The present invention is related to an apparatus and a method for the measurement of mass and/or moisture of dielectric objects.
With respect to the measurement of mass and/or moisture of dielectric objects, the present invention is based on the per se known microwave method, in which the object to be measured is put into a resonator. Due to its dielectric properties, the object changes an electromagnetic resonance impressed to the resonator. The mass and the moisture of the dielectric object is then determined from the change of the resonance curve and from the shift of the resonance frequency.
From EP 1 669 755 B1, the entire contents of which is incorporated herein by reference, a method for the measurement of the mass and/or moisture of the content of capsules is known. A measurement apparatus is provided for the measurement, which hast at least two resonators. The shift of the resonance frequency (A) and the broadening of the resonance curve (B) caused by the capsule are determined and analysed in both resonators. The first resonator has a measurement field which is homogeneous across the capsule extension, for determining the total mass and/or the moisture of the capsule. In the second resonator, in which the capsule is guided through a format-dependent sample guiding, the capsule content is not homogeneously distributed in the capsule due to the force of gravity, instead it is located in a part of the capsule by which a narrow measurement field for determining a location dependent profile of the mass and/or moisture is passed through. When the capsule format is changed, back fitting of the measurement arrangement with a new format dependent sample guiding is necessary.
From EP 1 467 191 B1, the entire contents of which is incorporated herein by reference, a method and an apparatus for determining the mass in portioned units of active ingredient is known. In the method, capsules, tablets or dragées are guided through a microwave resonator, which determines a shift of the resonance frequency and a broadening of the resonance curve. The measured variables serve for the determination of the mass with compensation of the moisture influence, wherein the mass is supposed to be directly proportional to the shift of the resonance frequency and directly proportional to the broadening of the resonance curve. However, it has come out that the results remain always affected by a certain degree of inaccuracy in certain applications.
From EP 0 372 992 A1, the entire contents of which is incorporated herein by reference, a measurement apparatus is known which has a spherical resonator. Into the resonator, two identical resonance modes are supplied, which have essentially the same resonance frequency, but different field orientations with respect to each other. The measurement assembly is intended for the determination of the mass of longitudinal filaments. The analysis of the results is based on the difference of the resonance frequency of the two modes. The difference of the resonance frequencies strongly depends on the mass as well as of the moisture, so that a measurement of the moisture not depending on the mass is not possible.
From U.S. Pat. No. 5,124,662, the entire contents of which is incorporated herein by reference, a method for classifying objects which are accommodated in a resonator is known. In the centre of the resonator, the objects to be classified are penetrated by an electric field which is as strong as possible. In order to be able to measure the sample in a way which does not depend on its location in the centre of the resonator, the microwave radiation of the different directions is superimposed, so that they differentiate to a field of maximal field strength in the centre of the resonator. In that the sample moves through the superposition of three orthogonal fields with about the same resonances, the shape and the orientation of the sample is averaged, and the result does not depend on the location of the sample. The information is achieved by the rotation of the electric field vector and it does not represent an independent analysis in different directions of space. In this classification method, it is disadvantageous that only spatial arithmetic means can be measured, and thus the measurement resolution is limited. Further it is disadvantageous that the method works properly only when the sample body is placed exactly into the resonator centre. For this purpose, an additional sensor arrangement is necessary.
From DE 102 26 845 A1, the entire contents of which is incorporated herein by reference, an arrangement for the determination of the distribution of the complex permittivity of an object to be observed is known. Microwaves of one single frequency are fed into the resonator, and the amplitude and the phase of the transmitted and reflected signals are analysed. There is no analysis of the resonance of the resonator. In the measurement, the object to be measured rests in the resonator, which has only the function of shielding. The spatial distribution of the permittivity is examined in that microwaves are coupled in and out at different positions.
The present invention is based on the objective to provide an apparatus and a method for the measurement of the mass and/or the moisture of dielectric objects which permits a rapid and accurate measurement on the dielectric objects.