Ultrasonic flowmeter and flow rate measurement method

Abstract

To suppress power consumption while maintaining high measurement accuracy of the flow rate measurement value regardless of the magnitude or the tendency of increase or decrease of the flow rate.SOLUTION: An ultrasonic flow meter includes: a zero cross time measuring unit 16 that measures, at each of measurement cycles and each of forward and reverse directions, a zero-cross time of an ultrasonic wave reception signal at the measurement cycle of the forward direction in which ultrasonic waves are transmitted from an ultrasonic oscillator 11 and received by an ultrasonic oscillator 12, and a zero-cross time of the ultrasonic wave reception signal at the measurement cycle of the reverse direction in which ultrasonic waves are transmitted from the ultrasonic oscillator 12 and received by the ultrasonic oscillator 11; an index calculation unit 20 that calculates, based on the zero-cross time or the ultrasonic wave reception signal, an index value indicating magnitude of variation caused by a decrease in a signal-to-noise ratio, in a flow rate measurement value; and a setting unit 21 that sets, into a transmission unit 13, a number of ultrasonic transmission / reception repetitions per fixed time based on the index value calculated by the index calculation unit 20.SELECTED DRAWING: Figure 2

Description

[Technical field]

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

[0002] Conventionally, there is known an ultrasonic flowmeter in which a pair of ultrasonic 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 ultrasonic transducers, and the flow rate is calculated based on the difference between the accumulated propagation time of the ultrasonic waves from the upstream side to the downstream side and the accumulated propagation time from the downstream side to the upstream side (see, for example, Patent Document 1).

[0003] In such ultrasonic flowmeters, the signal-to-noise ratio, which is determined by the ratio of the ultrasonic reception signal strength to the variance of the noise in the measurement system, may decrease, and the error and variance of a single flow measurement value may increase. In such a situation, it is effective to increase the number of repetitions of ultrasonic transmission and reception. In the ultrasonic flowmeter disclosed in Patent Document 1, the number of repetitions of ultrasonic transmission and reception is changed in response to a situation in which the variance of the flow measurement value increases due to fluctuations in the measured flow rate, and the number of repetitions is increased when the flow rate fluctuation is large.

[0004] However, the ultrasonic flowmeter disclosed in Patent Document 1 has a problem that the signal-to-noise ratio, which is determined by the ratio of the signal to the noise of the measurement system, decreases, and it is not possible to selectively detect only the situation in which the error and variance of the single flow measurement value increases, resulting in an increase in current consumption. The flow rate of the fluid to be measured is expected to fluctuate even under normal conditions, and when the flow rate changes, the standard deviation of the flow rate often increases. However, such fluctuations in the flow measurement value can be said to be the result of correctly measuring the flow rate change of the fluid, albeit discretely, so there is no need to increase the measurement frequency. Conversely, if the number of repetitions of ultrasonic transmission and reception is increased every time a flow rate change occurs, the current consumption will increase unnecessarily.

[0005] As described above, in the conventional ultrasonic flowmeter, the current consumption increases, and therefore, in particular in the ultrasonic flowmeter driven by a battery, a problem occurs in that the battery runs out in a short period of time. To address such problems, an ultrasonic flowmeter has been proposed that calculates the cumulative or average value of ultrasonic propagation time, calculates the flow rate of the fluid from this cumulative or average value, and sets the number of repetitions of ultrasonic transmission and reception according to the flow rate, thereby reducing power consumption (see, for example, Patent Document 2). This ultrasonic flowmeter can reduce power consumption by measuring the flow rate at time intervals appropriate for the flow rate.

[0006] However, in the ultrasonic flowmeter disclosed in Patent Document 2, the number of times ultrasonic waves are transmitted and received is set based on the flow rate or the tendency of the flow rate to increase or decrease. This makes it possible to reduce power consumption, but there is an issue in that the measurement accuracy of the flow rate measurement value changes depending on the flow rate conditions. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent No. 4889253 [Patent Document 2] JP 2003-121220 A Summary of the Invention [Problem to be solved by the invention]

[0008] The present invention has been made to solve the above-mentioned problems, and aims to provide an ultrasonic flowmeter that can reduce power consumption while maintaining high measurement accuracy of the flow measurement value regardless of the flow rate or the tendency of the flow rate to increase or decrease. [Means for solving the problem]

[0009] The ultrasonic flowmeter of the present invention includes a pipe configured to allow a fluid to flow as a measurement target, a pair of ultrasonic transducers arranged upstream and downstream of the pipe, a transmitting unit configured to transmit ultrasonic waves from one of the ultrasonic transducers, and a measuring unit configured to measure the zero-cross time of an ultrasonic reception signal in a forward measurement in which an ultrasonic transducer on the upstream side transmits an ultrasonic wave and receives it at the ultrasonic transducer on the downstream side, and the zero-cross time of an ultrasonic reception signal in a reverse measurement in which an ultrasonic transducer on the downstream side transmits an ultrasonic wave and receives it at the ultrasonic transducer on the upstream side, for each measurement and for each forward and reverse direction. a flow rate calculation unit configured to calculate a propagation time difference between ultrasonic waves in a forward direction and a backward direction based on a zero cross time in a forward direction and a zero cross time in a backward direction, and calculate a flow rate measurement value of the fluid from the propagation time difference; an index calculation unit configured to calculate an index value indicating a magnitude of variation in the flow rate measurement value caused by a decrease in a signal-to-noise ratio based on the zero cross time or the ultrasonic reception signal; and a setting unit configured to set the number of ultrasonic transmission and reception repetitions per certain time for the transmission unit based on the index value calculated by the index calculation unit, The index calculation unit acquires values ​​of zero cross times for the number of times that ultrasonic transmission and reception are repeated for both forward and reverse directions, calculates differences between adjacent zero cross times in the same measurement for each measurement and for each forward and reverse direction, and calculates a standard deviation of all the calculated differences as the index value. It is characterized by the above.

[0010] The ultrasonic flowmeter of the present invention includes a pipe configured to allow a fluid to flow as a measurement target, a pair of ultrasonic transducers arranged upstream and downstream of the pipe, a transmission unit configured to transmit ultrasonic waves from one of the ultrasonic transducers, and a time measurement unit configured to measure the zero-cross time of an ultrasonic reception signal in a forward measurement in which an ultrasonic transducer transmits an ultrasonic wave from the upstream ultrasonic transducer and receives it at the downstream ultrasonic transducer, and the zero-cross time of an ultrasonic reception signal in a reverse measurement in which an ultrasonic transducer transmits an ultrasonic wave from the downstream ultrasonic transducer and receives it at the upstream ultrasonic transducer, for each measurement and for each forward and reverse direction, and a time measurement unit configured to calculate a propagation time difference between ultrasonic waves in the forward and reverse directions based on the zero-cross time in the forward direction and the zero-cross time in the reverse direction, and to estimate a forward time from the propagation time difference. The present invention is characterized in that it comprises a flow calculation unit configured to calculate a flow measurement value of the fluid, an index calculation unit configured to calculate an index value indicating the magnitude of variation in the flow measurement value caused by a decrease in signal-to-noise ratio based on the zero cross time or the ultrasonic reception signal, and a setting unit configured to set the number of ultrasonic transmission / reception repetitions per certain time for the transmission unit based on the index value calculated by the index calculation unit, and the index calculation unit acquires zero cross time values ​​for the number of ultrasonic transmission / reception repetitions in both forward and reverse directions, calculates the difference between adjacent zero cross times in the same measurement for each measurement and for each forward and reverse direction, and calculates the difference between the maximum and minimum values ​​of all the calculated differences as the index value. The ultrasonic flowmeter of the present invention includes a pipe configured to allow a fluid to flow as a measurement target, a pair of ultrasonic transducers arranged upstream and downstream of the pipe, a transmission unit configured to transmit ultrasonic waves from one of the ultrasonic transducers, a time measurement unit configured to measure a zero-cross time of an ultrasonic reception signal in a forward measurement in which an ultrasonic transducer on the upstream side transmits an ultrasonic wave and receives it at the ultrasonic transducer on the downstream side, and a zero-cross time of an ultrasonic reception signal in a reverse measurement in which an ultrasonic transducer on the downstream side transmits an ultrasonic wave and receives it at the ultrasonic transducer on the upstream side, for each measurement and for each forward and reverse direction, and a time measurement unit configured to calculate a propagation time difference between ultrasonic waves in the forward and reverse directions based on the zero-cross time in the forward direction and the zero-cross time in the reverse direction, and to measure a flow rate of the fluid from the propagation time difference. and a setting unit configured to set the number of ultrasonic transmission / reception repetitions per certain time period for the transmitting unit based on the index value calculated by the index calculation unit, and the index calculation unit acquires zero-cross time values ​​for the number of ultrasonic transmission / reception repetitions in both forward and reverse directions, calculates differences between adjacent zero-cross times in the same measurement for each measurement and for each forward and reverse direction, and calculates standard deviations for all the calculated differences for each position of the zero-cross point in the ultrasonic reception signal to set the index value. 。

[0011] The flow rate measurement method of the present invention includes a first step of measuring a zero-cross time of an ultrasonic reception signal in a forward measurement in which an ultrasonic transducer on the upstream side of a pipe through which a fluid to be measured flows transmits an ultrasonic wave and receives it at an ultrasonic transducer on the downstream side of the pipe, and a zero-cross time of an ultrasonic reception signal in a reverse measurement in which an ultrasonic transducer on the downstream side transmits an ultrasonic wave and receives it at the ultrasonic transducer on the upstream side, for each measurement and for each forward and reverse direction; a second step of calculating a propagation time difference between ultrasonic waves in the forward and reverse directions based on the zero-cross time in the forward direction and the zero-cross time in the reverse direction, and calculating a flow rate measurement value of the fluid from this propagation time difference; a third step of calculating an index value indicating a magnitude of variation in the flow rate measurement value caused by a decrease in the signal-to-noise ratio based on the zero-cross time or the ultrasonic reception signal; and a fourth step of setting the number of ultrasonic transmission and reception repetitions per fixed time based on the index value calculated in the third step. The third step includes a step of acquiring values ​​of zero cross times for the number of times that the ultrasonic transmission and reception is repeated for both the forward and reverse directions, calculating differences between adjacent zero cross times in the same measurement for each measurement and for each forward and reverse direction, and calculating a standard deviation of all the calculated differences as the index value. It is characterized by the above.

[0012] The flow rate measurement method of the present invention includes a first step of measuring a zero-cross time of an ultrasonic reception signal in a forward measurement in which an ultrasonic transducer on the upstream side of a pipe through which a fluid to be measured flows transmits an ultrasonic wave and receives it at an ultrasonic transducer on the downstream side of the pipe, and a zero-cross time of an ultrasonic reception signal in a reverse measurement in which an ultrasonic transducer on the downstream side transmits an ultrasonic wave and receives it at the ultrasonic transducer on the upstream side, for each measurement and for each forward and reverse direction; a second step of calculating a propagation time difference between ultrasonic waves in the forward and reverse directions based on the zero-cross time in the forward direction and the zero-cross time in the reverse direction, and calculating a flow rate measurement value of the fluid from this propagation time difference; The method includes a third step of calculating an index value indicating the magnitude of variation in the flow measurement value caused by a decrease in the signal-to-noise ratio based on time or the ultrasonic reception signal, and a fourth step of setting the number of ultrasonic transmission / reception repetitions per certain time based on the index value calculated in the third step, and the third step includes a step of acquiring zero-cross time values ​​for the number of ultrasonic transmission / reception repetitions in both forward and reverse directions, calculating the difference between adjacent zero-cross times in the same measurement for each measurement and for each forward and reverse direction, and calculating the difference between the maximum and minimum values ​​of all the calculated differences as the index value. The flow rate measurement method of the present invention includes a first step of measuring a zero-cross time of an ultrasonic reception signal in a forward measurement in which an ultrasonic transducer on the upstream side of a pipe through which a fluid to be measured flows transmits an ultrasonic wave and receives it at an ultrasonic transducer on the downstream side of the pipe, and a zero-cross time of an ultrasonic reception signal in a reverse measurement in which an ultrasonic transducer on the downstream side transmits an ultrasonic wave and receives it at the ultrasonic transducer on the upstream side, for each measurement and for each forward and reverse direction; a second step of calculating a propagation time difference between ultrasonic waves in the forward and reverse directions based on the zero-cross time in the forward direction and the zero-cross time in the reverse direction, and calculating a flow rate measurement value of the fluid from this propagation time difference; The method includes a third step of calculating an index value indicating the magnitude of the variation in the flow measurement value caused by a decrease in the signal-to-noise ratio based on the ultrasonic reception signal, and a fourth step of setting the number of ultrasonic transmission / reception repetitions per fixed time based on the index value calculated in the third step, and the third step includes a step of acquiring zero cross time values ​​for the number of ultrasonic transmission / reception repetitions in both forward and reverse directions, calculating differences between adjacent zero cross times in the same measurement for each measurement and for each forward and reverse direction, and calculating standard deviations for all the calculated differences for each position of the zero cross point in the ultrasonic reception signal to set the index value. 。 Effect of the Invention

[0013] According to the ultrasonic flowmeter of the present invention, an index value indicating the magnitude of the variation in the flow measurement value caused by the decrease in the signal-to-noise ratio is calculated based on the zero crossing time or the ultrasonic reception signal, and the number of times the ultrasonic transmission and reception is repeated per fixed time is set for the transmitting unit based on the index value, thereby realizing the adjustment of the measurement frequency according to the variation in the flow measurement value caused by the decrease in the signal-to-noise ratio. The variation in the flow measurement value itself increases even if the flow rate fluctuates, for example, but the present invention can eliminate the influence of the flow rate fluctuation and the propagation time fluctuation, calculate an index of the magnitude of the random variation in the flow measurement value caused by the decrease in the signal-to-noise ratio, and change the number of times the ultrasonic transmission and reception is repeated only when the signal-to-noise ratio is decreased. In the present invention, when the variation in the flow measurement value caused by the decrease in the signal-to-noise ratio is small, the number of times the ultrasonic transmission and reception is repeated can be reduced, and power consumption can be suppressed. In addition, since the propagation time of the ultrasonic can be measured in a state where the variation in the flow measurement value caused by the decrease in the signal-to-noise ratio is small, the measurement accuracy can be improved.

[0014] Furthermore, in the present invention, the standard deviation of the differences between the zero crossing times can be calculated as the index value.

[0015] Furthermore, in the present invention, the difference between the maximum value and the minimum value of the differences between the zero crossing times can be calculated as the index value.

[0016] Furthermore, in the present invention, the standard deviation of the difference between the zero crossing times can be calculated for each position of the zero crossing point in the ultrasonic reception signal, and used as an index value.

[0017] Furthermore, in the present invention, the maximum amplitude of the ultrasonic reception signal is obtained, and the index value is obtained based on the maximum amplitude, so that the index value can be obtained while reducing the calculation load and current consumption. [Brief description of the drawings]

[0018] [Figure 1] FIG. 1 is a diagram for explaining the relationship between the signal-to-noise ratio of a measurement unit of an ultrasonic flowmeter and the number of ultrasonic transmission / reception repetitions. [Diagram 2] FIG. 2 is a block diagram showing a configuration of an ultrasonic flowmeter according to a first embodiment of the present invention. [Diagram 3] FIG. 3 is a signal waveform diagram showing the relationship between an ultrasonic reception signal and a zero crossing point. [Figure 4] FIG. 4 is a flowchart explaining the operation of the ultrasonic transducer, the transmitting unit, the receiving unit, the switching unit, the zero-cross time measuring unit, the memory 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. [Diagram 5] FIG. 5 is a flowchart illustrating the operation of the index calculation unit and the setting unit according to the first embodiment of the present invention. [Figure 6] FIG. 6 is a diagram for explaining a shift process for aligning the positions of the zero-cross points in the ultrasonic reception signal with respect to the zero-cross times of elements in each zero-cross sequence in the first embodiment of the present invention. [Figure 7] FIG. 7 is a block diagram showing the configuration of an ultrasonic flowmeter according to the second embodiment of the present invention. [Figure 8] FIG. 8 is a flowchart illustrating the operation of the index calculation unit and the setting unit according to the second embodiment of the present invention. [Figure 9] FIG. 9 is a signal waveform diagram illustrating the maximum amplitude of an ultrasonic reception signal. [Figure 10] FIG. 10 is a diagram showing the relationship between the maximum amplitude of the ultrasonic reception signal and the magnitude of variation in the flow rate measurement value. [Figure 11] FIG. 11 is a block diagram showing an example of the configuration of a computer that realizes the ultrasonic flowmeters according to the first and second embodiments of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] [Principle of the invention] The subject of the present invention is an ultrasonic flowmeter that needs to be operated for a long period of time on a battery. In order to operate an ultrasonic flowmeter for a long period of time on a battery, low current consumption is required. Furthermore, since it is battery-powered, the power supply voltage during operation is not constant. When the power supply voltage drops, the strength of the ultrasonic transmission signal drops, and so the ultrasonic transmission and reception signal strength during operation changes. Furthermore, it is assumed that the ambient temperature and the composition of the fluid will also change, and the ultrasonic transmission and reception signal strength changes in response to these external factors.

[0020] The measurement unit of the ultrasonic flowmeter periodically outputs flow measurement values ​​to the connected higher-level device. The higher-level device calculates the average value and integrated value of the flow measurement values. The higher-level device then compares the calculated average value and integrated value with a preset threshold value, and based on the comparison result, opens and closes the valve installed in the flow path in which the ultrasonic flowmeter is installed, and determines the soundness of the measurement target. The higher-level device also records the average flow rate and integrated flow rate, and outputs the average flow rate and integrated flow rate to the outside.

[0021] The higher-level device can grasp the flow rate state and perform various calculations and judgments using the flow rate measurement values ​​sent sequentially from the measurement unit of the ultrasonic flowmeter, but it cannot grasp the state of the measurement unit, such as the temperature or actual signal-to-noise ratio, or change the method of processing the flow rate measurement values ​​based on the grasped state.

[0022] Therefore, in order for the host device to correctly compare and determine the average value or integrated value of the flow measurement value per specified time with the threshold value, it is required that the magnitude of variation contained in the flow measurement value that is periodically output from the measurement unit to the host device, which changes depending on the signal-to-noise ratio of the measurement unit, always falls within a specified range.

[0023] Therefore, it is desirable to prevent an increase in current consumption due to an increase in the number of measurements, and to ensure that the magnitude of variation in the flow measurement values ​​periodically output from the measurement unit of the ultrasonic flowmeter to a higher-level device is always within a specified range. The magnitude of variation in the measurement values ​​due to the signal-to-noise ratio tends to be inversely proportional to the square root of the population of the data used to calculate the average value. Therefore, if the number of ultrasonic transmission / reception repetitions per certain period of time is increased to calculate the average from multiple flow measurement values, the variation due to the signal-to-noise ratio contained in the flow measurement values ​​per certain period of time will be reduced, but the number of ultrasonic transmission / reception repetitions required will differ depending on the signal-to-noise ratio at each time.

[0024] Figures 1(A) and 1(B) are diagrams explaining the relationship between the signal-to-noise ratio of the measurement section of an ultrasonic flowmeter and the required number of ultrasonic transmission / reception repetitions. Figure 1(A) shows a case where the signal-to-noise ratio is large due to low temperature or high ultrasonic transmission / reception signal strength, while Figure 1(B) shows a case where the signal-to-noise ratio is small due to high temperature or low ultrasonic transmission / reception signal strength. When the signal-to-noise ratio is large, the number of measurements per unit time can be reduced, reducing current consumption. On the other hand, when the signal-to-noise ratio is small, it is necessary to increase the number of measurements per unit time.

[0025] In the present invention, the influence of flow rate changes is eliminated, and the degree of variation in the flow rate measurement value that occurs according to the signal-to-noise ratio is grasped. In order to reduce the current consumption, it is desirable to reduce the number of ultrasonic transmission / reception repetitions as much as possible, so the number of ultrasonic transmission / reception repetitions per certain time is increased or decreased according to the degree of variation in the flow rate measurement value that occurs according to the signal-to-noise ratio.

[0026] As described above, when the signal-to-noise ratio is reduced and the random variation in the flow measurement value is increased, the number of ultrasonic transmission / reception repetitions is increased to reduce the variation in the flow measurement value. On the other hand, when the signal-to-noise ratio is large and the random variation in the flow measurement value is small, the number of ultrasonic transmission / reception repetitions is decreased to save power. As a result, the number of ultrasonic transmission / reception repetitions can be adjusted so that the magnitude of variation contained in the flow measurement value output from the measurement unit to the upper device at regular intervals, which changes depending on the signal-to-noise ratio of the measurement unit, always falls within a specified range.

[0027] The inventors have devised a method of using the following index as a method for understanding the degree of variation in flow measurement values ​​caused by the signal-to-noise ratio while eliminating the influence of flow rate changes. (I) The difference between the zero-crossing times of the ultrasonic received signal. (II) The strength of the ultrasonic received signal.

[0028] [First Example] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Fig. 2 is a block diagram showing the configuration of an ultrasonic flowmeter according to a first embodiment of the present invention. This embodiment is an example in which the degree of variation in flow measurement values ​​is grasped based on the difference between zero cross times of ultrasonic reception signals.

[0029] The ultrasonic flowmeter includes a pipe 10 through which a fluid to be measured flows, a pair of ultrasonic transducers 11, 12 arranged upstream and downstream of the pipe 10, a transmission unit 13 that transmits ultrasonic waves from one of the ultrasonic transducers, a reception unit 14 that amplifies an ultrasonic reception signal received by the other ultrasonic transducer, a switching unit 15 that switches the connection between the ultrasonic transducers 11, 12, the transmission unit 13, and the reception unit 14, a zero-cross time measurement unit 16 that measures a zero-cross time at which the ultrasonic reception signal crosses zero voltage (0V) after the ultrasonic reception signal exceeds a threshold voltage, multiple times for each measurement and for each forward and reverse direction, and a zero-cross time counter 17 that measures the zero-cross time at which the ultrasonic reception signal crosses zero voltage (0V) after the ultrasonic reception signal exceeds a threshold voltage. The device is equipped with a memory unit 17 that stores time, a flow rate calculation unit 18 that calculates the propagation time difference between forward and reverse ultrasonic waves based on the forward zero cross time and the reverse zero cross time, and calculates the flow rate of the fluid from this propagation time difference, a flow rate output unit 19 that transmits the flow rate measurement value to a higher-level device, an index calculation unit 20 that calculates an index value that indicates the magnitude of variation in the flow rate measurement value based on the zero cross time or the ultrasonic reception signal, and a setting unit 21 that sets the number of ultrasonic transmission and reception repetitions per fixed time for the transmission unit 13 based on the index value calculated by the index calculation unit 20.

[0030] In this embodiment, a pair of ultrasonic transducers 11, 12 are arranged upstream and downstream of the pipe 10. In the forward direction, in which ultrasonic waves are transmitted from the ultrasonic transducer 11 on the upstream side and received by the ultrasonic transducer 12 on the downstream side, the switching unit 15 connects the transmitting unit 13 to the ultrasonic transducer 11 and connects the ultrasonic transducer 12 to the receiving unit 14. At this time, the transmitting unit 13 supplies a driving transmission pulse to the ultrasonic transducer 11. As a result, the ultrasonic transducer 11 transmits ultrasonic waves in an oblique direction to the fluid flowing in the pipe 10 in response to the transmission pulse from the transmitting unit 13. The ultrasonic transducer 12 receives the ultrasonic waves transmitted from the ultrasonic transducer 11. The receiving unit 14 amplifies the output signal of the ultrasonic transducer 12 and outputs an ultrasonic reception signal Vin.

[0031] Conversely, in the reverse direction where ultrasonic waves are transmitted from the ultrasonic transducer 12 on the downstream side and received by the ultrasonic transducer 11 on the upstream side, the switching unit 15 connects the transmitting unit 13 to the ultrasonic transducer 12, and connects the ultrasonic transducer 11 to the receiving unit 14. At this time, the transmitting unit 13 supplies a driving transmission pulse to the ultrasonic transducer 12. As a result, the ultrasonic transducer 12 transmits ultrasonic waves in an oblique direction to the fluid flowing in the pipe 10 in response to the transmission pulse from the transmitting unit 13. The ultrasonic transducer 11 receives the ultrasonic waves transmitted from the ultrasonic transducer 12. The receiving unit 14 amplifies the output signal of the ultrasonic transducer 11 and outputs an ultrasonic reception signal Vin.

[0032] The zero-cross time measurement unit 16 measures multiple zero-cross times at which the ultrasonic reception signal Vin (voltage signal) amplified by the receiving unit 14 crosses zero voltage (0V) after the signal 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 the memory unit 17.

[0033] In this embodiment, in order to facilitate calculation, the zero cross time is set to a relative time (the time elapsed from the transmission time of the ultrasonic waves) rather than an absolute time. In the case of the forward direction, the time when the ultrasonic waves are transmitted from the ultrasonic transducer 11 may be set to the time when the transmission unit 13 supplies a driving transmission pulse to the ultrasonic transducer 11. In the case of the reverse direction, the time when the ultrasonic waves are transmitted from the ultrasonic transducer 12 may be set to the time when the transmission unit 13 supplies a driving transmission pulse to the ultrasonic transducer 12.

[0034] 3 is a signal waveform diagram showing the relationship between the ultrasonic reception signal and the zero crossing point. As shown in FIG. 3, the ultrasonic reception signal Vin (voltage signal) amplified by the receiving unit 14 is composed of a plurality of sinusoidal AC pulses whose amplitude increases and decreases along the time axis.

[0035] In order to extract zero-crossing points that may be used for calculation from among the multiple zero-crossing points, the zero-crossing time measurement unit 16 detects a trigger point at which the ultrasonic reception signal Vin exceeds a preset threshold voltage Vs, and then detects H zero-crossing points (H is an integer equal to or greater than 2) after this trigger point to measure the zero-crossing time.

[0036] In the example of Fig. 3, H = 5 zero cross times are measured. Because the ultrasonic reception signal Vin#1 exceeds the threshold voltage Vs at time Ts1, the zero cross time measurement unit 16 starts detecting zero cross points at time Ts1 and detects zero cross points Z3, Z4, Z5, Z6, and Z7. The zero cross time measurement unit 16 stores the values ​​of the zero cross times T3, T4, T5, T6, and T7 corresponding to the zero cross points Z3, Z4, Z5, Z6, and Z7 in the storage unit 17 as the zero cross sequence D#1.

[0037] Furthermore, because the next ultrasonic reception signal Vin#2 exceeds the threshold voltage Vs at time Ts2, the zero-cross time measurement unit 16 starts detecting zero-cross points at time Ts2 and detects zero-cross points Z1, Z2, Z3, Z4, and Z5. The zero-cross time measurement unit 16 stores the values ​​of the zero-cross times T1, T2, T3, T4, and T5 corresponding to the zero-cross points Z1, Z2, Z3, Z4, and Z5 in the storage unit 17 as the zero-cross sequence D#2.

[0038] FIG. 4 is a flowchart illustrating the operations of the ultrasonic transducers 11, 12, the transmitting section 13, the receiving section 14, the switching section 15, the zero cross time measuring section 16, the storage section 17, the flow rate calculating section 18, and the flow rate output section 19 of this embodiment.

[0039] In this embodiment, the number of times ultrasonic transmission and reception is repeated per certain time period for transmitting and receiving ultrasonic waves in both forward and reverse directions is X (X is an integer of 2 or more), and this number of times ultrasonic transmission and reception is repeated X, as described later, is set by the setting unit 21. Also, H zero cross times are measured for one transmission and reception of ultrasonic waves.

[0040] First, the zero crossing time measurement unit 16 initializes the measurement count i (i is an integer from 1 to X) to 1 (step S100 in FIG. 4). The ultrasonic transducer 11 or 12 transmits ultrasonic waves to the fluid flowing in the pipe 10 in response to a transmission pulse from the transmitter 13 (step S101 in FIG. 4). As described above, in the forward direction, ultrasonic waves are transmitted from the ultrasonic transducer 11, and in the reverse direction, ultrasonic waves are transmitted from the ultrasonic transducer 12. In this embodiment, measurement is started from the forward direction.

[0041] The receiving unit 14 amplifies the output signal of the ultrasonic transducer 11 or 12 and outputs the ultrasonic reception signal Vin#i (step S102 in FIG. 4). In the forward direction, the ultrasonic transducer 12 receives the ultrasonic waves transmitted from the ultrasonic transducer 11, and the receiving unit 14 amplifies the output signal of the ultrasonic transducer 12. In the reverse direction, the ultrasonic transducer 11 receives the ultrasonic waves transmitted from the ultrasonic transducer 12, and the receiving unit 14 amplifies the output signal of the ultrasonic transducer 11.

[0042] The zero-crossing time measurement unit 16 compares the ultrasonic reception signal Vin#i with a preset threshold voltage Vs (Step S103 in FIG. 4). The zero-cross 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 zero-cross 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.

[0043] When the ultrasonic reception signal Vin#i exceeds the threshold voltage Vs, the zero-cross time measurement unit 16 initializes the element number k of the zero-cross sequence D#i to a preset K (e.g., K=1) (step S104 in FIG. 4). Then, the zero-cross time measurement unit 16 checks whether the ultrasonic reception signal Vin#i is at a zero-cross point (step S105 in FIG. 4).

[0044] The zero-cross 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. 4), and stores the value of this zero-cross time Tz in the memory unit 17 as the element with element number k of the zero-cross sequence D#i (step S107 in FIG. 4).

[0045] After storing the zero cross time Tz, the zero cross time measurement unit 16 increments the element number k by 1 (step S108 in FIG. 4), and determines whether the element number k reaches K+H, that is, whether H zero cross times Tz have been measured (step S109 in FIG. 4). If the zero cross time measurement unit 16 has not finished measuring H zero cross times Tz, the process returns to step S105. In this manner, while updating the element number k of the zero cross sequence D#i, H zero cross times Tz are measured in order and stored in the storage unit 17.

[0046] When the measurement of H zero cross times Tz has been completed, the measurement in one direction is completed. If the measurement in both the forward and reverse directions has not been completed (NO in step S110 in FIG. 4), the switching unit 15 switches the direction (step S111 in FIG. 4). For example, when the measurement of H zero cross times Tz has been completed in the forward direction but the measurement in the reverse direction has not been completed, the switching unit 15 switches to the reverse direction. As described above, in the case of the reverse direction, the switching unit 15 connects the transmitting unit 13 to the ultrasonic transducer 12 and connects the ultrasonic transducer 11 to the receiving unit 14.

[0047] In this way, the processes of steps S101 to S109 are performed in the reverse direction in the same manner as described above. Note that the zero cross strings D#i are stored in the storage unit 17 separately for the forward and reverse directions. 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, so the zero cross time measurement unit 16 increments the measurement count i by 1 (step S112 in FIG. 4).

[0048] If the number of measurements i does not exceed the number of repeated ultrasonic transmissions and receptions X, and measurements in both the forward and reverse directions X times have not been completed (NO in step S113 in FIG. 4), 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 ultrasonic transducer 11, and connects the ultrasonic transducer 12 to the receiving unit 14.

[0049] In this manner, 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 have been completed in both the forward and reverse directions.

[0050] Next, the flow rate calculation unit 18 acquires X zero cross time Tz values ​​for both the forward and reverse directions from the storage unit 17. As described above, the number of zero cross times Tz per measurement is H. The flow rate calculation unit 18 calculates the average value of the acquired forward zero cross times Tz to set it as the forward ultrasonic wave propagation time t1. Similarly, the flow rate calculation unit 18 calculates the average value of the acquired reverse zero cross times Tz to set it as the reverse ultrasonic wave propagation time t2. Then, the flow rate calculation unit 18 calculates the difference between the propagation time t1 and the propagation time t2 as the propagation time difference Δt (step S114 in FIG. 4).

[0051] The flow rate calculation unit 18 calculates the flow rate measurement value from the propagation time difference Δt (FIG. 4, step S115). A known calculation formula used in a general ultrasonic flowmeter may be used as a calculation method for obtaining the flow rate measurement value, and detailed description thereof will be omitted.

[0052] The flow rate output unit 19 is connected to a higher-level device (not shown) via a communication network, and transmits the flow rate measurement value calculated by the flow rate calculation unit 18 to the higher-level device (step S116 in FIG. 4). The above-described process in FIG. 4 is performed at regular intervals.

[0053] The host device calculates the average or integrated value of the flow measurement value, and compares the calculated value with a threshold value, and based on the comparison result, opens and closes a valve provided in the flow path in which the ultrasonic flowmeter is installed, or judges the soundness of the measurement target.

[0054] FIG. 5 is a flowchart illustrating the characteristic operations of this embodiment, and is a flowchart illustrating the operations of the index calculation unit 20 and the setting unit 21. When X number of measurements have been completed in each of the forward and reverse directions (YES in step S200 in FIG. 5), the index calculation unit 20 calculates an index value indicating the magnitude of variation in the flow rate measurement values ​​(step S201 in FIG. 5).

[0055] In this embodiment, the standard deviation of the differences between adjacent zero crossing times is calculated as an index value indicating the magnitude of variation in the flow rate measurement values. In Fig. 3, T1, T2, T3, T4, T5, etc. are zero crossing times, but the difference between adjacent zero crossing times ideally shows a constant value due to the frequency of the ultrasonic wave. In other words, if the frequency of the ultrasonic wave is f, the difference between adjacent zero crossing times is 1 / f.

[0056] For example, the difference T2-T1 between the zero-crossing times of the ultrasonic reception signal Vin#2 should be 1 μsec when the ultrasonic frequency f is 500 kHz. If the difference between a plurality of zero-crossing times fluctuates, it can be determined that the difference between the zero-crossing times fluctuates due to the influence of voltage fluctuations due to noise contained in the ultrasonic reception signal Vin, the strength of the ultrasonic reception signal Vin (the magnitude of the gradient of the ultrasonic reception signal Vin at the zero-crossing point), and voltage variations of the 0V voltage level comparator for zero-crossing detection inside the zero-crossing time measurement unit 16, that is, the signal-to-noise ratio is low.

[0057] The relationship between the difference between the zero crossing times and the signal-to-noise ratio is not affected by changes in flow rate. When the flow rate changes, the zero crossing time changes due to changes in the ultrasonic propagation time, but the difference between adjacent zero crossing times does not change. Similarly, it is not affected by the propagation time or the propagation time difference.

[0058] Therefore, the difference between the zero-cross times can be evaluated as an indication of the signal-to-noise ratio of the measurement section of the ultrasonic flowmeter (piping 10, ultrasonic transducers 11, 12, transmission section 13, reception section 14, switching section 15, zero-cross time measurement section 16), i.e., an indication of the degree of variation in the flow measurement value derived from the signal-to-noise ratio.

[0059] Therefore, the index calculation unit 20 of this embodiment acquires the values ​​of X zero cross times Tz for both the forward and reverse directions from the memory unit 17, calculates the difference between adjacent zero cross times in the same measurement (same zero cross string) for each measurement and for each forward and reverse direction, and calculates the standard deviation σ of all the calculated differences as an index value (step S201).

[0060] In the example of Fig. 3, the differences T7-T6, T6-T5, T5-T4, and T4-T3 are calculated for the zero cross sequence D#1. The differences T5-T4, T4-T3, T3-T2, and T2-T1 are calculated for the zero cross sequence D#2. Then, the standard deviation σ is calculated for these differences.

[0061] Next, the setting unit 21 sets the number of times X to transmit and receive ultrasonic waves per certain time period for the transmission unit 13 based on the index value calculated by the index calculation unit 20 (step S202 in FIG. 5). As explained above, when the frequency f of the ultrasonic waves is 500 kHz, the difference between adjacent zero crossing times should be 1 μsec. It is assumed that the number of times X to transmit and receive ultrasonic waves is set to n in a normal state where the standard deviation σ of the difference is a reference value of 1 nsec. At this time, the transmission unit 13 causes the ultrasonic transducers 11 and 12 to transmit ultrasonic waves n times in each of the forward and reverse directions per certain time period (a total of 2n times in the forward and reverse directions).

[0062] In response to this, when the standard deviation σ becomes, for example, 2 nsec, twice the reference value, due to a decrease in the signal-to-noise ratio, the setting unit 21 increases the number of ultrasonic transmission / reception repetitions X to 4n. As a result, the magnitude of variation in the flow rate measurement value output from the flow rate calculation unit 18 at regular intervals, which changes according to the signal-to-noise ratio of the measurement unit, is maintained within the same range as when the standard deviation σ is the reference value.

[0063] The predetermined reference value of the standard deviation σ is ref , the standard deviation σ calculated by the index calculation unit 20 is σ measure When the number of repetitions of ultrasonic transmission and reception that is a predetermined reference is n, the setting unit 21 sets the standard deviation σ measure The number of ultrasonic transmission and reception repetitions X corresponding to the above can be determined and set using the following formula. X = n × (σ measure / σ ref ) 2 (1)

[0064] The purpose of this embodiment is to deal with the situation where the standard deviation increases due to the influence of the signal-to-noise ratio even at zero or low flow rates, not depending on the magnitude of flow rate changes. With the above configuration, this embodiment can reduce power consumption while maintaining high measurement accuracy of the flow rate measurement value regardless of the magnitude of the flow rate or the tendency of the flow rate to increase or decrease.

[0065] In this embodiment, by evaluating the standard deviation σ of the difference between zero crossing times, a statistically significant number of samples can be secured even if the number of ultrasonic transmission and reception repetitions X per certain time is small. Therefore, a decrease in the signal-to-noise ratio can be determined in a short time, and it is possible to quickly determine whether or not the number of repetitions needs to be changed. This embodiment is excellent in that it can evaluate the effects of voltage fluctuations due to noise contained in the ultrasonic reception signal Vin, the strength of the ultrasonic reception signal Vin (the magnitude of the gradient of the ultrasonic reception signal Vin at the zero crossing point), and the voltage variation of the 0V voltage level comparator for zero crossing detection inside the zero crossing time measurement unit 16, without being affected by fluctuations in the flow rate, propagation time, or propagation time difference.

[0066] In particular, when the voltage fluctuation due to noise contained in the ultrasonic reception signal Vin and the voltage variation of the 0V voltage level comparator are considered to be approximately constant, it is advantageous in that it is possible to evaluate the magnitude state of the strength of the ultrasonic reception signal Vin (the magnitude of the slope of the ultrasonic reception signal Vin at the zero crossing point) actually used to calculate the propagation time.

[0067] Note that instead of calculating the standard deviation σ of the differences between the zero crossing times as the index value, the index calculation unit 20 may calculate the difference between the maximum difference and the minimum difference among all the calculated differences as the index value. This can further reduce calculation resources and memory compared to the case of calculating the standard deviation.

[0068] The predetermined reference value of the difference between the maximum difference and the minimum difference is Sub ref The difference calculated by the index calculation unit 20 is Sub measure If the number of times of ultrasonic transmission and reception that is a predetermined reference is n, the setting unit 21 calculates the difference Sub between the maximum value of the difference and the minimum value of the difference. measure The number of ultrasonic transmission and reception repetitions X corresponding to the above can be determined and set using the following formula. X = n × (Sub measure / Sub ref ) 2 (2)

[0069] The ultrasonic transmission / reception repetition count X that is actually set by the setting unit 21 is an integer value based on the calculation result of formula (1) or formula (2). For example, the calculation result of formula (1) or formula (2) may be rounded off to an integer. In addition, in a device in which the ultrasonic transmission / reception repetition count X can only be set as a multiple of 3, an integer value that is a multiple of 3 among integers close to the calculation result of formula (1) or formula (2) may be set as the ultrasonic transmission / reception repetition count X.

[0070] In addition, since the signal-to-noise ratio differs depending on the amplitude of the ultrasonic reception signal Vin, the magnitude of the standard deviation observed differs depending on the position of the zero-crossing point in the ultrasonic reception signal Vin. For example, the magnitude of the standard deviation differs between the zero-crossing times T2-T1 and T4-T3 in Figure 3. Specifically, the standard deviation of the difference T4-T3 is smaller.

[0071] Therefore, the index calculation unit 20 may calculate the difference between adjacent zero-crossing times in the same measurement for each position of the zero-crossing point in the ultrasonic reception signal Vin, for each measurement and for each forward and reverse direction, and calculate the standard deviation of all the calculated differences for each position of the zero-crossing point in the ultrasonic reception signal Vin to use it as an index value.

[0072] For example, in the example of FIG. 3, the standard deviation of the difference T2-T1, the standard deviation of the difference T3-T2, the standard deviation of the difference T4-T3, the standard deviation of the difference T5-T4, the standard deviation of the difference T6-T5, and the standard deviation of the difference T7-T6 are calculated as index values.

[0073] The setting unit 21 may set the number of times X that ultrasonic transmission and reception are repeated per certain time period based on the index value calculated for each position of the zero cross point in the ultrasonic reception signal Vin.

[0074] For example, the timing at which the ultrasonic reception signal Vin exceeds the threshold voltage Vs may change due to the influence of superimposition of noise components, etc., and the timing at which the zero-crossing point is detected will change. For example, in the example of Fig. 3, the ultrasonic reception signal Vin#1 exceeds the threshold voltage Vs at time Ts1, and detection of the zero-crossing point begins, whereas the ultrasonic reception signal Vin#2 exceeds the threshold voltage Vs at time Ts2, which is earlier than time Ts1, and the zero-crossing point is detected earlier than in the case of the ultrasonic reception signal Vin#1.

[0075] Therefore, when the index calculation unit 20 calculates the standard deviation of the difference between zero cross times for each position of the zero cross point in the ultrasonic reception signal Vin, it is necessary to shift the storage positions of the zero cross times in each zero cross sequence so that the difference between zero cross times (the elapsed time from the ultrasonic transmission time) that have the same storage position (element number k) in each zero cross sequence and are measured differently is minimized, and then calculate the standard deviation of the difference between zero cross times.

[0076] In the example of Fig. 3, before the shift process, the zero cross sequence D#1 = {T3, T4, T5, T6, T7}, and the zero cross sequence D#2 = {T1, T2, T3, T4, T5}. That is, the zero cross sequences D#1 and D#2 are stored in the storage unit 17 as shown in Fig. 6(A), and for example, the zero cross time T3 of the zero cross sequence D#1 and the zero cross time T1 of the zero cross sequence D#2 are stored in the same storage position, and the zero cross times at different positions in the ultrasonic reception signal Vin are stored in the same storage position.

[0077] 6B, for example, by shifting the storage position of the zero cross time of the zero cross sequence D#1 to the right by two, so that D#1={○,○,T3,T4,T5,T6,T7} (○ is empty data), the position of the zero cross point in the ultrasonic reception signal Vin can be aligned with the zero cross sequence D#2. By performing such a shift process for each zero cross sequence, the position of the zero cross point can be aligned for the zero cross time in each zero cross sequence.

[0078] After aligning the positions of the zero crossing points in this way, the index calculation unit 20 calculates the difference T2-T1 between adjacent zero crossing times in the same measurement (same zero crossing sequence) for each measurement and for each forward and reverse direction, and calculates the standard deviation of all the calculated differences T2-T1 as an index value. Similarly, the standard deviations are calculated for the differences T3-T2, T4-T3, T5-T4, T6-T5, and T7-T6.

[0079] difference T N -T N-1(N is an integer of 2 or more) is the predetermined standard deviation of Nref , the difference T calculated by the index calculation unit 20 N -T N-1 The standard deviation of Nmeasure When the number of repetitions of ultrasonic transmission and reception that is a predetermined reference is n, the setting unit 21 sets the standard deviation σ Nmeasure The number of times that ultrasonic transmission and reception is repeated according to X N can be calculated using the following formula: X N =n×(σ Nmeasure / σ Nref ) 2 (3)

[0080] In this way, the standard deviation reference value σ Nref is defined, and the number of ultrasonic transmission and reception repetitions X is set for each zero crossing point. N Then, the setting unit 21 calculates the number of times each ultrasonic wave is transmitted and received repeatedly, X N The number of ultrasonic transmission / reception repetitions X may be set to an integer value based on the average value or maximum value of the number of ultrasonic transmission / reception repetitions X. N Simply round off the average or maximum value to an integer.

[0081] [Second Example] Next, a second embodiment of the present invention will be described. Fig. 7 is a block diagram showing the configuration of an ultrasonic flowmeter according to the second embodiment of the present invention, and the same components as those in Fig. 2 are given the same reference numerals. This embodiment is an example in which the degree of variation in flow measurement values ​​is grasped based on the magnitude of the ultrasonic reception signal Vin.

[0082] The ultrasonic flowmeter of this embodiment includes a pipe 10, ultrasonic transducers 11, 12, a transmitting unit 13, a receiving unit 14, a switching unit 15, a zero-crossing time measuring unit 16, a memory unit 17, a flow rate calculation unit 18, a flow rate output unit 19, an index calculation unit 20a, and a setting unit 21a.

[0083] The operations of ultrasonic transducers 11, 12, transmitter 13, receiver 14, switch 15, zero cross time measurement unit 16, memory 17, flow rate calculation unit 18 and flow rate output unit 19 are as described in the first embodiment. FIG. 8 is a flowchart for explaining the operations of the index calculation unit 20a and the setting unit 21a of this embodiment.

[0084] The variation in the flow rate measurement value due to the signal-to-noise ratio of the measurement unit is caused by the influence of voltage fluctuations due to noise contained in the ultrasonic reception signal Vin, the strength of the ultrasonic reception signal Vin (the magnitude of the slope of the ultrasonic reception signal Vin at the zero-crossing point), and voltage variations in the 0V voltage level comparator for zero-cross detection inside the zero-crossing time measurement unit 16, but of these, it is the strength of the ultrasonic reception signal Vin that fluctuates greatly during measurement operation and has a major impact on the variation in the flow rate measurement value.

[0085] Therefore, the magnitude of the variation in the flow rate measurement value resulting from the signal-to-noise ratio of the measurement unit can be estimated using the intensity of the ultrasonic reception signal Vin as a guide. Specifically, the index calculation unit 20a sequentially receives X ultrasonic reception signals Vin for both the forward and reverse directions from the receiver 14, and when X measurements are completed for both the forward and reverse directions (YES in step S300 in FIG. 8), it calculates the maximum amplitude Amax of the received ultrasonic reception signals Vin (step S301 in FIG. 8). The maximum amplitude Amax can be calculated, for example, as shown in FIG. 9.

[0086] The relationship between the maximum amplitude Amax of the ultrasonic reception signal Vin and the magnitude of the variation in the flow measurement value resulting from the signal-to-noise ratio can be approximated, for example, as shown in Fig. 10. This relationship is registered in advance in the index calculation unit 20a. The index calculation unit 20a obtains the magnitude of the variation in the flow measurement value from the maximum amplitude Amax of the ultrasonic reception signal Vin as an index value based on the registered relationship (Fig. 8, step S302).

[0087] A characteristic graph like that in Figure 10 is considered to be determined depending on the performance and characteristics of the ultrasonic flowmeter. Using an actual ultrasonic flowmeter, measure the maximum amplitude Amax and the standard deviation (guideline for variation) of the flow measurement value multiple times in advance while changing the strength of the ultrasonic reception signal Vin to create a scatter plot, and then create an approximation curve that matches the actual measurement data from the scatter plot to create a characteristic graph like that in Figure 10. In most cases, the characteristic graph in Figure 10 can be commonly used for ultrasonic flowmeters of the same design.

[0088] The setting unit 21a may set the number of times X that the ultrasonic transmission and reception is repeated per certain time period for the transmission unit 13 based on the index value calculated by the index calculation unit 20a (Step S303 in FIG. 8).

[0089] The predetermined reference value of the index value is I ref The index value obtained by the index calculation unit 20a is I measure If the number of times of ultrasonic transmission and reception that is a predetermined reference is n, the setting unit 21a sets an index value I measure The number of ultrasonic transmission and reception repetitions X corresponding to the above can be determined and set using the following formula. X = n × (I measure / I ref ) 2 (4)

[0090] As in the above, the setting unit 21a may round off the calculation result of the formula (4) to an integer, for example.

[0091] In this embodiment, it is possible to omit the calculation for obtaining the standard deviation of the difference between the zero crossing times as in the first embodiment, and it is possible to reduce the calculation load and current consumption of the ultrasonic flowmeter. Also, at the stage where the signal strength is acquired, it is possible to easily determine the decrease in the signal-to-noise ratio in a short time, and it is possible to quickly determine whether or not the number of repetitions needs to be changed.

[0092] The transmitter 13, receiver 14, switch 15, zero-cross 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 flow rate calculator 18, flow rate output unit 19, index calculators 20, 20a, and setting units 21, 21a can be realized by a computer equipped with a CPU, a storage device, and an interface, and a program that controls these hardware resources. An example of the configuration of this computer is shown in FIG.

[0093] 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 zero-cross time measuring unit 16, the storage unit 17, etc. In such a computer, a program for realizing the flow rate measuring method of the present invention is stored in the storage device 201. The CPU 200 executes the processes described in the first and second embodiments in accordance with the program stored in the storage device 201. [Industrial Applicability]

[0094] The present invention can be applied to an ultrasonic flow meter. [Explanation of symbols]

[0095] 10...piping, 11, 12...ultrasonic transducer, 13...transmitter, 14...receiver, 15...switching unit, 16...zero-cross time measuring unit, 17...storage unit, 18...flow rate calculation unit, 19...flow rate output unit, 20, 20a...index calculation unit, 21, 21a...setting unit.

Claims

1. A pipe configured so that a fluid to be measured flows through it; A pair of ultrasonic transducers disposed upstream and downstream of the piping; A transmitting unit configured to transmit ultrasonic waves from one of the ultrasonic transducers; A time measurement unit configured to measure a zero-cross time of an ultrasonic reception signal in a forward measurement in which an ultrasonic transducer on an upstream side transmits an ultrasonic wave and receives it at the ultrasonic transducer on a downstream side, and a zero-cross time of an ultrasonic reception signal in a reverse measurement in which an ultrasonic transducer on a downstream side transmits an ultrasonic wave and receives it at the ultrasonic transducer on an upstream side, for each measurement and for each forward and reverse direction; A flow rate calculation unit configured to calculate a propagation time difference between ultrasonic waves in a forward direction and a backward direction based on a zero cross time in a forward direction and a zero cross time in a backward direction, and to calculate a flow rate measurement value of the fluid from the propagation time difference; An index calculation unit configured to calculate an index value indicating a magnitude of variation in the flow measurement value caused by a decrease in the signal-to-noise ratio based on the zero crossing time or the ultrasonic reception signal; a setting unit configured to set a number of ultrasonic transmission / reception repetitions per certain time period for the transmission unit based on the index value calculated by the index calculation unit, the index calculation unit acquires values ​​of zero cross times for the number of ultrasonic transmission and reception repetitions in both forward and reverse directions, calculates a difference between adjacent zero cross times in the same measurement for each measurement and for each forward and reverse direction, and calculates a standard deviation of all the calculated differences as the index value.

2. A pipe configured so that a fluid to be measured flows through it; A pair of ultrasonic transducers disposed upstream and downstream of the piping; A transmitting unit configured to transmit ultrasonic waves from one of the ultrasonic transducers; A time measurement unit configured to measure a zero-cross time of an ultrasonic reception signal in a forward measurement in which an ultrasonic transducer on an upstream side transmits an ultrasonic wave and receives it at the ultrasonic transducer on a downstream side, and a zero-cross time of an ultrasonic reception signal in a reverse measurement in which an ultrasonic transducer on a downstream side transmits an ultrasonic wave and receives it at the ultrasonic transducer on an upstream side, for each measurement and for each forward and reverse direction; A flow rate calculation unit configured to calculate a propagation time difference between ultrasonic waves in a forward direction and a backward direction based on a zero cross time in a forward direction and a zero cross time in a backward direction, and to calculate a flow rate measurement value of the fluid from the propagation time difference; An index calculation unit configured to calculate an index value indicating a magnitude of variation in the flow measurement value caused by a decrease in the signal-to-noise ratio based on the zero crossing time or the ultrasonic reception signal; a setting unit configured to set a number of ultrasonic transmission / reception repetitions per certain time period for the transmission unit based on the index value calculated by the index calculation unit, the index calculation unit acquires values ​​of zero cross times for the number of ultrasonic transmission and reception repetitions in both forward and reverse directions, calculates a difference between adjacent zero cross times in the same measurement for each measurement and for each forward and reverse direction, and calculates a difference between a maximum value and a minimum value among all the calculated differences as the index value.

3. A pipe configured so that a fluid to be measured flows through it; A pair of ultrasonic transducers disposed upstream and downstream of the piping; A transmitting unit configured to transmit ultrasonic waves from one of the ultrasonic transducers; A time measurement unit configured to measure a zero-cross time of an ultrasonic reception signal in a forward measurement in which an ultrasonic transducer on an upstream side transmits an ultrasonic wave and receives it at the ultrasonic transducer on a downstream side, and a zero-cross time of an ultrasonic reception signal in a reverse measurement in which an ultrasonic transducer on a downstream side transmits an ultrasonic wave and receives it at the ultrasonic transducer on an upstream side, for each measurement and for each forward and reverse direction; A flow rate calculation unit configured to calculate a propagation time difference between ultrasonic waves in a forward direction and a backward direction based on a zero cross time in a forward direction and a zero cross time in a backward direction, and to calculate a flow rate measurement value of the fluid from the propagation time difference; An index calculation unit configured to calculate an index value indicating a magnitude of variation in the flow measurement value caused by a decrease in the signal-to-noise ratio based on the zero crossing time or the ultrasonic reception signal; a setting unit configured to set a number of ultrasonic transmission / reception repetitions per certain time period for the transmission unit based on the index value calculated by the index calculation unit, the index calculation unit acquires values ​​of zero cross times for the number of repeated ultrasonic transmissions and receptions in both the forward and reverse directions, calculates a difference between adjacent zero cross times in the same measurement for each measurement and for each forward and reverse direction, and calculates a standard deviation for all the calculated differences for each position of the zero cross point in the ultrasonic reception signal to obtain the index value.

4. a first step of measuring a zero-cross time of an ultrasonic reception signal in a forward measurement in which an ultrasonic transducer on an upstream side of a pipe through which a fluid to be measured flows transmits ultrasonic waves and receives them at an ultrasonic transducer on a downstream side of the pipe, and a zero-cross time of an ultrasonic reception signal in a reverse measurement in which an ultrasonic transducer on the downstream side transmits ultrasonic waves and receives them at an ultrasonic transducer on the upstream side, for each measurement and for each forward and reverse direction; A second step of calculating a propagation time difference between the forward and reverse ultrasonic waves based on the forward zero cross time and the reverse zero cross time, and calculating a flow rate measurement value of the fluid from the propagation time difference; A third step of calculating an index value indicating a magnitude of variation in the flow rate measurement value caused by a decrease in a signal-to-noise ratio based on the zero crossing time or the ultrasonic reception signal; and a fourth step of setting the number of ultrasonic transmission / reception repetitions per certain time based on the index value calculated in the third step, The flow rate measurement method, characterized in that the third step includes a step of acquiring values ​​of zero cross times for the number of ultrasonic transmission and reception repetitions in both the forward and reverse directions, calculating differences between adjacent zero cross times in the same measurement time for each measurement time and for each forward and reverse direction, and calculating a standard deviation of all the calculated differences as the index value.

5. a first step of measuring a zero-cross time of an ultrasonic reception signal in a forward measurement in which an ultrasonic transducer on an upstream side of a pipe through which a fluid to be measured flows transmits ultrasonic waves and receives them at an ultrasonic transducer on a downstream side of the pipe, and a zero-cross time of an ultrasonic reception signal in a reverse measurement in which an ultrasonic transducer on the downstream side transmits ultrasonic waves and receives them at an ultrasonic transducer on the upstream side, for each measurement and for each forward and reverse direction; A second step of calculating a propagation time difference between the forward and reverse ultrasonic waves based on the forward zero cross time and the reverse zero cross time, and calculating a flow rate measurement value of the fluid from the propagation time difference; A third step of calculating an index value indicating a magnitude of variation in the flow rate measurement value caused by a decrease in a signal-to-noise ratio based on the zero crossing time or the ultrasonic reception signal; and a fourth step of setting the number of ultrasonic transmission / reception repetitions per certain time based on the index value calculated in the third step, The flow rate measurement method, characterized in that the third step includes a step of acquiring values ​​of zero cross times for the number of ultrasonic transmission and reception repetitions in both the forward and reverse directions, calculating a difference between adjacent zero cross times in the same measurement time for each measurement time and for each forward and reverse direction, and calculating a difference between a maximum value and a minimum value among all the calculated differences as the index value.

6. a first step of measuring a zero-cross time of an ultrasonic reception signal in a forward measurement in which an ultrasonic transducer on an upstream side of a pipe through which a fluid to be measured flows transmits ultrasonic waves and receives them at an ultrasonic transducer on a downstream side of the pipe, and a zero-cross time of an ultrasonic reception signal in a reverse measurement in which an ultrasonic transducer on the downstream side transmits ultrasonic waves and receives them at an ultrasonic transducer on the upstream side, for each measurement and for each forward and reverse direction; A second step of calculating a propagation time difference between the forward and reverse ultrasonic waves based on the forward zero cross time and the reverse zero cross time, and calculating a flow rate measurement value of the fluid from the propagation time difference; A third step of calculating an index value indicating a magnitude of variation in the flow rate measurement value caused by a decrease in a signal-to-noise ratio based on the zero crossing time or the ultrasonic reception signal; and a fourth step of setting the number of ultrasonic transmission / reception repetitions per certain time based on the index value calculated in the third step, The third step of the flow measurement method includes a step of acquiring values ​​of the zero cross time for the number of repeated ultrasonic transmissions and receptions in both the forward and reverse directions, calculating the difference between adjacent zero cross times in the same measurement for each measurement and for each forward and reverse direction, and calculating a standard deviation for all the calculated differences for each position of the zero cross point in the ultrasonic reception signal to obtain the index value.

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