WO2009047310A1

WO2009047310A1 - Filling level measuring apparatus for flexible silos

Info

Publication number: WO2009047310A1
Application number: PCT/EP2008/063570
Authority: WO
Inventors: Andreas Pfister; Andreas Eibner
Original assignee: Delox Elektronik Gmbh; A.B.S. Silo Und Förderanlagen Gmbh
Priority date: 2007-10-09
Filing date: 2008-10-09
Publication date: 2009-04-16
Also published as: DE202007014056U1; EP2201339A1

Abstract

A filling level sensor for determining a filling level in a silo made of a flexible material is provided, wherein the flexible material forms a flexible container (102) with a flexible wall. The sensor contains a first electrode (103) which is provided adjacent to or inside the flexible wall, a second electrode (103) which is provided at a predetermined distance from the first capacitor electrode and adjacent to or inside the flexible wall, sensor electronics (110) which contain a resonant circuit (112), wherein the first electrode and the second electrode are electrically connected to the sensor electronics and are electrically insulated from one another, and a monitoring unit (250) which is suitable for converting a value provided by the sensor electronics into a filling level.

Description

Level gauge for flexible silos

The invention relates to devices for measuring a level in flexible silos. In particular, the invention relates to capacitive level sensors for measuring a level in a flexible silo, ie in a sack silo, for example polyester fabric capacitive level sensors for liquids and fine, ie fine-grained solids are, for example, from the European patent application EP 0338400 or European patent application EP 0470483 known. Document EP 0470483, for example, describes a method for DK compensated capacitive level measurement with a probe arrangement comprising a capacitor for level measurement and a capacitor for DK compensation, which have different capacitive slopes and extend together over a same level height measurement range. Document EP 0470483 describes that from the measured value of the level measuring probe and the measured value of the compensation probe, a ratio value Q is formed, which depends solely on the dielectric constant ε _r of the filling substance wetting the measuring and compensation probe, and in that the filling level height H of the filling material is determined from the measured value of Level measurement probe is formed, wherein the measured value is electronically corrected with a correction value K, which depends on the geometry and the dielectric of the level measuring probe and the ratio Q.

For bulk goods level measuring devices have been developed in the past, which are described for example in German Utility Model DE 202006009381 and which, in contrast to the above-mentioned publications, allow a level measurement for bulk materials in an improved manner. For this purpose, rod electrodes are used, which are arranged, for example, within the storage container.

In many technical fields silos with flexible outer skin are used. For this purpose, such flexible silos are used for example for the breathable and dust-tight storage of grain and feed, food, for wood pellet storage, for the storage of plastic parts, plastic agglomerates and plastic granules and other materials. These silos form flexible silos, warehouses of fabric or other flexible materials used, for example, in industrial applications as flex silos. This type of limp silos or flexible silos are referred to below as sack silos. An expansion of the tissue during filling results in a change of the siloform depending on the filling level. An electronic level measurement for these bag silos needs further improvements.

The present invention has for its object to provide a device for level measurement available that does not have the aforementioned disadvantages or at least reduced, and cost and easily provides a level measurement for bag silos available. This object is achieved by the devices specified in claims 1 and 20.

Advantageous embodiments will become apparent from the dependent claims, the accompanying drawings and the description.

According to one embodiment, a level sensor for determining a level, in particular of bulk materials such. Fuels, in a silo made of a flexible material, wherein the flexible material forms a flexible container with a flexible wall provided. The level sensor includes a first electrode provided adjacent to or within the flexible wall, a second electrode provided at a predetermined distance from the first capacitor electrode and adjacent to or within the flexible wall, including a resonant circuit Sensor electronics, wherein the first electrode and the second electrode are electrically connected to the sensor electronics and electrically isolated from each other, and a control unit which is adapted to convert a value provided by the sensor electronics available value to a level.

According to another embodiment, a level-monitored silo made of a flexible material is provided. The silo includes a flexible container made of a flexible material having a flexible wall, a frame for supporting the container; a first electrode provided adjacent to or within the flexible wall, a second electrode provided at a predetermined distance from the first capacitor electrode and adjacent to or within the flexible wall, including a resonant circuit Sensor electronics, wherein the first electrode and the second electrode are electrically connected to the sensor electronics and electrically isolated from each other, and a control unit which is adapted to convert a value provided by the sensor electronics available value to a level.

Hereinafter, embodiments of the invention will be illustrated schematically with reference to the drawings. Show it:

Fig. Ia shows a schematic representation of a bag silo with a measuring device, which illustrates embodiments of a device for measuring the level of dry contents in a bag silo;

Fig. Ib shows a further side view of Fig. Ia; and

FIG. 2 illustrates further embodiments of a device for measuring the filling level of dry products in a sack silo.

The embodiments described in the following figures are described with reference to wood pellets as dry bulk materials. However, the invention is not limited thereto. It can be used as bulk materials and natural products such as grain and feed, plastic components, plastic granules, plastic agglomerates, powders, tablets or a variety of other bulk materials. In general, these are substances that are not provided in the form of a liquid. The term "dry" is not limited to the fact that the bulk materials can not have any moisture content The term "dry" refers to the fact that the filling of the container is not or only partially liquid or moist, but in the form of granules, pellets, Brickets or other pieces is introduced into the container. In addition, pasty substances and liquids can be filled into bag silos.

In terms of level measurement of sack silos, the characteristic of these flexible silos that the walls of these silos lengthen under load plays a role. This means that a bag silo changes its volume by loading with the filling of the bulk material. Therefore, it is difficult or impossible filling electrodes of a solid given geometry within the sack silo so that a reliable level measurement can be provided.

Fig. Ia and Ib show an embodiment of a sack silo with a level measurement. The sack silo comprises a fabric or fabric bag 102 or other pliable, i. flexible material forming the bag 102, and a frame having a frame 101a and a stand 101b supporting the bag 102. In contrast to previously known capacitive level gauges, electrodes for capacitive level measurement are not within the container, i. inside the silo, provided in the form of solid electrodes. The electrodes 103 are attached to the tissue within the bag 102 or outside the bag or integrated into the tissue of the bag 102. The electrodes are provided at the edge of the container.

The actual container for infestation with bulk materials is provided by the bag 102. The flexible material expands or lengthens during filling by the gravitational force of the filling material.

As shown in Figures Ia and Ib, the electrodes 103 are connected to a sensor unit 110 via cable 105. The sensor unit is connected via a connecting cable 252 to the control unit 250.

According to various embodiments, the electrodes 103 are made of metal strips, a foil of electrically conductive material, a stranded wire, a metal mesh, a copper strip or other, preferably flexible and / or flexible, electrically conductive strips. In preferred embodiments, the electrodes, e.g. in the form of a strand, a band or a knit so that they can follow a change in length of the fabric.

By using flexible electrically conductive electrodes, which are attached to or in the tissue of the bag, it is possible to leave the space inside the bag silo completely unmodified and thus not to influence or to affect a filling of the bag silo. In addition, it allows the Flexibility of the electrodes that the bag silo behaves similar or identical to its other filling behavior.

A band, a knitted fabric or another form of the electrode, for example a conductive band, can be provided flexibly, preferably with an additional extensibility in the longitudinal direction. For example, an extensibility may be provided that elastically or only partially elastically corresponds to a modulus of elasticity of 0.01 to 1 kN / mm ² . In this case, in the ratio of a full to an empty silo, an elongation Δl / lo of an electrode of at least 1%, or in a range of 1% to 12%, may be possible.

In this case, the use of electrically conductive electrodes on the edge of the container, within the bag fabric or on the sack fabric means that despite the suitability for the level measurement of bulk solids, a capacitor is formed from the electrodes 103. In contrast to heretofore known electrode arrangements of cylinder capacitors or plate capacitors, the capacitors of the electrically conductive strips fastened in the electrodes 103 or in the silo housing form a relatively small capacitance. The capacity is up to the filling level 150 (see FIG. 1b) of the bulk goods from the capacity with a dielectric constant of the bulk materials (see area 152). Above the filling level, a region 154 adjoins the dielectric constant of air. Here, the variable component of the capacitance forms only in a part of the space that is not directly between the electrodes. When the fill level is changed, the capacitance of the fill capacitor consisting of the electrodes 103 changes since the range of the dielectric constant of air and the range of the dielectric constant of the bulk material change.

According to some embodiments, this arrangement of electrodes may also be used with tissue materials that have sufficient electrical conductivity to comply with explosion protection regulations. These materials may, for example, have an electrical conductivity corresponding to a resistivity of 10 ⁸ to 10 ¹⁰ ohm-m or more. According to further embodiments, which can be combined with embodiments described herein, it is optionally possible to provide the first and second electrodes, for example in the form of a metal strip, a metal mesh, a metal knit, or the like, with an insulating layer or an insulating sheath, before the Electrode is attached to or in the flexible material of the flexible silo. The insulating layer or sheath is hereby formed to form an insulation of the electrodes with respect to the flexible material. The electrodes with the insulating material may be arranged adjacent to or within the flexible wall. The electrodes may thus be either directly adjacent to or separated from the wall by an insulating layer adjacent to the flexible wall. This makes it possible, especially at high conductivities of the flexible fabric of the flexible silo to improve the level measurement.

According to some embodiments, the electrodes 103 may run parallel to each other vertically along the outer skin of the bag silo. According to further embodiments, the electrodes can be sewn or woven into the fabric of the sack silo itself, at a parallel distance of about 0.5 cm to about 10 cm. According to further embodiments, which may be combined with other embodiments, the bands may be mounted inside or outside at a parallel distance of about 0.5 cm to about 10 cm. In FIGS. 1a and 1b the electrodes are shown with dashed lines. This illustrates that the electrodes within the bag may be in contact with the tissue or may be incorporated into the tissue itself. According to other embodiments that may be combined with other aspects of the embodiments described herein, the electrodes may also be sewn or attached to the outside of the bag 102.

For the embodiments in which the electrodes 103 do not come into contact with the filling material, ie if the electrodes are arranged outside the fabric bag 102, inside or outside in isolated form, or optionally also in the fabric material itself, the level measuring device described herein can also be used for electrical conductive products or even liquids. In general, embodiments and combinations of Embodiments described herein may be used for bulk materials, pastes, or liquids filled into bag silos.

The arrangement of electrodes given in accordance with embodiments described herein makes possible the use for e.g. Bulk solids and the use of capacitive level measurement for bag silos. The resulting low capacity, however, complicates the measurement of the level. The electrodes 103 are connected to lines 105 to a sensor electronics 110. Due to the difficult level measurement, the wires should be as short as possible, preferably they are shorter than 10 cm or even 3 cm. In addition, a capacitor 120 is additionally provided to the resonant circuit 112 within the sensor electronics 110, which enables a stable behavior of the resonant circuit 112.

The resonant circuit within the sensor electronics can, for. B. be a Wien-Robinson oscillator. This is preferably an oscillator which oscillates with a sinusoidal oscillation. A typical frequency of the resonant circuit in the empty state of the silo is in the range of 70 to 200 kHz, preferably 100-120 kHz. The frequency decreases when the silo is filled.

The electrodes 103 typically have a capacitance of 70 to 120 pF / m or 25 to 120 pF / m. The additional capacitor 120 typically has a capacity of 40 to 60 pF, preferably 47 pF.

During the filling of the silo 102 with the dry bulk material, a dust development takes place. Therefore, the sensor electronics, which may also be located within the silo, be designed explosion-proof. When dealing with substances that can react with oxygen, eg. As fuels, is expected to explode if inside the silo of the combustible material is present as a fine-grained dust in the air. Since little influence can be exerted on the size and density of the dust grains, in particular when filling the silo, the sensor electronics are designed accordingly for explosion protection. For this purpose, sparks on the electrical components within the potentially explosive atmosphere as well as static charging of ungrounded components and hot surfaces are avoided. Another measure for explosion protection is the above-mentioned conductivity of the sacked fabric. In particular, when the electrodes 130 are mounted on the outside of the silo or a passage of the cable 150 takes place from the inside of the bag 102 to the outside thereof, positioning of the sensor electronics 110 can also take place outside. In this case, even with a positioning of the sensor electronics outside of the bag 102, a cable length of the cable 105, as described in other embodiments, can be achieved. According to typical

Embodiments, the sensor electronics can be provided inside or outside the bag. The control unit 250 is typically provided outside the bag 102.

The output signal of the oscillator 112 located in the sensor electronics 110 is amplified and converted for a microcontroller utilizable signal (square wave signal, PWM signal or analog signal). The microcontroller measures the frequency and calculates an average value which it transmits via the line 252 to a control unit 250. According to further embodiments that can be combined with the embodiments described herein, instead of a microcontroller, a field programmable gate array (FPGA) or the like can also be used.

In the control unit, the value determined by the sensor electronics is converted in order to be brought into relation to the size of the silo and / or to the silo form. The control unit includes a CPU and control devices that allow the level z. B. to visualize or further process. Typically, an alarm can be set when falling below a predetermined level. Line 252 also typically powers the sensor electronics and monitors for any malfunctioning to prevent damage or fire by shutting down the sensor electronics in an emergency. The control unit switches the sensor electronics off. The control unit may further include a memory for storing the values. According to a further embodiment, the control unit may also include other display elements such as a screen, as well as controls such as a keyboard or a mouse to allow a more extensive evaluation of the level. As a result, z. For example, an average consumption of the dry bulk or other statistics can be selected, calculated and presented. According to a further embodiment, the control unit can essentially also be replaced by a display unit. In this case, the sensor electronics; directly, for example, a pulse width modulated signal output, which is converted by a display unit in the corresponding display. The sensor electronics therefore assumes additional functions, so that the control unit described with reference to the figures can be reduced to a display unit.

During initial commissioning or when calibrating the level measurement at a different time, the silo is empty and the control unit stores the signal of the sensor electronics in an empty state. Via an input device, the control unit is supplied with the shape of the silo and its dimensions in a memory. Via a switch a menu "Siloabglεich when empty" can be selected. This allows a level of 0% to be defined. After the silo has been completely filled in, a switch or an input element is used to select a "full-scale silo calibration". This value corresponds to the level of 100%. This allows the control unit to be adjusted to the south, including its dimensions and the maximum filling height. A corresponding memory unit of the control unit can store the values even in the event of a power failure, so that after a power failure no emptying and refilling is necessary.

According to still further embodiments, a sensor calibration for calibrating the filling level is possible such that the system is put into operation in the empty state. During filling, the system is in operation and measures the values during the filling process. After filling, the system can be calibrated as described above by setting the "full silo" and the measurement data during filling, with the control unit and the sensor electronics turned on throughout the filling process and measuring the level at regular intervals thus to obtain an improved calibration during filling.

The embodiments according to the invention have the advantage that a capacitive fill level measurement can be carried out in a simple and cost-effective manner for bulk goods or for use in bag silos. The problems occurring in this case are caused by an arrangement of the electrodes within the wall or the Tissue of the silo or in direct contact with the wall of the silo inside or outside solved

According to a further embodiment, which can be combined with one of the other embodiments, the sensor contains at least one pair of electrodes, which are connected to a sensor electronics. Typically, for example, 2, 3, 4 or more pairs of electrodes may also be provided as capacitor electrodes. In this case, a measurement in different areas of the silo is possible. According to further embodiments, the plurality of pairs may also be connected to a sensor electronics.

According to still further embodiments, which may be combined with any of the embodiments described herein, the sensor electronics include means for reducing or preventing static charging of the electrodes. By way of example, pairs of tens diodes and / or resistors are connected to the potential equalization or ground, respectively, by the terminals of the respective electrodes in the sensor electronics. In this case, the pairs of decimal diodes are typically connected in series with each other, so that only at a predetermined potential difference between an electrode terminal and the potential equalization, for example in the range of 3 V to 12 V, a grounding of the connection to prevent static charges. By means of reducing or preventing static charging of the electrodes, the sensor electronics can be protected and further sparking prevented, which is a danger in potentially explosive atmospheres.

According to still further embodiments, a sensor calibration for calibrating the filling level is possible such that the system is put into operation in the empty state. During filling, the system is in operation and measures the values during the filling process. After filling, the system can be calibrated as described above by setting the "silo calibration in full" and the measurement data during filling.

FIG. 2 illustrates further embodiments. The sack silo in Figure 2 is shown as a larger bag, eg for industrial applications, and includes the Fabric bag 202 and the holder formed by the frame 201a and the stand 201b. The embodiments sensor electronics and the control unit can be provided analogously to the embodiments and combinations thereof explained with reference to FIGS. 1a and 1b. The shape as well as the properties of the electrodes 103 can also be provided analogously to the embodiments of the electrodes 103 in FIGS. 1a and 1b.

In Figure 2, the bag 202 includes pockets 202 into which the flexible electrodes are inserted. In this case, it is possible for the electrodes 203 to be connected to the pockets at a plurality of positions along the longitudinal direction of the pockets 204 in order to provide uniform expansion of the electrodes when the bag expands. Alternatively, the electrodes can also be sewn onto the flexible material of the bag silo.

The above-described embodiments are illustrated to illustrate the invention, and the invention is not to be construed as being limited thereto.

Claims

claims

A level sensor for determining a level, in particular of bulk materials, in a silo made of a flexible material, the flexible material forming a flexible container (102) having a flexible wall, comprising: a first electrode (103) adjacent to or within the flexible wall is provided; a second electrode (103) spaced at a predetermined distance from the first

Capacitor electrode and adjacent to or within the flexible wall to

Is made available; a sensor electronics (110) containing a resonant circuit (112), wherein the first

Electrode and the second electrode are electrically connected to the sensor electronics and electrically isolated from each other; and a control unit (250) adapted to receive one from the sensor electronics

To convert the provided value into a fill level.

2. Level sensor according to claim 1, wherein the first and the second electrode extend at least in one dimension vertically from at least the maximum level measurement height to at least the minimum level measurement height.

3. Level sensor according to one of the preceding claims, wherein the first and the second electrode made of a conductive tape, preferably made of a metal strip, more preferably made of a strand, a tape, a knitted fabric or a metal mesh.

4. Level sensor according to one of the preceding claims, wherein the first and the second electrode are flexible, preferably with a stretchability in the longitudinal direction, particularly preferably with a tensile strength corresponding to a modulus of elasticity of 0.01 to 1 kN / mm ² and an elongation .DELTA.l / l ₀ with maximum filling of the silo of 1% to 12%, where I ₀ denotes the length in an empty silo state.

5. Level sensor according to one of the preceding claims, wherein the first and the second electrode have a vertical dimension, at least from the maximum Level measuring height starting in vii essential to an opposite, lower end of the silo ranges, preferably from 0 cm to about 5 cm in front of the opposite end of the silo reaches.

6. Level sensor according to claim 5, wherein the vertical dimension is designed such that the first and the second electrode is not completely formed to the lower end of the silo.

7. Level sensor according to one of the preceding claims, wherein the first and the second electrode are formed substantially parallel to each other.

8. Level sensor according to claim 7, wherein the first and the second electrode (103) at a distance of at least 3 mm, preferably at a distance of 0.5 cm to 20 cm, particularly preferably at a distance of 1 cm to 10 cm are attached.

9. Level sensor according to one of the preceding claims, wherein the flexible material is a fabric.

10. Filling level sensor according to one of the preceding claims, wherein the first and the second electrode are woven, sewn or sewn into the flexible material.

11. Filling level sensor according to one of the preceding claims, wherein the flexible wall has a first pocket and a second pocket, in each of which the first and the second electrode is provided, in particular sewn.

12. A level sensor according to any one of the preceding claims, wherein the first and second electrodes are provided within the flexible container adjacent to the flexible wall and outside the flexible container adjacent to the flexible wall.

13. Level sensor according to one of the preceding claims, wherein the sensor electronics within the silo and the control unit is arranged outside of the silo.

14. Level sensor according to one of the preceding claims, wherein the first and the second electronics (103) form a capacitor with a capacity per unit length of at most 120 pF / 'm.

15. Level sensor according to one of the preceding claims, wherein the sensor electronics includes a resonant circuit, preferably a Wien-Robinson-Ozillator, and additionally a capacitor (120) having a capacitance with a value of about 25 pF to 75 pF, preferably from about 45 to 55 pF, is connected in parallel.

16. Level sensor according to one of the preceding claims, wherein the resonant circuit and the sensor electronics is adapted to resolve a capacitance change in the range of 2-6 pF or 1-6 pF.

17. Level sensor according to one of the preceding claims, wherein the sensor electronics is formed explosion-proof.

18. Level sensor according to one of the preceding claims, wherein the first and the second electrode are each connected to an electrical conductor (105) to the sensor electronics and wherein the electrical conductors have a maximum length of 30 cm, preferably 20 cm, more preferably about 5 cm.

19. Level sensor according to one of the preceding claims, wherein the first and the second electrode (102) made of metal, preferably made of copper.

20. Level-controlled silo made of a flexible material comprising silo: a flexible container (102) made of a flexible material with a flexible wall; a frame (101a, 101b, 201a, 201b) for supporting the container; a level sensor according to one of the preceding claims.