JP2012154667A - Ultrasonic flow meter - Google Patents

Abstract

An object of the present invention is to provide an ultrasonic flowmeter capable of detecting inundation in a meter case while suppressing the trouble of additional processing or design change of the meter case, the number of parts and assembly.
In an ultrasonic flowmeter of the present invention, a wave height of a specific peak is set in advance among a plurality of peaks included in an ultrasonic wave received by an ultrasonic transducer 30 on a receiving side. An abnormality determining means (steps S15 and S16) is provided for determining that there is water intrusion when the value falls below the reference value. Specifically, it is determined whether or not the amplification degree set for amplifying the received wave to a preset reference wave height exceeds a predetermined reference amplification degree (S15). If the reference amplification degree is exceeded (Yes in S15), it is determined that there is water in the meter case 20 (S16).
[Selection] Figure 4

Description

  The present invention relates to an ultrasonic flow rate in which a pair of ultrasonic transducers are arranged opposite to each other in a meter case.

  Conventionally, in this type of ultrasonic flowmeter, the flow rate is calculated based on the propagation time of ultrasonic waves between a pair of ultrasonic transducers, and the flow rate is multiplied by the cross-sectional area of the flow path through which the gas flows. (For example, refer to Patent Document 1).

Japanese Patent Laying-Open No. 2005-180988 (paragraph [0020], FIG. 1)

  However, when the conventional ultrasonic flowmeter described above is used as a city gas meter, the following problems may occur. That is, the water that has entered the gas pipe due to the damage of the gas pipe buried in the ground and the water contained in the gas are accumulated in the meter case, and the accumulated water blocks the flow path through which the gas can actually pass. The area becomes smaller than the original channel cross-sectional area. Therefore, the flow rate (gas usage amount) calculated based on the original cross-sectional area of the flow path is larger than the actual flow rate (gas usage amount), which may cause a disadvantage to the gas user. .

  As a means to solve this problem, it is conceivable to install a submersion sensor for detecting the water accumulated in the meter case. However, in order to add a submersion sensor, additional processing or design change of the existing meter case is required. There arises a new problem that it becomes necessary and the number of parts and the labor for assembly increase.

  The present invention has been made in view of the above circumstances, and an ultrasonic flowmeter capable of detecting water immersion in the meter case while suppressing the additional processing or design change of the meter case, the number of parts, and the assembly work. The purpose is to provide.

  The ultrasonic flowmeter according to the invention of claim 1 made to achieve the above object is based on the propagation time of ultrasonic waves between a pair of ultrasonic transducers arranged opposite to each other in a meter case. In the ultrasonic flowmeter that measures the flow rate of the gas passing through the meter case, the wave height of a specific peak among a plurality of peaks included in the ultrasonic wave received by the ultrasonic transducer is predetermined. It has a feature in that it includes an abnormality determining means for determining that there is water intrusion when it falls below the reference value.

  According to a second aspect of the present invention, in the ultrasonic flowmeter according to the first aspect, an amplification unit that amplifies the ultrasonic wave received by the ultrasonic transducer, and a wave height of the specific peak after the amplification An amplification degree setting means for changing and setting the amplification degree in the amplification section so that the reference wave height is set, and the wave height abnormality determining means is a reference in which the amplification degree set by the amplification degree setting means is predetermined. It is characterized in that it is determined whether or not it is greater than or equal to the amplification degree, and it is determined that there is water immersion if it is greater than or equal to the reference amplification degree.

  The invention according to claim 3 is the ultrasonic flowmeter according to claim 1 or 2, wherein one ultrasonic transducer transmits an ultrasonic wave, and then the other ultrasonic transducer receives an ultrasonic wave. Time determination means for determining whether or not the propagation time until the time is equal to or less than a predetermined reference propagation time that cannot be an ultrasonic wave propagating in the gas, and when the propagation time is equal to or less than the reference propagation time, It has a feature in that it includes auxiliary abnormality determining means for determining.

  According to a fourth aspect of the present invention, in the ultrasonic flowmeter according to any one of the first to third aspects, the internal space of the meter case is connected to an inflow space into which gas flows from the outside of the meter case and to the outside of the meter case. And a partition that divides the gas into an outflow space, and a measurement tube that penetrates the partition and communicates the inflow space and the outflow space. A part of the pair of ultrasonic transducers passes through the measurement tube. In addition to being arranged oppositely, the lowermost end of the transmission / reception surface for transmitting / receiving ultrasonic waves, of the pair of ultrasonic transducers, is characterized by being disposed below the end opening of the measurement tube.

  The invention according to claim 5 is characterized in that, in the ultrasonic flowmeter according to claim 4, the cross section of the pipe through which the gas flows in the measurement pipe has a flat shape that is long in the horizontal direction with respect to the vertical direction. Have.

  A sixth aspect of the invention is the ultrasonic flowmeter according to any one of the first to fifth aspects, further comprising a shutoff valve that shuts off gas supply to the meter case when it is determined that there is water immersion. However, it has characteristics.

  The invention according to claim 7 is characterized in that the ultrasonic flowmeter according to any one of claims 1 to 6 is provided with a warning means for issuing a warning when it is determined that there is water immersion.

[Inventions of Claims 1 and 2]
According to the first aspect of the present invention, when the ultrasonic transducer on the transmission side comes into contact with the water accumulated in the meter case, the ultrasonic wave transmitted from the ultrasonic transducer passes through the meter case. It propagates not only to the passing gas but also to water accumulated in the meter case and the meter case itself. At this time, since the energy of the ultrasonic wave is dispersed, the wave height of the ultrasonic wave propagated through the gas passing through the meter case and received by the ultrasonic wave transmitter / receiver on the receiving side becomes smaller than that in the normal state. Therefore, there is flooding when the peak height of a specific peak among the multiple peaks contained in the ultrasonic wave received by the ultrasonic transducer on the receiving side falls below a preset reference value. Can be determined. And according to the present invention, since it is possible to detect inundation in the meter case using an ultrasonic transducer for flow rate measurement, when adding an inundation detection function to an existing ultrasonic flow meter, No additional processing or design change of the meter case is required, and an increase in the number of parts and assembly work can be suppressed. In addition, since at least one of the pair of ultrasonic transducers comes into contact with water, it can detect inundation as described above. It becomes possible to do.

  Here, the received ultrasonic wave may be directly monitored to determine whether or not a specific peak has dropped below a predetermined reference value, but normally the wave height is affected by the influence of the gas flow. Therefore, it is necessary to change the reference value, which is a criterion for inundation, at any time. On the other hand, according to the invention of claim 2, the amplification degree is changed so that a specific peak wave height in the received ultrasonic wave becomes a predetermined reference wave height, and the amplification degree is set in advance. Since it is determined that there is flooding when the temperature exceeds the specified level, the reference amplification degree that is a criterion for flooding can be made constant.

[Invention of claim 3]
According to the invention of claim 3, the ultrasonic wave transmitted from the ultrasonic transducer on the transmission side is not only in the gas passing through the meter case but also in the water accumulated in the meter case and the meter case itself. When propagating, the propagation time between the pair of ultrasonic transducers becomes equal to or shorter than a predetermined reference propagation time that cannot be an ultrasonic wave propagating in the gas. Therefore, it is possible to determine the presence or absence of water immersion by determining whether or not the propagation time between a pair of ultrasonic transducers is equal to or shorter than the reference propagation time. Also, two different abnormality determining means, that is, an abnormality determining means for determining inundation based on the wave height of a specific peak contained in the received ultrasonic wave, and an auxiliary abnormality for determining inundation based on the propagation time of the ultrasonic wave Since the determination means is provided, even if any one of the determination means becomes impossible, the other determination means can detect the flooding, and the reliability of the flood detection is improved.

[Inventions of Claims 4 and 5]
According to the fourth aspect of the present invention, all of the gas flowing into the inflow space of the meter case moves through the measuring tube to the outflow space and is discharged from the outflow space to the outside of the meter case. Then, the flow rate is calculated by multiplying the flow velocity obtained from the propagation time of the ultrasonic wave by the cross-sectional area of the pipe line of the measurement pipe. According to the invention of claim 4, since the wave receiving / receiving surface of the ultrasonic transducer is in contact with water at a water level lower than the level at which water enters the pipe of the measuring pipe, water enters the pipe of the measuring pipe. Intrusion can be detected before entering. As a result, measures can be taken before the flow passage cross-sectional area through which the gas can pass decreases and an error occurs in the flow rate measurement value.

  Here, the cross section of the pipe of the measuring pipe may be circular, or may be a flat shape whose horizontal direction is longer than the vertical direction (invention of claim 5). If the measuring tube has a flat cross section, a relatively large flow rate can be measured.

[Inventions of Claims 6 and 7]
According to the sixth and seventh aspects of the present invention, it is possible to prevent an inaccurate ultrasonic flowmeter from being used without knowing it.

1 is a side sectional view of an ultrasonic flowmeter according to a first embodiment of the present invention. (A) Block diagram of control processing unit, (B) Block diagram of receiving circuit Graph showing the relationship between the received wave and the reference wave height Amplitude setting program flowchart Cross-sectional side view of ultrasonic flowmeter in flooded condition Cross-sectional side view of ultrasonic flowmeter in flooded condition Flowchart of propagation time determination program according to the second embodiment Graph showing the relationship between the received wave and the reference wave height during normal and flooded (A) Perspective view of measurement tube according to modification, (B) Plan sectional view showing positional relationship between measurement tube and ultrasonic transducer Side sectional view of meter case according to modification

[First Embodiment]
Hereinafter, a first embodiment of an ultrasonic flowmeter to which the present invention is applied will be described with reference to FIGS. The ultrasonic flow meter 10 of the present embodiment is, for example, a city gas meter, and includes a meter case 20 connected in the middle of a city gas pipe 90.

  The meter case 20 has a cylindrical structure with bottoms at both ends. From the upper surface of the meter case 20, two pipe connection portions 21, 21 stand up in the longitudinal direction and communicate with the measurement tube housing chamber 22 inside the meter case 20.

  In the meter case 20, a pair of ultrasonic transducers 30, 30 are held on the inner surfaces of both end walls 23, 23 in the longitudinal direction.

  The ultrasonic transducers 30 and 30 have a substantially cylindrical structure, and an ultrasonic transmission / reception surface 31 is provided on one end face, and a connection terminal (not shown) is provided on the other end face. The connection terminal passes through both end walls 23 and 23 of the meter case 20 in an airtight state and is exposed to the outside. The connection terminal and a control processing unit 40 provided outside the meter case 20 are electrically connected to each other. Has been.

  Inside the meter case 20, a partition wall 24 is provided that separates the measurement tube housing chamber 22 into two rooms at the center in the longitudinal direction (left-right direction in FIG. 1). That is, the partition wall 24 divides the measurement tube housing chamber 22 into an upstream inflow chamber 22A and a downstream outflow chamber 22B. Ultrasonic transducers 30 and 30 are accommodated in the inflow chamber 22A and the outflow chamber 22B, respectively. Further, a circular pipe-shaped measuring tube 25 passes through the partition wall 24, and openings at both ends thereof are arranged in the inflow chamber 22A and the outflow chamber 22B. A part of the ultrasonic transducers 30, 30 are arranged to face each other via the measuring tube 25. Hereinafter, when a pair of ultrasonic transducers 30 and 30 is distinguished, they are referred to as “upstream ultrasonic transducer 30A” and “downstream ultrasonic transducer 30B”.

  When the city gas pipe 90 is connected to both pipe connection parts 21 and 21, gas flows into the inflow chamber 22A of the meter case 20 from the upstream pipe connection part 21 as shown by the dotted arrow in FIG. It passes through the pipe 25 and is discharged from the pipe connection portion 21 on the downstream side to the outside of the meter case 20 through the outflow chamber 22B.

  Here, in the present embodiment, the lowermost ends of the wave transmitting / receiving surfaces 31, 31 in the pair of ultrasonic transducers 30, 30 are disposed below the end opening of the measuring tube 25.

  In addition, as for each ultrasonic transducer 30 and 30, parts other than the transmission / reception surfaces 31 and 31 are covered with the vibration proof member (for example, rubber | gum).

  FIG. 2A shows details of the control processing unit 40 in the ultrasonic flowmeter 10. The operation of the ultrasonic flowmeter 10 of this embodiment will be described with reference to FIG.

  The control unit 41 controls the transmission / reception change-over switches 45 and 46 to connect the upstream ultrasonic transducer 30A to the transmission circuit 42 and to connect the downstream ultrasonic transmission / reception wave as shown in FIG. After the device 30B is connected to the wave receiving circuit 43, the wave sending command signal is output to the wave sending circuit 42 and the clock counter 44. Then, the transmission circuit 42 drives the upstream ultrasonic transducer 30A, and at the same time, the ultrasonic waves are transmitted from the upstream ultrasonic transducer 30A toward the downstream ultrasonic transducer 30B. The clock counter 44 starts measuring time based on the clock pulse.

  The ultrasonic wave transmitted from the upstream ultrasonic transducer 30A is received by the downstream ultrasonic transducer 30B. The received ultrasonic wave (hereinafter referred to as “received wave” as appropriate) is input to the receiving circuit 43 connected to the downstream ultrasonic transducer 30B, and the receiving circuit 43 receives the received wave when detecting the received wave. The wave detection signal d is output to the clock counter 44. The clock counter 44 stops counting by receiving the received wave detection signal d, outputs the count value (that is, the ultrasonic wave propagation time) to the control unit 41, and is reset to zero.

  When the count value is input to the control unit 41, the transmission circuit 42 stops driving the ultrasonic transducer 30 on the upstream side, and then waits for a transmission command signal output from the control unit 41. During this time, the control unit 41 drives the transmission / reception change-over switches 45 and 46, connects the transmission circuit 42 to the downstream ultrasonic transducer 30B, and connects the reception circuit 43 to the upstream ultrasonic transducer 30A. Connect to.

  Next, the control unit 41 outputs a transmission command signal to the transmission circuit 42. As a result, this time, the same processing as described above is performed with the ultrasonic wave transmission direction reversed. Then, the control unit 41 obtains the reciprocal difference (reciprocal difference in propagation time) of the count value of the clock counter 44 measured in both the forward direction and the reverse direction with respect to the gas flow. The flow velocity of the flowing gas is calculated. Further, the flow rate is calculated by multiplying the flow velocity by the cross-sectional area of the pipe line 25 </ b> A of the measurement pipe 25.

  FIG. 2B shows details of the receiving circuit 43. In the receiving circuit 43, the reference wave height setting unit 50 is preset with a plurality of (for example, four) reference wave heights Lv1 to Lv4.

  FIG. 3 shows the relationship between the received wave W amplified by the amplifier 51 provided in the wave receiving circuit 43 and the reference wave heights Lv1 to Lv4. As shown in the figure, in this embodiment, when the amplification degree of the amplifying unit 51 is set so that the wave height of the first peak P1 in the received wave W exceeds only the lowest first reference wave height Lv1. The reference wave heights Lv1 to Lv4 are set so that the wave height of the three peaks P3 exceeds the first to fourth reference wave heights Lv1 to Lv4 at a stretch. Further, the amplification unit 51 changes and sets the amplification degree according to the wave height of the reception wave before amplification so that the reception wave W after amplification satisfies the above relationship with the reference wave heights Lv1 to Lv4. It has become. Here, the first peak P1 and the third peak P3 correspond to “specific peaks” in the present invention, the first reference wave height Lv1 is the “reference wave height” with respect to the first peak P1, and the fourth reference wave height. Lv4 is a “reference wave height” with respect to the third peak P3. The change and setting of the amplification degree will be described in detail later.

  Returning to FIG. 3 and continuing the description, the reference wave height setting unit 50 selects a plurality of continuous (for example, three steps) reference wave heights from the four reference wave heights Lv1 to Lv4 and outputs them to the comparison unit 52. To do. Specifically, first, the first to third reference wave heights Lv1 to Lv3 including the smallest reference wave height Lv1 are selected and output. The received wave received by the ultrasonic transducer 30 on the receiving side is amplified with the amplification degree set in the amplification unit 51 and then input to the comparison unit 52 and the zero cross detection unit 53.

  In the comparison unit 52, the first peak P1 of the amplified received wave W is compared with the first to third reference wave heights Lv1 to Lv3. When the amplified received wave has the received waveform shown in FIG. 4, the first peak P1 exceeds the first reference wave height Lv1, but does not exceed the second and third reference wave heights Lv2, Lv3. At this time, the comparison unit 52 notifies the zero cross detection unit 53 that the first peak P1 has exceeded the first reference wave height Lv1.

  Then, the zero cross detection unit 53 detects the zero cross point immediately after the first peak P1, and outputs the zero cross detection signal a to the reference wave height setting unit 50. Further, the comparison unit 52 transmits a signal b indicating that the first peak P1 exceeds only the first reference wave height Lv1 among the three reference wave heights Lv1 to Lv3 to the reference wave height setting unit 50.

  Based on the signal b from the comparison unit 52, the reference wave height setting unit 50 newly sets a fourth reference wave height Lv4 instead of the first reference wave height Lv1 that has exceeded the first peak P1, and the fourth reference wave height Lv4 is set. The reference wave height Lv4 and the second and third reference wave heights Lv2 and Lv3 that have not exceeded the first peak P1 are output to the comparison unit 52.

  The switching of the reference wave height is performed immediately when the zero-cross detection signal a and the signal b are input. That is, before the third peak P3 exceeding the first reference wave height Lv1 after the first peak P1 is input to the comparison unit 52, three new reference wave heights Lv2 to Lv4 are set in the comparison unit 52. When the third peak P3 exceeds these three reference wave heights Lv2 to Lv4 at a stretch, the comparison unit 52 determines that the third peak P3 is a specific peak aimed at the third peak P3, and outputs the specific peak detection signal c. It outputs to the zero cross detection part 53. The zero cross detection unit 53 detects a zero cross point immediately after the third peak P3 and outputs a received wave detection signal d to the clock counter 44.

  By the way, the amplifying unit 51 is a “gain variable amplifier” whose gain (gain) can be changed stepwise, for example, and sets an optimum gain according to the wave height of the received wave before amplification. It has become. The amplification degree is set periodically (for example, at intervals of 1 minute) between normal flow rate measurements, for example.

  The amplification level is set according to the amplification level setting program PG1 described below. That is, as shown in FIG. 4, first, the amplification is set to the lowest value (S11), and the received wave actually received by the ultrasonic transducer 30 on the receiving side is amplified with the set amplification. . Then, whether or not the received wave is successfully detected by the amplified received wave, that is, as described above, the amplified received wave satisfies the relationship shown in FIG. 4 with each of the reference wave heights Lv1 to Lv4. Thus, it is determined whether or not the target specific peak (specifically, the third peak P3) can be detected (S12).

  If the amplification level is small and reception wave detection is not successful (No in S12), the amplification level is increased by one level (S13), the reception wave is amplified again, and reception wave detection (S12) is attempted. . The amplification level is increased by one step until reception wave detection is successful. When reception wave detection is successful (Yes in S12), the amplification level (the minimum amplification level at which reception wave detection is possible) is set in the amplification unit 51. (S14).

  The amplification setting process (S11 to S14) described above is performed when the ultrasonic wave is transmitted and received in the forward direction along the gas flow and when the ultrasonic wave is transmitted and received in the reverse direction opposite to the gas flow. Is performed, and the forward amplification and the reverse amplification are set. Then, at least until the next amplification level is set (for example, after one minute), the received wave is amplified with this amplification level and the flow rate is measured. The amplification degree setting processing (S11 to S14) corresponds to “amplification degree setting means” of the present invention.

  By the way, when water enters the city gas pipe for some reason or moisture contained in the gas is condensed, water gradually accumulates in the meter case 20. Then, as shown in FIG. 5 or FIG. 6, when the accumulated water comes into contact with the transmission / reception surface 31 of at least one of the ultrasonic transducers 30, the ultrasonic transmission / reception unit 30 in contact with water transmits the water. The waved ultrasonic waves propagate not only to the gas flowing through the pipe line 25A of the measurement tube 25 but also to the measurement tube 25 through accumulated water or water. At this time, since the energy of the ultrasonic waves is dispersed, the magnitude of the received wave that propagates through the gas flowing through the measurement tube 25 and is received by the ultrasonic transducer 30 on the receiving side, that is, included in the received wave. The peak height of each peak is smaller than normal. Then, the amplification degree (minimum amplification degree at which the received wave can be detected) set in the amplification degree setting process (S11 to S14) described above becomes larger than that in the normal state.

  Therefore, in the ultrasonic flowmeter 10 of the present embodiment, as shown in FIG. 4, the amplification degree set in the amplification unit 51 in the amplification degree setting process (S11 to S14) is a predetermined reference amplification degree set in advance. (S15), and if the reference amplification degree is exceeded (Yes in S15), it is determined that there is water in the meter case 20 (S16) and is provided outside the meter case 20. An alarm (inundation) is reported by an alarm device 47 (including an existing flow rate indicator and lamp, see FIG. 2). Further, the shutoff valve 18 (see FIG. 2) built in the meter case 20 is operated to stop the gas supply. Furthermore, when a communication means is provided, it automatically reports to a gas company or a gas meter administrator. Steps S15 and S16 correspond to “abnormality determination means” of the present invention.

  As described above, according to the present embodiment, it is possible to detect the inundation in the meter case 20 using the ultrasonic transducers 30 and 30 for flow rate measurement. When adding a function, additional processing and design change of the meter case 20 are unnecessary, and an increase in the number of parts and assembly work can be suppressed. Moreover, when at least one ultrasonic transducer 30 out of the pair of ultrasonic transducers 30 and 30 comes into contact with water (state shown in FIG. 5), it is possible to detect inundation. Can be dealt with relatively early.

  In addition, since the lowermost ends of the transmission / reception surfaces 31 and 31 of the ultrasonic transducers 30 and 30 are disposed below the end opening of the measurement tube 25, the water level at which water enters the pipe line 25 </ b> A of the measurement tube 25. At a lower water level, the transmitting and receiving surfaces 31 and 31 come into contact with the accumulated water, and the peak height of the received wave is lowered. Accordingly, before the cross-sectional area through which the gas in the pipe 25A of the measurement pipe 25 can pass is narrowed, that is, before the flow measurement error occurs, the inundation is detected and measures such as replacement of the ultrasonic flowmeter 10 are taken. Can do.

  Furthermore, since the alarm device 47 and the shutoff valve 18 are actuated when inundation is detected, it is possible to prevent continuous use without knowing that the ultrasonic flowmeter 10 is inaccurate.

[Second Embodiment]
The second embodiment has a configuration in which a function of detecting inundation based on the propagation time of ultrasonic waves is added to the configuration of the first embodiment. Hereinafter, only differences from the first embodiment will be described, and the same parts as those in the first embodiment will be denoted by the same reference numerals, and redundant description will be omitted.

  As shown in FIG. 6, water accumulated in the meter case 20 is interposed between a pair of ultrasonic transducers 30 and 30 and the measurement tube 25, and the water between the ultrasonic transducers 30 and 30 is water. When the measurement tube 25 is connected, the ultrasonic wave propagating through the water and the measurement tube 25 is received by the ultrasonic transducer 30 on the receiving side faster than the ultrasonic wave propagating in the gas. On the other hand, in the ultrasonic flowmeter 10 of the present embodiment, for example, in the gas (city gas) preset based on the speed of sound in the gas, the temperature, the maximum flow velocity of the gas at the time of use, and other use conditions. When a predetermined reference propagation time that cannot be an ultrasonic wave propagating through the ultrasonic wave is set and the ultrasonic wave propagation time between the pair of ultrasonic transducers 30 and 30 is equal to or less than the reference propagation time, It is determined that there is water in the meter case 20.

  Specifically, as shown in FIG. 7, in the propagation time determination program PG2, first, based on the count value of the clock counter 44, the ultrasonic transducer 30 on the transmission side transmits an ultrasonic wave, and then the predetermined time. It is determined whether or not the time limit has elapsed (S21). For example, the time limit is slightly longer than the propagation time of the ultrasonic wave when the ultrasonic wave is transmitted and received in a direction opposite to the gas flow at the maximum flow velocity.

  When the time limit has not been exceeded (No in S21), it is determined whether or not the ultrasonic transducer 30 on the receiving side has received an ultrasonic wave that satisfies a predetermined condition (S22). Specifically, whether or not the amplified received wave satisfies the relationship shown in FIG. 4 with each of the reference wave heights Lv1 to Lv4 and detects a target specific peak (for example, the third peak P3). Determine. This process (S22) is repeated until a received wave satisfying a predetermined condition is detected. If the time limit elapses before detecting a received wave satisfying a predetermined condition (Yes in S21), the received wave detection has failed (S23), and this process is immediately exited.

  On the other hand, when an ultrasonic wave satisfying a predetermined condition is received within the time limit (Yes in S22), the reception wave detection is successful (S24), and the reception wave detection signal d is output to the clock counter 44, and the ultrasonic wave Is determined (S25). Next, the measured propagation time is compared with the reference propagation time (S26). If the propagation time exceeds the reference propagation time (No in S26), it is assumed that the received wave is an ultrasonic wave propagating gas. Exit processing. On the other hand, when the propagation time is equal to or shorter than the reference propagation time (Yes in S26), the propagation medium other than the gas, that is, the water accumulated in the meter case 20 and the measurement tube 25 as shown in FIG. As a result, it is determined that there is water immersion (S27). When it is determined that there is flooding, the alarm device 47 notifies the abnormality and operates the shutoff valve 18 to stop the gas supply.

  Here, the process of step S26 corresponds to the “time determination means” of the present invention. Further, the propagation time determination program PG2 having the processes of steps 26 and S27 corresponds to the “auxiliary abnormality determination means” of the present invention. Note that the processing of steps S21 to S27 in the propagation time determination program PG2 may be performed at the time of each ultrasonic wave transmission / reception at the time of flow rate measurement, or during normal times, the processing of steps S21 to S25 is performed periodically. In addition, the processes of steps S26 and S27 may be additionally performed.

  According to the present embodiment, the same effects as those of the first embodiment can be obtained, and the following effects can be obtained. That is, abnormality determination processing of two different methods, that is, processing for determining inundation based on the wave height of a specific peak included in received ultrasonic waves (processing in steps S15 and S16 in FIG. 4), and ultrasonic processing Since it is possible to perform the process of determining the inundation based on the propagation time (the processes of steps S26 and S27 in FIG. 7), even if one of the determination processes becomes impossible, It can be detected, and the reliability of inundation detection is improved.

  Although not included in the technical scope of the present invention, only inundation detection (see FIG. 8) based on the propagation time of the received wave is performed, and based on the wave height of a specific peak included in the received ultrasonic wave. It is good also as a structure which does not perform inundation detection (refer FIG. 4. More specifically, step S15, S16).

[Other Embodiments]
The present invention is not limited to the above-described embodiment. For example, the embodiments described below are also included in the technical scope of the present invention, and various other than the following can be made without departing from the scope of the invention. It can be changed and implemented.

  (1) In the first embodiment, it is determined whether or not the wave height of the specific peak (third peak P3) included in the received wave has dropped below a predetermined reference wave height based on the magnitude of the amplification degree. However, when the amplification unit 51 always amplifies the received wave with a constant amplification factor, the following may be performed.

  The waveform shown by the solid line in FIG. 8 is the received waveform after amplification in the normal state, and the waveform shown by the dotted line is after the amplification when the ultrasonic transducer 30 on the transmission side is in contact with water. It is a received waveform. At this time, the predetermined reference wave height Lv is smaller than the third peak P3 in the normal received wave, and is larger than the third peak P3 in the received wave when the ultrasonic transducer 30 on the transmission side is in contact with water. Is set to

  Then, as shown in FIG. 8, the number of peaks equal to or higher than a predetermined reference wave height Lv among a plurality of peaks included in the amplified received wave is less than a preset reference number (in the received waveform shown in FIG. It may be determined that the wave height of a specific peak (third peak P3) included in the received ultrasonic wave has decreased beyond a predetermined reference wave height Lv.

  (2) Zero crossing immediately after a peak (fifth peak P5 in FIG. 8) that first exceeds a predetermined reference wave height Lv from ultrasonic transmission (when a transmission command signal is input to the clock counter 44). When the time T2 until the point is detected exceeds the latest time T1 at which the zero-cross point of the third peak P3 that has been experimentally obtained in advance under normal conditions can be detected, the specified included in the received ultrasonic wave It may be determined that the wave height of the peak (the third peak P3) has dropped below a predetermined reference wave height Lv.

  (3) In the above-described embodiment, the measurement tube 25 has a circular pipe shape. However, as shown in FIG. 9A, the cross-section of the pipe 26A has a flat shape in which the horizontal direction is longer than the vertical direction. The tube 26 may be used. In the case of such a measurement tube 26, as shown in FIG. 9B, the pair of ultrasonic transducers 30 and 30 are arranged in a direction that obliquely intersects the longitudinal direction of the measurement tube 26. You may arrange it facing. If such a flat cross-section measuring tube 26 is used, a relatively large flow rate can be measured.

  (4) In the above embodiment, the measurement tube 25 is accommodated in the meter case 20. However, unlike the meter case 27 shown in FIG. It is good also as a structure which narrowed down the part and formed 27 A of pipe lines.

  (5) In the above embodiment, ultrasonic waves are alternately transmitted and received in the forward and reverse directions of the gas flow, and the flow rate is calculated based on their propagation time. Good. That is, first, ultrasonic waves are transmitted and received a predetermined number of times in the forward direction, and the time required from the start of the first transmission to the detection of the plurality of receptions is measured by the clock counter 44. Next, ultrasonic waves are transmitted / received a predetermined number of times in the reverse direction, and the time required from the start of the first transmission to the detection of the plurality of receptions is measured by the clock counter 44. Then, based on the count value of the clock counter 44 measured in both the forward and reverse directions, the gas flow velocity and flow rate are calculated. In this way, the resolution is improved and the measurement accuracy is improved as compared with the configuration of the first embodiment.

DESCRIPTION OF SYMBOLS 10 Ultrasonic flow meter 18 Shut-off valve 20 Meter case 24 Bulkhead 25 Measurement pipe 25A Pipe line 26 Measurement pipe 26A Pipe line 27 Meter case 27A Pipe line 30 Ultrasonic transducer 31 Transmission / reception surface 40 Control processing part 43 Reception circuit 47 Alarm 51 Amplifying part Lv Reference wave height Lv1 to Lv4 Reference wave height P1 1st peak P3 3rd peak

Claims (7)

In the ultrasonic flowmeter for measuring the flow rate of the gas passing through the meter case based on the propagation time of the ultrasonic wave between the pair of ultrasonic transducers arranged opposite to each other in the meter case,
Abnormality determination that determines that there is inundation when the peak height of a specific peak among a plurality of peaks included in the ultrasonic wave received by the ultrasonic transducer has dropped below a predetermined reference value An ultrasonic flowmeter comprising means. An amplifying unit for amplifying the ultrasonic wave received by the ultrasonic transducer;
Amplification degree setting means for changing and setting the amplification degree in the amplification unit so that the wave height of the specific peak after amplification becomes a preset reference wave height,
The wave height abnormality determining means determines whether or not the amplification degree set by the amplification degree setting means is equal to or higher than a predetermined reference amplification degree, and determines that there is flooding if it is equal to or higher than the reference amplification degree. The ultrasonic flowmeter according to claim 1, wherein: The propagation time from when one ultrasonic transducer transmits an ultrasonic wave until the other ultrasonic transducer receives the ultrasonic wave may be an ultrasonic wave propagating in the gas. Time determination means for determining whether or not a predetermined reference propagation time or less,
The ultrasonic flowmeter according to claim 1, further comprising auxiliary abnormality determination means that determines that there is water immersion when the propagation time is equal to or shorter than the reference propagation time. A partition that divides the internal space of the meter case into an inflow space into which the gas flows from the outside of the meter case and an outflow space from which the gas flows out of the meter case; and the inflow through the partition A measuring pipe that communicates the space and the outflow space;
A part of the pair of ultrasonic transducers is disposed opposite to each other via the measurement tube;
The lowermost end of a wave transmitting / receiving surface for transmitting / receiving ultrasonic waves among the pair of ultrasonic transducers is disposed below an end opening of the measurement tube. The ultrasonic flowmeter according to any one of the above.   The ultrasonic flowmeter according to claim 4, wherein a cross section of the pipe through which the gas flows in the measurement pipe has a flat shape whose horizontal direction is long with respect to the vertical direction.   6. The ultrasonic flowmeter according to claim 1, further comprising a shutoff valve that shuts off the supply of the gas to the meter case when it is determined that there is water immersion. 7.   The ultrasonic flowmeter according to any one of claims 1 to 6, further comprising alarm means for issuing an alarm when it is determined that the water has been submerged.