Event-based status detection during level measurement

Abstract

The invention relates to a method for detecting event-based states, such as foam formation or an operating stirring mechanism in a container (2), during radar-based measurement of a fill level (L) of a filling material (3) in a container (2). The method is characterized by the following steps, which are repeated in successive measuring cycles (n): generating an analysis curve (ZF) and detecting a specified characteristic value (A) of the analysis curve (ZF) in at least one specified sub-area (s1, s2, s3) of a measuring area (h); m , f). Characteristic value (A m , f) may be, for example, the amplitude of the local maximum (A m ) or the area under the analytical curve (f n According to the present invention, the characteristic value (A m The change or dispersion (σ) of the measured value (f) is determined during the measurement cycle (n). If the change or dispersion (σ) exceeds the corresponding threshold value (A m,lim ), the level measuring device 1 detects an event-based state. Thus, the occurrence of different events in the container (2) can be automatically given to the system controller (4) without the need for additional measuring instruments.

Description

Technical Field

[0001] The invention relates to a method for detecting an event-based state by means of a radar-based fill-level measuring device and also to a fill-level measuring device for carrying out the method. Background Art

[0002] In process automation technology, field devices are often used for capturing or modifying process variables. To this end, the function of the field device is based in each case on a suitable measuring principle in order to capture the corresponding process variable, such as fill level, flow rate, pressure, temperature, pH value, redox potential or conductivity. A wide variety of such field devices are manufactured and distributed by Endress+Hauser.

[0003] In order to measure the level of fillers in containers, radar-based measurement methods have been established because they are robust and require minimal maintenance. Within the scope of the present invention, the term "container" also refers to an unclosed container, such as a basin, a lake or a flowing body of water. The key advantage of radar-based measurement methods is its ability to quasi-continuously measure the level. In the context of this patent application, the term "radar" refers to a signal or electromagnetic wave with a frequency between 0.03 GHz and 300 GHz. Typical frequency bands in which level measurements are performed are 2 GHz, 6 GHz, 26 GHz or 78 GHz.

[0004] In the case of radar-based fill level measurement, the pulsed time-of-flight principle is an established measuring principle. Here, a pulse-shaped microwave signal is cyclically emitted in the direction of the filler and the flight time until a corresponding pulse-shaped reception signal is received is measured. Based on this measuring principle, fill level measuring devices can be implemented with relatively low circuit complexity. For example, a radar-based fill level measuring device operating according to the time-of-flight method is described in the unexamined patent application DE 10 2012 104 858 A1.

[0005] If more complex circuit technology is acceptable, FMCW (Frequency Modulated Continuous Wave) is a possible measuring principle for radar-based fill level measurement. For a typical construction of a fill level measuring device based on FMCW, reference is made to the unexamined patent application DE 10 2013 108 490 A1 as an example.

[0006] The measuring principle in the distance measurement method based on FMCW radar is based on the continuous but modulated emission of microwave signals. Here, the frequency of the microwave signal lies in a defined frequency band in the standard center frequency range. Here, the characteristic of FMCW is that the transmission frequency is not constant, but varies periodically within a defined frequency band. The change over time is linear as a standard in this case and has a sawtooth or triangular shape. However, in principle, sinusoidal changes can also be used. Compared with the pulse flight time method, the distance or material level when implementing the FMCW method is determined based on the instantaneous frequency difference between the current received signal and the microwave signal just emitted.

[0007] In addition to free-radiation radar measurement, in which microwave signals are emitted or received by an antenna, a variant of guided radar also exists independently of the pulsed time-of-flight method or FMCW. In this case, the microwave signal is guided by a conductive probe (e.g., a coaxial cable or a metal rod) that is lowered into the container. At the location of the filler surface, the received signal is generated in the probe and reflected along the probe toward the level measuring device. This variant of radar-based level measurement is also referred to by the term TDR (time domain reflectometry). This variant is advantageous because less power is required to operate the level measuring device due to the guided signal radiation.

[0008] For each of the aforementioned measuring principles (pulse time of flight and FMCW; independent of guided or free emission), a corresponding analysis curve is recorded to determine the material level from the received signal. In the case of the pulse radar-based method, due to the high pulse frequency, the analysis curve is generated by undersampling the reflected received signal. Therefore, the analysis curve represents the actual reflected received signal in a time-expanded manner. When the FMCW method is implemented, the analysis curve is generated by mixing the just transmitted microwave signal with the reflected received signal. Regardless of the measuring principle, the analysis curve reflects the amplitude of the reflected received signal as a function of the measured distance.

[0009] The fill level is determined from the analysis curve by detecting and locally specifying the corresponding local maxima. Ideally, there would be no further maxima besides those generated by the fill surface. Due to additional reflecting surfaces inside the container, in addition to the fill level maximum, further corresponding maxima may occur in the analysis curve in practice. However, only the maxima generated by the fill surface are relevant for the fill level measurement. Therefore, if possible, the additional information in the analysis curve is filtered out in order to make the fill level measurement more reliable.

[0010] Depending on the process plant, it may be advantageous to detect further events during the process of the fill level measurement, such as foam or sediment formation in the container, in order to be able to resolve these events if possible. It is therefore an object of the present invention to provide a fill level measuring device with which not only the fill level but also further properties or states can be detected in conjunction with the fill level measurement. Summary of the invention

[0011] The invention achieves this object by a method for detecting an event-based state by means of a radar-based fill level measuring device for measuring the fill level of a fill material located in a container. The method comprises the following method steps which are repeated in a continuous measuring cycle:

[0012] - emitting a microwave signal in the direction of the filler,

[0013] - receiving the received signal after reflecting the microwave signal inside the container,

[0014] - generating an analysis curve based at least on the received signal, the analysis curve being generated in such a way that the signal strength of the received signal is reproduced as a function of the measured distance,

[0015] - detecting a specified characteristic value of the analysis curve in the measurement region or in at least one defined sub-region of the measurement region.

[0016] According to the invention, in the measurement cycle that is being performed, a change and / or a deviation of a characteristic value is determined, wherein an event-based state is detected if the change or the deviation exceeds a specified threshold value.

[0017] In the context of the present invention, an event-based state is associated with the occurrence of a specific state during the process of the level measurement. This can be, for example, agitation of the stirring mechanism, the formation of foam or sediment in the container. When such an event-based state is detected by the level measurement device, this information can therefore be transmitted to the process system controller, for example, in order to output a corresponding control command based thereon, such as switching off a heater or switching off a stirring mechanism.

[0018] However, an event-based state according to the invention may also be the occurrence of a fault in the fill level measuring device itself. Depending on the type of event-based state, the occurrence of such a state can therefore also be associated with the fact that the fill level value detected by the fill level measuring device is inaccurate or unreliable. The cause of this may be, for example, an antenna of the fill level measuring device 1 that is affected by deposits. Even if such a state exists, it can be transmitted again to a higher-level unit in order, for example, to output a corresponding warning.

[0019] The solution according to the invention therefore offers the advantage that the occurrence of various events in the container can be communicated to the system controller in an automatic manner without the need for additional measuring instruments. Thus, the operational reliability of the entire process plant can be increased.

[0020] The characteristic value according to which the analysis curve is detected can be defined in various ways within the scope of the invention. On the one hand, the area under the analysis curve can be detected as a characteristic value at least in a sub-region of the measurement area. In the case of such a definition, for example, the power of the received signal reflected from this sub-region can be determined. An increase in area or power in a sub-region adjacent to the antenna with increasing measurement cycles exceeding a threshold value defined for this purpose can be interpreted as, for example, an accumulation of deposits on the antenna. A decrease in power in a more distant sub-region below the corresponding threshold value can be caused by foam formation.

[0021] As an alternative or in addition to the area, the amplitude (especially the local maximum) can be detected as a characteristic value in the analysis curve. Assuming that the sub-area to be observed is at the same height as the stirring mechanism, changes in the amplitude greater than a specified threshold can be interpreted as, for example, a rotating stirring mechanism.

[0022] A third possibility for defining a characteristic value is to detect the number of local maxima in at least one sub-area of ​​the measuring area as a characteristic value. For example, depending on the type of filler, exceeding a threshold value for the number of maxima can be interpreted as the presence of disruptive objects, such as deposits on the inner wall of the container.

[0023] Analogously to the method according to the invention, the object on which the invention is based is also achieved by a radar-based fill level measuring device, which is suitable for carrying out the method according to at least one of the above-described embodiment variants. It therefore comprises the following components:

[0024] a signal generating unit which is designed to emit a microwave signal in the direction of the filler in each of the consecutive measuring cycles,

[0025] - a receiving unit designed to receive the reception signal after reflecting the microwave signal inside the container,

[0026] - an evaluation unit, which is designed

[0027] o generating, at least based on the received signal, in each measurement cycle an analysis curve representing the signal strength of the received signal as a function of the measured distance,

[0028] o detecting a defined characteristic value of an analysis curve in at least one defined sub-area of ​​the measuring area,

[0029] o determining changes and / or dispersions of characteristic values ​​in the measuring cycles carried out,

[0030] o If the change or deviation exceeds a specified threshold, an event-based state is detected,

[0031] o The fill level is determined by analyzing the curve, at least in the case where the change or deviation does not exceed a specified threshold value.

[0032] In the context of the present invention, the term "unit" is understood to refer in principle to any electronic circuit designed to be suitable for its intended purpose. Thus, as required, it can be an analog circuit for generating or processing the corresponding analog signal. However, it can also be a (semiconductor-based) digital circuit, such as an FPGA or a storage medium that interacts with a program. In this case, the program is designed to perform the corresponding method steps or apply the necessary computing operations of the unit in question. In this case, in the sense of the present invention, the various electronic units of the level measuring device can also potentially access a common physical memory or operate via the same physical digital circuit.

[0033] In a further embodiment of the fill level measuring device, the evaluation unit can preferably be designed so that if a threshold value is exceeded or fallen below, the occurrence of a specific event state is output, in particular graphically or as an electrical signal. For example, the corresponding electrical signal can be transmitted to the system controller via a suitable bus system.

[0034] Depending on the event-based definition of the state, the fill level measuring device can also be designed such that a new fill level value is not determined from the current analysis curve if a change or deviation exceeds or falls below a specified threshold value.

[0035] Furthermore, it is advantageous if the sub-area for detecting the characteristic value can be manually configured at the level measuring device. Thus, the level measuring device can be adapted to a specific container or a specific filling material. For example, if the antenna is prone to deposits due to dusty filling materials or due to moist filling materials, the sub-area can be manually placed at a location adjacent to the measuring area of ​​the antenna. If a stirring mechanism is present in the center of the container or in the center of the measuring area, the sub-area in which the characteristic value is to be determined can be placed at this location in the measuring area. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The present invention is explained in more detail with reference to the following drawings. Shown below is:

[0037] Figure 1 : Arrangement of radar level measuring device,

[0038] Figure 2 : Circuit technology structure of the material level measuring device, and

[0039] Figure 3 : Analysis curve according to the present invention. DETAILED DESCRIPTION

[0040] In order to understand the present invention, Figure 1 A typical arrangement of a fill level measuring device 1 based on a free-radiation radar on a container 2 is shown. In the container 2 is a filling material 3, whose fill level L is determined by the fill level measuring device 1. For this purpose, the fill level measuring device 1 is mounted on the container 2 above the maximum permissible fill level L. Depending on the field of application, the installation height h of the fill level measuring device 1 above the container bottom can be greater than 100 m.

[0041] Typically, the fill level measuring device 1 is connected to a higher-level unit 4, such as a process control system or a decentralized database, via a bus system, such as "Ethernet", "PROFIBUS", "HART" or "WirelessHART". On the one hand, information about the operating state of the fill level measuring device 1 can thus be communicated. On the other hand, information about the fill level L can also be transmitted in order to control any inflow and / or outflow that may be present at the container 2.

[0042] because Figure 1 The level measuring device 1 shown in FIG. 1 is designed as a free-radiating radar, so it comprises a corresponding antenna. As indicated, the antenna can be designed as a horn antenna, for example. In particular, in the case of radar frequencies above 100 GHz, the antenna can also be implemented as a planar antenna. Regardless of the design, the antenna is oriented in such a way that a corresponding microwave signal S is emitted in the direction of the filler 3. HF .

[0043] Microwave signal S HF It is reflected at the surface of the fill material 3 and, after a corresponding signal flight time, is emitted as a received signal E at the antenna of the fill level measuring device 1 . HF In this case, the microwave signal S HF 、E HF The signal flight time of φL depends on the distance d=hL between the fill level measuring device 1 and the filler surface.

[0044] During the level measurement, the filler 3 often undergoes a chemical reaction, a grinding process or a stirring process. Figure 1 In contrast to the illustration shown in FIG, the filler 3 can therefore have a foamed filler surface. Due to high temperatures or a dusty atmosphere, deposits also form on the inner wall of the container or on the antenna. Such states during the level measurement can therefore lead to the determination of inaccurate or incorrect filler level values ​​L. For the operation of a process plant, it is therefore advantageous to be able to identify the respective state in order to stop the chemical reaction, for example in the case of undesired foam formation, in the simplest case by stopping the inflow or by switching off the heating system.

[0045] According to the invention, this state can be determined, depending on the event, by means of analysis curves ZF1, ZF2 generated by the fill-level measuring device 1. n In principle, by converting the received signal E HF The microwave signal S HF When the FMCW method is implemented by mixing, the level measuring device 1 generates analysis curves ZF1, ZF n , where the microwave signal S HF For this purpose, the transmission is continuous and within a frequency band with a sawtooth frequency variation.

[0046] In the case of the pulse time-of-flight method, the received signal E of the pulse is HF Undersampling is performed to generate analysis curves ZF1, ZF n , where the pulse frequency of the sampling signal for this purpose is the same as the microwave signal S HF or receive signal E HF The pulse frequencies are slightly different.

[0047] In the case of both FMCW and pulsed time-of-flight methods, the analysis curves ZF1, ZF n represents the signal amplitude A of the received signal EHF according to the measuring distance d. In the case of fill level measurement, the corresponding measuring area h extends from the antenna of the fill level measuring device 1 to the bottom of the container 2. The fill level L can be determined by the fill level measuring device 1 based on the analysis curves ZF1, ZF n To determine, because the microwave signal S HF The reflection at the filler surface is shown in the analysis curves ZF1, ZF n Generate a local maximum A in m，1 , A m，n Since the level measuring device 1 is designed to determine the distance from the local maximum value A m，1 , A m，n The fill level measuring device 1 can calculate the fill level L based on the corresponding distance d.

[0048] exist Figure 2 In FIG. 1 , two analysis curves ZF1, ZF2 recorded in a first measurement cycle 1 and also in a subsequent measurement cycle n are schematically shown. n Based on these two analysis curves ZF1 and ZF n The method according to the invention for detecting possible event-based states is shown in more detail: As can be seen, the measuring region h is in this case divided into three sub-regions s1, s2, s3, wherein the first sub-region s1 adjoins the antenna of the fill level measuring device 1. The third sub-region s3 adjoins the bottom of the container. In the second central sub-region s2, the analysis curves ZF1, ZF2 correspond to the measurement distance d from the filling surface. nrespectively have corresponding amplitudes A m，1 , A m，n The filling level measuring device 1 uses this maximum value to determine the filling level L.

[0049] According to the invention, for event-based detection of states, use is made of the effect that, with the measurement cycle n carried out, the curves ZF1, ZF n At least in each sub-area s1, s2, s3. n The third sub-area s3 is visible, towards the measurement cycle n, the area f n The decrease in can be caused, for example, by the foaming of the filler 3. According to the invention, in this event state, in the analysis curves ZF1, ZF n The area f in the third sub-region s3 under n can be defined as a characteristic value, wherein the area f in this sub-region s3 is additionally determined by the fill level measuring device 1 n s1, s2, s3 with the measurement cycles n being performed. If a previously defined minimum area is below a threshold value, the fill level measuring device 1 can infer from this that foam formation has occurred as a specific event-based state. In this respect, it is suitable according to the invention to design the fill level measuring device 1 in such a way that the number and the respective positions of the subareas s1, s2, s3 can be manually adapted to the respective container 2 or filling material 3.

[0050] In addition to the area f n In addition, the maximum amplitude of the material level A m，1 , A m，n Can also be used as a characteristic value: Amplitude A m，n Below the specified minimum amplitude A m，min The following can be assigned, for example, foam formation as an event-based state. Amplitude A of the maximum level m，1 , A m，n Other causes of the attenuation may lie, for example, in boiling of the filler 3 or changes in the dielectric value of the filler 3 .

[0051] As the area f n or Amplitude A m，1 , A m，n Alternatively to , the number of maxima (in the third sub-range s3) can also be used as a characteristic value for monitoring over a measuring cycle n. n The reduction in the number of peripheral maxima in φ can again be interpreted by the fill level measuring device 1 as foam formation.

[0052] On the other hand, if the corresponding threshold value is exceeded, the analysis curves ZF1, ZF nAn area or an amplitude of φ that increases with measuring cycle n can be detected by the fill level measuring device 1 as an accumulation of deposits on the antenna, if this area is defined as a characteristic value to be monitored.

[0053] According to the invention, not only the change in the possible characteristic values ​​but also their dispersion σ over the past measurement cycles n can be used to detect event-based states. This is illustrated by way of example based on Figure 3 The maximum value of the material level in m σ of the amplitude. In this case, the term "deviation" is not limited to a specific mathematical definition, such as variance or mean square error. If the fill level measuring device 1 determines a deviation σ of the amplitude as a characteristic value, which again lies above a predetermined threshold value, the fill level measuring device 1 can detect, for example, an operation of a stirring mechanism inside the container 2 as an event-based state. Conversely, a fall below the deviation σ can be interpreted by the fill level measuring device 1 as a malfunction of the stirring mechanism.

[0054] Depending on how high the threshold of the deviation σ is chosen, foam formation can again be assigned as an event-based state if the deviation σ is exceeded. m，1 , A m，n , it is also possible to determine the dispersion σ of other characteristic values, such as the area f over the measurement cycle n performed n The deviation.

[0055] If the fill-level measuring device 1 detects one of the possible event-based states, it can use this to declare that the fill-level measuring device 1 has been detected according to the evaluation curves ZF1, ZF n The fill level value L determined is an implausible, incorrect measurement or is deleted.

[0056] On the other hand, if an event-based state is detected, the fill level measuring device 1 can transmit this to the higher-level unit 4. If appropriate, this makes it possible to react to the event-based state, for example by shutting down a pump or a heating system in the process plant. To this end, the fill level measuring device 1 must be designed to output a corresponding electrical signal via a suitable bus protocol in the case of an event-based state. Of course, if the fill level measuring device 1 has a display or other (light) indicator, it can also display the event-based state in a graphical manner.

[0057] Reference numerals list

[0058] 1 Level measurement device

[0059] 2 Container

[0060] 3. Filling

[0061] 4 More advanced units

[0062] A Amplitude

[0063] d Measurement distance

[0064] E HF Receiving Signals

[0065] f n Analyze the area under the curve

[0066] h Installation height or measurement area

[0067] L Material level

[0068] n Measuring cycle

[0069] S HF Microwave signal

[0070] s 1,2,3 Sub-areas of the measurement area

[0071] ZF 1,n Analysis curve

[0072] σ Deviation

Claims

1. A method for detecting an event-based state by means of a radar-based fill level measuring device (1) for measuring the fill level of a filling material (3) located in a container (2), the method comprising the following method steps which are repeated in a continuous measuring cycle: - emitting a microwave signal in the direction of the filler (3), - receiving a reception signal after reflecting the microwave signal inside the container (2), - generating an analysis curve based at least on the received signal, wherein the analysis curve is generated such that the signal strength of the received signal is reproduced as a function of the measured distance, - detecting a defined characteristic value of the analysis curve in at least one defined sub-area of ​​the measurement region, wherein a change and / or a deviation of the characteristic value is determined over the measuring cycles carried out, and wherein the event-based state is detected if the change or the deviation exceeds a prescribed threshold value, Therein, the area under the analysis curve is detected as a characteristic value at least in a sub-region, and wherein foam formation can be detected as an event-based state.

2. A material level measuring device based on radar, for performing the method according to claim 1, the material level measuring device comprising the following components: a signal generating unit, which is designed to emit a microwave signal in the direction of the filler (3) in each of the successive measuring cycles, a receiving unit, which is designed to receive a reception signal after reflecting the microwave signal inside the container (2), - an evaluation unit, the evaluation unit being designed o generating, at least based on the received signal, in each measurement cycle an analysis curve representing the signal strength of the received signal as a function of the measured distance, o detecting a defined characteristic value of the analytical curve in at least one defined sub-area of ​​the measuring area, o determining the change and / or the dispersion of the characteristic value over the measuring cycles carried out, o if the change or deviation exceeds a specified threshold, detecting the event-based state, o At least when the change or deviation does not exceed a specified threshold, the material level is determined by the analysis curve. 3 . Fill level measuring device according to claim 2 , wherein the evaluation unit is designed to output the occurrence of the event state. 4 . Fill level measuring device according to claim 3 , wherein the evaluation unit is designed to output the occurrence of the event state graphically or as an electrical signal. 5 . The fill level measuring device according to claim 2 , wherein the sub-range for detecting the characteristic value is manually configurable.

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