Electricity: measuring and testing – Impedance – admittance or other quantities representative of... – Distributive type parameters
Reexamination Certificate
2000-06-05
2002-06-25
Metjahic, Safet (Department: 2858)
Electricity: measuring and testing
Impedance, admittance or other quantities representative of...
Distributive type parameters
Reexamination Certificate
active
06411103
ABSTRACT:
Priority is claimed with respect to Application No. 199 25 468.0 filed in Germany on Jun. 3, 1999, the disclosure of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
The invention relates to a stray-field sensor for measuring dielectric properties of substances, having generating elements for generating an electrical field, and shielding elements for shielding the generated electrical field, the shielding elements being configured such that the electrical field is located at least partially outside of the shielding elements.
Stray-field sensors of this type are known. The known stray-field sensors employ an electromagnetic stray field to measure dielectric properties of substances located in the electromagnetic stray field. For example, these stray-field sensors can be used to measure the effective dielectric constant of a substance for indirectly drawing conclusions about the type of substance, its moisture content, density, etc. To promote a better understanding of these stray-field sensors, and particularly of the present invention, the general technical background of the sensors is discussed below.
The aforementioned stray-field sensors are more commonly referred to as dielectrometer sensors. Dielectrometer sensors of this type preferably generate an electrical, high-frequency AC field. The substance to be examined is then brought into the high-frequency AC field, which increases the displacement current. A capacitor made in this manner is preferably a component of a resonant circuit. This resonant rise of the field intensity increases the sensitivity of the dielectrometer sensor with respect to ascertaining changes in the dielectric constant. A dielectric constant that increases when the substance to be examined is brought in lowers the resonant frequency, while losses in the substance to be examined damp the resonance.
There are two possible ways to examine the substance. First, the substance to be examined can be brought into the resonator. This method is known from, for example, from German application DE 197 05 260 A1 and the associated supplemental application DE 197 34 978 A1, both owned by the assignee of the present application. In the apparatuses described therein, the resonator of the dielectrometer sensor is disposed in a housing having an entrance opening and an exit opening. A rope of tobacco, particularly a cigarette rope, can be guided through the entrance or exit opening of the apparatus described here. Thus, in this apparatus, when the cigarette rope is guided through the resonator, this influences the resonant frequency of the resonant circuit, and permits a measurement of the properties of the cigarette rope, such as its moisture content or density. The cited documents also describe a method (not reiterated here) for precisely measuring these resonance shifts.
The cited arrangements and methods for measuring the density of a substance, particularly for measuring the density of a tobacco rope, have been proven effective because the cited methods and arrangements can be used to measure density in a control circuit, which simultaneously influences the density. Hence, these apparatuses can be used in the precise determination of the density of a substance to be examined, for example, the aforementioned tobacco rope.
The method described in the cited documents measures the resonance value at at least two points on the resonance curve of the resonator through which the substance is guided. In addition to the average value of the measured values and the difference, the dielectric properties, such as the moisture content of the substance and, consequently, the density of the substance, can be calculated.
In the tobacco-processing industry, it is particularly desirable to measure the moisture content of the substance to be examined as early as possible. Thus, in the tobacco-processing industry, it is desirable to examine the tobacco while it is still in bulk form, or before it has been rolled. This is because it is only at this point that the moisture content of the tobacco can still be influenced satisfactorily. If the tobacco has already been processed into a rope, the moisture content of the processed tobacco can no longer be influenced satisfactorily. It is therefore necessary to guide the substance to be examined past the resonator, which emits a stray field, rather than insert the substance as a sample into the resonator itself. The present invention, notably the stray-field sensor of the present invention, relates to this type of embodiment of a resonator.
In stray-field sensors of this type, the substance to be examined is guided through a stray field present outside of the actual resonator. For this purpose, the resonator is preferably embodied such that its electrical field is at least partially located outside of a shielding element, while the remainder of the electrical field, and the magnetic field, are located within the shielding element, so they do not interact with the substance to be examined, for example, the bulk tobacco to be examined. Thus, in the stray-field sensors of the type mentioned at the outset, only a portion of the electrical field, which is located inside the shielding element, is coupled into the outside space. Measuring in the microwave range has proven especially advantageous in measuring the moisture content of substances to be examined, for example the moisture content of tobacco.
For utilizing such stray-field sensors in precisely ascertaining the aforementioned losses in the substance to be examined, it is necessary to avoid emission losses of the stray-field sensor. This is imperative because, in non-magnetic materials, besides the losses in the substance to be examined, only dielectric losses occur in addition to known ohmic losses in the conductors. Dielectric losses are the objective of the measurement. It is therefore advisable to suppress the emission losses to the greatest possible extent. A suppression of the emission losses means that the far field of the electrical field is suppressed, so only a near field is still present in the vicinity of the stray-field sensor. The aforementioned emission losses are notably avoided if the emission components of the far field are canceled out for as many angular positions as possible due to their phase opposition. This mutual cancellation of the emission components in the far field is only possible, however, if the diameter of the opening through which the stray field exits the shielding elements of the stray-field sensor is significantly smaller than the used wavelength. A drawback of this is that, because of the small diameter of the stray-field openings in the stray-field sensor, measurements of the moisture content of the substance to be examined, for example, can only be taken in this region. Therefore, stray-field sensors of this design, that is, stray-field sensors having small openings, produce only point-wise measurements of the dielectric constants of the substance to be examined. This is also disadvantageous if the substance to be examined is non-homogeneous. This lack of homogeneity is characteristic of bulk goods, for example. In loose tobacco, for example, as is used by the tobacco-processing industry, the arbitrary arrangement of the individual tobacco fibers in the loose tobacco presents a severe non-homogeneity. Stray-field sensors that measure point-wise can only provide imprecise measurements of the moisture content of such non-homogeneous tobacco.
To overcome the above-described disadvantage, it has been proposed to use a plurality of such stray-field sensors. The use of a plurality of stray-field sensors or resonators permits the approximate determination of the moisture content of leaf tobacco, for example, which is often partly not in climatic equilibrium, even with a non-uniform moisture distribution in the individual tobacco leaf; specifically, the plurality of stray-field sensors determines the moisture content. An arrangement of numerous sensors is known from, for example, EP-A-0 558 759 A1.
A drawback of the described arrangem
Busse Matthias
Knöchel Reinhard
Tobias Jörg
Hauni Maschinenbau AG
Kinberg Robert
LeRoux Etienne
Metjahic Safet
Venable
LandOfFree
Stray-field sensor does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Stray-field sensor, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Stray-field sensor will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2969093