameters for a temperature treatment in a treatment unit.

4. Method according to claim 3, further comprising receiving data representing the temperature distribution or temperature of a plurality of products treated in a plurality of treatment units and based on said received data determining said set of process parameters for a temperature treatment in a treatment unit.

5. Method according to claim 1, wherein the second signal is a signal providing a, in time and position, local change of the density of said product and locally, in time and position, influencing the dielectric constant distribution.

6. Method according to claim 1, wherein the second signal is an ultrasound signal.

7. Method according to claim 1, wherein the electromagnetic signal is a microwave signal.

8. System for determining a set of process parameters of a temperature treatment unit, the system comprising: a first transmitter adapted to subject a product to a transmitted electromagnetic signal before, during and/or after a temperature treatment of said product, wherein the transmitted electromagnetic signal is adapted to interact with said product, the product having a dielectric constant distribution and wherein said transmitted electromagnetic signal interacts with said product dependent upon the dielectric constant distribution of said product, a second transmitter adapted to subject said product to a second signal providing a local change, in time and position, of the dielectric constant distribution of said product, the second transmitter being adapted to provide an interference between the second signal and the transmitted electromagnetic signal as the transmitted electromagnetic signal interacts with the product being subjected to said local, in time and position, change of the dielectric constant distribution, a receiver adapted to receive an electromagnetic signal which has interacted with said product, a signal analyser adapted to analyse the electromagnetic signal received by the receiver in comparison with the electromagnetic signal transmitted by the transmitter and, by analyzing the electromagnetic signal, determining a response being dependent upon the dielectric constant distribution of said product and, based on said response, determining the temperature distribution of said product or the temperature in a predetermined location of said product or the water content of said product before, during and/or after said temperature treatment, and a temperature analyser adapted to analyse said temperature distribution, temperature or the water content of said product or a plurality of said products and based thereupon determine a set of process parameters for a temperature treatment in a treatment unit.

9. System according to claim 8, further comprising a control unit adapted to provide said determined process parameters to a treatment unit.

10. System according to claim 8, wherein said temperature analyser is adapted to receive data representing said temperature distribution or temperature of a plurality of products and to based upon said received data determine said set of process parameters for a temperature treatment in a treatment unit.

11. System according to claim 10, wherein said temperature analyser is adapted to receive data representing said temperature distribution or temperature of a plurality of products treated in a plurality of treatment units and based thereupon determine said set of process parameters for a temperature treatment in a treatment unit.

12. System according to claim 8, wherein the second transmitter is adapted to subject said product to a second signal providing a, in time and position, local change of the density of said product and locally, in time and position, influencing the dielectric constant distribution.

13. System according to claim 8, wherein the second transmitter is an ultrasound transmitter.

14. System according to claim 8, wherein the first transmitter is a microwave transmitter.

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Description

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FIELD OF INVENTION

The invention relates to a method of determining a set of process parameters of a treatment unit in which unit a product is subjected to a temperature treatment.

The invention further relates to a system for determining a set of process parameters of a temperature treatment unit.

TECHNICAL BACKGROUND

There exist a number of different kinds of methods for measuring the temperature of a product.

U.S. Pat. No. 4,499,357 discloses an electronically controlled cooking apparatus in which an article to be heated is heated for cooking through measurement of temperature thereof by an infrared sensor. The infrared sensor is arranged to detect surface temperature of the article to be heated in electronically controlled cooking apparatuses of this kind. A problem with heating of food products is that the surface often reaches a high temperature fairly quickly whereas it often takes considerable time before the inside of the product reaches the required temperature. U.S. Pat. No. 4,499,357 addresses this problem by introducing a predetermined minimum heating time period being set such that heating of the article to be heated is unconditionally continued during the predetermined minimum heating time period after starting of heating of the article to be heated. This method relies on some kind of comparative temperature measurement, on that the heating process actually behaves as expected and that the products all have size and shape within relatively narrow intervals compared to the product used for the comparative temperature measurements. If something deviates from the expected ranges this method may indicate satisfactory surface temperature while the inside of the product may still be far from the desired temperature. It may especially be noticed that the operator may not even be aware of the fact that the inside has not reached the desired temperature.

GB2,145,245, on the other hand discloses an induction heating cooking apparatus adapted to be able to determine the temperature of the inside of the product. The apparatus is provided with a probe being inserted into the foodstuff to be cooked and detecting the temperature of the product. It is however often not acceptable to use a probe being inserted into the inside of the product. It is also difficult to use this kind of probing in an industrial process where a large number of products are treated simultaneously on a conveyor or the like.

EP0232802A1 discloses an apparatus for monitoring the cooking state of a substance, comprising an infrared light emitter and a sensor adapted to receive infrared light sent through product. The apparatus relies on that an alimentary substance being cooked varies its infrared light transparency, and thus the infrared light transmission and reflection coefficients, as the cooking process proceeds. As recognised in EP0232802A1 itself this method has its limitations and proposes that the light emitter and sensor are properly inserted into the substance to be monitored in order to give detailed results. As mentioned above is this kind of apparatus not satisfactory.

US2003024315, assigned to the present applicant, discloses a device for measuring the distribution of selected properties of materials. The device comprises an emitter of electromagnetic radiation and furthermore at least one sensor of a first type. The emitter emits electromagnetic radiation in a selected frequency range towards said materials and a sensor of the first type detects electromagnetic radiation in a selected frequency range coming from said materials. The detected electromagnetic radiation having been emitted by said emitter. The device also comprises means to generate a three-dimensional image contour information regarding the said material's position in space, and an analyser which (a) receives information from said sensors, (b) processes this information, and (c) generates signals containing information about the distribution of said properties as output.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a method of determining a set of process parameters of a treatment unit in which unit a product is subjected to a temperature treatment.

It is a further object of the invention to provide a system for determining a set of process parameters of a temperature treatment unit.

In accordance with the invention a method of determining a set of process parameters of a treatment unit in which treatment unit a product is subjected to a temperature treatment has been provided. The method comprises providing a product, subjecting said product to a temperature treatment in a treatment unit, subjecting said product to a transmitted electromagnetic signal before, during and/or after said temperature treatment, wherein said transmitted electromagnetic signal is adapted to interact with said product, the product having a dielectric constant distribution and wherein said transmitted electromagnetic signal interacts with said product dependent upon the dielectric constant distribution of said product, receiving an electromagnetic signal which has interacted with said product, analysing the received electromagnetic signal in comparison with the transmitted electromagnetic signal and thereby determining a response being dependent upon the dielectric constant distribution of said product and based on said response determine the temperature distribution of said product or the temperature in a predetermined location of said product or the water content within the product, and analysing said temperature distribution, temperature, or water content of said product or a plurality of said products and based thereupon determining a set of process parameters for a temperature treatment in a treatment unit.

By using the above method the determined appropriate process parameters may take into account the actual temperature distribution within the product. The temperature treatment, such as heating, cooking, frying, freezing, cooling or the like, may thereby be optimised to an extent not before disclosed. If an analysis of a product e.g. before the introduction into an oven reveals that the central portion of the product to be cooked in the oven is frozen while the outer portion is thawed it may e.g. be suitable to heat the product slowly in the beginning until all of the product is thawed before the actual cooking occurs at a higher temperature. A similar consideration may also be taken into account if the temperature measurement is performed after the treatment and it is found that the temperature distribution within the product is unsatisfactory in that the coldest portion is too close to a minimum temperature, while the surface is heated to a satisfactory level.

The method may also be used to determine the water content within the product. Applications where this is the case includes bakery and bakery products such as bread, cakes, cookies, crackers, crispbread and different kinds of dough and dough substances. Its uses also includes grain storage and mills where it is used to ensure that the water content is not too high (risk for mould and spores in grain and flour, and of course in bakeries to ensuring the quality of the flour used for the baking. Too high water content in grain may pose a fire hazard and moreover the price on grain is often dependent upon the water content. The method may also be used in production of different kinds of products with mixed in meat such as sausages and delicatessen. It is also useful for dairies where it is used for determining the water content in milk, butter and cheese. Also when drying and storing different food products it may used to ensure that the product is stored at a water content being below a certain percentage in order to avoid mould and spores, etc.

Moreover, the method is non-invasive and it may be used for different kinds of control set-ups, such as controlling a treatment unit directly or to determine calibration parameters.

Process parameters include flow rate of a heating or cooling medium (e.g. air), temperature of a heating or cooling medium, temperature of e.g. heaters in an oven or the like or cooling blocks in a freezer or the like, time of temperature treatment (set e.g. by holding time or by speed of conveyor carrying the products through the treatment unit), amount of mixed cooling medium (e.g. CO.sub.2 in ground meat), mixing rate (e.g. by drying), the different settings of process parameters in different parts of the treatment unit, the different settings of several treatment units in parallel (adapted e.g. to treat products with different preconditions) and in series (adapted e.g. to treat a product in several steps), degree of impingement (in e.g. impingement freezers or impingement ovens).

A number of different ways to make use of the inventive method will be discussed in more detail in the detailed description.

It may also be noted that the different actions of the method may be performed by different units and even at different locations. Transmitting and receiving the electromagnetic signal is performed where the product to be analysed is located. In practice this will be inside or in the vicinity (before or after) of the treatment unit, such as when the product is transported on a conveyor to, inside, or from the treatment unit. The method will require handling of an considerable amount of data. Especially the analysis of the received electromagnetic signal in comparison with the transmitted electromagnetic signal and the determination of a response being dependent upon the dielectric constant distribution involves handling of an considerable amount of data. The actions of the method up until and including this analysis will thereby preferably be performed at site. The result will be that the temperature distribution or at least the dielectric constant distribution will be known. In the latter case, the final action of determining the temperature may be performed at site or at a different location.

The analysis of the temperature or temperature distribution may be performed on site or at a different centralised location. One advantage with using a centralised location is that temperature measurements from several treatment units at completely different locations may be used as input in the determination of appropriate process parameters. It is also easier to provide expert operators supervising or guiding the analysis and determination of appropriate process parameters. It is also easier to update the equipment (hardware and software) used to perform the analysis and determination of appropriate process parameters.

It may also be noted that a semi-centralised system may be used. Such a set-up may be provided with an on-site analysis and determination of the appropriate process parameters, while the dielectric constant or temperature distribution also is transmitted to a centralised analysis centre. In such a case the on-site analysis may be used for more immediate changes necessitated by local circumstances, such as controlling start-up, controlling treatment temperature and time, discarding of defectively treated products, whereas the centralised analysis centre may be used for determination of more complex process control parameters, such as the suitable temperature profile in the cooking equipment.

Preferred embodiments of the invention are apparent from the dependent claims.

The method may further comprise providing said determined process parameters to a treatment unit. This way an expedient and secure control of the treatment unit is achieved. The feedback to the treatment unit may be provided automatically in response to the temperature analysis or be provided by an operator in response to the performed analysis.

The method may further comprise receiving data representing the temperature distribution or temperature of a plurality of products and based on said received data determining said set of process parameters for a temperature treatment in a treatment unit. This way e.g. trends may be detected and the appropriate change of process parameters may in such a case be changed even before a predetermined limit is reached.

The method may further comprise receiving data representing the temperature distribution or temperature of a plurality of products treated in a plurality of treatment units and based on said received data determining said set of process parameters for a temperature treatment in a treatment unit. By analysing data from several treatment units it will e.g. be possible to detect if a specific treatment unit has a non-typical response to a change in process parameters thereby making it possible to investigate treatment units with too low yield. It will also be possible to determine a set of process parameters that will provide a robust treatment process that can be performed on different treatment units even if they run under slightly different circumstances. The set of process parameters determined from data from several treatment units may also be provided to other treatment units than those that has provided the data.

The method may further comprise subjecting said product to a second signal capable of providing a local change, in time and position, of the dielectric constant distribution of said product, thereby providing an interference between the second signal and the transmitted electromagnetic signal as the transmitted electromagnetic signal interacts with the product being subjected to said local, in time and position, change of the dielectric constant distribution.

The interference phenomenon makes it possible to determine the point where the two signals have interfered and from where the dielectric constant has given rise to change of the received the electromagnetic signal compared to the transmitted electromagnetic signal. The electromagnetic (e.g. microwave) signal exhibits damping and phase delay by travelling through the product leaving the frequency unchanged. In those volumes of the product under test where the interference occurs (e.g. where the ultrasound wave creates a density displacement) a part of the electromagnetic (e.g. microwave) signal is shifted in frequency and upper and lower sidebands are created. By receiving these frequency shifted signals and studying e.g. the damping and phase delay it is possible to get information concerning the dielectric constant between the point of interference and the point of receipt of the signal. By creating a interference patter in e.g. a layer-by-layer fashion it will be possible to simplify and to speed up the analysis considerably. This may e.g. be done by measuring the dielectric constant initially in an outermost surface layer by creating an interference close to the surface and then measure the signal as it passes through this layer. This will give information concerning the dielectric constant in this layer and this will then be a known parameter when analysing the response from an interference in a second outermost layer giving rise to a interfered signal travelling through the second (unknown) outermost layer and the outermost (known) layer. Other kinds of controlled interference sweeps or systems may also be used. The actual sweep of the interference may be optimised considering practical aspects as long as the information may draw benefit from the fact that the known origin of the interfered signal facilitates the analysis. It is also contemplated that the analysis may be performed in the fly, i.e. during the sweep of the interference but it is also contemplated that the analysis is performed at a later time after the complete data set has been collected. If the practically feasible sweep pattern correlates with a convenient analysis set-up it is possible to determine the temperature in the fly (and thereby to end the measurement when enough information has been received). With a double interference system it will e.g. also be possible to provide two virtual probes within a product. This is discussed in more detail in the detailed description.

The second signal may be a signal capable of providing, in time and position, a local change of the density of said product and thereby locally, in time and position, influencing the dielectric constant distribution. This is a preferred way of creating the above mentioned interference between the transmitted electromagnetic signal and the second signal.

The second signal may be an ultrasound signal. This is a preferred way of creating the above mentioned local change of the density of the product. The short wavelength of the ultrasound will noticeably also be determining the resolution of the measurement, since the frequency shift of the electromagnetic signal will be provided where the ultrasound signal provides the local change in density.

The electromagnetic signal may be a microwave signal. This signal is preferred since it experiences a measurable phase delay and damping but is not absorb too much by food products or the like.

In accordance with the invention a system for determining a set of process parameters of a temperature treatment unit has been provided.

The system comprising: a first transmitter adapted to subject a product to a transmitted electromagnetic signal before, during and/or after a temperature treatment of said product, wherein the transmitted electromagnetic signal is adapted to interact with said product, the product having a dielectric constant distribution and wherein said transmitted electromagnetic signal interacts with said product dependent upon the dielectric constant distribution of said product, a receiver adapted to receive an electromagnetic signal which has interacted with said product, a signal analyser adapted to analyse the electromagnetic signal received by the receiver in comparison with the electromagnetic signal transmitted by the transmitter and thereby determining a response being dependent upon the dielectric constant distribution of said product and based on said response determine the temperature distribution of said product or the temperature in a predetermined location of said product or the water content of said product before, during and/or after said temperature treatment, and a temperature analyser adapted to analyse said temperature distribution, temperature or water content of said product or a plurality of said products and based thereupon determine a set of process parameters for a temperature treatment in a treatment unit.

The advantages of the system has been discussed in detail with reference to the method and reference is made to that discussion. It may however especially be noted that the system may be separate from any treatment unit or may form an integral part of the control system of the treatment unit. It may also especially be noted that the different analysing units may be provided on site or on a centralised location as discussed in more detail above.

Preferred embodiments of the system will be apparent from the dependent claims. The advantages of respective feature of the dependent claims has also been discussed in detail with reference to the method and reference is made to that discussion.

The system may further comprise a control unit adapted to provide said determined process parameters to a treatment unit.

The temperature analyser may be adapted to receive data representing said temperature distribution or temperature of a plurality of products and to based upon said received data determine said set of process parameters for a temperature treatment in a treatment unit.

The temperature analyser may be adapted to receive data representing said temperature distribution or temperature of a plurality of products treated in a plurality of treatment units and based thereupon determine said set of process parameters for a temperature treatment in a treatment unit.

The system may further comprise a second transmitter adapted subject said product to a second signal capable of providing a local change, in time and position, of the dielectric constant distribution of said product, thereby being adapted to provide an interference between the second signal and the transmitted electromagnetic signal as a transmitted electromagnetic signal interacts with the product being subjected to said local, in time and position, change of the dielectric constant distribution.

The second transmitter may adapted subject said product to a second signal capable of providing a, in time and position, local change of the density of said product and thereby locally, in time and position, influencing the dielectric constant distribution.

The second transmitter may be an ultrasound transmitter.

The first transmitter may be a microwave transmitter.

It may also be noted that the features of each dependent claim may be combined with the features of the other independent claims except where the features of two or more independent claims relates to each other excluding alternatives.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will by way of example be described in more detail with reference to the appended schematic drawings, which shows presently preferred embodiments of the invention.

FIG. 1 shows a system according to the invention.

FIG. 2 illustrates the transmitted signal into a product under test.

FIG. 3 shows a flow chart for determining a physical property, such as temperature, inside a product under test.

FIG. 4 shows a flow chart illustrating the process for obtaining an ultrasound metric.

FIGS. 5a and 5b show flow charts illustrating two embodiments of the process for determining the spatial distribution of the dielectric function within a product under test.

FIG. 6 shows a principal function of a first embodiment of the present invention.

FIGS. 7a-7d show a principal function of a second embodiment of the present invention.

FIG. 8 shows a mathematical representation of the dielectric constant dependent upon the water content and temperature in a sample.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

It may be noted that parts of the detailed description relating to the analysis of the response has already been described in an earlier not yet published application filed by the present applicant.

The system described is preferably to be used in the food industry. In the food industry, it is often important to accurately control the temperature of food products. When treating a product in a oven or the like, the process often aims at providing a specific minimum product temperature in order to secure required reduction of bacteria. When it cannot be ensured that the required temperature has been reached throughout the product one may have to discard the product. However, in order to get a high yield of the process and to secure good quality one must not treat the product by excessive temperatures. Therefore, there is a need for a non-destructed and non-contact control of the freezing of products. This problem may be solved by means of measuring the dielectric function and converting it to a distribution of temperature, as will be described in the following.

In a preferred embodiment the method of determining a set of process parameters of a treatment unit in which unit a product is subjected to a temperature treatment, the method comprises providing a product and subjecting the product to a temperature treatment in a treatment unit. The product is further subjected to a transmitted electromagnetic signal (microwave signal) in connection with the temperature treatment. The transmitted microwave signal interacts with the product in dependence upon the dielectric constant distribution of the product.

The product is further subjected to a second signal (ultrasound signal) capable of providing a local change, in time and position, of the dielectric constant distribution of said product. The ultrasound provides a local change of the dielectric constant by providing a local change in the density of the product as the ultrasound wave propagates through the product. This will result in an interference between the second (ultrasound) signal and the transmitted electromagnetic (microwave) signal as the transmitted electromagnetic signal interacts with the product being subjected to said local, in time and position, change of the dielectric constant distribution.

The electromagnetic signal which has interacted with the product (and thereby interfered with the ultrasound signal) is received and then analysed in comparison with the transmitted electromagnetic signal. Thereby a response being dependent upon the dielectric constant distribution of said product is determined and based on this response is the temperature distribution of the product determined.

Alternatively is the temperature in a predetermined location of the product determined. The temperature distribution or temperature of the product(s) is analysed and based thereupon is a set of process parameters for a temperature treatment in a treatment unit determined. The determined process parameters is then provided to a treatment unit.

In one embodiment the temperature measurement system is located at the exit of the temperature treatment unit, and thereby measures the temperature after the temperature treatment has been performed. This is especially suitable for ovens, fryers, steamers, cookers, etc where a specific temperature often has to be met to secure required log reduction of bacteria. The temperature measurements may be used to discard single products not meeting the required temperature. The measurements may also be used to control the treatment as discussed in more detail below. When the temperature measurement system is located at the exit of a freezer or cooler, it is contemplated that the temperature measurements are primarily used to optimise the process in respect of yield. If a certain freezing temperature has to be met to secure product quality during the marked the shelf life, the temperature measurement may also in this case be used for discarding single products.

Formers for forming e.g. dough and pasta, ground meat or the like, are often sensitive to product viscosity and temperature. The temperature measurement may in such a case e.g. be used to determine when a product in a cooler or thawing equipment is ready to be introduced into the forming equipment. It is also common to mix CO.sub.2 with products to provide the correct viscosity before introducing it to a former. This is e.g. used for ground meat provided in a continuous flow to the forming equipment. In such an instance the temperature measurement may be used to determine the temperature of the flowing product and to thereby determine the amount of CO.sub.2 to mix with the product.

The temperature measurement system described may be used to directly control the treatment unit in a feedback loop. However, in many cases this will introduce a process dynamics being difficult to control. The temperature measurement system of the invention is especially suitable for gathering data from a large number of products and in some cases also from a plurality of treatment units and then based on a statistical analysis determine a set of appropriate process parameters for a treatment unit (not necessarily being the one from which the data originates). Since the measuring method is non-destructive and does not require that any probe is in contact with or inserted into a product it may be used to determine the temperature or temperature distribution of in principal every single product treated in the treatment unit.

Another application where the measurement method may by used is in a two step process where the temperature is measured in-between the two treatment steps. When cooking in a two step process it is common that the first process is adapted to relatively rapid raise the temperature to a certain temperature and the second process is adapted to raise the temperature only slightly but to hold it for a longer time in order to ensure sufficient bacteria reduction. If the temperature of the first step is getting close to a lower acceptable temperature limit the holding time may be increased in order to still ensure sufficient bacteria reduction. Without the intermediate temperature measurement the problem would only be noticed after the complete process cycle, thereby often requiring cleaning of the complete process equipment before production is resumed.

When treating a product in a stack or some other process equipment with a considerable treatment time it may also be useful to measure the product temperature during the temperature treatment. The data may be analysed in order to provide an adjustment of the process parameters. Such a process may e.g. be a freezer, cooler, steamer or the like where the product is transported on a conveyor running in a helical path, thereby subjecting the product to a treatment during a considerable time period.

One application where temperature measurement before the treatment unit is especially suitable is when there are more than one parallel treatment unit or more than one parallel way through the treatment unit. It may e.g. be the case with an oven with more than one product conveyor running through the oven. In such a case the conveyors may run at different speeds and the products may be put on respective conveyor dependent upon the temperature before entering the oven. Relatively cold products are placed on the slowly running conveyor and relatively warm products are placed on the faster conveyor.

It may also be noted that it is of course possible to combine different temperature measurement systems such that the temperature is measured before and after a treatment, or before and during a treatment, or during and after a treatment, or even before, during and after a treatment in a treatment unit.

It may also be said that the method may be used to evaluate a treatment unit performance and for continuous control of a treatment unit. When used for evaluating a treatment unit it may be used to set parameters based on a statistical analysis based on a large number of data. It may also be used to set parameters based on knowledge of a response with greater prediction quality than today. When using it for continuous control it may e.g. be used for slow control based on a statistical analysis, e.g. taking into account trends even when the process still runs well within the acceptable limits. It may also be used to set parameters as a automatic control based on knowledge of a response. It may also be used to update a model for selection of which properties a product may have and still be allowed.

The system may however be used for other kinds of applications, such as for drying tobacco, roasting coffee beans, or other temperature treatments of products with properties similar to food products.

A non-exclusive list of equipments where the temperature measurement method may be used comprises ovens, steamers, pasteurizers, fryers, freezers (spiral, fluidized beds, impingement, for liquids, pre-freezers, chillers, product stabilizers), blanchers, formers, mixers, grinders, char makers, batter and bread equipments, sorters, batch and continuous retorts (for cans, pouches and jars), fillers for cans, tube fillers e.g. for in-container-sterilisation.

There are a number of products which today are especially difficult to process in a way that ensures correct temperature treatment. Such products will benefit especially by the introduction of this temperature measurement method and system. Such products are e.g. formed and fully cooked chicken, meat balls or beef patties (both batter/breaded and not), whole muscle chicken parts/breasts (both batter/breaded and not).

Below the temperature measurement method as such will be discussed in more detail.

In a preferred embodiment, ultrasound and microwave methods are combined. Object reconstruction can be done by pure microwave inverse scattering methods and by pure ultrasound tomography methods with their respective limitations. In this embodiment ultrasound is not used as an object reconstruction tool but as a tool to generate a density variation in the object to be investigated. This density variation creates a change of phase and frequency in the transmitted microwave radiation that is used for object reconstruction. Therefore the available resolution of this method is determined by the resolution of the ultrasonic wave (smaller than a millimeter for typical medical ultrasound frequencies). The density readout is performed using microwave radiation (at a frequency where attenuation still allows reasonable penetration depths e.g. S, ISM5.8 or X band). This method avoids the fundamental difficulty of microwave tomography approaches that a millimeter resolution requires millimeter wavelengths. Unfortunately, most objects of interest absorbs millimeter radiation within a material thickness of some wavelengths and does therefore not allow any interior parameters to be extracted.

In the following a continuous wave (CW) microwave and pulse wave train ultrasound based system is described for sake of simplicity. The method described is not limited to this case. Other modulation schemes for both, electromagnetic waves and ultrasound waves such as amplitude modulation (AM), frequency modulation (FM) frequency modulated continuous wave (FMCW), pulse code modulation (PCM), phase modulation (PM) and wavelet based modulation techniques (WM) are applicable and are optimal for certain other applications.

FIG. 1 describes an apparatus or system 40 for temperature measurement. The temperature measurement system is placed close to a conveyor means 11, which transports the products under test 12 through the sensor measurement gap 13. The system 40 consists of a microwave system 50, an ultrasound system 70 and an evaluation unit 60. The system comprises in this embodiment two fixed-frequency microwave generators 51 and 52 and a fixed frequency ultrasound generator 71. The first microwave generator 51 has a first fixed microwave frequency f.sub.1 (e.g. 5.818 GHz) and is coupled to at least one transmit antenna 42, and the second microwave generator 52 has a second fixed microwave frequency f.sub.2 (e.g. 5.8 GHz) and is preferably coupled to a down converter 54, such as a mixer. The down converter shifts the transmitted microwave signal, which is collected by at least one receive antenna 43, and the received microwave signal from the second microwave generator 52 to a low intermediate frequency IF. This allows the microwave signal transmitted through the product under test 12 to be evaluated in amplitude and phase. It furthermore comprises a filter unit 59, an analog to digital converter ADC 55, a set of signal processors 56 and an evaluation processor 60 that contains necessary algorithms to control the system and to evaluate the data. The result is submitted to a display unit 65. The system 40 also comprises a set of transducers 72 (only one shown for sake of clarity), in addition to the transmit antenna 42 and receive antenna 43, all grouped around the measurement gap 13. The transducers emit an ultrasound signal having an ultrasound frequency f.sub.US (e.g. 4.5 MHz) through the product under test 12. This causes a density displacement travelling at ultrasound speed. At the same time a microwave signal from the first microwave generator 51 is emitted from the transmit antenna 42. This signal also travels through the product under test 12. The microwave signal exhibits damping and phase delay by travelling through the product leaving the microwave frequency unchanged. In those volumes of the product under test 12 where the ultrasound wave creates a density displacement, a part of the microwave signal is shifted in frequency and upper and lower sidebands are created. The transmitted microwave signal is collected using the microwave receive antenna 43. The received signal is down converted using the down converter unit 54. The low frequency signal is then filtered using a filter unit 59 and analog-digital converted using the ADC 55. The digital signal is evaluated using a receive signal processor 56. The receive signal processor 56 converts the incoming digital signal to zero frequency using standard state-of-the-art digital filters.

The outcome of this filtering corresponds to the S.sub.21 parameter, which is not shifted in frequency, between the transmit 42 and receive 43 antenna as well known to a person familiar with the art. In the above we refer to the receive antenna 43 as microwave port 2 and the transmit antenna 42 as the microwave port 1.

In the system described by this invention there is a second set of bandpass filter 58, another ADC 55 and a second digital signal processor 57 in parallel to the first signal path 59, 55, 56.

The bandpass filter 59 is tuned to the difference frequency between the both microwave generators 51 and 52, which in the present embodiment is 5.818 GHz-5.8 GHz=18 MHz. The second bandpass filter 57 is tuned to the difference frequency between the microwave generators (e.g. 18 MHz) added the centre frequency (e.g. 4.5 MHz) of the ultrasound signal generator 71. Therefore this second digital signal processor path, containing 58, 55 and 57, converts the incoming signal to zero frequency that has been shifted in frequency by the ultrasound frequency. The measurement result is therefore limited to the cross section between the ultrasound and the microwave signal.

The IF bandwidth of the first 59, 55, 56 and second 58, 55, 57 digital receivers are chosen to be half the ultrasound frequency f.sub.US generated by the ultrasound generator 71. This is required to optimize the frequency shift by varying the ultrasound transducer phases. During the first stage of obtaining an ultrasound metric of the product 12, an ultrasound receiver 73 is present which collects the ultrasound radiation emitted from the transducers 72 and evaluate the damping, T.sub.56, and runtime as described in more detail below. In the above we refer to the ultrasound receiver 73 as microwave port 6 and the transducers 72 as the microwave port 5. The damping and runtime is evaluated in an ultrasound evaluation unit 74, but this may naturally be integrated in the evaluation unit 60.

FIG. 2 illustrates the emitted radiation into a product under test. The transducers 72 emit, in this example, an ultrasound pulse 91 through the product under test 12. This causes a density displacement travelling at ultrasound speed. At the same time a microwave signal 90 is emitted from the transmit antennas 42, travels through the product 12 and exhibit damping and phase delay with unchanged microwave frequency except in the area 95, where the ultrasound wave cause density displacement. In this area a part of the microwave signal is shifted in frequency, as described above, and upper and lower sidebands are created. The transmitted microwave signal 90 is collected using the receive antenna 43. The ultrasound wave 91 is collected in a receiver 73 during the process of obtaining the ultrasound metric, which is used during the next stage of determining the spatial distribution of the dielectric function.

FIG. 3 show a flow chart describing the measurement principle according to the invention using a system as described in connection with FIG. 1.

Basically, the method of this invention is a microwave-ultrasound combination measurement method of the dielectric and the acousto-electric properties of matter where the resolution is inherited from the ultrasound wavelength.

The measurement procedure consists of three phases as described below.

Phase 1: Obtaining the Ultrasound Metric

In this phase a map of the local ultrasound runtime and damping properties are established which is henceforth referred to as the ultrasound metric.

By varying the phases between the ultrasound transducers 72 using a phase programming logic, any desired phase form of the ultrasound field can be generated. It is possible to control the phases of all ultrasound transducers in a way to focus the ultrasound power to a point with a geometrical size of the order of a half wavelength of the ultrasound wave. Focusing the ultrasound wave in the medium on the smallest possible volume causes the frequency displacement of the transmitted microwave signal to reach a maximum. Therefore, the phase of the ultrasound transducers is varied to optimize the microwave signal. Evaluating the delay time between the ultrasound pulse and the achieved maximum frequency shift allows determining at what distance from the antenna the focus point is located inside the product under test 2. This measurement is repeated for a set of points covering the whole product under test with a predetermined resolution.

As a result, a table comprising the phases to be chosen for each independent focus point and the location with respect to the antenna is obtained. At the same time, the strength of the maximum signal is obtained from each of these measurement points from all over the measurement object which allows to map the local ultrasound damping.

The local strength of the ultrasound signal is calculated by measuring runtimes and damping values between all ultrasound transducers. (Of course, any choice of phase is optimized by maximising the microwave signal for each point in this layer). Assuming these delay time and damping values for the layer of the product close to the transducers, the phase for the closest focus points are obtained.

Tuning the phases for transmission to focus the ultrasound power in one focus point and tuning the phases for reception to focus on another focus point, the runtime between the two focus points of the first layer is obtained.

Assuming these values to be valid around the focus points and also close to the next layer of points, phase and amplitude values for one after the other point of the next layer are obtained. (Of course, any choice of phase is optimized by maximizing the microwave signal for each point in any layer.)

This process is repeated until the whole product under test is scanned.

The result is a table of the local damping of the ultrasound signal and the local phase delay of the ultrasound signal between all scanned focal points, the "ultrasound metric" together with the microwave signal strength for all the focal points.

The ultrasound metric may be obtained on a reference object, which is representative to the objects that are to be analysed. Thereafter, measurements may be made on such objects without the need of obtaining an ultrasound metric for each of the objects.

The metric by itself can also be considered as a substantial result of the invention and can be used as autonomous applications. Furthermore, metrics obtained on reference objects may be used as means to speed up measurements according to phase 1.

Phase 2: Evaluating the Microwave Interaction

Based on the above generated ultrasound metric and the microwave response the acousto-electric interaction is obtained in a layer-by-layer wise starting from the layer closest to the microwave antennas. It is not required to proceed this analysis in a layer by layer way but it proves convenient for a subsequent 3D image processing to do so.

The strength of the microwave signal measured in each focal point is determined by the product of the (a) local strength of the ultrasound signal, (b) the compressibility, and (c) the dielectric function of the material in the focus point.

Since the local strength of the ultrasound signal in all focal points is known from the metric, the interaction between the incident and the frequency-shifted transm