Determination of volume flow based on level measurement

Abstract

The invention relates to a method for determining a volume flow rate (ΔV / Δt) of a fill material (2) in a container (3) using a level measuring device (1), comprising the following method steps: Emitting high-frequency signals (S HF ) surface of the filling material and reception of corresponding reception signals (R HF ); Determination of fill level values ​​(L i-n , L i ) and / or a change in fill level over time (ΔL / Δt) based on the received signals (R HF ); Determination of the volume flow rate (ΔV / Δt) using a known linearization model, and the change in fill level over time (ΔL / Δt), or using a volume difference (ΔV) resulting from the linearization model and the fill level values ​​(L i-n , L i) and a corresponding time difference (Δt). The invention is therefore based on the finding that a volumetric flow rate (ΔV / Δt) or flow rate can also be determined based on level measurement, provided that the linearization model is available for the corresponding container. An advantage of the method according to the invention is that, in processes that inherently require level measurement, separate flow meters at the inlet (31) or outlet (32) of the container (2) can be dispensed with.

Description

[0001] The invention relates to flow rate or volume flow rate measurement based on level measurement.

[0002] 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.

[0003] 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 measurement methods have also become established, based, for example, on the pulse transit-time or FMCW (Frequency Modulated Continuous Wave) principles. The FMCW-based level measurement method is described, for example, in German patent application DE 10 2013 108 490 A1.

[0004] 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.

[0005] According to the invention, this problem is solved by a method for determining the volume flow of a filling material in a container using high-frequency methods, wherein the method comprises the following process steps: - Emitting high-frequency signals towards the surface of the contents and receiving corresponding signals, - Determination of ◯ Fill level values ​​or corresponding distance values ​​and / or ◯ a change in fill level over time based on the received signals, and - Determination of the volume flow ◯ based on ▪ of a known linearization model, and ▪ the change in fill level over time, ◯ or based on ▪ a volume difference resulting from the linearization model and the distance or fill level values, and ▪ a corresponding time difference.

[0006] 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.

[0007] 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.

[0008] Alternatively, the volume flow can also be determined without implementing the Doppler method by calculating a volume difference based on the level measurement. This requires taking measurements at a defined rate in successive measurement cycles. - to transmit the high-frequency signal and to receive the corresponding receiving signal, and - to measure a fill level value of the contents in the container or a corresponding distance value based on the received signal for each measurement cycle.

[0009] Either in this case - based on ◯ of the fill level or distance value of the current measurement cycle and ◯ of the linearization model a current fill volume in the container can be determined, as well as - based on ◯ of the current fill volume, and ◯ of the fill volume determined in a previous measurement cycle The volume difference can be determined.

[0010] Or - based on ◯ of the fill level / distance value of the current measurement cycle and ◯ of the level distance value determined in a previous measurement cycle A level difference is determined, so that - based on ◯ the level difference or the distance difference, and ◯ of the linearization model the volume difference can be determined.

[0011] 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.

[0012] 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 this number of previous 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.

[0013] To carry out the method according to the invention, a corresponding measuring system requires at least the following components: - 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 measuring rate in successive measuring cycles, and - a superior unit designed to ◯ based on ▪ of the linearization model, ▪ of the fill level / distance value of the current measurement cycle, and ▪ to determine the volume difference of the fill level value or distance value of a previous measurement cycle, ◯ to determine the volume flow rate based on the volume difference and the corresponding time difference.

[0014] The level sensor can be designed as a radar-based, ultrasound-based, 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.

[0015] The invention is explained in more detail with reference to the following figure. It shows: Fig. 1: A measuring system according to the invention on a container.

[0016] To understand the invention, in Fig. Figure 1 shows a container 3 containing a liquid substance 2, such as fuel. In the case of the Fig. In the variant shown in Figure 1, the container comprises 3 - an inlet 31 through which a defined volume flow rate ΔV / Δt of filling material 2 can be supplied, as well as - an outlet 32 ​​through which a defined volume flow rate ΔV / Δt of the filling material 2 can be discharged.

[0017] Depending on the process underway, the fill level L of the material 2 in the container, the corresponding fill volume, or the volumetric flow rate ΔV / Δt 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 container base. Furthermore, the level sensor 1 is oriented such that, depending on the implemented measuring principle, a high-frequency signal S is generated in successive measuring cycles i at a measuring rate r of, for example, 10 Hz to 100 Hz. HF approximately vertically downwards in the direction of the filling material 2.

[0018] After reflection of the high-frequency signal S HF The level measuring device 1 receives the corresponding reception signal R at the surface of the product being filled. HFEach measurement cycle i is triggered after a defined signal propagation time, which depends on the distance d of the level measuring device 1 to the corresponding point on the surface of the contents. The reflected high-frequency signal R is used to determine the measurement cycle. HF The level gauge 1 can measure the signal transit time and assign it to the corresponding distance d. This enables the level gauge 1 to determine the level value L in successive measurement cycles i according to Li=h−di to be determined or updated in each case, provided that the installation height h of the level gauge 1 above the tank brine is stored in the level gauge 1. In contrast to the one 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 means of which the fill level L can be determined. In addition to 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.

[0019] Typically, the level measuring device 1 is connected via a suitable interface, such as "PROFIBUS", "HART", "Wireless HART", "4-20mA", "Bluetooth", "Sakura V1", "GSM", "WM550" or "Ethernet", to a higher-level unit 4, such as a process control system or a decentralized server, thereby forming a corresponding measuring system. In the Fig. In the implementation variant shown, the higher-level unit 4 is implemented as a decentralized server. The fill level value L can be accessed via the interface to the higher-level unit 4. ior the pure distance value d or the underlying measurement curve are transmitted. In the event that only the distance value d is transmitted. i or the underlying measurement curve is transmitted, the calculation of the fill level L based on it can be carried out in the higher-level unit 4, provided that the installation height h of the level measuring device 1 above the container brine is stored there.

[0020] In general, within the scope of the invention, the term "unit" is understood to mean any electronic circuit or hardware suitable for the intended purpose. Depending on the requirements, this could be an analog circuit for generating or processing corresponding analog signals. However, it could also be a digital circuit, such as an FPGA or a storage medium, interacting with a program. The program is designed to execute the corresponding process steps or to apply the necessary arithmetic operations of the respective unit. In this context, an electronic unit can also be composed of a plurality of networked storage / processing units.

[0021] The fill level L can be determined using ultrasound, FMCW, TDR or pulse transit time methods. iThe level measurement can be resolved point by point per measurement cycle i with sub-micrometer accuracy. To determine the fill volume V currently occupied by the material 2 in the interior of container 3 based on the measured level value L, a corresponding linearization model must be created for the specific container 3. The linearization model describes the relationship between the measured level L and the corresponding fill volume V in the respective container, whereby 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 level value L can be performed directly in the level gauge 1 or in the higher-level unit 4. The linearization model can, for example, be derived from the design documentation or...The linearization model can be determined from the CAD files for the corresponding container 3. Methods such as ray tracing, the discrete element method (DEM), or the Lagrange particle model (LPM) can be used to generate the linearization model.

[0022] According to the invention, it is possible to determine the volume flow rate ΔV / Δt using the level measuring device 1 and the stored linearization model: This is based on the level value L measured in the respective measurement cycles i. i or based on the respective measured distance value d i A volume difference ΔV of the filling material 2 in the container 3 is determined, which results from a filling or emptying and a corresponding change in fill level over time ΔL / Δt.

[0023] The volume difference ΔV can be determined either by applying the linearization model to the measured value d 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. i , L i is applied to determine the current fill volume V i to determine the volume of the contents 2 in the container 3. This is done by determining the current fill volume V for all measurement cycles i or in the defined measurement cycles i at that time. i The calculation can be done by subtracting the current fill volume V. i and the fill volume V determined in a previous measurement cycle i-n The corresponding volume difference ΔV can be determined. Another way to determine the volume difference ΔV is to first determine a level difference ΔL by measuring the level value L i of the current measurement cycle i and a level value L i-nfrom a previous measurement cycle can be subtracted from each other. In this context, it is also conceivable to calculate the fill level difference ΔL based on the corresponding distance values ​​d. i , d i.n to determine. Using the linearization model, the corresponding volume difference ΔV can be assigned to the level difference ΔL.

[0024] 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 ​​L i , L i-n or d i , d i-n , on the basis of which the volume difference ΔV is determined. Accordingly, according to Δt=n∗r−1 the time difference Δt between the determination of these measured values ​​L i , L i-n or d i , d i-n, which has passed, can be determined. Based on this, the calculated volume difference ΔV can be used according to ΔV / Δt=ΔVΔt The volume flow rate ΔV / Δt can then be calculated. It goes without saying that the sign of the volume flow rate ΔV / Δt represents whether a gross inflow or outflow is occurring.

[0025] If the linearization model is stored in the level gauge 1 itself, the previously described calculation of the volumetric flow rate ΔV / Δt 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 volumetric flow rate ΔV / Δt can be assigned to the corresponding inlet 31 or outlet 32 ​​based on its sign.

[0026] According to the invention, it is not necessarily required to directly determine fill level values ​​L i or underlying distance values ​​d ito measure in order to determine the volume flow ΔV / Δt based on the linearization model: If the level measuring device 1 is equipped to directly measure the temporal change in level ΔL / Δt, for example based on the Doppler method, it can be used to determine the volume flow ΔV / Δt according to the linearization model. ΔV / Δt=(ΔL / Δt)∗∂V(L)∂L The volume flow rate ΔV / Δt 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. Reference symbol list 1 level gauge 2 Filling material 3 containers 4. Higher-level unit 31 Admission 32 Outlet d i Distance value h Installation height i Index of the measurement cycle L i Level value r measurement rate R HF Reflected high-frequency signal S HFHigh-frequency signal V(L) function of the linearization model V i Filling volume ΔL level difference ΔL / Δt level change Δt time difference Δt p Period ΔV Volume Difference ΔV / Δt Volume flow QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2013 108 490 A1

[0003] WO 2020 / 216462

[0004]

Claims

[1] Method for high-frequency-based determination of a volume flow rate (ΔV / Δt) of a fill material (2) in a container (3), comprising the following process steps: - Emitting high-frequency signals (S HF ) surface of the filling material and reception of corresponding reception signals (R HF ), - Determination of ◯ Fill level values ​​(L i-n , L i ) or underlying distance values ​​(d i-n , d i ) and / or ◯ a temporal change in fill level (ΔL / Δt) based on the received signals (R HF ), and - Determination of the volume flow rate (ΔV / Δt) ◯ based on ▪ of a known linearization model, and ▪ the change in fill level over time (ΔL / Δt), ◯ or based on ▪ a volume difference (ΔV) resulting from the linearization model and the fill level values ​​(L i-n , L i ) or the corresponding distance values ​​(di-n , d i ) results, and ▪ a corresponding time difference (Δt). [2] Method according to claim 1, wherein the change in fill level over time (ΔL / Δt) is determined using the Doppler method. [3] Method according to claim 1, wherein the volume difference (ΔV) is determined by measuring at a defined measurement rate (r) in successive measurement cycles (i) - the high-frequency signal (S HF ) is sent out and the corresponding received signal (R) HF ) is received, - based on the received signal for each measurement cycle (i), a distance value (d) i ) to the filling material (2) or a corresponding fill level value (L i ) is measured in the container (3), - based on ◯ of the fill level or distance value (d i , L i ) of the current measurement cycle (i) and ◯ of the linearization model a current fill volume (V i) is determined in the container (3), as well as - based on ◯ the current filling volume (V i ), and ◯ of the filling volume (V) determined in a previous measurement cycle (in) i-n ) The volume difference (ΔV) is determined. [4] Method according to claim 1, wherein the volume difference (ΔV) is determined by measuring at the defined measurement rate (r) in successive measurement cycles (i) - the high-frequency signal (S HF ) is sent out and the corresponding received signal (R) HF ) is received, - based on the received signal for each measurement cycle (i), a distance value (d) i ) to the contents (2) in the container (3) or a corresponding fill level value (L i ) is measured, - based on ◯ of the fill level or distance value (d i , L i ) of the current measurement cycle (i) and ◯ of the fill level value (L) determined in a previous measurement cycle (in) i-n ) a level difference (ΔL) is determined, and - based on ◯ of the level difference (ΔL) and ◯ of the linearization model The volume difference (ΔV) is determined. [5] Method according to claim 3 or 4, wherein the time difference (Δt) corresponding to the volume difference (ΔV) is determined using the known measurement rate (r). [6] Method according to claims 3 to 5, wherein the fill level values ​​(L i-n, i ) can be determined using the FMCW or pulse transit time method. [7] Method according to claims 3 to 6, wherein the volume difference (ΔV) in relation to the filling volume (V) i-1 ) or to the fill level value (L i-1 ) of the immediately preceding measurement cycle (i-1) is determined. [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 measure the level (L) at a defined measurement rate (r) in successive measurement cycles (i). i ) of the filling material (2), and - a superior unit (4) designed to ◯ based on ▪ of the linearization model, ▪ of the fill level or distance value (d i , L i ) of the current measurement cycle (i), ▪ of the distance or fill level value (d i-1 , L i-n ) of a previous measurement cycle (in) to determine the volume difference (ΔV), ◯ to determine the volume flow rate (ΔV / Δt) based on the volume difference (ΔV) and the corresponding time difference (Δt). [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 superior 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 (Δt) or the corresponding number (n) of preceding measurement cycles (in) on the basis of which the volume difference (ΔV) is determined can be specified to the superior unit (4).

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