Abstract:
A method for determining a volume or a mass of a filling material is provided, in which firstly an empty profile detection mode is assumed in the absence of a filling material, and then a volume or mass determination mode is assumed when the filling material is present. In the empty profile detection mode, an interference point profile is created from echo curves obtained by scanning a container surface. The interference point profile is then taken into account when determining the volume or the mass of the filling material in the volume or mass determination mode, such that volumes or masses of the filling material are determined with increased accuracy.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to the determination of the volume and mass of filling materials or bulk materials. The invention relates in particular to a method for determining the volume or the mass of a filling material, to a fill level measurement device for determining the volume or the mass of a filling material, to a program element, and to a computer-readable medium. 
       BACKGROUND 
       [0002]    Fill level measurement devices are known that can be used for three-dimensional fill level measurement. “Three-dimensional fill level measurement” is understood to mean that the surface form (topology) of the filling material can be measured. Such detection of the topology of the filling material surface is achieved for example by scanning the surface, by correspondingly tilting or rotating the antenna and/or the entire fill level measurement device. In addition to this mechanical control of the main emission direction of the fill level radar antenna, electronic beam control is also possible (or a combination of the two). 
         [0003]    An advantage of this three-dimensional fill level measurement is, inter alia, that determining the surface topology of the bulk material surface permits more accurate determination of the volume and/or the mass of the filling material, since, in the case of a coarse-grained bulk material or a moving filling material, the surface often does not extend in the horizontal plane. 
       SUMMARY OF THE INVENTION 
       [0004]    An object of the invention is that of further improving the determination of the volume or mass of filling materials. 
         [0005]    This object is achieved by the features of the independent claims. Developments of the invention can be found in the dependent claims and the following description. 
         [0006]    According to a first aspect of the invention, a method for determining the volume or the mass of a filling material is specified, in which firstly an empty profile detection mode is assumed, in the absence of a filling material. In the empty profile detection mode, a transmission signal is emitted by the antenna of the fill level measurement device to the surface of the filling material in various directions, and echo curves from various regions of the surface of the filling material are detected. This detection of echo curves from various regions of the surface can be made possible by a direction change of the transmission signal by changing the main emission direction of the transceiver antenna of the fill level measurement device. Alternatively or in addition, the detection of echo curves from various regions of the surface can be made possible by changing the main receive direction of the transceiver antenna of the fill level measurement device. 
         [0007]    In the present context, the absence of a filling material can be understood as a state in which residual amounts of a filling material which may be present in the container do not lead to significant reflections of the transmission signal. It is therefore possible that a container that was previously filled may still contain traces of the filling medium after emptying but, in the context of the present invention, an absence of a filling material can be assumed. 
         [0008]    The main emission direction and/or main receive direction of the antenna can occur by tilting and/or rotating the antenna, by tilting and/or rotating the entire fill level measurement device, by rotating a mirror that deflects the transmission signal, by rotating one or more prisms, or in another mechanical manner. Alternatively or in addition thereto, electronic beam control (“digital beam forming”) is also possible, in which case an antenna array is used. 
         [0009]    The transmission signal, which is reflected at least at the surface of the filling material, is then received by the antenna or by a plurality of receive antennas, and echo curves are generated from the reflected and received transmission signal. The corresponding emission direction of the transmission signal from which the relevant echo curve originates is also detected. It can also be provided to detect the direction from which signals are received by the antenna. 
         [0010]    In other words, the empty container is scanned in the empty profile detection mode by continuously or discontinuously (incrementally) changing the main emission direction and/or the main receive direction of the fill level measurement device. In each case, an echo curve is generated for selected main emission directions and/or main receive directions. The interference point profile in the container can then be determined from this series of echo curves, which profile corresponds to the position of interfering objects. 
         [0011]    For example, it is possible to identify, in each echo curve, those portions of the echo curve that originate from interfering objects, which portions have therefore occurred because the transmission signal was reflected at the interfering object in question. The interference point profile can therefore consist, for example, of individual portions of a series of echo curves, each of these echo curves being generated at a specific main emission direction of the antenna/of the fill level measurement device. 
         [0012]    However, it is also possible for a topology of the interference points in the container to be calculated from these echo curves, and for this topology to be the interference point profile. 
         [0013]    In each case, this interference point profile makes it possible to identify the particular angle of the main emission direction at which the main emission direction intersects an interfering object, and at which, therefore, the transmission signal is reflected by an interfering object. 
         [0014]    When a filling material is present, the fill level measurement device assumes a volume or mass determination mode, in which further echo curves are generated. The further echo curves can be generated as described above, by scanning the surface of the filling material. The volume or the mass of the filling material is then determined from the further echo curves and taking account of the interference point profile. 
         [0015]    The result of the volume or mass determination is thus further improved, since the effects of the interference points, which can distort the measurement result, can be eliminated. 
         [0016]    It should be noted, at this point, that the filling material may be a liquid or a bulk material. 
         [0017]    When, in the following, a container is mentioned in which the filling material is located, this can be understood to be a container in the literal sense, which contains the filling material, a conveyor belt, on which the bulk material is located, or an open stockpile. 
         [0018]    The term “interfering object” used in the following refers to an object which is located between the antenna of the fill level measurement device and the filling material, but which does not form part of the container or of the conveyor belt. The interfering object is therefore in particular not the container base or the container walls, and likewise not the filling material itself. Rather, an interfering object of this kind is a foreign body in the container, for example a ladder or a pipe. 
         [0019]    According to a further embodiment of the invention, the interference point profile is determined from the echo curves that were generated in the empty profile detection mode, also using the geometry of a container in which the filling material is located. 
         [0020]    Taking account of the container geometry when determining the interference point profile makes it possible to avoid reflections that originate from the container from being taking into account when creating the interference point profile. 
         [0021]    According to a further embodiment of the invention, the overall profile is determined from the echo curves that were generated in the empty profile detection mode, the overall profile being a combination of the container profile and the interference point profile. The interference point profile is then determined from the overall profile. 
         [0022]    Therefore, the empty container, including the interfering objects, is scanned, and the container profile is then removed from the overall profile, with the result that only the interference profile remains. 
         [0023]    The overall profile as well as the container profile and the interference point profile can each be a data record that makes it possible to find out in which main emission direction and at what distance from the fill level measurement device a part of the container or an interfering object is located. Accordingly, the coordinates of the corresponding reflectors (an interfering object or a part of the container) can be determined from this data record. It is not necessary for these profiles to be converted into a surface. For example, the data record can be shown in the form of a list (cf.  FIG. 9 ) or in the manner of a matrix (cf.  FIG. 10 ). 
         [0024]    According to a further embodiment of the invention, the interference echo profile is determined from the overall profile using a consistency (i. e. continuity) analysis in order to divide the particular overall profile into a container profile and the interference point profile. 
         [0025]    According to a further embodiment of the invention, the geometry of the container in which the filling material is located is determined from echo curves that were generated in the empty profile detection mode in the absence of a filling material and in the absence of interfering objects. 
         [0026]    According to a further embodiment of the invention, the volume or the mass of the filling material is determined from the further echo curves that were generated in the volume or mass determination mode, and taking account of the geometry of the container in which the filling material is located. 
         [0027]    According to a further embodiment of the invention, a topology curve that represents the surface topology of the filling material is determined from the further echo curves that were generated in the volume or mass determination mode. This step comprises eliminating those portions of the topology curve that are behind an interference point when viewed from the antenna of the fill level measurement device. 
         [0028]    In other words, in the volume or mass determination mode, the surface topology of the filling material, including any possible interference points and parts of the container, is detected, and then those portions that originate from an interference point and thus form a shadow on the filling material surface are removed from the topology curve. 
         [0029]    According to a further embodiment of the invention, the echo curves generated in the empty profile detection mode, and the associated angle of the main emission direction and/or the main receive direction of the antenna, are stored in a volatile and/or non-volatile memory of the fill level measurement device. 
         [0030]    According to a further embodiment of the invention, the empty profile detection mode is assumed when a filling material is present, i.e. when the container or stockpile is partly filled. 
         [0031]    According to a further aspect of the invention, a fill level measurement device is specified for determining the volume or the mass of a filling material according to a method described above and in the following. 
         [0032]    According to an embodiment of the invention, the fill level measurement device is designed to be connected to a 4-20 mA two-wire line for supplying the fill level measurement device with the energy required for the measurement operation, and for transmitting the measured values generated by the fill level measurement device. 
         [0033]    According to a further aspect of the invention, a program element is specified which, when executed on a processor of the fill level measurement device, instructs the fill level measurement device to carry out the steps described above and in the following. 
         [0034]    According to a further aspect of the invention, a computer-readable medium is specified, on which a program element of the above-described type is stored. 
         [0035]    The computer program product may be part of a piece of software which is stored on a processor of the fill level measurement device. The processor here can likewise be the subject matter of the invention. In addition, the program element can be a program element which uses the invention right from the start, and also a program element that, by an update, causes an existing program to use the invention. 
         [0036]    In the following, embodiments of the invention will be described with reference to the figures. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0037]      FIG. 1  shows a measurement arrangement for measuring bulk material. 
           [0038]      FIG. 2  shows a measurement arrangement for measuring a filling material in a container. 
           [0039]      FIG. 3  shows examples of echo curves according to an embodiment of the invention. 
           [0040]      FIG. 4  shows a measurement arrangement and echo curves according to an embodiment of the invention. 
           [0041]      FIG. 5  shows a measurement arrangement according to a further embodiment of the invention. 
           [0042]      FIG. 6  shows an interference point profile according to an embodiment of the invention. 
           [0043]      FIG. 7  shows an overall profile according to an embodiment of the invention. 
           [0044]      FIG. 8  shows a filling material profile after taking into account the interference point profile. 
           [0045]      FIG. 9  shows a form of representation of a container profile or interference point profile according to an embodiment of the invention. 
           [0046]      FIG. 10  shows an alternative form of representation according to an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       [0047]    The depictions in the drawings are schematic and not to scale. 
         [0048]    Where the same reference numerals are used in different figures in the following description of the figures, they denote the same or similar elements. However, the same or similar elements may also be denoted by different reference numerals. 
         [0049]      FIG. 1  shows a fill level measurement device  105 , for example a fill level radar device, that is capable of detecting the topology of a filling material surface. The measurement device comprises a transceiver antenna  108  and an electronics unit  109  connected thereto. 
         [0050]    The measurement device is capable of detecting echo signals or echo curves from different angle ranges  101 ,  102 ,  103 . For each detected echo curve, the distance from the relevant point of the surface of the bulk material  104  is determined. By numerically integrating these distance values, and when postulating a planar surface  106  below the bulk material, the volume of the bulk material stockpile  107  can be determined. In addition, when the density is known, the bulk material mass can be calculated. 
         [0051]    The conditions are completely different in containers that are typical in industry.  FIG. 2  shows a corresponding example. The antenna  108  emits a transmission signal  202 ,  203 ,  204 ,  205  towards the filling material at a plurality of angles. The reflected transmission signal  208 ,  209 ,  210 ,  211  is subsequently received again by the antenna. 
         [0052]    In this case, integrating the distance values detected for the angular directions  1  to  4  can lead to an entirely false result. Firstly, in this case no distinction is made between reflections from the container  201  and those from the bulk material  206 . Secondly, the oblique profile of the container base  207  is not taken into account in any way when calculating the volume. 
         [0053]      FIG. 3  shows a plurality of echo curves according to an embodiment of the invention. The radar measurement device is transferred into an empty profile detection mode immediately after being installed on an empty container  201  (cf.  FIG. 2 ). In this case, the radar measurement device detects the echo curves from different angle ranges  202 ,  203 ,  204 ,  205  of the empty container and stores said curves, together with the respective angles, directly or in a compressed form in the memory (volatile and/or non-volatile) of the measurement device. 
         [0054]    The corresponding echo curves  307 ,  308 ,  309 ,  310  are shown by dashed lines in  FIG. 3 . In addition, the topology of the empty container (i.e. the distance from the container base and/or the container wall) is calculated on the basis of the respective detection angles. 
         [0055]    During the subsequent normal operating mode of the device, which is also referred to in this context as the volume or mass determination mode, echo curves  301 ,  302 ,  303 ,  304  are then continuously detected from the different regions of the container and compared with the previously learned echo curves of the empty container. In this manner, it is possible to distinguish between reflections  305 ,  306  from the filling material surface and reflections  311 ,  312  from the container surface. 
         [0056]    In addition, the volume of the bulk material can be correctly determined, taking account of the topology of the empty container and using the echo identified as originating from the filling material. 
         [0057]    The above-mentioned storage of the echo curves of the empty container can advantageously also be used to simplify the identification of the echo caused by the bulk material.  FIG. 4  shows a corresponding example. The radar measurement device  105  detects, in angular direction no.  5  ( 402 ), an echo curve  403  that also comprises an echo  408  of the pipe  405  located in the container, in addition to the echo  407  caused by the filling material surface  406 . Deciding which echo originates from the bulk material surface  406  becomes trivial when the detected echo curve  403  is compared with the echo curve  404  of the empty container at the same angular position. 
         [0058]    The conditions set out above always arise when the physical extension of an interfering object or interferer  405  is less than the width of the radar beam  409  at the corresponding point, since only then can reflections from the region behind the interfering object also be detected and processed. 
         [0059]    However, the conditions are completely different when the above-mentioned emission over an interfering object between the radar measurement device and the bulk material surface does not occur. 
         [0060]      FIG. 5  shows a corresponding situation. A ladder  501  located in the container  502  has a plurality of steps  503  that, on account of the small distance from the radar measurement device  105 , cannot be emitted over by said device, i.e. almost all of the energy of the radar signal is reflected at the steps when the main beam direction  505  is correspondingly positioned. However, if the main beam direction of the radar measurement device is pointing in a direction  506  that permits propagation between the steps, the distance from the filling material surface  507  can then be correctly determined. 
         [0061]    If an empty profile detection is carried out in the container according to  FIG. 5 , i.e. if the empty container were measured by the radar measurement device, the ladder could thus be erroneously detected as a container boundary. A subsequent calculation of the volume in the container would be incorrect in principle. 
         [0062]      FIG. 6  shows a profile of the apparently empty container  502  that has been detected by the radar measurement device, the position of the container walls  601 ,  608  and of the container base  607  being correctly detected, but the distance values from the steps of the ladder erroneously giving an incorrect profile  602 ,  603 ,  604 ,  605 ,  606  of the container boundary. 
         [0063]    The problem shown can be overcome in various ways. It is possible for the customer to input the fundamental container shape as a parameter. It is possible, from the profile of the detected surface and/or with the aid of consistency analyses, to further divide the determined profile ( FIG. 6 ) into sub-profiles which can in turn be classified (“empty container”, “inserts/interferers”). The empty profile of the container accordingly consists of the boundary lines  601 ,  607 ,  608 , and the interference point profiles of the inserts consist of the profile  602 ,  603 ,  604 ,  605 ,  606 . 
         [0064]    Alternatively or in addition, an automatic plausibility analysis can be carried out in the fill level measurement device, in which atypical, i.e. solid, discontinuous, profiles of the surface of an empty container profile are identified and classified as interference point profiles. 
         [0065]    The above-mentioned determination of two different profiles offers significant advantages for signal processing during ongoing operation. 
         [0066]      FIG. 7  shows the corresponding principle. The raw topology  701  of the bulk material and the ladder, which is determined by the fill level measurement device according to known methods, contains the high measured values  702 ,  703 ,  704 ,  705 ,  706  caused by the rungs of the ladder. In a further signal processing step, the determined topology profile  701  is then compared with the previously determined interference point profile  707  (see the dashed curve), and portions of the topology curve that are below the interference point profile are eliminated. 
         [0067]    The curve line  801  in  FIG. 8  shows the topology curve that results therefrom which is, in practice, two-dimensional, and has the resulting gaps  802 ,  803 ,  804 ,  805 ,  806 . In order to supplement the missing information from the angle ranges of the gaps, the topology curve can now advantageously be interpolated, preferably two-dimensionally interpolated. The actual volume calculation is made by numerically integrating the optionally interpolated topology curve, taking account of the topology curve of the empty container (empty profile  601 ,  607 ,  608 ) which can be previously subtracted. 
         [0068]      FIG. 9  shows a storage-optimised form of representation of an empty profile topology (also referred to in this context as a container profile) or of an interference echo topology, which is also referred to in this context as an interference point profile. 
         [0069]    Instead of the entire echo curves  307 ,  308 ,  309 ,  310 , here only the distance values from the corresponding container boundary or the corresponding interferer are stored in the memory of the radar device. For this purpose, each distance value must be marked with the associated angular position. 
         [0070]      FIG. 10  shows an alternative form of representation of an empty profile topology or of an interfering echo topology in Cartesian coordinates. The coordinates of the matrix correspond to the location coordinates x  110 , y  111  and z  112  of the radar measurement device or of the measured points of the container or of the interfering object. The matrix entries represent the distance, at the corresponding point, between the radar device and the surface of the container wall (empty profile topology), or between the radar device and the surface of an interferer in the container (interfering echo topology). 
         [0071]    It should also be noted that “comprising” and “having” do not exclude the possibility of other elements or steps, and “one”, “a” or “an” does not exclude the possibility of a plurality. It should also be pointed out that features or steps that have been described with reference to one of the above embodiments can also be used in combination with other features or steps of other embodiments described above. Reference numerals in the claims should not be treated as limiting.