Flow measurement system

Abstract

System (1) for flow measurement comprising a first flow meter (2) and a second flow meter (3), wherein the first flow meter (2) and the second flow meter (3) each have an evaluation unit (4, 5) generating data from the flow measurement, wherein a monitoring device (6) is provided, wherein the monitoring device (6) is connected to the evaluation units (4, 5) in such a way that the monitoring device (6) receives data generated by the evaluation units (4, 5), and wherein the monitoring device (6) is configured in such a way that, based on a comparison of the data generated by the evaluation units (4, 5), the monitoring device (6) generates at least one comparison result and signals at least the occurrence of an error condition associated with at least one comparison result.wherein the first flow meter (2) and the second flow meter (3) are each an ultrasonic flow meter with a measuring tube (7, 8), wherein the first flow meter (2) and the second flow meter (3) are arranged one after the other along the flow direction of a medium, namely wherein the two ultrasonic flow meters each have a separate measuring tube (7, 8) and wherein the measuring tubes (7, 8) are arranged one after the other along the flow direction of a medium, and wherein the first flow meter (2) and the second flow meter (3) differ from each other and / or have different orientations for flow measurement, namely wherein the first flow meter (2) and the second flow meter (3) differ from each other with respect to the type of flow measurement, namely differ at least with respect to the path of the ultrasonic signals in the respective measuring tube (7, 8),characterized in that both evaluation units (4, 5) generate secondary data from a measurement of the flow rate in addition to a value of the flow rate, and that the monitoring device (6) compares at least the secondary data with each other.

Description

[0001] The invention relates to a system for flow measurement according to the preamble of patent claim 1.

[0002] Aside from the fact that high measurement accuracy is always desirable from a technical perspective for any flow measurement, especially with high-value liquid or gaseous goods, such as crude oil and natural gas, there is a significant interest in ensuring that, from the supplier's perspective, the quantity to be delivered—and only the quantity to be delivered—is delivered, and from the buyer's perspective, that the quantity—and at least the quantity requested—is received. Measurement tolerances always fall to the detriment of one of the parties involved in the trade, usually the supplier.

[0003] Known flow measurement methods, for example, utilize the transit time of ultrasonic waves, which are either transmitted directly between two ultrasonic transducers or reflected off the wall of the measuring tube (see, for example, patents DE 196 48 784 C2 or DE 103 12 034 B3). Flowmeters with the highest possible measurement accuracy are particularly preferred for this application. Ultrasonic measurement methods are particularly advantageous for large pipe diameters, since with the appropriate arrangement of the ultrasonic transmitter and receiver, the flow-through pipe cross-section can be monitored almost completely using ultrasonic waves. This is especially true for measuring devices that implement multiple measuring paths that traverse the flow cross-section in different areas.

[0004] For example, from the documents US 4 090 179 A, ​​a system for flow measurement is known which has two vortex flow meters arranged at two different measuring locations.

[0005] EP 0 465 182 A2 discloses a flow measurement system in which a thermal flowmeter is combined with a non-thermal flowmeter. The measurements of the thermal flowmeter are corrected with the measurements of the non-thermal flowmeter.

[0006] Further flow measurement systems with two flowmeters are known from the publications US 2010 / 0223976 A1 and DE 10 2009 046 758 A1. Furthermore, US 2010 / 0005900 A1 describes a flow measurement system with two subsystems in the form of a dual ultrasonic flowmeter.

[0007] However, due to changing measurement conditions or aging of the measuring devices, measurement uncertainties or even measurement errors may arise. To identify such phenomena, it is known in the art to arrange different flow meters in series, whereby the measuring devices differ from one another in their measuring principle or manufacturer. This is accompanied by the expectation that the measuring devices will, for example, exhibit different aging behavior and also react differently to changes in the measuring conditions (e.g., contamination or deposits). To the extent that this is the case and to the extent that deviations in the measured data are observed and detected, this diversity in flow measurement serves to monitor the system.

[0008] The disadvantage of such systems is that the diversity must be reconciled, which can be challenging. If different measurement principles are used, the values ​​may not be directly comparable, or different error tolerances must be observed. Furthermore, if measuring devices from different manufacturers are used, additional information about the specific characteristics may be required. Therefore, it would be advantageous to have a simplified system so that more computational effort is spent on the actual evaluation rather than on ensuring data comparability.

[0009] The flow measurement applications described above often involve so-called custody transfer, which places special demands on the accuracy of the measuring instruments and, above all, on the verification of this accuracy. To verify accuracy, it is generally necessary to remove the system—that is, the measuring instruments with their respective measuring tubes, and possibly also the connecting pipes between them—from the surrounding pipe system at regular intervals and subject them to calibration / verification. Conformity with specific accuracy requirements is confirmed by authorized institutes, such as the Physikalisch-Technische Bundesanstalt (PTB) in Germany. This process is very complex, as such systems can be heavy and necessary bypasses, etc., must be provided.It would therefore be advantageous to use systems that have the longest possible calibration intervals, ideally with an “infinite” calibration period after an initial calibration.

[0010] The invention is therefore based on the object of proposing a system for flow measurement that allows self-monitoring in a simple manner.

[0011] The stated object is achieved according to the invention, initially and essentially in the system for flow measurement in question, in that the first flow measuring device and the second flow measuring device differ from one another and / or have different orientations for the flow measurement. The first flow measuring device and the second flow measuring device each have an evaluation unit that generates data from the flow measurement. In addition, a monitoring device is provided which is connected to the evaluation units in such a way that the monitoring device receives data generated by the evaluation units. Furthermore, the monitoring device is designed in such a way that, based on a comparison of the data generated by the evaluation units, the monitoring device generates at least one comparison result and at least signals the occurrence of an error state associated with at least one comparison result.The system according to the invention has two flowmeters that differ from each other. The differences may lie in the manufacturer and the type of application or implementation of the measuring principle. The difference is particularly such that measurement errors or changes in the measurement setup, e.g., contamination, have different effects on the individual flowmeters and can be derived differently from the measured data obtained.

[0012] Alternatively or additionally, the first and second flowmeters have different orientations for the respective flow measurement. The orientation refers in each case to the arrangement of the respective components of the two flowmeters relevant for the flow measurement at least in a plane perpendicular to the flow direction of the measuring medium. If the two flowmeters are arranged one behind the other along the flow direction, they also have different orientations with regard to the measurements. The orientation results in particular from the arrangement of the relevant components or from the interaction with the measuring tube through which the measuring medium flows that is relevant for the measurement. The orientations preferably differ in such a way that disturbances (for example deposits or adhesions) have different effects on the respective flow measurements.If, for example, one orientation is such that an interaction occurs with the part of the measuring tube located at the bottom in the direction of gravity, and the other orientation is essentially perpendicular to this, for example halfway up the measuring tube, a sediment will have different effects on the measurements of the two flow meters. The two orientations can be arranged at the same or different axial positions along the flow of the measuring medium. In other words: the flow meters react differently to disturbances - regardless of their nature. This different behavior is exploited in such a way that the monitoring device compares the evaluation data of the evaluation units assigned to the flow meters and generates a corresponding comparison result.For this purpose, the monitoring device has a corresponding logic or a neural network, which in one embodiment also allows at least a learning phase.

[0013] By evaluating the data from two evaluation units, the amount of information about the measuring conditions can be increased, as data is generated by two measuring devices. On the other hand, plausibility checks, for example, allow the status of one measuring device to be monitored by the other. This results in very advantageous self-monitoring. In implementation, for example, excessive differences between the measured values ​​for the flow are signaled. Alternatively or additionally, differences between additional - secondary - data obtained from the measurements, e.g. about deposits on the pipe wall or on an element of a measuring device or about the temperature of the measuring medium, are displayed as errors. For this purpose, it is possible for at least one evaluation unit to generate secondary data from a flow measurement in addition to a flow value.In addition to the data mentioned above, these secondary data include, for example, statements about the shape of the flow of the medium, the presence of different phases, etc. Secondary data also include, for example, intermediate results on the way to evaluation, e.g. the transit time of a measurement signal to the value for the flow of the measuring medium.

[0014] This is accompanied by a further embodiment of the invention in which both evaluation units generate secondary data from a flow measurement in addition to a flow value. The monitoring device compares at least the secondary data with each other. Preferably, the actual measurement data on the flow is also included for the comparison. The flow measuring devices used for the system according to the invention have special evaluation units that contain monitoring and control functions and thus make statements about the measurement accuracy and about variables influencing the measurement. For the output of such secondary data, the flow measuring devices or, in particular, the evaluation units usually have a so-called service interface, which is provided in addition to the normal interface for the measurement data.The measuring medium is a liquid, a flowable mixture or, in particular, a gas or a gas mixture.

[0015] In one embodiment, the monitoring device compares the data generated by the evaluation units from different measurement times. Data from previous measurements, i.e. so-called history data, allow the detection of trends and developments, such as those caused by deposits or wear. If developments are so significant that they allow extrapolation, errors can be signaled before they result in incorrect measured values ​​for the flow rate. For the evaluation of the data from previous measurements, at least one storage unit for storing data is provided in one embodiment. In one embodiment, the storage unit is connected in particular to the evaluation unit.

[0016] In one embodiment, the monitoring device stores data generated by the evaluation units at an initialization time and at at least one - in particular known - flow value as reference data. The initialization time is, for example, the commissioning of the system. For this time, the data generated by the evaluation units, which result from the respective measurements with the assigned flow meters, are stored as reference data. Preferably, the data are determined at previously known velocities of the measuring medium or at previously known flow rates. In one embodiment, the data are stored for six different flow rates. Six velocities are tested, for example, during a so-called high-pressure calibration, so that the data generated can be used appropriately.The stored data creates a kind of fingerprint of the system during the initialization or reference time. During operation, at a predefined comparison time, at least the data generated by the evaluation units at this comparison time are compared by the monitoring device with the reference data. This is preferably based on different velocities of the measuring medium. If data is not available for all velocities for which the reference data has been stored, the available data is interpolated or extrapolated if necessary. The current data for the comparison may also originate from previous measurements at these velocities, if no data is currently available for all velocities.During the comparison performed for the system's self-monitoring, the data is compared between the flow meters and also with the reference data. This results in the system's self-monitoring over time by comparing a target fingerprint with a current actual fingerprint, preferably depending on the different velocities or flow values.

[0017] The following designs refer specifically to flow meters.

[0018] In the embodiment according to the invention, it is provided that the first flowmeter and the second flowmeter differ from one another with regard to the type of flow measurement. This embodiment is particularly associated with an embodiment in which both flowmeters are manufactured by the same manufacturer. In one embodiment, at least one flowmeter allows the flow to be measured in both flow directions through the associated measuring tube.

[0019] Furthermore, according to the invention, the type of flow measurement differs in the specific implementation of the same measuring principle. Therefore, the inventive design provides that the first flowmeter and the second flowmeter are each ultrasonic flowmeters with a measuring tube, wherein the first flowmeter and the second flowmeter differ from each other at least with regard to the path of the ultrasonic signals in the respective measuring tube. Thus, in a flowmeter, the ultrasonic transducers are arranged opposite one another at different locations in the measuring tube, so that the ultrasonic signals convert directly from ultrasonic transducer to ultrasonic transducer.In the other flowmeter, the ultrasonic transducers are located on the same side of the measuring tube, and the ultrasonic signals are reflected off the wall of the measuring tube after being emitted, before being detected by the other ultrasonic transducer. The different lengths of the ultrasonic signals also result in different evaluations and a different dependence on the measuring conditions. This, in turn, has the advantage that errors or malfunctions do not have the same effect on both flowmeters, but remain detectable due to their differences.

[0020] If both flow meters operate using ultrasonic signals, in a further embodiment, both devices are identical and differ only in the orientation of the measurement paths through which the ultrasonic signals travel for the respective measurements. In one variant, the required pairs of transmitter and receiver of the two devices are rotated relative to each other relative to the circumference of the measuring tubes.

[0021] Ultimately, it is important to ensure that, when selecting and / or arranging the first and second flowmeters, relevant influences / disturbances affect the first and second flowmeters differently—especially for accuracy verification. Once this has been verified, flowmeter systems with a very long, and practically infinite, calibration period can be implemented.

[0022] In one embodiment of the invention, at least one flow measuring device is designed such that at least two - in particular six - different measuring paths - in particular propagation paths for the ultrasonic signals - are used for the flow measurement, which differ from one another with regard to arrangement and / or orientation in the measuring tube.

[0023] In an advantageous embodiment, a measuring tube of the first flowmeter and a measuring tube of the second flowmeter are arranged directly next to each other and connected to each other. This results in a very short system design. Typically, space is left between different measuring devices in the form of a normal pipe section. In this embodiment, however, the flowmeters are arranged directly flange to flange and connected to each other.

[0024] In one embodiment, the monitoring device is provided as a component of the first flowmeter or the second flowmeter. In this embodiment, the two flowmeters communicate directly with each other, and one flowmeter transmits its data to the other flowmeter, which has the monitoring device.

[0025] In detail, there are numerous possibilities for designing and developing the measuring device according to the invention. Reference is made, on the one hand, to the claims subordinate to claim 1 and, on the other hand, to the following description of exemplary embodiments in conjunction with the drawing. The drawing shows Fig. 1 a schematic representation of a flow measurement system, essentially illustrating the functional relationships.

[0026] The Fig.1 shows a purely schematic view of a system 1 according to the invention for measuring the flow of a measuring medium (not shown), which is in particular a gas or gas mixture. Two flowmeters 2, 3 are provided for this purpose, which are designed as ultrasonic flowmeters. The first 2 and the second flowmeter 3 differ in the arrangement of the ultrasonic transducers and thus in the path taken by the ultrasonic signals for the measurement: once with and once without reflection on the wall of the respective measuring tube. The measurement signals are evaluated in the evaluation units 4, 5, which generate not only a value for the flow but also secondary data about the measurement or the flow, and which transmit this secondary data to the monitoring device 6.Such secondary data are, for example, uncertainties in the measured flow value, interference signals or intermediate quantities that result from the measured signals and that are relevant for determining the flow or that affect the measured quantity - in this case the propagation time of the ultrasonic signals.

[0027] The monitoring unit 6 now compares the data from the two evaluation units 4, 5 and generates comparison results from them. Depending on the respective comparison result, an error signal is generated if necessary. If, for example, a measurement with the first flow meter 2 shows that the measuring tube 7 of the first flow meter 2 is contaminated, but this is not indicated by the measurement with the second flow meter 3, i.e. if the data from the evaluation unit 5 of the second flow meter 3 indicates that the measuring tube 8 of the second flow meter 3 is not contaminated, this can be interpreted as meaning that there is increased uncertainty regarding the measured values ​​or that a measurement is correspondingly uncertain. For such comparisons, the monitoring unit 6 has in particular a neural network or is designed for the application of fuzzy logic.Furthermore, types of comparison results that are inadmissible and therefore associated with an error condition are stored.

[0028] In order to be able to derive developments from previous measurements or to detect inadmissible jumps in the measured values, the monitoring unit 6 is connected to a storage unit 9 in which such older measured values ​​of the flow or older secondary data can be stored.

[0029] If the measured values ​​of the two evaluation units 4, 5 for the flow are identical within a predeterminable tolerance band, the monitoring unit 6 determines the measurement accuracy in a variant for the output of the - for example averaged - flow value based on the large number of different secondary data.

[0030] Furthermore, in the embodiment shown, the monitoring unit 6 also has a corresponding interface for connection to a fieldbus 10, to which, in addition to a measured value for the flow, the error signals are also transmitted if necessary.

[0031] The flowmeters 2, 3 themselves, in particular, have a logic system that serves to monitor the measured values ​​and measurement conditions. The fact that both function differently results in the required diversity, which in turn is used for control purposes in the monitoring device 6. System 1 thus monitors itself, and by selecting the flowmeters 2, 3, errors, in particular, have different effects and are therefore detectable.

[0032] If, as in this case, both flow meters 2 and 3 are from the same manufacturer, they can be designed so that they do not influence each other's measurements, or at least influence each other to a known extent. Therefore, both flow meters 2 and 3 are installed directly next to each other, i.e., flange 11 to flange 11, in the pipe system 12 through which the measuring medium flows.

[0033] If the type of interaction is known in the case of measuring instruments from different manufacturers or of different types and if this can be appropriately taken into account by the monitoring device 6 for the evaluation of the data from the evaluation units 4, 5, these are also arranged directly next to one another in an alternative variant (not shown) in order to require only a small amount of installation space.

Claims

[1] System (1) for flow measurement with a first flow measuring device (2) and a second flow measuring device (3), wherein the first flow measuring device (2) and the second flow measuring device (3) each have an evaluation unit (4, 5) generating data from the flow measurement, wherein a monitoring device (6) is provided, wherein the monitoring device (6) is connected to the evaluation units (4, 5) in such a way that the monitoring device (6) receives data generated by the evaluation units (4, 5), and wherein the monitoring device (6) is designed in such a way that the monitoring device (6) generates at least one comparison result based on a comparison of the data generated by the evaluation units (4, 5) and at least signals the occurrence of an error state associated with at least one comparison result,wherein the first flowmeter (2) and the second flowmeter (3) are each an ultrasonic flowmeter with a measuring tube (7, 8), wherein the first flowmeter (2) and the second flowmeter (3) are arranged one behind the other along the flow direction of a medium, namely wherein the two ultrasonic flowmeters each have a separate measuring tube (7, 8) and wherein the measuring tubes (7, 8) are arranged one behind the other along the flow direction of a medium, and wherein the first flowmeter (2) and the second flowmeter (3) differ from one another and / or have different orientations for the flow measurement, namely wherein the first flowmeter (2) and the second flowmeter (3) differ from one another with regard to the type of flow measurement, namely differ from one another at least with regard to the path of the ultrasonic signals in the respective measuring tube (7, 8), ,characterized by that both evaluation units (4, 5) generate secondary data from a flow measurement in addition to a flow value and that the monitoring device (6) compares at least the secondary data with each other. [2] System (1) according to claim 1, characterized by that the monitoring device (6) compares the data generated by the evaluation units (4, 5) from different measuring times with one another, that at least one memory unit (9) is provided for storing data, that the monitoring device (6) stores data generated by the evaluation units (4, 5) at an initialization time and at at least one - in particular known - value of the flow as reference data and that the monitoring device (6) compares data generated by the evaluation units (4, 5) at least at one predeterminable comparison time with the reference data. [3] System (1) according to claim 1 or 2, characterized bythat the measuring tube (7) of the first flow meter (2) and the measuring tube (8) of the second flow meter (3) are arranged directly next to each other and connected to each other. [4] System (1) according to one of claims 1 to 3, characterized by that the monitoring device (6) is a component of the first flow meter (2) or the second flow meter (3).

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