Fluid measurement system and fluid measurement method

Abstract

To provide a fluid measurement system and fluid measurement method that can measure the flow velocity of a measurement fluid with high accuracy.SOLUTION: A fluid measurement system includes a first sensor and a second sensor disposed on the same pipe and spaced apart from each other by a predetermined distance, and a measurement controller that calculates the flow velocity of a fluid flowing through the pipe on the basis of first output that is output from the first sensor and second output that is output from the second sensor. The measurement controller performs the steps of: (a) comparing the first output and the second output in a first period so as to repeatedly calculate a first time difference between the first output and the second output while shifting the first period; (b) calculating a second time difference on the basis of frequency of occurrence of a plurality of first time differences each calculated in the first period included in a second period that is longer than the first period; and (c) calculating the flow velocity on the basis of the second time difference.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a fluid measurement system and a fluid measurement method.

Background Art

[0002] Patent Document 1 discloses a method for calculating the phase composition ratio of a two-phase mixture in a pipe. Patent Document 1 discloses that the flow rate of a two-phase mixture is calculated by comparing the measurement patterns of load cells at two locations using load cells arranged upstream and downstream of the pipe.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the flow rate measurement of a correlation formula that compares measurement patterns as disclosed in Patent Document 1, a desired response may not be obtained due to the influence of noise caused by vibration or sound.

[0005] The present disclosure provides a fluid measurement system and a fluid measurement method capable of measuring the flow rate of a measurement fluid with high accuracy.

Means for Solving the Problems

[0006] According to one aspect of the present disclosure, a fluid measurement system is provided comprising: a first sensor and a second sensor installed in the same pipe at a certain distance apart; and a measurement control unit that calculates the flow velocity of a fluid flowing through the pipe based on a first output output from the first sensor and a second output output from the second sensor, wherein the measurement control unit performs the steps of: (a) comparing the first output and the second output in a first period and repeatedly calculating a first time difference of the second output with respect to the first output while shifting the first period; (b) calculating a second time difference based on the frequency of occurrence of a plurality of first time differences calculated in the first period included in a second period which is longer than the first period; and (c) calculating the flow velocity based on the second time difference. [Effects of the Invention]

[0007] According to the fluid measurement system and fluid measurement method of this disclosure, the flow velocity of the fluid to be measured can be measured with high accuracy. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 shows the overall configuration of the fluid measurement system according to this embodiment. [Figure 2] Figure 2 illustrates the output of the sensor in the fluid measurement system according to this embodiment. [Figure 3] Figure 3 shows the measurement results of the time difference in the fluid measurement system according to this embodiment. [Figure 4] Figure 4 shows the frequency distribution of time differences in the fluid measurement system according to this embodiment. [Figure 5] Figure 5 is a flowchart illustrating the processing of the fluid measurement system according to this embodiment. [Figure 6] Figure 6 is a flowchart illustrating the processing of the fluid measurement system according to this embodiment. [Figure 7] Figure 7 is a flowchart illustrating the processing of the fluid measurement system according to this embodiment. [Modes for carrying out the invention]

[0009] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the description and drawings of each embodiment, components having substantially the same or corresponding functional configurations may be denoted by the same reference numerals, thereby omitting redundant explanations. Furthermore, for ease of understanding, the scale of parts in the drawings may differ from that of actual parts.

[0010] ≪Fluid Measurement System 1≫ Figure 1 shows the overall configuration of the fluid measurement system 1 according to this embodiment when in use. The fluid measurement system 1 is a system for measuring the flow velocity of a fluid flowing through a pipe P. The fluid measurement system 1 determines the flow velocity of a two-phase fluid, for example, a mixture of liquid and gas. The two-phase fluid to be measured is, for example, a mixture of hot water and steam in geothermal power generation. Alternatively, the fluid measurement system 1 may determine the flow rate by multiplying the determined flow velocity by the cross-sectional area of ​​the flow path. The arrows in Figure 1 indicate the direction of fluid flow.

[0011] The fluid measurement system 1 comprises a first sensor 11 and a second sensor 12, and a measurement control unit 20. The fluid measurement system 1 measures the flow velocity of the fluid flowing through the pipe P using the first sensor 11 and the second sensor 12, which are attached to the pipe P. The first sensor 11 and the second sensor 12 are installed in the same pipe, i.e., pipe P. Furthermore, the first sensor 11 and the second sensor 12 are installed in pipe P at a certain distance (installation distance L) apart.

[0012] The second sensor 12 is the same type of sensor as the first sensor 11. Both the first sensor 11 and the second sensor 12 are, for example, load sensors that measure the load applied to the pipe P. A load sensor is, for example, a load cell. However, the first sensor 11 and the second sensor 12 are not limited to load sensors. Each of the first sensor 11 and the second sensor 12 may be any of the following that can measure quantities related to the fluid flowing through the pipe: a vibration sensor, a volume sensor, a pressure sensor, a radio wave sensor, a humidity sensor, a density sensor, a temperature sensor, an electrical resistance sensor, and an ultrasonic sensor.

[0013] The first sensor 11 and the second sensor 12 each perform measurements in real time. Then, the first sensor 11 and the second sensor 12 each output the measurement results measured in time series to the measurement control unit 20 in real time.

[0014] Figure 2 illustrates the sensor output of the fluid measurement system according to this embodiment. Figure 2(A) shows the time-series measurement waveform output from the first sensor 11. Figure 2(B) shows the time-series measurement waveform output from the second sensor 12. The vertical axis represents the signal intensity of the signal output from the first sensor 11 or the second sensor 12, and the horizontal axis represents time. The horizontal axis is aligned between (A) and (B).

[0015] The second sensor 12 is installed downstream of the piping P of the first sensor 11, at a predetermined distance (installation distance L) along the piping P. Therefore, the fluid measured by the first sensor 11 is measured by the second sensor 12 with a time delay as the fluid moves from the first sensor 11 to the second sensor 12. Consequently, when comparing the measurement results of the first sensor 11 and the measurement results of the second sensor 12, the measurement results of the second sensor 12 are measured with a delay from the measurement results of the first sensor 11. In other words, the output of the second sensor 12 is measured with a time difference ΔT after the output of the first sensor 11.

[0016] The time difference ΔT (in seconds (s)) is expressed by Equation 1, where V is the fluid velocity (in meters per second (m / s)) and L is the installation distance (in meters (m)).

[0017] ΔT = L / V ··· Equation 1

[0018] For example, when the fluid flowing inside the pipe P is a two-phase fluid, depending on the location of the pipe P, the mixing ratio of, for example, liquid and gas in the two-phase fluid is different. When the mixing ratio of liquid and gas is different, the weight of the internal fluid varies depending on the location of the pipe. Therefore, by adopting load sensors for each of the first sensor 11 and the second sensor 12 and measuring the load applied from the pipe P at different positions in the pipe P, the fluid measurement system 1 can calculate the time it takes for the fluid to move between the first sensor 11 and the second sensor 12. Then, the fluid measurement system 1 uses the time it takes for the fluid to move between the first sensor 11 and the second sensor 12, that is, the time difference, to obtain the velocity (flow rate) of the fluid.

[0019] The fluid measurement system 1 determines the time difference ΔTm by which the measurement result of the second sensor 12 lags behind the measurement result of the first sensor 11. That is, the time difference ΔTm obtained by the fluid measurement system 1 represents the time it takes for the fluid to move from the first sensor 11 to the second sensor 12 inside the pipe P. Therefore, the fluid measurement system 1 calculates the flow velocity Vm of the fluid by dividing the installation distance L, which is the distance along the pipe P between the first sensor 11 and the second sensor 12, by the calculated time difference ΔTm.

[0020] The flow velocity Vm (unit: meters per second (m / s)) is calculated by Equation 2 using the time difference ΔTm (unit: seconds (s)) and the installation distance L (unit: meters (m)).

[0021] Vm = L / ΔTm ··· Equation 2

[0022] The installation distance L should be increased so that the time difference between the measurement results of the first sensor 11 and the measurement results of the second sensor 12 is large. However, if the installation distance L is increased, the correlation between the measurement results of the first sensor 11 and the measurement results of the second sensor 12 decreases, making it difficult to measure the time difference. Therefore, the installation distance L should be increased within a range where the time difference between the measurement results of the first sensor 11 and the measurement results of the second sensor 12 can be measured.

[0023] The measurement control unit 20 acquires the first measurement result from the first sensor 11 and the second measurement result from the second sensor 12 as time-series data. The measurement control unit 20 then processes the acquired first and second measurement results to calculate the velocity of the fluid flowing inside the pipe P.

[0024] The measurement control unit 20 acquires, for example, the waveform of the load over time as the first measurement result and the second measurement result. By comparing these waveforms, it calculates the time difference between when a waveform similar to the waveform detected by the first sensor 11 is detected by the second sensor 12. For example, the measurement control unit 20 uses the cross-correlation method or the dynamic time stretching method when calculating the time difference.

[0025] Figure 3 shows the results of calculating the time difference using the fluid measurement system 1 according to this embodiment. Figure 3 is a diagram showing the calculation results of the time difference in the fluid measurement system 1 according to this embodiment. The horizontal axis of Figure 3 shows the time (in seconds) since the start of measurement. The vertical axis of Figure 3 shows the calculated time difference (in seconds).

[0026] In the results shown in Figure 3, the time difference was calculated within the range of 0 to 5 seconds. The results shown in Figure 3 represent measurements of a two-phase fluid with a flow velocity that resulted in a time difference of approximately 0.5 seconds in pipe P. The time difference calculation was performed over a period of approximately 650 seconds.

[0027] In Figure 3, as indicated by the arrow PA, the sensor transit time (time difference ΔT in Figure 2) shows a strong response at approximately 0.5 seconds. However, responses are also widely observed in time differences other than approximately 0.5 seconds, ranging from 0 to 5 seconds. The presence of responses other than fluid velocity is thought to be due to the influence of noise, such as vibration or wind.

[0028] Figure 4 shows the frequency distribution of time differences measured in the fluid measurement system 1 according to this embodiment. Figure 4 shows the results of Figure 3 as a frequency distribution. In Figure 4, the highest frequency is around a time difference of 0 seconds, but a time difference of 0 seconds indicates an error such as the inability to calculate the passage time by cross-correlation. Therefore, when determining the flow velocity, a time difference of 0 seconds should be excluded. The interval in Figure 4 that contains the mode value other than a time difference of 0 seconds is the interval between 0.49 seconds and 0.50 seconds, as indicated by the arrow PB. In other words, by determining the frequency distribution of the measured time differences, measurement results that match the theoretical value can be obtained.

[0029] In fluid measurement system 1, in order to further improve the accuracy of flow velocity measurement, it is necessary to reduce the impact of erroneous responses due to noise.

[0030] The fluid measurement system 1 according to this embodiment reduces the effect of erroneous responses due to noise by calculating a frequency distribution for the measured time difference at regular intervals. By reducing the effect of erroneous responses due to noise, the fluid measurement system 1 can improve the accuracy of flow velocity measurement and measure flow velocity with higher precision.

[0031] To explain the process in more detail, first, the fluid measurement system 1 calculates the frequency distribution of the time difference measurement results shown in Figure 3 at regular intervals. Next, the fluid measurement system 1 calculates the mode from the calculated frequency distribution. Then, the fluid measurement system 1 determines the mode as the sensor transit time (time difference).

[0032] In the fluid measurement system 1, the inter-sensor transit time detected by cross-correlation is considered to occur more frequently than erroneous responses that occur like white noise. Therefore, in the fluid measurement system 1, erroneous responses can be suppressed by calculating the frequency distribution at regular intervals.

[0033] This document will specifically describe the processing of the fluid measurement system 1. It will also describe the steps performed by the measurement control unit 20 of the fluid measurement system 1. By describing the processing of the fluid measurement system 1, the fluid measurement method using the fluid measurement system 1 will be explained. Figure 5 is a flowchart illustrating the processing of the fluid measurement system 1 according to this embodiment.

[0034] (Step S10) When processing begins, the measurement control unit 20 in the fluid measurement system 1 measures the time difference over a predetermined period (measurement period) (time difference calculation step).

[0035] The time difference calculation process will be explained using Figure 6. Figure 6 is a flowchart illustrating the processing of the time difference calculation process in the fluid measurement system 1 according to this embodiment.

[0036] (Step S12) The measurement control unit 20 acquires the first output from the first sensor 11 and the second output from the second sensor 12 during a predetermined period (measurement period). The measurement control unit 20 samples each of the first output from the first sensor and the second output from the second sensor with a sampling period of, for example, 3 milliseconds. The measurement control unit 20 stores each of the sampled first and second outputs in a memory having a length equal to the measurement period. The measurement period is, for example, 10 seconds.

[0037] (Step S14) Next, the measurement control unit 20 calculates the time difference ΔT (first time difference) between the first output and the second output from the first and second outputs acquired in step S12. The measurement control unit 20 calculates the similarity between the waveforms of the first output and the second output by shifting the data of the second output stored in memory over time relative to the data of the first output stored in memory. The waveform similarity is determined by the cross-correlation method or the dynamic time stretching method. The measurement control unit 20 then calculates the time shift at which the similarity is maximized as the time difference ΔT (first time difference).

[0038] The cross-correlation method is a technique that determines the similarity between time series data by examining their cross-correlation. The dynamic time stretching method, on the other hand, calculates the distance between each point in two time series by exhaustive calculation and uses the path that results in the shortest possible path between the two time series as the measure of similarity.

[0039] (Step S16) Next, the measurement control unit 20 determines whether it has calculated a predetermined number of time differences. If it has calculated a predetermined number of time differences ΔT (Yes in step S16), the measurement control unit 20 terminates the time difference calculation process. If it has not calculated a predetermined number of time differences ΔT (No in step S16), the measurement control unit 20 returns to step S12 and repeats the process.

[0040] Returning to step S12, the measurement control unit 20 acquires the first output from the first sensor 11 and the second output from the second sensor 12 for a predetermined period (measurement period), shifted from the measurement period for the most recent measurement. Note that the measurement period for the most recent measurement and the period for the next measurement may overlap. In other words, the measurement control unit 20 may discard older results for the stored data of the first and second outputs and add new results equivalent to the discarded data. The measurement control unit 20 then repeats the process.

[0041] As described above, the measurement control unit 20 repeatedly calculates the time difference ΔT while shifting the measurement period. For example, the measurement control unit 20 repeats the calculation of the time difference ΔT with a period of 0.01 seconds (10 milliseconds).

[0042] (Step S20) Next, the measurement control unit 20 calculates the frequency distribution over a predetermined period (frequency calculation period) and calculates the time difference with the highest frequency of occurrence (frequency calculation step). The frequency calculation period is longer than the measurement period. For example, the frequency calculation period is set to include a predetermined number (e.g., 100) or more measurement periods, that is, so that a predetermined number or more time differences ΔT can be obtained. The frequency calculation period is, for example, 11 seconds.

[0043] The frequency calculation process will be explained using Figure 7. Figure 7 is a flowchart illustrating the processing of the frequency calculation step in the fluid measurement system 1 according to this embodiment.

[0044] (Step S22) The measurement control unit 20 calculates a frequency distribution from the multiple time differences ΔT calculated in step S10. For example, the measurement control unit 20 calculates the frequency of how many times a time difference ΔT is included in a time interval (time difference interval) divided by a time width of 0.01 seconds (10 milliseconds).

[0045] (Step S24) Next, the measurement control unit 20 calculates the interval that represents the mode based on the frequency distribution calculated in step S22.

[0046] (Step S26) Next, the measurement control unit 20 calculates a time difference (second time difference) based on the time differences included in the interval that is the mode. The time difference (second time difference) may be, for example, the center value of the interval that is the mode, or the mean or median of the time differences included in the interval that is the mode.

[0047] (Step S30) Next, the measurement control unit 20 calculates the flow velocity based on the time difference calculated in step S30 (flow velocity calculation step). The measurement control unit 20 calculates the flow velocity from the calculated time difference, for example, based on equation 2.

[0048] (Step S40) Next, the measurement control unit 20 determines whether to continue or terminate the process (step to determine whether to continue the process). If the process is to continue (Yes in step S40), the measurement control unit 20 returns to step S10 and repeats the process. If the process is to be terminated (No in step S40), the measurement control unit 20 terminates the process.

[0049] <Summary> The fluid measurement system of this disclosure can measure the flow velocity of the fluid being measured with high accuracy. Specifically, the fluid measurement system of this disclosure can improve the accuracy of flow velocity measurement by using a frequency distribution.

[0050] Note that the measurement period is an example of the first period, and the frequency calculation period is an example of the second period.

[0051] It should be noted that the embodiments disclosed herein are illustrative and not restrictive in all respects. The above embodiments may be omitted, replaced, or modified in various ways without departing from the scope and spirit of the attached claims. [Explanation of Symbols]

[0052] 1. Fluid Measurement System 11. First Sensor 12. Second Sensor 20 Measurement Control Unit L Installation distance P piping

Claims

1. A first sensor and a second sensor are installed in the same piping at a certain distance apart, A measurement control unit that calculates the flow velocity of the fluid flowing through the piping based on the first output output from the first sensor and the second output output from the second sensor, A fluid measurement system for determining the flow velocity of a two-phase fluid, which is a mixture of a liquid and a gas, comprising: The first sensor and the second sensor are load sensors that measure the load applied to the piping. The measurement control unit, (a) A step of comparing the first output and the second output in the first period, and calculating the first time difference of the second output with respect to the first output, while shifting the first period, (b) A step of calculating a second time difference based on the frequency of occurrence of a plurality of first time differences calculated in the first period which is included in the second period which is longer than the first period, (c) A step of calculating the flow velocity based on the second time difference, Execute Fluid measurement system.

2. The above step (b) is, (b1) A step of calculating the frequency distribution of the first time difference for a plurality of first time differences in the first period included in the second period, (b) A step of calculating the second time difference based on the first time difference included in the time difference interval with high frequency in the frequency distribution, including, The fluid measurement system according to claim 1.

3. In step (a) above, the first time difference is calculated for the first output and the second output using the cross-correlation method or the dynamic time stretching method. A fluid measurement system according to either claim 1 or claim 2.

4. A fluid measurement method for determining the flow velocity of a two-phase fluid in which a liquid and a gas are mixed, (a) A step of comparing a first output output from a first sensor during a first period with a second output output from a second sensor installed at a certain distance from the first sensor in the same piping, and repeatedly calculating the first time difference between the first output and the second output while shifting the first period, (b) A step of calculating a second time difference based on the frequency of occurrence of a plurality of first time differences calculated in the first period which is included in the second period which is longer than the first period, (c) A step of calculating the flow velocity based on the second time difference, Includes, The two-phase fluid flows through the aforementioned pipe. The first sensor and the second sensor are load sensors that measure the load applied to the piping. Fluid measurement method.

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