Ultrasonic flowmeter and flow rate measuring method

Abstract

To reduce a flow rate error.SOLUTION: The time measurement unit 16 measures the zero-cross time of the ultrasound reception signal in the forward direction in which the ultrasound is transmitted from the transducer 11 and received by the transducer 12 and the zero-cross time in the reverse direction in which the ultrasound 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. When an absolute value of a difference between a reference coherent zero cross time stored in a predetermined coherent storage position of the time array and a zero cross time to be compared derived from the same type of peak as the peak of the ultrasonic reception signal corresponding to the coherent zero cross time among the zero cross times stored in the time array of the measurement time different from the coherent zero cross time is equal to or greater than a threshold value, the determination unit 18 determines that the time array including the zero cross time to be compared is abnormal.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an ultrasonic flowmeter and a flow rate measurement method. [Background technology]

[0002] Conventionally, an ultrasonic flowmeter is known in which a pair of transducers are placed at a fixed distance upstream and downstream of a fluid flow path, ultrasonic waves are repeatedly transmitted and received between the pair of transducers, and the flow rate is determined based on the difference between the propagation time of the ultrasonic waves from the upstream side to the downstream side and the propagation time from the downstream side to the upstream side.

[0003] One method for detecting the propagation time of ultrasonic waves is the so-called zero-crossing method, which detects the propagation time based on the zero-crossing time when the received wave of the ultrasonic signal crosses zero voltage (0 V). In this zero-crossing method, when calculating the propagation time, it is necessary to always use the zero-crossing point corresponding to the same pulse out of the multiple pulses contained in the received wave.

[0004] However, if noise components are superimposed on the received wave, causing waveform distortion, the time position of the zero-crossing point may shift forward or backward by one ultrasonic cycle. When this shift in the zero-crossing point occurs, the ultrasonic propagation time changes accordingly, which can cause flow measurement errors. As shown in Figure 10, the ultrasonic reception signal Vin (voltage signal) consists of multiple sinusoidal AC pulses whose amplitude increases and decreases along the time axis. To extract zero-crossing points that may be used for calculation, a trigger point is detected when the ultrasonic reception signal Vin exceeds a predetermined threshold voltage Vs, and multiple zero-crossing points after this trigger point are detected to measure the zero-crossing time.

[0005] If the ultrasonic reception signal Vin#1 has an ideal waveform, since the ultrasonic reception signal Vin#1 exceeds the threshold voltage Vs at time Ts1, detection of the zero-cross point begins at time Ts1, zero-cross points Z3, Z4, Z5, Z6, and Z7 are detected, and the zero-cross times T3, T4, T5, T6, and T7 corresponding to the zero-cross points Z3, Z4, Z5, Z6, and Z7 are stored as time array D#1.

[0006] On the other hand, the amplitude of the ultrasonic reception signal increases due to the influence of factors such as the superposition of noise components, and as a result, the ultrasonic reception signal Vin#2 exceeds the threshold voltage Vs at time Ts2, which is earlier than time Ts1, as shown in Fig. 10, and therefore the zero-crossing point is detected one ultrasonic cycle earlier than in the case of the ultrasonic reception signal Vin#1. That is, zero-crossing point detection begins at time Ts2, zero-crossing points Z1, Z2, Z3, Z4, and Z5 are detected, and the zero-crossing times T1, T2, T3, T4, and T5 corresponding to zero-crossing points Z1, Z2, Z3, Z4, and Z5 are stored as time array D#2.

[0007] As a technique for reducing flow measurement errors due to such shifts in zero-crossing points, the inventors have proposed a technique for shifting the storage positions of zero-crossing times in individual time arrays so that the time difference between zero-crossing times stored in the same storage position between time arrays is minimized (see Patent Document 1).

[0008] The technology disclosed in Patent Document 1 will be described with reference to Figures 11(A), 11(B), and 12. A time array D#i is stored for each ultrasonic reception signal Vin#i. Figure 11(A) shows an example in which the number of zero-crossing points detected for each ultrasonic reception signal Vin#i is five. First, a preset matching storage position to be matched, in this case the zero-crossing time D#1[5] = 180000 nsec at the fifth storage position from the beginning of the time array, is selected as the matching zero-crossing time.

[0009] Next, in the case of time array D#2, the time difference of 22 nsec between the matched zero cross time D#1[5] and the zero cross time D#2[7]=180022 nsec at the seventh storage position of D#2 is the smallest compared to the time difference of 19969 nsec with other zero cross times such as D#2[5]=160031 nsec. Therefore, each zero cross time in time array D#2 is shifted two positions to the left in FIG. 11(A) so that D#2[7] becomes the matched storage position. The shifted zero cross time D#2[5]=180022 nsec is selected as the matched zero cross time.

[0010] In the case of the next time array D#3, the time difference between the matched zero cross time D#2[5] and the zero cross time D#3[5]=180011nsec stored in the fifth storage position of D#3 is the smallest, so the zero cross times for time array D#3 are not shifted. For time array D#3, the shift process is unconditionally considered to have been completed, and the zero cross time D#3[5]=180011nsec is selected as the matched zero cross time.

[0011] In the case of time array D#4, the time difference between the matched zero cross time D#3[5] and the zero cross time D#4[5]=180053nsec stored in the fifth storage position of D#4 is the smallest, so the zero cross times for time array D#4 are not shifted. For time array D#4, the shift process is unconditionally considered to have been completed, and the zero cross time D#4[5]=180053nsec is selected as the matched zero cross time.

[0012] In the case of time array D#5, the time difference between the matched zero cross time D#4[5] and the zero cross time D#5[3]=180005 nsec at the third storage position of D#5 is the smallest. Therefore, each zero cross time of time array D#5 is shifted two positions to the right in Figure 11(A) so that D#5[3] becomes the matched storage position. The results of performing this shift process for each time array D#i are shown in Figure 11(B).

[0013] Next, the target zero-cross time stored in the target storage position for each post-shift time sequence D#i is identified as the reception time of the corresponding ultrasonic reception signal Vin#i, and the reception time is used to calculate the propagation time of the ultrasonic wave. Figure 12 is an explanatory diagram showing the target storage position identification process. The target storage position identification process counts the number of time sequences after shift processing that have the same leading storage position where the zero-cross time is first stored, and identifies the predetermined reference storage position in the post-shift processing time sequence with the largest obtained number of time sequences as the target storage position.

[0014] 12, as in FIGS. 11(A) and 11(B), an example is shown in which the number of zero-crossing points detected for each ultrasonic reception signal Vin#i is five. Time array D#1 stores zero-crossing times starting from storage position k=3, and time array D#2 stores zero-crossing times starting from storage position k=1. Time array D#3 stores zero-crossing times starting from storage position k=3, and time array D#4 stores zero-crossing times starting from storage position k=5. Time array D#5 stores zero-crossing times starting from storage position k=5, and time array D#6 stores zero-crossing times starting from storage position k=3.

[0015] First, for each time sequence D#i, the number of time sequences Ntop that have the same initial storage position where the zero-cross time is first stored is counted. As a result, the number of time sequences Ntop[1] for k=1 is 1, and similarly, Ntop[3]=3, Ntop[5]=2, Ntop[7]=0, Ntop[9]=0 are obtained.

[0016] Next, the time array D#i with the largest time array count Ntop is selected. In the example of FIG. 12, Ntop[3]=3 is the maximum value, and the time array D#1 (D#3, D#6) corresponding to Ntop[3] is selected. After this, the target storage position kt is identified from the first storage position k0=3 of the selected D#1 and the preset reference storage position ks=+(1,2). The reference storage position ks is the offset position from the first storage position k0 to the target storage position kt, and ks=+(1,2) indicates that kt is one position behind and two positions behind k0. Therefore, kt=k0+ks, and in the example of FIG. 12, ks=(4,5). As a result, the target storage position kt is identified as the fourth and fifth positions from the beginning k=1 of the time array D#1. As a result, the two target zero-cross times, the fourth and fifth from the beginning of the time array D#1, are used to calculate the propagation time. [Prior art documents] [Patent documents]

[0017] [Patent Document 1] Japanese Patent Publication No. 2020-063974 Summary of the Invention [Problem to be solved by the invention]

[0018] However, with the technology disclosed in Patent Document 1, when repeated measurements are performed, as shown in FIG. 13, if a normal ultrasonic reception signal Vin#2, an ultrasonic reception signal Vin#1 whose zero-crossing point is detected one cycle earlier than the ultrasonic reception signal Vin#2, and an ultrasonic reception signal Vin#3 whose zero-crossing point is detected one cycle later than the ultrasonic reception signal Vin#2 are obtained, the shift process may not be performed correctly, and after the shift process, zero-crossing times stored in the same column in each time array D#i may include zero-crossing times corresponding to different peaks of the received wave. As a result, a zero-crossing point that is not the target zero-crossing point may be determined to be the target zero-crossing point, resulting in a flow rate error. The following describes the conventional problems in more detail.

[0019] In the example of Figure 14(A), the zero-cross times detected from the ultrasonic reception signal Vin#1 in Figure 13 are stored as time array D#1, the zero-cross times detected from the ultrasonic reception signal Vin#2 are stored as time array D#3, and the zero-cross times detected from the ultrasonic reception signal Vin#3 are stored as time array D#5.

[0020] First, a preset matching storage position to be matched, here the zero cross time D#1[5]=160031 nsec at the fifth storage position from the beginning of the time array, is selected as the matching zero cross time.

[0021] In the case of time array D#2, the time difference between the matched zero-cross time D#1[5] and the zero-cross time D#2[3]=160000 nsec, which is the third storage position of D#2, is the smallest. Therefore, each zero-cross time in time array D#2 is shifted two positions to the left in Figure 14(A) so that D#2[3] becomes the matched storage position. The shifted zero-cross time D#2[5]=160000 nsec is selected as the matched zero-cross time.

[0022] In the case of the next time array D#3, the time difference between the matched zero-cross time D#2[5] and the zero-cross time D#3[3]=16011 nsec, which is the third storage position of D#3, is the smallest. Therefore, each zero-cross time in the time array D#3 is shifted two positions to the left in Figure 14(A) so that D#3[3] becomes the matched storage position. The shifted zero-cross time D#3[5]=160011 nsec is selected as the matched zero-cross time.

[0023] In the case of time array D#4, the time difference between the matched zero-cross time D#3[5] and the zero-cross time D#4[3]=16033 nsec, which is the third storage position of D#4, is the smallest. Therefore, each zero-cross time in time array D#4 is shifted two positions to the left in Figure 14(A) so that D#4[3] becomes the matched storage position. The shifted zero-cross time D#4[5]=160033 nsec is selected as the matched zero-cross time.

[0024] In the case of the next time array D#5, the time difference between the matched zero-cross time D#4[5] and the zero-cross time D#5[3]=180005 nsec, which is the third storage position of D#5, is the smallest. Therefore, each zero-cross time in the time array D#5 is shifted two positions to the right in Figure 14(A) so that D#5[3] becomes the matched storage position. The shifted zero-cross time D#5[5]=180005 nsec is selected as the matched zero-cross time.

[0025] In the case of time array D#6, the time difference between the matched zero cross time D#5[5] and the zero cross time D#6[5] = 180043 nsec in the fifth storage position of D#6 is the smallest, so the zero cross times for time array D#6 will not be shifted.

[0026] The results of performing the above shift processing for each time array D#i are shown in Figure 14(B). In this shift processing, the difference between D#5[3] and D#4[5] after the shift processing is smallest in time array D#5, so D#5[3] and D#4[5] are erroneously determined to be zero-cross times corresponding to the same pulse of the ultrasonic reception signal, and time array D#5 is shifted to the right. Therefore, when the above target storage position identification processing is performed on time arrays D#1 to D#6 after the shift processing in Figure 14(B), the sixth and seventh zero-cross times of time arrays D#1 to D#6 become the target zero-cross times, and zero-cross times D#5[6] and D#5[7], which are shifted by one period from the other time arrays D#1 to D#4 and D#6, are included in the target zero-cross times. If D#5[3] is compared with the shifted D#4[5] and then compared with the shifted D#4[7], the shift can be performed correctly, but this requires a large amount of calculation and is not practical for use in the field.

[0027] Another example is shown in Figure 15(A), and the result after shift processing is shown in Figure 15(B). In this example, when target storage position identification processing is performed on the time arrays D#1 to D#6 after shift processing in Figure 15(B), the fourth and fifth zero cross times of the time arrays D#1 to D#6 become the target zero cross times, and zero cross times D#1[4] and D#1[5], which are shifted by one period from the other time arrays D#2 to D#6, are included in the target zero cross times.

[0028] Another example is shown in Figure 16(A), and the result after shift processing is shown in Figure 16(B). In this example, when target storage position identification processing is performed on the time arrays D#1 to D#6 after shift processing in Figure 16(B), the fourth and fifth zero cross times of the time arrays D#1 to D#6 become the target zero cross times, and zero cross times D#1[4] and D#1[5], which are shifted by one period from the other time arrays D#2 to D#6, are included in the target zero cross times.

[0029] Another example is shown in Figure 17(A), and the result after shift processing is shown in Figure 17(B). In this example, when target storage position identification processing is performed on the time arrays D#1 to D#6 after shift processing in Figure 17(B), the fourth and fifth zero cross times of the time arrays D#1 to D#6 become the target zero cross times, and the zero cross times D#1[4], D#1[5], D#2[4], and D#2[5], which are shifted by one period from the other time arrays D#3 to D#6, are included in the target zero cross times.

[0030] As described above, in the technology disclosed in Patent Document 1, in each time array D#i after shift processing, there is a possibility that zero-cross times stored in the same column may include zero-cross times corresponding to different peaks of the received wave, which may result in flow rate errors.

[0031] The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide an ultrasonic flowmeter and a flow rate measurement method that can reduce flow rate errors. [Means for solving the problem]

[0032] The ultrasonic flowmeter of the present invention includes 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 for each measurement and for each forward and reverse direction, in which the zero-cross times of the ultrasonic reception signal in 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 in a reverse measurement in which ultrasonic waves are transmitted from the downstream transducer and received by the upstream transducer, are stored, and the zero-cross times are measured multiple times for each measurement and for each forward and reverse direction, and a memory unit configured to store a time array for each measurement and for each forward and reverse direction, in which the zero-cross times are stored, in which the zero-cross times are measured multiple times for each measurement and for each forward and reverse direction, and the zero-cross times are stored for each corresponding measurement and for each corresponding direction. a flow rate calculation unit configured to obtain a target zero cross time for use in calculating the propagation time from the time array for each of the forward and reverse directions, calculate a difference in propagation time of 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 determination unit that determines that the time array including the zero cross time to be compared is abnormal when the absolute value of the difference between a reference matched zero cross time stored in a predetermined matched storage position of the time array and a zero cross time to be compared that is derived from a peak of the same type as the peak of the ultrasonic reception signal corresponding to the matched zero cross time, among zero cross times stored in the time array for a measurement time different from the matched zero cross time, is equal to or greater than a threshold.

[0033] In addition, in one configuration example of the ultrasonic flowmeter of the present invention, the determination unit is characterized by performing peak determination processing to determine that, among the zero cross times stored in the time array of a measurement time different from the matched zero cross time, the zero cross time that has the smallest difference from the matched zero cross time is the zero cross time derived from the same type of peak as the matched zero cross time. Furthermore, in one configuration example of the ultrasonic flowmeter of the present invention, when the number of times that the time sequence has been determined to be abnormal in at least one of the forward direction and the reverse direction is equal to or greater than a predetermined number of times, the judgment unit overwrites the time sequence of the measurement times of the matched zero cross times of the peak judgment process with the zero cross times stored in the time sequence excluding the matched zero cross time sequence of the peak judgment process for the direction in which the number of times that the time sequence has been determined to be abnormal is equal to or greater than a predetermined number of times, and then performs the peak judgment process again, and when the absolute value of the difference between the matched zero cross time and the zero cross time of the comparison target after this peak judgment process is equal to or greater than a threshold value, judges the time sequence including the zero cross time of the comparison target to be abnormal.

[0034] In addition, in one configuration example of the ultrasonic flowmeter of the present invention, the judgment unit selects the zero cross time located in the alignment storage position of the time array immediately preceding the time array that is the target of the judgment process as the aligned zero cross time, selects the zero cross time located in the alignment storage position of the time array when the number of the time array that is the target of the judgment process is the initial value as the aligned zero cross time, or selects a predicted value obtained from past zero cross times stored in the alignment storage position as the aligned zero cross time. In one configuration example of the ultrasonic flowmeter of the present invention, the flow rate calculation unit does not use information on the time sequence that the determination unit has determined to be abnormal for flow rate calculation. In addition, in one configuration example of the ultrasonic flowmeter of the present invention, the flow calculation unit is characterized in that, when the number of times that the judgment unit judges the time sequence to be abnormal is less than a predetermined number of times per direction, the flow calculation unit obtains the target zero cross time for each forward and reverse direction from the time sequence that the judgment unit judges to be normal.

[0035] The flow rate measurement 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; a second step of storing the plurality of measured zero-cross times in order from a specific storage position in a time array prepared for the corresponding measurement and the corresponding direction; and a second step of storing the plurality of zero-cross times stored in a predetermined matching storage position in the time array. a third step of determining that the time sequence including the zero cross time to be compared is abnormal if the absolute value of the difference between the reference matched zero cross time stored in the time sequence and a zero cross time to be compared that is derived from a peak of the same type as the peak of the ultrasonic reception signal corresponding to the matched zero cross time, among the zero cross times stored in the time sequence for a measurement time different from the matched zero cross time, is equal to or greater than a threshold value; and a fourth step of obtaining target zero cross times to be used in calculating the propagation time from the time sequence for each forward and reverse direction, calculating the difference in propagation time of 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. [Effects of the Invention]

[0036] According to the present invention, by detecting abnormal data, it is possible to reduce the possibility that the target zero crossing time for calculating the propagation time will include a zero crossing time corresponding to a different peak of the received wave, thereby reducing the possibility of a flow rate error occurring. [Brief explanation of the drawings]

[0037] [Figure 1] FIG. 1 is a block diagram showing the configuration of an ultrasonic flowmeter according to a first embodiment of the present invention. [Figure 2]FIG. 2 is a flowchart illustrating the operations of the transducer, transmitting unit, receiving unit, switching unit, time measuring unit, and storage unit of the ultrasonic flowmeter according to the first embodiment of the present invention. [Figure 3] FIG. 3 is a flowchart illustrating the operations of the determining unit, the flow rate calculating unit, and the flow rate output unit of the ultrasonic flowmeter according to the first embodiment of the present invention. [Figure 4] FIG. 4 is a diagram illustrating the shift process in the first embodiment of the present invention. [Figure 5] FIG. 5 is a block diagram showing the configuration of an ultrasonic flowmeter according to a second embodiment of the present invention. [Figure 6] FIG. 6 is a flowchart illustrating the operations of the determination unit, the flow rate calculation unit, and the flow rate output unit of the ultrasonic flowmeter according to the second embodiment of the present invention. [Figure 7] FIG. 7 is a diagram illustrating the shift process in the second embodiment of the present invention. [Figure 8] FIG. 8 is a diagram illustrating the shift process in the second embodiment of the present invention. [Figure 9] FIG. 9 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 10] FIG. 10 is a signal waveform diagram showing the relationship between the ultrasonic reception signal and the zero crossing points. [Figure 11] FIG. 11 is a diagram illustrating a conventional shift process. [Figure 12] FIG. 12 is a diagram illustrating a conventional target storage position specifying process. [Figure 13] FIG. 13 is a signal waveform diagram showing an example of a normal ultrasonic reception signal and an abnormal ultrasonic reception signal. [Figure 14] FIG. 14 is a diagram illustrating the problem with the conventional shift process. [Figure 15] FIG. 15 is a diagram illustrating the problem with the conventional shift process. [Figure 16] FIG. 16 is a diagram illustrating the problem with the conventional shift process. [Figure 17] FIG. 17 is a diagram illustrating the problem with the conventional shift process. DETAILED DESCRIPTION OF THE INVENTION

[0038] [First Example] Hereinafter, embodiments 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 a first embodiment of the present invention. The ultrasonic flowmeter comprises 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 and the transmitter 13 and receiver 14, and a zero-cross time after the ultrasonic reception signal exceeds a threshold voltage, which is calculated for each measurement. and a time measurement unit 16 that takes multiple measurements in each of the forward and reverse directions, a memory unit 17 that stores the zero-cross times, a determination unit 18 that determines whether the time sequence stored in the memory unit 17 is normal or abnormal, a flow rate calculation unit 19 that obtains a target zero-cross time for each of the forward and reverse directions to be used in calculating the propagation time from the time sequence, calculates the difference in propagation time between the ultrasonic waves in the forward and reverse directions based on the obtained target zero-cross times, and calculates the flow rate of the fluid from the difference in propagation time, and a flow rate output unit 20 that transmits the flow rate value to a higher-level device.

[0039] In this embodiment, a pair of transducers 11, 12 are arranged facing each other upstream and downstream of the pipe 10. Alternatively, 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.

[0040] 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.

[0041] 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.

[0042] The time measurement 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 exceeds a preset threshold voltage Vs, for each measurement and for both the forward and reverse directions, 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).

[0043] Next, the operation of this embodiment will be described with reference to Figures 2 and 3. Figure 2 is a flowchart explaining the operation of transducers 11 and 12, transmitter 13, receiver 14, switch 15, time measurement unit 16, and memory unit 17. Figure 3 is a flowchart explaining the operation of determination unit 18, flow rate calculation unit 19, and flow rate output unit 20.

[0044] In this embodiment, measurements are made by transmitting and receiving ultrasonic waves in both forward and reverse directions X times (X is an integer equal to or greater than 2) per direction. Here, X=6 times. Furthermore, H=5 zero-cross times are measured for each ultrasonic wave transmission and reception.

[0045] First, the time measurement unit 16 initializes the measurement count i (i is an integer between 1 and X) to 1 (step S100 in FIG. 2). Transducer 11 or 12 transmits ultrasonic waves to the gas flowing in pipe 10 in response to transmission pulses from transmitter 13 (step S101 in FIG. 2). 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.

[0046] 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. 2). 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.

[0047] The time measurement unit 16 compares the ultrasonic wave reception signal Vin#i with a preset threshold voltage Vs (step S103 in FIG. 2). The time measurement unit 16 does not start detecting zero-cross times when Vin#i≦Vs, i.e., when the ultrasonic reception signal Vin#i is equal to or less than the threshold voltage Vs. The time measurement unit 16 starts detecting zero-cross times when Vin#i>Vs, i.e., when the ultrasonic reception signal Vin#i exceeds the threshold voltage Vs.

[0048] When the ultrasonic wave reception signal Vin#i exceeds the threshold voltage Vs, the time measurement unit 16 initializes the storage position k of the time sequence D#i in the memory unit 17 to a preset K (e.g., K=3) position (step S104 in FIG. 2). Then, the time measurement unit 16 checks whether the ultrasonic wave reception signal Vin#i is at a zero-cross point (step S105 in FIG. 2).

[0049] The time measurement unit 16 determines the time when the zero-cross point of the ultrasonic reception signal Vin#i is detected as the zero-cross time Tz (step S106 in FIG. 2), and stores the value of the zero-cross time Tz at storage position k in the time array D#i of the storage unit 17 (step S107 in FIG. 2). The time array D#i of the storage unit 17 is provided separately for the forward direction and the reverse direction.

[0050] After storing the zero cross times Tz, the time measurement unit 16 increments the storage position k by 1 (step S108 in FIG. 2), and determines whether the storage position k has reached K+H, i.e., whether H zero cross times Tz have been measured (step S109 in FIG. 2). If the time measurement unit 16 has not finished measuring H zero cross times Tz, the process returns to step S105. In this way, while updating the storage position k of the time array D#i, H zero cross times Tz are measured in order and stored in the storage position k.

[0051] When measurement of H zero cross times Tz 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 S110 in FIG. 2), the switching unit 15 switches the direction (step S111 in FIG. 2). For example, if measurement of H zero cross times Tz has been completed in the forward direction 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 transmitter 13 to the transducer 12 and connects the transducer 11 to the receiver 14.

[0052] In this way, the processing of steps S101 to S109 is carried out in the reverse direction in the same manner as above. Note that the time arrays D#i in the storage unit 17 are provided separately for the forward direction and the reverse direction. When the measurement of H zero cross times Tz in the reverse direction is completed, the measurement in both the forward and reverse directions is completed, and the time measurement unit 16 increments the measurement count i by 1 (step S112 in FIG. 2).

[0053] If the number of measurements i does not exceed X and measurements have not been completed X times in both the forward and reverse directions (NO in step S113 in FIG. 2), the switching unit 15 switches the direction (step S111). 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.

[0054] In this way, measurements are repeatedly performed in both the forward and reverse directions. When the number of measurements i exceeds X (YES in step S113), X measurements in both the forward and reverse directions are completed.

[0055] Next, after completing X measurements in both the forward and reverse directions, the determination unit 18 performs shift processing. Specifically, the determination unit 18 shifts the storage positions of the zero cross times in each time array D#i (i is an integer from 1 to X) so that the storage positions k in the time array D#i (i is an integer from 1 to X) are the same and the time difference between zero cross times measured differently is minimized. The shift processing is performed in both the forward and reverse directions, but here we will only explain the shift processing in one direction, either the forward or reverse direction.

[0056] FIG. 4A shows an example of zero-crossing times stored in the time arrays D#1 to D#6 of the storage unit 17. First, the determination unit 18 initializes the number i (i is an integer from 1 to X) of the time array to be shifted to 1 (step S200 of FIG. 3). In this embodiment, if the time array number i is the initial value, i.e., if the time array D#1 is the target of the shifting process (YES in step S201 of FIG. 3), the determination unit 18 unconditionally assumes that the shifting process has been completed, and proceeds to step S206. The determination unit 18 updates the number i of the time array to be shifted to 2 by shifting it back by 1 (step S206 of FIG. 3). When the updated number i is X+1 (=7), i.e., when the shifting process has been completed for all time arrays D#i where i=1 to X (YES in step S207 of FIG. 3), the operation of the determination unit 18 ends. Here, i=2, so the determination unit 18 proceeds to step S208.

[0057] The judgment unit 18 selects the zero cross time D#1[5]=160031 nsec, which is the preset matching storage position in the time array D#1 immediately preceding the target time array D#2, in this case the fifth storage position from the beginning of the time array, as the matching zero cross time (Figure 3 step S208).

[0058] In the case of time array D#2 that is the target of the shift process, the time difference between the zero cross time D#2[3]=160000 nsec at the third storage position and the aligned zero cross time D#1[5]=160031 nsec is the smallest in time array D#2. Therefore, the determination unit 18 shifts each zero cross time in time array D#2 by two positions to the right in FIG. 4(A) so that D#2[3] becomes the aligned storage position (step S202 in FIG. 3).

[0059] After the shifting process of the time array D#2 is completed, the determination unit 18 determines whether the absolute value |D#1[5]-D#2[5]| of the difference between the matched zero-cross time D#1[5]=160031 nsec and the zero-cross time D#2[5]=160000 nsec, which is located at the same matched storage position k=5 as D#1[5] in the shifted time array D#2, is less than a predetermined threshold value TH (step S203 in FIG. 3). The threshold value TH is set to, for example, half the period (10000 nsec) of the ultrasonic reception signal Vin#i. In this case, because the absolute value |D#1[5]-D#2[5]| of the difference between the zero-cross times is less than the threshold value TH, the determination unit 18 determines that the time array D#2 is normal (step S204 in FIG. 3).

[0060] Next, the determination unit 18 shifts the number i of the time array to be shifted backward by 1 to update it to 3 (step S206 in FIG. 3). When the updated number i is X+1 (=7), that is, when the shifting process is completed for all time arrays D#i where i=1 to X (YES in step S207 in FIG. 3), the operation of the determination unit 18 ends. Here, since i=3, the process proceeds to step S208.

[0061] The determination unit 18 selects the zero cross time D#2[5]=160000 nsec at the matching storage position k=5 in the time array D#2 immediately preceding the target time array D#3 as the matching zero cross time (step S208).

[0062] In the case of time array D#3 that is the target of the shift process, the time difference between the zero cross time D#3[3]=160011 nsec at the third storage position and the aligned zero cross time D#2[5]=160000 nsec is the smallest in time array D#3. Therefore, the determination unit 18 shifts each zero cross time in time array D#3 by two positions to the right in FIG. 4(A) so that D#3[3] becomes the aligned storage position (step S202).

[0063] After the shifting process of the time array D#3 is completed, the determination unit 18 determines whether the absolute value of the difference |D#2[5]-D#3[5]| between the matched zero cross time D#2[5]=160000 nsec and the zero cross time D#3[5]=160011 nsec, which is located at the same matched storage position k=5 as D#2[5] in the shifted time array D#3, is less than the threshold value TH (step S203). Here, since the absolute value of the difference of the zero cross times |D#2[5]-D#3[5]| is less than the threshold value TH, the determination unit 18 determines that the time array D#3 is normal (step S204).

[0064] Next, the determination unit 18 shifts the number i of the time array that is the target of the shift process backward by 1 to update it to 4 (step S206). Since i=4, the process proceeds to step S208, and the determination unit 18 selects the zero cross time D#3[5]=160011 nsec, which is located at the matching storage position k=5 in the time array D#3 that is immediately before the target time array D#4, as the matching zero cross time.

[0065] In the case of time array D#4 that is the target of the shift process, the time difference between the zero cross time D#4[3]=160033 nsec at the third storage position and the aligned zero cross time D#3[5]=160011 nsec is the smallest in time array D#4. Therefore, the determination unit 18 shifts each zero cross time in time array D#4 by two positions to the right in FIG. 4(A) so that D#4[3] becomes the aligned storage position (step S202).

[0066] After the shifting process of the time array D#4 is completed, the determination unit 18 determines whether the absolute value |D#3[5]-D#4[5]| of the difference between the matched zero cross time D#3[5]=160011 nsec and the zero cross time D#4[5]=160033 nsec, which is located at the same matched storage position k=5 as D#3[5] in the shifted time array D#4, is less than the threshold value TH (step S203). Here, since the absolute value |D#3[5]-D#4[5]| of the difference between the zero cross times is less than the threshold value TH, the determination unit 18 determines that the time array D#4 is normal (step S204).

[0067] Next, the determination unit 18 shifts the number i of the time array that is the target of the shift process backward by 1 to update it to 5 (step S206). Since i=5, the process proceeds to step S208, and the determination unit 18 selects the zero cross time D#4[5]=160033 nsec, which is located at the matching storage position k=5 in the time array D#4 that immediately precedes the target time array D#5, as the matching zero cross time.

[0068] In the case of time array D#5 that is the target of the shift process, the time difference between the zero cross time D#5[3]=180005 nsec at the third storage position and the aligned zero cross time D#4[5]=160033 nsec is the smallest in time array D#5. Therefore, the determination unit 18 shifts each zero cross time in time array D#5 by two positions to the right in FIG. 4(A) so that D#5[3] becomes the aligned storage position (step S202).

[0069] After the shifting process of the time array D#5 is completed, the determination unit 18 determines whether the absolute value |D#4[5]-D#5[5]| of the difference between the matched zero cross time D#4[5]=160033 nsec and the zero cross time D#5[5]=180005 nsec, which is located at the same matched storage position k=5 as D#4[5] in the shifted time array D#5, is less than the threshold value TH (step S203). Here, the absolute value |D#4[5]-D#5[5]| of the difference between the zero cross times is greater than or equal to the threshold value TH, so the determination unit 18 determines that the time array D#5 is abnormal (step S205 in FIG. 3).

[0070] Next, the determination unit 18 shifts the number i of the time array that is the target of the shift process backward by 1 to update it to 6 (step S206). If the immediately preceding time array D#5 is determined to be abnormal, the process of selecting the consistent zero-cross time differs from the above. That is, since the determination unit 18 has determined that the time array D#5 immediately preceding the target time array D#6 is abnormal, it does not select D#5[5] as the consistent zero-cross time, but instead selects, as the consistent zero-cross time, the zero-cross time D#4[5]=160033 nsec at the consistency storage position k=5 of the time array D#4 that is closest to the target time array D#6 among the normal time arrays that precede the target time array D#6 (step S208).

[0071] In the case of time array D#6 that is the target of the shift process, the time difference between the zero cross time D#6[3]=160031 nsec at the third storage position and the aligned zero cross time D#4[5]=160033 nsec is the smallest in time array D#6. Therefore, the determination unit 18 shifts each zero cross time in time array D#6 by two positions to the right in FIG. 4(A) so that D#6[3] becomes the aligned storage position (step S202).

[0072] The result of the above shifting process is shown in Figure 4(B). After the shifting process of time array D#6 is completed, the decision unit 18 determines whether the absolute value of the difference |D#4[5]-D#6[5]| between the matched zero-cross time D#4[5]=160033 nsec and the zero-cross time D#6[5]=160031 nsec, which is located at the same matched storage position k=5 as D#4[5] in the shifted time array D#6, is less than the threshold value TH (step S203). In this case, because the absolute value of the difference in the zero-cross times |D#4[5]-D#6[5]| is less than the threshold value TH, the decision unit 18 determines that the time array D#6 is normal (step S204).

[0073] The determination unit 18 shifts the number i of the time sequence that is the target of the shift process backward by 1 to update it to 7 (step S206). Since the updated number i is now X+1 (=7), the operation of the determination unit 18 ends. The determination unit 18 may perform the processes of steps S200 to S208 in both the forward and reverse directions.

[0074] Next, the flow rate calculation unit 19 identifies the target zero cross time stored in the target storage position for each post-shift time array D#i as the reception time of the corresponding ultrasonic reception signal Vin#i (step S209 in FIG. 3). The target storage position identification process for identifying the target zero cross time is the same as the process described in FIG. 12. The difference from the technology disclosed in Patent Document 1 is that the flow rate calculation unit 19 of this embodiment does not acquire, as the target zero cross time, the zero cross time included in the time array D#5 that the determination unit 18 determined to be abnormal. Therefore, when the target storage position identification process is performed on the post-shift time arrays D#1 to D#6 in FIG. 4(B), the sixth and seventh zero cross times in the time arrays D#1 to D#4 and D#6 become the target zero cross times. The flow rate calculation unit 19 only needs to perform the process of step S209 in both forward and reverse directions.

[0075] The flow rate calculation unit 19 calculates the average value of the forward direction target zero cross times acquired in step S209 and sets this as the forward direction ultrasonic wave propagation time t1. Similarly, the flow rate calculation unit 19 calculates the average value of the reverse direction target zero cross times acquired in step S209 and sets this as the reverse direction ultrasonic wave propagation time t2. Then, the flow rate calculation unit 19 calculates the difference between the propagation time t1 and the propagation time t2 as the propagation time difference Δt (FIG. 3 step S210).

[0076] The flow rate calculation unit 19 calculates the flow rate Q from the propagation time difference Δt (step S211 in FIG. 3). A known calculation formula used in a general ultrasonic flowmeter may be used as the calculation method for determining the flow rate Q, and detailed description thereof will be omitted.

[0077] The flow rate output unit 20 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 19 to the higher-level device (step S212 in FIG. 3). The above-described processing in FIGS. 2 and 3 is performed at regular intervals.

[0078] In this embodiment, by detecting abnormal data after shift processing, it is possible to reduce the possibility that the target zero crossing time for calculating the propagation time includes a zero crossing time corresponding to a different peak of the received wave, and as a result, it is possible to reduce the possibility of a flow rate error occurring.

[0079] [Second Example] Next, a second embodiment of the present invention will be described. Fig. 5 is a block diagram showing the configuration of an ultrasonic flowmeter according to the second embodiment of the present invention. The ultrasonic flowmeter of this embodiment includes a pipe 10, transducers 11 and 12, a transmitting unit 13, a receiving unit 14, a switching unit 15, a time measuring unit 16, a memory unit 17, a determining unit 18a, a flow rate calculating unit 19, and a flow rate output unit 20.

[0080] The operations of the transducers 11 and 12, the transmitting section 13, the receiving section 14, the switching section 15, the time measuring section 16 and the storage section 17 are the same as those described in the first embodiment. FIG. 6 is a flowchart illustrating the operations of the determining unit 18 a, the flow rate calculating unit 19, and the flow rate output unit 20.

[0081] The operation of the decision unit 18a in steps S200 to S208 in FIG. 6 is the same as the operation of the decision unit 18 in the first embodiment. When the number i updated in step S206 becomes X+1 (=7) and the shift process has been completed for all time arrays D#i where i=1 to X (YES in step S207 in FIG. 6), the determination unit 18a determines whether the number of times an abnormality has been determined in step S205 is equal to or greater than a predetermined number N (N is an integer equal to or greater than 1) per direction (step S213 in FIG. 6). If the number of times an abnormality has been determined is less than the predetermined number N per direction, the determination unit 18a ends the process.

[0082] On the other hand, if the number of times that an abnormality has been determined is equal to or greater than the predetermined number N in at least one of the forward direction and the reverse direction, the determination unit 18a determines that there is a possibility that the time array D#1 is abnormal for the direction in which the number of times that an abnormality has been determined is equal to or greater than the predetermined number N. Then, for the direction in which the number of times that an abnormality has been determined is equal to or greater than the predetermined number N, the determination unit 18a overwrites the time array D#1 with the zero-cross times stored in the time arrays excluding the time array D#1, and then initializes the number i of the time array to be shifted to 1 (step S214 in FIG. 6), and returns to step S201.

[0083] As described above, in this embodiment, when the number i is the initial value, that is, when the shift process target is time array D#1, it is unconditionally assumed that the shift process has been completed, and the process proceeds to step S206. The determination unit 18a updates the number i to 2 by shifting it back by 1 (step S206 in FIG. 6). When the updated number i is X+1 (=7), that is, when the shift process has been completed for all time arrays D#i where i=1 to X (YES in step S207 in FIG. 6), the operation of the determination unit 18a ends.

[0084] In this way, the processing of steps S201 to S208 is performed again for all time arrays D#i where i=1 to X. Note that the shift processing needs to be performed again only in the direction where the number of times an abnormality has been determined is equal to or exceeds the predetermined number N. When the number of times that an abnormality is determined in step S205 becomes less than the predetermined number N per direction (NO in step S213 in FIG. 6), the operation of the determining unit 18a ends.

[0085] The operations of the flow rate calculation unit 19 and the flow rate output unit 20 (steps S209 to S212 in FIG. 6) are the same as those described in the first embodiment.

[0086] The operation of the determination unit 18a will be specifically described using Figures 7(A), 7(B), 8(A), and 8(B). In this example, X=7. Figure 7(A) shows an example of the zero-cross times stored in the time arrays D#1 to D#7 of the storage unit 17, and Figure 7(B) shows the results of the shift processing. By the processing of the determination unit 18a of this embodiment, time arrays D#3 and D#6 are determined to be abnormal.

[0087] Here, if the predetermined number of times N is 2, the judgment unit 18a judges that there is a possibility that the time array D#1 is abnormal, overwrites the time array D#1 with the zero-cross times stored in the time arrays excluding the time array D#1, initializes the number i of the time array to be shifted to 1 (step S214 in FIG. 6), and returns to step S201. Here, the time array D#1 is overwritten with the time array D#2. The result of overwriting the time array D#1 with the time array D#2 is shown in FIG. 8(A). Note that in the example in FIG. 8(A), the states of the time arrays D#1 to D#7 are returned to the states after the measurement is completed (FIG. 7(A)).

[0088] In this way, steps S201 to S208 are performed again for all time arrays D#i where i = 1 to X. The results of the second shift process are shown in Fig. 8(B). In the second shift process, all of the time arrays D#2 to D#7 are determined to be normal, so when the target storage position identification process is performed on the time arrays D#1 to D#7 after the shift process in Fig. 8(B), the fourth and fifth zero cross times of the time arrays D#1 to D#7 become the target zero cross times.

[0089] As described above, in this embodiment, it is possible to determine whether the time sequence D#1 is abnormal in step S213, and when it is determined that the time sequence D#1 may be abnormal, it is possible to exclude the abnormal time sequence D#1 from the targets for acquiring the target zero cross time by overwriting the time sequence D#1 with a normal time sequence. As a result, in this embodiment, compared to the first embodiment, it is possible to further reduce the possibility that the target zero cross time will include a zero cross time corresponding to a different peak of the received wave, and it is possible to further reduce the possibility of a flow rate error occurring.

[0090] In this embodiment, time sequence D#1 is overwritten with time sequence D#2, but this is not limited to time sequence D#2, and time sequence D#1 may be overwritten with a normal time sequence other than D#2. For example, in the example of Figure 7(B), time sequence D#1 may be overwritten with any of time sequences D#4, D#5, and D#7. Selection rules for which time sequence to use to overwrite time sequence D#1 can be specified in advance. When time array D#1 is used, the absolute value of the difference from the matched zero-crossing time is equal to or greater than a threshold, and the time array D#1 may be overwritten with a zero-crossing time determined to be abnormal. For example, in the example of FIG. 7(B), time array D#1 may be overwritten with either time array D#3 or D#6.

[0091] Furthermore, in the example of FIG. 8(A), even after time array D#2 overwrites time array D#1, time array D#2 remains, but the time array D#2 used for the overwrite may be deleted. In addition, in the explanation of FIG. 6, the shift process is repeated until the number of times that an abnormality is determined becomes less than the predetermined number N. However, in reality, if the number of times that an abnormality is determined becomes equal to or greater than the predetermined number N even after performing the shift process again and the determination is YES in step S213, it is desirable to terminate the abnormal data detection process and stop calculating the propagation time based on the acquired X number of time sequences.

[0092] In the first and second embodiments, the zero cross time at the preset alignment storage position in the time array D#(i-1) immediately preceding the time array D#i to be shifted is selected as the aligned zero cross time, but this is not limited thereto, and another aligned zero cross time may be selected. For example, when the number i is the initial value i0, the zero cross time at the preset alignment storage position in the time array D#i0 may always be selected as the aligned zero cross time. For example, in the first and second embodiments, if i0=1, then the zero cross time D#1[5] is always selected as the aligned zero cross time for numbers i=2 to X.

[0093] Alternatively, a predicted value obtained from a past zero-cross time stored in the consistency storage position k=5 of the time array D#i may be set as the consistency zero-cross time. In this case, however, it is necessary to actually perform shift processing on the time array D#i0 when the number i is the initial value i0, and therefore it is necessary to omit the processing of step S201 in Fig. 3. Furthermore, because shift processing is also performed on the time array D#i0, the example in which a predicted value is set as the consistency zero-cross time is applicable only to the first embodiment.

[0094] The transmitter 13, receiver 14, switch 15, time measurement unit 16, and memory unit 17 described in the first and second embodiments can be realized by an IC such as an FPGA (Field Programmable Gate Array). The determiners 18, 18a, flow rate calculation unit 19, and flow rate output unit 20 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 Figure 9.

[0095] 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 time measuring unit 16, the storage unit 17, etc. In such a computer, a program for realizing the flow rate measurement 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. [Explanation of symbols]

[0096] 10... piping, 11, 12... transducer, 13... transmitting unit, 14... receiving unit, 15... switching unit, 16... time measuring unit, 17... memory unit, 18, 18a... determination unit, 19... flow rate calculation unit, 20... flow rate 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 time measurement unit configured to measure the zero cross time a plurality of times 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 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 between the forward and reverse directions of ultrasonic waves based on the acquired target zero cross time, and calculate the flow rate of the fluid from this difference in propagation time; an ultrasonic flowmeter comprising a determination unit that determines a time array including a zero cross time to be compared as abnormal when an absolute value of a difference between the reference matched zero cross time stored in a predetermined matched storage position in the time array and a zero cross time to be compared that is derived from a peak of the same type as the peak of the ultrasonic reception signal corresponding to the matched zero cross time, among zero cross times stored in the time array for a measurement time different from the matched zero cross time, is equal to or greater than a threshold value.

2. 2. The ultrasonic flowmeter according to claim 1, The ultrasonic flowmeter is characterized in that the determination unit performs peak determination processing to determine that, among the zero cross times stored in the time array of measurement times different from the matched zero cross time, the zero cross time that has the smallest difference from the matched zero cross time is the zero cross time that originates from the same type of peak as the matched zero cross time.

3. 3. The ultrasonic flowmeter according to claim 2, the determination unit, when the number of times that the time sequence has been determined to be abnormal in at least one of the forward and reverse directions is equal to or greater than a predetermined number of times, overwrites the time sequence of the measurement of the matched zero-cross time of the peak determination process with the zero-cross times stored in the time sequence excluding the matched zero-cross time sequence of the peak determination process for the direction in which the number of times that the time sequence has been determined to be abnormal is equal to or greater than a predetermined number of times, and then performs the peak determination process again; and, when the absolute value of the difference between the matched zero-cross time and the zero-cross time to be compared is equal to or greater than a threshold value after this peak determination process, determines the time sequence including the zero-cross time to be compared to be abnormal.

4. 2. The ultrasonic flowmeter according to claim 1, The ultrasonic flowmeter is characterized in that the judgment unit selects the zero cross time in the alignment storage position of the time array immediately preceding the time array that is the target of the judgment process as the aligned zero cross time, selects the zero cross time in the alignment storage position of the time array when the number of the time array that is the target of the judgment process is its initial value as the aligned zero cross time, or sets a predicted value obtained from past zero cross times stored in the alignment storage position as the aligned zero cross time.

5. 2. The ultrasonic flowmeter according to claim 1, The ultrasonic flowmeter according to claim 1, wherein the flow rate calculation unit does not use information on a time sequence that the determination unit determines to be abnormal for flow rate calculation.

6. 4. The ultrasonic flowmeter according to claim 3, The ultrasonic flowmeter is characterized in that the flow rate calculation unit obtains the target zero cross time for each direction from the time sequence that the determination unit determines to be normal when the number of times that the determination unit determines the time sequence to be abnormal is less than a predetermined number of times per direction.

7. 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 storing the measured zero crossing times in order from a specific storage position in a time array prepared for a corresponding measurement time and a corresponding direction; a third step of determining that the time array including the zero cross time to be compared is abnormal when an absolute value of a difference between a reference matched zero cross time stored in a predetermined matched storage location of the time array and a zero cross time to be compared that is derived from a peak of the same type as the peak of the ultrasonic reception signal corresponding to the matched zero cross time, among zero cross times stored in the time array for a measurement time different from the matched zero cross time, is equal to or greater than a threshold value; and a fourth step of obtaining a target zero cross time for each of the forward and reverse directions from the time sequence to be used in calculating the propagation time, calculating a difference in the propagation time of 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.

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