container scale or platform scale

Abstract

In a container scale or platform scale (1), the weighing platform or the weighing container (2) of the container scale or platform scale is placed on three or four analog weighing cells (3), the individual signals (8) of the weighing cells (3) are added together in a summing device (7) to a total signal (9), and an evaluation device (6) derives a weight value (11) from the total signal and outputs the weight value. According to the invention, the summing device (7) is designed to add the individual signals (8) without interaction. The evaluation device (6) comprises an analog / digital converter (19) for digitizing the individual signals (8) and a diagnostic device (20) which evaluates the digitized individual signals (8) as diagnostic information (21) and outputs the diagnostic information.

Description

TECHNICAL FIELD

[0001] The invention relates to a container scale or platform scale, whose weighing platform or weighing container is placed on three or four analog weighing cells, which has a summation device that adds the individual signals of the weighing cells to a total signal, and has an evaluation device that derives a weight value from the total signal and outputs the weight value. BACKGROUND

[0002] Industrial container scales or platform scales consist of a weighing electronics (evaluation device) that has a field display, in part, and a weighing container (e.g. silo) or a weighing platform that stands on three or four weighing cells, depending on the configuration. Analog weighing cells with strain gauges (DMS) are primarily used in bridge circuits. The weighing cells are connected via electrical leads to junction boxes (distribution boxes) in which the DMS bridge circuits are connected in parallel, so that the analog measurement signals (individual signals) of the weighing cells are added to a total signal. The total signal is further forwarded via a signal cable to the evaluation device, which also contains a measurement amplifier and an analog / digital converter, and evaluates the total signal of the weighing cells to a weight value, and displays the weight value and / or transmits it to a superior control device.

[0003] There is a need for diagnostic and monitoring functions to support the user during commissioning, maintenance of the scale or also in operation, and to provide information about the current state of the scale to the user. Thereby the time for commissioning and maintenance can be reduced, also the downtime of the facility with the production failure resulting therefrom. SUMMARY

[0004] According to the invention, this object is achieved by a container scale or platform scale as defined in the invention, whose advantageous improvements are described in the invention.

[0005] The subject matter of the invention is therefore a container scale or platform scale, whose weighing platform or weighing container is placed on three or four analog weighing cells, which has a summation device that adds the individual signals of the weighing cells to a total signal, and has an evaluation device that derives a weight value from the total signal and outputs the weight value, characterized in that the summation device is designed to add the individual signals without interaction, and the evaluation device contains an analog / digital converter for digitizing the individual signals of the weighing cells and a diagnostic device that evaluates the digitized individual signals to diagnostic information and outputs this diagnostic information.

[0006] By adding the individual signals of the load cells without interaction to a total signal which is decisive for the weight to be measured, the individual signals are used without distortion for a differentiated evaluation for diagnostic purposes. The summation device can comprise an analog summation amplifier (inverting adder) with operational amplifiers which add the analog individual signals without interaction. Since the individual signals are digitized for the diagnostic evaluation which is carried out digitally, the summation device can be designed alternatively to the addition of the digitized individual signals.

[0007] The diagnostic device can be designed to receive information about the spacing of the load cells or the placement point of the weighing platform or the weighing container and to calculate and output the center of gravity of the scale from the information and the digitized individual signals of the load cells. The information about the spacing of the load cells or the placement point of the weighing platform or the weighing container can be input, for example, by an operator or an assembler of the scale via a suitable user interface. Via the same user interface, the calculated center of gravity of the scale, in particular the lateral coordinate of the scale parallel to the placement surface, can also be output visually, in particular graphically.

[0008] In the simplest case, the center of gravity distribution can also be shown without input by outputting the values of the digitized individual signals or a graphic representation thereof, for example in the form of a histogram.

[0009] The automatic calculation of the center of gravity simplifies the construction and orientation of the scale, in which the force diversion or lateral forces can also be identified. The diagnostic device is preferably designed to store the position of the calculated center of gravity of the unloaded scale in a memory and to calculate and output the position of the center of gravity of the loaded scale and / or the position of the center of gravity of the load on the scale as a deviation from the stored center of gravity of the unloaded scale. In this way, information about the material distribution or the movement of the center of gravity in the weighing container can be obtained, for example, when the container is subsequently changed, modified or expanded.

[0010] The danger of a lifting of the weighing container or the load in the case of wind or due to other external influences, i.e. in the unloaded case of the scale, can be detected in an advantageous manner by storing the obtained values of the digitized individual signals as zero point values of the respective load cell in a memory and comparing the digitized individual signals obtained during the continuous operation of the scale with one another after subtraction of the respective zero point value. Thus, in the case of a change in the force diversion, the ratio of the individual weight values at the load cells to one another changes, so that in the case of a large deviation an indication of a possible force diversion can be output and thus an erroneous measurement can be output. Thus, when the load of one load cell or of an adjacent load cell becomes zero compared to the zero point (static load) or its direction of action changes from a pressure load to a tensile load, the danger of a lifting of the container or the scale can be monitored by a comparison of the individual weight values at the load cells with the zero point.

[0011] Different sensitivities of the individual weighing cells can lead to an angular load error, i.e. to different weight values for the same load depending on the position of the load on the scale, for example on a weighing platform. In order to achieve a digital angular load compensation, the diagnostic device can derive the angular load error of the scale from the values of the digitized individual signals, which are obtained with the same calibration weight loaded at different points of the scale, and calculate a correction factor from the angular load error, which is used to add the individual signals to a total signal.

[0012] In the event of a failure of an individual weighing cell, the entire industrial scale usually fails. In order to prevent this, the evaluation device is preferably designed to detect a failure of an individual weighing cell by monitoring the impedance of the connected weighing cells; the diagnostic device then calculates a replacement value for the individual signal of the corresponding failed weighing cell from the digitized individual signals of the intact weighing cells and provides the replacement value for the purpose of deriving the weight value of the load to be measured.

[0013] Finally, the diagnostic device can be designed to evaluate the frequency components of the individual signals and to derive therefrom information about the dynamic weighing process or treatment of the load on the scale and to output this information. It is thereby possible, for example, to monitor a dosing process or to mix a medium in a weighing container with the aid of a stirrer without additional sensor devices, or to perform an automatic calculation of filter parameters of a filter with which the individual signals to be added for the purpose of deriving the weight value are filtered. BRIEF DESCRIPTION OF DRAWINGS

[0014] In the following, the application is explained according to embodiments and with reference to the drawings; in detail:

[0015] Figure 1 An embodiment of a container scale is shown,

[0016] Figure 2 An example for an evaluation device is shown,

[0017] Figure 3 Another example for an evaluation device is shown,

[0018] Figure 4 and 5 Examples for the visualization of diagnostic information are shown.

[0019] The same reference signs have the same meaning in the different figures. The illustrations are purely schematic and do not represent any dimensional relationship. DETAILED DESCRIPTION

[0020] Figure 1A container scale 1 with a weighing container 2 is shown, which is placed on three simulated weighing cells 3. The shown weighing container 2 is a stirred tank with a stirrer 4. However, the container 2 can also be a silo, a box, a filling hopper, etc. Four weighing cells can also be used, for example when the container 2 or a here not shown weighing platform instead of the container has a square or rectangular base surface. The load on the weighing cells 3 without the effective load to be measured, here for example the medium in the container 2, through the entire mechanical structure is described as static load. The weighing cells 3 are connected via lines 5 at an evaluation device (weighing electronics) 6, in which a summation device 7 adds the individual signals 8 of the weighing cells 3 to a total signal or sum signal 9. A computing unit 10 of the evaluation device 6 derives a weight value 11 from the total signal 9, which is displayed for a user 13 on a display 12 of the scale 1 and / or is otherwise transmitted via a connection means 14 to a superior device or control device 15 for the purpose of control, recording, display, billing, etc. The display 12 is a component of a user interface 16, which also has a mechanism 17 for inputting information about the scale 1, for example the position of the weighing cells 3.

[0021] The evaluation device 6 also contains a monitoring device 18, which measures and monitors the impedance of the connected weighing cells 3 in order to detect a failure of the individual weighing cells 3 or a line break or short circuit of the lines 5.

[0022] Finally, the evaluation device 6 contains an analog / digital converter 19, which digitizes the individual signals 8 of the weighing cells and feeds them to a diagnostic device 20, which derives diagnostic information 21 from the digitized individual signals 8 and displays them for the user 13 on the display 12 and / or, if necessary, transmits them to the superior device 15.

[0023] Figure 2 An embodiment of the evaluation device 6 is shown, in which the individual signals 8 of here for example four weighing cells 3 are digitized in the analog / digital converter 19 and then fed to the diagnostic device 20 and here the digital summation device 7. The computing unit 10 derives the weight value 11 from the digital total signal provided by the summation device 7. The diagnostic device 20 contains a plurality of diagnostic modules 20', 20", 20"' which process the digitized individual signals 8 into different diagnostic information 21', 21", 21"'. Here, the diagnostic device 20 can be controlled by the monitoring device 18, which measures the impedance of the connected weighing cells 3, in order to calculate a replacement value for the individual signal 8 of the respective failed weighing cell 3, for example 21"', when a failure of the individual weighing cells 3 is detected, and to provide the replacement value for deriving the weight value 11.

[0024] As in Figure 2It is further shown that each analog weighing cell 3 comprises a strain gauge (DMS) 22 in a bridge circuit 23.

[0025] Figure 3 Another embodiment of the evaluation device 6 is shown, wherein, in contrast to the example according to Figure 2 , the individual signals 8 of the weighing cells 3 are added in an analog summing amplifier (inverting adder) 24 and subsequently digitized in an analog / digital converter 19 and fed to the computing device 10. This embodiment is in principle not different from the embodiment according to Figure 2 , wherein here too a monitoring device can be present which measures the impedance of the connected weighing cells 3, which monitoring device is not shown for reasons of clarity.

[0026] The mechanical construction of the scale 1 is decisive for the measurement result, since here in practice the most common errors occur in the construction and operation of the scale. Thus, it is necessary in the scale construction that, for example, the same load is generated at all weighing cells 3 or at the point of placement of the weighing container 2 or the weighing platform. If, for example, the center of gravity of the scale is not in the center or the weighing cells are not all the same height and oriented flat, then, for example, the scale stands on only two of the four weighing cells, overloading of the individual weighing cells can result, while other weighing cells can be subjected to a load, i.e. to a pulling force. Furthermore, it is necessary that there is no or a force diversion, i.e. that the weighing container or the weighing platform is mechanically decoupled from the bottom on which the scale is located. Such a force diversion can be formed, for example, by an imprecisely adjusted component, i.e. for example a mechanical safety device which overcomes an overload, a lateral force or a lifting (tilting) of the scale, by a contamination of the scale or by an un-decoupled pipe line from or to the weighing container 2.

[0027] Furthermore, external influences act on the weight measurement. Belonging to the external influences are temperature influences, for example natural temperature fluctuations of the container 2, cooling or heating, the temperature of the medium in the container 2 or exothermic or endothermic chemical reactions which cause thermal expansion or contraction of the container structure, wind forces acting on the container 2, vibrations of the facility in which the scale is constructed, contamination build-up at the weighing cells 3, etc., which can lead to problems in the region of the weighing cells 3, such as lateral forces, axial forces, moments or force diversion.

[0028] As explained in more detail below, the diagnostic modules 20', 20", 20"' of the diagnostic device 20 can perform different monitoring and diagnostic tasks in order to support the user in the commissioning, maintenance and also in the operation of the scale 1 and to provide him with information about the current state of the scale 1.

[0029] It is assumed that the scale 1 has four weighing cells 3. By digitization of the individual signals 8 of the weighing cells 3, the following digital values are obtained for each nth weighing cell (corresponding to the weighing cell Wn, n = 1, 2, 3, 4) from the load of the scale 1:

[0030] DWn measured value of the load cell Wn,

[0031] J0Wn zero point value of the load cell Wn when the scale is unloaded,

[0032] J1Wn adjustment value of the load cell Wn when the scale is loaded with the calibration weight.

[0033] First, the zero point of the unloaded scale 1 is taken, wherein the resulting zero point value J0Wn is stored in the memory 26 of the diagnostic device 20. Figure 2 and Figure 3 ). In order to determine the center of gravity of the scale 1, the user 13 can input information about the relative positions of the load cells W1, W2, W3 and W4 to each other into the evaluation device 6 via the input means 17, wherein the information can be shown in a graphical manner on the display 12 of the user interface 16.

[0034] Figure 4 The case of a container 2 having a square base surface and side length a is shown exemplarily. The diagnostic device 20, for example the diagnostic module 20', calculates from the information the position or the lateral coordinates (xn, yn) of the individual load cells Wn:

[0035]

[0036]

[0037]

[0038]

[0039] and furthermore the coordinates (x s0 , y s0 ) of the center of gravity S0 of the unloaded scale 1 are calculated:

[0040] and

[0041]

[0042] The position of the center of gravity S0 of the unloaded scale 1 is shown exemplarily in Figure 4The center of gravity S0 can be visualized on the display 12 as shown in the diagram. In the ideal case, i.e. in the case of an optimal setting of the scale 1, the center of gravity S0 lies in the intersection of the x-axis and the y-axis, which correspond to the axes of symmetry of the scale 1 or the container 2. Different tolerance ranges 27, 28 can indicate whether the determined center of gravity position can be tolerated for the operation of the scale 1. The determination of the center of gravity S0 and its visualization simplify the construction and orientation of the scale 1, wherein also force shunts or lateral forces can be identified. Here, the manner and the method of visualization can of course be very different. Thus, for example, it is also possible that the zero point values J0W1, J0W2, J0W3 and J0W4 are shown in the form of bars in a bar chart, wherein the deviation of the individual bars from the average value of the zero point values indicates the calibration requirement for the respective weighing cell W1, W2, W3 and W4.

[0043] Figure 5 Example of the visualization of the center of gravity in a scale with three weighing cells W1, W2 and W3.

[0044] The determined coordinates (x s0 , y s0 ) of the center of gravity S0 of the unloaded scale 1 are stored in the memory 26. This enables the monitoring of the center of gravity S of the medium in the weighing container 2 or the payload on the weighing platform during the continuous operation of the scale 1. This is done in that the diagnostic device 20 or one of its modules 20', 20", 20"' determines the position (x s , y s ) of the center of gravity S of the loaded scale 1 in the following way:

[0045]

[0046]

[0047] and the deviation AS between the position (x s , y s ) of the center of gravity S of the loaded scale 1 and the position (x s0 , y s0 ) of the center of gravity S0 of the unloaded scale 1 or between the two centers of gravity S, S0 is visualized on the display 12. The center of gravity monitoring can be used, for example, to detect bridge formations or clumps at the inner walls of the weighing container 2 at an early stage in the case of bulk goods. However, the center of gravity monitoring also enables the detection of a load of the scale caused by wind, for example.

[0048] Without inputting and knowing the relative positions of the weighing cells W1, W2, W3 and W4, at least the center of gravity distribution can be displayed in that the measurement values, zero point values or adjustment values DWn, J0Wn, J1Wn of the weighing cells W1, W2, W3 and W4 are output directly, for example, or in the form of a graphical representation, for example in a column chart.

[0049] In the scope of the diagnosis, a force diversion can be recognized by comparing the digital measured values DWn of the individual load cells Wn, which are preferably adjusted by the zero point values J0Wn, wherein in the case of a large difference between the measured values DWn, a diagnosis information 21 is output as a warning.

[0050] By monitoring the digital measured values DWn of the individual load cells Wn compared to the zero point values J0Wn, a risk of the container scale 1 being lifted by wind forces is recognized. An indication of this is, for example, in the case of one load cell or two adjacent load cells, the digital measured values DWn adjusted by their zero point values J0Wn become zero or become negative.

[0051] As described above, the diagnosis device 20 can be controlled by the monitoring device 18, which measures the impedance of the connected load cells 3 in order to calculate, in the case of a detected failure of an individual load cell 3, a replacement value 21"' for the individual signal 8, more precisely the corresponding digital measured value DWn, of the corresponding failed load cell 3 and to provide this replacement value for the determination of the weight value 11.

[0052] In order to compensate for a failed load cell, for example W2, an average value can be calculated from the digital measured values DW1, DW3, DW4 of the remaining load cells W1, W3, W4 and used as a replacement value for the failed load cell W2:

[0053]

[0054] In order to eliminate the effects of possible asymmetries and tensions when installing the scale 1, the calculation of the replacement value DW2 can be adjusted by the zero point values J0Wn in the memory 26:

[0055]

[0056] An adjustment according to an adjustment value J1Wn can also be made, which is determined when a calibration weight is loaded onto the scale 1 and is likewise stored in the memory 26:

[0057]

[0058] Here, an adjustment by the zero point values J0Wn can also be made:

[0059]

[0060] Similarly, in the case of a simultaneous failure of two load cells, for example W1 and W2, a replacement value D1 and D2 for these two load cells can be calculated from the remaining load cells W3, W4 in the following way:

[0061]

[0062]

[0063] Below, we take a scale with three weighing units W1, W2 and W3 as an example. Figure 5 ) as an example to explain how to automatically and digitally compensate for angular load on a scale 1. As mentioned above, the varying sensitivities of the individual weighing cells 3 can lead to angular load errors. The variation in the weight value 11 when the same load is placed at different locations on the scale is called the angular load error.

[0064] In a first step, a calibration weight, for example 100 kg, is placed successively at the three corner points of the scale 1, i.e., at the locations of the weighing cells 3. Adjustment values ​​J1W1, J1W2, and J1W3 are obtained. Due to the varying sensitivities of the weighing cells 3, these adjustment values ​​may differ. The adjustment values ​​are now adjusted using the zero value J0Wn in the memory 26:

[0065] ΔW1=J1W1-J0W1

[0066] ΔW2=J1W2-J0W2

[0067] ΔW3=J1W3-J0W3

[0068] From the set values ​​ΔWn, the minimum value is selected, here for example ΔW3 .

[0069] In the next step, the correction factors Fn are calculated for the individual signals 8 to be added to the overall signal 11 and stored in the memory 26 in the following manner:

[0070]

[0071]

[0072]

[0073] In the weight measurement, the individual signals 8 to be added, here for example the digital measured values ​​DWn adjusted by the zero value J0Wn, are multiplied by a calculated factor Fn to obtain the measured value DWEn compensated for the angular load:

[0074] DWE1=F1·(DW1-J0W1)

[0075] DWE2=F2·(DW2-J0W2)

[0076] DWE3=F3·(DW3-J0W3)=(DW3-J0W3)

[0077] Finally, in the digital summing device 7 ( Figure 2) the measured values DWEn of the compensating angle load are added together to a total signal DWE1+DWE2+DWE3, which represents the weight value 11.

[0078] Finally, in one of the diagnostic modules 20', 20", 20'" the frequency components of the digitized individual signals 8 are evaluated and information about the dynamic weighing process or treatment of the load on the scale 1 is derived therefrom and output. Thus, for example, the stirrer 4 in the container 2 Figure 1 ) generates vibrations and oscillations which are recorded by the weighing cells 3 and reappear in the individual signals 8. By filtering or frequency analysis (for example Fourier transformation) of the digitized individual signals, for example the rotational frequency of the stirrer 4 can be extracted and, if necessary, the direction of rotation can be detected from the phase shift of the individual signals. The frequency spectrum also allows conclusions to be drawn about the technical state of the stirrer 4. Depending on the amplitude of the signal components which are related to the rotational speed, for example the state of the medium in the weighing container 2 can be checked or it can be estimated when a mixing or reaction process ends.

[0079] It can be necessary when deriving the weight value 11, for example when the scale 1 is used for dosing purposes and should be dosed while the stirrer 4 is running, to filter the summed individual signals 8 of the weighing cells 3 in the filter 29 of the evaluation device 6 in order to eliminate interference. Although so far manual adjustment or adaptation of the filter parameters had to be carried out, there is now the possibility of automating the filter adaptation by deriving the frequency of the digitized individual signals. The frequency can also be compared with the adjusted rotational speed of the stirrer 4 and deviations therefrom can be reported to the plant operator.

Claims

1. A container scale or platform scale, whose weighing platform or weighing container (2) rests on three or four analog weighing cells (3), with a summing device (7) that adds the individual signals (8) of the weighing cells (3) to a total signal (9) and an evaluation device (6) that derives a weight value (11) from the total signal (9) and outputs it, the summing device (7) being designed to add the individual signals (8) without interaction, and the evaluation device (6) comprising an analog / digital converter (19) for digitizing the individual signals (8) of the weighing cells (3) and a diagnostic device (20) that evaluates the digitized individual signals (8) as diagnostic information (21) and outputs it, the diagnostic device (20) being designed to receive information about the position or spacing of the weighing cells (3) or the placement point of the weighing platform or the weighing container (2) and to derive and output the position of the center of gravity of the container scale or platform scale from this information and the digitized individual signals (8) of the weighing cells (3), and wherein the diagnostic device (20) is designed to store the derived position of the center of gravity of the unloaded container scale or platform scale in a memory (26) and to derive and output the position of the center of gravity of the loaded container scale or platform scale and / or the position of the center of gravity of the load on the container scale or platform scale as a deviation from the stored center of gravity of the unloaded container scale or platform scale. characterized in that The summing device (7) comprises an analog summing amplifier (24).

2. A container scale or platform scale according to claim 1, characterized in that The summing device (7) is designed to add the digitized individual signals (8).

3. A container scale or platform scale according to claim 1, characterized in that The diagnostic device (20) is designed to store the values of the digitized individual signals (8) obtained in the case of an unloaded container scale or platform scale as zero point values of the associated weighing cells (3) in a memory (26) and to compare the digitized individual signals (8) obtained during the ongoing operation of the container scale or platform scale with one another after subtraction of the associated zero point values in order to detect force shunts at the weighing cells (3) and / or lifting of the load.

4. A container scale or platform scale according to any one of claims 1 to 3, characterized in that The diagnostic device (20) is designed to derive an angular load error of the container scale or platform scale from the values of the digitized individual signals (8) obtained in the case of the same calibration weight being loaded at different locations on the container scale or platform scale and to calculate correction factors for the individual signals (8) to be added to the total signal (9) from the angular load error.

5. A container scale or platform scale according to any one of claims 1 to 3, characterized in that ​ 6. A container scale or platform scale according to any one of claims 1 to 3, characterized in that The evaluation device (6) is designed to detect a failure of an individual load cell (3) by monitoring the impedance of the connected load cell (3), and the diagnostic device (20) is designed to calculate a replacement value for the individual signal (8) of the respective failed load cell (3) from the digitized individual signals (8) of the intact load cells (3) and to provide the replacement value for the determination of the weight value (11).

7. A container scale or platform scale according to any one of claims 1 to 3, characterized in that The diagnostic device (20) is designed to evaluate the frequency components of the individual signals (8) and to derive information about a dynamic weighing process or treatment of the load on the container scale or platform scale from the frequency components and to output this information.

8. A container scale or platform scale according to claim 7, characterised in that, The evaluation device (6) comprises a filter (29) which filters the individual signals (8) which are added for the determination of the weight value (11), and which automatically adjusts the filter characteristic of the filter in accordance with the evaluation of the frequency components of the individual signals (8).

Images