EP2291619A1

EP2291619A1 - Method and measurement system for determining and/or monitoring the flow of a measurement medium through a measuring tube

Info

Publication number: EP2291619A1
Application number: EP09769099A
Authority: EP
Inventors: Andreas Berger; Achim Wiest; Finn Bloch Jensen; Rolf Sonderkamp
Original assignee: Endress and Hauser Flowtec AG; Flowtec AG
Current assignee: Endress and Hauser Flowtec AG
Priority date: 2008-06-25
Filing date: 2009-06-02
Publication date: 2011-03-09
Also published as: WO2009156250A1; RU2478190C2; RU2011102597A; CN202092690U; DE102008029772A1; US20110094309A1; US8347734B2

Abstract

Measurement system (1) and method for determining and/or monitoring the flow of a measurement medium (5) through a measuring tube (4), comprising a first ultrasound sensor (2) and at least one second ultrasound sensor (3), said first ultrasound sensor (2) comprising at least one electromechanical ultrasound converter element (6.1-6.6) and said second ultrasound sensor (3) comprising at least two electromechanical ultrasound converter elements (7.1-7.6). The ultrasound signals sendable by the first ultrasound sensor (2) through the measurement medium (5) can be received by the second ultrasound sensor (3) and the ultrasound signals sendable by the second ultrasound sensor (3) through the measurement medium can be received by the first ultrasound sensor (2). At least one control/evaluation unit determines the volumetric and/or mass flow of the measurement medium (5) flowing in the measurement tube (4) by way of a run-time difference method. During a diagnosis phase, ultrasound signals are sent from the first ultrasound sensor (2) through the measurement medium (5) to the second ultrasound sensor (3) and at least one process parameter is determined from the ultrasound signals received for each electromechanical ultrasound converter element (7.1-7.6) of the second ultrasound sensor (3), and the electromechanical ultrasound converter element (7.1-7.6) of the second ultrasound sensor (3) active in a subsequent measurement phase is selected based on the process parameter of the received ultrasound signals.

Description

Method and measuring system for determining and / or monitoring the flow of a measuring medium through a measuring tube

The present invention relates to methods for determining and / or monitoring the flow of a measuring medium through a measuring tube having a first ultrasonic sensor and at least one second ultrasonic sensor, which first ultrasonic sensor at least one eiektromechanisches ultrasonic Wandierelement and is mounted in a first region of the measuring tube and softer second Ultrasonic sensor has at least two electromechanical ultrasonic transducer elements and is mounted in a second region of the measuring tube so that the ultrasound signals transmitted by the first ultrasonic sensor are received by the second ultrasonic sensor and that the Uitraschallsignale sent by the second Uftraschailsensor are received by the first ultrasonic sensor , and with at least one control / evaluation unit, which sin based on the Uitraschail- measuring signals or on the basis of measurement data derived from the ultrasonic measurement signals d, the volume flow and / or the mass flow of the measuring medium flowing in the measuring tube are determined by means of a transit time difference method and a corresponding measuring system.

Uitraschall flowmeters are widely used in process and automation technology. They allow in a simple way to determine the volume flow and / or mass flow in a pipeline.

The known Uitraschall flowmeters often work after Doppieroder after the transit time difference principle.

When running time difference principle, the different maturities of ultrasound pulses are evaluated relative to the flow direction of the liquid.

For this purpose, ultrasonic pulses are sent at a certain angle to the pipe axis both with and against the flow. From the transit time difference The flow rate and thus the known diameter of the piping section can be used to determine the volume flow.

When Doppier principle ultrasonic waves are coupled with a certain frequency in the liquid and evaluated by the liquid reflected ultrasonic waves. From the frequency shift between eingen coupled and reflected waves can also determine the flow rate of the liquid.

Reflections in the liquid, however, only occur when air bubbles or

Contaminants are present in this, so this principle is mainly used in contaminated liquids use.

The Ultraschallwelien be generated or received with the help of so-called ultrasonic transducer. For this purpose, ultrasonic transducers are firmly attached to the pipe wall of the pipe section in question. Recently, Ciamp-on ultrasonic flowmeter systems are also available. In these systems, the ultrasonic transducers are pressed against the pipe wall only with a tension lock. Such systems are for. Example, from EP 686 255 B1, US-A 44 84 478 or US-A 45 98 593 known.

Another ultrasonic flow meter, which operates on the transit time difference principle, is known from US-A 50 52 230. The transit time is determined here by means of short ultrasound pulses.

A big advantage of clamp-on ultrasonic flowmeters is that they do not touch the medium being measured and are mounted on an existing pipeline. A disadvantage is a high expenditure in the assembly of the clamp-on systems in order to align the individual Ultraschallwandier each other, which of many parameters, such as. Pipe wall thickness, pipe diameter, speed of sound in the medium to be measured.

The ultrasonic transducers usually consist of an electromechanical

Converter, in industrial process measurement usually a piezoceramic, and a Coupling layer, also called coupling wedge or rare precursor body. The coupling layer is usually made of plastic. In the electromechanical transducer element, the ultrasonic waves are generated and guided via the coupling layer to the pipe wall and from there into the liquid. Since the speeds of sound in liquids and plastics are different, the ultrasonic waves are refracted during the transition from one medium to another. The angle of refraction is determined in a first approximation by the Sneil ^''s law. The angle of refraction is thus dependent on the ratio of the propagation velocities in the media.

Between the piezoelectric element and the Koppetschicht may be arranged a further coupling layer, a so-called adaptation layer. The adaptation layer assumes the function of the transmission of the ultrasonic signal and at the same time the reduction of a reflection caused by different acoustic impedances at boundary layers between two materials.

In numerous sources, e.g. in DE 10 2006 029 199 B3, the flow rate of a measuring medium in a measuring tube on the drift of an ultrasonic signal is determined by the flow of the measuring medium in the measuring tube.

In WO 2007/039394 A2 an ultrasonic flowmeter is disclosed with at least one Uitraschaliwandler in a first region of the measuring tube and at least two UltraschallaNwandlern in a second area. Due to the different distances of the transducers in the second region to that in the first region, a transit time difference of the ultrasonic signals results. This difference in transit time is used to calculate the flow. The disadvantage is that the ultrasound transducer in the first region of the measuring tube an energy-intensive signal with high signal strength and wide

Signal angle must be generated so that the Signa! reaches the other two ultrasonic transducers in the second region of the measuring tube. DE 102 21 771 A1 shows an ultrasonic sensor for an ultrasonic flowmeter with a plurality of piezoelectric elements, which are combined to form what is known as a piezo-array, which piezoelectric elements can be actuated with a time delay. This makes it possible, with an ultrasonic sensor mounted flat on the measuring tube wall, to achieve different angles of the ultrasonic signal radiated into the measuring medium with a width front to the measuring tube axis. However, the time-delayed driving is very computationally intensive. Even the change of the angle makes sense only in a limited area. If the ultrasound signal is radiated very flatly, longitudinal waves may be excited and the transmission through the tube wall is reduced and a significant portion of the sound wave is reflected.

The object of the invention is to provide a method and a corresponding flow measuring system whose sensors can be attached to a pipeline and require no complex mutual alignment.

The object is achieved by a method for determining and / or monitoring the flow of a measuring medium through a measuring tube with a first ultrasonic sensor and at least one second ultrasonic sensor, which first ultrasonic sensor has at least one electromechanical ultrasonic transducer element and is mounted in a first region of the measuring tube and which second ultrasound sensor has at least two electromechanical ultrasound transducer elements and is mounted in a second region of the measuring tube in such a way that the ultrasound signals transmitted by the first ultrasound sensor through the measurement medium are received by the second ultrasound sensor and if the ultrasound signal transmitted by the second ultrasound sensor through the measurement medium is received by the first ultrasound sensor are received, and with at least one control / evaluation unit, which sin based on the Uitraschall- or on the basis of measurement data derived from the ultrasonic measurement signals d, determines the volume flow and / or the mass flow of the measuring medium flowing in the measuring tube by means of a transit time difference method, wherein ultrasound signals are transmitted from the first ultrasonic sensor through the measuring medium to the second ultrasonic sensor during a diagnostic phase and from At least one process variable is determined and / or derived for each electromechanical ultrasonic wall element of the second ultrasonic sensor and the electromechanical ultrasonic transducer elements of the second ultrasonic sensor active in a subsequent measuring phase are selected on the basis of the process variable of the received ultrasound signals. Thus, a distinction is made between a diagnosis phase and a measurement phase. In the diagnostic phase, the ultrasound transducer elements which determine and / or receive ultrasound signals for the measurement during the measurement phase are determined.

Usually, the ultrasonic sensors have coupling elements which bring about an angle between the ultrasonic wall-mounted elements mounted on them and the main flow direction of the measuring medium in the measuring tube, which usually runs approximately axially to the central axis of the measuring tube. This is how the ultrasound signal gets! between the sensors, a directional component in and / or against the main flow direction of the measuring medium in the measuring tube. In certain forms of conditioned flow, an ultrasound signal! Irradiate perpendicular to the pipe wall or pipe axis and yet can be determined by means of the transit time difference method, the flow.

The sensors are mounted or installed in different areas of the measuring tube. In clamp-on systems, the sensors are mounted on opposite sides of the measuring tube outer wall from the outside or they are located on the same side of the measuring tube and the signal is reflected on the opposite side of the measuring tube wall, preferably with a

Reflector on the inside of the measuring tube. For inline systems, the sensors are usually located in fixed locations, fixed in or with the measuring tube wall.

The process variables determined during the diagnostic phase are, in particular, the signal strength of the received ultrasound signal, its amplitude, its amplitude

Phase position, the envelope or the transfer function. Derivable quantities are eg the intensity or the transit time of the ultrasonic signal. The electromechanical ultrasonic transducer element is preferably a piezoelectric element. However, eietrostrictive and / or magnetostrictive elements are also capable of generating and / or receiving suitable ultrasound signals.

A first ultrasonic sensor with at least one electromechanical ultrasonic transducer element is mounted in a first region of the measuring tube. Relative to this, a second ultrasonic sensor is mounted in a second region of the measuring tube. For clamp-on systems, both sensors are attached to the outside of the measuring tube wall. The sensors are roughly aligned, i. their spacing is governed by a specific rule, e.g. at a distance from the size of the diameter of the measuring tube, roughly or in coarse steps. The cost of this device is very low compared to the prior art.

By changes of measuring medium parameters, e.g. the measuring medium itself or its temperature, change now u.a. the refraction angles of the ultrasonic signals. This would require a realignment of the sensors to each other in the prior art. Alternatively, the signal intensity for determining the flow would be lower and / or the measurement results associated with a larger error.

Here, however, the optimum combination of ultrasonic transducer elements of the sensors for the measurement is determined. Even a non-optimal combination can be used for the measurement, but this measurement would be associated with a greater uncertainty.

During the diagnostic phase, for example, exactly one ultrasound transducer element alternately transmits ultrasound signals. The parameters determined and / or derived from the received ultrasound signals are determined individually for the receiving ultrasound transducer elements. This can be done in only one direction, ie from the first to the second ultrasonic sensor. Alternatively, ultrasonic signals in both directions upstream and downstream can be included in the diagnostics because of a phase shift between the directional component signal in the main flow direction of the measurement medium in the measuring tube and the ultrasound signal! with directional component counter to the main flow direction of the medium to be evaluated in the measuring tube.

The diagnostic phase then consists of determining and / or deriving the process variables of all possible combinations of ultrasound transducer elements in both directions. Thus, at the end of this phase there is a record with a description of the measurement results of all combinations during the diagnostic phase. Using the desired process variables, the best possible combination is selected and the process variables saved as reference values. These are now always available for comparison with a current measurement.

Only after determining the active for the measurement sensors, the actual measurement begins. The diagnostic phase is possible before and after each measurement, but even during a measurement phase, the selection of active electromechanical ultrasonic transducer elements in the subsequent measurement phase can take place. By means of other transmission frequencies and / or other pulse sequences, this selection is possible, for example, without disturbing the measuring operation. Since a flow measurement takes place with the evaluation of individual ultrasound packets, either these measurements can be compared directly with the stored reference variables, or one or more measurements are taken for diagnosis between two parcels of the flow measurement.

This arrangement also allows the speed of sound in the medium to be determined easily. In the case of a known measuring medium, it is thus possible to determine its temperature or, if the temperature is known, it is thus possible to detect a change in the measuring medium.

Other strategies for accelerated diagnosis include u.a. in that not all combinations of Uitraschall transducer elements are measured. With two ultrasonic sensors with a large number of converter elements, it is advisable to use the

Combination with the smallest distance perpendicular to the tube axis to each other to select the combination with the greatest distance perpendicular to the tube axis to each other and a medium combination. The distances are then iteratively halved on the side of the cheaper process sizes. The diagnosis can take place both in the case of flowing measuring medium and in the case of a so-called zero flow, ie, when the measuring medium is stationary in the measuring tube. The diagnosis is advantageously carried out with a measuring medium flowing in the measuring tube, since in this case an interference signal, for example caused by a so-called tube wave, ie an ultrasound signal in the measuring tube itself or the measuring tube wall, can be better distinguished from the useful signal, ie the ultrasonic signal for diagnosis.

An advantageous development of the method according to the invention provides that, during the diagnostic phase, the electromechanical ultrasonic transducer elements of the second ultrasound sensor active in the subsequent measurement phase are selected for the greatest signal strength of the received ultrasound signals.

The ultrasound transducer element or ultrasound transducer elements having the largest received signal strength are selected. A variant is that the Uitraschall transducer element is selected, which receives the largest signal strength. However, since many ultrasound transducer elements can be combined to both transmit and / or receive ultrasound signals, it is very advantageous to combine a plurality of ultrasound transducer elements together, in particular the selected ultrasound transducer and its direct neighbors and / or further ultrasound juxtaposed - Transducer elements.

Particularly advantageously, the ultrasonic sensors each have matching layers between coupling elements and ultrasonic transducer elements, which, like a filter, are designed such that the proportions of the ultrasonic measuring signals, which in Einbzw. Direction of the Uitraschall measuring signals are oriented pass the matching layers approximately undisturbed, while the proportions of the ultrasonic measuring signals, which are oriented transversely to the input and / or Ausstrahlrichtung, are largely attenuated by the matching layers. A very advantageous development of the solution according to the invention can be seen in that the first ultrasonic sensor has at least two electromechanical ultrasonic transducer elements and during the diagnostic phase the electromechanical ultrasonic transducer elements of the first ultrasonic sensor active in a subsequent measuring phase are selected.

The selection is made e.g. on the basis of the signal intensity of the ultrasound signals of the first sensor received by the second ultrasound sensor and / or the signal strength of the ultrasound signals received from the first ultrasound sensor which were transmitted by the second ultrasound sensor.

According to an advantageous embodiment of the invention, during the diagnostic phase, the electromechanical ultrasound transducer elements of the second ultrasound sensor active in the subsequent measurement phase are selected for the optimum phase difference between transmission and reception of the received ultrasound signal.

According to a further advantageous embodiment of the invention, during the diagnostic phase, the electromechanical ultrasonic transducer elements of the second ultrasonic sensor active in the subsequent measuring phase are selected for the optimum phase difference between the ultrasonic signal received from the second ultrasonic sensor and the ultrasonic signal received from the first ultrasonic sensor. The ultrasonic signal emitted by the first ultrasonic sensor Sent and received by the second ultrasound sensor, it has at least one directional component in or against the

Main flow direction of the measuring medium in the measuring tube and the ultrasonic signal, which is sent from the second ultrasonic sensor and received by the first ultrasonic sensor is in opposite directions. It is used in this case that due to the flow of the measuring medium, phase differences occur in certain time segments of the two ultrasonic signals, in and against the flow.

According to a further advantageous embodiment of the invention, during the diagnostic phase, the electromechanical ultrasonic transducer elements of the second ultrasonic sensor active in the subsequent measuring phase selected according to the optimum transfer function of the received ultrasonic signals.

According to a further advantageous development of the solution according to the invention, a plurality of electromechanical ultrasound transducer elements of the first ultrasound sensor are activated simultaneously and / or a plurality of electromechanical ultrasound transducer elements of the second ultrasound sensor are simultaneously activated. This is particularly advantageous for directly adjacent ultrasound transducer elements.

According to a further advantageous embodiment of the method according to the invention, the respectively active electromechanical ultrasonic transducer elements are switched by at least one M ultiplexer, wherein the multiplexer is controlled by the control / evaluation unit and wherein the electromechanical ultrasonic transducer elements of the first ultrasonic sensor and the electromechanical ultrasonic Wandierelemente of the second ultrasonic sensor are connected to the control / evaluation unit. In addition to the known selection switching network, for selecting a single signal, a multiplexer is also a switch unit of a plurality of independently controllable individual switches.

An advantageous embodiment of the method according to the invention is that the process variable detected during the diagnostic phase is stored and that during the measurement phase the stored process variable is compared with the currently detected process variable, wherein when a certain deviation of the stored process variable from the currently detected process variable is exceeded, a renewed Diagnosis phase is initiated. The comparison is possible with one and / or with several recorded process variables. The flow can be calculated, for example, by means of the phase shift from transmitter to receiver in and against the direction of flow, while the optimum combination of ultrasound transducer elements is determined by means of the signal strength. As described above, the combination of the ultrasonic Wandierelemente can also be determined with the phase shift. Furthermore, the object underlying the invention is achieved by a measuring system for determining and / or monitoring the flow of a measuring medium through a measuring tube having a first Uitraschatlsensor and at least a second ultrasonic sensor, which first Uitraschallsensor at least one eiektromechanisches ultrasonic transducer element and in a first region of the measuring tube is attachable and which second Uitraschallsensor has at least two eiektromechanische ultrasonic transducer elements and in a second region of the measuring tube is attachable so that the first Uitraschallsensor sendable by the measuring medium ultrasonic signals from the second Uitraschallsensor are receivable and that of the second Uitraschallsensor by the measuring medium sendable ultrasonic signals from the first ultrasonic sensor are receivable, and with at least one control / evaluation unit, which on the basis of the ultrasonic measurement signals or on the basis of measurement data, which from the Ultras Chall-measuring signals are derived, the volume and / or mass flow of the flowing in the measuring tube measuring medium by means of a

Determines transit time difference method, wherein during a diagnostic phase UitraschaSIsignale from the first Uitraschallsensor by the measuring medium to the second Uitraschallsensor be sent and from the receivable UStraschallsignalen for each eiektromechanische ultrasonic transducer element of the second Uttraschallsensors at least one process variable is determined and / or derivable and due to the process size of the receivable ultrasonic signals the in a subsequent measurement phase active electromechanical ultrasonic transducer elements of the second ultrasonic sensor can be selected.

The ultrasonic transducer elements are controlled by the control / evaluation unit. With several ultrasonic transducer elements on a Uitraschallsensor the signals are passed, for example via at least one Multipiexer. This Multipiexer is then also controlled by the control / evaluation.

According to an advantageous development of the measuring system according to the invention, the first ultrasonic sensor has at least two electromechanical ultrasonic transducer elements and during the diagnostic phase they are in one subsequent measurement phase active eieelektromechanischen ultrasonic transducer elements of the first Ultraschallaüsensors selectable.

A very advantageous development of the measuring system according to the invention is the fact that the measurement signals of eiektromechanischen ultrasonic wall lerelemente or the derivable from the measurement signals measurement data of exactly one Rege! - / Evaluation unit are evaluated, the active eiektromechanischen ultrasonic transducer elements by means of at least one Multiplexers of the control / evaluation are controllable.

The circuit of the active ultrasonic transducer elements is controllable by at least one multiplexer. The control / evaluation unit, which receives and processes the signals of the ultrasonic transducer elements, controls the multiplexer. The combination of the active ultrasonic transducer elements is obtained according to the described method. The individual ultrasonic wall elements sequentially transmit a predetermined signal. The acquired process parameters are evaluated and the control / evaluation unit decides based on the specified criteria, soft combination of ultrasonic transducer elements is activated in the measurement phase. In addition to the known selection switching network, for selecting a single signal, a multiplexer is also a switch unit of a plurality of independently controllable individual switches.

According to an advantageous embodiment of the invention, the first ultrasonic sensor and the second ultrasonic sensor can be connected to one another via a detachable connection.

According to a further advantageous embodiment of the invention, the first ultrasonic sensor and the second ultrasonic sensor in a common housing. Thus, only the housing is aligned parallel to the tube axis and vertically above the tube center. The housing can correspond to a defined housing protection, for example, it is dust, gas and / or waterproof. In addition, the housing can not have any external moving parts. According to a further advantageous embodiment of the invention, the second coupling element is an integral part of the first Koppeieiements. Both ultrasonic sensors thus have a single monolithic coupling element.

An advantageous development of the measuring system according to the invention proposes that the electromechanical ultrasonic transducer elements of the first ultrasonic sensor each have a first surface for transmitting and / or receiving ultrasonic signals, which first surfaces has a first surface area, and which electromechanical ultrasonic transducer elements of the second ultrasonic sensor each a second surface for transmitting and / or receiving ultrasound signals, the second surface having a second surface area, wherein the first surface area is unequal to the second surface area. Thus, e.g. a plurality of electromechanical ultrasonic transducer elements of the second ultrasonic sensor taken together the surface of an electromechanical ultrasonic transducer element of the first ultrasonic sensor. The magnitudes of the areas of the electromechanical ultrasound transducer elements of the first ultrasound sensor and those of the electro-mechanical ultrasound transducer elements of the second ultrasound sensor are in a ratio not equal to one another. Preferred ratios are e.g. nine to ten or nineteen to twenty, etc.

A further advantageous development of the measuring system according to the invention provides that the electromechanical ultrasonic transducer elements of the first ultrasonic sensor have approximately constant first distances and that the electromechanical ultrasonic transducer elements of the second ultrasonic sensor have approximately constant second distances, wherein the first distances are not equal to the second distances.

The distances are usually based on the surface ridge points of Uϊtraschall Wandlereϊemente. The center of area in this context is the geographical center or the center of gravity of the area. It is not so much the calculation of the centroid as such, but rather, that the area centers are calculated equally for all ultrasound transducer elements. Here are the first distances of the electromechanical ultrasonic transducer elements of the first ultrasonic sensor and the second distances of the electromechanical ultrasonic transducer elements of the second ultrasonic sensor in a ratio not equal to one another. Preferred ratios are for example nine to ten or nineteen to twenty etc.

With the above conditions, a division is achieved on the model of a vernier. It can be realized by the many possible combinations of active Ultraschallatl transducer elements most different distances between them. Thus, even small changes in process parameters can be compensated, which would lead to a loss of signal quality in the prior art or would require a readjustment of the sensors to each other.

In a very advantageous development of the invention, a plurality of electromechanical ultrasonic transducer elements can be activated simultaneously.

Several, in particular juxtaposed, electromechanical ultrasonic transducer elements are then activated simultaneously, i. they are ready to send and / or ready to receive.

According to an advantageous development of the measuring system according to the invention, it is proposed that the first ultrasonic sensor has a coupling element which is designed such that an ultrasound signal transmitted by the electromechanical Uitraschail transducer element has a directional component in or against the main flow direction of the measuring medium in the measuring tube and / or that the second Ultrasonic sensor has a coupling element, which is designed so that an ultrasound signal sent from the electromechanical ultrasonic transducer element has a directional component in or against the main flow direction of the measuring medium in the measuring tube.

An advantageous embodiment of the invention provides that the active in the measuring phase electromechanical ultrasonic transducer elements of the first UltraschallaNsensors and / or the second ultrasonic sensor, from the outside, ie from an external unit, are selectable, for example by the user himself via a corresponding interface or an external field device, via a analog frequency or current input, electromechanical via switch or digitally adjustable via a signal.

The invention will be explained in more detail with reference to the following figures. Fig. 1 shows a longitudinal section of a measuring tube with inventive measuring system, Fig. 2 shows a distributor circuit according to the invention, Fig. 3 shows in longitudinal section two ultrasonic sensors of an inventive

Measurement system

4 shows a flowchart of the method according to the invention, FIG. 5 shows a further distributing circuit according to the invention.

In Fig. 1, an inventive measuring system 1 with two ultrasonic sensors 2, 3, which are mounted on a measuring tube 4, shown. Both ultrasonic sensors 2, 3 have a plurality of ultrasonic transducer elements 6.1-6.6, 7.1 -7.6. So these are so called

Transducer arrays, not to be confused with arrays in individual sensors. With a single combination of individually operable ultrasonic transducer elements 6.1 - 6.6, 7.1 - 7.6, the flow measurement can be performed. The selection and positioning of the sensors 2, 3 is facilitated by the variety of possible combinations.

The ultrasonic sensors 2, 3 are mounted on the same outside of the measuring tube 4. Their ultrasound Wandierelementen 6.1 -6.6, 7.1-7.6 face each other at an angle so that the ultrasound signal emitted by them 10 is passed through the measuring medium 5 to the respective other ultrasonic sensor 2, 3. A directional component of the ultrasound signal 10 points in the direction of the main flow direction of the measuring medium 5 in the measuring tube 4. Thus, a transit time difference can be measured with mutual transmission and reception, via which the flow velocity of the measuring medium 5 in the measuring tube 4 and thus the flow can be determined.

The UltraschallaSI transducer elements 6.1-6.6 have a distance 11 to each other. The ultrasonic transducer elements 7.1-7.6, however, have a distance 12 to each other. The distances 11, 12 are considered to be approximately constant, are but not the same. In this embodiment, the distances 11 are 10mm and the distances 12 9mm.

The diagnostic phase of the measuring system 1 is preceded by the structure of the measuring system 1. First, the clam-on ultrasonic sensors 2, 3 on the outside of the

Metering 4 aufnallt. Thereafter, the power is turned on and put into operation of the measuring system. 1

During the diagnostic phase, one after the other of the ultrasonic transducer elements 6.1-6.6 is activated or activated and excited to transmit a presettable Uitraschalisignals. In doing so, e.g. the signal strength of the received ultrasonic signals for each ultrasonic transducer element 7.1-7.6 measured individually. This can be done both sequentially, i. by sequentially measuring all possible Kombinatäonen, as well as done simultaneously. There are, so to speak, all ultrasonic Wandierelemente 7.1 -7.6 to receive, while a certain ultrasonic Wandiereϊement 6.1-6.6 sends. With the illustrated embodiment of the measuring system 1 according to the invention, however, only the sequential measurement is possible.

Thereafter, the same procedure may be repeated in the other direction, ie, transmit the ultrasonic transducer elements 7.1-7.6 and receive the Uitraschall transducer elements 6.1-6.6. The optimal pair, which guarantees eg the maximum signal strength, is selected for the measurement. The measured process parameters are stored. During the measurement phase, only the selected ultrasonic transducer elements 6.1 -6.6, 7.1 -7.6 are activated to determine the flow. At the same time, the other ultrasonic Wandierelemente 6.1-6.6, 7.1-7.6 continue to be excited, for example, with a significantly different frequency to the measurement frequency. Thus, during the measurement phase, it is possible to continue to search for changes in the measurement conditions which might necessitate changing the optimum pair of ultrasound transducer elements. Such a change in the measurement conditions can be recognized, for example, by the fact that the stored process parameters deviate from the measured ones in a certain manner, for example by undershooting or exceeding a threshold value, or by another pair of ultrasound transducer elements 6.1-6.6, 7.1 -7.6 Process parameters provides, for example, a higher signal strength. The diagnosis can also take place temporally separate from the measurement phase.

The information about the ongoing measurement and / or diagnosis phases and / or their results or findings can also be provided, e.g. on a display, or an alarm signal can be output if the measurement conditions change.

The ultrasonic sensors 2, 3 are, as shown in FIG. 2, connected to multiplexers 9.1-9.4, which respectively activate two opposing ultrasonic transducer elements 6.1-6.6, 7.1-7.6. The multiplexers 9.1 - 9.4 are controlled by the control / evaluation unit 8.

The ultrasonic transducer elements 6.1-6.6, 7.1-7.6 are shown in Fig. 2 only schematically. There is only one combination, i. a pair of ultrasonic transducer elements 6.1-6.6, 7.1-7.6 are activated, i. sends only one ultrasonic Wandiereiement 6.1 -6.6 and receives an ultrasonic transducer element 7.1-7.6 and / or vice versa. The advantage lies in the small amount of data to be processed. The control / evaluation unit 8 must always process only one signal. The control of the multiplexer 9.1-9.4 is also control / evaluation 8 taken over. The

Control of the individual ultrasonic Wandiereiemente 6.1 -6.6, 7.1 -7.6 by the multiplexer 9.1-9.4, however, is very fast. As a result, this system 1 is very error-prone, cost-effective and yet highly accurate and fast.

In order to simultaneously activate a plurality of ultrasonic transducer elements 6.1-6.6, 7.1-7.6, at least one of the illustrated multiplexers 9.3, 9.4 would have to be replaced by a plurality of individually controllable switches, as shown in FIG. As a multiplexer here is generally understood a switch unit of several, independently controllable individual switches. In addition, this circuit has an interface 17. This is for communication with a control unit, for example, to connect to a bus or it is a man-machine interface. Fig. 3 discloses an inventive measuring system 1 with two opposing, mounted on the same side of the measuring tube 4 Ultraschallaüsensoren 2, 3. Again, the coupling elements 13, 14 an angle between the ultrasonic wall lerelementen 6, 7.7-7.21 and the measuring tube. 4 , so that the UStraschallsignale, not shown here for clarity, have a direction component in the main flow direction of the measuring medium in the measuring tube 4.

During the diagnostic phase, the ultrasonic transducer 2 transmits ultrasonic signals to the ultrasonic transducer 3 and vice versa. Here, for the sake of simplicity, only the first case should be considered. The signal strengths and / or further process parameters received by the ultrasound transducer elements 7.7-7.21 are compared with each other and the ultrasound transducer element 7.7-7.21 at which the process parameters most suitable for the measurement are applied are selected for the measurement and thus the signal path for the measurement is determined , But also the combination of several adjacent elements 7.7-7.21 is conceivable.

In the measuring system shown, the ultrasonic transducers 2, 3 have different sized Ultraschallail-Wandlereiemente 6, 7.7-7.21. The approximately square ultrasound transducer element 6 measures 8x8mm by way of example, while the size of the ultrasound transducer elements 7.7-7.21 is 2x8mm in each case. In order to obtain the same area as in the Uitraschall transducer element 6, four adjacent ultrasonic transducer elements 7.7-7.21 are switched together active. This is usually done with the direct neighbors of the Uitraschall- transducer element 7.7-7.21 with the most suitable process parameters. Of the

Zusammenschiuss can apply to sending and / receiving, as well as take place separately. Transmit can be combined ultrasound transducer elements 7.7-7.21 by being driven simultaneously. This happens again via appropriately configured, not shown here Muitiplexer. 9

4 shows a flow chart of the method described. The start of the diagnostic phase is preceded by the installation and coarse positioning of the ultrasonic sensors 2, 3. Analogous to Fig. 1 would have the Wandlereiemente of first ultrasonic sensor 2 with 6.i and the transducer elements of the second Uitraschailsensors be denoted by 7.j. For the sake of simplicity, they are only denoted by i and j. The combination (i, j), which would be analogous to FIG. 1 (6.i, 7.j), is measured, ie the process parameters P _{N are} determined and / or derived. They are then saved. This is done for all combinations of i = 1 to i = i _ma χ and j = 1 to j = j _max . The comparison of the process parameters P ₁ , all combinations provides the most suitable combination of ultrasonic transducer elements. With these, the measurement is completed.

Of course, a different process as shown here conceivable, where the aktuel! measured process variables are compared with the held in the memory, so far most suitable process variables.

The measurement can then be interrupted again from diagnosis phases from time to time, eg, time-controlled and / or user-controlled and / or process-controlled. Alternatively, the diagnosis may take place during the measurement phase and / or by the evaluation of the measurement signals themselves.

LIST OF REFERENCE NUMBERS

I Flow measurement system 2 First UJ-scan sensor

3 Second ultrasonic sensor

4 measuring tube

5 measuring medium

6 Electromechanical Ultrasonic Transducer Elements 7 Electromechanical Ultrasound Transducer Elements

8 control / evaluation unit

9 multiplexers

10 ultrasound signal path

I 1 distance of eiektromechanischen ultrasonic transducer elements 12 distance of eiektromechanischen ultrasonic transducer elements

13 coupling element

14 coupling element

15 First surface

16 Second surface 17 external interface

Claims

claims

1. A method for determining and / or monitoring the flow of a measuring medium (5) through a measuring tube (4) with a first ultrasonic sensor

(2) and at least one second ultrasonic sensor (3), soft first ultrasonic sensor (2) at least one electromechanical ultrasonic transducer element (6) and in a first region of the measuring tube (4) is mounted and which second ultrasonic sensor (3) at least two electromechanical Ultrasonic Wandierelemente (7) and in a second region of the measuring tube (4) is mounted so that the first ultrasonic sensor (2) by the measuring medium (5) sent ultrasonic signals (10) from the second ultrasonic sensor (3) are received and the ultrasound signals (10) sent by the second ultrasound sensor (3) are received by the first ultrasound sensor (2) and at least one control / evaluation unit (8) based on the ultrasound measurement signals or on the basis of measurement data , which are derived from the ultrasonic measurement signals, the volume and / or the mass flow of the measuring medium (5) flowing in the measuring tube (4) by means of e Ines transit time difference method determined, characterized in that during a diagnostic phase ultrasonic signals (10) from the first ultrasonic sensor (2) through the measuring medium (5) to the second ultrasound sensor (3) are sent and of the received ultrasound signals (10) for each electromechanical ultrasound!

Wandlereiement (7) of the second ultrasonic sensor (3) at least one process variable is determined and / or derived and due to the process size of the received ultrasound signals (10) active in a subsequent measurement phase electromechanical ultrasonic wall lere elements (7) of the second ultrasonic sensor (3 ) to be selected.

2. The method according to claim 1, characterized during the diagnosis phase, the electromechanical ultrasound transducer elements (7) of the second ultrasound sensor (3) active in the subsequent measurement phase are selected according to the greatest signal strength of the received ultrasound signal (10).

3. The method according to claim 1 or 2, characterized in that the first ultrasonic sensor (2) has at least two electromechanical ultrasonic transducer elements (6) and during the diagnostic phase, the active in a subsequent measurement phase eiektromechanischen

Ultrasonic transducer elements (6) of the first ultrasonic sensor (2) can be selected.

4. The method according to any one of claims 1 to 3, characterized in that a plurality of electromechanical ultrasound transducer elements (6) of the first UltraschallaNsensors (2) are activated simultaneously and / or that a plurality of electromechanical ultrasound transducer elements (7) of the second ultrasonic sensor (3) be activated simultaneously.

5. The method according to any one of claims 1 to 4, characterized in that the respectively active electromechanical Ultraschallalan-Wandlereiemente (6, 7) of at least one multiplexer (9) are switched, wherein the multiplexer (9) of the control / Auswerteeänheit ( 8) is controlled and wherein the electromechanical Uitraschail Wandiereäemente (6) of the first ultrasonic sensor (2) and the eiektromechanischen Uitraschail- Wandlereiemente (7) of the second Uitraschallsensors (3) with the control / evaluation unit (8) are connected.

6. The method according to any one of claims 1 to 5, characterized in that the recorded during the diagnostic phase process variable is stored and that during the measurement phase, the stored process variable with the currently detected process variable is compared, wherein when a certain deviation of the stored process variable from the currently detected process variable is exceeded, a renewed diagnostic phase is initiated.

7. Measuring system (1) for determining and / or monitoring the flow of a measuring medium (5) through a measuring tube (4) having a first ultrasonic sensor (2) and at least one second ultrasonic sensor (3), which first ultrasonic nozzle (2) at least one electromechanical Having ultrasonic transducer element (6) and in a first region of the measuring tube (4) is attachable and which second ultrasonic sensor (3) at least two electromechanical ultrasonic transducer elements (7) and in a second region of the measuring tube (4) is attachable, in that the ultrasound signals (10) which can be transmitted by the first ultrasound sensor (2) through the measuring medium (5) can be received by the second ultrasound sensor (3) and by the second ultrasound sensor (3)

Measuring medium (5) sendable ultrasound signals (10) from the first Uitraschallsensor (2) are receivable, and with at least one control / evaluation unit (8), which are based on the ultrasonic measurement signals or based on measurement data derived from the ultrasonic measurement signals , the volume flow and / or the mass flow of the in the measuring tube (4) flowing

Measuring medium (5) determined by means of a transit time difference method, characterized in that during a diagnostic phase ultrasound signals (10) from the first Uitraschallsensor (2) by the measuring medium (5) to the second Uitraschallsensor (3) are sendable and from the receivable

Ultrasound signals (10) for each electromechanical ultrasonic transducer element (7) of the second ultrasonic sensor (3) at least one process variable is determined and / or derivable and due to the process size of the receivable ultrasonic signals (10) the active in a subsequent measurement phase electromechanical ultrasonic

Transducer elements (7) of the second ultrasonic sensor (3) are selectable.

8. Measuring system (1) according to claim 7, characterized in that the first ultrasound sensor (2) has at least two electromechanical ultrasound wall elements (6) and during the diagnostic phase the electromechanical ultrasound transducer elements (6) of the first ultrasound sensor (2) active in a subsequent measuring phase can be selected.

9. measuring system (1) according to claim 7 or 8, characterized in that the measurement signals of eiektromechanischen ultrasonic transducer elements (6, 7) or the derivable from the measurement signals measurement data of exactly one

Rege! - / evaluation unit (8) are evaluable, wherein the active electromechanical ultrasonic transducer elements (6, 7) by means of at least one multiplexer (9) of the control / evaluation unit (8) are controllable.

10. Measuring system (1) according to one of claims 7 to 9, characterized in that the electromechanical ultrasonic transducer elements (6) of the first ultrasonic sensor (2) each have a first surface (15) for transmitting and / or receiving ultrasonic signals, which first surfaces (15) has a first surface area, and which electromechanical

Ultrasonic transducer elements (7) of the second ultrasonic sensor (3) each have a second surface (16) for transmitting and / or receiving ultrasonic signals, which second surfaces (16) has a second surface area, wherein the first surface area is not equal to the second surface area.

11. Measuring system (1) according to one of claims 8 to 10, characterized in that the electromechanical ultrasonic transducer elements (6) of the first ultrasonic sensor (2) have approximately constant first distances (11) and that the electromechanical ultrasonic transducer elements (7) of the second UStraschailsensors (3) have approximately constant second distances (12), wherein the first distances (11) are not equal to the second distances (12).

12. Measuring system (1) according to any one of claims 7 to 11, characterized in that a plurality of electromechanical UltraschallaSI transducer elements (6, 7) are activated simultaneously.

13. Measuring system (1) according to one of claims 7 to 12, characterized in that the first ultrasonic sensor (2) has a coupling element (13), which is designed so that an ultrasound signal (10) sent by the electromechanical ultrasonic wall element (6) ) one

Directional component in or against the main flow direction of the measuring medium (5) in the measuring tube (4) and / or that the second ultrasonic sensor (3) has a coupling element (14) which is designed such that one of the electromechanical ultrasound transducer element (7) sent Ultraschallsigna! (10) one

Directional component in or against the main flow direction of the measuring medium (5) in the measuring tube (4).