JP4703700B2 - Ultrasonic transducer and ultrasonic flowmeter - Google Patents

Description

  The present invention relates to an ultrasonic flowmeter and a gas meter that measure the flow rate of a fluid using ultrasonic waves. The present invention also relates to an ultrasonic transducer used for a measuring instrument or the like.

  The ultrasonic flow meter has features such as a simple structure, a small number of mechanically movable parts, a wide range in which the flow rate can be measured, and no pressure loss due to the flow meter. In addition, recent advances in electronics technology have made it possible to improve the measurement accuracy of ultrasonic flowmeters. For this reason, studies using ultrasonic flowmeters have been made in various fields that require measurement of gas and liquid flow rates, including gas meters.

  Hereinafter, the structure and measurement principle of a conventional ultrasonic flowmeter will be described. FIG. 16 is a block diagram showing an example of a conventional ultrasonic flowmeter. The ultrasonic flow meter shown in FIG. 16 is disclosed in Non-Patent Document 1, for example. As shown in FIG. 16, the ultrasonic transducers 1 and 2 are arranged so as to sandwich the flow path 12 through which the fluid flows. The ultrasonic transducers 1 and 2 function as a transmitter and a receiver, respectively. Specifically, when the ultrasonic transducer 1 is used as a transmitter, the ultrasonic transducer 2 is used as a receiver, and when the ultrasonic transducer 2 is used as a transmitter, the ultrasonic transducer 1 is a receiver. Used as As shown in FIG. 16, the ultrasonic wave propagation path formed between the ultrasonic transducers 1 and 2 is inclined by an angle θ with respect to the fluid flow direction.

  When the ultrasonic wave is propagated from the ultrasonic vibrator 1 to the ultrasonic vibrator 2, the ultrasonic wave travels in the forward direction with respect to the fluid flow, and thus the speed is increased. On the other hand, when an ultrasonic wave is propagated from the ultrasonic transducer 2 to the ultrasonic transducer 1, the ultrasonic wave travels in the opposite direction to the fluid flow, and therefore the velocity is slow. Accordingly, the velocity of the fluid is obtained from the difference between the time for the ultrasonic wave to propagate from the ultrasonic vibrator 1 to the ultrasonic vibrator 2 and the time for the ultrasonic wave to propagate from the ultrasonic vibrator 2 to the ultrasonic vibrator 1. Can do. Further, the flow rate can be obtained from the product of the cross-sectional area of the flow path 12 and the flow velocity.

  As a specific method for obtaining the flow rate of the fluid in accordance with the above-described principle, a measurement method based on the single-around method will be specifically described.

  As shown in FIG. 16, the ultrasonic flowmeter includes a transmission unit 3 and a reception unit 6, and the ultrasonic transducer 1 is selectively connected to one of the transmission unit 3 or the reception unit 6 by a switching unit 10. At this time, the ultrasonic transducer 2 is connected to the other of the transmission unit 3 or the reception unit 6 to which the ultrasonic transducer 1 is not connected.

  When the transmission unit 3 and the ultrasonic transducer 1 are connected, the transmission unit 3 drives the ultrasonic transducer 1, and the generated ultrasonic wave reaches the ultrasonic transducer 2 across the flow of the fluid. The ultrasonic wave received by the ultrasonic transducer 2 is converted into an electric signal, and the received signal is amplified by the receiving unit 6. The level of the received signal is detected by the level detector 5.

  FIG. 17 shows an example of zero cross detection in a conventional ultrasonic flowmeter. The peak hold unit 13 generates a peak hold signal 15 from the received signal 19. The level detector 5 detects that the peak hold signal 15 has reached a predetermined level 16 and generates a detection signal 17. The zero cross detection unit 7 detects a zero cross point immediately after the detection signal 17 is generated, and generates a zero cross detection signal 18. The zero cross point is a point where the amplitude of the received signal changes from positive to negative or from negative to positive. This zero cross point is the time when the ultrasonic wave reaches the ultrasonic vibrator 2. A trigger signal is generated at a timing delayed by a predetermined time by the delay unit 4 based on the zero-crossing detection signal 18, and it is determined whether or not to repeat the signal by the repetition unit 8. The time from the generation of the zero cross detection signal 18 to the generation of the trigger signal is called a delay time.

  The transmission unit 3 drives the ultrasonic transducer 1 based on the trigger signal to generate the next ultrasonic wave. Repeating the ultrasonic transmission-reception-amplification / delay-transmission loop in this manner is called sing around, and the number of loops is called the number of sing around.

  The timer 9 measures the time required to repeat the loop a predetermined number of times, and sends the measurement result to the flow rate calculator 11. Next, the switching unit 10 is switched, and the ultrasonic transducer 2 is used as a transmitter and the ultrasonic transducer 1 is used as a receiver to perform the same measurement.

  A value obtained by subtracting a value obtained by multiplying the delay time and the number of sing-around times from the time measured by the above-described method, and further dividing the value by the number of sing-around times is the ultrasonic wave propagation time.

  The propagation time when the ultrasonic transducer 1 is on the transmission side is t1, and the propagation time when the ultrasonic transducer 2 is on the transmission side is t2. In addition, as shown in FIG. 16, the distance between the ultrasonic transducer 1 and the ultrasonic transducer 2 is L, and the fluid flow velocity and the ultrasonic sound velocity are V and C, respectively. At this time, t1 and t2 are expressed by the following equations.

From these equations, the flow velocity V is expressed by the following equation.

If the flow velocity V of the fluid is obtained, the flow rate Q is obtained from the product of the cross-sectional area of the flow path 14 and the flow velocity V.
Japan Electrical Measuring Instruments Manufacturers Association Standard, JEMIS 5032 "Flow Measurement Method Using Ultrasonic Wave" (Nippon Electric Measuring Manufacturers Association, 1987)

  In general, in a measuring instrument, it is preferable that the characteristics of the detection element do not change because the change in characteristics of the detection element used affects the measurement result. In the case of the above-described ultrasonic flowmeter, the characteristics of the ultrasonic transducer 1 and the ultrasonic transducer 2 change when the humidity or the like of the outside air in contact with the ultrasonic transducer 1 and the ultrasonic transducer 2 changes. The waveform of the ultrasonic reception signal 19 shown in FIG. 4 changes, and the zero cross point shifts. This means that even if there is no change in the flow velocity of the fluid, the propagation times t1 and t2 of the ultrasonic wave fluctuate and a measurement error occurs.

  In order to prevent such measurement errors, it is considered that the ultrasonic vibrator is cut off from the outside air by storing the ultrasonic vibrator in a case and filling the case with an inert gas and sealing it. ing. By adopting this structure, since the ultrasonic transducer is isolated from the outside air, the weather resistance of the ultrasonic transducer is also improved. Moreover, since the explosion-proof property of the ultrasonic vibrator is also improved, it can be suitably used even when the fluid measured by the ultrasonic flowmeter has flammability. That is, the reliability of the ultrasonic flowmeter is improved.

  However, when the seal is broken due to a crack in the welded portion of the case housing the ultrasonic transducer, the outside air flows into the case, changing the characteristics of the ultrasonic transducer. In particular, when the ultrasonic vibrator includes a piezoelectric ceramic, the piezoelectric ceramic made of a porous material absorbs moisture, so that the electrical characteristics of the ultrasonic vibrator may change significantly. Further, corrosion of the electrodes of the ultrasonic vibrator due to moisture may occur, and the ultrasonic vibrator may be deteriorated or broken down.

  Therefore, when a gas meter is manufactured using a conventional ultrasonic flowmeter, the case containing the ultrasonic transducer is cracked and the seal is broken, which causes many errors in gas flow measurement. End up. In addition, when the ultrasonic transducer is deteriorated or broken, it is necessary to replace the ultrasonic transducer. In particular, in order to improve the measurement accuracy of the ultrasonic flowmeter, when two ultrasonic vibrators having substantially the same characteristics are used, even if one of the ultrasonic vibrators deteriorates or breaks down, both ultrasonic waves It is necessary to replace the vibrator.

  The present invention provides an ultrasonic flowmeter that solves such a conventional problem, can maintain a highly accurate measurement, and can detect an abnormality that may cause a detection error. For the purpose. The present invention also relates to an ultrasonic transducer capable of knowing a change in characteristics.

  The ultrasonic flowmeter of the present invention has a piezoelectric element and a case for housing the piezoelectric element in a sealed state, and forms a path through which ultrasonic waves propagate in a fluid flow path by transmitting and receiving ultrasonic waves. First and second ultrasonic transducers, a measuring unit for measuring electrical characteristic values of the piezoelectric elements, and the first and second ultrasonic transducers based on the electrical characteristic values An abnormality determination unit that determines the abnormality of the flow rate, and measures the flow rate of the fluid flowing through the flow path based on the propagation time of the ultrasonic wave.

  In a preferred embodiment, each piezoelectric element of the first and second ultrasonic transducers includes a piezoelectric body and an electrode having a network structure provided on the piezoelectric body.

  The ultrasonic flowmeter of the present invention has a piezoelectric element including a piezoelectric body, a humidity sensor, and a case that houses the piezoelectric element and the humidity sensor in a sealed state, and transmits and receives ultrasonic waves. First and second ultrasonic transducers arranged so as to form a path for ultrasonic waves to propagate in the flow path, a measurement unit for measuring an electrical characteristic value of the humidity sensor, and the electrical characteristics An abnormality determination unit that determines abnormality of the first and second ultrasonic transducers based on the value, and measures the flow rate of the fluid flowing through the flow path based on the propagation time of the ultrasonic wave.

  In a preferred embodiment, the humidity sensor detects absolute humidity.

  In a preferred embodiment, the humidity sensor detects relative humidity.

  The ultrasonic flowmeter of the present invention includes a piezoelectric body having first and second main surfaces facing each other, a first electrode for electroacoustic conversion provided on the first main surface, and the first electrode A second electrode for measuring electrical characteristics of the piezoelectric body, a piezoelectric element having a common electrode provided on the second main surface, and the piezoelectric element; First and second ultrasonic transducers each having a case to be stored in a sealed state and arranged to form a path for ultrasonic waves to propagate in the fluid flow path by transmitting and receiving ultrasonic waves; A measurement unit that measures an electrical characteristic value between the common electrode and the second electrode of the piezoelectric element, and an abnormality determination that determines abnormality of the first and second ultrasonic transducers based on the electrical characteristic value And the fluid flows through the flow path based on the propagation time of the ultrasonic wave. To measure the flow rate.

  In a preferred embodiment, the second electrode is provided on the first main surface so as to surround the first electrode.

  In a preferred embodiment, at least the second electrode of the first and second electrodes has a network structure.

  In a preferred embodiment, the ultrasonic flowmeter further includes a temperature estimation unit that obtains an ultrasonic sound velocity using the first and second ultrasonic transducers and estimates the temperature of the fluid from the sound velocity, The abnormality determination unit corrects the electrical characteristic value using the temperature obtained from the temperature estimation unit, and determines an abnormality of the first and second ultrasonic transducers using the corrected value. .

  In a preferred embodiment, each of the first and second ultrasonic transducers further includes a temperature sensor housed in the case, and the abnormality determination unit uses a temperature obtained by the temperature sensor, The electrical characteristic value is corrected, and the abnormality of the first and second ultrasonic transducers is determined using the corrected value.

  In a preferred embodiment, the piezoelectric body has at least one groove.

  In a preferred embodiment, the electrical characteristic value is a resistance value or a capacitance value.

  The gas meter according to the present invention is based on any of the ultrasonic flowmeters provided in the flow path through which the gas flows, a shut-off valve that shuts off the gas flowing through the flow path, and the detection result of the abnormality determination unit And a control device for controlling the valve.

  The ultrasonic transducer according to the present invention includes a piezoelectric element, a temperature detection element, and a case that houses the piezoelectric element and the temperature detection element in a sealed state.

  In a preferred embodiment, the piezoelectric element includes a piezoelectric body and an electrode having a network structure provided on the piezoelectric body.

  Another ultrasonic transducer according to the present invention includes a piezoelectric element, a humidity detection element, and a case that houses the piezoelectric element and the temperature detection element in a sealed state.

  Another ultrasonic transducer according to the present invention includes a piezoelectric body having first and second main surfaces facing each other, and a piezoelectric element having first and second electrodes provided on the first main surface. And a case for housing the piezoelectric element in a sealed state.

  In a preferred embodiment, the second electrode is provided on the first main surface so as to surround the first electrode.

  In a preferred embodiment, at least the second electrode of the first electrode and the second electrode has a network structure.

  In a preferred embodiment, the piezoelectric body has at least one groove.

  The method for controlling an ultrasonic flowmeter according to the present invention includes a piezoelectric element and a case for housing the piezoelectric element in a sealed state, and is disposed so as to form a path through which ultrasonic waves propagate in a fluid flow path. 1 and 2 ultrasonic transducers, transmitting and receiving ultrasonic waves between the first and second ultrasonic transducers, and detecting the propagation time of the ultrasonic waves propagating between the paths, thereby detecting the flow rate of the fluid Measure. This control method includes a step of obtaining information on humidity in the cases of the first and second ultrasonic transducers, and whether the first and second ultrasonic transducers are abnormal based on the information. Determining whether or not.

  In a preferred embodiment, the step of acquiring the information acquires information related to electrical characteristics of the piezoelectric elements of the first and second ultrasonic transducers.

  In a preferred embodiment, the first and second ultrasonic transducers each have a humidity sensor in a case, and the step of acquiring the information measures the humidity in the case using the humidity sensor. .

  In a preferred embodiment, the humidity sensor measures absolute humidity.

  In a preferred embodiment, the method for controlling the ultrasonic flowmeter includes a step of measuring the flow rate of the fluid using the first and second ultrasonic transducers, and a temperature of the fluid based on the measured flow rate. And the step of correcting the information on the humidity based on the estimated temperature, and performing the step of determining using the information on the corrected humidity.

  In a preferred embodiment, the method for controlling the ultrasonic flowmeter further includes a step of stopping the movement of the fluid based on a determination result of the determining step.

  The computer-readable recording medium of the present invention records a program for causing a computer to execute each step defined in any of the above-described ultrasonic flowmeter control methods.

  According to the present invention, it is possible to obtain an ultrasonic transducer that is not easily affected by outside air or the like, but is capable of sensitively detecting a change in an unexpected environment that causes damage to the case. . By using this ultrasonic transducer, it is possible to obtain an ultrasonic flowmeter that can maintain highly accurate measurement and can detect an abnormality that may cause a detection error.

(First embodiment)
First, the ultrasonic transducer 81 used in the first embodiment of the ultrasonic flowmeter according to the present invention will be described. FIGS. 1A and 1B are a perspective view and a cross-sectional view of the ultrasonic transducer 81, respectively. The ultrasonic transducer 81 includes a piezoelectric body 82 and a case 85 including a case main body 83 and a terminal plate 84. The case body 83 has a convex shape having a cylindrical space 85s, and the piezoelectric body 82 is accommodated in the space 85s. A case top 83a of the case body 83 is located above the space 85s. The piezoelectric body 82 has a first main surface 82b and a second main surface 82a facing each other, and an electrode 91 is formed on the first main surface 82b. The second main surface is fixed to the case top portion 83a. A support portion 83b extending in the radial direction is provided below the cylindrical space 85s, and the support portion 83b and the terminal plate 87 are joined to block the space 85s. The case body 83 is preferably formed by deep drawing or the like so that a joint portion such as welding does not occur in the case body 83. The space 85s is filled with an inert gas such as nitrogen.

  A through hole 87 h is provided near the center of the terminal plate 87, and the conductive rubber 90 connected to the terminal 88 a and the tip of the terminal 88 is inserted into the through hole. The conductive rubber 90 is in contact with the electrode 91. The through hole 87 h is closed by an insulator 89 so that the terminal 88 a and the conductive rubber portion are not in electrical contact with the terminal plate 87. The case main body 83 and the terminal board 87 are made of a conductive material such as metal. A terminal 88 b is connected to the terminal plate 87. An acoustic matching layer 86 may be provided outside the case top portion 83a.

  The case top portion 83a of the case body 83 functions as an electrode provided on the second main surface of the piezoelectric body 82, and the second main surface 82a of the piezoelectric body 82 from the terminal 88b via the case main body 83 and the terminal plate 87. Can be applied with a voltage. On the other hand, a voltage can be applied to the first main surface 82b from the terminal 8a through the electrode 91 and the conductive rubber 10. Thus, a piezoelectric element including the case top portion 83a, the piezoelectric body 82, and the electrode 91 is configured.

  According to the ultrasonic transducer 81, since the piezoelectric element is housed in a sealed space, the ultrasonic transducer 81 is not affected by the outside air in contact with the ultrasonic transducer 81. For this reason, even if the humidity of the outside air changes, the characteristics of the ultrasonic transducer 81 are kept constant. Further, even if the outside air contains a gas that corrodes or alters the piezoelectric body 82, the electrode 91, or the like, the characteristics of the piezoelectric element can be maintained without changing the characteristics of the piezoelectric element over a long period of time.

  In particular, by forming the case body 83 by deep drawing, it is possible to reduce the joint portion of the case that accommodates the piezoelectric element, and by providing the support body 3b on the case body 83, the case body 83 and the terminal plate 7 can be provided. The area of the joining portion can be increased to ensure the joining. For this reason, the strength of the case 85 can be increased.

  However, in FIG. 1 (b), the portion indicated by the arrow X has a possibility that processing distortion may occur or a member of a different material is joined, so that the strength is relatively higher than other portions of the case 85. weak. For this reason, if the case 2 is damaged due to an unexpected impact, a crack or the like occurs at the location indicated by the arrow X. Then, outside air may enter the space 85s and the characteristics of the piezoelectric element may change.

  Such a change in the characteristics of the piezoelectric element is caused by the outside air entering the space 85s and the humidity of the space 85s increasing, so that the piezoelectric body of the piezoelectric element absorbs moisture. When the piezoelectric body absorbs moisture, the electrical characteristics change. For this reason, the ultrasonic flow meter of this embodiment monitors the electrical characteristics of the piezoelectric element of the ultrasonic transducer 81 used for measuring the flow rate, and detects the change in the electrical characteristic value, thereby detecting the ultrasonic wave. It is detected that the case 85 of the vibrator 81 is damaged and its characteristics are changed. In particular, it is preferable to monitor the dielectric constant of the piezoelectric element caused by the moisture absorption by the piezoelectric body, and the change in dielectric constant can be suitably detected as a change in the resistance value or capacitance value of the piezoelectric element. Therefore, it can be said that the change in the resistance value or the capacitance value of the piezoelectric element represents information on the humidity in the case 85.

  FIG. 2 is a block diagram showing the configuration of the ultrasonic flowmeter 101 of this embodiment. The ultrasonic flowmeter 101 includes a first ultrasonic transducer 1 and a second ultrasonic transducer 2 that are disposed in the fluid flow path 12 so as to form a path through which ultrasonic waves propagate in both directions. A transmission unit 3 and a reception unit 6 are provided.

  The first ultrasonic transducer 1 and the second ultrasonic transducer 2 function as a transmitter and a receiver, respectively. The ultrasonic wave transmitted from the first ultrasonic transducer 1 is received by the second ultrasonic transducer 2, and the ultrasonic wave transmitted from the second ultrasonic transducer 2 is the first ultrasonic transducer 1. Receive by. These bidirectional propagation paths form an angle θ with respect to the flow direction of the fluid flowing through the flow path 12. The magnitude of the angle θ is selected from the range of 10 to 40 degrees.

  The ultrasonic transducer 81 described in FIG. 1 is used for the first ultrasonic transducer 1 and the second ultrasonic transducer 2. For example, the first ultrasonic transducer 1 and the second ultrasonic transducer 2 are driven at a frequency of approximately 20 kHz or more by vibration modes such as a thickness vibration mode, a side-slip vibration mode, and a longitudinal vibration mode. In addition, an acoustic matching layer 86 is provided to efficiently propagate the vibration of the piezoelectric body 82 to the fluid flowing through the flow path 12. The space 85s is filled with nitrogen gas.

  The ultrasonic flowmeter 101 includes a transmission / reception switching unit 10, a first mode switching unit 20, a second mode switching unit 21, a measurement unit 22, an abnormal book bottom 23, a peak hold unit 13, a level detection unit 5, and a zero cross detection unit 7. , A delay unit 4, a repetition unit 8, and a flow rate calculation unit 11. As described in detail below, the ultrasonic flowmeter 101 has a flow rate measurement mode and an ultrasonic transducer monitoring mode, and the first mode switching unit 20 and the second mode switching unit 21 switch between these two modes. . In the flow rate measurement mode, the first ultrasonic transducer 1 and the second ultrasonic transducer 2 are connected to the transmission / reception switching unit 10 so that the flow rate of the fluid moving through the flow path 12 can be measured. Further, in the ultrasonic transducer monitoring mode, the first ultrasonic transducer 1 and the second ultrasonic transducer 1 and the second ultrasonic transducer 2 can be measured so that the characteristics of the first ultrasonic transducer 1 and the second ultrasonic transducer 2 can be measured. The sound wave vibrator 2 is connected to the measurement unit 22.

  The transmission / reception switching unit 10 selectively connects the transmission unit 3 and the reception unit 6 to the first mode switching unit 20 and the second mode switching unit 21. For example, when the transmission unit 3 and the first mode switching unit 20 are connected, the reception unit 6 and the second mode switching unit 21 are connected. Therefore, in the flow rate measurement mode, the first ultrasonic transducer 1 is selectively connected to one of the transmission unit 3 and the reception unit 6. At this time, the second ultrasonic transducer 2 is connected to the other of the receiving unit 6 or the transmitting unit 3 to which the first ultrasonic transducer 1 is not connected.

  The transmission / reception switching unit 10, the first mode switching unit 20, and the second mode switching unit 21 may be mechanical such as a toggle switch, or may be configured by electronic components or the like. Good.

  The first ultrasonic transducer 1 or the second ultrasonic transducer 2 driven by the transmission unit 3 transmits ultrasonic waves to the fluid in the flow path 12. The ultrasonic wave that has reached the second ultrasonic transducer 2 or the first ultrasonic transducer 1 is converted into an electrical signal, and the reception signal is amplified by the reception unit 6. When the electrical signal generated by the ultrasonic wave that reaches the first ultrasonic transducer 1 or the second ultrasonic transducer 2 is sufficiently large, the receiving unit 6 does not necessarily amplify the received signal.

  The reception signal amplified by the reception unit 6 is sent to the zero cross detection unit 7 and the peak hold unit 13. The peak hold unit 13 holds the peak value of the received signal 18 and generates an output using the peak value as the peak hold signal. The level detection unit 5 detects that the peak hold signal has reached a predetermined level, and generates a zero cross command signal. The zero cross detection unit 7 detects the zero cross point immediately after the zero cross command signal is generated, and outputs the zero cross detection signal to the delay unit 4. Assume that this zero cross point is the propagation time of the received signal, and the received signal is detected at this point. The zero cross detection signal is also input to the peak hold unit 13. The peak hold unit 13 resets the peak hold signal based on the zero cross detection signal.

  The delay unit 4 generates an output signal at a timing delayed by a predetermined time based on the zero cross detection signal. The repetition unit 8 counts the output signal of the delay unit 4 and outputs the output signal of the delay unit 4 to the transmission unit 3 as a trigger signal if the number is less than a predetermined number. The transmission unit 3 drives the first ultrasonic transducer 1 or the second ultrasonic transducer 2 based on the trigger signal.

  The timer unit 9 measures the time required to repeat the sing-around for a predetermined number of times, and sends the measurement result to the flow rate calculation unit 11. The flow rate calculation unit 11 obtains the flow rate and the flow rate from the data regarding the time required to repeat the sing-around output from the time measuring unit 9, the delay time, and the number of sing-around times.

  In the ultrasonic transducer monitoring mode, the first ultrasonic transducer 1 or the second ultrasonic transducer 2 is selectively transferred to the measuring unit 21 by the first mode switching unit 20 and the second mode switching unit 21. Connected. The measurement unit 21 measures the resistance value or the capacitance value of the piezoelectric body of the first ultrasonic transducer 1 or the second ultrasonic transducer 2 and outputs the measured value to the abnormality determination unit 23.

  At this time, the temperature estimation unit 14 determines the flow rate V, the propagation time t1 or t2 obtained immediately before from the flow rate calculation unit 11, and the first ultrasonic transducer 1 and the second ultrasonic transducer 2. Using the distance L, the sound velocity of the ultrasonic wave propagating in the fluid is obtained from the equation (1). The temperature estimation unit 14 holds data relating to the temperature dependence of the sound speed, and estimates the temperature of the fluid when the flow rate is measured immediately before based on this data.

  The abnormality determination unit 23 receives the resistance value or the capacitance value from the measurement unit 22, and uses the temperature received from the temperature estimation unit 14 to obtain the resistance value or the capacitance value at the reference temperature. When the resistance value or the capacitance value is different from the initial value of the first ultrasonic transducer 1 or the second ultrasonic transducer 2 by a predetermined level or more, the abnormality determination unit 23 selects the first ultrasonic wave. It is determined that the vibrator 1 or the second ultrasonic vibrator 2 is abnormal, and a signal indicating that the first ultrasonic vibrator 1 or the second ultrasonic vibrator 2 is abnormal is output. For example, an alarm is generated based on this signal. Alternatively, a shutoff valve may be provided in the flow path 12 and the shutoff valve may be operated based on this signal.

  FIG. 3 is a block diagram illustrating an example of a specific configuration of the measurement unit 22. The measurement unit 22 includes a triangular wave generation unit 31, a resistance voltage conversion unit 32, a differentiation unit 33, and an integration unit 34. The triangular wave generation unit 31 generates a triangular wave (alternating current) signal having a frequency of about 1 kHz, for example, and applies the generated signal to the first ultrasonic transducer 1 via the first mode switching unit 20. The resistance voltage conversion unit 32 detects the resistance value of the first ultrasonic transducer 1 as a voltage value, differentiates the detected signal by the differentiation unit 33, and then integrates it by the integration unit 34. The resistance value of the piezoelectric element of the acoustic wave vibrator 1 is obtained. The resistance value obtained by applying an AC voltage is generally called impedance. As described above, the resistance value of the piezoelectric element may be obtained by applying an AC voltage or by applying a DC voltage.

  Each unit described above can be configured by hardware using electronic components or the like, or can be configured by software. The ultrasonic flowmeter 101 includes a microcomputer 30 that controls these units.

  Next, a procedure for measuring the flow rate of the fluid using the ultrasonic flowmeter 101 will be described. The procedure described below is performed by sequentially controlling each component by the microcomputer 30, and a program for causing the computer to execute the procedure is stored in an information recording medium such as a ROM, a RAM, a hard disk, or a magnetic recording medium. Has been.

  As described above, the ultrasonic flowmeter 101 operates in the flow rate measurement mode and the ultrasonic transducer monitoring mode. First, the operation of the ultrasonic flowmeter 101 in the flow rate measurement mode will be described. In order to set the ultrasonic flowmeter 101 in the flow rate measurement mode, the microcomputer 30 sets the first mode so that the first ultrasonic transducer 1 and the second ultrasonic transducer 2 are connected to the transmission / reception switching unit 10. The switching unit 20 and the second mode switching unit 21 are controlled.

  As shown in FIG. 2, using the transmission / reception switching unit 10, first, the transmission unit 3 is connected to the first ultrasonic transducer 1, and the reception unit 4 is connected to the second ultrasonic transducer 2.

  As shown in FIG. 4, a trigger signal 39 is input to the transmission unit 3 to generate a drive signal, and an ultrasonic wave is generated from the first ultrasonic transducer 1. The ultrasonic wave propagated through the flow path 12 is received by the second ultrasonic transducer 2, and the reception signal is sent to the reception unit 6 and amplified as the reception signal 18.

  The zero cross point immediately after the reception signal 18 exceeds a predetermined level is detected by the zero cross detection unit 7 by the peak hold unit 13 and the level detection unit 5. The delay unit 4 outputs a trigger signal 39 ′ to the transmission unit 3 after a predetermined delay time 40 based on the zero cross detection signal output from the zero cross detection unit 7. Thus, one loop of single-around is configured. After repeating the sing-around for a predetermined number of times (for example, 50 to 1000 times), the time measuring unit 9 measures the total time 41 required to repeat the loop and sends the measurement result to the flow rate calculating unit 11. In the flow rate calculation unit, the total time 41 is divided by the number of times of sing-around, and a value obtained by subtracting the delay time 40 from the value is t1 shown in Expression (1).

  Next, using the transmission / reception switching unit 10, the transmission unit 3 is connected to the second ultrasonic transducer 2, and the reception unit is connected to the first ultrasonic transducer 1. Then, ultrasonic waves are generated from the second ultrasonic transducer 2 by the same procedure as described above, and the first ultrasonic transducer 1 receives the ultrasonic waves. After repeating the sing-around for a predetermined number of times, the timing unit 9 measures the total time 41 required to repeat the loop, and sends the measurement result to the flow rate calculation unit 11. In the flow rate calculation unit, the total time 41 is divided by the number of times of sing-around, and a value obtained by subtracting the delay time 40 from the value is t2 shown in Expression (1).

  By substituting the values of t1 and t2 and the angle θ into the equation (2), the flow velocity V of the fluid is obtained. Further, if the cross-sectional area of the flow path 12 is S, the flow rate Q can be obtained by V × S. The flow rate Q is an amount by which the flow rate moves per unit time, and the amount of fluid can be obtained by integrating the flow rate Q.

  Next, the operation of the ultrasonic flowmeter 101 in the ultrasonic transducer monitoring mode will be described. The ultrasonic flowmeter 101 normally operates in the flow rate measurement mode, and whether or not the characteristics of the first ultrasonic transducer 1 and the second ultrasonic transducer 2 have changed at a predetermined time interval. In order to measure, the ultrasonic transducer monitoring mode is operated. The time interval for operating in the ultrasonic transducer monitoring mode can be set to an arbitrary interval such as once a day, once a week, once a month.

  When it is time to measure the characteristics of the first ultrasonic transducer 1 and the second ultrasonic transducer 2, the microcomputer 30 interrupts the flow rate measurement, and the ultrasonic flow meter in the ultrasonic transducer monitoring mode. 101 is operated. First, the microcomputer 30 controls the first mode switching unit 20 so that the first ultrasonic transducer 1 is connected to the measurement unit 22. The measurement unit 22 measures the resistance value of the piezoelectric body of the first ultrasonic transducer 1 and outputs the measured value to the abnormality determination unit 23. Further, the abnormality determination unit 23 receives from the temperature estimation unit 14 an estimated temperature of the fluid based on the propagation time of the ultrasonic wave when the flow rate is measured in the flow rate measurement mode immediately before the ultrasonic transducer monitoring mode.

  The abnormality determination unit 23 converts the resistance value received from the measurement unit 22 into the resistance value at the reference temperature using the estimated temperature. When the resistance value is different from the initial value of the first ultrasonic transducer 1 by a predetermined level or more, the abnormality determination unit 23 determines whether the first ultrasonic transducer 1 or the second ultrasonic transducer 2 is used. A signal indicating that is abnormal is output.

  FIG. 5 is a graph showing a change in impedance with respect to the relative humidity around the piezoelectric element used in the first ultrasonic transducer 1. As shown in FIG. 5, as the relative humidity around the piezoelectric element increases, the piezoelectric body absorbs moisture, the dielectric constant changes, and the impedance decreases. Therefore, it can be seen that when the impedance is greatly reduced, the case of the first ultrasonic transducer 1 is damaged, and the relative humidity around the piezoelectric element is increased by the flow of outside air from the case.

For example, in the first ultrasonic transducer 1, when the piezoelectric element enclosed in the inert gas having the relative humidity RH _{0 at} the reference temperature has the initial value of the impedance R ₀ , the first ultrasonic wave When the impedance of the transducer 1 is reduced to 1/10 or 1/100 of the initial value R ₀ , the abnormality determination unit 23 determines that the first ultrasonic transducer 1 is abnormal. At this time, the relative humidity in the case increases to RH ₁ . This is because outside air having a high relative humidity flows into the case due to damage to the case.

  Next, the microcomputer 30 controls the first mode switching unit 20 and the second mode switching unit 22 so that the second ultrasonic transducer 2 is connected to the measurement unit 22, and the second mode is the same as described above. The impedance of the ultrasonic transducer 2 is measured to determine whether or not the second ultrasonic transducer 2 is abnormal.

  When at least one of the first ultrasonic transducer 1 and the second ultrasonic transducer 2 is abnormal, the abnormality determination unit 23 determines whether the first ultrasonic transducer 1 or the second ultrasonic transducer 2 is abnormal. A signal indicating that is abnormal is output. At this time, information indicating which ultrasonic transducer is abnormal may be output at the same time.

  As described above, in the ultrasonic flow meter 101, the piezoelectric elements of the first and second ultrasonic vibrators 1 and 2 are housed in a case filled with an inert gas. For this reason, even if the humidity of the outside air changes, the characteristics of the first and second ultrasonic transducers 1 and 2 are kept constant, and flow rate measurement with less error is possible. Even if the gas that corrodes or alters the piezoelectric body 82 or the electrode 91 is included in the outside air, the characteristics of the piezoelectric element do not change. Can perform highly accurate measurements over a long period of time. That is, the ultrasonic flow meter 101 is excellent in reliability.

  On the other hand, when an unexpected impact or environmental change occurs due to an earthquake or the like and the case of the first ultrasonic vibrator 1 or the second ultrasonic vibrator 2 is damaged, the outside air flows into the case, and the piezoelectric element Since the surrounding humidity changes, the dielectric constant of the piezoelectric body changes. For this reason, in the ultrasonic transducer monitoring mode, the impedance of the first ultrasonic transducer 1 and the second ultrasonic transducer 2 is periodically monitored, and the first ultrasonic wave is detected by detecting the impedance change. It can be known that the characteristics of the transducer 1 and the second ultrasonic transducer 2 have changed and a measurement error has occurred.

  If the ultrasonic flow meter 101 is provided with a seismic sensor, and the seismic sensor detects that an earthquake of a predetermined magnitude or larger has occurred, the ultrasonic vibrator monitoring mode is immediately executed, and the first You may make it confirm whether abnormality has arisen in the ultrasonic transducer | vibrator 1 and the 2nd ultrasonic transducer | vibrator 2. FIG.

  In particular, this embodiment utilizes the fact that the characteristics of the piezoelectric elements themselves of the first ultrasonic transducer 1 and the second ultrasonic transducer 2 change sensitively to changes in ambient humidity. In other words, the first ultrasonic transducer 1 and the second ultrasonic transducer 2 serve as elements for detecting humidity. For this reason, it is not necessary to newly provide a humidity detection element or the like. Further, as shown in FIG. 1B, when the groove 2g is provided in the piezoelectric body 82, the surface area of the piezoelectric body 82 is increased, and the piezoelectric body 82 is more piezoelectric with respect to the humidity change around the piezoelectric body 82. The dielectric constant of the body is likely to change. For this reason, it becomes easy to detect damage of case 85 more sensitively.

  That is, according to the ultrasonic flow meter 101, the piezoelectric elements of the first and second ultrasonic vibrators 1 and 2 are housed in a case filled with an inert gas, and thus are not easily affected by outside air or the like. For unexpected environmental changes that may cause damage to the case, it is possible to detect the changes sensitively. Therefore, it is possible to stably measure the flow rate without including a measurement error with respect to a certain environmental change, and when the piezoelectric characteristics of the piezoelectric elements of the first and second ultrasonic vibrators 1 and 2 change. Can reliably detect the change and know that a measurement error may occur.

  In the present embodiment, the piezoelectric elements of the first and second ultrasonic transducers 1 and 2 include the electrode 26 that completely covers a part of the second main surface of the piezoelectric body. As described above, the piezoelectric element may include a mesh electrode 26 ′. In the piezoelectric element shown in FIG. 6, since the surface of the piezoelectric body 82 is exposed from the mesh of the electrode 26 ', the surface area where the piezoelectric body 82 is exposed increases, and the dielectric constant becomes more sensitive to changes in the surrounding humidity. Change. For this reason, by accommodating the piezoelectric element shown in FIG. 6 in a case filled with an inert gas, the first and second sensors are more sensitive to unexpected environmental changes that cause damage to the case. The change in the piezoelectric characteristics of the piezoelectric elements of the ultrasonic vibrators 1 and 2 can be detected. Even in this case, as long as the case is kept in a sealed state, the inert gas covering the periphery of the piezoelectric element does not change, and thus the piezoelectric element exhibits stable characteristics.

(Second Embodiment)
Hereinafter, a second embodiment of the ultrasonic flowmeter according to the present invention will be described. FIG. 7 schematically shows the structure of the ultrasonic transducer 51 used in this embodiment. The ultrasonic vibrator 51 has a temperature sensor 53 in a case 85 that seals a piezoelectric element including the piezoelectric body 82. The piezoelectric element and the temperature sensor 53 are connected to the wiring 52, and the wiring 52 is drawn out of the case 85. As in the first embodiment, the space 85s of the case 85 is filled with an inert gas.

  FIG. 8 is a block diagram showing the configuration of the ultrasonic flowmeter 102 of the present embodiment. The ultrasonic flow meter 102 includes a first ultrasonic transducer 55 and a second ultrasonic transducer 56. An ultrasonic transducer 51 shown in FIG. 7 is used for the first ultrasonic transducer 55 and the second ultrasonic transducer 56.

  The ultrasonic flowmeter 102 includes a temperature measurement unit 41 instead of the temperature estimation unit 14 of the ultrasonic flowmeter 101 of the first embodiment, and includes the first ultrasonic transducer 55 and the second ultrasonic wave. The temperature sensor 53 provided in the case 85 of the vibrator 56 is connected to the temperature measurement unit 41. The output of the temperature measurement unit 41 is input to the determination unit 23 as described above.

  The other components of the ultrasonic flow meter 102 are the same as those of the ultrasonic flow meter 101 of the first embodiment, and in the flow measurement mode, the flow rate of the fluid is measured by the same procedure as described in the first embodiment. To do.

  On the other hand, in the ultrasonic transducer monitoring mode, the ultrasonic flowmeter 102 uses the temperature sensor 53 and the temperature measuring unit 41 to place the first ultrasonic transducer 55 and the second ultrasonic transducer 56 in the case 85. Measure temperature directly. The abnormality determination unit 23 converts the resistance value received from the measurement unit 22 into the resistance value at the reference temperature using the measured temperature. When the resistance value is different from the initial value of the first ultrasonic transducer 55 or the second ultrasonic transducer 56 by a predetermined level or more, the abnormality determination unit 23 sets the first ultrasonic transducer 55. Alternatively, a signal indicating that the second ultrasonic transducer 56 is abnormal is output.

  Thus, according to this embodiment, the temperature in the case 85 is directly measured. Since the temperature in the case 85 substantially coincides with the temperature of the piezoelectric elements of the first ultrasonic transducer 55 and the second ultrasonic transducer 56, the change in the resistance value of the piezoelectric element due to the temperature variation is corrected, It is possible to know changes in the characteristics of the first ultrasonic transducer 55 and the second ultrasonic transducer 56 more accurately.

  In addition, the temperature in the case 85 can be directly measured independently of the flow rate measurement. For this reason, when the flow measurement has not been performed for a while using the ultrasonic flowmeter 102, the ultrasonic flowmeter 102 is first set to the ultrasonic vibrator monitoring mode, and the first ultrasonic vibrator 55 and the first ultrasonic vibrator 55 are set. It is also possible to measure the flow rate after determining whether the second ultrasonic transducer 56 is normal.

(Third embodiment)
Hereinafter, a third embodiment of the ultrasonic flowmeter according to the present invention will be described. FIG. 9 schematically shows the structure of the ultrasonic transducer 57 used in this embodiment. The ultrasonic vibrator 57 has a humidity sensor 58 in a case 85 that seals a piezoelectric element including the piezoelectric body 82. The piezoelectric element and the humidity sensor 58 are connected to the wiring 52, and the wiring 52 is drawn out of the case 85. As in the first embodiment, the space 85s of the case 85 is filled with an inert gas.

  In the first and second embodiments, the change in the characteristics of the piezoelectric element is directly measured by measuring the resistance value or the capacitance value of the piezoelectric element. In the present embodiment, however, the humidity sensor 58 is used for the case. Measure humidity in 85 directly.

  FIG. 10 is a block diagram showing a configuration of the ultrasonic flowmeter 103 of the present embodiment. The ultrasonic flow meter 103 includes a first ultrasonic transducer 61 and a second ultrasonic transducer 62. As the first ultrasonic transducer 61 and the second ultrasonic transducer 62, an ultrasonic transducer 57 shown in FIG. 9 is used.

  The ultrasonic flowmeter 103 includes an element switching unit 63 connected to the wiring of the humidity sensor 58 of the first ultrasonic transducer 61 and the second ultrasonic transducer 62, and the element switching unit 63 is the measurement unit 22 ′. Connected to. Further, similarly to the first embodiment, the temperature estimation unit 14 that estimates the temperature of the fluid from the measured flow rate is provided, and the abnormality determination unit 23 receives an estimated temperature signal from the temperature estimation unit. If the humidity sensor 58 of the first ultrasonic transducer 61 and the second ultrasonic transducer 62 detects absolute humidity, the temperature estimating unit 14 may not be provided. Further, as described in the second embodiment, the temperature sensor 53 is provided in the first ultrasonic transducer 61 and the second ultrasonic transducer 62 in place of the temperature estimation unit 14, and the temperature in the case is directly measured. You may measure.

  The humidity sensor 58 may be a resistance type or a capacitance type. When the humidity sensor 58 is a resistance type, a measurement unit 22 ′ having the same configuration as the measurement unit shown in FIG. 3 can be used. On the other hand, when the humidity sensor 58 is an electrostatic capacitance type, in the measurement unit 22 shown in FIG. 3, a measurement unit that employs a capacitive voltage conversion unit instead of the resistance voltage conversion unit 32 is employed in the measurement unit 22 ′. .

  In the present embodiment, the piezoelectric elements of the first ultrasonic transducer 61 and the second ultrasonic transducer 62 are used only for flow rate measurement, and the humidity in the case is measured by the humidity sensor 58. Since the humidity in the case can be measured by the humidity sensor 58 even during the measurement of the flow rate, there is no need to switch between the two operations of the flow rate measurement mode and the ultrasonic transducer monitoring mode. Can be performed in parallel.

  Specifically, the ultrasonic flow meter 103 uses the humidity sensor 58 of the ultrasonic vibrator selected by the element switching unit 63 at a predetermined time interval regardless of whether the flow rate is measured or not. Measure humidity. When the humidity sensor 58 can measure the absolute humidity, it is not necessary to correct the temperature of the measured value. When the measured value differs from the initial value of the humidity sensor 58 by a predetermined level or more, the abnormality determination unit 23 indicates that the first ultrasonic transducer 1 or the second ultrasonic transducer 2 is abnormal. Output a signal. When the humidity sensor 58 measures the relative humidity, the abnormality determination unit 23 converts the measured value into a resistance value or a capacitance value at the reference temperature using the estimated temperature received from the temperature estimation unit 14. When the measured value is different from the initial value of the humidity sensor 58 by a predetermined level or more, the abnormality determination unit 23 indicates that the first ultrasonic transducer 1 or the second ultrasonic transducer 2 is abnormal. A signal indicating is output.

FIG. 10 is a graph showing the change in capacitance with respect to the relative humidity around the piezoelectric element used in the first ultrasonic transducer 1. As shown in FIG. 10, as the relative humidity around the piezoelectric element increases, the piezoelectric body absorbs moisture, the dielectric constant changes, and the capacitance increases. Therefore, for example, in the first ultrasonic vibrator 1, the piezoelectric element enclosed in the inert gas having the relative humidity RH _{0 at} the reference temperature has the initial value of the capacity C ₀ , and the first ultrasonic wave When the capacity of the transducer 1 increases by 5% with respect to the initial value C ₀ , the abnormality determination unit 23 determines that the first ultrasonic transducer 1 is abnormal. At this time, the relative humidity in the case 85 increases to RH ₁ at the reference temperature. Such a change in the relative humidity indicates that the case 85 is damaged such as a crack and the outside air having a high relative humidity flows in.

  According to the present embodiment, since the humidity in the case is measured by the humidity sensor provided in the case of the sealed ultrasonic transducer, the humidity in the case can be measured independently of the flow rate measurement. . For this reason, it becomes possible to monitor the ultrasonic transducer without interrupting the flow rate measurement, and the ultrasonic flow meter according to the present embodiment can be suitably used particularly for applications in which the flow rate needs to be constantly measured. Further, since there is no need to switch between the flow rate measuring operation and the ultrasonic transducer monitoring operation, the mode switching unit is not required, and the configuration of the ultrasonic flowmeter can be simplified. Further, by adopting a humidity sensor that detects absolute humidity, it is not necessary to perform correction by temperature.

(Fourth embodiment)
Hereinafter, a fourth embodiment of the ultrasonic flowmeter according to the present invention will be described. FIG. 12 schematically shows the structure of the ultrasonic transducer 66 used in this embodiment. FIG. 13 shows the structure of a piezoelectric element 67 that is the main part of the ultrasonic transducer 66. As shown in FIG. 13, the piezoelectric element 67 includes a piezoelectric body 82 having a first main surface 2b and a second main surface 2a facing each other, a first electrode 26a provided on the first main surface, and a first main surface 2a. 2 electrodes 26b and a common electrode 27 provided on the second main surface 82a.

  The first electrode 26a is provided at the center of the first main surface 2b, and the second electrode 26b is provided around the first main surface 2b so as to surround the first electrode 26a. The common electrode 27 covers almost the entire second main surface 2a. As shown in FIG. 13, the second electrode 26b preferably has a network structure. The first electrode 26a may also have a network structure. Wirings 52a, 52b and 52c are connected to each electrode.

  The first electrode 26 a applies a voltage to the piezoelectric body 82 and is used for electroacoustic conversion for detecting a voltage generated by the vibration of the piezoelectric body 82. On the other hand, the second electrode 26 b is used for measuring the electrical characteristics of the piezoelectric body 82. More specifically, the electroacoustic transducer element 67a for transmitting and receiving ultrasonic waves is configured by the first electrode 26a and the common electrode 27 and the piezoelectric body 82 sandwiched therebetween. Further, the humidity sensor portion 67b is configured by the second electrode 26b and the common electrode 27 and the piezoelectric body 82 sandwiched between them. The piezoelectric element 67 is housed in the case 85 and sealed in a state where the space 85s in the case is filled with an inert gas.

  In the piezoelectric body 82, the region where the second electrode 26b is formed has little displacement when the piezoelectric body 82 is in a vibrating state, and the ultrasonic wave is relative to the first main surface 82b or the second main surface 82a. It is difficult to inject vertically. For this reason, even if an electrode for electroacoustic conversion is formed in the peripheral portion of the piezoelectric body 82, it is difficult to contribute to accurate flow rate measurement, and the electrode in this portion is used for detecting the characteristics of the piezoelectric body 82. However, the flow rate measurement is not greatly affected.

  FIG. 14 is a block diagram showing the structure of the ultrasonic flowmeter 104 of the present embodiment. The ultrasonic flowmeter 104 includes a first ultrasonic transducer 68 and a second ultrasonic transducer 69, and the first ultrasonic transducer 68 and the second ultrasonic transducer 69 are shown in FIGS. 13 is used. The first electrodes 26 a of the first ultrasonic transducer 68 and the second ultrasonic transducer 69 are each connected to the switching unit 10. The second electrodes 26b are connected to the element switching unit 63, respectively. The other part of the ultrasonic flow meter 104 is configured in the same manner as the ultrasonic flow meter 103 of the third embodiment.

  In the ultrasonic flowmeter 104, the piezoelectric elements 67 of the first ultrasonic vibrator 68 and the second ultrasonic vibrator 69 include an electroacoustic transducer element portion 67a and a humidity sensor portion 67b for transmitting and receiving ultrasonic waves. Including. These can be operated independently, and the characteristics of the ultrasonic transducer can be monitored while measuring the flow rate in the same manner as the ultrasonic transducer 57 shown in FIG.

  Specifically, the flow rate is measured using the electroacoustic transducer elements 67 a of the piezoelectric elements 67 of the first ultrasonic transducer 68 and the second ultrasonic transducer 69. This procedure is the same as the procedure in the flow rate measurement mode described in the first embodiment.

  On the other hand, regardless of whether or not the flow rate is measured using the electroacoustic transducer element 67a, the humidity sensor part 67b of the ultrasonic transducer selected by the element switching unit 63 at a predetermined time interval is used. Measure humidity. The measurement unit 22 ′ measures the resistance value or the capacitance value of the humidity sensor unit 67 b and outputs the value to the abnormality determination unit 23. The abnormality determination unit 23 converts the measured value into a resistance value or a capacitance value at the reference temperature using the estimated temperature received from the temperature estimation unit 14. When the measured value is different from the initial value of the humidity sensor 58 by a predetermined level or more, the abnormality determination unit 23 indicates that the first ultrasonic transducer 1 or the second ultrasonic transducer 2 is abnormal. A signal indicating is output.

  As described above, according to this embodiment, a part of the piezoelectric element is used as an electroacoustic transducer for transmitting and receiving an ultrasonic wave, and a part is used as a humidity sensor. Can do. Moreover, since these two elements can be operated simultaneously, the characteristics of the piezoelectric element can be monitored simultaneously while measuring the flow rate.

  In the ultrasonic vibrator 69 of the present embodiment, the piezoelectric body 82 is not provided with a groove, but a groove as shown in FIG. 1B may be provided in the piezoelectric body 82. In the present embodiment, wiring is connected to the electroacoustic transducer element portion 67a and the humidity sensor portion 67b and pulled out of the case. However, the structure shown in FIG.

(Fifth embodiment)
Hereinafter, the gas meter provided with the ultrasonic flowmeter of the present invention will be described.

  FIG. 15 shows a block diagram of the gas meter 106 for measuring the flow rate of the gas flowing in the pipe 70. The gas flowing in the pipe 70 may be other gases such as hydrogen and oxygen, in addition to those used in general households such as natural gas and propane gas.

  The gas meter 106 controls the ultrasonic flow meter 71 for measuring the flow rate of the gas flowing in the pipe 70, the cutoff valve 72 for shutting off the gas flowing in the pipe 70 in an emergency, the ultrasonic flow meter 71 and the cutoff valve 72. And a display unit 74 that displays the flow rate measured using the ultrasonic flowmeter 106, the integrated value of the flow rate, and other information. As the ultrasonic flow meter 71, the ultrasonic flow meters of the first to fourth embodiments can be used. The microcomputer 73 may be the microcomputer of the ultrasonic flowmeter 71 (the microcomputer 30 in FIG. 2 and the like). As shown in the figure, the gas meter 106 may include a communication unit 75 for transmitting data relating to the measured flow rate to a gas company or the like, or for controlling the gas meter 106 from the gas company.

  The microcomputer 73 displays data on the flow rate measured by the ultrasonic flowmeter 71 on the display unit 74 and monitors whether there is an abnormality in the measured flow rate. For example, when a large flow rate of gas suddenly starts to flow, it is determined that a gas leak has occurred, the shutoff valve 72 is operated, and the gas supply is stopped.

  Further, as described in the first to fourth embodiments, the ultrasonic flowmeter 71 monitors whether the characteristics of the ultrasonic transducer have changed at a predetermined time interval. Instead of a predetermined time interval, when an earthquake or the like occurs, a control signal may be received from a gas company or the like through the communication unit 75, and the characteristics of the ultrasonic transducer may be measured based on the control signal. The resistance value or the capacitance value of the ultrasonic transducer is measured according to the procedure described in the first to fourth embodiments, and the abnormality determination unit 23 indicates that one of the two ultrasonic transducers is abnormal. When the signal is output, the microcomputer 73 operates the shutoff valve 72 based on the signal from the abnormality determination unit 23 to stop the gas supply.

  According to the gas meter 106, the piezoelectric elements of the first and second ultrasonic transducers are housed in a case filled with an inert gas. For this reason, even if the humidity of the outside air changes, the characteristics of the first and second ultrasonic transducers 1 and 2 are kept constant, and flow rate measurement with less error is possible. Even if the gas that corrodes or alters the piezoelectric body 82, the electrode 91, or the like is contained in the outside air, the characteristics of the piezoelectric element do not fluctuate. Therefore, even in such an environment, the gas meter 106 is long. A highly accurate measurement can be performed over a period of time. That is, the gas meter 106 is excellent in reliability.

  On the other hand, when an unexpected impact or environmental change occurs due to an earthquake or the like, and the case of the first ultrasonic transducer or the second ultrasonic transducer is damaged, the outside air flows into the case and the surroundings of the piezoelectric element. Since the humidity of the piezoelectric material changes, the dielectric constant of the piezoelectric material changes. For this reason, the resistance value or the capacitance value of the first ultrasonic transducer 1 and the second ultrasonic transducer 2 is periodically monitored and detected to detect the first ultrasonic transducer 1 and the second ultrasonic transducer 1. It is possible to know that the characteristics of the two ultrasonic transducers 2 have changed and a measurement error has occurred.

  The ultrasonic transducers described in the first to fifth embodiments can be suitably used for measuring devices such as distance meters, speedometers, and the like other than ultrasonic flowmeters. By using the ultrasonic vibrator of the present invention for these measuring instruments, measurement errors are less likely to occur due to changes in the outside air, and when the characteristics of the ultrasonic vibrator change due to unexpected impacts or environmental changes. , A measuring instrument that can know the abnormality is realized.

  In the first to fifth embodiments, the resistance value and the capacitance value are shown as characteristics to be measured in order to detect a change in the dielectric constant of the piezoelectric element. However, in addition to the resistance value and the capacitance value, a current value, a voltage value, or the like may be measured, and based on the change, it may be determined that the case of the ultrasonic transducer has been damaged and the outside air has flowed.

  In the first to fifth embodiments, the ultrasonic wave is propagated bidirectionally using the first ultrasonic transducer and the second ultrasonic transducer, and the flow velocity and flow rate of the fluid are determined by the propagation time difference. I was asking. However, as is clear from the equation (1), when the sound velocity C of the ultrasonic wave in the fluid is known, the propagation time t1 from the first ultrasonic vibrator to the second ultrasonic vibrator or the first By measuring the propagation time t2 from the second ultrasonic transducer to the first ultrasonic transducer, the flow velocity V of the fluid can be obtained. That is, in the first to fifth embodiments, the flow velocity and flow rate of the fluid are obtained by measuring the propagation time of the ultrasonic wave in one direction between the first ultrasonic transducer and the second ultrasonic transducer. Also good.

  According to the present invention, it is possible to obtain an ultrasonic transducer that is not easily affected by outside air or the like, but is capable of sensitively detecting a change in an unexpected environment that causes damage to the case. . By using this ultrasonic transducer, it is possible to obtain an ultrasonic flowmeter that can maintain highly accurate measurement and can detect an abnormality that may cause a detection error.

(A) And (b) is the perspective view and sectional drawing which show the structure of the ultrasonic transducer | vibrator used in 1st Embodiment of the ultrasonic flowmeter by this invention. 1 is a block diagram showing a first embodiment of an ultrasonic flowmeter according to the present invention. It is a block diagram which shows the specific structure of the measurement part shown in FIG. It is a figure explaining the measurement by a sing-around method. It is a graph which shows the impedance change with respect to the relative humidity around the piezoelectric element. It is a figure which shows another example of the electrode structure of the piezoelectric element of an ultrasonic flowmeter. It is sectional drawing which shows the structure of the ultrasonic transducer | vibrator used by 2nd Embodiment of the ultrasonic flowmeter by this invention. It is a block diagram which shows 2nd Embodiment of the ultrasonic flowmeter by this invention. It is sectional drawing which shows the structure of the ultrasonic transducer | vibrator used by 3rd Embodiment of the ultrasonic flowmeter by this invention. It is a block diagram which shows 3rd Embodiment of the ultrasonic flowmeter by this invention. It is a graph which shows the electrostatic capacitance change with respect to the relative humidity of the circumference | surroundings of a piezoelectric element. It is sectional drawing which shows the structure of the ultrasonic transducer | vibrator used in 4th Embodiment of the ultrasonic flowmeter by this invention. It is a perspective view which shows the principal part of the ultrasonic transducer | vibrator used in 4th Embodiment of the ultrasonic flowmeter by this invention. It is a block diagram which shows 4th Embodiment of the ultrasonic flowmeter by this invention. It is a block diagram which shows the structure of the gas meter of this invention. It is a block diagram which shows the conventional ultrasonic flowmeter. It is a graph explaining the zero crossing point of a received signal.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 1st ultrasonic transducer 2 2nd ultrasonic transducer 3 Transmission part 4 Delay part 5 Level detection part 6 Reception part 7 Zero cross detection part 8 Repetition part 9 Timing part 10 Transmission / reception switching part 11 Flow rate calculation part 13 Peak hold Unit 14 temperature estimation unit 20 first mode switching unit 21 second mode switching unit 22 measurement unit 23 abnormality determination unit 82 piezoelectric body 85 case 86 matching layer 101, 102, 103, 104, 105 ultrasonic flowmeter

Claims (14)

An ultrasonic flowmeter that measures the flow rate of fluid flowing through a flow path based on the propagation time of ultrasonic waves,
A first and second piezoelectric element and a case for housing the piezoelectric element in a sealed state are arranged so as to form a path through which ultrasonic waves propagate in a fluid flow path by transmitting and receiving ultrasonic waves. An ultrasonic transducer,
A measuring unit for measuring an electrical characteristic value of the piezoelectric element;
A temperature estimation unit that obtains an ultrasonic sound velocity using the first and second ultrasonic transducers and estimates the temperature of the fluid from the sound velocity;
An abnormality determination unit for determining an abnormality of the first and second ultrasonic transducers based on the electrical characteristic value and the estimated temperature;
An ultrasonic flow meter comprising.   The abnormality determination unit converts the electrical characteristic value using the temperature estimated by the temperature estimation unit, and uses the converted electrical characteristic value to detect abnormality of the first and second ultrasonic transducers. The ultrasonic flowmeter according to claim 1, wherein: An ultrasonic flowmeter that measures the flow rate of fluid flowing through a flow path based on the propagation time of ultrasonic waves,
A piezoelectric element, a case for housing the piezoelectric element in a sealed state, and a temperature sensor housed in the case, and forming a path through which the ultrasonic wave propagates in the fluid flow path by transmitting and receiving ultrasonic waves First and second ultrasonic transducers arranged to
A measuring unit for measuring an electrical characteristic value of the piezoelectric element;
An ultrasonic flowmeter comprising: an abnormality determining unit that determines abnormality of the first and second ultrasonic transducers based on the electrical characteristic value and the temperature in the case measured by the temperature sensor.   The abnormality determining unit converts the electrical characteristic value using the temperature in the case measured by the temperature sensor, and uses the converted electrical characteristic value to convert the first and second ultrasonic vibrations. The ultrasonic flowmeter according to claim 3, wherein a child abnormality is determined. An ultrasonic flowmeter that measures the flow rate of fluid flowing through a flow path based on the propagation time of ultrasonic waves,
A piezoelectric element, a case for housing the piezoelectric element in a sealed state, and a humidity sensor housed in the case, and forming a path through which the ultrasonic wave propagates in the fluid flow path by transmitting and receiving ultrasonic waves First and second ultrasonic transducers arranged to
A measurement unit for measuring an electrical characteristic value of the humidity sensor;
An ultrasonic flowmeter comprising: an abnormality determining unit that determines abnormality of the first and second ultrasonic transducers based on the electrical characteristic value.   Each of the first and second ultrasonic transducers further includes a temperature sensor housed in the case, and the abnormality determination unit uses the temperature obtained by the temperature sensor to calculate the electrical characteristic value. 6. The ultrasonic flowmeter according to claim 5, wherein the ultrasonic flowmeter is converted and an abnormality of the first and second ultrasonic transducers is determined using the converted electrical characteristic value.   The ultrasonic flowmeter according to claim 1, wherein the electrical characteristic value is a resistance value or a capacitance value. A piezoelectric element and a case for housing the piezoelectric element in a sealed state, the first and second ultrasonic vibrators arranged to form a path for ultrasonic waves to propagate in a fluid flow path, An ultrasonic flowmeter control method for measuring a flow rate of a fluid by transmitting and receiving ultrasonic waves between first and second ultrasonic transducers and detecting a propagation time of ultrasonic waves propagating between the paths. ,
Obtaining information on electrical characteristic values of the piezoelectric element;
A temperature estimation step of obtaining an ultrasonic sound speed using the first and second ultrasonic vibrators, and estimating a temperature of the fluid from the sound speed;
Determining whether the first and second ultrasonic transducers are abnormal based on the estimated temperature and the information of the electrical characteristic values;
A method for controlling an ultrasonic flowmeter including:   In the determining step, the electrical characteristic value is converted using the temperature estimated in the temperature estimating step, and the abnormalities of the first and second ultrasonic transducers are converted using the converted electrical characteristic value. The method for controlling an ultrasonic flowmeter according to claim 8, wherein: A piezoelectric element, a case for housing the piezoelectric element in a sealed state, and a temperature sensor housed in the case, are arranged so as to form a path for ultrasonic waves to propagate in a fluid flow path. And a second ultrasonic transducer, transmitting and receiving ultrasonic waves between the first and second ultrasonic transducers, and detecting a propagation time of the ultrasonic waves propagating between the paths to control the flow rate of the fluid A method for controlling an ultrasonic flowmeter to be measured,
Obtaining information on electrical characteristic values of the piezoelectric element;
A temperature estimation step of measuring temperature by the temperature sensor;
Determining whether the first and second ultrasonic transducers are abnormal based on the temperature in the case measured by the temperature sensor and information on the electrical characteristic values;
A method for controlling an ultrasonic flowmeter including:   The determining step converts the electrical characteristic value using the temperature measured by the temperature sensor, and uses the converted electrical characteristic value to determine abnormality of the first and second ultrasonic transducers. The method of controlling an ultrasonic flowmeter according to claim 10 for determination. A piezoelectric element, a case for housing the piezoelectric element in a sealed state, and a humidity sensor housed in the case, are arranged so as to form a path for ultrasonic waves to propagate in a fluid flow path. And a second ultrasonic transducer, transmitting and receiving ultrasonic waves between the first and second ultrasonic transducers, and detecting a propagation time of the ultrasonic waves propagating between the paths to control the flow rate of the fluid A method for controlling an ultrasonic flowmeter to be measured,
A humidity estimation step for measuring an electrical characteristic value of the humidity sensor;
Determining whether the first and second ultrasonic transducers are abnormal based on the electrical characteristic values;
A method for controlling an ultrasonic flowmeter including:   Each of the first and second ultrasonic transducers further includes a temperature sensor housed in the case, and the determining step uses the temperature obtained by the temperature sensor to calculate the electrical characteristic value. The method of controlling an ultrasonic flowmeter according to claim 12, wherein the abnormalities of the first and second ultrasonic transducers are determined using the converted electrical characteristic values.   The method for controlling an ultrasonic flowmeter according to claim 8, wherein the electrical characteristic value is a resistance value or a capacitance value.

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