Determining a volume flow on the basis of filling level measurement

Abstract

The invention relates to a method for determining a volume flow (ΔV / Δt) of a filling material (2) in a container (3) by means of a filling level measuring device (1), comprising the following method steps: emitting high-frequency signals (SHF) towards the filling material surface and receiving corresponding received signals (RHF); determining filling level values (Li- n , Li) and / or a filling level change over time (ΔL / Δt) on the basis of the received signals (RHF); ascertaining the volume flow (ΔV / Δt) on the basis of a known linearisation model and the filling level change over time (ΔL / Δt), or on the basis of a volume difference (ΔV) which results from the linearisation model and the filling level values (Li-n, Li) and a corresponding time difference (Δt). The invention is therefore based on the knowledge that a volume flow (ΔV / Δt) or flow rate can also be determined on the basis of filling level measurement, provided that the linearisation model is available for the corresponding container. The method according to the invention advantageously makes it possible to dispense with separate flow rate measuring devices at the inlet (31) and at the outlet (32) of the container (2) in processes which require a filling level measurement per se.

Description

[0001] Determination of volume flow based on level measurement

[0002] The invention relates to flow rate or volume flow rate measurement based on level measurement.

[0003] In process automation technology, field devices are used to acquire relevant process parameters. Suitable measurement principles are implemented in the respective field device types to acquire these parameters, such as fill level, flow rate, 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] For measuring the fill level of contents in containers, high-frequency-based measurement methods have become established. These methods include probe-based techniques, such as those based on the TDR (Time Domain Reflectometry) principle. Ultrasound- or radar-based methods have also become established, based, for example, on the pulse transit-time or FMCW (Frequency Modulated Continuous) principles. The FMCW-based level measurement method is described, for example, in German patent application DE 10 2013 108 490 A1.

[0005] Starting with the measured fill level or the underlying distance value, it is often of primary interest to determine the volume currently occupied by the contents in the container. This is possible if a linearization model, also known as a linearization table, tank table, linearization function, or linearization curve, exists for the respective container. This establishes the relationship between the respective fill level or distance value and the corresponding volume currently occupied by the contents in the specific container. The linearization model is, in principle, independent of the type of contents 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 publication WO 2020 / 216462.Based on this, the invention aims to enable the determination of further process parameters using level measuring devices. According to the invention, this objective is achieved by a method for the high-frequency-based determination of the volume flow of a product in a container, the method comprising the following process steps:

[0006] Emitting high-frequency signals towards the surface of the contents and receiving corresponding signals, determining fill level values ​​or corresponding distance values ​​and / or changes in fill level over time based on the received signals, and

[0007] Determination of the volume flow rate o based on

[0008] ■ of a known linearization model, and

[0009] ■ the change in fill level over time, or based on

[0010] ■ a volume difference resulting from the linearization model and the distance or fill level values, and

[0011] ■ a corresponding time difference.

[0012] The invention is therefore based on the finding that a volumetric flow rate or flow rate can also be determined based on level measurement, provided that the linearization model is available for the corresponding container. From this, the flow rate at the inlets or outlets of the container can be determined, if necessary.

[0013] The method according to the invention can be implemented, for example, by modifying the level measuring device to determine the change in level or distance over time using the Doppler method. The Doppler method is particularly suitable for rapid changes in level.

[0014] Alternatively, the volumetric flow rate can also be determined without implementing the Doppler method by calculating a volume difference based on the fill level measurement. For this purpose, the high-frequency signal is transmitted and the corresponding received signal is received at a defined measurement rate in successive measurement cycles, and a fill level value of the material in the container or a corresponding distance value is measured based on the received signal for each measurement cycle.

[0015] In this case, either the current fill volume in the container can be determined based on the fill level or distance value of the current measurement cycle and the linearization model, or the volume difference can be determined based on the current fill volume and the fill volume determined in a previous measurement cycle.

[0016] Or, based on the level / distance value of the current measurement cycle and the level / distance value determined in a previous measurement cycle, a level difference is determined, so that the volume difference can be determined based on the level difference or distance difference, and the linearization model.

[0017] Regardless of how the volume difference is determined, the corresponding time difference can be calculated using the known measurement rate of the level gauge in order to determine the volumetric flow rate. The measurement method for level measurement is not strictly prescribed within the scope of the invention. The level values ​​can be determined, for example, using the FMCW or pulse transit-time method.

[0018] Furthermore, there is no fixed requirement for the number of measurement cycles between individual level measurements to determine the level difference or volume difference. In the simplest case, the volume difference can be determined in relation to the fill volume or level value of the immediately preceding measurement cycle. This results in a very real-time calculation of the volume flow rate with low latency. However, this can lead to abrupt changes in the calculated volume flow rate if, for example, ripples form on the surface of the material being measured. This can be mitigated, for instance, by setting or specifying a higher number of preceding measurement cycles on the level gauge, on which the volume difference is based, than 1. This increases the latency and thus dampens short-term level fluctuations.Alternatively, abrupt changes can also be prevented by setting the number of preceding measurement cycles to 1, by averaging or filtering the resulting volume flow value over a multiple of measurement cycles, for example, using a low-pass filter. To carry out the method according to the invention, a corresponding measurement system requires at least the following components:

[0019] A container in which the contents are stored, a high-frequency-based level measuring device designed and arranged on the container to determine the level of the contents or a corresponding distance value at a defined measurement rate in successive measurement cycles, and a higher-level unit designed to...

[0020] ■ of the linearization model,

[0021] ■ of the fill level / distance value of the current measurement cycle, and

[0022] ■ to determine the volume difference of the fill level value or distance value of a previous measurement cycle, o to determine the volume flow rate based on the volume difference and the corresponding time difference.

[0023] The level sensor can be designed as a radar-based, ultrasonic, or TDR-based sensor. The higher-level control unit can be integrated into the level sensor, allowing the volumetric flow rate to be calculated within the sensor itself. Alternatively, a decentralized server, a higher-level process control system, or a portable computer can act as the higher-level control unit, performing the volumetric flow rate calculation there.

[0024] The invention is explained in more detail with reference to the following figure. It shows:

[0025] Fig. 1 : A measuring system according to the invention on a container.

[0026] To illustrate the invention, Fig. 1 shows a container 3 containing a liquid substance 2, such as fuel. In the embodiment shown in Fig. 1, the container 3 comprises an inlet 31 through which a defined volume flow rate AV / At of the substance 2 can be supplied, and an outlet 32 ​​through which a defined volume flow rate AV / At of the substance 2 can be discharged.

[0027] Depending on the process underway, the fill level L of the material 2 in the container, the corresponding fill volume, or the volume flow rate AV / At must be measured as precisely as possible for its control. In the illustrated embodiment, a freely radiating radar level sensor 1 is mounted at a known installation height h above the bottom of the container. Furthermore, the level sensor 1 is oriented such that, depending on the implemented measuring principle, a high-frequency signal SHF is emitted approximately vertically downwards towards the material 2 in successive measuring cycles i at a measuring rate r of, for example, 10 Hz to 100 Hz.

[0028] After reflection of the high-frequency signal SHF at the surface of the contents, the level gauge 1 receives the corresponding received signal RHF at the surface of the contents for each measurement cycle i after a defined signal propagation time, which depends on the distance d of the level gauge 1 to the corresponding point on the surface of the contents. Based on the reflected high-frequency signal RHF, the level gauge 1 can measure the signal propagation time and assign it to the corresponding distance d. This enables the level gauge 1 to determine or update the level value L in each successive measurement cycle i according to j — h cfj, provided that the installation height h of the level gauge 1 above the container bottom is stored in the level gauge 1. In contrast to the diagram in Fig.In the embodiment shown in Figure 1, it is also possible within the scope of the invention to use any other measuring method, instead of the radar-based measuring method, by which the fill level L can be determined. Besides the radar-based FMCW or pulse transit-time method, it is also conceivable to implement an ultrasound or TDR-based measuring principle in the level measuring device 1.

[0029] The level sensor 1 is typically connected via a suitable interface, such as PROFIBUS, HÄRT, Wireless HART, 4-20mA, Bluetooth, Sakura V1, GSM, WM550t, or Ethernet, to a higher-level unit 4, such as a process control system or a decentralized server, thereby forming a corresponding measurement system. In the embodiment shown in Fig. 1, the higher-level unit 4 is implemented as a decentralized server. The level value Lj, ​​the distance value d, or the underlying measurement curve can be transmitted via the interface to the higher-level unit 4. If only the distance value d or the underlying measurement curve is transmitted, the level L can be calculated in the higher-level unit 4 based on this value, provided that the installation height h of the level sensor 1 above the tank bottom is stored there.In general, the term “unit” is used within the scope of the invention. 1 In principle, any electronic circuit or hardware suitable for its intended purpose can be considered an electronic unit. Depending on the requirements, this could be an analog circuit for generating or processing analog signals. However, it could also be a digital circuit, such as an FPGA or a storage medium working in conjunction with a program. The program is designed to execute the relevant process steps or perform the necessary calculations for the respective unit. In this context, an electronic unit can also consist of multiple networked storage / processing units.

[0030] Using ultrasonic, FMCW, TDR, or pulse transit-time methods, it is possible to resolve the fill level Lj at a specific point per measurement cycle i with sub-micrometer accuracy. To determine the fill volume V currently occupied by the material 2 within container 3 based on the measured fill level L, a corresponding linearization model must be created for that specific container 3. This linearization model describes the relationship between the measured fill level L and the corresponding fill volume V in the respective container. The linearization model can be stored either in the level gauge 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 L can be performed directly in the level gauge 1 or in the higher-level unit 4.The linearization model can be determined, for example, from the design documents or CAD files for the corresponding container. Methods such as ray tracing, the discrete element method (DEM), or the Lagrange particle model (LPM) can be used to generate the linearization model.

[0031] According to the invention, it is possible to determine the volume flow AV / At using the level measuring device 1 and the stored linearization model: The basis for this is that a volume difference AV of the filling material 2 in the container 3 is determined based on the level value Lj measured in the respective measuring cycles i or on the distance value d measured in each cycle; which results from a filling or emptying and a corresponding change in level AL / At over time.

[0032] The volume difference AV can be determined either by applying the linearization model to the measured value dj, Lj in the current measurement cycle i in each measurement cycle i, or at least in defined measurement cycles i, such as every 10th measurement cycle, in order to determine the current fill volume V; of the material 2 in the container 3. By calculating the current fill volume V; for all measurement cycles i, or in the defined measurement cycles i, the difference between the current fill volume V; and the fill volume Vj determined in a previous measurement cycle can be calculated. n The corresponding volume difference AV can be determined. Another way to determine the volume difference AV is to first determine a level difference AL by comparing the level value Lj of the current measurement cycle i with a level value Lj. nfrom a previous measurement cycle can be subtracted from each other. In this context, it is also conceivable to calculate the fill level difference AL based on the corresponding distance values ​​di, dj. n to determine. Using the linearization model, the corresponding volume difference AV can be assigned to the fill level difference AL.

[0033] Within the scope of the invention, it is, for example, controllable or adjustable by the superior unit 4 or by the level measuring device 1 itself how many measurement cycles n between the measurements of those measured values ​​Lj, Lj. n or di, dj- n , on the basis of which the volume difference AV is determined. Accordingly, according to

[0034] At = n * r -1 the time difference At, which is the difference between the determination of these measured values ​​Li, Lj. n or di, dj- n, past, can be determined. Based on this, the calculated volume difference AV can be used according to The volume flow rate AV / At is then calculated. It goes without saying that the sign of the volume flow rate AV / At indicates whether there is a gross inflow or outflow.

[0035] If the linearization model is stored in the level gauge 1 itself, the previously described calculation of the volume flow rate AV / At can be implemented there. Otherwise, it is also conceivable to have this calculation performed by the higher-level unit 4. An overall advantage of the method according to the invention is that separate flow meters at the inlet 31 or outlet 32 ​​can potentially be dispensed with: If the higher-level unit 4 knows whether and which of the inlets 31 or outlets 32 is currently open, the volume flow rate AV / At can be assigned to the corresponding inlet 31 or outlet 32 ​​based on its sign. According to the invention, it is not necessarily required to directly obtain level values ​​Lj or L1.underlying distance values ​​d; to measure in order to determine the volume flow AV / At on the basis of the linearization model: If the level measuring device 1 is equipped to directly measure the temporal level change AL / At, for example on the basis of the Doppler method, it can be used to determine the volume flow according to this. The volume flow rate AV / At can be calculated directly, provided the container cross-sectional area is constant and known over the container height h. Here, V(L) represents the mathematical function of the linearization model.

[0036] Reference symbol list

[0037] 1 level gauge

[0038] 2 Filling material

[0039] 3 containers

[0040] 4. Higher-level unit

[0041] 31 Admission

[0042] 32 Outlet dj Distance value h Installation height i Index of the measuring cycle

[0043] Lj level value r measurement rate

[0044] RHF Reflected High Frequency Signal

[0045] SHF high-frequency signal

[0046] V(L) function of the linearization model

[0047] Vi filling volume

[0048] AL level difference

[0049] AL / At level change

[0050] At time difference

[0051] At p Period

[0052] AV volume difference

[0053] AV / At volume flow

Claims

Patent claims 1. Method for high-frequency-based determination of a volume flow rate (AV / At) of a fill material (2) in a container (3), comprising the following process steps: Emitting high-frequency (SHF) signals towards the surface of the product and receiving corresponding receiving signals (RHF), Determination of fill level values ​​(Lj- n , Lj) or underlying distance values ​​(dj- n , dj) and / or a temporal level change (AL / At) based on the received signals (RHF), and determination of the volume flow (AV / At) based on ■ of a known linearization model, and ■ the change in fill level over time (AL / At), or based on ■ a volume difference (V) resulting from the linearization model and the fill level values ​​(Lj- n , Lj) or the corresponding distance values ​​(dj- n , dj) results, and ■ a corresponding time difference (At).

2. Method according to claim 1, wherein the change in fill level over time (AL / At) is determined using the Doppler method.

3. Method according to claim 1, wherein the volume difference (AV) is determined by transmitting the high-frequency signal (SHF) and receiving the corresponding received signal (RHF) at a defined measurement rate (r) in successive measurement cycles (i), measuring a distance value (dj) to the fill material (2) or a corresponding fill level value (Lj) in the container (3) based on the received signal for each measurement cycle (i), determining a current fill volume ( ) in the container (3) based on the fill level or distance value (dj, Lj) of the current measurement cycle (i) and the linearization model, and determining the fill volume ( Vj- ) determined in a previous measurement cycle (in) based on the current fill volume ( ), and the fill volume (Vj- ) determined in a previous measurement cycle (i). n ) The volume difference (V) is determined.

4. Method according to claim 1, wherein the volume difference (AV) is determined by transmitting the high-frequency signal (SHF) and receiving the corresponding received signal (RHF) at the defined measurement rate (r) in successive measurement cycles (i), and measuring a distance value (dj) to the contents (2) in the container (3) or a corresponding fill level value (Lj) based on the received signal for each measurement cycle (i), based on the fill level or distance value (dj, Lj) of the current measurement cycle (i) and the fill level value (Lj) determined in a previous measurement cycle (in). n ) a level difference (AL) is determined, and the volume difference (AV) is determined based on the level difference (AL) and the linearization model.

5. Method according to claim 3 or 4, wherein the time difference (At) corresponding to the volume difference (AV) is determined using the known measurement rate (r).

6. Method according to claims 3 to 5, wherein the fill level values ​​(Lj- n , i) determined using the FMCW or pulse transit time method.

7. Method according to claims 3 to 6, wherein the volume difference (AV) is determined in relation to the filling volume (VM) or the fill level value (LM) of the immediately preceding measurement cycle (i-1).

8. Measuring system for carrying out the method according to any one of claims 3 to 7, comprising the following components: A level measuring device (1) designed and arranged on the container (3) to determine the level (Lj) of the contents (2) at a defined measurement rate (r) in successive measurement cycles (i), and a higher-level unit (4) designed to determine the level (Lj) of the contents (2) based on the level measuring device (1). ■ of the linearization model, ■ of the fill level or distance value (dj, Lj) of the current measurement cycle (i), ■ of the distance or fill level value (du, Lj- n) to determine the volume difference (AV) of a previous measurement cycle (in), or to determine the volume flow (AV / At) based on the volume difference (AV) and the corresponding time difference (At).

9. Measuring system according to claim 8, wherein the level measuring device (1) is designed as a radar-based measuring device, as an ultrasound-based measuring device or as a TDR-based measuring device.

10. Measuring system according to claim 8 or 9, wherein the higher-level unit is designed as a component of the level measuring device (1).

11. Measurement system according to claim 8 or 9, wherein a decentralized server (4), a higher-level process control or a portable computing device acts as the higher-level unit.

12. Measuring system according to one of claims 8 to 11, wherein the time difference (At) or the corresponding number (n) of preceding measuring cycles (in) on the basis of which the volume difference (AV) is determined can be specified to the superior unit (4).

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