JP4139302B2 - Flowmeter - Google Patents

Description

  The present invention relates to a flow meter for measuring a flow rate of a fluid such as gas.

  In recent years, it has been considered to employ an ultrasonic flow meter to measure the amount of gas used in a gas meter. As shown in FIG. 1, the ultrasonic flowmeter is disposed at an appropriate location in the fluid (gas) flow path 1 and transmits and receives ultrasonic waves to the upstream side and the downstream side of the flow path 1, respectively. 3a and 3b are arranged. The two ultrasonic sensors 3a and 3b face each other, and the traveling direction of the ultrasonic waves transmitted and received between the ultrasonic sensors 3a and 3b and the direction in which the fluid passes through the flow path 1 form an angle θ. Arranged to intersect.

In order to measure the flow rate using the ultrasonic flowmeter having the illustrated configuration, the ultrasonic wave propagation time t1 when the ultrasonic wave is transmitted from the upstream ultrasonic sensor 3a toward the downstream ultrasonic sensor 3b. And the ultrasonic wave propagation time t2 when the ultrasonic wave is transmitted from the downstream ultrasonic sensor 3b toward the upstream ultrasonic sensor 3a. Assuming that the distance between the ultrasonic sensors 3a and 3b is d, the fluid flow velocity is v, and the sound velocity is c, the following relationship is obtained.
(C + v · cos θ) t1 = d
(Cv−cos θ) t2 = d
Therefore, the flow velocity v can be expressed as follows:
v = (d / 2 cos θ) {(1 / t1) − (1 / t2)}
A value obtained by multiplying the flow velocity v thus determined by the cross-sectional area S of the flow path 1 is the instantaneous flow rate q. That is, the instantaneous flow rate q is expressed by the following equation.
q = v · S
In the ultrasonic flowmeter, each ultrasonic sensor 3a, 3b is used as a transmission side to transmit and receive an ultrasonic wave once to form a set of operations. If at least one set of operations is performed, an instantaneous flow rate q is obtained. Can do. Also, the instantaneous flow rate q is measured intermittently, and the integrated flow rate Q is obtained by multiplying the instantaneous flow rate q by the time interval obtained by the instantaneous flow rate q. The flow integrated value obtained by integrating the integrated flow Q obtained in this way corresponds to the total amount of fluid that has passed through the flow path 1 (the amount of gas used).

  By the way, some devices connected to the flow path of fluid (particularly gas such as city gas) cause fluctuations in the gas pressure in the flow path. For example, pressure fluctuations occur in the flow path in the vicinity of gas-using equipment that uses a gas engine as a drive source, such as a gas heat pump or a generator, and a membrane meter that is widely used as a gas meter. In addition, pressure fluctuation with periodicity (hereinafter referred to as “pressure pulsation”) occurs in the vicinity of this type of equipment. Incidentally, it is known that the frequency of the pressure pulsation generated in the flow path in the vicinity of the device is about 3 to 6 Hz in the membrane meter and about 10 to 20 Hz in the gas heat pump.

  As described above, when the pressure of the gas in the flow path changes due to the equipment connected to the gas flow path, the gas flows, and the ultrasonic flowmeter generally physically changes the pressure in the flow path. Since it does not have a mitigating function, the pressure fluctuation in the flow path becomes a flow fluctuation (pulsating flow) and directly affects the measurement value, which causes an error in the measurement value of the ultrasonic flowmeter. Here, fluctuations in pressure that occur at the start and end of use of gas-using equipment are transient and can be ignored. However, pressure pulsations with periodicity as described above may have a large error. There is. Therefore, in order to reduce this type of error, at least two types of measurement modes with different time intervals for measuring the instantaneous flow rate q are prepared, and the measurement mode can reduce the measurement value error depending on the presence or absence of pressure pulsation. A technique for selecting is proposed.

  This type of technology includes a first measurement mode in which the instantaneous flow rate q is measured at irregular time intervals, and a propagation time t1, at a constant time interval that is 1 / n of the average value of the normal time interval. a second measurement mode for measuring the total flow rate Q by multiplying the instantaneous flow rate q obtained from the average value of the n times of propagation times t1 and t2 by n, When the difference in the instantaneous flow rate q for each measurement is equal to or greater than the determination value, it is determined that a pulsating flow has occurred, and the process proceeds to the second measurement mode, where the propagation times t1 and t2 obtained n times in the second measurement mode A technique is known in which a pulsating flow is not generated when the difference between the maximum value and the minimum value of the difference is equal to or less than a determination value (see, for example, Patent Document 1).

In addition, the instantaneous flow rate based on the propagation time when the ultrasonic wave is transmitted to the upstream side and the downstream side at a normal sampling cycle time which is constant during a period when the pressure pulsation is not detected in the ultrasonic flow meter. In the first measurement mode for obtaining q and the period during which pressure pulsation is detected, ultrasonic waves are transmitted a plurality of times upstream and downstream at a constant high resolution sampling cycle time sufficiently shorter than the normal sampling cycle time. A second measurement mode in which an instantaneous flow rate q is obtained using an average value of propagation time when the wave is transmitted, and a difference between the differences in the instantaneous flow rate q for each measurement obtained in the first measurement mode is generated as a pulsation. When the value is equal to or greater than the determination value, the mode shifts to the second measurement mode, and in the second measurement mode, the propagation times t1 and the propagation times t2 obtained in the period of the normal sampling period in each time series are obtained. If both the value and the minimum value is less than the pulsation stop determining value is also a technique for transition to the first measurement mode (for example, see Patent Document 2).
Japanese Patent Laid-Open No. 11-258018 (page 9-10, FIG. 1) Japanese Unexamined Patent Publication No. 11-281430 (page 11-12, FIG. 3-5)

  In any of the above-described techniques, if a short-period pressure pulsation is detected by a gas heat pump or the like, the number of ultrasonic waves transmitted per unit time increases compared to a period in which no pressure pulsation is detected. Electric power increases. Generally, a battery is used as a power source in a gas meter, and a gas meter installed in a consumer is required to reduce power consumption as much as possible so that battery replacement is unnecessary for 10 years. In order to reduce power consumption, it is desirable to reduce the opportunity to shift to the second measurement mode described above.

  However, in the techniques described in Patent Documents 1 and 2, when the difference in the instantaneous flow rate q for each measurement is greater than or equal to the determination value in the first measurement mode, it is determined that a pulsating flow has occurred, or the first measurement mode The difference between the instantaneous flow rate q for each measurement and the difference between the instantaneous flow rates q obtained at the previous measurement is greater than or equal to the pulsation occurrence determination value, it is determined that pulsating flow is occurring. Since there is only one type of determination condition for shifting from the first measurement mode to the second measurement mode, there is a possibility of shifting from the first measurement mode to the second measurement mode due to erroneous determination. . That is, in the configuration in which the difference in the instantaneous flow rate q for each measurement is compared with the determination value, even if the flow rate monotonously increases or decreases, there is a possibility that it may be mistaken for the occurrence of pulsating flow. In the configuration in which the difference between the two is compared with the pulsation occurrence determination value, even if there is no pulsation in the flow rate, there is a possibility that a change in the flow rate at the start or end of use of the gas-using device is mistaken as the occurrence of pulsation.

  The present invention has been made in view of the above-mentioned reasons, and the purpose thereof is to compare the power consumption from the first measurement mode in which the flow rate can be measured even when the pressure fluctuation occurs and the power consumption is relatively small. An object of the present invention is to provide a flow meter that can reduce the possibility of transition to a large second measurement mode.

  In the first aspect of the present invention, the instantaneous flow rate of the fluid passing through the flow path is intermittently measured and the time interval for measuring the instantaneous flow rate is long and the time interval for measuring the instantaneous flow rate is long. A flow rate measurement unit capable of selecting a second measurement mode that is short and consumes a large amount of power, and a time interval and a flow path for measuring the instantaneous flow rate using a change pattern of the instantaneous flow rate obtained for each predetermined number in the first measurement mode In the first measurement mode when there is synchronism, and an operation selection unit that discriminates whether or not there is synchronism with the period of pressure fluctuation of the fluid passing through An interval adjustment unit that changes a time interval for measuring the instantaneous flow rate, and a mode selection unit that selects the second measurement mode when the fluctuation range of the pressure fluctuation is equal to or greater than a specified value although there is no synchronization. To.

  According to a second aspect of the present invention, in the first aspect of the present invention, the time interval for measuring the instantaneous flow rate in the first measurement mode is longer than the predicted cycle of the pressure fluctuation of the fluid, and the instantaneous measurement is instantaneous in the second measurement mode. The time interval for measuring the flow rate is set to be less than or equal to one half of the predicted cycle of pressure fluctuation of the fluid.

  According to this configuration, in the first measurement mode, the instantaneous flow rate is less frequently measured and the power consumption can be suppressed. In the second measurement mode, the instantaneous flow rate is instantaneous at a time interval of 1/2 or less of the period of the pressure fluctuation. Since the flow rate is measured, it is possible to accurately measure the flow rate even if pressure fluctuation occurs.

  According to a third aspect of the present invention, in the first or second aspect of the present invention, the operation selecting unit sets a period for acquiring a predetermined number of instantaneous flow rates from the flow rate measuring unit as a determination period, and sets the time within one determination period. The sum of absolute values of the difference between each pair of adjacent instantaneous flow rates in the series and the difference between the maximum value and the minimum value of the instantaneous flow rate in one determination section are obtained, and the value obtained by dividing the sum by the difference is defined. If the interval adjustment unit is instructed to change the time interval for measuring the instantaneous flow rate when the value is less than the cycle determination threshold, and the value obtained by dividing the sum by the difference is equal to or greater than a predetermined cycle determination threshold, one determination interval If the difference between the maximum value and the minimum value of the instantaneous flow rate is less than the specified amplitude determination threshold value, the current state is maintained, and if it is equal to or greater than the amplitude determination threshold value, the mode selection unit is instructed to shift to the second measurement mode. It is characterized by

  According to this configuration, in the determination section for acquiring a predetermined number of instantaneous flow rates, the two values of the sum of absolute values of the difference between each pair of adjacent instantaneous flow rates and the difference between the maximum value and the minimum value of the instantaneous flow rate By using, the instantaneous flow rate change pattern can be easily categorized only by comparing the magnitude with the period determination threshold and the amplitude determination threshold.

  According to a fourth aspect of the present invention, in the third aspect of the invention, the number of differences in absolute values of instantaneous flow rates acquired in the determination section is 15, the period determination threshold is 3, and the amplitude determination threshold is 20. It is characterized by.

  According to this configuration, by using these values, the above-described operation can be performed with substantially no erroneous determination.

  According to the configuration of the present invention, the first measurement mode in which the time interval for measuring the instantaneous flow rate is long and the power consumption is always selected is selected, and the pressure fluctuation cycle and the instantaneous flow rate of the fluid passing through the flow path are measured. When there is synchronization, the synchronization is canceled by changing the time interval for measuring the instantaneous flow rate. If there is no synchronization, the fluctuation range of pressure fluctuation is more than the specified value. The transition to the second measurement mode in which the time interval for measuring the instantaneous flow rate is short and the power consumption is large, and the possibility of the transition to the second measurement mode in which the power consumption is large can be reduced as compared with the conventional configuration. In addition, since the instantaneous flow rate is measured in the first measurement mode that consumes as little power as possible, an increase in power consumption can be suppressed.

  In this embodiment, an example in which a flow meter is applied to a gas meter is assumed. That is, as shown in FIG. 1, a shutoff valve 2 and a flow rate measuring unit 3 are provided in a flow path 1 through which a gas as a fluid passes. In the illustrated example, the shut-off valve 2 is disposed upstream of the flow rate measuring unit 3 in the flow path 1. The flow rate measuring unit 3 includes two ultrasonic sensors 3a and 3b arranged so as to face each other. Both ultrasonic sensors 3a and 3b are connected to a control circuit unit 4 whose main component is a microcomputer (hereinafter abbreviated as "microcomputer"), and the control circuit unit 4 controls the operation of the flow rate measuring unit 3, Measurement of the gas flow rate based on the output of the flow rate measuring unit 3, control of the shutoff valve 2 based on the output of the flow rate measuring unit 3, and the like are performed. The amount of gas used is obtained by the control circuit unit 4 based on the measurement result of the gas flow rate by the flow rate measurement unit 3 and displayed on the display unit 5 including a liquid crystal display connected to the control circuit unit 4.

  A rewritable nonvolatile memory 6 such as an EEPROM is connected to the control circuit unit 4. Further, the control circuit unit 4 drives one of the shut-off valve drive circuit 7 that drives the shut-off valve 2 and the ultrasonic sensors 3a and 3b by the control signal to transmit the ultrasonic wave and the ultrasonic wave received by the other. An ultrasonic sensor driving circuit 8 that performs the waveform shaping is also connected. The control circuit unit 4 controls the transmission timing of the ultrasonic sensors 3a and 3b via the ultrasonic sensor drive circuit 8, and outputs an output corresponding to reception by the ultrasonic sensor drive circuit 8 after instructing the transmission. Is obtained as the propagation time of the ultrasonic wave. As described in the related art, if the propagation time of the ultrasonic wave is obtained, the flow velocity of the fluid in the flow path 1 can be obtained, and the instantaneous flow rate can be obtained from the flow velocity. In the present invention, the function of displaying the amount of gas used as a gas meter and the pressure sensor for detecting the pressure in the flow path 1 are not the gist and will not be particularly described. Moreover, although the function which interrupts | blocks the cutoff valve 2 when the leak of gas etc. are detected in the flow path 1 is also provided, since this operation | movement is not a summary, it does not explain in particular.

  The flow rate measurement unit 3 in the present embodiment intermittently measures the instantaneous flow rate. In the control circuit unit 4, two types of measurement modes with different methods for measuring the instantaneous flow rate can be selected. In one measurement mode (hereinafter referred to as “first measurement mode”), the time interval for measuring the instantaneous flow rate is variable within a minute range (for example, less than 5% of the reference time interval) with respect to the reference time interval. In the measurement mode (hereinafter referred to as “second measurement mode”), the time interval for measuring the instantaneous flow rate is sufficiently larger than the time interval (2 to 3 [s]) for measuring the instantaneous flow rate in the first measurement mode. Set short. Specifically, the time interval for measuring the instantaneous flow rate in the first measurement mode is longer than the period of pressure pulsation (0.05 to 0.1 [s]) generated in the fluid in the flow path 1 (for example, 2 to 3 [s]), and the time interval for measuring the instantaneous flow rate in the second measurement mode is the period of pressure pulsation (0.05 to 0.1 [s]) generated in the fluid in the flow path 1. It is set to 1/2 or less. In the first measurement mode, the number of ultrasonic waves transmitted in one measurement of the instantaneous flow rate is larger than that in the second measurement mode. For example, when measuring the instantaneous flow rate once, In the measurement mode, ultrasonic waves are transmitted 100 times from each ultrasonic sensor 3a, 3b, and in the second measurement mode, ultrasonic waves are transmitted twice from each ultrasonic sensor 3a, 3b. That is, in the first measurement mode, ultrasonic waves are transmitted 100 times from one ultrasonic sensor 3a, and after a certain delay time (for example, 10 [ms]), ultrasonic waves are transmitted 100 times from the other ultrasonic sensor 3b. The instantaneous flow rate is measured once by wave. On the other hand, in the second measurement mode, in order to measure the instantaneous flow rate once, ultrasonic waves are transmitted twice from one ultrasonic sensor 3a, and after the delay time, ultrasonic waves are transmitted twice from the other ultrasonic sensor 3b. To wave.

  By the way, in the second measurement mode, the time interval for measuring the instantaneous flow rate is set to be shorter than the period of pressure pulsation that is expected to occur in the fluid passing through the flow path 1, so that pressure pulsation occurs in the fluid. However, if the integrated flow rate obtained from the instantaneous flow rate is integrated, the pressure pulsation component is canceled out, and the obtained fluid passage amount can be regarded as a true value. In other words, in the second measurement mode, the instantaneous flow rate measured within several cycles of pressure pulsation is almost equal to the case where the instantaneous flow rate is larger and smaller than the true value. The amount of fluid passing through can be regarded as a true value.

  On the other hand, as described above, the number of ultrasonic wave transmissions required to measure the instantaneous flow rate once is larger in the first measurement mode than in the second measurement mode, but in the first measurement mode, the instantaneous flow rate is reduced. The measurement time interval is set sufficiently longer than that in the second measurement mode, and the power consumption is larger in the second measurement mode. Therefore, it is desirable that a device using a battery power source such as a gas meter be operated in the first measurement mode as much as possible in order to reduce battery consumption.

  Therefore, in the present embodiment, even if pressure pulsation occurs in the fluid passing through the flow path 1, the first measurement mode is selected when the time interval for measuring the instantaneous flow rate can be changed and the amplitude is relatively small, The increase in power consumption is suppressed by selecting the second measurement mode only when the amplitude is so large that it cannot be dealt with only by changing the time interval for measuring the instantaneous flow rate. Now, it is assumed that the fluid passage amount is obtained using the instantaneous flow rate measured in the first measurement mode when pressure pulsation occurs. In this case, compared with the case where the fluid passage amount is obtained using the instantaneous flow rate measured in the second measurement mode, the time until the passage amount can be regarded as a true value is longer, but in a gas meter, the time is short. Since it is not necessary to detect the change in the passage amount at 10 minutes and there is a delay of about 10 minutes, the true value of the fluid passage amount can be obtained even if the instantaneous flow rate obtained in the first measurement mode is used to obtain the fluid passage amount. Can be requested.

  However, if the difference between the time interval for measuring the instantaneous flow rate and the integral multiple of the period of pressure pulsation is small (for example, a difference of less than 0.5%), the variation in the average value of the instantaneous flow rate becomes large and the time is relatively long. Even if (for example, 10 minutes) elapses, the average value of the instantaneous flow rate does not converge to a constant value. If the average value of the instantaneous flow rate converges to a constant value, the average value of the instantaneous flow rate can be regarded as a true value even if pressure pulsation occurs, so that the amount of fluid passing through the flow path 1 can be obtained. However, the fluid passage amount cannot be obtained unless the average instantaneous flow rate converges. Thus, even if a relatively long time has passed, the state where the average value of the instantaneous flow rate does not converge is considered to be due to the synchronization between the time interval for measuring the instantaneous flow rate and the period of the pressure pulsation, This is called “synchronized state”. The synchronization state occurs in the first measurement mode but does not normally occur in the second measurement mode. Therefore, in the conventional configuration, the configuration in which the second measurement mode is selected in order to avoid the synchronization state is adopted, whereas in the present embodiment, when the synchronization state is detected in the first measurement mode, The synchronization state is avoided by shifting the time interval for measuring the instantaneous flow rate within a relatively small range. That is, as described above, in the first measurement mode, a reference time interval that is a constant value is set as the reference value of the time interval for measuring the instantaneous flow rate, and the time interval is within a range of 5% with respect to the reference time interval. Is made variable.

  As is clear from the above description, in the present embodiment, it is necessary to select the first measurement mode and the second measurement mode, and the time interval for measuring the instantaneous flow rate in the first measurement mode. It is necessary to select whether to maintain or change. Therefore, the control circuit unit 4 is set with a mode selection unit 4a for switching the measurement mode of the flow rate measurement unit 3 and a time interval for measuring the instantaneous flow rate when the first measurement mode is selected by the mode selection unit 4a. And an operation selection unit that determines the presence or absence of the occurrence of a synchronized state in the flow path 1 and the magnitude of the amplitude of the pressure pulsation using the time change of the instantaneous flow rate obtained by the flow rate measurement unit 3. 4c. When the operation selection unit 4c is in the first measurement mode, the pressure pulsation is not generated or the pressure pulsation is generated but in a synchronized state, the pressure pulsation is generated but the amplitude is small, and the amplitude Are distinguished from each other, and an instruction is given to the mode selection unit 4a and the interval adjustment unit 4b according to each case. That is, in each case, the change of the time interval for measuring the instantaneous flow rate, the maintenance of the time interval for measuring the instantaneous flow rate, and the transition from the first measurement mode to the second measurement mode are instructed.

  This will be described in more detail. In the state in which the mode selection unit 4a selects the first measurement mode in the operation selection unit 4c, a period in which the instantaneous flow rate reaches a certain number is set as the determination interval, and each pair of instantaneous instantaneously adjacent in the determination interval in time series Using the flow rate change pattern, it is determined whether or not it is in a synchronized state (that is, the presence or absence of synchronism). Therefore, in the operation selection unit 4c, first, an absolute value of a difference between each pair of adjacent instantaneous flow rates in time series within the determination section is obtained. The determination section is a period during which a certain number of absolute values are obtained, and the number of absolute values obtained in the determination section is set to 15 for example. If the time interval for measuring the instantaneous flow rate in the first measurement mode is about 2 [s], the determination interval is about 30 [s]. The number of instantaneous flow rates included in the determination section is 16, and the last instantaneous flow rate among the instantaneous flow rates arranged in time series in the determination section is the first instantaneous flow rate in the next determination section.

The sum D of absolute values obtained in the determination section set as described above and the difference W between the maximum value and the minimum value of the instantaneous flow rate in the determination section are obtained, and both values D and W are used to determine the synchronization state. The presence / absence of occurrence and the magnitude of the amplitude are determined. Now, if 15 absolute values of differences in instantaneous flow rates are obtained in the determination section, 16 instantaneous flow rates are required. Therefore, the time series of the instantaneous flow rate in the determination section is represented by q (0), q (1), ..., q (15). The absolute value d (i) of the difference is d (i) = | q (i) −q (i−1) | (where i = 1, 2,..., 15), and the instantaneous flow rate q ( 0) coincides with the instantaneous flow rate q (15) in the determination section one period before. When the instantaneous flow rate and the absolute value of the difference are used, the sum D and the difference W between the maximum value and the minimum value are expressed by the following equations.
D = d (1) + d (2) +... + D (15)
W = qmax-qmin
However, qmax is the maximum value (max) of 16 instantaneous flow rates in the determination section, and qmin is the minimum value (min) of 16 instantaneous flow rates in the determination section, which can be expressed by the following equation.
qmax = max {q (0), q (1),..., q (15)}
qmin = min {q (0), q (1),..., q (15)}
Here, the sum D of absolute values indicates the presence or absence of a change in flow rate within the determination section. The larger the sum D of absolute values, the greater the change in flow rate. That is, if the pressure pulsation is not generated in the synchronized state, the sum D of absolute values becomes a large value. On the contrary, if the pressure pulsation does not occur or the pressure pulsation occurs, the total sum D of the absolute values becomes a relatively small value in the synchronized state. However, the total sum D of absolute values is not generally 0 when in a synchronized state, and the total sum D of absolute values increases as the amplitude of pressure pulsation increases. Therefore, normalization is performed by dividing the sum D of absolute values by a value that can be regarded as the amplitude of pressure pulsation (that is, the difference W between the maximum value and the minimum value). In short, by comparing the D / W with the synchronization determination threshold value Tth1 that defines D / W, it is determined whether pressure pulsation has occurred or is in a synchronized state. In the first measurement mode, when the pressure pulsation does not occur or is in a synchronized state, the time interval for measuring the instantaneous flow rate is changed within a range of 5% with respect to the reference time interval. The degree of change will be described later.

  On the other hand, when the operation selection unit 4c determines that there is a pressure pulsation but is not in a synchronized state, the measurement is maintained without changing the time interval for measuring the instantaneous flow rate according to the amplitude of the pressure pulsation, It is determined whether the measurement mode is shifted to the second measurement mode. That is, the operation selection unit 4c uses the difference W between the maximum value and the minimum value of the instantaneous flow rate obtained in the determination section as a value reflecting the amplitude of the pressure pulsation, and if the difference W is less than the amplitude determination threshold value Tth2, The time interval for measurement in the first measurement mode is maintained, and if the difference W is greater than or equal to the amplitude determination threshold Tth2, the process proceeds to the second measurement mode.

  The above operations are summarized as shown in FIG. In the illustrated example, the synchronization determination threshold value Tth1 is set to 3, and the amplitude determination threshold value Tth2 is set to 20. However, these values can be changed as appropriate. As shown in FIG. 2, the operation selection unit 4c first compares the value D / W obtained by normalizing the absolute value D of the difference between the instantaneous flow rates with the value 3 as the synchronization determination threshold Tth1 (S1). If / W <3, it is considered that no pressure pulsation has occurred or pressure pulsation has occurred and is in a synchronized state, and the interval adjustment unit 4b is instructed to change the time interval for measuring the instantaneous flow rate (S2). The degree of changing the time interval for measuring the instantaneous flow rate is appropriately set within a range of ± 5% with respect to the reference time interval. In addition, the time interval is set in a plurality of stages within this range, the time interval is cyclically selected in an appropriately set order, and the time interval is set such that the time for convergence to a value that can be regarded as a true value is as short as possible. It is also possible to adopt a configuration in which determination is performed by a separate means. On the other hand, if D / W ≧ 3, pressure pulsation has occurred but it can be regarded as not in a synchronized state. Therefore, the difference W between the maximum value and the minimum value of the instantaneous flow rate in the determination section and the amplitude determination threshold Tth2 of 20 Are compared (S3), and if W <20, the amplitude of the pressure pulsation is regarded as small, and the current time interval in the first measurement mode is maintained (S4). If W ≧ 20, it is considered that the amplitude of the pressure pulsation is large, and the mode selection unit 4a is instructed to shift to the second measurement mode (S5).

  Even if pressure pulsation is caused by the above-described operation, if it is possible to cope with it only by changing the time interval for measuring the instantaneous flow rate, the first measurement mode should be maintained and the second measurement mode should not be entered. Therefore, it is possible to reduce the time for operating in the second measurement mode as compared with the conventional configuration, and as a result, an increase in power consumption can be suppressed.

  An example of operation is shown below. First, an example of the synchronization state is shown in FIG. 3 to 6 are examples in which the time interval for measuring the instantaneous flow rate is 2 [s], and the frequency of the pressure pulsation is 10.1 [Hz], 10.02 [Hz], 10. The case of 03 [Hz] and 10.04 [Hz] is shown. In the example of FIG. 3, the instantaneous flow rate value monotonously decreases in the determination section. In the example of FIG. 4, the change direction of the instantaneous flow rate is once in the determination section. In the examples of FIGS. The change in the flow rate change direction is twice. Regarding the operation examples shown in FIGS. 3 to 6, changes in the average value of the instantaneous flow rate over time are shown in FIGS. 7A to 7D, respectively. As can be seen from FIG. 7, the average value of the instantaneous flow rate does not converge in 10 minutes in any of the operations shown in FIGS.

  On the other hand, in the example shown in FIG. 8, the instantaneous flow rate for each measurement (2 [s] interval) in one determination section is a constant value (in the illustrated example, 100 [L / h]: L is liter). In this case, the pressure pulsation does not occur at all, or the time interval for measuring the instantaneous flow rate in the state where the regular pressure pulsation occurs and the period of the pressure pulsation are completely the same. Yes. If no pressure pulsation has occurred, this value is true. However, if pressure pulsation occurs and is in a synchronized state, this value is not a true value but a meaningless value. However, it is not possible to determine whether or not the value is a true value only by the value of the determination section. Therefore, it is assumed that the result shown in FIG. 9 is obtained when the time interval for measuring the instantaneous flow rate in the next determination section is changed by 0.05% to 2.01 [s]. As described above, when the instantaneous flow rate obtained in the determination section is changed by changing the time interval for measuring the instantaneous flow rate, the pressure pulsation is generated. Moreover, if the instantaneous flow rate is distributed as shown in FIG. 9, the average value of the instantaneous flow rate converges in a relatively short time.

  When there is no pressure pulsation and the flow rate changes monotonously, that is, when the gas using device is opened or closed, the instantaneous flow rate changes as shown in FIG. 10 or FIG. 11, for example. In such an operation, since D / W = 1, the time interval for measuring the instantaneous flow rate is changed in the next determination section. However, since no pressure pulsation occurs, it can be determined that no pressure pulsation occurs after two periods of the determination section.

  In order to return to the first measurement mode after shifting to the second measurement mode, any technique may be adopted as long as it determines whether or not the pressure pulsation amplitude has decreased. . For example, even in the second measurement mode, when the difference between the maximum value and the minimum value of the instantaneous flow rate obtained at the time specified in the same degree as the determination interval (for example, 30 [s]) is less than the specified threshold value. A technique for determining that the amplitude of the pressure pulsation has decreased, or a difference between the maximum value and the minimum value of the propagation time for each wave transmitted from one of the ultrasonic sensors 3a and 3b at a time specified in the same degree as the determination interval ( That is, the amplitude of the pressure pulsation decreases when both the difference between the maximum value and the minimum value of the propagation time t1 and the difference between the maximum value and the minimum value of the propagation time t2) are equal to or less than a predetermined threshold value. It is possible to use a technique that determines that the

  Furthermore, in the above-described embodiment, an ultrasonic flow meter is used as the flow rate measuring unit 3, but a flow rate can be instantaneously detected (for example, a fluidic flow meter, a flow meter using a flow sensor (heat wire) If it is a type | formula flow meter)), the flow volume measurement part 3 will not be restrict | limited to an ultrasonic flow meter. Moreover, although the example which measures the flow volume of gas in a flow path was shown in embodiment mentioned above, the technical thought of this invention is applicable also to fluids other than gas.

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Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Flow path 3 Flow measurement part 4 Control circuit part 4a Mode selection part 4b Space | interval adjustment part 4c Operation | movement selection part

Claims (4)

  The first measurement mode in which the instantaneous flow rate of the fluid passing through the flow path is intermittently measured and the time interval for measuring the instantaneous flow rate is long and the power consumption is small, and the time interval for measuring the instantaneous flow rate is short and the power consumption is second. The measurement mode can be selected, the time interval for measuring the instantaneous flow rate using the change pattern of the instantaneous flow rate obtained for each predetermined number in the first measurement mode, and the pressure fluctuation of the fluid passing through the flow path An operation selection unit that determines whether or not there is synchronism with the period of time and determines the fluctuation range of the pressure fluctuation when there is no synchronism, and a time interval for measuring the instantaneous flow rate in the first measurement mode when there is synchronism A flow meter comprising: an interval adjustment unit that changes the pressure, and a mode selection unit that selects the second measurement mode when the fluctuation range of the pressure fluctuation is not less than a specified value although there is no synchronization.   The time interval for measuring the instantaneous flow rate in the first measurement mode is longer than the period of the predicted fluid pressure fluctuation, and the time interval for measuring the instantaneous flow rate in the second measurement mode is the predicted fluid pressure fluctuation. The flowmeter according to claim 1, wherein the flowmeter is set to be equal to or less than half of the period.   The operation selection unit has a period in which a predetermined number of instantaneous flow rates are acquired from the flow rate measurement unit as a determination interval, and a sum of absolute values of differences between a pair of instantaneous flow rates adjacent in time series within one determination interval; Change the time interval for measuring the instantaneous flow rate when the difference between the maximum value and the minimum value of the instantaneous flow rate in one determination section is obtained, and the value obtained by dividing the sum by the difference is less than the specified cycle determination threshold value When the value obtained by dividing the sum by the difference is equal to or greater than a specified period determination threshold, the difference between the maximum value and the minimum value of the instantaneous flow rate in one determination section is the specified amplitude determination. The flowmeter according to claim 1 or 2, wherein the current state is maintained if the value is less than the threshold value, and the mode selection unit is instructed to shift to the second measurement mode if the value is equal to or greater than the amplitude determination threshold value.   4. The flow meter according to claim 3, wherein the number of differences in absolute values of instantaneous flow rates acquired in the determination section is 15, the period determination threshold is 3, and the amplitude determination threshold is 20.

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