Determining the filling volume in containers

Abstract

The invention relates to a method for verifying whether a correct linearization model is stored in a measuring system. In the context of the invention, linearization models serve the purpose of calculating from a transit-time-based filling-level measurement (L) the corresponding filling volume of the contents (1) of the container (3). For the verification, according to the invention a checksum of the linearization model is calculated, in order to be able to determine whether the checksum has been changed or to what extent the checksum has been changed. If this is the case, the model is interpreted as an incorrectly stored linearization model and this can be correspondingly output as a message. Calculating and outputting the checksum as provided by the invention allows the data processing involved for verifying the correct linearization model to be reduced significantly because all that is required is for just the checksum to be reconciled, rather than the entire linearization model, in order for any change in the stored linearization model to be detected.

Description

[0001] Determination of filling volume in containers

[0002] The invention relates to the verification of the linearization model in the course of determining the filling volume in containers by means of runtime-based filling level measurement.

[0003] In process automation technology, appropriate field devices are used to record relevant process parameters. To record the respective process parameters, suitable measurement principles are implemented in the respective field device types, enabling them to record process parameters such as level, flow, pressure, temperature, pH value, redox potential, media density, or conductivity. A wide variety of such field device types are manufactured and distributed by the Endress+Hauser Group.

[0004] Time-of-flight-based measurement methods have become established for measuring the fill level of products in containers. Probe-based measurement methods based on, for example, the TDR (Time Domain Reflectometry) principle can be used for signal time-of-flight measurement. Ultrasound or radar-based measurement methods based on, for example, the pulse time-of-flight or the FMCW (Frequency Modulated Continuous Wavelength) principle have also become established, and these methods emit corresponding high-frequency signals via a suitable antenna. The FMCW-based level measurement method is described, for example, in the published patent application DE 10 2013 108 490 A1.

[0005] Based on the measured fill level, it is often of interest to determine the fill volume currently occupied by the filling material in the container. This is possible if a linearization model, also known as a linearization table, tank table, or linearization curve, is available for the respective container. This establishes the relationship between the respective fill level value and the corresponding fill volume currently occupied by the filling material in the specific container. The linearization model is independent of the type of filling material stored in the container and can also be in the form of an analytical function or a numerical table. The creation of a linearization model is described, for example, in the publication WO 2020 / 216462.

[0006] If the linearization model is implemented in tabular form, this can include up to 100 or more columns, depending on the container height and resolution, with each column assigned to a corresponding fill level value. In addition to the fill level value and the corresponding volume value, each column may contain additional rows with further individual parameters, such as the corresponding mass value of the stored product. The data volume of each linearization model is correspondingly large. If required, the density of the type of product to be stored can be stored in the level measuring device or the measuring system into which the level measuring device is integrated. This makes it possible to determine the mass of the currently stored product based on the measured fill level, the linearization model, and the density.

[0007] Since a separate linearization model is required for each container type, it is crucial that the correct linearization model for the application location is stored in the level measuring device, or that this model is not changed after implementation. Accordingly, it is an object of the invention to ensure this. The invention solves this problem by the method according to claim 1 and the measuring system according to claim 6. Advantageous embodiments thereof are described in subclaims 2-5 and 7-10, respectively.

[0008] The invention is explained in more detail using the following figure. It shows:

[0009] Fig. 1 : A level gauge for determining the filling volume of a container.

[0010] To understand the invention, Fig. 1 shows a container 3 containing a liquid filling material 2. For example, to control the filling or emptying process, the filling volume currently occupied by the filling material 2 in the container 3 must be measured. For this purpose, a freely radiating radar level gauge 1 is mounted at a known installation height h above the container brine 2. Furthermore, the level gauge 1 is aligned such that, depending on the implemented radar principle, corresponding radar signals SHF are emitted approximately vertically downwards in the direction of the filling material 2.

[0011] After reflection of the radar signal SHF at the product surface, the level measuring device 1 receives the radar signals RHF reflected at the product surface after a defined signal propagation time, whereby the signal propagation time depends on the distance d of the level measuring device 1 to the corresponding point on the product surface. Since the level measuring device 1 can measure the signal propagation time based on the reflected radar signal RHF and assign it to the corresponding distance d, the level measuring device 1 can determine the level value L according to

[0012] L = h — d

[0013] To be determined at this point on the filling material surface, provided that the installation height h of the level measuring device 1 above the container brine is stored in the level measuring device 1. In contrast to the embodiment shown in Fig. 1, it is also possible within the scope of the invention to use a different time-of-flight method instead of a radar-based measuring method, for example an ultrasound-based level measuring device or a probe-based level measuring device based on the TDR ("Time Domain Reflectometry") method.

[0014] As a rule, the level measuring device 1 is connected to a higher-level unit 4, such as a process control system or a decentralized server, via a suitable interface, such as PROFIBUS, HART, Wireless HART, 4-20 mA, Bluetooth, GSM, or Ethernet, thereby forming a corresponding measuring system. The level value L can be transmitted via the interface. However, the pure distance value d or the pure measurement curve can also be transmitted. The advantage of this is that the installation height h of the level measuring device 1 for calculating the level value L is not stored in the level measuring device 1 itself, but can be stored or modified decentrally.

[0015] In general, in the context of the invention, the term “unit 1In principle, it can be understood as any electronic circuit or hardware that is suitably designed for the intended purpose. Depending on the requirements, it can be an analog circuit for generating or processing corresponding analog signals. However, it can also be a digital circuit, such as an FPGA or a storage medium in conjunction with a program. The program is designed to carry out the corresponding process steps or apply the necessary computing operations of the respective unit. In this context, an electronic unit can also be composed of a plurality of networked storage and computing units.

[0016] According to the state of the art, it is possible to resolve the fill level L at specific points with an accuracy in the sub-micrometer range using appropriate methods such as ultrasound, FMCW, TDR, or pulse transit time methods. In order to determine the fill volume currently occupied by the filling material 2 in the interior of the container 3 based on the fill level value L, a corresponding linearization model that establishes this relationship must be created for the specific container 3. The linearization model can be stored in the level measuring device 1 itself or in the higher-level unit 4. Depending on where the linearization model is stored, the fill volume calculation based on the currently determined fill level value L can be carried out directly in the level measuring device 1 or in the higher-level unit 4.

[0017] The linearization model can be determined, for example, from the design documents or the CAD files for the corresponding container 3. Methods such as "ray tracing," the "Discrete Element Method (DEM)," or the "Lagrangian Particle Model (LPM)" can be used to generate the linearization model. If the type of the stored filling material 2 is known, so that a homogeneous filling material density can be assumed, it is also possible to calculate the mass of the filling material 2 in the container 3 based on the determined filling volume, again either in the level measuring device 1 itself or in the evaluation unit 4.

[0018] Since the level gauge 1 is intended to be used on various container types, the stored linearization model can be overwritten with the new linearization model with appropriate rights and through appropriate configuration in the level gauge 1 or in the higher-level unit 4. However, this carries the risk that the linearization model may be inadvertently overwritten during measurement operation, for example, during maintenance, which will distort the fill volume measurement from that point on. Accordingly, it is necessary to regularly check whether the stored linearization model has been changed.

[0019] According to the state of the art, the target linearization model must be compared with the currently stored linearization model, which requires a correspondingly lengthy routine due to the volume of data. If the linearization model is stored in level gauge 1 and the comparison is performed in the higher-level unit 4, the data set must also be exported there, which in turn requires a corresponding amount of computational effort.

[0020] According to the invention, a checksum of the currently stored linearization model is therefore calculated. In principle, the form in which the checksum is calculated is irrelevant. In the simplest case, a checksum of the linearization model can be calculated as the checksum. To further increase security, however, a more complex calculation method can also be used, for example, in the form of a hash value. The checksum can be calculated in the level measuring device 1 itself, provided the linearization model is stored there.

[0021] However, it is also conceivable that the higher-level unit 4 performs this calculation. Depending on how and where the checksum is calculated, the current value of the checksum can either be output directly via a message, so that the value must be manually checked for any changes. Or the measuring system outputs a message indicating whether a change (yes / no) has taken place or as soon as a change has taken place. If this is the case, this can be interpreted according to the invention as an incorrectly stored linearization model if the change is not intentional. In the other case, i.e. without a change, it can be assumed that the currently stored linearization model is correct. This information (the currently stored linearization model is correct or incorrect) can also be output as a message by the measuring system, i.e. either by the level measuring device 1 or by the higher-level unit 4, if designed accordingly.The corresponding message can be output, for example, via a display or via the interface in the form of a digital value.

[0022] A further variant of the invention consists in outputting or displaying not only the current checksum value via a message, but also a previous value. This previous value can be the checksum determined, for example, during a previous parameterization of the level measuring device 1. In this case, the operator is responsible for comparing these values ​​and concluding that the linearization model has been changed.

[0023] Overall, the calculation and output of the checksum according to the invention significantly reduces the data processing effort with regard to such a check, since not the entire linearization model but only the value of the checksum has to be compared in order to detect any change in the stored linearization model.

[0024] Regardless of which of these forms the checksum is output or reported, it is advantageous to design the higher-level unit 4 or the level measuring device 1 of the measuring system in such a way that the checksum is recalculated in a defined cycle. In this case, with the appropriate design of the measuring system,

[0025] Cycle, it is checked again to see if the checksum has changed. This makes it possible to include the inventive verification of the linearization model as part of a cyclic redundancy test (CRC, Cyclic Redundancy Check), particularly in accordance with ISO 9000.

[0026] List of reference symbols

[0027] 1 level gauge

[0028] 2 Filling material 3 Container

[0029] 4 Evaluation unit d Distance h Installation height

[0030] L Level RHF Reflected radar signal

[0031] SHF radar signal

Claims

Patent claims 1 . Method for checking a linearization model which describes a relationship between a fill level value (L) measured by means of a transit time method and a fill volume of a filling material (2) in a container (3), comprising the following method steps: - Creation of a linearization model depending on the container (3), and - Calculation of a checksum of the linearization model.

2. The method according to claim 1, wherein the checksum is recalculated cyclically, and wherein it is determined in the same cycle whether the checksum changes.

3. Method according to claim 1 or 2, comprising the following method step: - Output of a message with the following content: o a value of the calculated checksum, o whether the checksum has changed, and / or o that the checksum has changed.

4. The method according to claim 3, wherein, in the event that a message is output with the value of the calculated checksum, this value is based on o the currently stored linearization model, o the linearization model which was stored before a defined period of time or before a defined event, in particular a parameterization of the level measuring device (1), or o a linearization model which was stored before the currently stored linearization model.

5. Method according to one of claims 1 to 4, wherein a checksum or a hash value is determined as the checksum.

6. Method according to one of claims 1 to 5, wherein the linearization Model is created as a numerical table or as a mathematical function.

7. Measuring system for determining a filling volume of a filling material (2) in a container (3), comprising the following components: - A runtime-based level measuring device (1) arranged on the container (3) in such a way as to determine the level (L) of the filling material (2) at specific points, and - an evaluation unit (4) which is designed to o calculate the filling volume on the basis of the measured filling level (L) and on the basis of the linearization model, and o calculate the checksum according to the method according to at least one of the preceding claims.

8. Measuring system according to claim 7, wherein a higher-level server (4) or a portable computing device acts as the evaluation unit.

9. Measuring system according to claim 7, wherein the evaluation unit is designed as an integral component of the level measuring device (1).

10. A method for determining a filling volume of a filling material (2) in a container (3) by means of the measuring system according to one of claims 6-9, comprising the following method steps: - Measurement of the filling level (L), and - Calculation of the filling volume or mass based on o the measured filling level value (L) and o the linearization model.

Images