Ultrasonic flowmeter and reception strength reliability determination method

Abstract

To quickly acquire maximum reception strength with high reliability.SOLUTION: The zero-cross detection unit 16 measures the zero-cross time of the ultrasonic reception signal in the forward direction in which the ultrasonic wave is transmitted from the transducer 11 and received by the transducer 12 and the zero-cross time in the reverse direction in which the ultrasonic wave is transmitted from the transducer 12 and received by the transducer 11, and stores the zero-cross times in the time array of the storage unit 17. A maximum reception strength detection part 22 detects the maximum reception strength of the ultrasonic reception signal in each of the forward and backward directions, and determines the reliability of the maximum reception strength based on the zero cross time of a plurality of measurement times.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an ultrasonic flowmeter and a method for determining the reliability of reception strength. [Background technology]

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

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

[0004] The propagation time difference Δt can be found by comparing the propagation time of the ultrasonic wave in the forward direction (the direction in which the fluid flows) from transducer 11 to transducer 12 with the propagation time of the ultrasonic wave in the reverse direction from transducer 12 to transducer 11. In principle, the propagation time difference is zero when the fluid flow rate is 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 transducer abnormalities, gas type, 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 ultrasonic reception signal has an amplitude within a predetermined range, and if the amplification degree adjusted by the amplification means changes beyond a determination value, it is determined that condensation has occurred in the flow path. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2018-25410 Summary of the Invention [Problem to be solved by the invention]

[0007] 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 where 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.

[0008] Figure 14 shows an example of the results of measuring the maximum reception strength in the forward and reverse directions every second. S is the maximum reception strength in the forward direction, and S' is the maximum reception strength in the reverse direction. Figure 14 shows an example in which noise and ultrasonic reception signals overlap in the time domain of 100, causing the maximum reception strength S in the forward direction to change.

[0009] To prevent erroneous judgment, there is a method of measuring the maximum reception intensity data multiple times and using the median or average value of the maximum reception intensity. The ultrasonic flowmeter disclosed in Patent Document 1 uses the average value of the multiple measurements.

[0010] Figure 15 is a diagram explaining the measurement timing of propagation time and maximum reception strength. In Figure 15, D#1, D#2,...,D#N indicate the measurement timing of propagation time in the forward direction, and D#1', D#2',...,D#N' indicate the measurement timing of propagation time in the reverse direction. S#1 indicates the measurement timing of maximum reception strength in the forward direction, and S#1' indicates the measurement timing of maximum reception strength in the reverse direction.

[0011] In a conventional ultrasonic flowmeter, for example, forward and reverse propagation time measurements are alternately performed multiple times, and the maximum forward reception strength is obtained once when the final forward propagation time measurement is completed, and the maximum reverse reception strength is obtained once when the final reverse propagation time measurement is completed. Such propagation time measurements and maximum reverse reception strength measurements are performed every second. Hereinafter, each measurement period per second is called a packet. Measuring the maximum reception strength multiple packets can take several seconds.

[0012] In this way, when using the median or average value of the maximum reception strength, it is necessary to measure the maximum reception strength over multiple packets, which causes delays in detecting fluctuations in the maximum reception strength, resulting in delays in determining transducer anomalies, gas type determinations, flow path anomalies, etc. Another problem is that measuring the maximum reception strength over multiple packets increases power and memory consumption.

[0013] On the other hand, there is a problem that the reliability of the maximum reception strength is low when trying to obtain it by measuring one packet.The following two reasons (I) and (II) are thought to be the reasons why the maximum reception strength changes in ultrasonic flowmeters. (I) Fluctuations due to temperature, gas type, water intrusion, etc. (II) Temporal fluctuations due to electrical noise.

[0014] It is desirable to detect phenomenon (I) as early as possible using the measurement results of received signal strength, but there is a possibility that an incorrect maximum received signal strength may be measured due to reason (II). Therefore, when obtaining the maximum received signal strength by measuring one packet, it is necessary to discard the maximum received signal strength that has fluctuated due to reason (II) as it is unreliable.

[0015] The present invention has been made to solve the above-mentioned problems, and aims to provide an ultrasonic flowmeter and a method for determining the reliability of reception strength that can quickly acquire a highly reliable maximum reception strength. [Means for solving the problem]

[0016] The ultrasonic flowmeter of the present invention comprises a pipe configured to allow a fluid to flow as a measurement target, a pair of transducers arranged upstream and downstream of the pipe, a transmitting unit configured to transmit ultrasonic waves from one of the transducers, a memory unit configured to store a time array that stores the zero-cross times of the ultrasonic reception signal during a forward measurement in which ultrasonic waves are transmitted from the upstream transducer and received by the downstream transducer, and the zero-cross times of the ultrasonic reception signal during a reverse measurement in which ultrasonic waves are transmitted from the downstream transducer and received by the upstream transducer, for each measurement and for each forward and reverse direction, a flow rate calculating unit configured to obtain a target zero-cross time to be used for calculating the propagation time from the time array for each forward and reverse direction, calculate the difference in propagation time between the ultrasonic waves in the forward and reverse directions based on the obtained target zero-cross times, and calculate the flow rate of the fluid from this difference in propagation time, and a maximum reception intensity detecting unit configured to detect the maximum reception intensity of the ultrasonic reception signal for each forward and reverse direction, wherein the maximum reception intensity detecting unit determines the reliability of the maximum reception intensity based on the zero-cross times of multiple measurements.

[0017] In addition, in one configuration example of the ultrasonic flowmeter of the present invention, the maximum reception intensity detection unit is characterized in that it determines the reliability of the maximum reception intensity based on a time sequence of zero-cross times of two or more ultrasonic reception signals that exceed a threshold at different times. Furthermore, one configuration example of the ultrasonic flowmeter of the present invention further includes a zero-cross detection unit configured to measure the zero-cross times after the point in time when the ultrasonic reception signal becomes equal to or greater than the threshold voltage for each measurement and for each forward and reverse direction, and to store the measured zero-cross times in order from a specific storage position in the time array prepared for the corresponding measurement and the corresponding direction; and a degree calculation unit configured to calculate, for each forward and reverse direction, a degree of a time array in which the leading zero-cross time stored in a specific position in each time array is a zero-cross time a predetermined period before a target zero-cross time used to calculate the propagation time, wherein the maximum reception strength detection unit determines the reliability of the maximum reception strength based on the degree. In one configuration example of the ultrasonic flowmeter of the present invention, when the detected maximum reception intensity increases, if the degree is greater than a predetermined upper limit value, the maximum reception intensity detection unit determines that the reliability of the maximum reception intensity is high, and if the degree is equal to or less than the upper limit value, the maximum reception intensity detection unit determines that the reliability of the maximum reception intensity is low. In one configuration example of the ultrasonic flowmeter of the present invention, when the detected maximum reception intensity decreases, if the degree is smaller than a predetermined lower limit value, the maximum reception intensity detection unit determines that the reliability of the maximum reception intensity is high, and if the degree is equal to or greater than the lower limit value, the maximum reception intensity detection unit determines that the reliability of the maximum reception intensity is low.

[0018] Furthermore, one configuration example of the ultrasonic flowmeter of the present invention is characterized in that it further comprises a threshold voltage adjustment unit configured to adjust the threshold voltage based on the degree so that the peak voltage of a wave of the AC pulse-shaped ultrasonic reception signal that is a target wave corresponding to the target zero-crossing time and that is a predetermined period before the target wave has the same value as the threshold voltage. In addition, in one configuration example of the ultrasonic flowmeter of the present invention, the degree calculation unit counts the detection frequency for each time interval on the time axis, which includes the leading zero cross time stored at a specific position in each time array, and from these detection frequencies, identifies the time interval including the target zero cross time and the time interval including the zero cross time a predetermined period before the target zero cross time, and calculates the degree by dividing the detection frequency of the leading zero cross time in the time interval including the zero cross time a predetermined period before the target zero cross time by the total number of counting results.

[0019] The reception strength reliability determination method of the present invention includes a first step of measuring a plurality of zero-cross times of an ultrasonic reception signal in a forward measurement in which an ultrasonic wave is transmitted from a transducer on the upstream side of a pipe through which a fluid to be measured flows and is received by a transducer on the downstream side of the pipe, and a plurality of zero-cross times of an ultrasonic reception signal in a reverse measurement in which an ultrasonic wave is transmitted from the transducer on the downstream side and is received by the transducer on the upstream side, for each measurement and for each forward and reverse direction; and a second step of measuring a plurality of zero-cross times measured after the ultrasonic reception signal becomes equal to or greater than a threshold voltage, for each corresponding measurement. a second step of sequentially storing the ultrasonic waves from a specific storage position in a time array prepared for each measurement and corresponding direction; a third step of obtaining a target zero cross time from the time array for each forward and reverse direction to be used in calculating the propagation time, calculating the difference in propagation time between the ultrasonic waves in the forward and reverse directions based on the obtained target zero cross times, and calculating the flow rate of the fluid from this difference in propagation time; a fourth step of detecting the maximum reception strength of the ultrasonic reception signal for each forward and reverse direction; and a fifth step of determining the reliability of the maximum reception strength based on the zero cross times of multiple measurement measurements. [Effects of the Invention]

[0020] According to the present invention, a maximum received signal strength detector is provided and the reliability of the maximum received signal strength can be determined simply by measuring the zero-crossing times multiple times in each of the forward and reverse directions, so that a highly reliable maximum received signal strength can be obtained more quickly than in the past. Furthermore, since the present invention does not require an increase in the number of measurements, power and memory consumption can be reduced compared to the past. [Brief explanation of the drawings]

[0021] [Figure 1] FIG. 1 is a block diagram showing the configuration of an ultrasonic flowmeter according to an embodiment of the present invention. [Figure 2] FIG. 2 is a signal waveform diagram showing the relationship between the ultrasonic reception signal and the zero crossing points. [Figure 3] FIG. 3 is a histogram showing the first zero crossing times. [Figure 4] FIG. 4 is a diagram for explaining the principle of evaluating the reliability of the maximum received signal strength. [Figure 5] FIG. 5 is a flowchart illustrating the operation of the ultrasonic flowmeter according to the embodiment of the present invention. [Figure 6] FIG. 6 is a diagram showing an example of a time sequence. [Figure 7] FIG. 7 is a diagram illustrating the degree calculation operation by the degree calculation unit of the ultrasonic flowmeter according to the embodiment of the present invention. [Figure 8] FIG. 8 is a flowchart illustrating the operation of the threshold voltage adjusting unit of the ultrasonic flowmeter according to the embodiment of the present invention. [Figure 9] FIG. 9 is a diagram illustrating the initialization operation of the threshold voltage by the threshold voltage adjustment unit of the ultrasonic flowmeter according to the embodiment of the present invention. [Figure 10] FIG. 10 is a flowchart illustrating the reliability determination operation by the maximum reception intensity detection unit of the ultrasonic flowmeter according to the embodiment of the present invention. [Figure 11] FIG. 11 is a block diagram showing an example of the configuration of a computer that realizes an ultrasonic flowmeter according to an embodiment 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 maximum reception strength in the forward and reverse directions every second. [Figure 15] FIG. 15 is a diagram illustrating the propagation time and the measurement timing of the maximum reception intensity in a conventional ultrasonic flowmeter. DETAILED DESCRIPTION OF THE INVENTION

[0022] [Example] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a block diagram showing the configuration of an ultrasonic flowmeter according to an embodiment of the present invention. The ultrasonic flowmeter includes a pipe 10 through which a fluid (gas or liquid) to be measured flows, a pair of transducers (ultrasonic piezoelectric elements) 11 and 12 arranged upstream and downstream of the pipe 10, a transmitter 13 that transmits ultrasonic waves from one of the transducers, a receiver 14 that amplifies the ultrasonic reception signal received by the other transducer, a switch 15 that switches the connections between the transducers 11 and 12, the transmitter 13, and the receiver 14, a zero-cross detection unit 16 that measures a plurality of zero-cross times for each measurement and for each forward and reverse direction after the ultrasonic reception signal becomes equal to or greater than a threshold voltage, a memory unit 17 that stores the zero-cross times, and a target zero-cross time that is used to calculate the propagation time from the time sequence stored in the memory unit 17 for each forward and reverse direction and the acquired target zero-cross times. a flow rate calculation unit 18 that calculates the difference in propagation time between ultrasonic waves in the forward and reverse directions based on the time and calculates the flow rate of the fluid from the difference in propagation time; a flow rate output unit 19 that transmits the flow rate value to a higher-level device; a degree calculation unit 20 that calculates the degree of a time sequence in which the leading zero-cross time stored at a specific position in each time sequence is the zero-cross time a predetermined number of cycles before the target zero-cross time, for each of the forward and reverse directions; a threshold voltage adjustment unit 21 that adjusts the threshold voltage based on the degree so that the peak voltage of a wave of the ultrasonic reception signal that is a predetermined number of cycles before the target wave corresponding to the target zero-cross time has the same value as the threshold voltage; a maximum reception intensity detection unit 22 that detects the maximum reception intensity of the ultrasonic reception signal for each of the forward and reverse directions; and an alarm output unit 23 that outputs an alarm when the amount of change in the maximum reception intensity exceeds the threshold.

[0023] In this embodiment, a pair of transducers 11, 12 are arranged facing each other upstream and downstream of the pipe 10. Alternatively, as shown in Fig. 12, the transducers 11, 12 may be arranged at the same circumferential position of the circular cross section of the pipe 10 but at different positions in the gas flow direction. In this case, the propagation path for transmitting and receiving ultrasonic waves is a V-shaped propagation path that is reflected by the inner wall of the pipe 10.

[0024] In the forward direction, where ultrasonic waves are transmitted from the upstream transducer 11 and received by the downstream transducer 12, the switching unit 15 connects the transmitting unit 13 to the transducer 11 and connects the transducer 12 to the receiving unit 14. At this time, the transmitting unit 13 supplies a driving transmission pulse to the transducer 11. As a result, the transducer 11 transmits ultrasonic waves in an oblique direction to the gas flowing inside the pipe 10 in response to the transmission pulse from the transmitting unit 13. The transducer 12 receives the ultrasonic waves transmitted from the transducer 11. The receiving unit 14 amplifies the output signal of the transducer 12 and outputs an ultrasonic reception signal Vin.

[0025] Conversely, when the ultrasonic wave is transmitted from the downstream transducer 12 and received by the upstream transducer 11 in the reverse direction, the switching unit 15 connects the transmitting unit 13 to the transducer 12 and connects the transducer 11 to the receiving unit 14. At this time, the transmitting unit 13 supplies a driving transmission pulse to the transducer 12. As a result, the transducer 12 transmits ultrasonic waves in an oblique direction toward the gas flowing inside the pipe 10 in response to the transmission pulse from the transmitting unit 13. The transducer 11 receives the ultrasonic waves transmitted from the transducer 12. The receiving unit 14 amplifies the output signal of the transducer 11 and outputs an ultrasonic reception signal Vin.

[0026] The zero-cross detection unit 16 measures multiple zero-cross times at which the ultrasonic reception signal Vin (voltage signal) amplified by the reception unit 14 crosses zero voltage (0 V) after it becomes equal to or greater than the threshold voltage Vs, for each measurement and for each forward and reverse direction, and stores the multiple measured zero-cross times in a time array in the storage unit 17 prepared for the corresponding measurement and the corresponding direction. Note that the zero-cross time in the present invention refers to the time at which the transmission time of the ultrasonic wave is set to 0 (i.e., the elapsed time until reception).

[0027] Next, the principle of the present invention will be described with reference to Figs. 2 to 4. Fig. 2 is a signal waveform diagram showing the relationship between an ultrasonic reception signal and zero crossing points. Fig. 3 is a histogram showing the first zero crossing time. Note that Fig. 2 shows either a forward or reverse direction ultrasonic reception signal. The forward direction ultrasonic reception signal and the reverse direction ultrasonic reception signal may have different amplitudes and propagation times.

[0028] The ultrasonic reception signal Vin (voltage signal) consists of multiple sinusoidal AC pulses whose amplitude increases and decreases along the time axis, as shown in Figure 2. As mentioned above, the forward and reverse ultrasonic reception signals may have different amplitudes, so the forward and reverse threshold voltages Vs are adjusted separately.

[0029] The amplitude of the ultrasonic reception signal Vin changes with each measurement. In the example of Figure 2, an ultrasonic reception signal with an average amplitude is shown as Vin#0, an ultrasonic reception signal with a small amplitude as Vin#1, and an ultrasonic reception signal with a large amplitude as Vin#2. As will be described later, the Nmth wave from the beginning of the ultrasonic reception signal Vin#0 is identified as the target wave, and the threshold voltage adjustment unit 21 adjusts the peak voltage of the wave immediately before this target wave so that it has the same value as the threshold voltage Vs. The wave immediately before this target wave is called the following wave. The effective zero-crossing point corresponding to the following wave is called the following zero-crossing point. Similarly, the zero-crossing point corresponding to the target wave is called the target zero-crossing point.

[0030] 2 shows an example where Nm = 3. As described above, when the threshold voltage Vs is set to a value approximately equal to the peak voltage of the leading wave in the ultrasonic reception signal Vin#0 of average amplitude, the amplitude of the ultrasonic reception signal Vin decreases (Vin#1) or increases (Vin#2), causing the leading zero crossing point to become the following zero crossing point (Z1) or the target zero crossing point (Z2).

[0031] In this case, if the threshold voltage Vs is set appropriately for the ultrasonic reception signal Vin, the leading zero crossing point will be either the tracking zero crossing point Z1 at time T1 or the target zero crossing point Z2 at time T2. As a result, as shown in Figure 3, the frequencies N(T1) and N(T2) at which the leading zero crossing points of both signals are detected at times T1 and T2 are approximately equal, with the probability of both being approximately 50%. Furthermore, these frequencies change depending on the intensity fluctuation of Vin relative to Vs.

[0032] In this embodiment, the leading zero crossing point may become a trailing zero crossing point or a target zero crossing point, and the threshold voltage Vs is adjusted based on the likelihood that the trailing zero crossing point will become the leading zero crossing point, so as to follow the intensity fluctuations of the ultrasonic reception signal Vin. Here, the trailing wave is set to be one cycle before the target wave, but this is not limited to this and may be set to be a predetermined number of cycles before. Note that the cycle is the cycle of the wave representing the ultrasonic reception signal Vin, and corresponds to the ultrasonic cycle.

[0033] Furthermore, when the first trigger point occurs in the target wave, the time of the target zero cross point is stored at the beginning of the time array D#i, whereas when the first trigger point occurs in the following wave, the time indicating the following zero cross point located before the target zero cross point is stored at the beginning of D#i. As shown in Figure 2, in the case of ultrasonic reception signal Vin#1, the threshold voltage Vs is exceeded for the first time at time Ts1, so zero-cross times T2, T3, and T4 corresponding to zero-cross points Z2, Z3, and Z4 detected after time Ts1 are stored in time array D#1. As a result, the first zero-cross point detected after the trigger point, i.e., the leading zero-cross time T2 stored at the beginning of time array D#1, becomes the time corresponding to the target zero-cross point. Time T0 in Figure 2 is the transmission time of the ultrasonic wave.

[0034] On the other hand, for ultrasonic reception signal Vin#2, the following wave just before P3 exceeds threshold voltage Vs at time Ts2. Therefore, zero-cross times T1, T2, and T3 corresponding to zero-cross points Z1, Z2, and Z3 detected after time Ts2, which is before time Ts1, are stored in time array D#2. As a result, the first zero-cross point detected after the trigger point, that is, the leading zero-cross time T1 stored at the beginning of time array D#2, becomes the time corresponding to the following zero-cross point.

[0035] This embodiment focuses on the relationship between the occurrence of trigger points in such a following wave or target wave and the position of the zero-cross point corresponding to the leading zero-cross point in the time sequence D#i, calculates the degree R that the leading zero-cross point detected first after the trigger point in the time sequence D#i corresponds to the following zero-cross point, and adjusts the threshold voltage Vs based on the results of comparing the obtained degree R with a preset threshold (degree threshold). The inventors have proposed a configuration for adjusting the threshold voltage Vs in this manner (Japanese Patent Application Laid-Open No. 2020-63972).

[0036] Furthermore, the inventors have come up with the idea that the reliability of the maximum reception strength can be evaluated by using the degree R. The principle of this reliability evaluation will be explained using Figures 4(A) and 4(B). Figure 4(A) shows a case where the maximum reception strength S in the forward direction changes temporarily due to electrical noise, and Figure 4(B) shows a case where the maximum reception strength S in the forward direction changes due to temperature, gas type, water intrusion, etc. Rmax is the upper limit value of the degree R, and Rmin is the lower limit value of the degree R.

[0037] As shown in Figure 4(A), even if the maximum reception strength S temporarily changes due to noise, the degree R is calculated based on the results of multiple measurements, so it is less susceptible to the influence of temporary noise and is above the lower limit Rmin and below the upper limit Rmax. On the other hand, if the waveform of the ultrasonic reception signal changes due to temperature, gas type, water intrusion, etc., the degree R will exceed the upper limit Rmax. Figure 4(B) shows a case where the maximum reception strength S increases due to temperature, gas type, water intrusion, etc., but if the maximum reception strength S decreases, the degree R will fall below the lower limit Rmin.

[0038] Therefore, when an increase in the maximum reception intensity S is detected, if R > Rmax, it can be determined that there is a high possibility of fluctuations due to temperature, gas species, water intrusion, etc. in the above reason (I) (the reliability of the maximum reception intensity S is high). Also, when an increase in the maximum reception intensity S is detected, if Rmax ≥ R ≥ Rmin, it can be determined that there is a high possibility of fluctuations due to noise in the above reason (II) (the reliability of the maximum reception intensity S is low). Further, when an increase in the maximum reception intensity S is detected and R < Rmin, neither (I) nor (II) can be determined (the reliability of the maximum reception intensity S is low).

[0039] Also, when a decrease in the maximum reception intensity S is detected, if R < Rmin, it can be determined that there is a high possibility of fluctuations due to temperature, gas species, water intrusion, etc. in reason (I) (the reliability of the maximum reception intensity S is high). Also, when a decrease in the maximum reception intensity S is detected, if Rmax ≥ R ≥ Rmin, it can be determined that there is a high possibility of fluctuations due to noise in reason (II) (the reliability of the maximum reception intensity S is low). Further, when a decrease in the maximum reception intensity S is detected and R > Rmax, neither (I) nor (II) can be determined (the reliability of the maximum reception intensity S is low). Based on the above principle, the reliability of the maximum reception intensity S can be evaluated.

[0040] Next, referring to FIG. 5, the operation of this embodiment will be described. FIG. 5 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 / reception repetitions per packet (1 second) is set to X (X is an integer of 2 or more).

[0041] First, the zero-crossing detection unit 16 initializes the measurement count i (i is an integer from 1 to X) to 1 (step S100 in FIG. 5). Transducer 11 or 12 transmits ultrasonic waves to the fluid flowing in pipe 10 in response to transmission pulses from transmitter 13 (step S101 in FIG. 5). As described above, in the forward direction, ultrasonic waves are transmitted from transducer 11, and in the reverse direction, ultrasonic waves are transmitted from transducer 12. In this embodiment, measurement is started from the forward direction.

[0042] The receiving unit 14 amplifies the output signal of the transducer 11 or 12 and outputs the ultrasonic reception signal Vin#i (step S102 in FIG. 5). In the forward direction, the transducer 12 receives the ultrasonic waves transmitted from the transducer 11, and the receiving unit 14 amplifies the output signal of the transducer 12. In the reverse direction, the transducer 11 receives the ultrasonic waves transmitted from the transducer 12, and the receiving unit 14 amplifies the output signal of the transducer 11.

[0043] As described in FIG. 2, the zero-cross detection unit 16 measures multiple zero-cross times after the ultrasonic reception signal Vin#i (voltage signal) becomes equal to or greater than the threshold voltage Vs for each measurement and for each forward and reverse direction, and stores the multiple measured zero-cross times in a time array in the memory unit 17 prepared for the corresponding measurement and the corresponding direction (step S103 in FIG. 5).

[0044] FIG. 6 shows an example of the time array D#i. Here, X=6. Furthermore, H=5 zero-cross times are measured for one transmission and reception of ultrasonic waves. The time array D#i is provided separately for the forward and reverse directions, and FIG. 6 shows the time array for the forward direction. For example, when the number of measurements i=1, the storage position k of the time array D#1 is updated, and H zero-cross times are measured in order and stored in storage position k.

[0045] When measurement of H zero crossing times has been completed, measurement in one direction is completed. If measurement in both the forward and reverse directions has not been completed (NO in step S104 in FIG. 5), the switching unit 15 switches the direction (step S105 in FIG. 5). For example, if measurement in the forward direction has been completed but measurement in the reverse direction 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 transducer 12 and connects the transducer 11 to the receiving unit 14.

[0046] In this way, the processes of steps S101 to S103 are performed in the reverse direction in the same manner as above. When the measurement in the reverse direction is completed, the measurement in both the forward and reverse directions is completed, so the zero-crossing detector 16 increments the measurement count i by 1 (step S106 in FIG. 5).

[0047] If the number of measurements i does not exceed the number of repeated ultrasonic transmissions and receptions X, and measurements have not been completed X times in both the forward and reverse directions (NO in step S107 in FIG. 5), 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 transducer 11, and connects the transducer 12 to the receiving unit 14.

[0048] In this way, measurement of the zero-crossing times is repeatedly executed in both the forward and reverse directions. When the Xth measurement of the forward propagation time is completed (YES in step S108 in FIG. 5), maximum reception intensity detector 22 detects the difference (Peak to Peak) between the maximum and minimum values ​​of the ultrasonic reception signal obtained in the Xth forward measurement as the maximum reception intensity in the forward direction (step S109 in FIG. 5).

[0049] Furthermore, when the Xth measurement of the propagation time in the reverse direction is completed (YES in step S110 of FIG. 5), the maximum reception intensity detection unit 22 detects the difference (Peak to Peak) between the maximum and minimum values ​​of the ultrasonic reception signal obtained in the Xth measurement in the reverse direction as the maximum reception intensity in the reverse direction (step S111 of FIG. 5). When the number of measurements i exceeds X (YES in step S107), the measurement of the zero crossing times in both the forward and reverse directions and the measurement of the maximum reception strength in both the forward and reverse directions are completed.

[0050] Next, the degree calculation unit 20 calculates the degree (proportion) R of the time array D#i in which the leading zero cross time stored at the beginning of each time array D#i (position k=3 in the example of Figure 6) is the following zero cross time, i.e., the zero cross time a predetermined period (one period in this embodiment) before the target zero cross time, for each forward and reverse direction (Figure 5 step S112).

[0051] Next, a degree calculation operation (leading zero cross determination operation) by the degree calculation unit 20 will be described with reference to Fig. 7. When calculating the degree R, the degree calculation unit 20 determines, for each forward / reverse direction and for each time array D#i, whether the leading zero cross time stored at the head of each time array D#i corresponds to the target zero cross time or the following zero cross time.

[0052] As described above, the height of the tracking wave, which is the wave immediately before the target wave, also changes in response to changes in the intensity of the ultrasonic reception signal Vin#i. The threshold voltage adjuster 21 for the previous packet adjusts the threshold voltage Vs to the average height of the tracking wave. Therefore, when the ultrasonic reception signal Vin#i increases, the height of the tracking wave exceeds the threshold voltage Vs, the leading zero crossing point becomes the following zero crossing point, and the leading zero crossing time becomes the following zero crossing time. Conversely, when the ultrasonic reception signal Vin#i decreases, the height of the tracking wave falls below the threshold voltage Vs, the leading zero crossing point becomes the target zero crossing point, and the leading zero crossing time becomes the target zero crossing time.

[0053] This embodiment focuses on the distribution characteristics of such leading zero cross times, sets J (J is an integer of 2 or greater) time intervals Sj (j is an integer from 1 to J) on a time axis on which the leading zero cross times of the time array D#i are arranged, and counts the detection frequency nj of the leading zero cross time for each of these Sj. With few exceptions, the leading zero cross time is included in either the time interval including the trailing zero cross time or the time interval including the target zero cross time. Therefore, when calculating the sum of the detection frequencies of the leading zero cross times in two adjacent time intervals, the sum of the detection frequencies in the adjacent time interval formed by the time interval including the trailing zero cross time and the time interval including the target zero cross time is the largest. Of these adjacent time intervals, the earlier time interval is the time interval including the trailing zero cross time, and the later time interval is the time interval including the target zero cross time.

[0054] The time length of Sj may be, for example, a time length equivalent to the ultrasonic wave period. Generally, the measurement variation of the zero-crossing time is smaller than the ultrasonic wave period, so the time of adjacent zero-crossing points can be sufficiently distinguished. Note that the time position of Sj may be shifted so that the distribution of the leading zero-crossing time is located at the center of the time interval.

[0055] The degree R can be found by dividing the detection frequency of the leading zero cross time in the time section including the trailing zero cross time by the total number of detection frequencies nj of the leading zero cross times, that is, by X. 7 shows an example in which four time intervals (j=4) of S1, S2, S3, and S4 are set and the detection frequencies n1, n2, n3, and n4 of the leading zero-cross times are counted. Here, the detection frequencies n1, n2, n3, and n4 of the leading zero-cross times measured from 32 ultrasonic reception signals Vin#i (X=32) in S1, S2, S3, and S4 are 0, 8, 24, and 0, respectively.

[0056] When the sum of the detection frequencies of the leading zero crossing times in two adjacent time intervals among these time intervals S1 to S4 is calculated, the sum n2+n3 of the detection frequencies in time intervals S2 and S3 is the largest. Therefore, according to the example of setting the target zero crossing point shown in FIG. 2, time interval S2 corresponds to trailing zero crossing point Z2, and time interval S3 corresponds to target zero crossing point Z3. Therefore, n2 (=8) is the detection frequency of the leading zero crossing times in the time intervals including the trailing zero crossing times, and by dividing n2 by the total number of detection frequencies X (=32), the degree R is obtained as 0.25 (=25%). The degree calculation unit 20 calculates the degree R in this manner for each of the forward and reverse directions.

[0057] Next, the threshold voltage adjusting unit 21 adjusts the threshold voltage Vs for each of the forward and reverse directions based on the degree R calculated by the degree calculating unit 20 (step S113 in FIG. 5). FIG. 8 is a flowchart illustrating the operation of the threshold voltage adjusting unit 21.

[0058] The threshold voltage adjusting unit 21 checks whether the degree R is greater than a preset threshold Rth2 (step S200 in FIG. 8 ). If the degree R is greater than the threshold Rth2 (YES in step S200), it adjusts the threshold voltage Vs to a value higher by a preset adjustment amount α (step S201 in FIG. 8 ). Here, α is treated as a fixed value, but α may also be a value proportional to the threshold voltage Vs. Alternatively, α may be a value proportional to the absolute value of R−Rth1 or the absolute value of R−Rth2 using a preset threshold Rth1 (Rth1≦Rth2). Alternatively, α may be a value proportional to the threshold voltage Vs and proportional to the absolute value of R−Rth1 or the absolute value of R−Rth2.

[0059] On the other hand, when the degree R is less than or equal to the threshold value Rth2 (NO in step S200), the threshold voltage adjustment unit 21 checks whether the degree R is less than a preset threshold value Rth1 (step S202 in FIG. 8). If the degree R is less than the threshold value Rth1 (YES in step S202), the threshold voltage Vs is adjusted to a value lower by a preset adjustment width α (step S203 in FIG. 8). If the degree R is greater than or equal to the threshold value Rth1 (NO in step S202), the threshold voltage Vs is not adjusted. The threshold values Rth1 and Rth2 have a relationship of Rth1 ≤ Rth2. It is possible to eliminate the dead zone by setting Rth1 = Rth2, or to provide a dead zone by setting Rth1 < Rth2.

[0060] After that, the threshold voltage adjustment unit 21 checks whether the threshold voltage Vs is outside the preset adjustment range Vaj (step S204 in FIG. 8). If the threshold voltage Vs is outside the range of Vaj (YES in step S204), the threshold voltage Vs is initialized to the preset initial value (step S205 in FIG. 8), and a series of threshold voltage adjustment processes are terminated. If the threshold voltage Vs is within the range of Vaj (NO in step S204), a series of threshold voltage adjustment processes are terminated without initializing the threshold voltage Vs.

[0061] Next, referring to FIG. 9, the initialization operation of the threshold voltage by the threshold voltage adjustment unit 21 will be described. FIG. 9 is a signal waveform diagram showing the relationship between the threshold voltage and the adjustment range. When initializing the threshold voltage Vs in step S205 of FIG. 8, the threshold voltage adjustment unit 21 specifies a new adjustment range Vaj based on the maximum peak voltage Vmax of the ultrasonic reception signal Vin#i, and sets an arbitrary value within the adjustment range Vaj as the new initial value of the threshold voltage Vs.

[0062] As shown in FIG. 9, the adjustment range Vaj consists of an adjustment lower limit voltage VajL and an adjustment upper limit voltage VajH, and the threshold voltage Vs at the start of measurement, that is, the initial value of the threshold voltage Vs, is assumed to be equal to an arbitrary value between the adjustment lower limit voltage VajL and the adjustment upper limit voltage VajH. When the threshold voltage Vs is repeatedly adjusted, if the intensity of the ultrasonic reception signal Vin#i continues to change, the threshold voltage Vs may fall below the adjustment lower limit voltage VajL or exceed the adjustment upper limit voltage VajH, and the threshold voltage Vs may fall outside the adjustment range Vaj.

[0063] For this purpose, for example, the maximum peak voltage Vmax is detected from one or more ultrasonic reception signals Vin#i input in a series of measurement processes, and a new adjustment lower limit voltage VajL (= k1 × Vmax) and adjustment upper limit voltage VajH (= k2 × Vmax) are calculated based on a preset lower limit coefficient k1 and upper limit coefficient k2, and the adjustment lower limit voltage VajL and adjustment upper limit voltage VajH are updated.

[0064] 8, if for some reason the threshold voltage Vs falls below the adjustment lower limit voltage VajL or exceeds the adjustment upper limit voltage VajH and falls outside the adjustment range Vaj, the threshold voltage Vs is initialized to an arbitrary value between the adjustment lower limit voltage VajL and the adjustment upper limit voltage VajH. Note that for simplicity, the initial value of the threshold voltage Vs is set to an arbitrary value between the adjustment lower limit voltage VajL and the adjustment upper limit voltage VajH, but a value calculated by dividing the adjustment lower limit voltage VajL and the adjustment upper limit voltage VajH internally using a predetermined method may also be used as the initial value.

[0065] Next, the flow rate calculation unit 18 acquires the target zero cross times to be used for calculating the propagation time from the time array D#i for each of the forward and reverse directions, calculates the difference Δt between the propagation times of the ultrasonic waves in the forward and reverse directions based on the acquired target zero cross times, and calculates the flow rate Q of the fluid from the difference Δt in propagation time (step S114 in Figure 5).

[0066] The target zero cross time can be identified by the degree calculation operation (leading zero cross determination operation) by the degree calculation unit 20. As described above, when the sum of the detection frequencies of the leading zero cross time in two adjacent time intervals is calculated, the sum of the detection frequencies in the adjacent time interval formed by the time interval including the following zero cross time and the time interval including the target zero cross time is the largest. Of these adjacent time intervals, the earlier time interval is the time interval including the following zero cross time, and the later time interval is the time interval including the target zero cross time.

[0067] Therefore, for the time array D#i in which the leading zero cross time was detected in the time section S2 in the example of Fig. 7, the leading zero cross time is the following zero cross time, so the flow rate calculation unit 18 can acquire the zero cross time a predetermined period after the leading zero cross time (in this embodiment, one storage position k after) as the target zero cross time. Also, for the time array D#i in which the leading zero cross time was detected in the time section S3 in the example of Fig. 7, the leading zero cross time is the target zero cross time, so the flow rate calculation unit 18 can acquire the leading zero cross time as the target zero cross time. The flow rate calculation unit 18 can acquire the target zero cross times in this way for each direction, forward and backward.

[0068] Next, the flow rate calculation unit 18 calculates the average value of the target zero cross times in the forward direction and sets this as the propagation time t1 of the ultrasonic waves in the forward direction. Similarly, the flow rate calculation unit 18 calculates the average value of the target zero cross times in the reverse direction and sets this as the propagation time t2 of the ultrasonic waves in the reverse direction. The flow rate calculation unit 18 then calculates the difference between the propagation time t1 and the propagation time t2 as the propagation time difference Δt, and calculates the flow rate Q from the propagation time difference Δt. A known calculation formula used in general ultrasonic flowmeters can be used as a calculation method for determining the flow rate Q, and a detailed description thereof will be omitted.

[0069] The flow rate output unit 19 is connected to a higher-level device (not shown) via a communication network, and transmits the value of the flow rate Q calculated by the flow rate calculation unit 18 to the higher-level device (step S115 in FIG. 5).

[0070] Next, the maximum reception intensity detection unit 22 determines the reliability of the maximum reception intensity detected in steps S109 and S111 for each forward and reverse direction based on the degree R calculated by the degree calculation unit 20 (step S116 in FIG. 5). FIG. 10 is a flowchart for explaining the reliability determination operation by the maximum reception intensity detection unit 22.

[0071] When the maximum reception intensity detected in the current packet increases compared to the maximum reception intensity detected in steps S109 and S111 in the previous packet (YES in step S301 of FIG. 10), if the degree R is greater than the predetermined upper limit value Rmax (R > Rmax) (YES in step S302 of FIG. 10), the maximum reception intensity detection unit 22 determines that the reliability of the maximum reception intensity is high (step S303 in FIG. 10). Also, when the degree R is greater than or equal to the predetermined lower limit value Rmin and less than or equal to the upper limit value Rmax (Rmax ≥ R ≥ Rmin), or when it is less than the lower limit value Rmin (R < Rmin), the maximum reception intensity detection unit 22 determines that the reliability of the maximum reception intensity is low (step S304 in FIG. 10).

[0072] Also, when the maximum reception intensity detected in the current packet decreases compared to the maximum reception intensity detected in steps S109 and S111 in the previous packet (NO in step S301), if the degree R is less than the lower limit value Rmin (R < Rmin) (YES in step S305 of FIG. 10), the maximum reception intensity detection unit 22 determines that the reliability of the maximum reception intensity is high (step S306 in FIG. 10). Also, when the degree R is greater than or equal to the predetermined lower limit value Rmin and less than or equal to the upper limit value Rmax (Rmax ≥ R ≥ Rmin), or when it is greater than the upper limit value Rmax (R > Rmax), the maximum reception intensity detection unit 22 determines that the reliability of the maximum reception intensity is low (step S307 in FIG. 10). The maximum reception intensity detection unit 22 performs the reliability determination process of steps S300 to S307 for each forward and reverse direction.

[0073] The upper limit value Rmax and lower limit value Rmin described in Figures 4(A) and 4(B) may be determined in advance based on past measurement data so that when the maximum reception strength temporarily changes due to noise, the degree R is greater than or equal to the lower limit value Rmin and less than or equal to the upper limit value Rmax, and so that when the waveform of the ultrasonic reception signal changes due to temperature, gas type, water intrusion, etc., the degree R exceeds the upper limit value Rmax or falls below the lower limit value Rmin.

[0074] Next, if the maximum reception strength detection unit 22 determines that the reliability of the maximum reception strength is low in at least one of the forward and reverse directions (YES in step S308 in FIG. 10), it discards the maximum reception strength detected in steps S109 and S111 (step S309 in FIG. 10). In this case, it will attempt to obtain the maximum reception strength again for the next packet. Furthermore, if the maximum reception strength detection unit 22 determines that the reliability of the maximum reception strength is high in both the forward and reverse directions, it passes the maximum reception strength detected in steps S109 and S111 to the alarm output unit 23 (step S310 in FIG. 10).

[0075] The alarm output unit 23 compares the latest maximum reception strength received from the maximum reception strength detection unit 22 with the maximum reception strength received immediately before, and outputs an alarm (step S118 in FIG. 5) when the absolute value of the amount of change in the latest maximum reception strength from the immediately previous maximum reception strength in at least one of the forward and reverse directions exceeds a predetermined threshold (YES in step S117 in FIG. 5). That is, it determines that the waveform of the ultrasonic reception signal has changed due to temperature, gas type, water intrusion, etc., and outputs an alarm. The above-described processing in FIG. 5 is performed for each packet (1 second in this embodiment).

[0076] The difference between this embodiment and a conventional ultrasonic flowmeter is that the conventional ultrasonic flowmeter uses the average value of the maximum reception strength measurement results of multiple packets in the same direction, which takes several seconds, causing delays in detecting fluctuations in the maximum reception strength. Furthermore, measuring the maximum reception strength multiple times increases power and memory consumption. On the other hand, in this embodiment, the reliability of the maximum received signal strength can be determined by measuring one packet, so that the maximum received signal strength can be obtained more quickly than before.

[0077] In the above example, the maximum reception strength is used to output an alarm, but the present invention does not limit how the maximum reception strength is used. Examples of using the maximum reception strength include determining an abnormality in a transducer, determining the type of gas, and determining an abnormality in a flow path, and the present invention can be applied to any of these examples.

[0078] In this embodiment, the maximum reception strength detection unit 22 determines the reliability of the maximum reception strength based on the degree, but the degree in this embodiment may be expressed as a number of times rather than a percentage. For example, in the above example, the degree R=0.25 is calculated by dividing the detection frequency n2 of the leading zero cross time in the time interval including the trailing zero cross time by the total number of detection frequencies X=32. However, when an increase in the maximum reception strength is detected, the maximum reception strength detection unit 22 may determine that the reliability of the maximum reception strength is high if n2 is equal to or greater than a set value (e.g., 20 times or more). Conversely, when a decrease in the maximum reception strength is detected, the maximum reception strength detection unit 22 may determine that the reliability of the maximum reception strength is high if n2 is equal to or less than a set value.

[0079] Furthermore, in this embodiment, the degree calculation unit 20 measures the leading zero cross time of the measurement signal to calculate the degree to which the time sequence of the measurement signal is a time sequence in which the leading zero cross time is a zero cross time a predetermined period before (one period before) the target zero cross time, but this degree may also be calculated from the measurement results of a specific zero cross time after the leading zero cross time (for example, the second zero cross time one period after the leading zero cross time, or the third zero cross time two periods after).

[0080] The transmitter 13, receiver 14, switch 15, zero-cross detector 16, and memory 17 described in this embodiment can be realized by an IC such as an FPGA (Field Programmable Gate Array). The flow rate calculator 18, flow rate output unit 19, degree calculator 20, threshold voltage adjuster 21, maximum received signal strength detector 22, and alarm output unit 23 can be realized by a computer equipped with a CPU (Central Processing Unit), a memory device, and an interface, and a program that controls these hardware resources. An example configuration of this computer is shown in FIG.

[0081] 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 hardware components of the transmitter 13, receiver 14, switch 15, zero-cross detector 16, storage device 17, flow rate output device 19, and alarm output device 23. 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 processing described in this embodiment in accordance with the program stored in the storage device 201. [Explanation of symbols]

[0082] 10... Piping, 11, 12... Transducer, 13... Transmitter, 14... Receiver, 15... Switching unit, 16... Zero cross detector, 17... Memory unit, 18... Flow rate calculator, 19... Flow rate output unit, 20... Degree calculator, 21... Threshold voltage adjuster, 22... Maximum receiving intensity detector, 23... Alarm output unit.

Claims

1. A pipe configured to allow a fluid to be measured to flow through; a pair of transducers disposed upstream and downstream of the piping; a transmitting unit configured to transmit ultrasonic waves from one of the transducers; a storage unit configured to store a time sequence that stores, for each measurement and for each forward and reverse direction, the zero-cross times of the ultrasonic reception signal during a forward measurement in which ultrasonic waves are transmitted from the upstream transducer and received by the downstream transducer, and the zero-cross times of the ultrasonic reception signal during a reverse measurement in which ultrasonic waves are transmitted from the downstream transducer and received by the upstream transducer; A flow rate calculation unit configured to acquire a target zero cross time for use in calculating the propagation time from the time sequence for each forward and reverse direction, calculate a difference in propagation time of the ultrasonic waves in the forward and reverse directions based on the acquired target zero cross time, and calculate the flow rate of the fluid from this difference in propagation time; a maximum reception intensity detection unit configured to detect the maximum reception intensity of the ultrasonic reception signal in each of the forward and reverse directions, The ultrasonic flowmeter according to claim 1, wherein the maximum reception intensity detection unit determines the reliability of the maximum reception intensity based on the zero cross times of a plurality of measurements.

2. 2. The ultrasonic flowmeter according to claim 1, The ultrasonic flowmeter is characterized in that the maximum reception intensity detection unit determines the reliability of the maximum reception intensity based on a time sequence of zero-cross times of two or more ultrasonic reception signals that exceed a threshold at different times.

3. 2. The ultrasonic flowmeter according to claim 1, a zero-cross detection unit configured to measure the zero-cross time after the point in time when the ultrasonic reception signal becomes equal to or greater than a threshold voltage for each measurement and for each forward and reverse direction, and to store the measured zero-cross times in order from a specific storage position in the time array prepared for the corresponding measurement and the corresponding direction; a degree calculation unit configured to calculate, for each forward and reverse direction, a degree of a time sequence in which a leading zero cross time stored at a specific position in each time sequence is a zero cross time a predetermined period before a target zero cross time used in calculating a propagation time; Furthermore, The ultrasonic flowmeter is characterized in that the maximum reception intensity detection unit determines the reliability of the maximum reception intensity based on the degree.

4. 4. The ultrasonic flowmeter according to claim 3, the maximum reception intensity detection unit determines that the reliability of the maximum reception intensity is high when the degree of the detected maximum reception intensity increases and is greater than a predetermined upper limit value, and determines that the reliability of the maximum reception intensity is low when the degree of the detected maximum reception intensity is equal to or less than the upper limit value.

5. 4. The ultrasonic flowmeter according to claim 3, the maximum reception intensity detection unit determines that the reliability of the maximum reception intensity is high when the degree of the detected maximum reception intensity decreases and that the degree is smaller than a predetermined lower limit value, and determines that the reliability of the maximum reception intensity is low when the degree of the detected maximum reception intensity is equal to or greater than the lower limit value.

6. 4. The ultrasonic flowmeter according to claim 3, an ultrasonic flowmeter further comprising a threshold voltage adjustment unit configured to adjust the threshold voltage based on the degree so that the peak voltage of a wave of the AC pulse-shaped ultrasonic reception signal that is a target wave corresponding to the target zero-crossing time and that is a predetermined period before the target wave has the same value as the threshold voltage.

7. 4. The ultrasonic flowmeter according to claim 3, the degree calculation unit counts the detection frequency for each time interval on the time axis, including the leading zero cross time stored at a specific position in each time array, identifies from these detection frequencies a time interval including the target zero cross time and a time interval including the zero cross time a predetermined number of cycles before the target zero cross time, and calculates the degree by dividing the detection frequency of the leading zero cross time in the time interval including the zero cross time a predetermined number of cycles before the target zero cross time by the total number of results of the counting.

8. a first step of measuring a plurality of zero-cross times of an ultrasonic reception signal in a forward measurement in which an ultrasonic wave is transmitted from a transducer on an upstream side of a pipe through which a fluid to be measured flows and received by a transducer on a downstream side of the pipe, and a plurality of zero-cross times of an ultrasonic reception signal in a reverse measurement in which an ultrasonic wave is transmitted from the transducer on the downstream side and received by the transducer on the upstream side, for each measurement and for both the forward and reverse directions; a second step of sequentially storing a plurality of zero-crossing times measured after the ultrasonic reception signal becomes equal to or greater than a threshold voltage, starting from a specific storage position in a time array prepared for a corresponding measurement time and a corresponding direction; A third step of acquiring a target zero cross time for use in calculating the propagation time from the time sequence for each forward and reverse direction, calculating a difference in propagation time between the forward and reverse ultrasonic waves based on the acquired target zero cross time, and calculating the flow rate of the fluid from this difference in propagation time; a fourth step of detecting a maximum reception strength of the ultrasonic reception signal in each of the forward and reverse directions; and a fifth step of determining the reliability of the maximum received signal strength based on the zero crossing times of a plurality of measurements.

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