The volume of the product defining space will preferably be slightly greater than the volume of the product.

The invention also relates to an arrangement for measuring the volume of a bread product by means of a pressure difference measurement and in accor- dance with significant features of the inventive method.

The invention is based on the known principle that when a delimited and closed space, having a chosen volume and under a chosen pressure, is supplied with a given amount of compressible gas or gas mixture, such as air, over a period of time, the gas pressure in the space will increase in time, and that if the same amount of gas is delivered but the volume of the space is smaller, for instance due to the presence of a bread product, the gas pressure within the closed space will time related rise more quickly.

It will be noted that the method and the arrangement are primarily in- tended for measuring the volume of a finished baked product, such as a bread product, in a production line and in a non-destructive manner of the bread con- cerned.

Although the following description is directed solely to the measurement of a volume, it will be understood that the density of such a product can be deter- mined very easily, by weighing the product on a weighing machine.

Description of the background art Methods of measuring the volume of bread are known to the art.

With regard to the application of measuring the volume of one or more bread products, it can be mentioned that Swedish Patent Publication SE-C2-504 557 describes a method and an arrangement for measuring the volume of baked

bread product.

This prior publication describes the possibility of using an ultrasound probe (10) for carrying out a plurality of distance measurements during the whole of a measuring sequence, where the ultrasound probe and ultrasound receiver are ori- entated so as to be able to evaluate a specific distance to a known reference point (R) related to the bread product.

Relative movement is caused or created between the bread product (2) and the ultrasound probe (10), so that essentially the whole of the bread product surface will be met by a measuring signal from the probe (10) successively during said relative movement. The distance from the probe (10) to the bread product (2) is measured several times during this relative movement.

Because the distance between the probe (10) and the reference point (R) is set and known, the distance from the reference point (R) to a number of meas- urement points on the surface of the bread product can be calculated, with the aid of the distances measured by using the probe (10).

A sub-volume of the bread product is determined with each distance measured from the reference point (R) to the surface of the bread, and the total volume of the actual bread product is determined by adding together all measured sub-volumes.

Methods of measuring the volume of baked bread products, other than the aforedescribed method and arrangement, are also known to the art.

In each industrial bread-baking process, the quality of the ingredients used, particularly the flour, and the baking process employed are fully decisive with respect to the baking result.

A typical method of determining the current quality of the flour used, is to bake a bread product in accordance with a standard baking test, for example a test authorised by the American Association of Cereal Chemists or by the Interna- tional Association for Science and Technology, and thereafter measure the volume of the bread product baked.

The bread volume is often determined by placing the baked bread product in a container of a known volume, and then filling the container with a calibrated quantity of rape seed or poppy seed, so that the seed is totally surrounding the bread. The bread product is then removed and the remaining volume of the seed is then read-off on a scale on the container, said scale being graded as a function

of the container volume and the amount of calibrated seed used.

It will be obvious that this method of measuring the volume of the bread product concerned is encumbered with a number of drawbacks. The measuring process is carried out fully manually. The process is both time-consuming and complicated.

The amount of seed used must be calibrated at regular intervals, due to the fact that seed often stick to and fasten in small pores in the outer structure of the bread product and accompany the bread product from the container. The method is also less than accurate and is not, at least, adapted for rational use in a more or less continuous production process.

For example, if the container is shaken during the measuring process, the rape seed will be compacted and the volume thus decreased. Moreover, it is nec- essary to adapt the volume of the container to the size of the bread product, in or- der to obtain the greatest accuracy possible. It may also be necessary to use and to work with a plurality of different bread volume measuring devices.

Patent Publication FR-A-2 544 072 teaches an alternative method of measuring the volume of a bread product, in which said bread product is placed on a rotating table and illuminated from behind.

A camera records a silhouette image of the bread product from a place diametrically opposite the place from which the bread is illuminated. The bread is then turned and the measuring process is repeated in respect of a number of dif- ferent angles of rotation. The volume of the bread product is determined by data processing of the silhouette images, wherein each silhouette is divided into a number of segments and the length and height of the segments are used to de- termine the volume of the segments, in accordance with a given formula.

One drawback with this method is that certain cavities in the outer surface of the baked bread product are not seen in such silhouette images.

Because bread products often include a number of larger and smaller cavities of this nature, the method is proven to be not as accurate as would be de- sired.

The earlier known standpoint of techniques also includes the contents of the following patent publications.

GB-A1-2 218 513 This publication illustrates and describes apparatus for the three-

dimensional measurement of the outer form of a product, where a particular adap- tation has been made to enable the outer form of a bread product or a loaf of bread to be determined with the aid of laser technology.

The apparatus is based on the use of laser-based distance measuring equipment and requires means for mounting the product within the range of the distance measuring equipment, means for turning the product, means for moving the equipment linearly in relation to the product, and a computer unit, for process- ing the distances measured, so as to be able to calculate and give desired infor- mation concerning the form and the volume of the product concerned.

The apparatus is also based on the determination of the distance to se- lected points on the surface of the product, in relation to a number of pre-chosen positions.

WO-A1-95/22744 This publication also describes a method and an arrangement for measur- ing the volume of a loaf of bread.

This method uses an ultrasound-emitting unit (10), which is placed, at a determined distance from a reference point (R) in relation to the loaf, during the whole of the measuring process or sequence.

The method also involves creating a relative movement between the loaf (2) and the unit (10), and to allow a detection of each measured point on the sur- face of the loaf.

The distance concerned is thus read-off a number of times during this rela- tive movement.

The arrangement of this type requires the distance between the emitter (10) and the reference point to be known. A sub-volume corresponding to the measuring point can be determined for each measurement made, and a summa- tion of all sub-volumes concerning or relating to all measurement points is able to give a measurement of the total volume of the loaf.

GB-A1-2 327 760 This publication illustrates and describes a measuring apparatus, which is based on gas displacement technique, and which includes a sensor (3) that is ac- tive in detecting an occurring pressure difference.

A first chamber (1) of the measuring apparatus communicates with a first input of the sensor (3), said chamber being intended to accommodate the product

(13) to be measured. The method is applied to measure the volume of a hard product (13).

A second chamber (4) of the apparatus communicates with a second inlet of the sensor (3).

The apparatus also includes means for modifying the volume of the first chamber (1) and the second chamber (4), with pre-chosen values by compression.

The apparatus is particularly adapted for measuring the volume of grain or other hard and non-compressible seeds.

A single seed (13) is placed in one of the chambers, such as the first chamber (1), and a piston (14) is placed in its respective chamber (1,4).

The pistons are connected together so that they can be moved simultane- ously and uniformly in their respective chamber and therewith decrease the vol- ume uniformly and time-wise in their respective chamber in the same way. The pressure difference caused by the reduction in volumes is detected and read-off.

The volume of the grain or seed (13) in the first chamber (1) reduces the volume that can be compressed by the piston (14), giving rise to different degrees of compression and different pressure variations in respect of the two chambers as a result of common and uniform displacement of the two pistons.

US-A-4, 184, 371 This publication teaches an apparatus for measuring the density of a body and uses to this end a measurement chamber, a reference chamber, and subsonic wave generating unit.

The unit functions to send said waves simultaneously and phase-correct and coordinated to both chambers simultaneously, and pressure differences be- tween the two chambers are determined so as to be able to calculate a value of the volume of said product.

The product in this publication is shown as a person.

WO-A1-92/00700 This publication illustrates and describes a method and an apparatus for measuring the volume of a product, such as a person.

This apparatus also includes two chambers, a first chamber (2) which functions as a test chamber and which includes a door (9) or some similar closure means through which the person can enter, a second chamber (3) functioning as a reference chamber, and means for cyclically changing the volumes of the two

chambers in a precise complementary fashion.

The apparatus includes an oscillating diaphragm (18), which is positioned between respective chambers (2 and 3) so as to be able to generate an opposi- tional oscillating change in the volumes of the two chambers.

This diaphragm (18) may have the form of a loudspeaker.

Special mention is made to a frequency of about 3Hz in respect of the os- cillating change in said volumes.

US-A-5, 824, 892 This publication illustrates and describes an embodiment of an acoustic device for measuring differences in volumes.

There is used to this end a container (1), which functions as a reference container, and a container (2) which is adapted for measuring purposes.

These containers (1,2) are separated from each other by a partition wall (4), which carries a loudspeaker unit (6).

Current pressure values are sensed and recorded via microphones (11, 12).

Complementary variations of the volumes in the two containers (1,2) are created in this arrangement through the medium of a vibrating part (7).

The device includes means for determining current pressures in each chamber, means for controlling the volume changes in real time, and means for analysing the sensed pressure values.

US-A-4,369,652 This publication illustrates and describes a method and a measuring chamber for determining the volume of a body, where the volume of the measuring chamber is changed with the aid of a piston (8), placed in a cylinder (7). There can also be used a reference chamber (5), in which the volume is changed with the aid of a piston (11) disposed and activated in a cylinder (10).

The pistons (8,11) and associated cylinders (7,10) have mutually differ- ent cross-sectional areas and are activated simultaneously by one and the same piston rod (9).

Summary of the present invention Technical problems When taking into consideration the technical deliberations that a person

skilled in this particular art must make in order to provide a solution to one or more technical problems that he/she encounters, it will be seen that on the one hand it is necessary initially to realise the measures and/or the sequence of measures that must be undertaken to this end, and on the other hand to realise which means is/are required to solve one or more of said problems. On this basis, it will be evi- dent that the technical problems listed below are highly relevant to the develop- ment of the present invention.

When considering the present state of the art, as described above, it will be seen that a technical problem exists in providing a method and an arrange- ment, in which the volume of a bread product can be measured with the aid of simple means and to afford a high degree of accuracy, and which is based on the principle of placing the bread product in a closed delimited space and of delivering an oscillating gas mixture to said space and determining the increase and de- crease of the pressure of the gas mixture within the space and establishing the volume of the bread product on the basis hereof.

Another technical problem resides in the ability to realise the significance of and the advantages associated with placing the bread product in said delimited space and to give said space a volume, which is slightly greater than the volume of the product, and to use information representative of the reduced volume of the bread product present in said space as a measuring magnitude so as to enable the volume of the bread product to be determined in a computer unit in a simple manner.

A technical problem also resides in the ability to realise the significance of and the advantages afforded by adapting a pressure source or a compressible gas or gas mixture, and to couple said pressure source, over a chosen measuring pe- riod, to said delimited space that functions as a measuring chamber on the one hand and directly to a pressure-difference establishing sensor on the other hand.

Another technical problem resides in the ability to realise the significance of connecting said delimited space to said pressure-difference establishing sensor, and to connect said sensor to a device, which is used to determine the volume of the bread product on the basis of information obtained from said sensor.

Another technical problem resides in the ability to realise the significance of and the advantages afforded by allowing said pressure source to have the form of a loudspeaker arrangement, that functions to emit the pressure waves con-

cerned.

Another technical problem resides in the ability to realise the significance of and the advantages afforded by causing the pressure source to send pressure waves of a pronounced pure and structured character, such as a sinusoidal char- acter.

It will also be seen that a technical problem resides in the ability to realise the significance of and the advantages that are afforded by adapting the pressure source to emit oscillating pressure waves, with a frequency beneath 20 Hz, par- ticularly in a region of slightly above 5 Hz. A frequency range of 10-18 Hz is pro- posed in accordance with the invention.

Another technical problem resides in the ability to realise the significance of and the advantages that are afforded by adapting the sensor so that it will be sufficiently sensitive to register relatively small pressure differences that occur dur- ing a chosen measuring period.

Another technical problem resides in the ability to realise the significance of choosing a measuring period that lies within a range beneath 10 sec., such as between 1.0 and 5.0 seconds.

Another technical problem resides in the ability to realise the significance of and the advantages that are afforded by adapting said device to allow informa- tion given by the sensor to be converted to digital information and therewith allow momentary differences between occurring pressure variations to be evaluated.

Still another technical problem resides in the ability to realise the signifi- cance of and the advantages that are afforded by comparing the pressure varia- tions evaluated during a measuring period with stored reference information relat- ing to a number of reference volumes or the like obtained from earlier measure- ments, and in the case of an agreement in said comparison to generate a signal that is representative of a volume value corresponding to an indicated reference volume.

Another technical problem resides in the ability to realise the significance of choosing said pressure waves with a maximised pressure change caused by an alternating voltage of 10 V amplitude or less connected to the loudspeaker ar- rangement.

When considering the earlier standpoint of techniques, it will also be seen that a technical problem resides in the ability to realise the significance of and the

advantages that are afforded by connecting together a common space and a de- limited space, that functions as the measuring chamber, such that the same fun- damental pressure will occur in said spaces not only during the beginning of said measuring period but also during said measuring period.

Another technical problem resides in the ability to realise the significance of and the advantages afforded by allowing a sound source arrangement to send generated sound waves to a space, located close to or adjacent to said source, said space being connected to the delimited space and the sensor via channels, which may be formed the same or formed different.

In addition, it will be seen that a technical problem resides in the ability to realise the significance of and the advantages that are afforded by choosing the volume of the measuring chamber in accordance with the size and structure of said product, such as to create conditions for a more accurate measuring result.

Yet another technical problem resides in the ability to realise the signifi- cance of and the advantages that are afforded by choosing the number of wave motions during the measuring period concerned and to make a required compari- son between each wave motion.

Solution The present invention thus relates to a method and to an arrangement for measuring the volume of a bread product, in the form of a bread product placed within a delimited space, wherein the volume of the delimited space is chosen to be slightly larger than the volume of the product itself, wherein information, repre- senting the reduced volume of the space due to the presence of the bread prod- uct, is allowed to constitute a measurement magnitude, such as to enable the vol- ume of the product to be determined on the basis thereof.

With the intention of solving one or more of the aforesaid technical prob- lems, it is proposed, in accordance with the present invention, that a pressure source, adapted for action on a compressible gas or gas mixture, is coupled to said delimited space that functions as a measuring chamber, and also to a sensor, that detects pressure differences.

It is also proposed that the delimited space shall thereafter be connected to said pressure-difference sensor, and that a device is used for calculating and evaluating the volume of the product on the basis of the information obtained from

said sensor.

By way of proposed embodiments that lie within the scope of the inventive concept, it is proposed that the pressure source has the form of a loudspeaker ar- rangement or equipment and is adapted to send or transmit sound related pres- sure waves to the common space from said loudspeaker equipment.

The pressure source is also adapted to send pressure waves of a pro- nounced and structured nature, such as of a pure sinusoidal character as far as possible.

The pressure source is also adapted to send or transmit pressure waves at a frequency of slightly beneath 20 Hz.

However, it is also proposed in accordance with the invention that the pressure source is adapted to send pressure waves at a frequency above 5 Hz, preferably above 10 Hz.

It is also proposed in accordance with the invention that the sensor shall be sufficiently sensitive to register small pressure differences that occur during such a measuring period.

It is proposed in accordance with the invention that the measuring period shall be shorter than 10 sec., such as between 1.0 and 5.0 seconds.

Said device is also adapted to convert or transpose sensor-given informa- tion to digital information and therewith evaluate momentary differences between occurring pressure variations.

It is also proposed in accordance with the invention that pressure varia- tions evaluated during a measuring period can be compared with stored informa- tion relating to a number of reference volumes, etc., in respect of earlier meas- urements, and to generate a signal corresponding to an indicated reference vol- ume concerning a volume value when such a comparison is in agreement.

It is also suggested in accordance with the invention that said pressure waves are chosen with the maximised pressure change that is obtained with a voltage variation to the loudspeaker arrangement of about 10 V or less.

Advantages Those advantages that can be considered primarily characteristic of an in- ventive method and an inventive arrangement reside in the fact that the invention can be used beneficially to quickly establish the volume of a bread product with

pronounced accuracy, even when the bread product is of a porous nature.

The method and the arrangement are also adapted for use in a production line so that the current volume of a bread product can be established within one or more production sequences.

This applies in particular to the production of bread products, since various bread properties can be monitored during the production process.

The primary characteristic features of a method, according to the present invention, are set forth in the characterising clause of the accompanying claim 1, and the primary characteristic features of an arrangement are set forth in the char- acterising clause of the accompanying claim 14.

Brief description of the drawings An embodiment of an arrangement at present preferred for carrying out the inventive method of measuring the volume of a bread product, placed in a de- limited space, will now be described in more detail with reference to the accompa- nying drawings, in which; Figure 1 is a highly schematic view of an arrangement adapted for carrying out the proposed method; Figure 2 shows simplified examples of pressure wave-related sinusoidal curves, which can be compiled in a sensor unit into a signal that represents the volume of a bread product; and Figure 3 is a diagrammatic example of a practical measuring process of a po- rous bread product of different sizes, so as to enable the volume of the bread product to be determined.

Description of an embodiment at present preferred It is pointed out initially that we have chosen, to use in the following de- scription of an embodiment at present preferred and including significant charac- teristic features of the invention and illustrated in the figures of the accompanying drawings, special terms and terminology with the intention of primarily illustrating the inventive concept more clearly.

However, it will be noted that the expressions chosen here shall not be seen as limited solely to the chosen terms used in the description, but that each

term chosen shall be interpreted as also including all technical equivalents that function in the same or at least essentially the same way so as to achieve the same or essentially the same intention and/or technical effect.

The inventive method and a system or an arrangement, for carrying out the method, are used to measure the volume of a bread product 1, placed in or enclosed in a delimited space 2, intended for accommodating the product 1, wherein the volume 2'of the delimited space 2 is slightly larger than the volume 1' of the product 1.

The relationship between the volume 1'of the product and the volume 2' of the measuring chamber 2 will normally exceed 50%, although there is nothing to prevent this relationship from being further increased, such as to up towards 95%, in special conditions.

The choice of this relationship shall conveniently be dependent on the ma- terial structure of the bread product.

A fundamental feature of the present invention is that the relationship be- tween the volume 1'of the product 1 and the volume 2'of the space 2 shall be chosen beneficially in accordance with the nature of the bread product, such that a high relationship, such as 80 to 95%, can be chosen in respect of a highly elastic and porous bread product, while a lower relationship, such as a relationship of 75- 90%, may conveniently be chosen in respect of less porous products.

In the case of more solid bread products, it can be assumed, and with good reason, that an excessively small difference in the volumes (the space 1/the space 2") can result in excessively large pressure differences, and that exces- sively high differences in the volumes can result in pressure differences that are too small to achieve accurate measurements under conditions that are at least substantially optimal.

The invention is based on the availability of a number of different pieces of information, such as a first stored piece of information 7g representing the empty volumes of the space 5, the space 2 and the space 3, and a second piece of in- formation 7f representing the reduction in volume 2"caused by the presence of a reference product 1 in the space 5, the space 2 and the space 3, this volume re- duction constituting a measurement magnitude that can be detected via pressure variations in measurement channels 2a, 3a for enabling the volume 1'of the prod- uct 1 to be established by pressure difference measuring in a sensor 6.

This information may also apply primarily to the time-wise increasing pres- sure change applicable in the spaces 2,3 as a result of the simultaneous supply of one or more pressure surges through respective inlet channels 2b, 3b.

With regard to the spaces 2 and 3, it shall be noted that in accordance with the embodiment shown in Figure 1 the effect of the channel 2a on the sensor 6 and the effect of the channel 2b on the space 5 shall be added to the volume 2" of the space 2.

The volume of the space 3 is considerably reduced in this respect, by vir- tue of the fact that the space 3 consists, in principle, of two mutually coupled channel sections, the channel 3a and the channel 3b, which together form the vol- ume 3'of the space 3.

An alternative embodiment is to cut-off the channel 3b, adjacent the space 5, and to cut-off the channel 3b, adjacent the sensor 6, for connection to the free surroundings. In this case, the introduction of pneumatic resistances 3b'and 3a' respectively is proposed.

Said information may also apply to the time-wise reduction in pressure change, evaluated in the pressure difference measurement, effected via the sen- sor 6 and applying to the space 2"when an overpressure exists in the space 2"as a result of a pressure surge or impulse or a number of chosen pressure surges, this overpressure being equalised via the channels 2b and 3b to a delimited com- mon space 5 adjacent a pressure source 4.

Thus, the invention proposes the use of a pressure source 4, which is adapted for direct action on a compressible gas or gas mixture 5', such as air, en- closed in the common space 5.

Compression and decompression of the gas 5'in the space 5, via the pressure source 4, shall take place with a well-defined form, such as a pro- nounced sinusoidal form or the like, in respect of the time-related pressure changes with the smallest possible contribution from harmonics.

This requires adaptation of the form and the size of each space, particu- larly with regard to the space 5, which for desired pressure equalisation of the ba- sic pressure in the sensor 6 and the space 5 between the measuring periods al- lows each of the spaces, such as the space 2, to be in communication with the space 5, via the channel 2b.

Moreover, the space 5 shall be formed so that the pressure waves gener-

ated by the pressure source 4 can be distributed uniformly to both of said spaces 2,3 or at least can be anticipated to distribute to the two spaces.

Thus, during a chosen measuring period, the pressure source 4 is acous- tically coupled directly to said delimited space or measuring chamber 2 through the medium of a channel 2b and via the space 5 and the gas mixture 5', and also acoustically coupled direct to the space 3, via channels 3b, 3a to the sensor 6.

The spaces 2,3 may beneficially be mutually identical during a measuring period, and space connections and space dimensioning, via the channels 2b and 3b, may also be identical. This also applies to the channels 2a, 3a.

It will, of course, be understood that the term"identical"as used here also includes similarity with regard to the acoustic and pneumatic properties concerned during the measuring period.

The space 2 is connected to the lower connection 6a of a sensor 6 that establishes momentary pressure differences, via a channel 2a located downstream of the pressure source 4.

The space 3 has the smallest possible size, in the form of a channel 3a resp. 3b, and connects the space 5 to the upper connection 6b of the sensor 6.

The sensor 6 shall be sufficiently sensitive to be able to evaluate small pressure variations between the spaces 2,3 during an ongoing measuring period.

Thus, it shall be able to evaluate a plurality of pressure pulse-related measure- ment values during a measuring period, so as to be able to establish a difference curve and a statistic value compilation of a number of measurement values.

The pressure difference sensor 6 may normally be adapted for measuring within pressure differences corresponding to 5 cm water column.

There is nothing to prevent an electric signal amplifier 16 and a lowpass filter 16a to be connected downstream of the sensor 6.

A data-loaded or computer device 7 can be used to evaluate the volume 1 of the product 1 from difference-related information in digital form from the sensor 6.

It is particularly proposed that the pressure source 4 is adapted to send requisite pressure waves from a loudspeaker arrangement 4a. These pressure waves shall be conveniently adapted to a simple and pure curve form, such as a pronounced simple sinusoidal curve or some other simple wave form.

This means that the time-wise pressure change generated by the loud-

speaker arrangement 4a shall exhibit positive and negative values corresponding to a sinusoidal form and superimposed on a momentary fundamental pressure ap- pliable to the spaces 2,3 and 5.

The loudspeaker arrangement 4a is driven by circuits 14 (not shown in de- tail in the figure) that include amplifiers, wave-forming generators, etc.

The circuits 14 may conveniently be controlled from the computer unit 7.

The pressure source or the loudspeaker arrangement 4 is adapted for sending pressure waves having a frequency slightly below 20 Hz during the measuring period.

Figure 1 indicates at 14 a circuit required to this end.

The pressure source or the loudspeaker 14 is also adapted and controlled for generating and sending pressure waves at a frequency above 5 Hz, between 5 and 15 Hz, 10 and 18 Hz, depending on the structure of the product material.

Said sensor 6 is connected to a respective one of the chambers 2,3 and is sufficiently sensitive to register even small pressure differences that occur dur- ing a measuring period.

In the illustrated case, the measuring period is assumed to be shorter than 10 sec., such as between 1.0 and 5.0 seconds.

The invention also includes the embodiment in which the frequency of the pressure waves can be varied during a selected measuring period, such as be in- creasing and/or decreasing.

For example, the wave form can be chosen to increase from 5 Hz to 10 Hz or to decrease from 20 Hz to 10 Hz, or vice versa, during said measuring period.

There is nothing to prevent both an increasing and a decreasing fre- quency, or vice versa, being used during one and the same measuring period.

The device or unit 7 is adapted to convert sensor-given information to digital information in a unit 7a, and therewith evaluate momentary differences in the sensor 6 between pressure variations occurring in the spaces 2,3 with the aid of digital signals.

The unit 7a is coupled to two further memories, referenced 7b and 7c.

A number of reference values may be stored in a first memory 7b. For ex- ample, values belonging to one and the same product of different volumes 1'may be stored. Values belonging to one and the same product having different forms and structures may also be stored.

Thus, it shall be possible to compare pressure variations evaluated during a chosen measuring period with one or more combinations of one or more items of information stored in the memory 7b and relating to earlier made measurements and/or reference volumes, etc.

Each measurement value obtained during a measuring period may be stored temporarily in a memory 7c.

These measurement values may also be stored as reference values in the memory 7b.

The measurement value 7c obtained during a chosen measuring period can be compared with measurement values stored in the memory 7b, via a circuit 7d, in which one or more lists containing measurement values and their corre- spondence in an evaluated volume of the product 1 are stored, and to indicate a volume corresponding to said measurement values and to generate a signal rep- resentative of said volume.

When an agreement is found in the comparison, a signal representative of a volume value corresponding to an indicated reference volume is generated, this volume value being displayed on a display 7e.

The pressure wave generated by the pressure source 4 is chosen with a maximum pressure change adapted to the volumes and forms of the spaces.

Figure 1 illustrates an arrangement in which the same basic pressure ex- ists in the spaces 2,3 both initially and during the entire measuring period, therewith avoiding otherwise necessary calibration.

Figure 2 shows schematically, under A, a sinusoidal wave motion gener- ated by the sound source 4 within the space 5.

When this wave motion, an increasing and decreasing of the basic pres- sure of the gas 5', enters the measuring chamber 2, the amplitude, under B, in- creases as a result of the delimited volume 2"of the product.

When a corresponding wave motion passes through a space 3 functioning as a reference chamber at the same time, it is assumed that the amplitude, under C, increases to a lesser extent because the volume 3'has, in this case, been given a larger value than the volume 2".

The sensor 6 is now able to detect the pressure difference, under D, in the chambers 2 and 3 and signal-process said pressure difference in the computer equipment 7.

The chosen volume 3'of the space 3 will thus depend on the remaining volume 2".

Any time delays between the momentary occurrence of pressure varia- tions generated in the pressure source 4 and the point at which these variations in- fluence the sensor 6 via the channel or the space 3 or via the measuring chamber 2 and channels 2a, 2b connected thereto can also be taken into account via cir- cuits included in the computer unit 7.

Figure 3 illustrates the measuring results obtained with a practical applica- tion on a porous bread product.

In the case of a bread product of this nature, it is important to adapt a pre- dominant basic pressure to current atmospheric pressure and to ensure that the pressure waves generated have small amplitude values, so that the product will not be deformed during the sub-pressure phase and/or the overpressure phase, i. e. so that the measuring process is not influenced by countless small gas bub- bles in the product (such as bread).

Figure 3 is intended to illustrate three different measuring processes with three bread products of mutually different size and of mutually the same structure.

The product 1 is subjected to pressure changes over a period of 5 sec. and at five measuring points during the measuring period. In this case, the product is relatively small in relation to the volume of the measuring chamber 2, say about 50%.

A somewhat larger product 1a, 1.5 times the size of product 1 above, is measured in the same way as above and has a measured curve form in the mid- dle of the graph.

A large product 1 b, 2 times the size of the product 1 above, is measured in the same way and fills the delimited space to an extent of about 95%, and has a measured curve form to the right in Figure 3.

It will be seen from this that in the case of a 50% fullness corresponding to the size of the product 1, the measured points are essentially equal, whereas the measured points are more spread when fullness increases.

The cross-sectional area of 2b and 3b can be chosen conveniently in ac- cordance with the chosen product.

The invention also proposes the use of different means for improving the measuring result.

The placement of the loudspeaker arrangement in the space 5 may be a factor, the forms of respective spaces 5,2', 3'may be another factor, and adapta- tion of the frequency chosen to the configuration of the space 5 yet another factor.

Primarily, there is proposed a statistic processing of the curve form of the result.

It will be understood that the invention is not restricted to the aforede- scribed and illustrated exemplifying embodiment of the invention and that modifi- cations can be made within the scope of the inventive concept as illustrated in the accompanying claims.