DE202015104869U1 - moisture meter - Google Patents

moisture meter

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Publication number
DE202015104869U1
DE202015104869U1 DE202015104869.6U DE202015104869U DE202015104869U1 DE 202015104869 U1 DE202015104869 U1 DE 202015104869U1 DE 202015104869 U DE202015104869 U DE 202015104869U DE 202015104869 U1 DE202015104869 U1 DE 202015104869U1
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DE
Germany
Prior art keywords
lid
measuring capacitor
dielectric plate
electrode
measured
Prior art date
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Active
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DE202015104869.6U
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German (de)
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Pce Deutschland GmbH
Design Bureau "fizelektronpribor" Ltd
Design Bureau Fizelektronpribor Ltd
Original Assignee
PCE DEUTSCHLAND GMBH
THE DESIGN BUREAU "FIZELEKTRONPRIBOR" LTD
THE DESIGN BUREAU FIZELEKTRONPRIBOR LTD
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Application filed by PCE DEUTSCHLAND GMBH, THE DESIGN BUREAU "FIZELEKTRONPRIBOR" LTD, THE DESIGN BUREAU FIZELEKTRONPRIBOR LTD filed Critical PCE DEUTSCHLAND GMBH
Priority to DE202015104869.6U priority Critical patent/DE202015104869U1/en
Publication of DE202015104869U1 publication Critical patent/DE202015104869U1/en
Application status is Active legal-status Critical
Anticipated expiration legal-status Critical

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    • GPHYSICS
    • G01MEASURING; TESTING
    • G01NINVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00Investigating or analysing materials by the use of electric, electro-chemical, or magnetic means
    • G01N27/02Investigating or analysing materials by the use of electric, electro-chemical, or magnetic means by investigating the impedance of the material
    • G01N27/22Investigating or analysing materials by the use of electric, electro-chemical, or magnetic means by investigating the impedance of the material by investigating capacitance
    • G01N27/223Investigating or analysing materials by the use of electric, electro-chemical, or magnetic means by investigating the impedance of the material by investigating capacitance for determining moisture content, e.g. humidity

Abstract

Moisture meter comprising a metal housing (1) and a housing mounted on the dielectric plate (2) whose outer surface is oriented towards a material to be measured, wherein the moisture meter further comprises a measuring capacitor comprising a first and a second electrode, wherein the first electrode of the measuring capacitor is formed by a conductive element which is in contact with the dielectric plate (2), whereas the second electrode of the measuring capacitor is formed by the metal housing (1) and wherein the first and the second electrodes of the measuring capacitor are connected to one another in the housing arranged electronic device (6) are connected, characterized in that on the outer surface (3) of the dielectric plate (2) made of a wear-resistant metal cover (4, 5) are mounted, wherein the first cover (4) in an opening of the second lid (5) is arranged such t, that between the side walls of the first lid (4) and the opening edges of the second lid (5), a distance (S) is formed, wherein the first lid (4) simultaneously forms the conductive element and thus the function of the first electrode of the measuring capacitor which is embedded in an opening of the dielectric plate (2) and fixed via a clamping plate (7) on the dielectric plate (2) and connected to the electronic device (6), whereas the second lid (5) on the metal housing (5) 1) is secured in such a manner that an electrical contact is formed between the second lid and the metal housing.

Description

  • The invention is in the field of measurement technology and can be used to measure the moisture of different materials under industrial conditions. The main function of the invention is to measure the water content of concrete directly in a concrete mixer. The invention is based on the dielectric measurement method for moisture measurement. The invention can also be applied to the measurement of other physical parameters which affect the dielectric constant, such as, for. B. for measuring the mixing ratio of various substances.
  • Moisture meters of different manufacturers are known:
    • 1) «M-Sens 2» of the company «SWR engineering»
    • 2) «Hydro-Mix VII» of the company «Hydronix Ltd»
    • 3) «Microwave Moisture Probe» of the company «Franz Ludwig GmbH»
  • These known moisture meters have a metal housing and a ceramic dielectric plate mounted on the housing, the outer surface of which is oriented towards the material to be measured, via a sensor, a sensor installed in the housing and generating an electromagnetic field which enters into the housing material to be measured enters via the dielectric plate, as well as via an electrical device connected to the sensor.
  • The disadvantage of existing moisture meters is their low sensitivity and low mechanical strength. In the known moisture meters, the dielectric plate directly contacts the material to be measured and separates the sensor from the material to be measured. The field lines of the electromagnetic field generated by the sensor for measuring the material to be measured pass through the dielectric plate and accumulate there.
  • Ceramic is sometimes a fragile material, therefore, the ceramic plate known moisture meters can be destroyed by blows. Such constructed and installed in a concrete mixer moisture meters fall out when coarse grains of the ballast fall from the blades of the concrete mixer on the surface of the dielectric plate, as the ceramic is broken. For this reason, such moisture meters can not be used for measuring in a gravel, gravel or ore stream.
  • To prevent wear, the dielectric plate of a wear-resistant ceramic, for. B. made of aluminum oxide. Since such ceramics have a high dielectric constant, they increase the concentration of the electromagnetic field in the dielectric plate all the more. Ultimately, only a small portion of the electromagnetic energy generated by the sensor reaches the material to be measured. This explains the low sensitivity of such moisture meters.
  • The closest prior art to the invention forms the US 5,969,243 A , which describes a moisture meter, which is implemented, for example, in the humidity meter «Litronic FMS II» of the company «Liebherr Mischtechnik GmbH». This moisture meter has a metal housing and an alumina dielectric plate attached to the housing, the outer surface of which faces the material to be measured and includes a measuring capacitor that generates an electromagnetic field that penetrates the material to be measured through the dielectric plate , In this case, the first electrode of the measuring capacitor is formed by a conductive element, which is accommodated on the inside of the dielectric plate. The second electrode of the measuring capacitor is formed by the metal housing. The first and second electrodes of the measuring capacitor are connected to the housed in the housing electronic device, which ensures the conversion of the capacitance of the measuring capacitor into an electrical signal.
  • This moisture meter, like the devices shown above, has low sensitivity and low mechanical strength for the reasons listed above. The ceramic plate, which is in direct contact with the material to be measured and placed between the material to be measured and the conductive element, concentrates the electromagnetic field of the measuring capacitor. This effect is enhanced by the high dielectric constant of the ceramic. As a result, the humidity meter has a low sensitivity. Due to the fragility of the ceramic plate, the moisture meter can not be used for measuring in a ballast or Erzförderung.
  • The object of the invention presented here is to increase the sensitivity and increase the mechanical strength and the impact resistance of moisture meters.
  • The object is achieved in that the moisture meter has a metal housing and a dielectric plate attached to the housing, whose outer surface in the direction of is aligned to be measured material. The humidity meter further comprises a measuring capacitor, which consists of the first and the second electrode and generates an electromagnetic field, which penetrates into the material to be measured. In this case, the first electrode of the measuring capacitor is formed by a conductive element, which is arranged on the dielectric plate. The second electrode of the measuring capacitor is formed by the metal housing. The first and second electrodes of the measuring capacitor are connected to the housed in the housing electronic device, which ensures the conversion of the capacitance of the measuring capacitor into an electrical signal.
  • According to the invention, two covers made of a wear-resistant metal are mounted on the outer surface of the dielectric plate. The first lid is installed in an opening of the second lid. The covers are arranged to each other so that between the side walls of the first lid and the opening edges of the second lid, a distance is formed. The first cover forms the conductive element and fulfills the function of the first electrode of the measuring capacitor. In the dielectric plate, under the first lid, there is an opening through which the first electrode is connected to the electronic device and via which the first lid is secured to the dielectric plate by means of a clamping plate. The second cover is attached to the metal housing in such a manner that an electrical contact is formed between the second cover and the metal housing.
  • The clamping plate may be mounted on the inside of the dielectric plate.
  • According to an advantageous embodiment, it is provided that the width of the distance between the side walls of the first lid and the opening edges of the second lid is selected so that the distance is smaller than coarse grains of the material to be measured.
  • According to a further advantageous embodiment of the moisture meter is provided that in the metal housing, an additional capacitor is arranged, which is connected in series with the measuring capacitor between the first electrode of the measuring capacitor and the electrical device. The capacitance of the additional capacitor is chosen to be approximately equal to the capacitance of the measuring capacitor when filling the distance between the side walls of the first lid and the opening edges of the second lid with the measuring material.
  • It can also be advantageously provided that an induction coil is arranged in the metal housing, which is connected in series with the measuring capacitor, in particular between the electrodes of the measuring capacitor.
  • Further details and advantages of the invention will be explained below with reference to the embodiments illustrated in the drawings. It shows:
  • 1 a moisture meter according to the invention according to a first embodiment;
  • 2 a moisture meter according to the invention according to a second embodiment.
  • The moisture meter of the 1 includes a metal housing 1 and one on the case 1 attached dielectric plate 2 , On the aligned in the direction of the material to be measured outer surface 3 the plate 2 are two of a wear-resistant metal, z. B. made of steel brands 30Х13, 40Х13, 66Mn4 or made of a titanium alloy lid 4 and 5 appropriate.
  • The first lid 4 is in an opening of the second lid 5 built-in. It is between the side walls of the first lid 4 and the opening edges of the second lid 5 a distance S is formed. The width of the distance S between the side walls of the first lid 4 and the opening edges of the second lid 5 is chosen so that when using the moisture meter in a concrete mixer in the distance S no coarse grains of the material to be measured, eg. B. coarse grains of gravel or gravel can get.
  • The second lid 5 is on the metal housing 1 fastened in such a way that between this lid 5 and the metal case 1 an electrical contact is created. The first lid 4 forms the conductive element and forms together with the second cover 5 the measuring capacitor. At the same time, the first lid will fill 4 the function of the first electrode of the capacitor. The second lid 5 which is electrically connected to the housing 1 is connected, forms the second electrode of the measuring capacitor. The electromagnetic field of the measuring capacitor passes directly into the material to be measured, as it is the surfaces of the lid 4 and 5 touched. The surface 3 the dielectric plate 2 is through metal lid 4 and 5 protected against mechanical effects. The first electrode 4 and the second electrode 5 of the measuring capacitor are in the housing 1 built-in electrical device 6 connected, which ensures the conversion of the capacitance of the measuring capacitor into an electrical signal.
  • In the dielectric plate 2 is under the first lid 4 an opening through which the first electrode to the electronic device 6 is connected and over which the first cover 4 on the dielectric plate 2 with the help of a clamping plate 7 is attached. The clamping plate 7 is on the inside of the dielectric plate 2 appropriate.
  • In the metal case 1 of the 1 is an additional capacitor 8th installed, which in series with the measuring capacitor between the first electrode 4 of the measuring capacitor and the electrical device 6 is switched. The capacity of the additional capacitor 8th is chosen so that it approximately corresponds to the capacitance of the measuring capacitor when filling the distance S with the material to be measured.
  • The 2 shows in metal case 1 an induction coil 9 , in series with the measuring capacitor, between its first electrode 4 and its second electrode 5 is switched.
  • The inductance of the coil 9 is chosen so that the reactance of the coil 9 and the measuring capacitor are approximately the same size and thus an RC resonant circuit is formed, which can be operated at a resonant frequency.
  • The moisture meter may also include a temperature sensor for the material to be measured that is in the housing 1 is arranged. The temperature sensor can also be arranged outside the housing of the moisture meter, but in such a way that the sensor allows the temperature measurement of the material to be measured.
  • The moisture meter according to the invention works as follows:
    The electrical device 6 generates a harmonic high frequency signal which is transmitted to the first and second electrodes of the measuring capacitor. The electromagnetic field of the measuring capacitor is distributed over three areas:
    • (a) - on the material to be measured;
    • (b) - in the housing 1 under the dielectric plate 2 ;
    • (c) - in the dielectric plate 2 ,
  • The total capacitance С ges of the measuring capacitor is determined by three components Са , С b , С c , which correspond to the three named ranges, and corresponds to: С ges = С а + С b + С c
  • The component СА is determined by the dielectric constant of the material to be measured. The component С а can be described as a sum: С а = С а0 + ΔС а , wherein С а the component of the total capacitance of the measuring capacitor is equal to the area of the material to be measured, С а0 is the component of the total capacitance of the measuring capacitor, which corresponds to the region of the material to be measured when the material to be measured is air and ΔС а is the change component of the total capacitance of the measuring capacitor in the region of the material to be measured at a filling of the distance S with the material to be measured.
  • The functioning of the moisture meter is based on the measurement of the total capacity С ges of the measuring capacitor and the separation of the component СА from the total capacity. From the component СА , the dielectric constant of the material to be measured is deduced. Furthermore, the moisture content of the material to be measured is determined on the basis of the dielectric constant of the material to be measured and its temperature. Therefore, it is necessary to measure the moisture of the material to be measured to calculate the component С а, which is determined by the field in the material to be measured. The greater the ratio of the component СА to the components С b and С c , the higher the sensitivity of the moisture meter and the more accurate the measurement.
  • Thanks to the fastening of the covers 4 and 5 on the outside surface 3 the dielectric plate 2 is the plate 2 wear. This allows the plate 2 from a material with a low dielectric constant (eg fluoroplastic). The plate 2 Such a material makes it possible to lower the component C b , which leads to an increase in the sensitivity of the moisture meter. The component С b is not large because it represents a condenser structure with an air filling. Thus, the total capacitance C ges of the measuring capacitor in the construction according to the invention of the moisture meter is determined to a much greater extent by the dielectric parameters of the material to be measured than in the prior art. Smaller changes in the humidity of the material to be measured lead to significantly larger changes in the total capacitance of the measuring capacitor, which by the electrical device 6 is converted into an electrical signal.
  • The achieved effect of increasing the sensitivity can also be explained by means of the analysis of the electromagnetic fields generated by the measuring capacitor. Since the material to be measured is the first and the second electrode 4 . 5 of the measuring capacitor directly touched, most of the energy of the electromagnetic field accumulates at the measuring capacitor in the material to be measured. Therefore, the humidity and consequently the dielectric constant of the material to be measured much more affect the parameters of the measuring capacitor than in the devices of the prior art. This results in the high sensitivity of the moisture meter according to the invention. For comparison: In the prior art described at the outset, most of the energy of the measuring capacitor accumulates in the dielectric plate 2 and only a small part of the measuring signal gets into the material to be measured.
  • Thanks to the fact that the dielectric plate 2 of metal lids 4 . 5 is covered, it is protected from knocks and wear by the material to be measured. For the measurement of coarse grains containing materials (gravel, ore, gravel) is the width of the distance S between the side walls of the first lid 4 and the opening edges in the second lid 5 chosen so that enter into this empty space no coarse grains of the material to be measured. At the same time this increases the mechanical strength of the moisture meter, its impact resistance.
  • To measure highly conductive materials (with a high dielectric loss factor), the additional capacitor is connected in series with the measuring capacitor 8th switched to exclude the blocking effect of this conductivity. The capacitor 8th disconnects the line current during the introduction into the electrical device 6 from. The capacity of the capacitor 8th is chosen so that it approximately corresponds to the capacitance of the measuring capacitor when filling the distance S with the material to be measured. This value is optimal. A too small capacity with the additional capacitor 8th would reduce the sensitivity of the moisture meter. The humidity meter with too much capacity of the additional capacitor 8th does not prevent bridging of the measuring capacitor in the form of an effective resistance generated by line current.
  • The increase in the sensitivity of the moisture meter is also due to the circuit of the induction coil 9 reached in series to the measuring capacitor. The inductance of the coil 9 is chosen so that the reactance of the coil and the measured capacitor are approximately equal and thus an RC resonant circuit is formed, which can be operated at resonant frequency.
  • When measurements are made on a fixed frequency, the optimum value of induction of the coil becomes 9 determined under the following condition: The reactance of the coil 9 corresponds approximately to the reactance of the measuring capacitor with a filling of the distance S with air. In this case, the initial capacity of the measuring capacitor is completely compensated. The signal at introduction to the electric device 6 Which ensures the conversion of the capacitance of the measuring capacitor into an electric signal, is determined exclusively by the component ΔС а, which depends on the material to be measured. That is, the components С а0 , С b and С c are compensated, which leads to increase the sensitivity of the moisture meter , as the output signal at the device 6 depends solely on the value of the dielectric constant of the material to be measured.
  • The circuit of the coil 9 in series with the measuring capacitor leads to the blocking of the line current of the material to be measured. This also increases the sensitivity of the moisture meter when working with high dielectric loss factor materials.
  • It is worth noting that the extra capacitor 8th and the induction coil 9 can be used separately in the moisture meter, however, these two solutions can also be used simultaneously.
  • The electrical device 6 allows the capacitance of the measuring capacitor to be converted into a high frequency electrical signal.
  • That in the device 6 Implemented methods for measuring the change in capacitance of the measuring capacitor with a high frequency can be arbitrary, there are many such methods.
  • In the practical implementation of the moisture meter according to the invention, the method for measuring the change in capacitance of the measuring capacitor is used, which is based on the measurement of the resonant frequency of the resonant structure, which of the measuring capacitor of the moisture meter and the additional induction coil 9 is formed. The additional induction coil 9 is in the case 1 of the moisture meter and was connected in two different ways:
    • - the additional induction coil 9 is connected in series with the measuring capacitor between the electrode 4 and the introduction of the device 6 switched, in the presence of the additional capacitor 8th it is connected in series with this capacitor;
    • - the additional induction coil 9 is in series with the introductions of the device 6 switched on, as on is shown.
  • In the last variant, the choice of the induction value of the coil depends 9 from the following Condition: The reactance of the coil 9 corresponds approximately to the reactance of the measuring capacitor at a filling of the distance S with the material to be measured at a resonant frequency of the moisture meter. The method implemented with the invention accordingly consists in the measurement of the two values of the resonant frequencies of the measuring capacitor and induction coil structure, in the filling of the distance S of the measuring capacitor with the material to be measured and in the filling of the distance S of the measuring capacitor with air.
  • Based on the difference and / or the ratio of said resonant frequencies, the dielectric constant of the material is determined. Taking into account the temperature of the material to be measured its moisture is calculated. The processing unit, which calculates the humidity based on the capacitance of the measuring capacitor and the temperature of the material, may be from the electrical device 6 includes his. However, it can also be designed as an independent electrical component to which the signal from the device 6 and transmitted by the temperature sensor. In this case, the temperature sensor both in the housing 1 the moisture meter installed as well as outside the housing 1 to be ordered.
  • The tests carried out on the manufactured test models of the moisture meter confirm the efficiency of the illustrated invention. In the humidity meters manufactured according to this invention, the operating frequency is between 40 and 500 MHz, the sensitivity of the change of the dielectric constant is not worse than 0.1%.
  • Comparative tests of the manufactured test models and the known moisture meters were performed. The tests carried out confirm the significantly higher sensitivity of the moisture measuring devices according to the invention in comparison with the known moisture meters. The use of the manufactured test models of moisture meters in concrete mixers confirmed the wear resistance as well as the impact resistance.
  • The moisture meters manufactured according to the illustrated invention were also tested with iron ore concentrate. The results confirm the possibility of moisture control in the high dielectric constant and high magnetization constant materials.
  • LIST OF REFERENCE NUMBERS
  • 1
    metal housing
    2
    dielectric plate
    3
    Außenöberfläche
    4
    first lid
    5
    second lid
    6
    electronic device
    7
    clamping plate
    8th
    additional capacitor
    9
    induction coil
    S
    distance
  • QUOTES INCLUDE IN THE DESCRIPTION
  • This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.
  • Cited patent literature
    • US 5969243 A [0007]

Claims (4)

  1. Moisture meter, which has a metal housing ( 1 ) and a dielectric plate (FIG. 2 ), the outer surface of which is oriented towards a material to be measured, wherein the moisture meter further comprises a measuring capacitor comprising a first and a second electrode, wherein the first electrode of the measuring capacitor is formed by a conductive element which is connected to the dielectric plate (10). 2 ), whereas the second electrode of the measuring capacitor passes through the metal housing (FIG. 1 ) and wherein the first and the second electrodes of the measuring capacitor are arranged on an electronic device ( 6 ) are connected, characterized in that on the outer surface ( 3 ) of the dielectric plate ( 2 ) two covers made of a wear-resistant metal ( 4 . 5 ), the first lid ( 4 ) in an opening of the second lid ( 5 ) is arranged such that between the side walls of the first lid ( 4 ) and the opening edges of the second lid ( 5 ) a distance (S) is formed, wherein the first lid ( 4 ) simultaneously forms the conductive element and thus fulfills the function of the first electrode of the measuring capacitor, which in an opening of the dielectric plate ( 2 ) and via a clamping plate ( 7 ) on the dielectric plate ( 2 ) and with the electronic device ( 6 ), whereas the second lid ( 5 ) on the metal housing ( 1 ) is secured in such a manner that an electrical contact is formed between the second lid and the metal housing.
  2. Moisture meter according to claim 1, characterized in that the width of the distance (S) between the side walls of the first lid ( 4 ) and the opening edges of the second lid ( 5 ) is selected so that the distance (S) is smaller than coarse grains of the material to be measured.
  3. Moisture meter according to claim 1 or 2, characterized in that in the metal housing ( 1 ) an additional capacitor ( 8th ) arranged in series with the measuring capacitor between the first electrode of the measuring capacitor and the electrical device ( 6 ) the capacity of the additional capacitor ( 8th ) is selected so that it approximately corresponds to the capacitance of the measuring capacitor at a filling of the distance (S) with the material to be measured.
  4. Moisture meter according to one of claims 1 to 3, characterized in that in the metal housing ( 1 ) an induction coil ( 9 ) arranged in series with the measuring capacitor and its electrodes.
DE202015104869.6U 2015-09-14 2015-09-14 moisture meter Active DE202015104869U1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
DE202015104869.6U DE202015104869U1 (en) 2015-09-14 2015-09-14 moisture meter

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
DE202015104869.6U DE202015104869U1 (en) 2015-09-14 2015-09-14 moisture meter

Publications (1)

Publication Number Publication Date
DE202015104869U1 true DE202015104869U1 (en) 2016-12-15

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Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5969243A (en) 1996-02-06 1999-10-19 Liebherr-Mischtechnik Gmbh Humidity sensor for capacitive measurement of humidity in bulk material

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5969243A (en) 1996-02-06 1999-10-19 Liebherr-Mischtechnik Gmbh Humidity sensor for capacitive measurement of humidity in bulk material

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