Method for measuring the amount of a substance in a mixture of substances

Abstract

The invention relates to a method for measuring amounts of substances (m1, m2) in a mixture of substances with two substances (M1, M2) using a microwave resonator: o determining a first moisture value of a first of the two substances (M1) and a second moisture value of a second of the two substances (M2) o measuring two measurement values (A, B) of the mixture of substances, o calculating two scalar factors (θ1, θ2) of two moisture vectors (I) from the two measurement values (A, B) of the mixture of substances, wherein the moisture vectors (I) each indicate a direction of a straight line of equal moisture for the substances using the first and second moisture values within a plane of the measurement values (A, B), o determining the amounts of substances (m1, m2) from the scalar factors (θ1, θ2).

Description

Technical Field

[0001] This invention relates to a method for measuring the amount of matter in a mixture of two substances using a microwave resonator.

[0002] This invention provides the possibility of measuring the amount of two non-dispersive or weakly dispersive substances in a mixture of substances using microwave resonance. Background Technology

[0003] In a mixture of two moist substances, the measurement of mass is essentially underdetermined when using a two-parameter method. Therefore, moisture cannot be determined independently of the fluctuating mass content in the mixture. Consequently, when measuring a mixture of substances using a microwave resonator, one of the mass fractions must remain constant, for example, in the sample container or the substrate of the second substance. The influence of this constant mass fraction can then typically be eliminated from the measurement, for example, using offsetting methods. Summary of the Invention

[0004] The measurement problem this invention aims to solve is where the proportions of two substances in a mixture fluctuate significantly, while the moisture content fluctuates only slightly or not at all, or where the moisture content of a single substance has been pre-measured. A simple rational consideration suggests that determining the amounts of the two substances in a mixture based on two measurements from a microwave resonator is not an underdetermined task.

[0005] The object of this invention is to provide a method for measuring the amount of matter in a mixture of two substances using a microwave resonator.

[0006] According to the invention, the objective is achieved by a method having the features of the invention. Preferred aspects of the invention form advantageous embodiments.

[0007] The method according to the invention provides two quantities of a mixture of substances. The substances are not necessarily chemically pure, but rather multiple substances in the mixture and their quantities are determined. Since the method according to the invention is not limited to pure substances, it is also possible to distinguish the quantities of two groups of substances from each other in a mixture having more than two substances.

[0008] The method according to the invention initially begins by determining a first moisture value for the first substance and a second moisture value for the second substance. The moisture value of a substance is a commonly used quantity in microwave measurement technology, determined, for example, by the quotient of two measurements from a microwave resonator. In subsequent steps, the two measurements of the mixture of substances are determined using a microwave resonator. Here, it is preferable to determine the shift in the resonant frequency and the broadening of the resonant curve.

[0009] Using the first and second moisture values, two scalar factors of two moisture vectors are calculated from the two measurements of the mixture of substances. The moisture vectors are vectors within the plane of the measurements that indicate the direction of straight lines representing equal moisture content of the substances using the first and second moisture values, respectively. Therefore, each moisture vector represents a direction within the plane of the measurements for a given substance, where the moisture value is constant.

[0010] In another step, the mass of the substance is determined by the two scalar factors. This final step demonstrates that the measurement problem is not underdetermined. The accuracy achievable using the measurement method according to the invention depends primarily on the degree of moisture fluctuation in the two substance fractions or the extent of knowledge regarding the moisture content of the two substance fractions. The inventors' analytical calculations have shown that even significant differences in moisture values ​​between the two substances can positively impact measurement accuracy. The accuracy achieved in determining the mass of the substance is surprising due to the use of a microwave resonator for measuring the mixture.

[0011] In a preferred embodiment, the determination of the mass depends on the scalar factor of the mixture and the temperature. Experiments have shown that, in addition to the scalar factor, the temperature of the mixture is also a determining factor, which is readily available in practical applications and helps improve measurement accuracy.

[0012] To determine the correlation between the mass and the scalar factor, multiple measurements are performed, followed by appropriate evaluations.

[0013] In a preferred embodiment of the method according to the invention, it has been shown that, regarding the correlation between the mass and the scalar factor, it can be assumed that the mass of the first substance depends on the scalar factor of the moisture value of the first substance, and the mass of the second substance depends on the scalar factor of the moisture value of the second substance. This independence of the two substances in the mixture makes it easier to determine the scalar factor. A calibration step can be performed beforehand regarding the moisture values ​​of the two substances, particularly when the moisture content of the two substances is constant or fluctuates little. Using this calibration step, the moisture values ​​of the two substances in the mixture can thus be determined as accurately as possible.

[0014] As an alternative or supplement to the calibration step for the moisture value, at least one additional measuring system can be provided, which measures the moisture value of one substance before mixing it with another substance. In this way, one of the moisture values ​​is precisely present in the measurement method. In a preferred embodiment, two additional measuring systems can be provided, each measuring a moisture value for one substance. In this embodiment, the method according to the invention can also be used for mixtures of substances in which the moisture values ​​of the substances forming the mixture fluctuate significantly. In the case of accurately detecting the moisture value of a single substance, the fluctuation in the measured value caused by the measurement of the mixture can be clearly attributed to changes in the amount of substance. It has proven advantageous to consider using two or more measuring systems by rescaling the moisture values ​​of one or more additional measuring systems. The scaling factor can be predetermined in the calibration step.

[0015] The preferred design of the present invention will be explained in more detail below based on embodiments. Attached Figure Description

[0016] In the attached diagram:

[0017] Figure 1 a and b show the measurements and associated moisture vectors plotted in the AB plane.

[0018] Figure 2 A measuring device for pre-measuring moisture values ​​is shown.

[0019] Figure 3 An AB plot showing the average values ​​of 12 samples with cellulose nonwoven fabric (Zellulosevlies) and with SAP layers is displayed.

[0020] Figure 4 An exemplary distribution plot of values ​​A and B is shown.

[0021] Figure 5 The distribution plots of A and B values ​​divided into θ values ​​are shown.

[0022] Figure 6 The areal density calibration was shown.

[0023] Figure 7 The longitudinal distribution of SAP and cellulose is shown using areal density.

[0024] Figure 8 With A and The value shows an alternative way of depicting the distribution plot.

[0025] To better understand this invention, a brief review of the physical basis is helpful. When a microwave resonator is used in the field of moisture measurement technology, two measurements, A and B, are generated. Measurement A here represents the change in the resonant frequency, which is in the form of a displacement of the resonant frequency. The second measurement, B, describes the change in the width of the resonant curve. The physical basis of measurement A is the wavelength shortening caused by the dielectric properties of the material being measured. The second effect leading to measurement B describes the absorption of microwaves in the sample being measured.

[0026] The polarization P of the dielectric material to be measured in the electric field E depends on its magnetic susceptibility. χ e and vacuum permittivity 0 is obtained.

[0027] .

[0028] Electromagnetic susceptibility is a complex number, which is actually not used. χ e ' It indicates that, and its imaginary part is used χ e " express.

[0029] .

[0030] In order to correlate with the measurements A and B of the microwave resonator, the magnetic susceptibility indicates that the measurement A is related to... χ e ' Proportional to, and the measured quantity B is proportional to χ e " Proportional.

[0031]

[0032] and

[0033] ,

[0034] in ' Let the real part of the relative permittivity be denoted by and . " It indicates its imaginary part.

[0035] For several materials M1 to M N For a mixture of materials, the electromagnetic susceptibility is obtained as the sum of the electromagnetic susceptibility of the materials:

[0036]

[0037] This behavior of the electromagnetic susceptibility of the mixture results in microwave measurements being additive. This means that the A value of the mixture is the sum of the A values ​​of the individual substances in the mixture. Similarly, the B value is the sum of the B values ​​of the individual substances in the mixture.

[0038]

[0039] and

[0040]

[0041] The following discussion will consider mixtures of substances consisting of two substances. In principle, mixtures of substances with more than two substances can also be analyzed, and some substances can then be combined together and considered as a single substance.

[0042] Figure 1 The plane formed by the measured values ​​A and B is shown. Lines representing the same moisture content were plotted for substances M1 and M2. The slope of the straight line representing the same moisture content is determined by the moisture value. 1. 2 represents the sum of the values ​​of A and B representing the mixture in the above equation, as shown below. Figure 1 As illustrated in diagram b, this results in a vector addition of the two quantities. This means that the measured values ​​A and B of the mixture can be determined as a vector sum of the moisture values ​​of substances M1 and M2. To better analyze this superposition in the mixture, it is advantageous to introduce moisture vectors, vector e1 and vector e2. Thus, each point on a line with constant moisture can be depicted by multiplying a scalar factor θ by the moisture unit vector.

[0043]

[0044] In the above equation, the exponent i represents substances 1 and 2.

[0045] Of course, the above correlation does not apply to water or other highly dispersive materials, such as glycerol. For such highly dispersive substances, the constant water content is not on a straight line.

[0046] If we recall the fact that, for the mixture, the A value is the sum of the A values ​​of the substances, and the B value is the sum of the B values ​​of the substances, then this correlation can be represented by a vector representation as follows:

[0047]

[0048] If the water vectors are not normalized, they each have a coordinate representation.

[0049]

[0050] Starting from this point, the measured values ​​A and B of the mixture of substances can now be written concisely:

[0051]

[0052] exist 1 does not equal Under condition 2, the system of equations can be inverted. In its inverted form, the following correlations are obtained:

[0053]

[0054] The above equations form the central aspect of the measurement method according to the present invention.

[0055] The moisture value can be used from the A and B values ​​measured in the mixture. 1, 2. Calculate the scalar factors θ1 and θ2. The above formula also clearly shows that the moisture value... 1, 2 is assumed to be either constant or slightly fluctuating during this process. In this case, the stated... 1 and Two values ​​are used for evaluation.

[0056] On the other hand, if the moisture content of the substance fluctuates greatly in the measurement application, it can be measured continuously. An advantage of the aforementioned correlation between the scalar factor and the measured value of the mixture is that this expression, as an analytical expression, allows the measured moisture value to be used directly. 1 and 2. And thus an evaluation is performed. The determined scalar factor now allows for the reliable determination of the quantities m1 and m2 of the substances. If we first ignore the temperature dependence, a linear scheme can be chosen here:

[0057]

[0058] In this case, parameters α and β represent the correlation between the scalar factor and the amount of substance. In principle, parameters α and β can be chosen based on the temperature. It has been found that the temperature dependence can also be considered directly in a linear manner. This leads to the following correlation:

[0059] .

[0060] Measurements evaluating mixtures of substances, such as the cellulose and superabsorbent content in diaper cores, have been demonstrated. The determination of the blending ratio of yarns with synthetic and natural fibers, and the determination of activated charcoal and other particles in cigarette filters, have shown that using scalar factors to determine the mass of these substances is a highly accurate method. Qualitatively, when considering the moisture content... When density is irrelevant, this can be reasonably interpreted. Such density-independent values ​​are included in the moisture vector e, such that the density-related effects on the measured quantities A and B are more expressed in the scalar factor. Therefore, determining the scalar factor from the measured values ​​of A and B of the mixture is a reliable component that allows for the determination of the amount of substance. Despite this qualitative consideration, the precision achieved in the determination process is still surprising.

[0061] In this context, it is impossible to accurately determine the moisture content of the substance beforehand. 1, 2. Or, in cases where measurements fluctuate due to the measurement conditions, the following methods can be used: Figure 2 The measuring device shown. Figure 2 The measuring device shown is a schematic diagram of the material flow 10 of material M1. The moisture content of the material flow M1 is measured using the measuring device 12, which is depicted schematically. Similarly, the moisture content of the material flow 14 of material M2 is measured using the measuring device 16. 2. Two materials, M1 and M2, are fed into feeder 18, where they become mixture 20 downstream of the second material feed 14. Mixture 20 is measured in measuring device 22. The A and B values ​​determined in this way can then be converted into scalar factors θ1 and θ2, based on constantly updated moisture values. 1, 2. The scalar factor can be directly converted.

[0062] If the moisture angle is determined using separate measuring devices 12 and 16, it has proven advantageous to convert the corresponding moisture value before processing.

[0063]

[0064] and

[0065]

[0066] Here, the moisture angle, represented by the dashed line, is the moisture angle of the individual devices 12, 16 before mixing. Parameter a i b i Perform calibration in a manner known to the public.

[0067] The above analysis will be repeated below in specific embodiments using 12 cellulose nonwoven fabric samples and for samples using 12 SAP layers (layers with superabsorbent powder). In the A, B plane, the average values ​​of the measurements are entered, where the A and B values ​​describe the shift and width of the resonant frequency as described above. Figure 3 The regression line plotted in the figure shows that SAP's tan( 1) The value is equal to 0.388, while the tan( ) of cellulose The value of 2) is 0.2636.

[0068] Figure 4 The A and B values ​​of the diaper core along its contour are shown, wherein SAP is dispersed in the cellulose nonwoven fabric within the diaper core. Using the slope of the regression line, the measured A and B values ​​for each case can be converted into scalar factors θ1 and θ2.

[0069] Figure 5 The same outline is shown, but this time the distribution of scalar factors θ1 and θ2 is plotted. Compared with the A and B values, it can be seen that the difference in θ values ​​between the cellulose and SAP is more significant, especially in the range of 10 to 22.

[0070] Figure 6 The calibration of the surface measurements is shown, where a temperature-independent calibration was performed in this case. In this calibration, the obtained θ values ​​were assigned linearly to values ​​in milligrams / cm². 2 The areal density is expressed in units of . For the equation...

[0071] ,

[0072] The following parameter values ​​were obtained:

[0073] .

[0074] Using the values ​​determined in this way, the measured A and B values ​​can be directly converted into areal density by converting them into the θ value. For the drawn profile, we obtain... Figure 7 The areal densities of SAP and cellulose are shown as trajectories. It can be clearly seen that the areal density of SAP extends substantially uniformly along the said profile, while cellulose has a significantly lower areal density in the range of 10 to 22.

[0075] For comparison, refer to Figure 4 The distribution chart of A and B values ​​in the figure, or refer to the following: Figure 8 Classic microwave moisture value It is not difficult to see that the moisture value... This is not a suitable measure for independently measuring the content of the two substances. In particular, the characteristicly low cellulose content in a segment cannot be determined by... Figure 4 and Figure 8 The filter distribution diagram shows this.

Claims

1. Measurement of two substances M 1 and M 2 The amount of matter in the mixture of substances m 1 and m 2 Method: The first substance was identified using a microwave resonator. M 1 First moisture value 1. And determine the second substance M 2 Second moisture value 2, Two measurements of the mixture of substances were measured using a microwave resonator. A and B One of the two measured values A Another measurement representing the resonant frequency shift. B This represents the change in the width of the resonance curve; Two measurements of the mixture of substances A and B Calculate two moisture vectors and Two scalar factors θ 1 and θ 2 The moisture vector and The measured value A and B The first moisture value is used within the plane. 1 and second moisture value 2. Each indicates for the first substance M 1 The second substance M 2 Regarding the direction of a straight line with equal water content, By the scalar factor θ 1 and θ 2 Determine the amount of substance in the mixture of substances. m 1 and m 2 .

2. The method according to claim 1, characterized in that, The mass m 1 and m 2 The determination depends on the scalar factor of the mixture of substances. θ 1 and θ 2 and temperature T conduct.

3. The method according to claim 1 or 2, characterized in that, The quantity of the substance was determined by multiple measurements of the mixture. m 1 and m 2 With the scalar factor θ 1 and θ 2 The correlation.

4. The method according to claim 3, characterized in that, The mass m 1 and m 2 With the scalar factor θ 1 and θ 2 The correlation between them is that the amount of matter in the first substance depends on the amount of matter in the second substance. M 1 scalar factor of moisture value θ 1 The amount of matter of the second substance depends on the amount of matter of the second substance. M 2 scalar factor of moisture value θ 2 .

5. The method according to claim 1 or 2, characterized in that, The scalar factor θ 1 and θ 2 It is determined by multiple individual measurements of the corresponding substance.

6. The method according to claim 1 or 2, characterized in that, The two substances M 1 and M 2 Moisture value 1 and 2. This is determined in advance during the calibration procedure.

7. The method according to claim 1 or 2, characterized in that, Provide at least one additional measuring system that measures a substance before mixing it with another substance.

8. The method according to claim 7, characterized in that, Two additional measurement systems are provided, each measuring the moisture content of a substance.

9. The method according to claim 7, characterized in that, One or more moisture values ​​from the additional measurement system are rescaled, wherein the parameters are calibrated to perform the rescaling.

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