Detection of foreign bodies in process media

Abstract

The invention relates to the detection of possible foreign bodies (4), such as splinters, metal chips or powder clumps in process media (2), which are located in a container segment (3) which is transparent for radar signals (S, R, THF) at least in some regions. A radar-based measurement signal (SHF) is emitted into the process medium (2) by a first high-frequency unit (11). After interaction has taken place between the measurement signal (SHF) and the process medium (2) or the foreign body (4), a transmitted portion (THF) and / or a reflected portion (RHF) hereof is detected by a corresponding high-frequency unit (11, 12, 13). Based on the detected portion (THF, RHF) of the emitted measurement signal (SHF), a superordinate evaluation unit (14) can detect a possible foreign body (4) as such in real time.

Description

[0001] Detection of foreign bodies in process media

[0002] The invention relates to the detection of foreign bodies in process media.

[0003] In process automation technology, field devices and measuring systems are often used to record or influence process variables. For the direct recording of specific process variables, individual field devices of a corresponding field device type are used. In this case, the field device type is equipped with a sensor or measuring principle specific to the process variable, as in the case of level measuring devices, flow meters, pressure and temperature measuring devices, pH-redox potential measuring devices, or conductivity measuring devices. Accordingly, such field device types directly record, for example, the level, flow, pressure, pH value, temperature, conductivity, or redox potential of corresponding process media as process variables.

[0004] In addition to process variables that can be determined directly, there are also those that cannot be measured on the basis of a single measuring principle, such as the complete implementation of a chemical or biological reaction.

[0005] The recording of such complex process variables, in particular, requires the use of measuring systems that combine various selected field device types or measuring principles. From the correlation of the correspondingly different physical variables, an evaluation unit of the measuring system can then determine the complex process variable, such as the completion of a fermentation process. A wide variety of such field device types and measuring systems are manufactured and distributed by the Endress + Hauser Group.

[0006] In addition to monitoring the actual process variable, it is also becoming increasingly important to determine any foreign bodies within the underlying process media. Depending on the type of process plant or the area of ​​application, the container segment in which any foreign bodies are to be detected can be a closed pipe, a section of an open line, or even a segment of the tank interior. In the context of the invention, a foreign body is generally understood to be a locally restricted, undesirable component in the process medium. This includes, for example, splinters, metal shavings, or nutshell pieces in liquid or pasty process media in the food industry, as well as powder lumps or hardened deposits resulting from insufficient mixing of the process medium.Another problem in this context is that any foreign bodies can cause a reduction in the flow velocity of the process medium. The publication DE 102021133787 A1 describes a measuring system based on various field devices or field device types. The various field devices each serve primarily to determine an independent process variable on a pipeline section. In addition to these actual process variables, any foreign bodies are detected incidentally by checking the various measured values ​​of the different field devices or field device types for a specific temporal correlation in the higher-level process control system. However, in most processes, this random circumstance whereby several field devices or different field device types are used on the relevant pipeline section per se does not exist.Due to the higher-level correlation test, it is also difficult to detect any foreign bodies in real time based on this principle.

[0007] The invention is therefore based on the object of providing a measuring system that is as simple as possible and by means of which any foreign bodies in process media can be detected reliably and as real-time as possible.

[0008] The invention solves this problem by means of a measuring system, described below, for detecting foreign bodies in a process medium located in a container segment that is at least partially transparent to radar signals. The measuring system is based on a first high-frequency unit, which is designed and arranged on the container segment in such a way as to be able to emit a radar-based measuring signal into the process medium in the direction of a first beam axis. In the context of this invention, the term "beam axis" corresponds to the vector along which the emission intensity of the measuring signal is maximum. Due to the reciprocal properties of radar antennas, this corresponds to the vector along which the reception sensitivity of the received measuring signal component is highest.

[0009] The measuring system according to the invention utilizes the effect of receiving the transmitted and / or reflected or scattered portion of the transmitted measurement signal after the radar-based measurement signal has been transmitted into the process medium and the corresponding interaction has occurred. Since reflection and scattering can have the same effect on the signal, or at least cannot be separated from one another in the case of purely transmissive measurements, the reflected portion is also understood to mean the scattered portion in the following. According to the invention, any foreign body is detected based on the transmitted portion and / or the reflected portion, or depending on how high this portion is at the moment. A suitably designed evaluation unit of the measuring system serves this purpose.The advantage of this is that, depending on the type of foreign body, the transmitted and / or reflected portion changes significantly and instantaneously, enabling real-time and reliable foreign body detection. The vessel segment on which the measuring system is located can therefore also be a section of pipeline through which the process medium flows, as instantaneous detection is possible here, even despite potentially high flow velocities.

[0010] Within the scope of the invention, it is conceivable to determine only one of the two components, i.e. either the transmitted component or the reflected component of the emitted measurement signal. In the simplest case, this can be implemented by arranging a reflector on the container segment opposite the first radio-frequency unit in the first beam axis. In this case, the first radio-frequency unit is to be designed such that, after the emitted measurement signal has been reflected by the reflector, it can also receive the transmitted component, for example via a transmit / receive switch. As an alternative to a reflector, it is conceivable to additionally provide a second radio-frequency unit to detect the transmitted component in order to receive the transmitted component of the emitted measurement signal from the direction of a second beam axis.For this purpose, the second high-frequency receiving unit should preferably be arranged directly opposite the first high-frequency unit on the container segment. This means that the angle between the first and second beam axes is 165° and 195°.

[0011] To detect the reflected portion of the transmitted measurement signal, the measurement system may comprise a third radio-frequency unit that receives this portion from the direction of a third beam axis. For this purpose, this third radio-frequency unit is preferably arranged relative to the first radio-frequency unit such that the first beam axis and the third beam axis intersect at an angle of no more than 90°, in particular approximately 45°.

[0012] In terms of evaluation technology, the measuring system according to the invention or its evaluation unit can detect any foreign body in the simplest case by comparing the detected portion with a corresponding reference value: If the transmitted portion falls below a first reference value, or if the reflected portion exceeds a second reference value, this is considered a foreign body detection. The reference value represents the transmitted portion or reflected portion that the corresponding high-frequency unit receives with a known process medium and demonstrably without any foreign body.

[0013] The frequency at which the high-frequency units transmit or receive the radar signals depends on the type of process medium and the expected foreign matter. In principle, the entire radar spectrum with frequencies between 0.1 GHz and 500 GHz is suitable. In the case of liquid process media with a dielectric value between 1 and 10, frequencies between 0.5 GHz and 10 GHz are particularly suitable. For improved coupling and decoupling, it is also advantageous in this context to arrange a dielectric matching structure between the respective high-frequency unit and the container segment. The dielectric value of the dielectric matching structure lies between that of the process medium and the dielectric value of the high-frequency unit.

[0014] Within the scope of the invention, it is not strictly specified that the measurement signal be generated at a constant frequency. Depending on the application or process medium, it is also conceivable for the first high-frequency unit to transmit the measurement signal in a temporally frequency-modulated manner, as in the case of frequency-modulated continuous wave radar, for example with a sawtooth-shaped frequency change. Furthermore, it is possible to design the measuring system or the high-frequency unit(s) so that radar signals are transmitted one after the other or periodically alternating at two or more differing frequencies and received proportionally. In this case, the evaluation unit can detect any foreign bodies at each frequency based on the respective transmitted or reflected portion. The advantage of this is that it may also detect foreign bodies that are difficult to detect using transmission or reflection measurements at certain radar frequency ranges.In this context, it is also conceivable to emit broadband noise as radar signals.

[0015] To increase the resolution of foreign body detection, the measuring system according to the invention can also be expanded with a fourth high-frequency unit, which, analogous to the first high-frequency unit, emits a radar-based measurement signal into the process medium, but in the direction of a fourth beam axis that runs at a different angle to the first beam axis. This at least increases the reflection or scattering from any foreign bodies, which in turn leads to higher resolution.

[0016] If the measuring system detects both a transmitted and a reflected portion of the transmitted measurement signal, the evaluation unit can mathematically weight the transmitted and reflected portions, respectively, and then add or subtract the weighted portions to detect any foreign bodies based on the sum or difference of the weighted portions. The weighting, in turn, depends on the type of process medium and the installation situation of the high-frequency units.

[0017] The term “unity 1Within the scope of the invention, "process control" is understood to mean, in principle, any electronic circuit or hardware that is suitably designed for the intended purpose. Depending on the requirements, it may be an analog circuit for generating or processing corresponding analog signals. However, it may also be a digital circuit, such as an FPGA or a storage medium in conjunction with a program. The program is designed to carry out the corresponding process steps or apply the necessary computing operations of the respective unit. In concrete terms, the evaluation unit may therefore also be, for example, a process control center of the process plant or a decentralized server.

[0018] Specifically, the high-frequency units can include, for example, an antenna arrangement for transmitting or receiving the measurement signals. The higher the frequency, the more suitable a planar antenna structure is. Depending on whether the signal is being received or transmitted, the respective high-frequency unit is based, for example, on a controlled high-frequency oscillator for high-frequency generation. For signal processing of the received measurement signal component, the corresponding high-frequency unit for frequency conversion from the RF range can be based, for example, on the principle of sampling or mixing.

[0019] The invention is explained in more detail with reference to the following figures. It shows: Fig. 1: A measuring system according to the invention for detecting any foreign bodies in a pipeline section, and

[0020] Fig. 2: a time-resolved measurement curve of the transmitted or reflected part of the measurement signal, which shows a temporally periodic pattern.

[0021] To understand the invention, Fig. 1 shows a pipe section 3 with a circular diameter through which a process medium 2 flows at a controlled flow rate. The pipe section 3 is part of a process plant, which is used, for example, for processing food. The process is controlled by a higher-level unit 14, such as a local process control system or a decentralized server. For this purpose, the higher-level unit 14 is connected to the process control system via a suitable interface, such as "4-20 mA", "PROFIBUS", "HART" 1, or "Ethernet" with the necessary actuators, such as pumps or valves, and field devices, such as flow meters. This allows the higher-level unit 14 to control inflows or outflows to or from pipe section 3 as needed to regulate the flow rate.

[0022] In addition, the higher-level unit 14 in the case shown in Fig. 1

[0023] 1 shows a component of a measuring system 1 according to the invention, by means of which any foreign bodies 4 flowing within the process medium 2 can be detected. For this purpose, the measuring system 1 in the embodiment shown in Fig. 1 also comprises three high-frequency units 11, 12, 13, which are arranged at the same height in the pipeline section 3 with respect to the flow direction and each in a region permeable to radar signals S, R, THF. The permeability in these regions can be achieved, for example, by correspondingly transparent windows in the pipeline section 3, which are based on a suitable plastic.

[0024] Each of the three high-frequency units 11, 12, 13 is characterized by a beam axis αs,R,T, along which a high-frequency measurement signal S HF is transmitted to the process medium 2 and subsequently received in part. As shown in Fig. 1, the three high-frequency units 11, 12, 13 are each arranged on the pipeline section 3, offset by 90° from one another, with the beam axes αs,R,T running in a common plane and being aligned towards a common center point in the pipeline section 3. This means that the first high-frequency unit 11 and the second high-frequency unit 12 are arranged directly opposite one another on the pipeline section 3 and are aligned with one another such that the first beam axis αs of the first high-frequency unit 11 and the second beam axis αs are virtually congruent with one another or are at an angle of 180° to one another.

[0025] The first high-frequency unit 11 is used to transmit the measurement signal SHF, while the second high-frequency unit 12 is used to receive it. Due to their alignment with one another, the second high-frequency unit 12 receives a transmitted component THF of the transmitted measurement signal SSHF, which is not absorbed or scattered when the measurement signal SHF passes through the process medium 2. The third high-frequency unit 13 is also used for reception. As is illustrated in Fig. 1, its third beam axis aR runs at an angle a of 90° to the first beam axis as. As a result, the third high-frequency unit 13 does not receive the transmitted component THF of the transmitted measurement signal SHF. Rather, the third high-frequency unit 13 receives the transmitted component THF of the transmitted measurement signal SHF, for which the angle aR is shown in Fig.In the case illustrated in Figure 1, in which a foreign body 4 is currently located in the process medium 2 at the level of the high-frequency units 11, 12, 13, a reflected portion RHF of the high-frequency signal SHF emitted by the first high-frequency unit 11 is detected. At the same time, under these circumstances, the transmitted portion Tnran of the second high-frequency unit 12 decreases.

[0026] In the embodiment shown in Fig. 1, the coupling and decoupling of the measurement signal S,T,RHF into and out of the process medium 2 is optimized by dielectric matching structures 110, which are arranged between each of the three high-frequency units 11, 12, 13 and the container segment 3. For this purpose, the material on which the matching structures 110 are based has a dielectric value that lies between that of the process medium 2 and the dielectric value of the high-frequency unit 11, 12, 13. In this regard, a suitable material, for example, is a suitable glass, a dielectric plastic or a ceramic. The coupling is further optimized by a funnel-shaped widening of the matching structures 110 towards the container segment 3 or towards the process medium 2, as shown in Fig. 1.

[0027] Since the high-frequency units 11, 12, 13 each have their own interface, such as “4-20 mA”, “PROFIBUS”, “HART 1, or “Ethernet 1 are connected to the higher-level evaluation unit 14, the second high-frequency unit 12 and the third high-frequency unit 13 can transmit the values ​​of the respectively detected components RHF, THF to the evaluation unit 14 so that they can be processed there. It is irrelevant whether the transmission of the corresponding values ​​takes place in analog form, for example as a raw signal, or on the basis of a digital protocol. It goes without saying that other information can also be transmitted via the respective interface, for example parameterization data for the high-frequency units 11, 12, 13 or information on their general operating status.

[0028] Based on the transmitted values ​​of the measured transmission / reflection components R,T HF, the evaluation unit 14 can infer the presence of any foreign bodies 4 in the process medium 2: If the transmission component THF decreases and / or the reflection component RHF increases, the current presence of a foreign body 14 can be inferred.

[0029] The evaluation unit 14 can determine any decrease or increase by comparing the currently measured transmission / reflection ratios R,THF with previously determined reference values ​​for the target transmission or target reflection. The only relevant requirement here is that the reference values ​​apply to the respective pipeline section 3 and the respective type of process medium 2. It must be ensured that the specific reference values ​​have been determined, for example, during a calibration under a process medium 2 that is demonstrably free of foreign matter.

[0030] Since the embodiment of the measuring system 1 according to the invention shown in Fig. 1 determines both the transmitted component THF and the reflected component RHF, it is possible in this embodiment to additionally check the detected components RHF, THF or the foreign body detection for plausibility: If a reduced, transmitted component THF is detected with a simultaneously increased, reflected component RHF, it can be assumed that the associated detection of a foreign body 4 can be regarded as plausible. In other cases, i.e., if only one of the components R,THF changes, or if both components R,THF change in the same direction, the measurement as a whole is implausible and it can be assumed, for example, that the second high-frequency unit 12 or the third high-frequency unit 13 is defective.

[0031] The foreign body detection system according to the invention allows for appropriate responses to any foreign bodies 4 detected within the process plant: If a foreign body 4 is detected, the evaluation unit 14 can, for example, initiate the closing of a shutoff valve located downstream of the foreign body 4 or the high-frequency units 11, 12, 13 in the flow direction to prevent the foreign body 4 from being inadvertently filled into the system. Alternatively, the process medium 2 can be diverted downstream of the high-frequency units into a bypass, through which any rejects are disposed of. This allows the process plant to be operated more safely and efficiently overall.

[0032] The monitoring according to the invention is all the more reliable the more often the measuring system 1 according to the invention examines the process medium 2 for any foreign bodies 4. The previously described inventive method, according to which a radar-based measuring signal SHF is emitted into the process medium 2 by the first high-frequency unit 11, the transmitted portion THF of the emitted measuring signal SHF is measured by the second high-frequency unit 12 and the reflected portion RHF of the emitted measuring signal SHF is measured by the third high-frequency unit 13, and any foreign body 4 is located by the higher-level evaluation unit 14 based on the transmitted portion THF and the reflected portion RHF, can be repeated at a defined periodicity. The periodicity can be freely selected, e.g., between one millisecond and up to one hour.A low periodicity in the range of one hour is only recommended if the process medium 2 is not flowing, or if, in contrast to the embodiment shown in Fig. 1, the container segment 3 is not a pipeline section, but, for example, a segment of a storage container. In this context, the measured components THF, RHF may need to be weighted differently by the evaluation unit 14 depending on the exact alignment of the high-frequency units 11, 12, 13 to one another, the type of process medium 2, and the foreign body 4 to be expected, in order to be able to determine the possible foreign body 4 more reliably based on the weighted components THF, RHF.

[0033] In contrast to periodic measurements, it is also conceivable to examine the process medium 2 for foreign bodies 4 virtually continuously and thus in real time. For this purpose, the previously described method must be carried out continuously. This means that the high-frequency units 11, 12, 13 must transmit and receive continuously and transmit the values ​​of the transmission component (THF) and the reflection component (RHF) to the evaluation unit 14 virtually continuously.

[0034] The temporal value curves of a quasi-continuously measured proportion THF, HF are shown schematically in Fig. 2. In addition, the special case is shown therein, according to which the measurement of the proportions THF, RHF is superimposed by a periodic event. This event can be, for example, an agitator which, during operation, periodically swings through at least one of the beam axes a5, R, T. As can be seen from the corresponding measurement curves (a) and (b), such a superposition takes the form of a periodically recurring offset M or, more generally, in the form of a characteristic curve pattern M in the recorded measurement curves (a, b). Measurement curve (a) represents a measurement period in which no foreign body 4 is present, whereas the measurement period on which measurement curve (b) is based is influenced by a foreign body 4, as the corresponding negative peaks in measurement curves (b) and (c) show.The underlying measurement scenario involves a foreign body 4 which flows through the pipe section 3 during the corresponding measurement period and accordingly causes only a pulse-shaped reduction of the transmission component THF, as outlined in the measurement curves (b) and (c) of Fig. 2.

[0035] As can be seen from the measurement curves (a) and (b) in Fig. 2, in the case of periodic superpositions, due to the temporary offset M, it is not possible to reliably infer the presence of any foreign bodies 4 simply by comparing the currently detected portion THF, RHF with a reference value. Therefore, in such a case, it is possible within the scope of the invention to detect any temporally periodic progression patterns M based on the time-resolved measurement curve (a, b) of the transmitted portion THF or the reflected portion RHF. From this, in turn, a compensated measurement curve (c) can be created which is compensated with regard to the temporally periodic progression pattern M, as shown in Fig. 2.

[0036] Accordingly, the compensated measurement curve (c) shown in Fig. 2 can be obtained by determining from the original measurement curve (b) those periodic time periods and the associated offset values ​​M caused by the periodic superposition, and subtracting the determined offset values ​​M in the respective time periods from the corresponding measurement points in the original measurement curve (b). In order to recognize or extract periodic patterns as such, self-learning algorithms or specific process knowledge can be used, for example. The advantage of this extension of the foreign body detection according to the invention is that the resulting values ​​for the transmission or reflection components T.RHF from the compensated measurement curve (c) can still be compared with a fixed reference value in order to be able to reliably identify any foreign bodies 4 as such despite systematic, periodic superpositions.

[0037] List of reference symbols

[0038] 1 measuring system

[0039] 2 Medium

[0040] 3 container segment

[0041] 4 foreign bodies

[0042] 11 First high-frequency unit

[0043] 12 Second high-frequency unit

[0044] 13 Third high-frequency unit

[0045] 14 Superior evaluation unit

[0046] 110 Dielectric matching structure as,R,T beam axes

[0047] RF Scattered or reflected part of the measurement signal

[0048] SHF High-frequency measurement signal

[0049] THF Transmitted portion of the measurement signal a Angle between the first and third beam axis

Claims

Patent claims 1 . Measuring system for detecting foreign bodies (4) in a process medium (2), comprising: A container segment (3) which is at least partially transparent to radar signals (S, R, THF) and in which the process medium (2) is located, a first high-frequency unit (11) which is designed and arranged on the container segment (3) in such a way to emit a radar-based measurement signal (SHF) in the direction of a first beam axis (as) into the process medium (2), a reflector which is arranged on the container segment (3) opposite the first high-frequency unit (11) in the first beam axis (as), wherein the first high-frequency unit (11) is designed to receive the transmitted portion (THF) after reflection of the emitted measurement signal (SHF) at the reflector, and / or a second high-frequency unit (12) which is designed and arranged on the container segment (3) in such a way to receive a transmitted portion (THF) of the emitted measurement signal (SHF) from the direction of a second beam axis (ai), and / or a third High frequency unit (13),which is designed and arranged on the container segment (3) to receive a reflected portion (RHF) of the transmitted measurement signal (SHF) from the direction of a third beam axis (3R), and an evaluation unit (14) which is designed to detect any foreign body (4) based on the transmitted portion (THF) and / or the reflected portion (RHF).

2. Measuring system according to claim 1, wherein the evaluation unit (14) is designed to detect any foreign body (4) by comparing the respective portion (RHF, THF) with a corresponding reference value.

3. Measuring system according to at least one of the preceding claims, wherein the container segment (3) is a pipeline section.

4. Measuring system according to one of the preceding claims, wherein the third high-frequency receiving unit (13) is arranged in relation to the first high-frequency unit (11) such that the first beam axis (as) and the third beam axis (3R) intersect at an angle (a) of a maximum of 90°, in particular approximately 45°.

5. Measuring system according to one of the preceding claims, wherein the high-frequency units (11, 12, 13) are designed to transmit or receive the radar signals (S, R, THF) with a frequency between 0.3 GHz and 250 GHz.

6. Measuring system according to one of the preceding claims, wherein the high-frequency units (11, 12, 13) are designed to transmit or receive radar signals (S, R, THF) with at least two different frequencies and / or temporally frequency-modulated, in particular sawtooth-shaped, and wherein the evaluation unit (14) is designed to detect any foreign body (4) at each frequency on the basis of the respectively transmitted or reflected portion (THF, RHF).

7. Measuring system according to one of the preceding claims, wherein the third high-frequency unit (13) is arranged on the container segment (3) approximately opposite to the first high-frequency unit (11).

8. Measuring system according to one of the preceding claims, comprising: a fourth high-frequency unit designed and arranged on the container segment (3) to emit the radar-based measuring signal (SHF) into the process medium (2) in the direction of a fourth beam axis, which runs at a different angle to the first beam axis (as), 9. Measuring system according to one of the preceding claims, wherein the evaluation unit (14) is designed to add or subtract the transmitted portion (THF) and the reflected portion (RHF) in a weighted manner, and wherein the evaluation unit (14) detects the possible foreign body (4) on the basis of the sum or difference of the weighted portions (THF, RHF).

10. Measuring system according to one of the preceding claims, wherein at least between one of the high-frequency units (11, 12, 123) and the container segment (3) a dielectric matching structure (110) is arranged, the dielectric value of which lies between that of the process medium (2) and the dielectric value of the high-frequency unit (11, 12, 13).

11. Method for detecting foreign bodies (4) in a process medium (2) located in a container segment (3) that is at least partially transparent to radar signals (S, R, THF) by means of the measuring system according to at least one of the preceding claims, comprising the following method steps: Emitting a radar-based measuring signal (SHF) into the process medium (2), Reception of a transmitted portion (THF) and / or a reflected portion (RHF) of the transmitted measurement signal (SHF), and Detection of any foreign body (4) based on the transmitted portion (THF) and / or a reflected portion (RHF).

12. The method according to claim 11, wherein a foreign body (4) is detected if the transmitted portion (THF) falls below a first reference value, or if the reflected portion (RHF) exceeds a second reference value.

13. The method according to claim 11 or 12, wherein a time-resolved measurement curve (a, b) of the transmitted portion (THF) and / or of the reflected portion (RHF) is recorded, wherein any time-periodic profile patterns (M) of the transmitted portion (THF) or of the reflected portion (RHF) are determined on the basis of the time-resolved measurement curve (a, b), wherein a measurement curve (c) compensated with regard to the time-periodic profile pattern (M) is created, and wherein the possible foreign body (4) is detected on the basis of the compensated measurement curve (c).

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