Method for defining a filling level measurement range

Abstract

The invention relates to a method for defining a filling level measurement range (0(%) - 100% / Lmax) for the time-of-flight-based measurement of filling levels (L(%)) in containers (3). The method is based on a procedure in which, with a container (3) having been emptied, the corresponding time-of-flight-based filling level measuring device (1) is mounted at the upper end region of the container (3) and the distance (d0) to the bottom of the container is measured. It is thereby possible to define the filling level measurement range (0(%) - 100% / Lmax) in both relative and absolute terms by determining the limits of the measurement range (0(%) - 100% / Lmax) on the basis of the measured distance value (d0): The measured distance value (d0) is defined as the lower limit (0(%)). In the case of a relative measurement range (0% - 100%) it is possible to define the upper measurement range limit (100%) by multiplying the measured distance value (d0) by a previously defined factor (x) of a maximum of 1. What is advantageous about this method is that the filling level measuring device (1) is usable without calibration or without knowledge about the geometry in the interior of the associated container (3).

Description

[0001] Procedure for determining a level measuring range

[0002] The invention relates to a method by means of which a relative or absolute fill level measuring range is defined in order to determine corresponding fill level values ​​of filling materials in containers by means of runtime-based measurement.

[0003] In process automation technology, appropriate field device types are used to record relevant process parameters. For this purpose, suitable measuring principles are implemented in the respective field device types, allowing the corresponding process parameters, such as level, flow, pressure, temperature, pH value, redox potential, or conductivity, to be recorded. A wide variety of such field device types are manufactured and distributed by the Endress + Hauser group of companies.

[0004] Time-of-flight measurement principles have become established for level measurement of filling materials in containers due to their robustness and the ability to perform non-contact measurements. The time-of-flight measurement principle is based either on freely radiating high-frequency signals, particularly radar or ultrasound, or on guided emission of high-frequency signals, such as TDR (Time Domain Reflectometry). In the case of freely radiating radar, the FMCW (Frequency Modulated Continuous Wavelength) method is primarily implemented. The pulse-flight-of-flight method, which is less frequently implemented in this field, is primarily used in ultrasonic-based level measuring devices.

[0005] Time-of-flight based level measurement is well known from the state of the art, in the case of FMCW radar based level measurement for example from the published patent application DE 10 2013 108490 A1.

[0006] What all transit time-based level measuring devices have in common is that the vertical distance from an upper end area in the container to the surface of the corresponding filling material is measured using the signal transit time of the high-frequency signal reflected there. Using the recorded signal transit time, the fill level of the filling material in the container can then be determined indirectly by taking the container geometry into account. The container geometry must be configured in the respective level measuring device according to the customer or application. This can be done, for example, by manually entering key geometric data, such as the distance value from the level measuring device to the inner base of the container. Manual entry is technically possible, for example using suitable software tools such as smartphone apps, via the interface to the process control center, or via a display menu on the level measuring device.However, this only reduces the effort required to commission the level measuring device on the container to a certain extent.

[0007] It is therefore an object of the invention to provide a level measuring device that can be easily put into operation on the container.

[0008] The invention solves this problem by providing a method for defining a level measurement range for the transit time-based measurement of a relative or absolute level value of a product in a container. The method comprises the following steps:

[0009] - Attaching the appropriate transit time-based level gauge to an upper end of the container, ensuring that the container is completely empty,

[0010] - Time-of-flight based measurement of a distance to the inner bottom of the container, and

[0011] - Determination of the level measuring range by defining the level value of zero (percent) based on the measured distance value.

[0012] The distance value measured when the container is empty can either be defined directly as a fill level value of 0 (percent). Or this distance value is corrected by a defined offset, whereby this corrected distance value is defined as a fill level value of 0 (percent). Correction by a defined offset is useful, for example, if the container geometry results in a dead volume forming above the container bottom from which the corresponding quantity of filling material cannot be emptied. The zero value of the fill level defined according to the invention represents the lower limit of the fill level measuring range, whereby the measuring range can be defined either as an absolute measuring range or as a relative measuring range between 0% and 100%. In the case of an absolute measuring range, the upper limit can be defined by subtracting a defined absolute distance value from that, if applicable.The corrected distance value is subtracted, which is based on the level value of zero meters or zero percent. Accordingly, the extent of the measuring range in this case is determined by the absolute distance value.

[0013] If the fill level measuring range is defined as a relative measuring range, the 100% fill level value can be determined by multiplying the distance value measured when the container is empty, or the distance value corrected for the offset, by a specified factor of up to 1. It is advantageous if the factor is selected to be at least 0.75, in particular 0.95, so that the relative measuring range includes the largest possible vertical portion of the container. The overall advantage of the method according to the invention is that no knowledge of the container geometry is required in order to configure the fill level measuring device for the respective container or application.

[0014] The method according to the invention can, for example, be implemented directly in the respective level measuring device or in an integrated evaluation unit. With this design, the evaluation unit of the level measuring device calculates the relative level value during regular measuring operation based on the distance value measured there. The advantage of a direct implementation of the method in the level measuring device is that the method can be started by a corresponding switching unit on the level measuring device, such as a switch or an equivalent, display-based input mask on the level measuring device. However, it is also conceivable that the method according to the invention is initiated by a higher-level unit connected to the level measuring device, such as a process control center or a cloud-based controller. The term "unit 1In the context of the invention, this term is understood to mean, in principle, any separate arrangement or encapsulation of those electronic circuits which are intended for the specific intended use, e.g. for measurement signal processing or as an interface. Depending on the intended use, the respective unit can therefore comprise corresponding analog circuits for generating or processing analog signals. However, the unit can also comprise digital circuits, such as FPGAs, microcontrollers or storage media in conjunction with corresponding programs. The program is designed to carry out the required method steps or apply the necessary computing operations. In this context, different electronic circuits of the respective unit within the meaning of the invention can potentially also access a common physical memory or be operated using the same physical digital circuit.It is not relevant whether different electronic circuits within the unit are arranged on a common circuit board or on several interconnected circuit boards.

[0015] In addition to the evaluation unit, transit time-based level measuring devices suitable for the method according to the invention generally include

[0016] - a transmitting / receiving arrangement by means of which high-frequency signals can be transmitted towards the filling material or the container bottom and, after reflection there, can be coupled in as receiving signals, and

[0017] - a high-frequency unit which is designed to generate the high-frequency signals according to a defined time-of-flight principle and to determine the distance to the filling material surface or to the bottom of the container based on the corresponding received signals.

[0018] The design of these components depends on the respective time-of-flight method implemented. Specifically, the transmit / receive arrangement can be designed either as an antenna, for example a homing or planar antenna, or as a measuring probe. The transmit / receive arrangement is to be designed as an antenna, for example, if the radio-frequency unit generates or processes the radio-frequency signals as radar signals, in particular according to the pulse time-of-flight or FMCW method. Correspondingly, the transmit / receive arrangement is also to be designed as an antenna if the radio-frequency unit generates or processes the radio-frequency signals as ultrasonic signals, in particular according to the pulse time-of-flight method. In contrast, the transmit / receive arrangement is to be designed as a rod- or rope-shaped measuring probe if the radio-frequency unit generates and processes the radio-frequency signals according to the TDR method.

[0019] The invention is explained in more detail with reference to the following figures. They show:

[0020] Fig. 1 : A radar-based level gauge on a container, and

[0021] Fig. 2: a schematic representation of the method according to the invention.

[0022] To understand the invention, Fig. 1 shows a container 3 with a filling material 2, the fill level L of which is to be determined. Depending on the type of filling material 2 and the area of ​​application, the container 3 can be up to more than 100 m high. To determine the fill level L, a radar-based fill level measuring device 1 is mounted on the container 3 above the filling material 2 relative to the interior floor at an installation height d0 that varies depending on the container type.

[0023] As a rule, the level measuring device 1 is connected via a suitable interface, such as “4-20 mA”, “PROFIBUS”, “HART 1, or "Ethernet, with a higher-level unit 4, such as a local process control center or a decentralized server system. The measured fill level values ​​L(%) can be transmitted via this, for example to control any inflows or outflows of the container 3. However, other information about the general operating status of the level measuring device 1 can also be communicated via this. According to the time-of-flight measurement principle, the level measuring device 1 is attached to an opening in an upper end region of the container 3 in such a way that radar signals SHF, RHF can be transmitted via an antenna 11 into the container 3 or received after they have been reflected from the surface of the filling material. The radar signals SHF, RHF are generated within a high-frequency unit of the level measuring device 1, for example using the FMCW or pulse time-of-flight method, or processed after receipt.Instead of the antenna 11, in contrast to the embodiment shown, it is also conceivable to use a measuring probe as a transmitting / receiving arrangement, which extends vertically downwards into the container 3, provided that the high-frequency unit operates according to the TDR method.

[0024] After reflection of the emitted radar signals SHF at the surface of the filling material, the level measuring device 1 receives the reflected radar signals RHF, as shown in Fig. 1. The resulting signal propagation time t between emission and reception of the respective radar signal SHF, RHF behaves according to accordingly proportional to the distance d between the level measuring device 1 and the surface of the filling material 2. In this context, the variable "c" is the media-dependent radar propagation speed. To determine the signal propagation time t, the FMCW or pulse propagation time method can be implemented in the level measuring device 1. Accordingly, in the case of the FMCW method, the high-frequency unit can, for example, include a corresponding phase-locked loop. In the case of the pulse propagation time method, the high-frequency unit can be based on the principle of pulse subsampling.

[0025] For example, after appropriate calibration, the

[0026] The high-frequency unit or the level measuring device 1 in turn assigns the measured signal propagation time t to the respective distance d. The level measuring device 1 can thus determine the fill level L at least at a specific point according to d - C / Q LJ, provided the installation height do of the level measuring device 1 on the respective container 3 is known.

[0027] In practice, however, the installation height do can only be determined via a corresponding calibration measurement or corresponding knowledge of the container geometry. For this purpose, for example, corresponding design documents for the respective container type must be used. Such geometric knowledge is also required in order to be able to define the limits of the level measuring range corresponding to the container type. In this case, an absolute determination of the level value L may not be of interest, so that the limits of the measuring range define a level L% of 100% or 0%, within which the currently measured level is given as a relative value L%. Therefore, according to Fig. 2, a method can be carried out according to the invention to define the level measuring range 0% - 100% or its upper and lower limits, regardless of the container type and container geometry.As a result, after carrying out the procedure, the level measuring device 1 can output the relative or absolute level value L(%) in relation to the previously determined level measuring range 0% - 100% or 0 - Lmax.

[0028] To determine the level measuring range 0 (%) - 100% or Lmax, the level measuring device 1 measures the distance do to the bottom of the container 3 when the container 3 is empty, analogous to the regular level measurement. The measured distance value do or the corresponding signal propagation time to / 2 is then defined as the lower measuring range limit and thus either as an absolute level value L of zero meters, or as a relative level value L% of zero%. In order to exclude any sediment or a lower dead volume below the outlet in the container 3 as part of the usable quantity of the filling material 2, it is also possible according to the method to

[0029] 0 (%) = d o korr= (d0— y) individually define an absolute offset y, by which the zero value of the relative level value L(%) is defined slightly above the container bottom, as illustrated in Fig. 1. In the case of a relative measuring range, its 100% value is determined by either the distance do to the bottom or the corrected distance to the bottom do.kon- according to or is multiplied by a defined factor x. It is mandatory that x < 1

[0030] According to this inventive definition of the upper and lower limits of the relative measuring range 0% - 100%, the signal propagation time t or the distance d measured by the level measuring device 1 during regular measuring operation is therefore exactly inversely proportional to the relative level value L%, or vice versa. The level value L% is specified in relation to the initially determined measuring range limits.

[0031] In the case of a relative measuring range of 0% - 100%, it is advisable to select the factor x as close to 1 as possible, e.g. x = 0.95, so that the level measuring range of 0% - 100% extends vertically over the entire interior of the container 3. With regard to the upper measuring range limit of the relative level measuring range of 0% - 100%, i.e. with regard to the 100% value, it is however conceivable, analogous to the possible offset y of the lower measuring range limit, to select the factor x such that the 100% value is at the same height as an inlet of the container 3, as shown in Fig. 1. Instead of defining the measuring range or the upper limit 100% relative, it is alternatively also possible to define the upper limit Lmax according to

[0032] To be defined as an absolute value. The selected absolute distance value z corresponds to the desired absolute extent of the measuring range 0 m - Lmax and has a metric or comparable unit. In this context, the absolute distance value z should be selected such that the absolute measuring range 0 m - Lmax extends vertically, if possible, across the entire interior of the respective type on container 3.

[0033] Within the scope of the invention, it is not relevant in which unit the method for defining the level measuring range 0 (%) - 100% / Lmax explained in Fig. 2 is implemented. On the one hand, it is conceivable that the method is implemented in the level measuring device 1 itself or in an integrated evaluation unit. In this case, after defining the level measuring range 0 (%) - 100% / Lmax, the level measuring device 1 can output the relative level value L% in the subsequent measuring operation based on the measured distance value d. The level measuring device 1 can output the level value L(%), for example, visually via a display, or as a digital value via the interface to the higher-level unit 4. In the event that the method is carried out by the level measuring device 1 itself, it can be equipped with a corresponding switch, button or the like, so that the implementation of the method according to the invention is thereby initiated.

[0034] On the other hand, it is also conceivable for the method according to the invention to be carried out in the higher-level unit 4 after the higher-level unit 4 has initiated the measurement of the distance do to the container bottom on the level measuring device 1 and has queried the distance value do from the level measuring device. In this case, the level measuring device 1 only has to transmit the measured distance value d to the higher-level unit 4 during the subsequent, regular measuring operation, in which the level value L(%) based on this value is determined. Regardless of whether the absolute or relative level measuring range 0 (%) - 100% / Lmax is determined in the level measuring device 1 itself or in the higher-level unit 4, the advantage of the invention is that after carrying out the method, the level measuring device 1 can be used directly on the respective container 3 without separate calibration and without having to know its geometry.

[0035] List of reference symbols

[0036] 1 level gauge

[0037] 2 Filling material 3 Container

[0038] 4 Superior unit

[0039] 11 Antenna d Distance do Installation height or distance to the tank bottom L Absolute level value

[0040] Lmax Upper limit of the absolute measuring range

[0041] L% Relative level value

[0042] RHF, SHF (Reflected) radar signal t Signal propagation time x Factor y Offset z Absolute distance value

Claims

Patent claims 1. Procedure for determining a level measuring range (0 (%) - 100% / Lmax) for the transit time-based measurement of a particularly relative level value (L%) of a filling material (2) in a container (3), comprising the following method steps: - Providing the emptied container (3), - Attaching a transit time-based level measuring device (1) to an upper end region of the container (3), - Time-of-flight based measurement of a distance (do) to the bottom of the container (3), and - Determination of the level measuring range (0% - 100%) by defining the level value of zero when the container is empty (3) based on the measured distance value (do).

2. Method according to claim 1, wherein the measured distance value (do) is set equal to the fill level value of zero, or wherein the measured distance value (do) is corrected by a defined offset (y) and the corrected distance value (do.korr) is set equal to the fill level value of zero.

3. Method according to at least one of the preceding claims, wherein the fill level measuring range is defined as a relative measuring range (0% - 100%), and wherein the relative fill level value of 100% is defined on the basis of the distance value (do) measured when the container (3) is empty or the corrected distance value (do.korr), in particular by multiplying the distance value (do) measured when the container (3) is empty or the corrected distance value (do.korr) by a factor (x) of at most 1.

4. The method according to claim 3, wherein the factor (x) is chosen to be at least 0.75, in particular 0.

95.

5. Method according to claim 1 or 2, wherein the level measuring range is defined as an absolute measuring range (0 - / Lmax), and wherein the upper limit value Lmax is defined by the level measured when the container (3) is empty. Distance value (do) or the corrected distance value (do.korr) is subtracted by an absolute distance value (z).

6. Level measuring device (1 ), comprising: - A transmitting / receiving arrangement (11 ) by means of which high-frequency signals (SHF) can be transmitted towards the filling material (2) or the container bottom (31 ) and, after reflection there, can be coupled in as receiving signals (RHF), - a high-frequency unit which is designed o to generate the high-frequency signals (SHF) according to a defined propagation time principle, and o to determine the distance (d, do) to the filling material surface or to the bottom of the container (3) based on the corresponding received signals (RHF), and - an evaluation unit in which the method according to one of the preceding claims is implemented in order to determine or output the fill level value (L%) in relation to the fill level measuring range (0 (%) - 100 % / Lmax) on the basis of the measured distance value (d).

7. Level measuring device according to claim 6, comprising: - A switching unit, the actuation of which causes the method according to one of claims 1 to 4 to be carried out.

8. Level measuring device according to one of claims 6 to 7, wherein the transmitting / receiving arrangement is designed as an antenna (11) or as a measuring probe.

9. Level measuring device according to one of claims 6 to 8, wherein the high-frequency unit is designed to generate or process the high-frequency signals (SHF, RHF) as radar signals, in particular according to the pulse transit time or the FMCW method, provided that the transmitting / receiving arrangement is designed as an antenna (11).

10. Level measuring device according to one of claims 6 to 9, wherein the high-frequency unit is designed to generate the high-frequency signals (SHF, RHF) in particular according to the pulse transit time method as ultrasonic signals, provided that the transmitting / receiving arrangement is designed as an antenna (11).

11. Level measuring device according to one of claims 6 to 10, wherein the High-frequency unit is designed to generate or process the high-frequency signals (SHF, RHF) according to the TDR method, provided that the transmitting / receiving arrangement is designed as a measuring probe.

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