Ultrasonic flowmeter and method for determining reliability of reception strength

Abstract

To assess the reliability of reception strength quickly with high accuracy.SOLUTION: An ultrasonic flowmeter comprises: a propagation time measurement unit 16 for measuring the propagation time of an ultrasonic wave when measured in a forward direction by transmitting an ultrasonic wave from an ultrasonic transducer 11 and receiving it by an ultrasonic transducer 12 and the propagation time of an ultrasonic wave when measured in a reverse direction by transmitting an ultrasonic wave from the ultrasonic transducer 12 and receiving it by the ultrasonic transducer 11; a reception strength detection unit 19 for detecting reception strength in the forward direction on the basis of each ultrasonic wave reception signal when measured a prescribed number of times per given time in the forward direction, and detecting reception strength in the reverse direction on the basis of each ultrasonic wave reception signal when measured a prescribed number of times per given time in the reverse direction; and a reliability assessment unit 20 for assessing the reliability of reception signal on the basis of a difference between the reception strength in the forward direction and the reception strength in the reverse direction.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to an ultrasonic flowmeter that measures the flow rate of a fluid by using ultrasonic waves. [Background technology]

[0002] An ultrasonic flowmeter that uses ultrasonic waves to measure the flow rate is known (see Patent Document 1). As shown in Fig. 12, the ultrasonic flowmeter has a pair of ultrasonic transducers 11 and 12 arranged in a pipe 10 through which a fluid to be measured flows. The upstream ultrasonic transducer 11 is driven at a resonant frequency of, for example, 500 kHz, causing the ultrasonic transducer 11 to transmit ultrasonic waves.

[0003] Ultrasonic waves propagate through the fluid in the pipe 10 and excite the ultrasonic transducer 12 on the downstream side. A received signal is obtained by amplifying the output of this ultrasonic transducer 12. The propagation time of the ultrasonic waves can be measured by measuring the time from the transmission timing of the ultrasonic waves to the arrival timing of the received signal. Similarly, ultrasonic waves are transmitted from the ultrasonic transducer 12 on the downstream side and received by the ultrasonic transducer 11 on the upstream side, and the propagation time of the ultrasonic waves is measured.

[0004] The propagation time difference Δt can be obtained by comparing the propagation time of the ultrasonic wave in the forward direction (the direction in which the fluid flows) from ultrasonic transducer 11 to ultrasonic transducer 12 with the propagation time of the ultrasonic wave in the reverse direction from ultrasonic transducer 12 to ultrasonic transducer 11. When the flow rate of the fluid is zero, the propagation time difference is in principle zero, but when the fluid is flowing, the propagation time difference Δt occurs depending on the flow rate. Therefore, the flow rate of the fluid can be calculated from the propagation time difference Δt.

[0005] In such ultrasonic flowmeters, fluctuations in reception intensity are used to determine abnormalities in the ultrasonic transducer, the type of gas, flow path abnormalities (flooding, condensation), etc. For example, in the ultrasonic flowmeter disclosed in Patent Document 1, the amplification degree of the amplification means is adjusted so that the amplitude of the ultrasonic reception signal falls within a predetermined range, and it is determined that condensation has occurred in the flow path when the amplification degree adjusted by the amplification means changes beyond a determination value.

[0006] However, electrical noise may cause temporary changes in the reception strength, which may lead to erroneous determinations. Fig. 13 is a waveform diagram showing an example of an ultrasonic reception signal when an abnormality occurs due to noise. Vin represents the ultrasonic reception signal, and N represents the noise. In the example of Fig. 13, the ultrasonic reception signal and noise overlap during period T1, and period T2 is a normal period in which the ultrasonic reception signal and noise do not overlap. The difference between the maximum and minimum values ​​of the ultrasonic reception signal within a certain period of time is detected as the reception strength, so when noise and the ultrasonic reception signal overlap, the reception strength changes.

[0007] Fig. 14 shows an example of the results of measuring the reception strength in the forward and reverse directions every second. S is the reception strength in the forward direction, and S' is the reception strength in the reverse direction. Fig. 14 shows an example in which noise and ultrasonic reception signals overlap in the time domain of 100, causing the forward reception strength S to change.

[0008] In order to prevent erroneous judgment, there is a method of measuring the reception intensity data multiple times and using the median value or average value of the reception intensity. In the ultrasonic flowmeter disclosed in Patent Document 1, the average value of the multiple measurements is used.

[0009] Fig. 15 is a diagram explaining the measurement timing of the propagation time and the reception strength. In Fig. 15, D#1, D#2,...,D#N indicate the measurement timing of the propagation time in the forward direction, and D#1', D#2',...,D#N' indicate the measurement timing of the propagation time in the reverse direction. S#1 indicates the measurement timing of the reception strength in the forward direction, and S#1' indicates the measurement timing of the reception strength in the reverse direction.

[0010] In a conventional ultrasonic flowmeter, in order to reduce current consumption, for example, forward and reverse propagation time measurements are alternately performed multiple times, and the forward propagation time measurement is acquired once when the final forward propagation time measurement is completed, and the reverse propagation time measurement is acquired once when the final reverse propagation time measurement is completed. Such propagation time measurement and reception strength measurement are performed every second. Hereinafter, the measurement period every second is called a packet. It takes several seconds to measure the reception strength multiple times in both the forward and reverse directions.

[0011] In this way, when using the median or average value of the reception strength, it is necessary to measure the reception strength multiple times, which causes delays in detecting fluctuations in the reception strength and delays in detecting condensation, etc. In addition, there is also the problem that measuring the reception strength multiple times increases power and memory consumption. On the other hand, there was a problem that trying to obtain the reception strength from a single measurement reduced the reliability of the reception strength. [Prior art documents] [Patent documents]

[0012] [Patent Document 1] JP 2018-25410 A Summary of the Invention [Problem to be solved by the invention]

[0013] The present invention has been made to solve the above-mentioned problems, and has an object to provide an ultrasonic flowmeter and a method for determining the reliability of reception strength that can determine the reliability of reception strength quickly and with high accuracy. [Means for solving the problem]

[0014] The ultrasonic flowmeter of the present invention comprises a pipe configured to allow a fluid to flow as a measurement target, a pair of ultrasonic transducers arranged upstream and downstream of the pipe, a transmitting unit configured to transmit ultrasonic waves from one of the ultrasonic transducers, and a propagation time measuring unit configured to measure the propagation time of ultrasonic waves in a forward measurement in which ultrasonic waves are transmitted from the upstream ultrasonic transducer and received by the downstream ultrasonic transducer, and the propagation time of ultrasonic waves in a reverse measurement in which ultrasonic waves are transmitted from the downstream ultrasonic transducer and received by the upstream ultrasonic transducer, for each measurement and for each forward and reverse direction. Obtained by measuring the forward direction a certain number of times per period Forward The average ultrasonic propagation time and , obtained by measuring the predetermined number of times in the reverse direction per fixed time period Reverse ultrasound The difference between the average propagation time and the propagation time difference is called the propagation time difference. a flow rate calculation unit configured to calculate a flow rate measurement value of the fluid based on a transit time difference; The above Per period The above Detecting the difference between the maximum and minimum values ​​of each ultrasonic reception signal obtained by a predetermined number of forward measurements as the forward reception intensity; The above Per period The above The present invention is characterized by comprising a reception strength detection unit configured to detect the difference between the maximum and minimum values ​​of each ultrasonic reception signal obtained by a predetermined number of reverse direction measurements as the reception strength in the reverse direction, and a reliability determination unit configured to determine the reliability of the reception strength based on the difference between the forward direction reception strength and the reverse direction reception strength.

[0015] Moreover, one configuration example of the ultrasonic flowmeter of the present invention is characterized in that it further includes a threshold setting unit configured to set a threshold for the reliability determination unit, and the reliability determination unit determines the reliability of the reception strength by comparing the difference between the forward reception strength and the reverse reception strength with the threshold. Moreover, one configuration example of the ultrasonic flowmeter of the present invention further includes a fluid type determination unit configured to calculate a sound speed based on the forward propagation time and the reverse propagation time, and determine the type of the fluid based on this sound speed and a temperature of the fluid, and the threshold setting unit sets the threshold corresponding to the type of the fluid for the reliability determination unit. In addition, in one configuration example of the ultrasonic flowmeter of the present invention, the threshold setting unit is characterized in that it sets the threshold corresponding to the type of the fluid and the flow measurement value calculated by the flow calculation unit for the reliability determination unit.

[0016] The reception strength reliability determination method of the present invention includes a first step of measuring the propagation time of ultrasonic waves in a forward measurement in which ultrasonic waves are transmitted from an ultrasonic transducer on an upstream side of a pipe through which a fluid to be measured flows and are received by an ultrasonic transducer on a downstream side of the pipe, and the propagation time of ultrasonic waves in a reverse measurement in which ultrasonic waves are transmitted from the ultrasonic transducer on the downstream side and are received by the ultrasonic transducer on the upstream side, for each measurement and for each forward and reverse direction; Obtained by measuring the forward direction a certain number of times per period Forward The average ultrasonic propagation time and , obtained by measuring the predetermined number of times in the reverse direction per fixed time period Reverse ultrasound The difference between the average propagation time and the propagation time difference is called the propagation time difference. A second step of calculating a flow rate measurement of the fluid based on the transit time difference; The above Per period The above Detecting the difference between the maximum and minimum values ​​of each ultrasonic reception signal obtained by a predetermined number of forward measurements as the forward reception intensity; The above Per period The above The method is characterized by including a third step of detecting the difference between the maximum and minimum values ​​of each ultrasonic reception signal obtained by a predetermined number of measurements in the reverse direction as the reception strength in the reverse direction, and a fourth step of determining the reliability of the reception strength based on the difference between the reception strength in the forward direction and the reception strength in the reverse direction.

[0017] Moreover, one configuration example of the reception strength reliability determination method of the present invention further includes a fifth step of setting a threshold value for determining the reliability of the reception strength before the fourth step, and the fourth step includes a step of determining the reliability of the reception strength by comparing the difference between the forward reception strength and the reverse reception strength with the threshold value. Furthermore, one configuration example of the reception strength reliability determination method of the present invention further includes a sixth step before the fifth step, of calculating a sound speed based on the forward propagation time and the reverse propagation time, and determining the type of the fluid based on this sound speed and the temperature of the fluid, and the fifth step is characterized in that it includes a step of setting the threshold value corresponding to the type of the fluid. In addition, in one configuration example of the reception strength reliability determination method of the present invention, the fifth step is characterized by including a step of setting the threshold value corresponding to the type of fluid and the flow rate measurement value calculated in the second step. Effect of the Invention

[0018] According to the present invention, by providing a reception strength detection unit and a reliability judgment unit, the reliability of the reception strength can be judged with high accuracy and quickly. Also, since the present invention does not require an increase in the number of calculations, it is possible to reduce power and memory consumption compared to the conventional method. [Brief description of the drawings]

[0019] [Figure 1] FIG. 1 is a diagram showing an example of the reception strength measured in a normal state without temporary fluctuations due to electrical noise or the like. [Diagram 2] FIG. 2 is a diagram showing an example of reception strength that temporarily fluctuates due to electrical noise or the like. [Diagram 3] FIG. 3 is a block diagram showing a configuration of an ultrasonic flowmeter according to a first embodiment of the present invention. [Figure 4] FIG. 4 is a flowchart illustrating the operation of the ultrasonic flowmeter according to the first embodiment of the present invention. [Diagram 5] FIG. 5 is a diagram showing an example of actual measurement of the difference between the reception strength in the forward direction and the reception strength in the reverse direction. [Figure 6] FIG. 6 is a diagram showing another example of measurements of the difference between the reception strength in the forward direction and the reception strength in the reverse direction. [Figure 7] FIG. 7 is a block diagram showing the configuration of an ultrasonic flowmeter according to the second embodiment of the present invention. [Figure 8] FIG. 8 is a flowchart illustrating the operation of the ultrasonic flowmeter according to the second embodiment of the present invention. [Figure 9] FIG. 9 is a diagram showing an example of the relationship between the difference between the forward reception strength and the reverse reception strength and the flow rate of a fluid. [Figure 10] FIG. 10 is a diagram showing another example of the relationship between the difference between the forward reception strength and the reverse reception strength and the flow rate of a fluid. [Figure 11] FIG. 11 is a block diagram showing an example of the configuration of a computer that realizes the ultrasonic flowmeters according to the first and second embodiments of the present invention. [Figure 12] FIG. 12 is a diagram illustrating the operating principle of a conventional ultrasonic flowmeter. [Figure 13] FIG. 13 is a waveform diagram showing an example of an ultrasonic reception signal when an abnormality occurs due to noise. [Figure 14] FIG. 14 is a diagram showing an example of the results of measuring the reception strength in the forward and reverse directions every second. [Figure 15] FIG. 15 is a diagram for explaining the measurement timing of the propagation time and the reception intensity of a conventional ultrasonic flowmeter. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] [Principle of the invention] In an ultrasonic flowmeter, the reception strength changes for the following two reasons: (I) and (II). (I) Variations due to temperature, gas type, water intrusion, etc. (II) Temporary fluctuations due to electrical noise.

[0021] It is desirable to detect the phenomenon (I) as early as possible using the measurement results of the reception strength, but there is a possibility that a false detection will occur due to the reason (II). The object of the present invention is to quickly determine whether the phenomenon (II) is occurring and to improve the reliability of the reception strength.

[0022] In the present invention, the determination is made based on the difference between the reception strength in the forward and reverse directions within the same packet. Figure 1 shows an example of reception strength measured every second under normal conditions without temporary fluctuations due to electrical noise, etc., and Figure 2 shows an example of reception strength that has temporarily fluctuated due to electrical noise, etc. S is the reception strength in the forward direction, and S' is the reception strength in the reverse direction.

[0023] Under normal conditions, the forward and reverse reception strengths in the same packet are close to each other, and the difference in reception strength is below a certain value. In the example of Figure 1, the reception strength decreases midway due to temperature, gas type, water intrusion, etc., but even when the reception strength changes in this way, both the forward and reverse reception strengths in the same packet fluctuate.

[0024] On the other hand, since the forward reception strength and reverse reception strength within the same packet are measured separately, if the reception strength fluctuates instantaneously due to electrical noise or the like, it is unlikely that both the forward and reverse reception strengths will be affected, and the difference between the forward and reverse reception strengths within the same packet will be larger than normal, as shown in the example of the time domain 100 in Figure 2. In the present invention, the above characteristics are utilized to determine the reliability of the reception strength in real time.

[0025] [First Example] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Fig. 3 is a block diagram showing the configuration of an ultrasonic flowmeter according to a first embodiment of the present invention. The ultrasonic flowmeter includes a pipe 10 through which a fluid to be measured flows, a pair of ultrasonic transducers 11 and 12 arranged upstream and downstream of the pipe 10, a transmission unit 13 that transmits ultrasonic waves from one of the ultrasonic transducers, a reception unit 14 that amplifies an ultrasonic reception signal received by the other ultrasonic transducer, a switching unit 15 that switches the connection between the ultrasonic transducers 11 and 12 and the transmission unit 13 and reception unit 14, a propagation time measuring unit 16 that measures the propagation time of ultrasonic waves in a forward measurement in which ultrasonic waves are transmitted from the ultrasonic transducer 11 and received by the ultrasonic transducer 12, and the propagation time of ultrasonic waves in a reverse measurement in which ultrasonic waves are transmitted from the ultrasonic transducer 12 and received by the ultrasonic transducer 11, for each measurement and for each forward and reverse direction, and a propagation time measuring unit 17 that measures the propagation time of ultrasonic waves in the forward direction and the propagation time of ultrasonic waves in the reverse measurement in which ultrasonic waves are transmitted from the ultrasonic transducer 12 and received by the ultrasonic transducer 11, for each measurement and for each forward and reverse direction. The device is equipped with a flow rate calculation unit 17 that calculates the propagation time difference between ultrasonic waves in the forward and reverse directions based on time and calculates a flow rate measurement value of the fluid from this propagation time difference, a flow rate output unit 18 that transmits the flow rate measurement value to a higher-level device, a reception strength detection unit 19 that detects forward reception strength based on each ultrasonic reception signal of a predetermined number of forward measurement times per fixed time (packet) and detects reverse reception strength based on each ultrasonic reception signal of a predetermined number of reverse measurement times per fixed time, a reliability judgment unit 20 that judges the reliability of the reception strength based on the difference between the forward reception strength and the reverse reception strength, a threshold setting unit 21 that sets a threshold for judging the reliability of the reception strength, and a judgment result output unit 22 that outputs the judgment result of the reliability judgment unit 20.

[0026] In this embodiment, a pair of ultrasonic transducers 11, 12 are arranged upstream and downstream of the pipe 10. In the forward direction, in which ultrasonic waves are transmitted from the ultrasonic transducer 11 on the upstream side and received by the ultrasonic transducer 12 on the downstream side, the switching unit 15 connects the transmitting unit 13 to the ultrasonic transducer 11 and connects the ultrasonic transducer 12 to the receiving unit 14. At this time, the transmitting unit 13 supplies a driving transmission pulse to the ultrasonic transducer 11. As a result, the ultrasonic transducer 11 transmits ultrasonic waves in an oblique direction to the fluid in the pipe 10 in response to the transmission pulse from the transmitting unit 13. The ultrasonic transducer 12 receives the ultrasonic waves transmitted from the ultrasonic transducer 11 and reflected by the inner wall of the pipe 10. The receiving unit 14 amplifies the output signal of the ultrasonic transducer 12 and outputs an ultrasonic reception signal.

[0027] Conversely, in the reverse direction where ultrasonic waves are transmitted from the ultrasonic transducer 12 on the downstream side and received by the ultrasonic transducer 11 on the upstream side, the switching unit 15 connects the transmitting unit 13 to the ultrasonic transducer 12 and connects the ultrasonic transducer 11 to the receiving unit 14. At this time, the transmitting unit 13 supplies a driving transmission pulse to the ultrasonic transducer 12. As a result, the ultrasonic transducer 12 transmits ultrasonic waves in an oblique direction to the fluid in the pipe 10 in response to the transmission pulse from the transmitting unit 13. The ultrasonic transducer 11 receives the ultrasonic waves transmitted from the ultrasonic transducer 12 and reflected by the inner wall of the pipe 10. The receiving unit 14 amplifies the output signal of the ultrasonic transducer 11 and outputs an ultrasonic reception signal.

[0028] 4 is a flowchart for explaining the operation of the ultrasonic flowmeter of this embodiment. In this embodiment, ultrasonic waves are transmitted and received in both forward and reverse directions, and the number of ultrasonic transmission and reception repetitions per packet (1 second) is set to N (N is an integer of 2 or more).

[0029] First, the propagation time measurement unit 16 initializes the measurement count i (i is an integer from 1 to N) to 1 (Step S100 in FIG. 4). The ultrasonic transducer 11 or 12 transmits ultrasonic waves to the fluid flowing in the pipe 10 in response to a transmission pulse from the transmitter 13 (step S101 in FIG. 4). As described above, in the forward direction, ultrasonic waves are transmitted from the ultrasonic transducer 11, and in the reverse direction, ultrasonic waves are transmitted from the ultrasonic transducer 12. In this embodiment, measurement is started from the forward direction.

[0030] The receiving unit 14 amplifies the output signal of the ultrasonic transducer 11 or 12 and outputs an ultrasonic reception signal (step S102 in FIG. 4). In the forward direction, the ultrasonic transducer 12 receives the ultrasonic waves transmitted from the ultrasonic transducer 11, and the receiving unit 14 amplifies the output signal of the ultrasonic transducer 12. In the reverse direction, the ultrasonic transducer 11 receives the ultrasonic waves transmitted from the ultrasonic transducer 12, and the receiving unit 14 amplifies the output signal of the ultrasonic transducer 11.

[0031] The propagation time measurement unit 16 measures the propagation time of the ultrasonic waves (step S103 in FIG. 4). The forward propagation time is the time from when the ultrasonic transducer 11 transmits an ultrasonic wave until when the ultrasonic transducer 12 receives it. The backward propagation time is the time from when the ultrasonic transducer 12 transmits an ultrasonic wave until when the ultrasonic transducer 11 receives it.

[0032] If measurements in both the forward and reverse directions have not been completed (NO in step S104 in FIG. 4), the switching unit 15 switches the direction (step S105 in FIG. 4). For example, if the forward measurement has been completed but the reverse measurement has not been completed, the switching unit 15 switches to the reverse direction. As described above, in the reverse direction, the switching unit 15 connects the transmitting unit 13 to the ultrasonic transducer 12 and connects the ultrasonic transducer 11 to the receiving unit 14.

[0033] In this way, the processes of steps S101 to S103 are performed for the reverse direction in the same manner as described above. When the measurement in the reverse direction is completed, the measurement in both the forward and reverse directions is completed, so the propagation time measurement unit 16 increments the measurement count i by 1 (step S106 in FIG. 4).

[0034] If the number of measurements i does not exceed the number of repeated ultrasonic transmissions and receptions N, and measurements have not been completed N times in both the forward and reverse directions (NO in step S107 in FIG. 4), the switching unit 15 switches the direction (step S105). Here, the switching unit 15 switches to the forward direction. As described above, in the forward direction, the switching unit 15 connects the transmitting unit 13 to the ultrasonic transducer 11, and connects the ultrasonic transducer 12 to the receiving unit 14.

[0035] In this way, the measurement of the propagation time in both the forward and reverse directions is repeatedly executed. When the Nth measurement of the propagation time in the forward direction is completed (YES in step S108 in FIG. 4), the reception intensity detection unit 19 detects the difference between the maximum and minimum values ​​of each ultrasonic reception signal obtained in the N forward measurements as the reception intensity in the forward direction (step S109 in FIG. 4).

[0036] Furthermore, when the Nth measurement of the propagation time in the reverse direction is completed (YES in step S110 of FIG. 4), the reception strength detection unit 19 detects the difference between the maximum and minimum values ​​of each ultrasonic reception signal obtained in the N measurements in the reverse direction as the reception strength in the reverse direction (step S111 of FIG. 4).

[0037] When the number of measurements i exceeds N (YES in step S107), the measurements of the propagation time in both the forward and reverse directions and the measurements of the reception intensity in both the forward and reverse directions are completed N times. In this embodiment, the measurement timing of the propagation time and the reception strength is the same as in FIG.

[0038] Next, the flow rate calculation unit 17 determines the difference between the average value of the forward propagation time and the average value of the backward propagation time obtained by the N measurements as the propagation time difference Δt, and calculates the flow rate measurement value from the propagation time difference Δt (FIG. 4, step S112). A known calculation formula used in a general ultrasonic flowmeter may be used as the calculation method for obtaining the flow rate measurement value, and detailed description thereof will be omitted.

[0039] The flow rate output unit 18 is connected to a higher-level device (not shown) via a communication network, and transmits the flow rate measurement value calculated by the flow rate calculation unit 17 to the higher-level device (step S113 in FIG. 4).

[0040] Next, the reliability determination unit 20 determines the reliability of the reception strength. Specifically, the reliability determination unit 20 calculates the difference between the reception strength in the forward direction and the reception strength in the reverse direction detected by the reception strength detection unit 19 for the same packet (FIG. 14, step S114).

[0041] Then, the reliability judgment unit 20 judges that the reliability of the reception strength is high if the calculated difference in reception strength is within a predetermined threshold range (±TH) centered on 0, and judges that the reliability of the reception strength is low if the difference in reception strength is outside the threshold range (Figure 14, step S115).

[0042] In this embodiment, the threshold value TH is a fixed value and is set by the threshold setting unit 21. FIG. 5 is a diagram showing an example of an actual measurement of the difference between the forward reception strength and the reverse reception strength under normal conditions. The example in FIG. 5 shows actual measurements when conditions such as temperature, fluid flow rate, and type of fluid (gas type) are changed. The propagation distance from the ultrasonic transducer 11 through the inner wall of the pipe 10 to the ultrasonic transducer 12 is known. The horizontal axis in FIG. 5 shows the sound speed of ultrasonic waves in the fluid calculated by dividing the propagation distance by the average value of the forward propagation time and the reverse propagation time.

[0043] Under normal conditions where there are no temporary fluctuations in reception strength due to electrical noise or the like, the difference between the forward reception strength and the reverse reception strength will not exceed, for example, 70 mV even if the temperature, flow rate, type of fluid, etc. change. Therefore, the threshold value TH can be determined in advance from the actual measurement data as shown in Figure 5.

[0044] 6 is a diagram showing an example of an actual measurement of the difference between the forward reception strength and the reverse reception strength when the reception strength fluctuates temporarily due to electrical noise, etc. When the reception strength fluctuates instantaneously due to electrical noise, etc., the difference between the forward reception strength and the reverse reception strength becomes larger than the threshold value TH.

[0045] Therefore, if the difference in reception strength is outside the threshold range (±TH), the reliability determination unit 20 can determine that the fluctuation in reception strength is likely caused by noise, and the reliability of the reception strength is low. Also, if the difference in reception strength is within the threshold range (±TH), the reliability determination unit 20 can determine that the reliability of the reception strength is high. If the difference in reception strength is within the threshold range (±TH), even if the reception strength fluctuates, it can be determined that this fluctuation is likely not due to noise, but due to temperature, gas type, water intrusion, etc.

[0046] The determination result output unit 22 outputs the determination result of the reliability determination unit 20 (step S116 in FIG. 4). An example of the output method is to transmit the determination result to a higher-level device. The above-described process of FIG. 4 is performed for each packet (every second in this embodiment).

[0047] The difference between this embodiment and the conventional ultrasonic flowmeter will be explained with the example of Fig. 15. In the conventional ultrasonic flowmeter, the average value of the measurement results of the reception strength of multiple packets in the same direction is used, which takes several seconds, and a delay occurs in detecting the fluctuation of the reception strength. In addition, if the reception strength is measured multiple times, the power and memory consumption increases.

[0048] On the other hand, in this embodiment, the reliability of the reception strength can be determined by measuring one packet, so that the determination can be made more quickly than in the past.

[0049] [Second Example] Next, a second embodiment of the present invention will be described. Fig. 7 is a block diagram showing the configuration of an ultrasonic flowmeter according to the second embodiment of the present invention, and the same components as those in Fig. 3 are given the same reference numerals. The ultrasonic flowmeter of this embodiment includes a pipe 10, ultrasonic transducers 11 and 12, a transmitting unit 13, a receiving unit 14, a switching unit 15, a propagation time measuring unit 16, a flow rate calculating unit 17, a flow rate output unit 18, a reception intensity detecting unit 19, a reliability determining unit 20, a threshold setting unit 21a, a determination result output unit 22, and a fluid type determining unit 23 for determining the type of fluid.

[0050] In this embodiment, in order to improve the accuracy of determining the reliability of the received signal strength, the threshold value TH is set as follows. Fig. 8 is a flow chart for explaining the operation of the ultrasonic flowmeter of this embodiment. The processes of steps S100 to S113 in Fig. 8 are the same as those explained in the first actual measurement example.

[0051] The fluid type determination unit 23 determines the type of fluid flowing through the pipe 10 (step S117 in FIG. 8). Specifically, the fluid type determination unit 23 calculates the sound speed of ultrasonic waves in the fluid by dividing the known propagation distance by the average value of the forward propagation time and the backward propagation time obtained from N measurements, and determines the type of fluid based on the calculated sound speed and the temperature of the fluid measured by a temperature sensor (not shown) provided in the pipe 10. If the sound speed and temperature are known, the molecular weight can be estimated, making it possible to determine the type of fluid. The relationship between the sound speed and temperature and the type of fluid is registered in advance in the fluid type determination unit 23.

[0052] Next, the threshold setting unit 21a sets a threshold TH corresponding to the type of fluid, or a threshold TH corresponding to the type of fluid and the flow rate measurement value calculated by the flow rate calculation unit 17, for the reliability determination unit 20 (Step S118 in FIG. 8).

[0053] For some fluids, the difference between the forward reception strength and the reverse reception strength in the same packet in a normal state depends on the flow rate, as shown in Fig. 9. Therefore, for fluids with such characteristics, it is desirable to set the threshold value TH according to the type of fluid and the flow rate measurement value.

[0054] Furthermore, for some fluids, the difference between the forward reception strength and the reverse reception strength has low dependency on the flow rate, as shown in Fig. 10. For fluids with such characteristics, the threshold value TH may be set according to the type of fluid, or the threshold value TH may be set according to the type of fluid and the flow rate measurement value. The relationship between the type of fluid, the flow rate, and the threshold value TH is registered in advance in the threshold value setting unit 21a. The relationship between the type of fluid, the flow rate, and the threshold value TH can be determined from actual measurement data obtained in a flow rate test in advance.

[0055] 8 are the same as those described in the first measurement example. Thus, in this embodiment, it is possible to further improve the accuracy of determining the reliability of the received signal strength compared to the first measurement example.

[0056] In the present invention, the method of using the result of the determination of the reliability of the reception strength is not important. As described above, examples of using the reception strength include abnormality determination of an ultrasonic transducer, gas type determination, and flow path abnormality determination, and the present invention can be applied to any of these examples.

[0057] The transmitter 13, receiver 14, switch 15, and propagation time measurement unit 16 described in the first and second embodiments can be realized by an IC such as an FPGA (Field Programmable Gate Array). The flow rate calculator 17, flow rate output unit 18, reception intensity detector 19, reliability judger 20, threshold setting units 21, 21a, judgement result output unit 22, and fluid type judger 23 can be realized by a computer equipped with a CPU (Central Processing Unit), a storage device, and an interface, and a program that controls these hardware resources. An example of the configuration of this computer is shown in FIG.

[0058] The computer includes a CPU 200, a storage device 201, and an interface device (I / F) 202. The I / F 202 is connected to the transmitting unit 13, the receiving unit 14, the switching unit 15, the propagation time measuring unit 16, and the like. In such a computer, a program for realizing the reception strength reliability determination method of the present invention is stored in the storage device 201. The CPU 200 executes the processes described in the first and second embodiments in accordance with the program stored in the storage device 201. [Industrial Applicability]

[0059] The present invention can be applied to an ultrasonic flow meter. [Explanation of symbols]

[0060] 10...piping, 11, 12...ultrasonic transducer, 13...transmitter, 14...receiver, 15...switching unit, 16...propagation time measuring unit, 17...flow rate calculation unit, 18...flow rate output unit, 19...receiving intensity detection unit, 20...reliability determination unit, 21, 21a...threshold setting unit, 22...determination result output unit, 23...fluid type determination unit.

Claims

1. A pipe configured so that a fluid to be measured flows through it; A pair of ultrasonic transducers disposed upstream and downstream of the piping; A transmitting unit configured to transmit ultrasonic waves from one of the ultrasonic transducers; A propagation time measuring unit configured to measure the propagation time of ultrasonic waves in a forward measurement in which ultrasonic waves are transmitted from the ultrasonic transducer on the upstream side and received by the ultrasonic transducer on the downstream side, and the propagation time of ultrasonic waves in a reverse measurement in which ultrasonic waves are transmitted from the ultrasonic transducer on the downstream side and received by the ultrasonic transducer on the upstream side, for each measurement and for each forward and reverse direction; A flow rate calculation unit configured to calculate a flow rate measurement value of the fluid based on a propagation time difference between an average value of a forward ultrasonic wave propagation time obtained by a predetermined number of forward measurements per fixed time period and an average value of a backward ultrasonic wave propagation time obtained by the predetermined number of backward measurements per fixed time period, the difference being a propagation time difference; a reception strength detection unit configured to detect a difference between a maximum value and a minimum value of each ultrasonic reception signal obtained in the predetermined number of forward direction measurements per fixed time period as a forward reception strength, and to detect a difference between a maximum value and a minimum value of each ultrasonic reception signal obtained in the predetermined number of reverse direction measurements per fixed time period as a reverse reception strength; and a reliability determination unit configured to determine reliability of reception strength based on a difference between the reception strength in the forward direction and the reception strength in the reverse direction.

2. 2. The ultrasonic flowmeter according to claim 1, A threshold setting unit configured to set a threshold for the reliability determination unit, The ultrasonic flowmeter according to claim 1, wherein the reliability determination unit determines reliability of the reception strength by comparing a difference between the reception strength in the forward direction and the reception strength in the reverse direction with the threshold value.

3. 3. The ultrasonic flowmeter according to claim 2, A fluid type determination unit is further configured to calculate a sound speed based on the forward propagation time and the reverse propagation time, and to determine a type of the fluid based on the sound speed and a temperature of the fluid, The ultrasonic flowmeter according to claim 1, wherein the threshold setting unit sets the threshold corresponding to a type of the fluid for the reliability determination unit.

4. 4. The ultrasonic flowmeter according to claim 3, The ultrasonic flowmeter according to claim 1, wherein the threshold setting unit sets the threshold corresponding to the type of the fluid and the flow rate measurement value calculated by the flow rate calculation unit for the reliability determination unit.

5. a first step of measuring the propagation time of ultrasonic waves in a forward measurement in which ultrasonic waves are transmitted from an ultrasonic transducer on an upstream side of a pipe through which a fluid to be measured flows and received by an ultrasonic transducer on a downstream side of the pipe, and in a reverse measurement in which ultrasonic waves are transmitted from the ultrasonic transducer on the downstream side and received by the ultrasonic transducer on the upstream side, for each measurement and for each forward and reverse direction; a second step of calculating a flow rate measurement value of the fluid based on a propagation time difference between an average value of a forward ultrasonic wave propagation time obtained by a predetermined number of forward measurements per fixed time period and an average value of a backward ultrasonic wave propagation time obtained by the predetermined number of backward measurements per fixed time period; a third step of detecting a difference between a maximum value and a minimum value of each ultrasonic reception signal obtained in the predetermined number of forward direction measurements per fixed time period as a forward direction reception intensity, and detecting a difference between a maximum value and a minimum value of each ultrasonic reception signal obtained in the predetermined number of reverse direction measurements per fixed time period as a reverse direction reception intensity; and a fourth step of determining reliability of the reception strength based on a difference between the reception strength in the forward direction and the reception strength in the reverse direction.

6. 6. The method for determining reliability of received signal strength according to claim 5, The method further includes a fifth step, prior to the fourth step, of setting a threshold value for determining reliability of the reception strength; The reception strength reliability determination method, wherein the fourth step includes a step of determining reliability of the reception strength by comparing a difference between the forward reception strength and the reverse reception strength with the threshold value.

7. 7. The method for determining reliability of a received signal strength according to claim 6, The method further includes, before the fifth step, a sixth step of calculating a sound speed based on the forward propagation time and the reverse propagation time, and determining a type of the fluid based on the sound speed and a temperature of the fluid; The method for determining reliability of received signal strength, wherein the fifth step includes a step of setting the threshold value corresponding to a type of the fluid.

8. 8. The method for determining reliability of a received signal strength according to claim 7, The method for determining reliability of received signal strength, wherein the fifth step includes a step of setting the threshold value corresponding to the type of fluid and the flow rate measurement value calculated in the second step.

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