Filling-level measurement device and method for measuring the filling level according to the propagation time principle

0001The invention relates to a fill level measuring device and a method for level measurement according to the running time principle with non-contact level measuring devices.

0002Such non-contact measuring devices are used in a variety of industrial branches, for example in the processing industry, in the chemical industry or in the food industry.

0003In the level measurement periodically, short transmitting signals, for example microwaves or ultrasonic waves, are sent by means of an antenna to the surface of a filling material, and their echo signals reflected at the surface are received again after a distance-dependent propagation time. A echo function representing the echo amplitudes as a function of the transit time is formed. Each value of this echo function corresponds to the amplitude of an echo reflected at a certain distance from the antenna.

0004A useful echo is determined from the echo function, which probably corresponds to the reflection of a transmission signal on the product surface. As a rule, it is assumed that the useful echo has a larger amplitude than the remaining echoes. The distance between the product surface and the antenna results directly from the transit time of the useful echo at a fixed propagation speed of the transmission pulses.

0005Usually a received raw signal is not used for the evaluation, but rather its so-called envelope curve. The envelope curve is generated by rectifying and filtering the raw signal. For the exact determination of a transit time of the useful echo, a maximum of the envelope curve is first determined.

0006This conventional approach works flawlessly in a variety of applications.

0007However, problems always occur when the echo from the filling level can not be identified without doubt. This can be the case, for example, if there are internals in the container which reflect the transmission signals better than the product surface.

0008In such cases, for example, during commissioning, the filling level measuring device can be given the current filling level once. The filling level measuring device can identify the associated echo as a useful echo on the basis of the predetermined fill level and can be followed, for example, by a suitable algorithm. Maxima of the echo signal or of the echo function are determined, for example, in each measuring cycle, and the useful echo is determined on the basis of the knowledge of the filling level determined in the preceding measuring cycle and an application-specific maximum expected rate of change of the filling level. The new filling level is then obtained from a signal propagation time of the thus determined actual useful echo.

0009Such an echo recording has the disadvantage that the useful echo must be tracked without interruption. If the level measuring device, for example for maintenance purposes, is taken out of service, the useful echo is generally lost. The level measuring device is then not able to reliably detect the useful echo during restarting. The current level must be set again. However, this may involve a considerable amount of effort. If, for example, no alternative measuring methods are available, it may be necessary to completely empty the container or to fill it completely or up to a reference mark. This often means an interruption in a manufacturing process in the industry and can involve considerable time and costs.

0010From the <patcit id="pcit0001" dnum="EP1139075A2"><text>EP 1 139 075 A2</text></patcit> A method and a device for measuring a filling level of a liquid in a container which change as a result of operation consumption are described. For this purpose, a query signal is sent to the container interior at certain time intervals and an answer signal is received and evaluated for a display. In particular, the respectively received response signal is compared with response signals stored in a memory, which correspond to certain filling levels. If a match is made, a display signal corresponding to the filling level of this stored response signal is formed for the display device. In the case of non-coincidence, a user-dependent liquid consumption is calculated and compared with the last determined filling level at which the received response signal and the stored response signal coincided,

0011It is an object of the invention to provide a level measuring device which operates on the basis of the running time principle and which can carry out level readings directly and independently during a restarting operation.

0012The invention achieves this by a filling level measuring device (5) for measuring a filling level Of a product in a container<ul><li>At least one antenna for transmitting transmission signals and for receiving echo signals,</li><li>A signal processing which is used to derive an echo function from the received echo signals, which contains amplitudes of the echo signal as a function of its runtime, </li><li>A memory in which bin-specific data are stored in a table,<ul><li>Wherein the columns of the table have a column index for recording an echo function in each case,</li><li>The echo functions are stored in the columns in an order such that the echo function stored in the table in the column with the column index corresponds to a specific filling level, and</li></ul></li><li>An evaluation unit which is designed in such a way that<ul><li>It accesses the table for determining the current level and compares the echo functions stored in the table with the actual echo function in which the echo function stored in the table which has the greatest correspondence with the current echo function is determined and the current filling level corresponds to the actual echo function Is assigned to the column index of the determined echo function.</li></ul></li></ul>

0013According to one embodiment, the data are stored in the memory in compressed form.

0014Furthermore, the invention consists in a method for measuring a filling level of a filling material in a container with a filling Level meter with<ul><li>At least one antenna which transmits transmit signals and receives echo signals,</li><li>A signal processing which derives from the received echo signals an echo function which contains the amplitudes of the echo signal as a function of its runtime,</li><li>A memory in which bin-specific data are stored in a table.<ul><li>Wherein the columns of the table have a column index for recording an echo function in each case, </li><li>Wherein the echo functions are stored in the columns in an order such that the echo function stored in the table in the column with the column index corresponds to a specific filling level,</li></ul>and</li><li>An evaluation unit which<ul><li>- for determining the current level, accesses the table which compares the echo functions stored in the table with the actual echo function in which the echo function stored in the table which has the greatest correspondence with the current echo function is determined and the filling level corresponds to the actual echo function Which corresponds to the column index of the determined echo function.</li></ul></li></ul>

0015According to an advantageous development of the invention in connection with the storage of container-specific data in the table of a level measuring device, it is provided that<ul><li>An echo reflected at a filling material surface is identified as a fill level echo by a predetermined filling level,</li><li>This echo is followed over a period of time,</li><li>During this time period transmission signals are emitted, the echo signals of which are recorded and echo functions are formed from the echo signals,<ul><li>- which is stored in the table in a column with a column index which corresponds to a fill level determined at this time by the monitoring of the fill level echo. Furthermore, in connection with the invention, in connection with the storage of vessel-specific data in the table of a fill level measuring device, it is provided that</li></ul></li><li>A transmitting signal is emitted, the echo signal of which is recorded and an echo function is derived from the echo signal,</li><li>A useful echo which is probably derived from a reflection on the product surface,</li><li>This useful echo is tracked over a period of time,</li><li>During this time period transmission signals are sent periodically, the echo signals of which are recorded and echo functions are determined from the echo signals,</li><li>Which are stored in the table in a column under a column index which corresponds to a level determined at this time by the tracking of the desired echo.</li></ul>

0016According to a development of the last-mentioned method, a plausibility consideration of the table is made, the result of which confirms or rejects the useful echo as an echo reflected on the product surface.

0017According to a development of the last-mentioned further development, the instantaneous filling level is found by means of the table when the plausibility consideration results that the useful echo does not originate from a reflection at the filling material surface and the entire process is repeated By means of the table.

0018According to a development of the last-mentioned method, in the plausibility consideration in the table, heights lines are recognized which correspond to a change in a running time of this echo as a function of the filling level. It is checked whether there is a vertical line section in which the running times fall as the fill level increases and the running times in one column are less than the running time of the useful echo in the same column. If such a vertical line section is present, the desired echo is rejected as an echo reflected at the product material surface. If such a vertical line section is not present, the useful echo is accepted as echo reflected at the product material surface.

0019According to a further development<ul><li>The instantaneous fill level is found by means of the table if the plausibility consideration shows that the useful echo does not originate from a reflection at the filling material surface, and</li><li>The entire process is repeated,</li><li>Wherein the echo which corresponds to the instantaneous filling level determined by means of the table is selected as the desired echo.</li></ul>

0020In addition, according to a further development of the method according to the invention, it is proposed that<ul><li>A transmission signal is transmitted,</li><li>Whose echo signal is recorded,</li><li>A plurality of echoes are selected from the echo signal,</li><li>One of these echoes is determined as probable from a reflection on the surface of the filling material,</li><li>During the period periodically transmitting signals, the echo signals of which are recorded, and </li><li>The elapsed time of the selected echoes is determined for each echo signal, and</li><li>For each echo signal, the probable fill level to be assigned to the useful echo,</li><li>The column corresponding to this probable level is determined, and</li><li>In which column a value is stored for each of the selected echoes in a row corresponding to the runtime of the respective echo.</li></ul>

0021In addition, it is suggested that<ul><li>A transmitting signal is emitted, the echo signal of which is received,</li><li>A plurality of echoes are selected from the echo signal,</li><li>One of these echoes is determined as probable from a reflection on the surface of the filling material,</li><li>During the period periodically transmitting signals, the echo signals of which are recorded, and</li><li>The elapsed time of the selected echoes is determined for each echo signal, and</li><li>For each echo signal, the probable fill level to be assigned to the useful echo,</li><li>The column corresponding to this probable level is determined, and</li><li>In which column a value is stored for each of the selected echoes in a line corresponding to the respective echo.</li></ul>

0022According to a development of the last-mentioned method, a plausibility consideration of the table is made, the result of which confirms or rejects the useful echo as an echo reflected on the product surface.

0023According to a further development of the aforementioned methods for storing tank-specific data in the table of a filling level measuring device according to the invention, missing data are determined by extrapolation in the table and are stored in the table.

0024The invention and further advantages will now be explained in more detail with reference to the figures of the drawing, in which an exemplary embodiment is illustrated; Identical elements are provided with the same reference symbols in the figures.<dl id="dl0001"><dt>FIG</dt><dd>10 shows an arrangement for level measurement with a filling level measuring device operating according to the running time principle;</dd><dt>FIG</dt><dd>Shows an echo signal E;</dd><dt>FIG</dt><dd>Shows the columns of the table, the echo function to be entered there being shown graphically in each column for illustration purposes;</dd><dt>FIG</dt><dd>12 is a diagram showing the vertical lines of the table in the case where the echo actually reflected on the product surface has been used as a useful echo; </dd><dt>FIG</dt><dd>FIG. 12 is a diagram showing the vertical lines of the table in the case where the echo reflected at the interferer has been used as the useful echo; FIG.</dd><dt>FIG</dt><dd>Shows an overview of the monitored echoes of the filling material surface, the interferer and the soil; and</dd><dt>FIG</dt><dd>Is a diagram showing the elevation lines of the table in the case where the echo-reflected echo is used as a useful echo.</dd></dl>

0025<figref idrefs="f0001">FIG</figref> Shows an arrangement for level measurement. A container 3 filled with a filling material 1 is shown. A filling level measuring device 5 operating according to the running time principle is arranged on the container 3. A filling level measuring device 5 is, for example, suitable for a microwave level measuring device or an ultrasonic level measuring device. The filling level measuring device 5 serves to measure a fill level 7 of the filling material 1 in the container. An interferer 9 is shown as an example in the container 3. Disturbers 9 are, for example, internals in the container 3, agitators and, of course, any other structure on which reflections can occur. Here, only one interferer 9 is provided, for easier understanding and clarity. Obviously, there may be a lot more interferers in real measurement situations.

0026The filling level measuring device 5 has at least one antenna 11 for transmitting transmission signals S and for receiving echo signals E. In the exemplary embodiment shown, a single antenna 11 is provided which both transmits and receives. Alternatively, however, an antenna for transmitting and at least one further antenna for receiving can also be provided.

0027The sending signals S are transmitted in the direction of the filling material 1 and are reflected at a filling material surface, but also at the container 3 and at the interferers 9 located in the container 3. The superposition of these reflections forms the echo signal E.

0028In the filling level measurement according to the propagation time principle, transmit signals S, eg short microwave or ultrasonic pulses, are emitted periodically in the direction of a filling material 1. The echo signals E of the transmission pulses S are recorded and fed to a signal processing unit 13 which serves to derive an echo function from the received echo signals E, which contains amplitudes A of the echo signal E as a function of its propagation time t.

0029In <figref idrefs="f0001">FIG</figref> Is an example of such an echo function for the arrangement of <figref idrefs="f0001">FIG</figref> Respectively. The echo function has three distinct maxima. These maxima are echoes L, S, B of which the echo L is attributable to a reflection at the filling material surface, the echo S to a reflection at the interferer 9 and the echo B to a reflection at a bottom 15 of the container 3. The echoes L, S, B occur after transit times tL, tS, tB, which correspond to a distance between the antenna 11 and the product surface, or the interferer 9 and the ground 15.

0030The filling level measuring device 5 has a memory 17, which serves to store tank-specific data.

0031These vessel-specific data are recorded and stored permanently on initial commissioning of the arrangement. They are also not erased when the filling level measuring device 5 is switched off or is interrupted by its power supply.

0032The container-specific data are stored in a table whose columns 1 to n serve to record an echo function in each case. The echo functions in the columns are stored in an order which corresponds to the filling levels associated with the respective echo functions. Equivalent to the associated filling points are, of course, the corresponding running times tL of the echoes L reflected at the filling material surface and likewise the associated distances between the antenna 11 and the product surface. These quantities are directly proportional to one and can be converted into one another by simple conversion by means of a known signal propagation speed.

0033In <figref idrefs="f0002">Fig. 3</figref> Are shown in columns 1 to n echo functions in the order in which they are also to be arranged in the table. In the table, each row corresponds to a column of a runtime.

0034For illustrative purposes, at the bottom of <figref idrefs="f0002">FIG</figref> An additional column is inserted in which a line index is entered for each line 1 to m. In the exemplary embodiment shown, the line index increases with the transit time t. Alternatively, the row index could drop with the runtime. Equivalent to the runtime is analogous to the distance previously explained for the columns, which corresponds to the runtime.

0035In the first column 1 of the table, an echo function is to be entered as it occurs when the container 3 is filled. In<figref idrefs="f0002">FIG</figref> This echo function is shown under column 1 as a function. In the actual table, no function is, of course, represented, but in some or all lines 1 to m of the first column 1, an amputee value of this echo function is stored which occurs with the runtime corresponding to the respective line index 1 to m. This applies to all other columns 2 to n of the table.

0036The echo function begins with a decay of the transmit signal S. This is followed directly by the echo L reflected at the filling material surface. The echo S of the interferer 9 appears in the middle of the first column 1 of the table, and the echo B of the ground 15 appears in the last lines (m, m-1 ..).

0037In the last column n of the table, an echo function is to be entered, as it is produced when the container 3 is empty. In<figref idrefs="f0002">FIG</figref> This echo function is shown under column n as a function. The echo function begins with the decay of the send signal S. This is followed by the echo S of the interferer 9, approximately at the center of the table, followed by the echo B of the ground 15 at some distance. An echo L reflected at the filling material surface does not occur in this echo function since the container 3 is empty.

0038Comparing the transit times tS and tB of the echoes S and B of the interferer 9 and the ground 15, it is noticeable that both echoes S and B occur in column n after shorter transit times tS, tB than in column 1. This is because, When the container 3 is full, the transmission signals S or their echo signals E have to travel long distances through the filling material 1 while they are propagating through the free space when the container 3 is empty. This difference is due to the propagation speed of microwaves, which is less in the filling material 1 than in the free space.

0039In addition to the two outer columns 1 and n, <figref idrefs="f0002">FIG</figref> Still further columns 2, 3 and 4 are shown.

0040The column 2 corresponds to a filling level, which lies between the highest filling level for the full container 3 and the interferer 9. The column 3 corresponds to a filling level at which the interferer 9 is just covered by the filling material 1 and the column 4 corresponds to a filling level at which the interferer 9 is no longer covered by the filling material.

0041Based on <figref idrefs="f0002">FIG</figref> Some basic structures are recognizable.

0042The echo B from the ground 15 has its largest running time tB in column 1, its smallest running time tB in column n. From column 1 to n, the propagation time tB of this echo B decreases continuously.

0043The echo L from the reflection on the product surface has its smallest running time tL in column 1, its largest running time tL in column n. From column 1 to n, the delay tL of this echo L increases continuously.

0044The echo S from the interferer 9 has its largest propagation time in column 1. Thereafter, the running time t.sub.S continuously decreases with decreasing filling level until the filling level is at the same level with the interferer 9. The filling level is equivalent with an increasing column index. Once the level has fallen below the level of the interferer 9, the delay time t.sub.S of the echo S from the interferer 9 no longer changes with a further falling level or a further rising column index. The runtime tS of the interferer 9 in column 4 is equal to that in column n. In column 1 it is greater than in column 2 in column 2 greater than in column 3 and in column 3 greater than in column 4.

0045Of course, not all the information contained in an echo signal need be reproduced in detail in the table. The echo functions stored in the table can rather be highly simplified images of the echo signals. In doing so, it is possible to compress data on a larger scale and, if possible, to include only essential information. It is also conceivable to store in the table echo functions which contain only the amplitudes and the running times of the maxima of the echoes occurring in an echo signal. You can even use echoes that only contain the run times of the maxima. In this case, the table contains a large number of free fields and requires correspondingly less memory space. In the same way, not every echo, however small, must be recorded. For example,

0046The data of the table are created and stored on site by and with the described arrangement. Various methods can be used for this purpose.

0047One possible method for generating the table is to initially set the current level. This can be determined, for example, by an additional measurement with another measuring device or by starting up a striking filling level, for example full or empty.

0048Based on this predetermined known filling level, an echo of an echo signal or the corresponding echo function reflected on a product material surface is identified.

0049This echo, which is once recognized as a fill level echo, is tracked over a period of time. If the filling level now changes, the fill level echo is known by the echo monitoring. From its running time tL, the respective filling level is then obtained.

0050During this period, transmit signals S are periodically transmitted. The echo signals E of the transmission signals S are recorded and echo functions are formed from the echo signals E.

0051These echo functions are stored in the table in each case in a column whose column index corresponds to the level determined at this time by the monitoring of the filling level echo. However, there are a number of applications where it is not possible or very expensive to set a current level once.

0052In these cases, a method is preferred that is capable of recording the table without a predetermined level.

0053Such a method is described below. At the beginning, a send signal S is emitted and its echo signal E is received. An echo function is derived from the echo signal E, and a desired echo which is probably derived from a reflection at the filling material surface is determined. The determination of the useful echo can take place in the same way as in the case of conventional level measuring devices. For example, as described above, the maximum with the largest amplitude can be selected, but the useful echo can also be selected taking into account a form of the echoes and / or runtime specifications and / or amplitude specifications.

0054This once selected useful echo is tracked over a period of time. In the same way as in the above-described method, transmit signals S are emitted periodically during this period, the echo signals E of which are emitted and echo functions are determined from the echo signals E.

0055The echo functions are stored in the table in each case in a column under a column index which corresponds to a filling level determined at this time by the tracking of the desired echo.

0056Preferably, a plausibility check of the table is then carried out. The result of the plausibility consideration is that it confirms or rejects the echo echo as an echo reflected on the surface of the filling material.

0057A particularly good form of plausibility consideration is based on the fact that the table shows treble lines which correspond to a variation of a run time of this echo as a function of the column index, which is here for the fill level. The maxima of the echo functions are determined, for example, in all the columns, and, for example, with column 1 as an output column, it is examined whether maxima are also located in the adjacent column in the immediate vicinity of the maxima of the output column. If this is the case, the adjacent maxima are connected by a vertical line segment. In this way, all the gaps are traversed and the adjacent vertical line segments are combined to form heights.

0058On the basis of the vertical lines, it can be seen whether the selected true echo is actually the correct useful echo, that is to say, is to be attributed to reflections on the product surface.

0059For a better understanding, the following characteristic curves of elevation lines are discussed, as they occur when the useful echo is actually the correct useful echo, and if not.

0060In the case of the <figref idrefs="f0002">FIG</figref> The correct echo reflected on the product surface was used in all columns. In<figref idrefs="f0002">FIG</figref> Treble lines are drawn in the manner described above. Three distinct heights HL, HB, HS can be seen. The height line HL originates from echoes reflected at the filling material surface and rises strictly monotonously. The height line HB is assigned to the ground 15 and falls strictly monotonously. The height line HS is assigned to reflections at the interferer 9 and intersects the vertical line HL. In<figref idrefs="f0003">FIG</figref> The elevation lines are shown in a two-dimensional diagram.

0061If an echo is selected as a useful echo, which is not caused by a reflection on the surface of the product, but by the interferer 9, a completely different image is formed. In<figref idrefs="f0003">FIG</figref> There is illustrated an example of elevation lines which occur in such a case.

0062For purposes of illustration, one can imagine the empty container 3, which fills slowly. When the container 3 is empty, the wanted echo and the echo B of the floor 15 are recorded. Since the useful echo is interpreted as a fill level echo, the corresponding echo function is entered in the table at the column X corresponding to the running time tx of the useful echo when the container is empty.

0063If the filling level rises slowly, a fill level echo occurs in the echo functions along with the useful echo, so that the desired echo is approaching as the fill level increases. These fill level echoes move in the table in column X vertical direction to the useful echo. This is in<figref idrefs="f0003">FIG</figref> By asterisks.

0064If the level rises further and exceeds the height of the interferer, the running time of the useful echo increases. The lengthened running time is here to be attributed to the lower propagation speed of the transmit and receive signals S, E in the filling material. Since the useful echo is interpreted as the echo-reflected echo, although it is actually the echo of the interferer 9, the corresponding echo functions are also stored here in the table, corresponding to the propagation time of the useful echo. Consequently, the useful echo in<figref idrefs="f0003">FIG</figref> Along the diagonals. This is indicated as a dotted line.

0065At the same time, of course, the elapsed time of the echo reflected from the filling material decreases further and further. This echo echoes in<figref idrefs="f0003">FIG</figref> Down to the right. The longer the propagation time of the useful echo is, the less is the echo reflected from the filling material. This is represented by triangles.

0066From these considerations, the generalization can be inferred that whenever a vertical line section emerges from the table in which the running times fall as the filling level increases, although the echo source associated with the vertical line section is not covered by the filling material, Filling material.

0067The echo source is not covered by the filling material if the running times of the vertical line section in a column are less than the running time of the useful echo in the same column. That is, the elevation line portion in the region shown in FIG<figref idrefs="f0003">FIG</figref> Is below the diagonal.

0068For the selected representation, in which column and row index increase with increasing runtime, this means that an occurrence of vertical line sections with a negative slope below the diagonals is equivalent to the fact that the useful echo has been selected incorrectly.

0069Therefore, in the plausibility consideration, the height lines are preferably determined. Subsequently, a check is made to determine whether there is a vertical line section in which the running times fall as the filling level increases and the run times in one column are less than the running time of the useful echo in the same column.

0070If such a vertical line segment is not present, the useful echo is accepted as echo reflected at the product surface.

0071If such a vertical line section is present, however, the useful echo is rejected as an echo reflected at the product material surface.

0072If the plausibility consideration shows that the useful echo does not originate from a reflection at the filling material surface, the instantaneous filling level is preferably found by means of the table. The entire process is then repeated, the echo being selected as the desired echo, which corresponds to an instantaneous filling level determined by means of the table.

0073In the determination of the instantaneous fill level on the basis of the table, the realization is utilized that the height line which decreases with increasing runtime and simultaneously has shorter running times in one and the same column than the useful echo is due to echoes which have been reflected on the product surface.

0074The current fill level can thus be determined from the table by sending out a send signal S whose echo signal E is recorded, from the latter the corresponding echo function is derived, and this is compared with the echo functions of the table. The comparison is used to determine the echo function that is closest to the currently recorded echo function. If the determined echo function is located in a column in which a segment of the descending vertical line section is located, the acute filling level is obtained directly from the runtime of the segment. In the embodiment shown in FIG<figref idrefs="f0003">FIG</figref> This would be the case if the column index of the determined column is greater than x.

0075If the column index is equal to x, then there are two possibilities. If, from the echoes of the acute echo function, the fill level echo is clearly identified from the echo of the acoustic echo function, then the actual filling level is determined, if this is not the case, further transmit signals S can be emitted and their echo signals E recorded and their corresponding echo functions compared with those of the table Until the comparison of the current echo function with the echo functions of the table yields an echo function whose column index is greater than x. For the operator, this means that he must wait until the level exceeds the height of the interferer to which the previous useful echo is to be traced.

0076Alternatively, of course, an echo of the current echo function, which of course is not equal to the previous useful echo, can be selected as a probable useful echo. The entire process is then repeated with this probable useful echo.

0077In addition to the previously described method for storing the container-specific data in the table, other methods can also be used.

0078An advantageous method is to emit a send signal S, to receive its echo signal, and to select a plurality of echoes from the echo signal. In the embodiment shown in FIG<figref idrefs="f0001">FIG</figref> The echoes L, S and B would be selected, for example.

0079All selected echoes, here L, S, and B, are tracked over a period of time, and one of these echoes is determined to be a useful echo from a reflection on the product surface.

0080In order to facilitate understanding, reference is made here to the method described in the <figref idrefs="f0001">FIGS</figref> and <figref idrefs="f0002">3</figref> Illustrated example. For the sake of explanation of the principle, for simplicity, a case in which the initially full container 3 completely empties during the time period will be traversed.

0081During this period, in which the echoes are tracked, transmit signals S are emitted periodically and their echo signals E are recorded. For each echo signal E, the run times of the selected echoes are determined.

0082When the container 3 is full, the recording of the table is started at time t0 and echo signals E are recorded during the period t0 to t5. As a rule, much more, eg a few hundred, echo signals E will be evaluated. The restriction to t0 to t5 serves here only for a better overview. The position of the selected echoes L, S, B is determined at each of the times t0 to t5.<figref idrefs="f0004">FIG</figref> Shows an overview in which the position of the echoes L, S, B are plotted at the times t0 to t5. The position of the echoes L, S, B is given by its propagation time, which in turn corresponds to a distance from the antenna 11 and can be directly assigned to a line index. Accordingly,<figref idrefs="f0004">FIG</figref> The row indices.

0083If one of the echoes L, S, B is identified as a useful echo from the product surface, the table can be created directly from the overview.

0084For this purpose, the probable fill level to be assigned to the useful echo is determined for each echo signal E. In our example, this corresponds to the row index entered under L in the first line of the overview.

0085The column corresponding to this probable level is then determined. The column index of this column is equal to the line index entered under L.

0086In this column, a value is then stored for each of the selected echoes L, S, B in a line corresponding to the runtime of the respective echo L, S, B. The line index of these lines is equal to the line index entered in the overview at the appropriate location. In the simplest case, the value to be entered is a constant, which merely indicates that a maximum is present at the corresponding location. Instead, the respective amplitude of the echoes L, S, B can also be entered here. All other fields in the table remain free. This offers the advantage that the table only has a very small storage space requirement.

0087Outgoing from the <figref idrefs="f0004">FIG</figref> Can be seen as one of the <figref idrefs="f0003">FIG</figref> Corresponding table, if one correctly recognizes the echo L as a useful echo.

0088If one holds the echo S for the wanted echo inadvertently, one reaches a table, as in <figref idrefs="f0003">FIG</figref> Is shown. If, inadvertently, the echo B is held for the useful echo, a table is obtained as shown in FIG<figref idrefs="f0004">FIG</figref> Is shown.

0089In the same way as in the above-described method, a plausibility consideration of the table is again performed, the result of which is confirmed or rejected by the useful echo as reflected at the surface of the filling material. The plausibility check can be carried out in the same way as in the previously described method. How to get to the<figref idrefs="f0003">Figures 4, 5</figref> and <figref idrefs="f0004">7</figref> , An examination of the elevation lines shows that only in <figref idrefs="f0003">FIG</figref> The right useful echo has been selected. In the<figref idrefs="f0003">FIGS</figref> and <figref idrefs="f0004">7</figref> There is in each case a vertical line segment in which the running times decrease as the filling level increases and the running times in one column are less than the running time of the useful echo in the same column. From this it follows directly that here the false echo was used as a useful echo. Just as in the above-described method, the correct useful echo can be determined by means of the table recorded with the wrong true echo.

0090The latter method offers the advantage that it does not have to be repeated completely. It is sufficient, if from the overview of<figref idrefs="f0004">FIG</figref> A new table is set up in the knowledge of the correct useful echo determined subsequently from the table.

0091A further advantage of the last-mentioned method is that the height-line segments in the table can be recognized in a very simple manner and especially without complex algorithms.

0092In addition, missing data from the table can be determined by extrapolation and stored in the table.

0093The process described last can, of course, also be applied in a modified and / or simplified form.

0094Such a method consists, for example, of sending out a send signal S, to receive its echo signal E, to select a plurality of echoes from the echo signal, and to track these selected echoes over a period of time. Like the above-described method, one of these echoes is determined to be a useful echo from a reflection on the product surface. Similarly, during the period, transmit signals S are emitted periodically, the echo signals E of which are emitted. The elapsed time of the selected echoes is determined for each echo signal E, and for each echo signal E, the probable filling level to be assigned to the useful echo is determined.

0095Subsequently, in this method, the column corresponding to this probable fill level is determined, and in this column a value is stored for each of the selected echoes in a line corresponding to the respective echo. The table thus obtained essentially corresponds to that in FIG<figref idrefs="f0004">FIG</figref> As shown in FIG. A separate line is provided for each echo L, S, B, and the run times of the echoes L, S, B are stored in the lines. As in the preparation of the overview of<figref idrefs="f0004">FIG</figref> A continuously emptying container 3 has been used, the columns of the overview are already arranged in the correct order. If this is not the case, the desired sequence is obtained directly by sorting the columns according to the run times entered in the row of the desired echo.

0096The table thus obtained, apart from the irrelevant assignment to the times at which the echo signals E were recorded, contains all the information that was also available in the above-described method. Correspondingly, a plausibility observation can be carried out on the basis of the table exactly as in the above-described method, the result of which is confirmed or reproduced by the useful echo as an echo reflected on the product surface.

0097Likewise, in this method, missing data can also be determined by extrapolation.

0098Once the table has been created and stored, level measurements can be carried out by the device at any time, even after longer measuring pauses, immediately after the filling level gauge has been switched on by the device, independently of the current filling level or another initialization procedure.

0099For this purpose, the filling level measuring device 5 has an evaluation unit 19 which has access to the table stored in the memory 17 in order to determine the filling level.

0100During the level measurement, a transmit signal S is emitted, the echo signal E of which is recorded, and a current echo function is derived from the echo signal E.

0101To determine the fill level, a comparison of the current echo function with the echo functions stored in the table is carried out, from which the current filling level is then derived.

0102This is done by comparing the echo function stored in the table with the greatest correspondence with the current echo function. The current fill level is then set equal to the level assigned to the column index of the determined echo function.

0103During a first commissioning, a filling level measuring device 5 according to the invention operates just as accurately and reliably as conventional level measuring devices. However, unlike conventional level gauges, it is capable of self-learning. By setting up the table, the level measuring device is able to detect measuring errors without external assistance and without additional cost and / or time.

0104Nor does it require any new commissioning after a long pause or a complete interruption of the measurements. The filling level measuring device 5 operates with a very high reliability immediately after re-operation due to the data in the table. In the case of difficult cases, it is also possible, by the method according to the invention, to clearly identify the echo that results from a reflection on the product surface.