JP5130085B2 - Ultrasonic flow meter - Google Patents

Description

  The present invention relates to an ultrasonic flowmeter that measures the flow rate of a fluid such as a gas using ultrasonic waves.

  Conventionally, a pair of ultrasonic transducers are provided at a certain distance on the upstream side and downstream side of the flow path, and the ultrasonic signal is transmitted and received between them repeatedly. 2. Description of the Related Art An ultrasonic flowmeter that obtains a flow rate based on a difference between a propagation integration time of a sound wave signal and a propagation integration time from a downstream side to an upstream side is known.

  FIG. 13 is a diagram showing a configuration of a conventional ultrasonic flowmeter. This ultrasonic flow meter is composed of a pair of ultrasonic transducers 2 a and 2 b, a transmission / reception changeover switch 3, a transmission circuit 4, a reception detection circuit 5, and a control circuit 6 disposed inside the flow path 1.

  The flow channel 1 allows a gas to be measured to flow inside. The pair of ultrasonic transducers 2a and 2b propagates ultrasonic waves between them.

  The ultrasonic transducer 2a is vibrated by a drive signal sent from the transmission circuit 4 via the transmission / reception selector switch 3 to generate ultrasonic waves. The ultrasonic wave generated by the ultrasonic transducer 2 a is received by the ultrasonic transducer 2 b, and the received signal is sent to the control circuit 6 via the transmission / reception changeover switch 3 and the reception detection circuit 5. In this case, the ultrasonic wave propagation direction is assumed to be the forward direction.

  Similarly, the ultrasonic transducer 2b vibrates in accordance with a drive signal sent from the transmission circuit 4 via the transmission / reception changeover switch 3, and generates ultrasonic waves. The ultrasonic waves generated by the ultrasonic transducer 2 b are received by the ultrasonic transducer 2 a, and the reception signal is sent to the control circuit 6 via the transmission / reception changeover switch 3 and the reception detection circuit 5. In this case, the propagation direction of the ultrasonic wave is the reverse direction.

  The transmission / reception change-over switch 3 switches which of the ultrasonic transducer 2a and the ultrasonic transducer 2b is used as a transmission-side ultrasonic transducer or a reception-side ultrasonic transducer. Specifically, the transmission / reception selector switch 3 switches between sending the drive signal from the transmission circuit 4 to the ultrasonic transducer 2a or the ultrasonic transducer 2b in response to an instruction from the control circuit 6, and In the former case, the reception signal from the ultrasonic transducer 2 b is sent to the reception detection circuit 5, and in the latter case, the reception signal from the ultrasonic transducer 2 a is switched to be sent to the reception detection circuit 5.

  The transmission circuit 4 generates a drive signal in response to an instruction (trigger signal) from the control circuit 6, and an ultrasonic transducer 2 a or an ultrasonic wave that becomes an ultrasonic transducer on the transmission side via the transmission / reception selector switch 3. Send to vibrator 2b.

  The reception detection circuit 5 detects the reception signal received by the ultrasonic transducer 2 a or 2 b that is the ultrasonic transducer on the reception side via the transmission / reception changeover switch 3 and outputs it to the control circuit 6.

  The control circuit 6 measures the propagation time until the ultrasonic wave generated from the transmission-side ultrasonic transducer reaches the reception-side ultrasonic transducer, and calculates the flow rate and the flow velocity based on the measured propagation time. To do. A difference in propagation time occurs between the forward direction and the reverse direction due to the flow of gas, and the control circuit 6 can obtain the flow velocity of the gas based on this difference in propagation time.

  As a measurement method when pulsation occurs due to the operation of a gas device (for example, a gas heat pump) that varies the gas pressure, the instantaneous flow rate is calculated by multiple measurements separately from the measurement mode that calculates the instantaneous flow rate from a single measurement. There is known a method of measuring by providing a measurement mode (measurement mode 2). As a result, the flow meter employing this method sets the measurement mode 2 when it is known in advance that the gas device that is the pulsation generation source is installed in the house or in the next house, thereby reducing the flow measurement accuracy. In addition, when it is known in advance that the pulsation generation source is not installed, the measurement mode 1 is set to prevent wasteful power consumption.

  Patent Document 1 describes a flow rate measuring device capable of reducing power consumption without causing a decrease in flow rate measurement accuracy. The flow rate measuring device measures a physical quantity that changes in accordance with a gas flow rate in a gas flow rate at a predetermined period, and measures an instantaneous flow rate by multiplying the measured physical quantity and a cross-sectional area of the gas flow path. A second measurement mode in which an instantaneous flow rate is measured by intermittently measuring a physical quantity for a predetermined number of times every predetermined period and multiplying the average value of the physical quantity measured a predetermined number of times and the cross-sectional area of the gas flow path. One of the measurement modes can be selected.

Therefore, according to the flow rate measuring apparatus described above, the pulsating flow is set by setting the second measurement mode when it is known in advance that a gas heat pump or the like serving as a pulsating flow generation source is installed in the house or the neighbor. Even if this occurs, it is possible to prevent the flow rate measurement accuracy from being lowered. In addition, when it is known in advance that a gas heat pump or the like as a pulsating flow generation source is not installed in the house or in the next house, the first measurement mode is set so that there is no fluctuation in the flow rate due to the pulsating flow. Therefore, it is not necessary to consume a large amount of power in the second measurement mode and obtain the instantaneous flow rate. In addition, the first measurement mode can suppress power consumption and accurately measure the instantaneous flow rate, thus preventing unnecessary power consumption. can do.
JP 2001-165740 A

  However, in the flow rate measuring apparatus as described above, there is a problem in how to deal with sudden pulsations or when the installer does not know the existence of pulsation sources in the vicinity. That is, the above-described flow rate measuring device can accurately measure the flow rate by switching the measurement mode when it is recognized in advance whether or not a gas device (for example, a gas heat pump) serving as a pulsation generation source is installed in the house or a neighbor. However, if you do not know in advance the installation of gas equipment that will be the source of pulsation, the measurement mode cannot be set properly, resulting in reduced flow measurement accuracy and wasteful power consumption. Incurs outbreaks.

  Further, when the gas device that is a pulsation generation source is repeatedly operated / stopped, the flow rate measuring device needs to switch the setting to the measurement mode 1 by means of communication or the like every time the gas device stops. In addition, when appropriate switching is not performed, the time period during which the gas equipment is stopped is also measured in the measurement mode 2, which causes an unnecessary increase in power consumption.

  The present invention solves the above-described problems of the prior art, when the presence or absence of installation of the gas equipment that is the source of pulsation in the house or in the neighboring house is not recognized, or when the gas equipment is repeatedly operated / stopped However, an object of the present invention is to provide an ultrasonic flowmeter that appropriately switches the measurement mode, prevents a decrease in measurement accuracy, and prevents an increase in power consumption.

In order to solve the above-described problem, an ultrasonic flowmeter according to the present invention includes a pair of ultrasonic transducers installed at a certain distance apart on the upstream side and the downstream side of the flow path through which the fluid to be measured flows, A time measuring unit that measures a propagation time of an ultrasonic signal transmitted and received between a pair of ultrasonic transducers, and an instantaneous flow rate of the fluid to be measured is calculated based on the propagation time measured by the time measuring unit. An ultrasonic flowmeter having an instantaneous flow rate calculation unit, wherein the pulsation of the fluid to be measured is based on at least one of the propagation time measured by the time measurement unit and the instantaneous flow rate calculated by the instantaneous flow rate calculation unit A pulsation detection unit for detecting the pulsation, a filter unit for filtering the instantaneous flow rate calculated by the instantaneous flow rate calculation unit when a pulsation is detected by the pulsation detection unit, and a filter unit for filtering A first determination unit that determines whether or not the fluid to be measured is leaked based on the instantaneous flow rate that is filtered, and the first determination unit is a standard within a predetermined time of the instantaneous flow rate calculated by the instantaneous flow rate calculation unit. A second determination unit that calculates a deviation, determines whether or not the measured fluid leaks only when the standard deviation is equal to or less than a predetermined value, and determines whether or not the measured fluid is used; and the measured fluid A first buffer used for integration when not in use, a second buffer used for integration when using the fluid to be measured, and a second buffer used for integration when the second determination unit is determining whether or not to use the fluid to be measured. 3 buffer and when the second determination unit is determining whether to use the fluid to be measured, the instantaneous flow rate is integrated into the third buffer, and the flow rate value integrated into the third buffer is Measurement fluid unused When it is determined that the value corresponds to the time, the flow value accumulated in the third buffer is accumulated in the first buffer, and the flow value accumulated in the third buffer corresponds to the time when the measured fluid is used. And a flow rate integrating unit that integrates the flow rate value accumulated in the third buffer in the second buffer when it is determined that the value is to be performed.

  According to the present invention, even when the presence or absence of the gas equipment that is the source of pulsation is not recognized in the home or in the neighboring house, or when the gas equipment is repeatedly operated / stopped, the pulsation is detected and appropriately The measurement mode can be switched to prevent a decrease in measurement accuracy and an increase in power consumption.

  Hereinafter, embodiments of the ultrasonic flowmeter of the present invention will be described in detail with reference to the drawings.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the configuration of the control circuit 6a of the ultrasonic flowmeter according to the first embodiment of the present invention. First, the configuration of the present embodiment will be described. The ultrasonic flowmeter according to the present embodiment is a pair of ultrasonographs arranged inside the flow channel 1 as in the conventional ultrasonic flowmeter shown in FIG. 1 includes a sound wave transducer 2a, 2b, a transmission / reception changeover switch 3, a transmission circuit 4, and a reception detection circuit 5, and further includes a control circuit 6a shown in FIG.

  The ultrasonic transducer 2a and the ultrasonic transducer 2b are installed at a certain distance from the upstream side and the downstream side of the fluid flow path 1 through which the fluid to be measured flows, and the ultrasonic transducer on the transmission side and the reception side Used as an ultrasonic transducer. Between the ultrasonic transducer 2a and the ultrasonic transducer 2b, the operation of transmitting and receiving ultrasonic waves to and from each other in the forward direction and the reverse direction of the fluid flow is repeatedly performed, and the difference in ultrasonic propagation integration time in each direction Based on the above, the flow rate is calculated.

  The transmission / reception change-over switch 3 switches which of the ultrasonic transducer 2a and the ultrasonic transducer 2b is used as a transmission-side ultrasonic transducer or a reception-side ultrasonic transducer. Specifically, the transmission / reception changeover switch 3 switches between sending the drive signal from the transmission circuit 4 to the ultrasonic transducer 2a or the ultrasonic transducer 2b in response to an instruction from the control circuit 6a, In the former case, the reception signal from the ultrasonic transducer 2 b is sent to the reception detection circuit 5, and in the latter case, the reception signal from the ultrasonic transducer 2 a is switched to be sent to the reception detection circuit 5.

  The transmission circuit 4 generates a drive signal in response to an instruction (trigger signal) from the control circuit 6a, and an ultrasonic transducer 2a or an ultrasonic wave that becomes an ultrasonic transducer on the transmission side via the transmission / reception selector switch 3. Send to vibrator 2b.

  The reception detection circuit 5 detects the reception signal received by the ultrasonic transducer 2a or 2b, which is the ultrasonic transducer on the reception side, via the transmission / reception selector switch 3, and outputs it to the control circuit 6a.

  The control circuit 6a measures the flow rate based on the propagation time obtained based on the ultrasonic signals transmitted and received from the ultrasonic transducers 2a and 2b. As a specific configuration, the control circuit 6a includes a propagation time measurement unit 10, an instantaneous flow rate calculation unit 11, a pulsation detection unit 12, pulsation removal units 14a and 14b, a gas leakage (inner pipe leakage) determination unit 16, a security unit 20, The gas use determining unit 22 and the flow rate integrating unit 24 are configured.

  The propagation time measurement unit 10 corresponds to the time measurement unit of the present invention, controls the timing at which the transmission circuit 4 transmits ultrasonic waves to the ultrasonic transducer on the transmission side, and receives signals detected by the reception detection circuit 5 Is used to detect the timing of reception of ultrasonic waves and measure the propagation time of ultrasonic signals transmitted and received between the ultrasonic transducers 2a and 2b.

  The instantaneous flow rate calculation unit 11 calculates the instantaneous flow rate of the fluid to be measured such as gas based on the propagation time measured by the propagation time measurement unit 10. Now, if the velocity of sound is c, the flow velocity of the fluid to be measured is v, and the distance from the ultrasonic transducer 2a to the ultrasonic transducer 2b is L, the propagation time of the forward ultrasonic signal is L / (c + v), The propagation time of the ultrasonic signal in the reverse direction is L / (cv). If the value of L is known, the sound speed and flow velocity can be obtained based on these propagation times. Therefore, the instantaneous flow rate calculation unit 11 can obtain the instantaneous flow rate by multiplying the obtained flow velocity of the fluid to be measured by the cross-sectional area of the fluid flow path 1.

  The pulsation detection unit 12 detects pulsation of the fluid to be measured based on at least one of the propagation time measured by the propagation time measurement unit 10 and the instantaneous flow rate calculated by the instantaneous flow rate calculation unit 11.

  Various methods of pulsation detection by the pulsation detection unit 12 can be considered. As one method, the pulsation detecting unit 12 is based on a change amount of a sum of a forward ultrasonic wave propagation time and a reverse ultrasonic wave propagation time measured by the propagation time measuring unit 10 at a predetermined time. The presence or absence of pulsation and the magnitude of pulsation are determined.

  For example, the pulsation detection unit 12 may select one of the following five conditions depending on the sum of the forward ultrasonic wave propagation time and the reverse ultrasonic wave propagation time measured by the propagation time measurement unit 10. The crab pulsation level is determined.

  The pulsation detection unit 12 determines that there is a continuous pulsation at an intermediate level when (1) “when an instantaneous flow rate that satisfies ΔT ≧ X1 [nS] occurs i times or more in t seconds”. Here, T represents the sum of propagation times of forward and reverse ultrasonic waves. T may be an average value of propagation times of forward and reverse ultrasonic waves (a value obtained by dividing the sum of propagation times of forward and reverse ultrasonic waves by 2).

Further, for ΔT, for example, the difference between the current T value (T (k)) and the previous T value (T (k−1)) can be used (| T (k) −T (k−)). 1) |). As another example, ΔT can use the difference between the current T value (T (k)) and the previous T average value (T _N (k−1)) (| T (k _{) -T N (k-1)} |).

  Further, the pulsation detection unit 12 determines that there is a single pulsation at an intermediate level when (2) “when an instantaneous flow rate that satisfies ΔT ≧ X1 [nS] occurs for j seconds or more in t seconds”. Here, i> j. Therefore, the pulsation detection unit 12 determines that there is a single pulsation at an intermediate level if it does not correspond to the case of (1) but corresponds to the case of (2).

  Further, the pulsation detection unit 12 determines that there is a large level of continuous pulsation when (3) “when an instantaneous flow rate that satisfies ΔT ≧ X2 [nS] occurs i times or more in t seconds”. Here, X2> X1.

  Further, the pulsation detection unit 12 determines that there is a single pulsation of a large level when (4) “when an instantaneous flow rate that satisfies ΔT ≧ X2 [nS] occurs for j seconds or more in t seconds”.

  Furthermore, the pulsation detection unit 12 determines that the pulsation level is low or no pulsation when “5” does not correspond to any of the conditions (1) to (4).

  The pulsation detection method described above performs detection using the propagation time of the ultrasonic wave. As another method, the pulsation detection unit 12 changes the instantaneous flow rate calculated by the instantaneous flow rate calculation unit 11 in a predetermined time. Based on this, the presence or absence of pulsation and the magnitude of pulsation can also be determined.

  For example, the pulsation detection unit 12 determines the pulsation level to one of the following five conditions according to the amount of change in the instantaneous flow rate calculated by the instantaneous flow rate calculation unit 11 in a predetermined time.

The pulsation detecting unit 12 determines that there is a continuous pulsation at an intermediate level (1) “when an instantaneous flow rate that satisfies ΔQ ≧ Y1 [L / h] occurs for t seconds or more” i times). Here, Q indicates an instantaneous flow rate. Also, for ΔQ, for example, the difference between the current Q value (Q (k)) and the previous Q value (Q (k−1)) can be used (| Q (k) −Q (k−)). 1) |). As another example, ΔQ may be a difference between the current Q value (Q (k)) and the previous N average value (Q _N (k−1)) of Q (| Q (k ) -Q _N (k-1) |).

  Further, the pulsation detection unit 12 determines that there is a single pulsation at a medium level (2) “when an instantaneous flow rate that satisfies ΔQ ≧ Y1 [L / h] occurs for j seconds or more in t seconds”.

  Further, the pulsation detecting unit 12 determines that there is a large level of continuous pulsation when (3) “when an instantaneous flow rate that satisfies ΔQ ≧ Y2 [L / h] occurs i times or more in t seconds”. Here, Y2> Y1.

  Further, the pulsation detecting unit 12 determines that there is a single pulsation of a large level when (4) “when an instantaneous flow rate that satisfies ΔQ ≧ Y2 [L / h] occurs more than j times in t seconds”.

  Furthermore, the pulsation detection unit 12 determines that the pulsation level is low or no pulsation when “5” does not correspond to any of the conditions (1) to (4).

  The pulsation detection method described above performs detection using an instantaneous flow rate. When the instantaneous flow rate calculation unit 11 in the ultrasonic flowmeter calculates the instantaneous flow rate based on a plurality of ultrasonic measurements, the pulsation detection unit 12 determines the ultrasonic propagation time in the multiple ultrasonic measurements. Based on this, the presence or absence of pulsation and the magnitude of pulsation can also be determined.

  Specifically, the pulsation detecting unit 12 obtains the maximum value and the minimum value of the forward ultrasonic wave propagation time measured a plurality of times by the propagation time measuring unit 10, and those “difference” and “difference are predetermined values” The pulsation level is determined based on one of the following three conditions according to “the above frequency”. Note that the pulsation detection unit 12 may obtain the maximum value and the minimum value of the propagation time of the ultrasonic waves in the reverse direction measured by the propagation time measurement unit 10 a plurality of times. When pulsation occurs, a steep increase or decrease in flow rate occurs in the forward or reverse direction, so the difference between the maximum and minimum propagation times of forward or reverse ultrasonic waves within the pulsation time is This is because it takes a large value.

  The pulsation detection unit 12 determines that the pulsation level is low or there is no pulsation when (1) “the maximum and minimum difference in propagation time in t seconds ≧ Z1 [nS] is less than m occurrences of instantaneous flow rate”. .

  Further, the pulsation detecting unit 12 (2) “Maximum and minimum difference in propagation time in t seconds ≧ Z1 [nS] is the number of occurrences of instantaneous flow rate is m times or more, and the maximum and minimum of propagation time in the t seconds. When “difference <Z2 [nS] is satisfied”, the pulsation level is determined.

  Further, the pulsation detection unit 12 determines that the pulsation level is high when (3) “maximum and minimum difference in propagation time in t seconds ≧ Z2 [nS]”. Here, Z2> Z1.

  As described above, the pulsation detection unit 12 detects the pulsation of the fluid to be measured based on either the propagation time measured by the propagation time measurement unit 10 or the instantaneous flow rate calculated by the instantaneous flow rate calculation unit 11. Can do. Therefore, the pulsation detection unit 12 shown in FIG. 1 has both the propagation time output by the propagation time measurement unit 10 (for example, the average value T of forward and reverse arrival times) and the instantaneous flow rate Q calculated by the instantaneous flow rate calculation unit 10. Is entered, but only one of them may be used.

  The pulsation removal units 14 a and 14 b correspond to the filter unit of the present invention, and perform filtering on the instantaneous flow rate calculated by the instantaneous flow rate calculation unit 11 when pulsation is detected by the pulsation detection unit 12.

  FIG. 2 is an image diagram of the pulsation removing unit 14a. As shown in FIG. 2, the pulsation removing unit 14a controls the output of the instantaneous flow rate Q input according to the presence or absence of pulsation. When there is no pulsation, the pulsation removing unit 14a outputs the input instantaneous flow rate Q as it is as the instantaneous flow rate Q ′. That is, Q = Q ′. In this case, the pulsation removing unit 14a is a filter having a filter coefficient = 1.

  On the other hand, when there is a pulsation, the pulsation removing unit 14a does not output the instantaneous flow rate Q and Q ′ = 0. Here, the case where “there is pulsation” is a case where, for example, the pulsation detection unit 12 determines that the pulsation level is medium or large.

  Further, the pulsation removing unit 14a may be configured not to output not only the instantaneous flow rate determined by the pulsation detecting unit 12 but also the instantaneous flow rate measured m times before and n times thereafter. FIG. 3 is a diagram showing an outline of the filtering means of the pulsation removing unit 14a in this case. In FIG. 3, m = 2 and n = 3.

  As shown in FIG. 3, since the instantaneous flow rate values for the two times immediately before the peak value determined to have pulsation are considered to be affected by the omens of pulsation, the pulsation removing unit 14 a The instantaneous flow rate for two times is not output and it is used for gas leak judgment.

  In addition, since it is considered that the instantaneous flow rate values for three times immediately after the peak value determined to have pulsation are affected by the tailing portion of the pulsation, the pulsation removing unit 14a performs the instantaneous flow value for three times immediately after the peak value. Does not output the flow rate and prevents it from being used for gas leak judgment.

FIG. 4 is a diagram showing actual fluctuations in the instantaneous flow rate calculated by the instantaneous flow rate calculation unit 11. Determining during the period from time _{t 1} to time _{t 2, the} pulsation detecting unit 12, the pulsation is with. However, as shown in FIG. 4, large fluctuations in the instantaneous flow rate value are also observed in the precursor portion between time t ₀ and time t ₁ and in the trailing portion between time t ₂ and time t _3. . When the instantaneous flow rate at the precursor part or the tail part is used for the gas leak judgment, there is a possibility that the correct judgment may not be performed. Therefore, the pulsation removing unit 14a is not limited to the part judged to have pulsation. As described above, the instantaneous flow rate in the precursor portion and the tail portion is not output.

  In this case, the pulsation removing unit 14a does not immediately output the input instantaneous flow rate Q even when there is no pulsation, but stores the fluctuation data of the instantaneous flow rate value within a certain period to detect pulsation. In this case, the instantaneous flow rate data output to the gas leak determination unit 16 is selected, and the instantaneous flow rate data before and after the occurrence of pulsation is deleted and output to the gas leak determination unit 16.

  The gas leakage determination unit 16 corresponds to the first determination unit of the present invention, and determines the presence or absence of leakage of the fluid to be measured (inner tube leakage) based on the instantaneous flow rate Q ′ filtered by the pulsation removing unit 14a. There are various leak determination methods. For example, the gas leak determination unit 16 continuously takes an instantaneous flow rate Q ′ of 0 or a very small value for a predetermined number of times within a predetermined period (for example, one month). In the case, it is determined that there is no gas leakage. This method is a determination method based on the premise that the possibility that the gas is continuously used for a long period such as one month is very low. Therefore, when this determination method is adopted, the gas leak determination unit 16 determines that there is a gas leak when the gas always flows over a predetermined amount for one month.

  When the pulsation removing unit 14a employs the filtering method as described above, the pulsation removing unit 14a stops the output to the gas leak determination unit 16 every time pulsation occurs. Therefore, in order to make a distinction between when the gas is not used and when the pulsation occurs, the pulsation removing unit 14a generates the pulsation instead of stopping outputting the instantaneous flow rate Q ′ to the gas leakage determining unit 16 when the pulsation occurs. It is good also as a structure which outputs a signal.

  Moreover, the gas leak determination part 16 is good also as a structure which determines the presence or absence of a gas leak based on the average value of the fixed time of instantaneous flow rate Q 'instead of each instantaneous flow rate value. Since the gas leak determination unit 16 uses Q ′, which is an instantaneous flow rate without pulsation, in the determination, it can perform gas leak determination with high accuracy. By performing the determination, it is possible to increase the accuracy of the gas leak determination and reduce the risk of erroneous determination.

  Further, the gas leak determination unit 16 may be configured not to perform the gas leak determination when the ratio of the instantaneous flow rate determined to have pulsation by the pulsation detection unit 12 is large. When the pulsation occurs, the pulsation removing unit 14a does not output to the gas leakage determining unit 16 as described above. Therefore, when the ratio of the instantaneous flow rate with pulsation increases, the number of instantaneous flow rate data input to the gas leak determination unit 16 decreases and the accuracy of the gas leak determination decreases.

  Further, the gas leak determination unit 16 calculates the standard deviation of the instantaneous flow rate calculated by the instantaneous flow rate calculation unit 11 within a predetermined time, and determines whether or not the fluid to be measured is leaked only when the standard deviation is a predetermined value or less. It may be determined. When the variation in the instantaneous flow rate average value used for the gas leak determination increases, the accuracy of the gas leak determination by the gas leak determination unit 16 decreases. Therefore, the gas leak determination unit 16 determines the presence or absence of leakage of the fluid to be measured only when the standard deviation of the instantaneous flow rate within a predetermined time is equal to or less than a predetermined value, so that the instantaneous flow rate average value used for the gas leak determination Guarantees measurement variations.

The pulsation removing unit 14a described above stops the output of the instantaneous flow rate Q ′ to the gas leakage determination unit 16 when pulsation occurs as filtering means. However, as will be described below, the pulsation removing unit 14a includes the pulsation detecting unit 12. When the pulsation is detected by the above, the instantaneous flow rate Q calculated by the instantaneous flow rate calculation unit 11 may be filtered using the following formula.
[Equation 1]
Q ′ (k) = aQ (k) + (1-a) Q ′ (k−1) (1)
In this case, the pulsation removing unit 14a determines the filter coefficient a based on the pulsation level determined by the pulsation detecting unit 12. Here, the filter coefficient a takes a value from 0 to 1.

  As shown in the equation (1), the pulsation removing unit 14a has a value obtained by multiplying Q (k), which is an actual measurement value of the current instantaneous flow rate, by a filter coefficient a, and Q ′ (k, which is a calculation value of the previous instantaneous flow rate. -1) is summed with a value obtained by multiplying (1-a), and the sum is output to the gas leak determination unit 16.

Further, when a pulsation is detected by the pulsation detection unit 12, the pulsation removal unit 14 b performs filtering on the instantaneous flow rate calculated by the instantaneous flow rate calculation unit 11 using the following formula.
[Equation 2]
Q ″ (k) = bQ (k) + (1−b) Q (k−1) (2)
The pulsation removing unit 14b determines the filter coefficient b based on the pulsation level determined by the pulsation detecting unit 12. Here, the filter coefficient b takes a value from 0 to 1.

  As shown in the equation (2), the pulsation removing unit 14b has a value obtained by multiplying the actual measured value of the instantaneous flow rate Q (k) by the filter coefficient b and the previous measured value of the instantaneous flow rate Q (k− The sum of the value obtained by multiplying 1) by (1−b) is obtained and output to the gas leak determination unit 16.

  That is, since the pulsation removing unit 14a uses Q ′ (k−1), which is the previous calculated value of the instantaneous flow rate, for filtering, it can be said that the pulsation removing unit 14a is influenced by the previous measured value of the instantaneous flow rate. In contrast, the pulsation removing unit 14b performs filtering based only on the actual measurement value Q (k) of the current instantaneous flow rate and the previous actual measurement value Q (k-1) of the previous instantaneous flow rate. Accordingly, the strength of the filter is stronger in the pulsation removing unit 14a than in the pulsation removing unit 14b. The reason for adopting such a configuration is that even if the instantaneous flow rate Q ″ input to the flow rate integrating unit 24 is slightly influenced by pulsation, the integrated flow rate is not greatly affected. This is because a strict instantaneous flow rate Q ′ that eliminates the influence of pulsation as much as possible is required to perform highly accurate gas leak determination.

  FIG. 5 is a diagram illustrating an example of a filter coefficient determination method for the pulsation level. The pulsation removing units 14a and 14b determine the value of the filter coefficient a or b as shown in FIG. 5 according to the pulsation level detected by the pulsation detecting unit 12. The pulsation removing units 14a and 14b reduce the influence of the instantaneous flow rate when pulsation occurs by reducing the filter coefficient a or b as the pulsation level increases.

  The measurement mode switching unit 18 has a plurality of measurement modes with different sampling counts, and when a pulsation is detected by the pulsation detection unit 12, the measurement mode switching unit 18 is based on at least one of the number of occurrences and the magnitude of the pulsation within a predetermined time. One measurement mode is selected from a plurality of measurement modes and switched.

  FIG. 6 is a diagram illustrating an example of a measurement mode included in the measurement mode switching unit 18. In the present embodiment, the measurement mode switching unit 18 has three measurement modes as shown in FIG. Measurement mode 1 is a measurement mode that is applied when the pulsation level where the flow rate fluctuation is less than Q1 [L / h] is small, and the number of times of sampling is small. Therefore, the measurement mode 1 consumes less current and can reduce power consumption. However, since measurement variation under pulsation increases, it is applied only when the pulsation level is small as described above.

  Conversely, the measurement mode 3 is a measurement mode that is applied when the pulsation level with a flow rate variation of Q2 [L / h] or more is large, and has a large number of samplings. Here, Q2> Q1. Therefore, measurement mode 3 consumes a large amount of current and consumes a large amount of power. However, since measurement variation under pulsation is small, it is applied when the pulsation level is large as described above, and more accurate measurement is possible. is there.

  The measurement mode 2 is a measurement mode that is applied when the pulsation level in which the flow rate fluctuation is Q1 [L / h] or more and less than Q2 [L / h] is medium, and is an intermediate role between the measurement mode 1 and the measurement mode 3. Fulfill. Therefore, in the measurement mode 2, all of the number of samplings, current consumption, and measurement variation under pulsation are medium.

  As a matter of course, the measurement mode switching unit 18 is not limited to three measurement modes, and can select various measurement modes corresponding to the pulsation state.

  The security unit 20 has a conventional security function other than a gas leak (inner pipe leak) determination. For example, it detects an instantaneous flow rate outside a predetermined flow rate range, or detects a defect in transmission / reception of ultrasonic waves, etc. Take appropriate measures such as shutting off gas, displaying warnings, and warnings.

  The gas usage determination unit 22 corresponds to the second determination unit of the present invention, and determines whether or not the measured fluid is used based on the instantaneous flow rate Q ″ filtered by the pulsation removing unit 14b. A specific determination method will be described later.

  The flow rate integrating unit 24 integrates the instantaneous flow rate Q ″ calculated by the instantaneous flow rate calculating unit 11 and filtered by the pulsation removing unit 14b. In this embodiment, the flow rate integrating unit 24 adds the determination result by the gas use determining unit 22 to the determination result. In response, one of a plurality of buffers is selected, and the instantaneous flow rate calculated by the instantaneous flow rate calculation unit 11 is added to the selected buffer.

  Next, the operation of the ultrasonic flowmeter of the present embodiment configured as described above will be described. First, the ultrasonic flowmeter starts ultrasonic measurement both in the forward direction and in the reverse direction. The propagation time measuring unit 10 controls the transmission / reception selector switch 3 via the transmission circuit 4 in order to determine whether the ultrasonic wave is transmitted in the forward direction or the reverse direction. The propagation time measuring unit 10 instructs the transmission circuit 4 to generate a drive signal.

  The transmission circuit 4 generates a drive signal in response to an instruction from the propagation time measurement unit 10 and sends it to the ultrasonic transducer 2a via the transmission / reception selector switch 3 (in the forward direction). As a result, the ultrasonic vibrator 2 a vibrates and generates ultrasonic waves in the fluid flow direction in the fluid flow path 1. The ultrasonic waves generated by the ultrasonic transducer 2a are received by the ultrasonic transducer 2b.

  The ultrasonic transducer 2 b generates a reception signal by oscillating according to the ultrasonic wave received from the ultrasonic transducer 2 a, and sends it to the reception detection circuit 5 via the transmission / reception changeover switch 3.

  The reception detection circuit 5 detects the reception signal received by the ultrasonic transducer 2b, which is the ultrasonic transducer on the reception side, via the transmission / reception changeover switch 3, and outputs it to the propagation time measurement unit 10 in the control circuit 6a. .

  As described above, the propagation time measuring unit 10 measures the propagation time of the ultrasonic signal transmitted and received between the ultrasonic transducers 2a and 2b. Similarly, the instantaneous flow rate calculation unit 11 calculates the instantaneous flow rate of the fluid to be measured such as gas based on the propagation time measured by the propagation time measurement unit 10.

  The propagation time measurement unit 10 measures the propagation time every predetermined time and outputs the measurement result to the instantaneous flow rate calculation unit 11. The instantaneous flow rate calculation unit 11 outputs the instantaneous flow rate Q of the fluid to be measured obtained based on the propagation time measured every predetermined time to the pulsation detection unit 12 and the pulsation removal units 14a and 14b.

  In the case where no pulsation is detected, the flow rate integration unit 24 determines the previous measurement time based on the instantaneous flow rate Q "output by the pulsation removal unit 14b and the time between the last measured time and the current measured time. From this time, the flow rate that has flowed between this time and the current measurement time is obtained, and the flow rate obtained this time is further integrated to the previous accumulated flow value stored in the buffer.

  The pulsation detection unit 12 detects pulsation of the fluid to be measured based on at least one of the propagation time measured by the propagation time measurement unit 10 and the instantaneous flow rate calculated by the instantaneous flow rate calculation unit 11. The pulsation removing units 14 a and 14 b perform filtering on the instantaneous flow rate calculated by the instantaneous flow rate calculation unit 11 when pulsation is detected by the pulsation detection unit 12.

  The measurement mode switching unit 18 has three measurement modes with different sampling counts, and when a pulsation is detected by the pulsation detection unit 12, the measurement mode switching unit 18 is based on at least one of the number of occurrences of the pulsation within a predetermined time and the magnitude of the pulsation. One measurement mode is selected from a plurality of measurement modes and switched. The propagation time measuring unit 10 measures the propagation time based on the measurement mode selected by the measurement mode switching unit 18.

  FIG. 7 is a diagram illustrating an example of state transition of the measurement mode included in the measurement mode switching unit 18. The measurement mode switching unit 18 selects the measurement mode 1 in the normal case (the pulsation level is low or no pulsation).

  When the pulsation detection unit 12 determines that the pulsation level is medium ([1] pulsation detected in FIG. 7A), the measurement mode switching unit 18 selects and switches to the measurement mode 2. . As a transition condition in this case, for example, the measurement mode switching unit 18 generates an instantaneous flow rate that satisfies ΔT ≧ X1 [nS] or ΔQ ≧ Y1 [L / h] i times or more in t1 seconds, and the pulsation detection unit 12 sets the intermediate level. When it is determined that there is continuous pulsation, measurement mode 2 is selected and switched. Alternatively, the measurement mode switching unit 18 determines that an instantaneous flow rate that satisfies ΔT ≧ X1 [nS] or ΔQ ≧ Y1 [L / h] is generated j times or more in t1 seconds, and the pulsation detection unit 12 determines that there is a single pulsation at an intermediate level. In such a case, the measurement mode 2 may be selected and switched.

  When the measurement mode 2 or the measurement mode 3 is selected and the pulsation detection unit 12 determines that the pulsation level is low ([2] small pulsation shown in FIG. 7A), The measurement mode switching unit 18 selects and switches the measurement mode 1. As a transition condition in this case, for example, the measurement mode switching unit 18 determines that the number of occurrences of the instantaneous flow rate satisfying the maximum and minimum difference in propagation time ≧ Z1 [nS] in t2 seconds is less than j times or Q1 [L / h]. When the above flow rate fluctuation is not detected, the measurement mode 1 is selected and switched.

  When the measurement mode 2 is selected and the pulsation detection unit 12 determines that the pulsation level is high ([3] large pulsation shown in FIG. 7A), the measurement mode switching unit 18 selects and switches the measurement mode 3. As a transition condition in this case, for example, the measurement mode switching unit 18 detects an instantaneous flow rate satisfying the maximum / minimum difference in propagation time ≧ Z2 [nS] in t2 seconds or detects a flow rate variation of Q2 [L / h] or more. If so, the measurement mode 3 is selected and switched.

  When the measurement mode 3 is selected and the pulsation detection unit 12 determines that the pulsation level is medium ([4] pulsation detected in FIG. 7A), the measurement mode switching unit 18 selects and switches measurement mode 2; As a transition condition in this case, for example, the measurement mode switching unit 18 generates an instantaneous flow rate such that the maximum and minimum difference in propagation time <Z2 [nS] in t2 seconds and the maximum and minimum difference in propagation time ≧ Z1 [nS]. Measurement mode 2 is selected and switched when an instantaneous flow rate that is j times or more occurs or when a flow rate fluctuation of Q1 [L / h] or more and less than Q2 [L / h] is detected.

  When the measurement mode 1 is selected and the pulsation detection unit 12 determines that the pulsation level is high ([5] pulsation large shown in FIG. 7A is detected), the measurement mode switching unit 18 selects and switches the measurement mode 3. As a transition condition in this case, for example, the measurement mode switching unit 18 generates an instantaneous flow rate that satisfies ΔT ≧ X2 [nS] or ΔQ ≧ Y2 [L / h] i times or more in t1 seconds, and the pulsation detection unit 12 sets a large level. When it is determined that there is continuous pulsation, measurement mode 3 is selected and switched. Alternatively, the measurement mode switching unit 18 determines that there is a large level single pulsation by the pulsation detection unit 12 when the instantaneous flow rate ΔT ≧ X2 [nS] or ΔQ ≧ Y2 [L / h] is generated j times or more in t1 seconds. In such a case, the measurement mode 3 may be selected and switched.

  FIG. 8 is a diagram illustrating another example of the state transition of the measurement mode possessed by the measurement mode switching unit 18. The measurement mode switching unit 18 selects the measurement mode 1 in the improved measurement mode 1 in the normal case (the pulsation level is low or no pulsation). Here, the improved measurement mode 1 is a measurement mode by a combination of the measurement mode 1 and the measurement mode 1 ′. Further, the measurement mode 1 ′ is a measurement mode in which the measurement mode 1 and the measurement mode 3 described in FIG.

  When the pulsation detection unit 12 determines that there is pulsation ([1] presence of pulsation shown in FIG. 8), the measurement mode switching unit 18 selects and switches to the measurement mode 1 ′. As a transition condition in this case, for example, the measurement mode switching unit 18 determines once every 2 seconds and determines that an instantaneous flow rate that satisfies ΔT ≧ X1 [nS] or ΔQ ≧ Y1 [L / h] has occurred. Then, the measurement mode 1 ′ is selected and switched. Here, the measurement mode 1 ′ is a measurement mode in which the determination in the measurement mode 3 is performed until the next determination (after 2 seconds). The measurement mode 3 is used for determining whether or not the occurrence of pulsation is true because the number of samplings is large.

  When the measurement mode 1 ′ is selected and the pulsation detection unit 12 determines that there is no pulsation ([2] no pulsation shown in FIG. 8 is detected), the measurement mode switching unit 18 uses the measurement mode 1 Select to switch. As a transition condition in this case, for example, the measurement mode switching unit 18 makes a determination once every 2 seconds, and when ΔT <X1 [nS] and ΔQ <Y1 [L / h], select the measurement mode 1. Switch. Therefore, when this condition is satisfied and measurement mode 1 is selected, determination by measurement mode 3 is not performed.

  The state transition condition determination between the measurement mode 1 and the measurement mode 1 ′ in the improved measurement mode 1 is determined once every 2 seconds as described above, but the pulsation occurrence frequency is also determined once every 30 seconds. Based on the determination result, the measurement mode switching unit 18 switches between the improved measurement mode 1 and the measurement mode 3.

  When the improved measurement mode 1 is selected and the pulsation detection unit 12 determines that the pulsation frequency is high ([3] high pulsation frequency shown in FIG. 8 is detected), the measurement mode switching unit 18 Selects and switches measurement mode 3. As a transition condition in this case, for example, the measurement mode switching unit 18 selects and switches the measurement mode 3 when the number of times the measurement mode 1 ′ is selected in 30 seconds ≧ r times. Here, for example, r satisfies the condition of “current consumption when measurement mode 1 ′ is selected r times in improved measurement mode 1 (30 seconds)”> “current consumption in measurement mode 3 (30 seconds)”. Value.

  When the measurement mode 3 is selected and the pulsation detection unit 12 determines that the pulsation frequency is low ([4] low pulsation frequency shown in FIG. 8 is detected), the measurement mode switching unit 18 Then, the improved measurement mode 1 is selected and switched. As a transition condition in this case, for example, the measurement mode switching unit 18 selects and switches the improved measurement mode 1 when the number of times that pulsation is detected in 30 seconds is less than s. Here, for example, s satisfies the condition “current consumption when measurement mode 1 ′ is selected s times in improved measurement mode 1 (30 seconds)” <“current consumption in measurement mode 3 (30 seconds)”. Value.

  FIG. 9 is a diagram for explaining the operation in the improved measurement mode 1. When the improved measurement mode 1 is selected by the measurement mode switching unit 18, the propagation time measurement unit 10 measures the propagation time at intervals of 2 seconds. In this case, the pulsation detecting unit 12 determines the presence or absence of pulsation immediately after the measurement by the propagation time measuring unit 10.

Immediately after the measurement has been performed due to the propagation time measurement unit 10 at time t ₀ shown in FIG. 9, the pulsation detecting unit 12 makes a determination of pulsating existence. Here, since no pulsation was detected, the measurement mode switching unit 18 does not switch the measurement mode and maintains the measurement mode 1. Further, since no pulsation was detected at time t ₁ after 2 seconds, the measurement mode switching unit 18 similarly maintains the measurement mode 1.

Immediately after the measurement has been performed due to the propagation time measurement unit 10 at time t ₂ after 2 seconds of time t _1, the pulsation detecting unit 12 determines that there is pulsating. Therefore, the measurement mode switching unit 18 selects and switches the measurement mode 1 ′. The measurement mode 1 ′ is a measurement mode in which the determination in the measurement mode 3 is performed until the next determination (after 2 seconds). Therefore, the propagation time measurement unit 10 measures the propagation time using the measurement mode 3 with a large number of samplings within 2 seconds, and immediately after that, the pulsation detection unit 12 determines the presence or absence of pulsation based on the measurement result. .

When the measurement mode 3 is used and the pulsation detection unit 12 determines that there is no pulsation, the measurement mode switching unit 18 selects and switches the measurement mode 1. Therefore, the measurement mode switching section 18, at time t ₃ after a 2 second time t _2, the return to the measurement mode 1 again measurement mode from the measurement mode 1 '.

  In addition, when intermittent use (single lever) is performed such as flowing hot water for a moment using a water heater or the like, the gas flowing in the flow path 1 may behave in a manner similar to that when pulsation occurs. However, while the single lever gas is used only in the forward direction, the gas flow reciprocates (gas flow in the forward and reverse directions) when pulsation occurs. Therefore, since the gas flow for a longer time can be observed by measuring using the measurement mode 3 with a large number of samplings, the pulsation detecting unit 12 can easily determine whether or not pulsation has occurred.

  The flow rate integrating unit 24 integrates the instantaneous flow rate Q ″ calculated by the instantaneous flow rate calculating unit 11 and filtered by the pulsation removing unit 14b. In this embodiment, the flow rate integrating unit 24 adds the determination result by the gas use determining unit 22 to the determination result. Accordingly, either one of the two buffers (buffer 1 and buffer 2) is selected, and the instantaneous flow rate calculated by the instantaneous flow rate calculation unit 11 is added to the selected buffer, where the buffer 1 is added at regular intervals. This is a buffer that clears digits of 1 L or less of the value, and buffer 2 is a buffer that is not cleared.

  The flow rate integrating unit 24 selects the buffer 1 when the determination result by the gas use determining unit 22 is not using the gas, and when the determination result by the gas use determining unit 22 is using the gas, the buffer 2 is selected. Select to integrate the instantaneous flow rate.

  The gas use determining unit 22 determines whether or not the fluid to be measured is used based on the instantaneous flow rate Q ″ filtered by the pulsation removing unit 14b. Specifically, the gas use determining unit 22 determines that the instantaneous flow rate Q ″ is If it is greater than or equal to the set threshold value, it is determined that the gas is being used.

  FIG. 10 is a diagram for explaining an addition process to each buffer included in the flow rate integrating unit 24. As shown in FIG. 10, the flow rate integrating unit 24 has a positive buffer switching threshold value and a negative buffer switching threshold value, and integrates a flow rate that is greater than or equal to the positive buffer switching threshold value or less than the negative buffer switching threshold value in the buffer 2. . Further, the flow rate integrating unit 24 integrates the buffer 1 with a flow rate that is greater than or equal to the negative buffer switching threshold and less than the positive buffer switching threshold.

In FIG. 10, since the instantaneous flow rate Q ″ calculated up to time t ₀ is a positive value but less than the positive buffer switching threshold, the flow integration unit 24 buffers the instantaneous flow rate Q ″ up to time t _0. Accumulate to 1.

Since the instantaneous flow rate Q ″ calculated from time t ₀ to time t _{1 is} equal to or greater than the positive buffer switching threshold, the flow integration unit 24 stores the instantaneous flow rate Q ″ from time t ₀ to time t ₁ in the buffer 2. Accumulate.

Similarly, since the instantaneous flow rate Q ″ calculated from time t ₁ to time t _{2 is} equal to or greater than the negative buffer switching threshold value and less than the positive buffer switching threshold value, the flow rate integrating unit 24 performs time t ₁ to time t _2. Is added to the buffer 1. In addition, since the instantaneous flow rate Q ″ calculated from time t ₂ to time t ₃ is less than the negative buffer switching threshold, the flow integration unit 24 buffers the instantaneous flow rate Q ″ from time t ₂ to time t _3. Accumulate to 2.

  If the flow rate when the gas is used and the flow rate when the gas is not used are accumulated in the same buffer, the ultrasonic flowmeter will not be used if the zero point drifts (shifts) to the positive side due to temperature change or aging. Regardless of use, the flow rate will be integrated. Also, if the zero point drifts to the negative side and the gas unused state continues for a long time, the ultrasonic flow meter will add up the negative flow rate, and if the gas is used thereafter, it will not immediately add up the flow rate to positive. There's a problem.

  However, the flow rate integration unit 24 in the ultrasonic flowmeter of the present invention has two buffers as described above, and a flow rate that does not reach the predetermined threshold is integrated in the buffer 1 and is a digit of 1 L or less every predetermined time. Is cleared, the accumulated value generated by the zero point drift is cleared, accurate flow rate accumulation is possible, and even if the zero point drifts to the negative side, it immediately becomes positive when using gas Accumulate flow to prevent miscounting of flow.

  It should be noted that the flow rate accumulated in both the buffer 1 and the buffer 2 is added to the accumulated value in the portion exceeding 1L. Accordingly, the portion of the buffer 1 that is less than 1L is cleared to zero when a predetermined buffer clear time has elapsed, but the portion that exceeds 1L is not cleared and is integrated as the flow rate of the gas actually used.

  In addition, with the above operation, the flow rate integrating unit 24 considers intermittent gas use as in a single lever device, and even if it is temporarily used, the flow rate integrating unit 24 is not affected by the passage of time as long as the flow rate is of a certain level. Do not clear the accumulation buffer to zero.

  Further, the number of buffers included in the flow rate integrating unit 24 is not limited to two and may be any number. For example, the flow rate integration unit 24 selects one of three buffers (buffer 1, buffer 2, buffer 3) according to the determination result by the gas use determination unit 22, and the instantaneous flow rate calculation unit 11 calculates the selected buffer. The instantaneous flow rate may be integrated.

  FIG. 11 is a diagram showing integration processing corresponding to the gas usage state when three buffers are used. When the determination result of the use state transitions from “in determination” to “in use of gas” by the gas use determination unit 22, the flow rate integration unit 24 adds the “determination buffer” value to the “buffer not cleared”. Clear the “judgment buffer”. On the other hand, when the determination result of the use state transitions from “being determined” to “gas not used” by the gas use determination unit 22, the flow rate integration unit 24 sets the “determination buffer” value to “cleared buffer”. To clear the “judgment buffer”.

  Specifically, the flow rate integrating unit has three buffers (buffer 1, buffer 2, buffer 3), and the buffer 1 and the buffer 2 are used for the same applications as the above-described buffers. That is, the buffer 1 is a buffer used for integration when the gas is not used, and clears a digit of 1L or less of the integrated value at regular time intervals. The buffer 2 is a buffer used for integration during gas use, and does not clear the integration value. The buffer 3 is a determination buffer used for integration when the gas use determining unit 22 is determining whether the gas is used or not used. Accordingly, the flow rate integrating unit 24 integrates the instantaneous flow rate Q ″ in the buffer 3 when the gas use state is being determined.

  The flow rate integrating unit 24 is integrated in the buffer 3 when the gas usage determining unit 22 (or the flow integrating unit 24) determines that the flow rate value integrated in the buffer 3 is a value corresponding to when the gas is not used. The flow value is accumulated in the buffer 1 and the flow value in the buffer 3 is cleared. Further, the flow rate integrating unit 24 is integrated in the buffer 3 when the gas use determining unit 22 (or the flow rate integrating unit 24) determines that the flow rate value integrated in the buffer 3 is a value corresponding to when the gas is used. The flow value is accumulated in the buffer 2 and the flow value in the buffer 3 is cleared.

  By performing such an operation, the flow rate accumulation unit 24 once accumulates the flow rate value accumulated in a state where the gas usage state is not clear to the buffer 3, and when the gas usage state is found, the flow rate accumulation unit 24 stores the flow rate value. Since the accumulated flow rate value can be transferred to an appropriate buffer (buffer 1 or buffer 2), more accurate flow rate measurement can be performed.

  Specifically, the gas usage determining unit 22 (or the flow rate integrating unit 24) determines the usage state of the gas as follows. First, the gas use determination unit 22 (or the flow rate integration unit 24) has two threshold values (k1, k2, k1> k2). Basically, the gas use is performed when the instantaneous flow rate Q ″ ≧ k1. The instantaneous flow rate Q ″ is accumulated in the buffer 2 by determining that the gas is medium, and if the instantaneous flow rate Q ″ <k2, it is determined that the gas is not used, and the instantaneous flow rate Q ″ is integrated in the buffer 1. In addition, when k2 ≦ instantaneous flow rate Q ″ <k1, the gas use determination unit 22 (or the flow rate integration unit 24) integrates the instantaneous flow rate Q ″ in the buffer 3 during the determination.

  FIG. 12 is a diagram showing the transition conditions of the gas usage state when three buffers are used. Now, when it is determined by the gas use determination unit 22 that the gas is not in use, the gas use determination unit 22 determines that the use state has changed during gas use when the transition condition A is satisfied. . Here, the transition condition A is, for example, a case where the instantaneous flow rate Q ″ ≧ k1 [L / h]. Also, when the gas use determination unit 22 satisfies the transition condition C, the use state changes during the determination. The transition condition C is, for example, a case where the instantaneous flow rate Q ″ ≧ k2 [L / h].

  In addition, when the gas use determination unit 22 determines that the gas is being used, the gas use determination unit 22 determines that the use state has changed during the determination when the transition condition B is satisfied. Here, the transition condition B is a case where the instantaneous flow rate Q ″ <k2 [L / h], for example.

  Further, when it is determined by the gas use determination unit 22 that the determination is being made, the flow rate integration unit 24 integrates the instantaneous flow rate Q ″ in the buffer 3 as described above. Here, the gas use determination unit 22 determines that the usage state has changed during gas use when the transition condition D is satisfied, and the flow rate value accumulated in the buffer 3 is accumulated in the buffer 2 and the flow rate in the buffer 3 is determined. The transition condition D is, for example, (1) instantaneous flow rate Q ″ ≧ k1 [L / h], (2) average flow rate for t seconds is equal to or greater than k2 [L / h] (3 This is a case where any one of the three conditions that the flow rate value accumulated in the buffer 3 exceeds 1L is satisfied.

  The transition condition E is a case where the transition condition D is not satisfied. Therefore, when it is determined that the gas use determination unit 22 is determining, if the transition condition D is not satisfied within a predetermined time, the gas use determination unit 22 determines that the gas is not used. The flow rate integrating unit 24 integrates the flow rate value integrated in the buffer 3 in the buffer 1 and clears the flow rate value in the buffer 3.

  As described above, according to the ultrasonic flowmeter of the first embodiment of the present invention, when the gas device that is the source of pulsation is not recognized as to whether or not the gas device is installed in the house or in the neighbor, Even when the stop is repeated, the pulsation can be detected. Therefore, by taking appropriate measures, it is possible to prevent a decrease in measurement accuracy and an increase in power consumption.

  In addition, since the pulsation removing unit 14a is provided, even when pulsation occurs, the instantaneous flow rate Q is filtered to prevent the pulsation from affecting the gas leak determination in the gas leak determination unit 16. .

  Further, the gas leak determination unit 16 calculates a standard deviation of the input instantaneous flow rate within a predetermined time, and performs a gas leak determination only when the standard deviation is equal to or less than a predetermined value, so that it is output by the pulsation removing unit 14a. It is possible to make a gas leak determination only when the variation in the instantaneous flow rate Q ′ is small, and to prevent erroneous determination.

  In addition, since the measurement mode switching unit 18 has a plurality of measurement modes with different sampling counts and selects and switches an appropriate measurement mode according to the occurrence of pulsation, it is more accurate in the measurement mode with many samplings when pulsation occurs. Information necessary for accurate flow rate measurement and pulsation detection can be obtained, and when no pulsation occurs, power consumption can be suppressed in a measurement mode with a small number of samplings.

  Furthermore, since the flow integration unit 24 having a plurality of buffers is provided, and the buffer that integrates according to the usage state of the gas is used, it is possible to cope with a shift of the zero point due to secular change, etc. Even when the gas usage state is unclear, such as when intermittent gas is used, the gas flow rate value is accumulated in the judgment buffer and it is determined to which buffer the flow rate value data will be transferred later. More accurate flow measurement is possible.

  The ultrasonic flow meter according to the present invention can be used for an ultrasonic flow meter such as an ultrasonic gas meter capable of measuring a gas flow rate.

It is a block diagram which shows the structure of the control circuit of the ultrasonic flowmeter of the form of Example 1 of this invention. It is an image figure of the pulsation removal part of the ultrasonic flowmeter of the form of Example 1 of the present invention. It is a figure which shows the outline | summary of the filtering means of the pulsation removal part of the ultrasonic flowmeter of the form of Example 1 of this invention. It is a figure which shows the actual fluctuation | variation of the instantaneous flow rate calculated by the instantaneous flow rate calculation part of the ultrasonic flowmeter of the form of Example 1 of this invention. It is a figure which shows one example of the determination method of the filter coefficient with respect to the pulsation level by the pulsation removal part of the ultrasonic flowmeter of the form of Example 1 of this invention. It is a figure which shows one example of the measurement mode which the measurement mode switching part of the ultrasonic flowmeter of the form of Example 1 of this invention has. It is a figure which shows one example of the state transition of the measurement mode which the measurement mode switching part of the ultrasonic flowmeter of Example 1 of this invention has. It is a figure which shows another example of the state transition of the measurement mode which the measurement mode switching part of the ultrasonic flowmeter of Example 1 of this invention has. It is a figure explaining operation | movement of the improvement measurement mode 1 of the ultrasonic flowmeter of the form of Example 1 of this invention. It is a figure explaining the addition process to each buffer which the flow volume integration part of the ultrasonic flowmeter of Example 1 of the present invention has. It is a figure which shows the integration process corresponding to the gas usage condition in case the flow volume integration part of the ultrasonic flowmeter of the form of Example 1 of this invention uses three buffers. It is a figure which shows the transition conditions of the gas use state in case the flow volume integration part of the ultrasonic flowmeter of the form of Example 1 of this invention uses three buffers. It is a block diagram which shows the structure of the conventional ultrasonic flowmeter.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Flow path 2a, 2b Ultrasonic vibrator 3 Transmission / reception changeover switch 4 Transmission circuit 5 Reception detection circuit 6, 6a Control circuit 10 Propagation time measurement part 11 Instantaneous flow rate calculation part 12 Pulsation detection part 14a, 14b Pulsation removal part 16 Gas leak determination Unit 18 measurement mode switching unit 20 security unit 22 gas use determination unit 24 flow rate integration unit

Claims (2)

A pair of ultrasonic transducers installed at a certain distance from the upstream side and downstream side of the flow path through which the fluid to be measured flows;
A time measuring unit for measuring a propagation time of an ultrasonic signal transmitted and received between the pair of ultrasonic transducers;
An ultrasonic flowmeter having an instantaneous flow rate calculation unit that calculates an instantaneous flow rate of the fluid to be measured based on the propagation time measured by the time measurement unit,
A pulsation detection unit that detects pulsation of the fluid to be measured based on at least one of the propagation time measured by the time measurement unit and the instantaneous flow rate calculated by the instantaneous flow rate calculation unit ;
A filter unit that filters the instantaneous flow rate calculated by the instantaneous flow rate calculation unit when a pulsation is detected by the pulsation detection unit;
A first determination unit that determines the presence or absence of leakage of the fluid to be measured based on the instantaneous flow rate filtered by the filter unit;
The first determination unit calculates a standard deviation of the instantaneous flow rate calculated by the instantaneous flow rate calculation unit within a predetermined time, and determines whether or not the fluid to be measured is leaked only when the standard deviation is a predetermined value or less. Judgment ,
A second determination unit that determines whether or not the fluid to be measured is used;
A first buffer used for integration when the fluid to be measured is not used;
A second buffer used for integration when the fluid to be measured is used;
A third buffer used for integration when the second determination unit is determining whether to use the fluid to be measured;
When the second determination unit is determining whether or not the fluid to be measured is being used, the instantaneous flow rate is integrated into the third buffer, and the flow rate value integrated into the third buffer is the unused fluid to be measured. When it is determined that the value corresponds to the time, the flow value accumulated in the third buffer is accumulated in the first buffer, and the flow value accumulated in the third buffer corresponds to the time when the measured fluid is used. A flow rate integrating unit that integrates the flow rate value accumulated in the third buffer in the second buffer when it is determined that
An ultrasonic flowmeter comprising:   A plurality of measurement modes based on at least one of the number of occurrences of the pulsation within a predetermined time and the size of the pulsation when the pulsation is detected by the pulsation detection unit; The ultrasonic flowmeter according to claim 1, further comprising a measurement mode switching unit that selects and switches one of the measurement modes.

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