Method for ascertaining creep flows, and device for ascertaining creep flows

Abstract

A method (200) serves to ascertain a creep flow in a pipeline (110) by means of two ultrasonic transducers (122, 124) arranged thereon by way of a transit time difference method; wherein the method (200) comprises the following steps: repeatedly determining (210) primary measured transit time difference values between first measured transit time values of ultrasonic signals that pass from the first ultrasonic transducer (122) to the second ultrasonic transducer (124), and second measured transit time values in the opposite direction; determining a transit time difference average (220) of a first type on the basis of a tuple of a first type of not less than 40, for example not less than 80 and in particular not less than 160 of the primary measured transit time difference values; comparing (230) the transit time difference average with a threshold value; and ascertaining a creep flow (240) when the transit time difference average of the first type exceeds the threshold value, wherein the threshold value is no more than 5 ns, for example no more than 2 ns, and in particular no more than 1 ns.

Description

[0001] Method for detecting creeping quantities and device for detecting creeping quantities

[0002] The present invention relates to a method for detecting creeping flows and a device for detecting creeping flows. A creeping flow is a flow rate of a medium that is so small that a flow meter can no longer reliably display it. A quantitative value of the creeping flow is usually given as a percentage of the measuring range and is related to a specified measuring accuracy of the measuring device. For flow measurement within the specified range of a measuring device, creeping flows are actually negligible; however, the occurrence of creeping flows, particularly as backflow or when a flow of strictly zero is expected, can be indicative of a fault condition. For detecting creeping flows, the published patent application DE 10 2007 045 101 A1 discloses an ultrasonic measuring method in which the medium stream is guided through measuring sections with different cross-sections depending on the flow rate.Narrower cross-sections lead to higher flow velocities, allowing even flow rates that would be considered creepage flows in measuring sections with larger cross-sections to be detected. However, this variable diversion of media into different measuring sections is very complex and hardly feasible for media that contain solids, for example. Therefore, the object of the present invention is to provide a simpler method and a corresponding device for detecting creepage flows.

[0003] The object is achieved according to the invention by the method according to independent patent claim 1 and the device according to independent patent claim 14.

[0004] The method according to the invention is used to detect a creeping flow in a pipeline by means of at least two ultrasonic transducers using the transit time difference method, wherein a first ultrasonic transducer and a second ultrasonic transducer are arranged on the pipeline at a distance from one another in the longitudinal direction of the pipeline; wherein the method comprises the following steps: repeatedly determining primary transit time difference measured values ​​between first transit time measured values ​​of ultrasonic signals that run from the first ultrasonic transducer to the second ultrasonic transducer, and second transit time measured values ​​of ultrasonic signals that run from the second ultrasonic transducer to the first ultrasonic transducer;

[0005] Determining a first-kind average time difference based on a first-kind tuple of not less than 40, for example not less than 80 and in particular not less than 160 of the primary time difference measurement values;

[0006] Comparing the mean transit time difference with a threshold value; and detecting a creep flow if the mean transit time difference of the first type exceeds the threshold value, wherein the threshold value is not more than 5 ns, for example not more than 2 ns and in particular not more than 1 ns.

[0007] In a further development of the invention, the tuple of the first type of transit time difference measured values ​​is collected over a period of not less than 4 s, in particular not less than 8 s.

[0008] In a further development of the invention, the transit time difference measured values ​​are determined with a measuring rate of not less than 8 Hz, for example not less than 16 Hz.

[0009] In a further development of the invention, the ultrasonic signals comprise pulses with a frequency of not less than 0.2 MHz, for example not less than 0.8 MHz and / or not more than 8 MHz, for example not more than 3 MHz.

[0010] In a further development of the invention, the pipeline has a diameter of not less than DN 50, for example not less than DN 150, wherein the creep flow corresponds to a flow of not more than 30 l / min.

[0011] In a further development of the invention, the method further comprises signaling a creep flow when a creep flow has been detected. In a further development of the invention, the method further comprises detecting flow rates based on transit time difference measurements.

[0012] In a further development of the invention, flow rates are recorded on the basis of second-type transit time difference mean values, wherein a second-type transit time difference mean value is determined on the basis of a second-type tuple of transit time difference measured values, wherein the second-type tuple comprises fewer transit time difference measured values ​​than the first-type tuple.

[0013] In a further development of the invention, at least the runtime difference mean values ​​of one of the first or second type are collected as moving averages.

[0014] In a further development of the invention, the number of runtime difference measured values ​​of the tuple of the second type depends on previous runtime difference mean values.

[0015] In a further development of the invention, the medium with respect to the pipeline is subjected to at least one disturbing oscillation, for example in a frequency range between 0.02 Hz and 120 Hz.

[0016] In a further development of the invention, the frequency or frequencies of the interference oscillations are determined using a spectral analysis on the basis of the transit time difference measured values, wherein a result of the spectral analysis is output, in particular in the form of a spectrum, for example in graphic form, and / or as frequency data and associated amplitudes of interference oscillations.

[0017] In a further development of the invention, the tuple of the first type of transit time difference measured values ​​is collected over a period of not less than 4 periods of the lowest frequency of the interference oscillations, the amplitude of which is not less than one third of a maximum amplitude of the spectrum of the interference oscillations.

[0018] The measuring arrangement according to the invention for detecting a creeping flow in a pipeline, in particular by means of the method according to the invention, comprises two ultrasonic measuring transducers for arranging on a pipeline whose volume is to be monitored for creeping flows; and a measuring and operating circuit configured to drive the ultrasonic transducers with transmission signals and to detect and evaluate received signals from the ultrasonic transducers; and to determine the transit time difference measured values, as well as the transit time difference mean values, and to detect a creeping flow.

[0019] In a further development of the invention, the pipeline is arranged in a tunnel boring machine.

[0020] The invention will now be explained in more detail with reference to the exemplary embodiments illustrated in the drawings. It shows:

[0021] Fig. 1 : a schematic representation of an inventive

[0022] measuring arrangement;

[0023] Fig. 2: a diagram with measurement data of an inventive

[0024] Low flow detection compared to reference data;

[0025] Fig. 3: a flowchart of an embodiment of the method according to the invention; and

[0026] Fig. 4: a schematic diagram of a spectrum of

[0027] Disturbing vibrations.

[0028] The measuring arrangement 100 according to the invention, schematically illustrated in Fig. 1, for detecting a creeping flow in a pipeline 110 comprises a first ultrasonic measuring transducer 122 and a second, essentially identical ultrasonic measuring transducer 124, which are arranged and secured to the pipeline 110, for example, with tensioning straps or magnets. The measuring arrangement 100 further comprises a measuring and operating circuit 130, which is configured to drive the ultrasonic transducers 122, 124 with transmitted signals and to detect and evaluate received signals from the ultrasonic transducers; and to determine transit time difference measured values, as well as transit time difference average values, and to detect a creeping flow. The measuring arrangement 100 can be arranged, in particular, in a tunnel boring machine.The measurement data shown in Fig. 2 originate from an experiment in which a variable volume flow was fed via a DN 20 supply line from DN 20 into a DN 150 pipeline of the measuring arrangement according to the invention. The volume flow in the supply line was measured using a reference device and is shown in the curve labeled r in Fig. 2. The measurement data of the creep flow monitoring carried out using the measuring arrangement according to the invention and the method according to the invention are shown in the curve labeled s in Fig. 2. According to curve r, the flow increases in steps of 0.1 l / s, which corresponds to velocity steps of approximately 0.017 m / s in a DN 150 pipeline. These creep flows are reliably detected, as can be seen from curve s.

[0029] An embodiment 200 of the method according to the invention is explained below using the flowchart in Fig. 3. The method 200 begins with the repeated determination 210 of primary transit time difference measured values ​​delta_tj between first transit time measured values ​​ti_j of ultrasonic signals traveling from the first ultrasonic transducer 122 to the second ultrasonic transducer 124 and second transit time measured values ​​t2_j of ultrasonic signals traveling from the second ultrasonic transducer 124 to the first ultrasonic transducer 122. The transit time difference measured values ​​delta_tj form a tuple of the first type {delta_tj}, which is used for further evaluation. The tuple of the first type {delta_tj} of the transit time difference measured values ​​can, for example, be collected over a period of several seconds, in particular no less than 8 s.The transit time difference values ​​delta_tj are preferably determined at a sampling rate of no less than 16 Hz, so that a statistically valid basis for the subsequent process steps is provided within an acceptable time. This is followed by the determination 220 of a transit time difference mean of the first kind.<delta_t> based on the tuple {delta_tj} of the first kind with in particular no fewer than 160 of the primary runtime difference measured values ​​delta_tj. This is followed by comparing 230 of the runtime difference mean of the first kind<delta_t> with a threshold value L and the detection 240 of a creep flow if the runtime difference mean of the first kind<delta_t> exceeds a threshold value L, wherein the threshold value L is not more than 5 ns, for example not more than 2 ns and in particular not more than 1 ns.The ultrasonic signals which are sent and / or received by the ultrasonic transducers here comprise pulses with a frequency of approximately 1.2 MHz, but can in principle be selected from a larger frequency range between, for example, 0.2 MHz and 8 MHz. If a creeping flow is detected, the signaling 250 of a creeping flow follows. This can comprise a sound or light signal, or a display on a screen, or a scattering signal which can be used to intervene in the operation of a system in which the creeping flow has been detected, if necessary without human intervention. The method 200 is carried out in particular when monitoring for creeping flows is necessary, i.e. when in particular no flow should occur. In particular when a creeping flow oran increasing flow rate is detected, it may be advisable to deviate from the routine described above for recording the tuples of the first type, as this may take up too much time. In this case, the flow rates can be recorded on the basis of travel time difference mean values ​​of the second type, whereby a travel time difference mean value of the second type is determined on the basis of a tuple of the second type of travel time difference measured values, whereby the tuple of the second type comprises fewer travel time difference measured values ​​than the tuple of the first type. This means that updated flow rate measured values ​​can be provided more quickly. To shorten response times, it may also be advantageous to record the travel time difference mean values ​​of one of the first or second type as moving averages.Furthermore, it is advantageous to define the number of transit time difference measured values ​​of the tuple of the second type as a monotonically decreasing function of the magnitude of the previous transit time difference mean values, which allows for a faster reaction to flow rate changes.

[0030] A further aspect of the invention relates to the handling of parasitic vibrations with which a medium in the pipeline can be exposed, in particular with parasitic vibrations in a frequency range between 0.02 Hz and 120 Hz. The frequencies and amplitudes of these parasitic vibrations are determined using a spectral analysis on the basis of the transit time difference measured values. The result of this spectral analysis can be output in various ways, as explained below with reference to Fig. 4. The curve a(f) can be output in its entirety, or the frequency position 1, 2, 3, 4 of individual peaks as well as their height can be output, wherein the selection criterion for the data to be output can be the exceeding of a comparison value a1, a2 by the height and / or the frequency position of the peaks in a monitored frequency range between f1 and f2.The comparison values ​​can be specified absolutely or set in relation to the maximum peak height a-max, for example, as a-max / 3. Depending on the output data or changes compared to the reference data, adjustments to the system's operation, including emergency shutdown, can be made if necessary, or maintenance measures can be initiated.

Claims

Patent claims 1. A method (200) for detecting a creep flow in a pipeline (110) by means of at least two ultrasonic transducers (122, 124) using the transit time difference method, wherein a first of the ultrasonic transducers (122) and a second of the ultrasonic transducers (124) are arranged on the pipeline at a distance from one another in the longitudinal direction of the pipeline (110); wherein the method (200) comprises the following steps: repeatedly determining (210) primary transit time difference measured values ​​between first transit time measured values ​​of ultrasonic signals that run from the first ultrasonic transducer (122) to the second ultrasonic transducer (124) and second transit time measured values ​​of ultrasonic signals that run from the second ultrasonic transducer (124) to the first ultrasonic transducer (122); Determining a first-type runtime difference average value (220) based on a first-type tuple of not less than 40, for example not less than 80 and in particular not less than 160 of the primary runtime difference measured values; and Comparing (230) the mean transit time difference value with a threshold value; and determining a creep flow (240) if the mean transit time difference value of the first type exceeds the threshold value, wherein the threshold value is not more than 5 ns, for example not more than 2 ns and in particular not more than 1 ns.

2. The method (200) according to claim 1, wherein the tuple of the first type of transit time difference measured values ​​is collected over a period of not less than 4 s, in particular not less than 8 s.

3. The method (200) according to claim 1 or 2, wherein the transit time difference measured values ​​are determined at a measuring rate of not less than 8 Hz, for example not less than 16 Hz.

4. The method (200) according to any one of the preceding claims, wherein the ultrasonic signals comprise pulses having a frequency of not less than 0.2 MHz, for example not less than 0.8 MHz and / or not more than 8 MHz, for example not more than 3 MHz.

5. Method (200) according to one of the preceding claims, wherein the pipeline (110) has a diameter of not less than DN 50, for example not less than DN 150, wherein the creep flow corresponds to a flow rate of not more than 30 l / min.

6. The method (200) according to any one of the preceding claims, further comprising signaling (250) a creep flow when the detection (240) of a creep flow has occurred.

7. The method (200) according to any one of the preceding claims, further comprising detecting flow rates based on transit time difference measurements.

8. The method (200) according to claim 7, wherein the detection of flow rates is carried out on the basis of transit time difference averages of a second type, wherein a transit time difference average of a second type is determined on the basis of a tuple of a second type of transit time difference measured values is determined, whereby the tuple of the second type contains fewer runtime difference measurements than the tuple of the first type.

9. Method according to one of the preceding claims, wherein at least the runtime difference mean values ​​of one type are collected as moving averages.

10. Method according to one of the preceding claims, wherein the number of transit time difference measured values ​​of the tuple of the second type depends on previous transit time difference mean values.

11. Method according to one of the preceding claims, wherein the medium is subjected to at least one disturbing oscillation with respect to the pipeline, for example in a frequency range between 0.02 Hz and 120 Hz.

12. The method according to claim 11, wherein the frequency or frequencies of the interference oscillations are determined using a spectral analysis on the basis of the transit time difference measured values, wherein a result of the spectral analysis is output, in particular in the form of a spectrum, for example in graphic form, and / or as frequency data and associated amplitudes of interference oscillations.

13. The method according to claim 11 or 12, wherein the tuple of the first type of transit time difference measured values ​​is collected over a period of not less than 4 periods of the lowest frequency of the interference oscillations, the amplitude of which is not less than one third of a maximum amplitude of the spectrum of the interference oscillations.

14. A measuring arrangement (100) for detecting a creeping flow in a pipeline (110), in particular by means of a method according to one of the preceding claims, comprising two ultrasonic measuring transducers (122, 124) for arranging on a pipeline in which the creeping flow is to be detected; a measuring and operating circuit (130) which is configured to drive the ultrasonic transducers (122, 124) with transmission signals and to detect and evaluate received signals of the ultrasonic transducers (122, 124); and to determine the transit time difference measured values, as well as the transit time difference mean values, and to detect a creeping flow.

15. A measuring arrangement according to one of the preceding claims, wherein the Pipeline is arranged in a tunnel boring machine.

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