JP5111847B2 - Ultrasonic flow meter - Google Patents

Description

  The present invention relates to an ultrasonic flowmeter.

JP 2004-251653 A

  Conventionally, an ultrasonic flowmeter for measuring a flow rate of city gas or water is known. In general, a “propagation time difference method” is used as a measurement principle at that time. This is provided with a pair of ultrasonic transmission / reception units upstream and downstream in the fluid flow direction of the flow path, alternately switching the ultrasonic transmission / reception direction between the ultrasonic transmission / reception units, and transmitted from the upstream ultrasonic transmission / reception unit. The time until the ultrasonic beam reaches the downstream ultrasonic transmission / reception unit (forward propagation time) and the time until the ultrasonic beam transmitted from the downstream ultrasonic transmission / reception unit reaches the upstream ultrasonic transmission / reception unit Time (reverse propagation time) is measured, and the average flow velocity and flow rate of the fluid flowing through the flow path are obtained from the time difference between the two (for example, Patent Document 1).

In the ultrasonic transmission / reception unit (ultrasonic transducer) used in the flow meter as described above, the vibration driving unit is constituted by a piezoelectric ceramic diaphragm. The flow meter, ultrasonic transmitting and receiving unit is used over a long term, have recently been envisaged also request age exceeds 10 years. During such long-term use, the output characteristics of the ultrasonic transmission / reception unit may drift due to aging of the vibration drive unit. In recent years, specs required for flowmeters have become more and more severe, and there is a concern that the above-described deterioration may make it impossible for the ultrasonic transmitting / receiving unit to meet the required service life. If the zero point of the flow rate output drifts, the measurement accuracy of the flow rate will deteriorate, leading to an inability to perform accurate measurement.

  Specifically, in the ultrasonic transmission / reception unit, there is a certain time delay from when the vibration driving unit is driven to when the ultrasonic wave is emitted into the fluid to be measured (medium: city gas, for example). That is, as shown in FIG. 7, when an external driving signal is received, the signal is converted into mechanical vibration by the piezoelectric ceramic diaphragm, and further propagated through the acoustic impedance matching layer and radiated to the fluid to be measured. Therefore, there is a certain delay time from the input timing of the driving signal until the ultrasonic wave is emitted to the fluid to be measured.

  In the conventional flow rate measurement, the emission timing of the ultrasonic wave to the fluid to be measured is replaced with the input timing of the drive signal and used as a measurement start point of the ultrasonic propagation time. If the delay time from the input timing of the drive signal to the emission timing of the ultrasonic wave to the fluid to be measured is constant, the contribution of the delay time to the measurement error is also constant and can be easily corrected. If the fluctuation varies with the deterioration of the vibration drive unit over time, the contribution is not constant, and correction is no longer possible. For example, if the initial zero point flow rate of the ultrasonic transmission / reception unit stored at the time of shipment from the factory drifts with time, it may be erroneously measured that there is a flow even though there is no flow, or conversely there is no flow even though there is a flow It will cause problems that you may recognize.

  An object of the present invention is to provide an ultrasonic flowmeter that can accurately measure a flow rate by correcting a delay time of an ultrasonic element.

Means for Solving the Problems and Effects of the Invention

In order to solve the above problems, the ultrasonic flowmeter of the present invention is
A flow path forming section for forming a flow path of the fluid to be measured;
Ultrasonic wave transmission / reception having piezoelectric ceramic diaphragms that are provided at different positions in the flow direction of the fluid to be measured with respect to the flow path forming part and polarized in the plate thickness direction, and electrodes formed on the piezoelectric ceramic diaphragm It is equipped with an element and functions so that one side becomes a transmission side of measurement ultrasonic waves to the fluid to be measured and the other side becomes a reception side of measurement ultrasonic waves, and each of the measurement ultrasonic waves has a predetermined orientation. A pair of ultrasonic transmission / reception units capable of transmitting an ultrasonic beam having directivity to,
Drive voltage application means for applying a pulsed drive voltage to the ultrasonic transmission / reception unit;
A propagation time measuring means for measuring a propagation time of an ultrasonic beam transmitted from an ultrasonic transmission / reception unit on a transmission side until reaching an ultrasonic transmission / reception unit on a reception side;
Flow rate calculating means for calculating the flow rate of the fluid to be measured based on the measured propagation time;
Propagation time measurement means
Monitor output voltage waveform acquisition means for acquiring an acoustic vibration waveform generated in the piezoelectric ceramic diaphragm of the ultrasonic transmission / reception unit as a monitor output voltage waveform generated in the electrode when a drive voltage is applied to the transmission / reception ultrasonic transmission / reception unit ,
Correction information generating means for generating propagation time correction information based on the acquired monitor output voltage waveform;
A propagation time correcting means for correcting the measured propagation time based on the correction information;
It is assumed that

  According to the above invention, the pair of ultrasonic transmission / reception units is provided on the upstream side and the downstream side of the flow path, and the ultrasonic beam is transmitted from one to the other. The ultrasonic transmission / reception unit includes a piezoelectric ceramic diaphragm and an electrode formed on the piezoelectric ceramic diaphragm. Then, the propagation time of the ultrasonic beam is measured by the propagation time measuring means, and the flow rate of the fluid to be measured flowing through the flow path is calculated based on the propagation time. When a drive voltage is applied to the ultrasonic transmission / reception unit, the piezoelectric ceramic diaphragm vibrates to generate an acoustic vibration waveform, which is extracted from the electrode as a monitor output voltage waveform. Then, propagation time correction information is generated based on the monitor output voltage waveform, and the propagation time of the ultrasonic beam is corrected based on the correction information. In this way, even if the delay time from when the drive voltage is applied to the ultrasonic transmission / reception unit to when the ultrasonic wave is sent drifts over time, the value is reflected in the correction, so flow measurement is accurate over many years. Can be performed.

  In this case, the correction information generation means can determine a measurement reference point of propagation time as correction information on the monitor output voltage waveform. In this way, the time from the input timing of the drive signal to the measurement reference point is used as the correction information, and the propagation time of the ultrasonic beam can be corrected using this correction information. Therefore, even when the time from the input timing of the drive signal to the measurement reference point drifts over time, the net propagation time of the ultrasonic beam (the ultrasonic reception unit on the receiving side from the measurement reference point is not affected by the value). The time until the ultrasonic wave is received can be obtained.

  More specifically, the correction information generating means determines a zero-cross point in a predetermined order generated in the monitor output voltage waveform as a measurement reference point, measures a delay time t0 from the drive signal input timing to the measurement reference point, and transmits the propagation time measurement means. The time from the input timing of the drive signal measured to the zero cross point of the predetermined order of the arrival waveform generated in the ultrasonic transmission / reception unit on the receiving side is calculated as the original measurement time tx, and the propagation time is calculated as tx−t0. . That is, the delay time t0 and the original measurement time tx are measured, and the propagation time of the ultrasonic beam is calculated as tx−t0. Thereby, even when the delay time t0 drifts in time, the time during which the ultrasonic beam actually propagates can be measured accurately. Therefore, the flow rate can be measured accurately.

In this case, the propagation time correction means is
A delay time storage means for storing a delay time t0 measured at a predetermined reference temperature;
Propagation time correction calculation means for reading the delay time t0 from the delay time storage means and correcting and calculating the propagation time as tx−t0 as the propagation time measurement means measures and acquires the original measurement time tx for flow rate measurement;
Fluid temperature measuring means for measuring the temperature of the fluid to be measured;
A delay time measuring means for measuring the delay time t0 ′ as a predetermined calibration timing arrives when the temperature measured by the temperature measuring means reaches the reference temperature;
Delay time updating means for updating the stored contents of the delay time storage means with the measured and acquired delay time t0 ′;
Can be equipped with In this way, the delay time t0 is stored in the delay time storage means, and the original measurement time tx-t0 is calculated using this stored value, so there is no need to measure the delay time t0 every time the flow rate is measured. . Further, since the delay time t0 of the ultrasonic element deteriorates with time, the delay time t0 ′ is periodically measured and the value is updated. Therefore, accurate flow measurement can be performed for many years. Since the delay time t0 of the ultrasonic element also changes depending on the temperature, the measurement of the delay time t0 ′ is performed when the temperature of the fluid to be measured has reached a predetermined reference temperature (calibration timing). ing.

  In this case, the calibration timing may be determined so as to arrive at a lower frequency than the flow rate measurement timing by the propagation time measuring means. That is, the frequency of measuring the delay time t0 may be less than the frequency of measuring the flow rate (frequency of measuring the ultrasonic propagation time). For example, the delay time t0 is measured once every six months or once a year. This eliminates the need to frequently measure the delay time t0, leading to lower power consumption of the ultrasonic flowmeter.

For example, in the propagation time correction means, only one reference temperature is determined, and the delay time storage means stores the delay time measured at the reference temperature, and further includes the delay time and the temperature stored in advance. A delay time calibration line determining means for determining a delay time calibration line based on the coefficient, and
The propagation time measuring means can measure the propagation time at an arbitrary temperature, read the delay time corresponding to the measured temperature at which the propagation time was measured from the delay time calibration line, and use this to calculate the propagation time. . In this way, even when the temperature at which the flow rate measurement is performed is different from the reference temperature at which the delay time t0 is measured, the delay time t0 is read from the delay time calibration line and the propagation time is calculated (tx−t0). Can be used. In other words, it is possible to correct the change in the delay time t0 of the ultrasonic element due to temperature and perform accurate flow measurement. If only one point is set as the reference temperature and the delay time calibration line is determined using only the reference temperature coefficient, the delay time calibration line can be defined only by determining only the intercept. Therefore, the method for determining the delay time calibration line can be simplified. The temperature coefficient is measured for each ultrasonic flowmeter at the time of factory shipment, and the value may be stored. If there is not much difference between products, the representative average value is adopted and stored. Also good.

Further, in the propagation time correction means, the reference temperatures are determined at a plurality of points different from each other, and the delay time storage means stores the delay times respectively measured at the plurality of reference temperatures, and further the delay time storage means A delay time calibration curve determining means for determining a delay time calibration curve based on a plurality of reference temperatures stored in
The propagation time measurement means may measure the propagation time at an arbitrary temperature, read the delay time corresponding to the measured temperature at which the propagation time was measured from the delay time calibration curve, and calculate the propagation time using this. Good. In this case, since the delay time t0 is measured and stored at a plurality of points different from each other, the relationship between the temperature and the delay time t0 (delay time calibration curve) can be accurately determined as compared with the case where only one point is measured. it can.

Next, the drive voltage applying means applies a pulsed drive voltage to the ultrasonic transmission / reception unit a plurality of times in a single flow rate measurement,
The correction information generation means can average the timings of occurrence of a plurality of zero cross points generated in the monitor output voltage waveform derived from a plurality of pulsed drive voltages, and determine it as a measurement reference point. In this way, since the pulsed driving voltage is continuously applied to the ultrasonic transmission / reception unit a plurality of times, the vibration of the ultrasonic transmission / reception unit can be stabilized. In addition, since the measurement reference point is determined by averaging the occurrence timings of a plurality of zero cross points, the time from the input of the drive voltage to the measurement reference point can be stabilized. It becomes possible to calculate tx-t0 with high accuracy. In this case, a plurality of drive signals are applied until the vibration of the ultrasonic transmission / reception unit is stabilized, and the measurement reference point is determined by averaging the occurrence timings of the zero cross points for the drive signals subsequently input. It is preferable.

Next, the ultrasonic transmitting / receiving element
A main electrode pair formed so as to sandwich the piezoelectric ceramic diaphragm so as to cover each main surface of the piezoelectric ceramic diaphragm, to which a driving voltage is applied to ultrasonically vibrate the piezoelectric ceramic diaphragm,
A monitor partial electrode for taking out a piezoelectric monitoring signal of ultrasonic vibration generated on the piezoelectric ceramic diaphragm when a drive voltage is applied; ,
The monitor output voltage waveform acquisition means can extract the piezoelectric monitoring signal of the monitor partial electrode as a monitor output voltage waveform. In this way, in order to take out the piezoelectric monitoring signal of the ultrasonic vibration generated in the piezoelectric ceramic diaphragm due to the application of the driving voltage, in addition to the driving electrode, in the piezoelectric ceramic diaphragm forming the main part of the vibration driving unit. Since the monitoring partial electrode is provided, the vibration waveform of the piezoelectric ceramic diaphragm to which the drive signal is input can be monitored in real time. As a result, the delay time can be accurately measured. In addition, in order to obtain a piezoelectric monitoring signal using an ultrasonic element that does not have a partial electrode for monitoring, it is necessary to switch the switch immediately after inputting the driving signal and to extract the piezoelectric monitoring signal from the driving electrode. However, if the monitor is provided with the partial electrode as described above, it is not necessary to switch the switch quickly, so that the burden on the circuit can be reduced. In addition, since it is not necessary to use a circuit that is faster than necessary, the cost can be reduced.

  For example, by monitoring the waveform of the partial electrode for monitoring, when the ultrasonic vibration is actually generated in the piezoelectric ceramic diaphragm, including the delay in the piezoelectric ceramic diaphragm after the drive signal is input. I can know. Therefore, if the time from the input timing of the drive signal to the appearance of the vibration waveform at the output of the monitor partial electrode is measured, the delay time from the input timing of the drive signal to the release timing of the ultrasonic wave to the fluid to be measured can be accurately determined. I can grasp. In particular, even when the delay time fluctuates with the deterioration of the vibration drive unit with time, by specifying the delay time by monitoring the output of the monitoring partial electrode, the ultrasonic propagation time can be measured as the measurement target of the ultrasonic wave. Therefore, the zero point flow rate of the ultrasonic output element is not easily affected by drift over time. Of course, it is also possible to detect the timing at which a specific vibration waveform appears in the output of the monitoring partial electrode and use this as a measurement standard for the ultrasonic propagation time. In this case, it is not always necessary to specify the delay time itself by measurement.

  In the above case, the main electrode pair includes a ground electrode that covers the first main surface of the piezoelectric ceramic diaphragm and a drive electrode that also covers the second main surface, and the monitor partial electrode includes the ground electrode and the drive electrode. It is desirable that the covering area of the piezoelectric ceramic diaphragm be smaller than any of the above.

  In addition, since it is necessary to provide the voltage reference for the output of the monitor partial electrode by grounding, the configuration in which the drive electrode and the monitor partial electrode share the ground electrode simplifies the structure of the vibration drive unit. This is also convenient. Specifically, the drive electrode has a smaller covering area on the piezoelectric ceramic diaphragm than the ground electrode, and a monitor partial electrode is formed in the remaining area not covered by the drive electrode on the second main surface of the piezoelectric ceramic diaphragm. Good.

  In this case, if the partial electrode for monitoring is formed in the outer peripheral area of the second main surface of the piezoelectric ceramic diaphragm, the influence of the partial electrode for monitoring on the vibration drive characteristics of the piezoelectric ceramic diaphragm can be reduced. it can.

  When the piezoelectric ceramic diaphragm is formed in a disk shape, the drive electrode can be formed to have a circular outer peripheral shape along the outer peripheral edge of the piezoelectric ceramic diaphragm. In this case, it is possible to cut out a part of the drive electrode in such a manner that a part of the circular outer peripheral edge is recessed inwardly in the radial direction, and a monitor partial electrode can be formed inside the cutout region. In this way, it is possible to easily form an output output wire and a soldering portion while sufficiently reducing the formation area of the monitor partial electrode.

  Further, the outer peripheral edge on the drive electrode side is formed at a position adjacent to the monitor partial electrode by forming a gap with a predetermined width between the drive electrode and the monitor partial electrode. It can be formed in a shape that follows the periphery. This minimizes the exposed portion between the drive electrode and the monitor partial electrode, which is a dead area in the vibration drive of the piezoelectric ceramic diaphragm, while ensuring insulation between the drive electrode and the monitor partial electrode. be able to. The width of the gap formed between the drive electrode and the monitor partial electrode is preferably 0.5 mm or more and 2.5 mm or less. If the thickness is 0.5 mm or less, sufficient insulation between the drive electrode and the monitor partial electrode may not be ensured (for example, bridging due to plating failure or conductive foreign matter adhesion), and if the thickness is 2.5 mm or less, the piezoelectric ceramic diaphragm This leads to a problem that the dead area on the vibration drive increases so much that the drive efficiency of the ultrasonic vibration is lowered.

The piezoelectric ceramic diaphragm can be disposed in the casing such that the second main surface side on which the drive electrode and the monitor partial electrode are formed faces the bottom inner surface of the casing. In this case, the drive electrode and the monitor partial electrode can be connected to the drive terminal and the monitor terminal that are formed to protrude from the bottom rear surface of the casing. As a result, it is possible to shorten the routing distance of the conduction path to the drive terminal and the monitor terminal of the drive electrode and the partial electrode for monitoring, simplify the wiring structure, and improve the reliability. In this case, an insulating layer can be disposed between the piezoelectric ceramic diaphragm and the bottom of the casing. The drive terminal, the drive electrode, the monitor terminal, and the monitor partial electrode can be bonded by individual wires penetrating the insulating layer, so that the length of the bonding wire can be reduced. Thereby, improvement in noise resistance, avoidance of mechanical interference between electrode wires, and the like can be achieved. It is also possible to adopt a configuration in which the connection end of the drive terminal and the monitor terminal is a pad formed on the substrate, and the drive electrode and the monitor partial electrode are surface-mounted here.

  On the other hand, the conduction path to the ground electrode is formed so as to wrap around from the second main surface side of the piezoelectric ceramic diaphragm to the first main surface side through the side peripheral surface of the piezoelectric ceramic diaphragm. In this case, the ground electrode can be connected via the conduction path to the ground terminal protruding from the bottom rear surface of the casing. Thereby, the ground terminal, the drive terminal, and the monitor terminal can be assembled on the back surface of the casing, and connection of a cable connector or the like is easy.

Further, the piezoelectric ceramic diaphragm can be disposed at a desired position in the opening opposite to the bottom of the casing. In this case, an acoustic impedance matching layer having an ultrasonic emission surface formed on the main surface opposite to the contact side with the piezoelectric ceramic diaphragm so as to close the opening is formed on the first main surface of the piezoelectric ceramic diaphragm. It can be provided in close contact with the formed ground electrode. By arranging the acoustic impedance matching layer in close contact with the piezoelectric ceramic diaphragm, it is possible to increase the radiation efficiency of ultrasonic waves from the piezoelectric ceramic diaphragm or the reception efficiency of ultrasonic waves by the piezoelectric ceramic diaphragm.

In the above configuration, the conduction path can be a wire whose one end is soldered to the ground electrode on the first main surface side of the piezoelectric ceramic diaphragm. In this case, by forming a concave portion that accommodates the soldered portion of the wire on the surface of the acoustic impedance matching layer that faces the ground electrode, accompanying the adhesion between the piezoelectric ceramic diaphragm and the acoustic impedance matching layer, Interference between the soldered portion and the acoustic impedance matching layer can be avoided, and the soldered portion can be protected. Further, it is not necessary to provide a pad conducting to the ground electrode on the first main surface side of the piezoelectric ceramic diaphragm, and a large area of the drive electrode can be secured.

As another configuration, the wiring portion is connected to the ground electrode at one end, and is grounded formed on the first main surface of the piezoelectric ceramic diaphragm so that both the drive electrode and the monitor partial electrode are insulated and separated. A ground lead layer formed on the peripheral side surface of the piezoelectric ceramic diaphragm so that the other end is connected to the connection pad, and a wire having one end soldered to the ground connection pad and the other end soldered to the ground terminal Can also be formed. In this way, it eliminates soldering portions of the ground wires from the first main surface side of the piezoelectric ceramic diaphragm, it is possible to contact disposed an acoustic impedance matching layer over the entire surface of the ground electrode, ultrasonic radiation efficiency ( Alternatively, the reception efficiency of ultrasonic waves can be further increased.

As another configuration, the casing is made of a metal member in which a bottom portion of the casing, a side wall portion that rises from a peripheral edge of the bottom portion, and a top surface portion that closes an opening opposite to the bottom portion of the side wall portion are electrically connected to each other. Can be formed. In this case, the ground electrode that covers the first main surface of the piezoelectric ceramic diaphragm on the inner surface of the top surface portion may be disposed in close contact via the conductive adhesive layer, and the ground electrode may be grounded via the casing. it can. With this configuration, the casing can be used as a grounding path for driving, and the grounding wiring portion can be simplified. In this case, an acoustic impedance matching layer having an ultrasonic emission surface formed on the main surface opposite to the contact surface with the top surface portion can be disposed in close contact with the outer main surface of the top surface portion, and the radiation efficiency of the ultrasonic waves (Or ultrasonic reception efficiency) can be increased.

  Next, the drive voltage applying means can apply the drive voltage to the main electrode pair without applying the drive voltage to the monitoring partial electrode. If it does in this way, the partial electrode for a monitor can be previously connected to the circuit for detecting a piezoelectric monitoring signal. That is, it is not necessary to switch to the signal detection circuit after applying the drive voltage to the monitor partial electrode.

  In addition, a changeover switch is provided to connect the monitor partial electrode to either the drive voltage power supply line or the piezoelectric monitoring signal output line in a switchable manner, and the drive voltage application means connects the monitor partial electrode to the power supply line. Thus, the drive voltage may be applied to the monitoring partial electrode together with the main electrode pair, and then the changeover switch may be switched to the output line side of the piezoelectric monitoring signal. In this way, since the drive voltage can be applied to the monitor partial electrode as well as the main electrode pair, the transmission efficiency of the ultrasonic beam can be increased.

  Next, a changeover switch for connecting the main electrode to the drive voltage power supply line and the piezoelectric monitoring signal output line is provided so as to be switchable, and the drive voltage application means connects the main electrode to the power supply line. Alternatively, a drive voltage may be applied, and then the changeover switch may be switched to the output line side of the piezoelectric monitoring signal. In this way, the piezoelectric monitoring signal can be taken out from the main electrode pair after the drive voltage is applied. For this reason, a signal having a relatively large amplitude can be taken out as the piezoelectric monitoring signal, so that it is less susceptible to noise and the like.

  On the other hand, the drive voltage applying means applies a pulsed drive voltage to the ultrasonic transmission / reception unit a plurality of times in a single flow rate measurement, and the last of the plurality of pulsed drive voltages. This can be applied as a marker pulse having a pulse voltage amplitude larger than that of the remaining preceding one. If it does in this way, vibration of an ultrasonic transceiver part can be stabilized.

Embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows the basic configuration of an embodiment of an ultrasonic flow meter used as a general residential gas meter or the like. FIG. 2 is an enlarged cross-sectional view of the ultrasonic transmission / reception unit 2. The ultrasonic flowmeter 1 is provided with a flow path forming part 3 that forms a flow path of the fluid to be measured GF, and a position different from each other in the flow direction O of the fluid to be measured GF with respect to the flow path forming part 3. An ultrasonic transmitting / receiving element having a piezoelectric ceramic diaphragm 21 (see FIG. 2) polarized in the thickness direction and electrodes 22 to 24 formed on the piezoelectric ceramic diaphragm 21 is provided, one of which is a fluid GF to be measured. The ultrasonic beam SW functions to be a measurement ultrasonic wave transmission side and the other is a measurement ultrasonic wave reception side, and has directivity in a predetermined direction as each measurement ultrasonic wave. And a pair of ultrasonic transmission / reception units 2 capable of transmitting. The flow path forming unit 3 and the ultrasonic transmission / reception units 2a and 2b constitute a flow meter main body 1M, and the flow meter main body 1M and the control circuit unit 1E constitute the entire ultrasonic flow meter 1.

  The flow path forming unit 3 is made of metal, for example. When the measurement target is gas, the axial cross-sectional shape of the flow path forming unit 3 only needs to form a space closed by the wall 3J. For example, any one of a circular shape, an elliptical shape, a square shape, a rectangular shape, etc. May be adopted. In the present embodiment, the flow path forming unit 3 is formed to have a rectangular channel cross section, the upstream ultrasonic wave transmitting / receiving unit 2a on the upper wall 3Ja, and the downstream ultrasonic wave transmitting / receiving unit on the lower wall 3Jb. 2b is attached. That is, the ultrasonic transmission / reception units 2a and 2b forming a pair are distributed and arranged so as to sandwich the flow path.

  The ultrasonic transmission / reception units 2a and 2b are ultrasonic transducers having an ultrasonic transducer. Each of them includes a composite of an ultrasonic transmission function for transmitting an ultrasonic beam by applying a driving voltage and an ultrasonic reception function for outputting an electric signal (reception signal) by receiving an ultrasonic beam. Since they all have the same structure, they will be described as representatives (hereinafter represented by reference numeral “2”).

  Next, the ultrasonic flowmeter 1 includes a driving voltage applying means (transmitting unit) 5 that applies a pulsed driving voltage to the ultrasonic transmitting / receiving unit 2 and an ultrasonic wave transmitted from the transmitting / receiving ultrasonic transmitting unit 2. A propagation time measuring means (control circuit) 1E for measuring the propagation time of the beam SW until it reaches the ultrasonic transmission / reception unit 2 on the receiving side, and the flow rate of the fluid GF to be measured is calculated based on the measured propagation time. And a flow rate calculation means (calculation unit) 11.

  Further, the propagation time measuring means 1E monitors the acoustic vibration waveform generated in the piezoelectric ceramic diaphragm 21 of the ultrasonic transmission / reception unit 2 and outputs the monitor output generated in the electrodes as the driving voltage is applied to the ultrasonic transmission / reception unit 2 on the transmission side. Monitor output voltage waveform acquisition means (reception unit) 6 that acquires as a voltage waveform, correction information generation means 8 that generates correction information of propagation time based on the acquired monitor output voltage waveform, and correction information on the measured propagation time And a propagation time correction means (calculation unit) 11 for correcting based on the above.

  According to the above invention, the propagation time of the ultrasonic beam SW is measured by the propagation time measuring means 1E, and the flow rate of the fluid GF to be measured flowing through the flow path is calculated based on the propagation time. When a driving voltage is applied to the ultrasonic transmission / reception unit 2, the piezoelectric ceramic diaphragm 21 vibrates to generate an acoustic vibration waveform, which is extracted from the electrode 24 as a monitor output voltage waveform. Then, propagation time correction information is generated based on the monitor output voltage waveform, and the propagation time of the ultrasonic beam SW is corrected based on the correction information. In this way, even when the delay time from when the drive voltage is applied to the ultrasonic transmission / reception unit 2 to when the ultrasonic wave is transmitted drifts over time, the delay time is reflected in the correction. Can be performed.

  FIG. 26 shows a block diagram of the calculation unit 11. As described above, the calculation unit 11 includes the CPU 111, the ROM 112, the RAM 113, the I / O 114, and the line 115 that connects these components. The ROM 112 stores a control program 112a, and the CPU 111 reads out and executes the control program 112a, whereby the flow rate calculation means, the propagation time correction means, the propagation time correction calculation means, the delay time measurement means, the delay time of the present invention. A time update unit, a delay time calibration straight line determination unit, and a delay time calibration curve determination unit are realized. The RAM 113 also has a temperature coefficient storage area 113a for storing the temperature coefficient when the delay time calibration line is determined, an intercept storage area 113b for storing the intercept, and a delay measured at the reference temperature Ta. A measurement data storage area 113c for storing time measurement data is provided.

  FIG. 4 shows a detailed example of the circuit configuration of FIG. In each of the two ultrasonic transmission / reception units 2a and 2b, the ground terminals 41a and 41b are connected to the ground line GND via individual switches SW3 and SW4. The ground line GND can be switched between ground conduction and float by starting the switch SW5. On the other hand, the drive terminals 43a and 43b are connected to the drive input line INP by switches SW1 and SW2 so as to be selectively switchable. The monitor terminals 44a and 44b are alternatively connected to the monitor line MNT by switches SW8 and SW9. Further, the drive input line INP and the monitor line MNT are connected to the amplifying unit 7 so as to be selectively switchable by switches SW6 and SW7.

  On the drive input line INP, a bootstrap circuit 51 for impedance conversion composed of parallel bidirectional diode pairs is provided. An overvoltage protection circuit 52 composed of a parallel bidirectional diode pair is disposed between the monitor line MNT and the ground line GND. Further, a resistor R2 is inserted between the drive input line INP and the ground line GND for improving noise resistance and stabilizing the drive input voltage. In addition, a resistor R1 for adjusting the input impedance to the amplifying unit 7 is inserted on the monitor line MNT. The amplifying unit 7 includes a charge amplifier 71 that converts a change in the amount of charge generated in the piezoelectric ceramic diaphragm from the upper input side, and an inverting amplifying unit 72 that inverts and amplifies the output voltage of the charge amplifier 71.

  FIG. 5 shows an example of the circuit configuration of the zero cross comparator unit 9. The waveform output input signal of the amplifying unit 7 is the same as the first comparator 91 that squares the input signal on the basis of the GND, and the lower limit amplitude ( The distribution is input to the second comparator 92 that forms a square wave while regulating the amplitude lower limit value Vs). The output of the first comparator 91 is input to the set terminal of the set-reset flip-flop (RSFF) circuit 93, the output of the second comparator 92 is also input to the reset terminal, and the output change edge of the set-reset flip-flop (RSFF) circuit 93 The zero cross point pulse generation circuit 94 constituted by a monostable circuit outputs a pulse waveform corresponding to the zero cross point by the half wave exceeding the amplitude Vs in the input waveform from the amplifier 7. This pulse waveform is measured by a pulse counter circuit 95 that operates in synchronization with the clock input from the clock pulse generation circuit 96, and a propagation time detection signal is output by counting a prescribed number of pulse inputs.

  FIG. 6 is a timing chart showing an operation sequence of each unit. The amplified output (Va) of the vibration waveform excited by the drive pulse input is square-waved by the first comparator 91 (Vb1), while the second comparator 92 is the inverted waveform with the amplitude Vs as a threshold value. Is squared. As a result, the square wave output of the first comparator 91 is latched by the RSFF circuit 93 only when a half wave exceeding the amplitude Vs is input, and an input edge serving as a pulse output trigger to the zero cross point pulse generation circuit 94 is generated. . In the present embodiment, it is recognized from the zero cross point of the predetermined order wave of the initial vibration waveform whose amplitude gradually increases (here, the zero cross point of the second positive half wave (that is, the third zero cross point from the waveform start point)). The amplitude threshold value of the second comparator 92 is determined.

  The circuit of FIG. 4 operates as follows (switch switching driving is performed by the calculation unit 11 of FIG. 1 executing the control program 112a). First, a drive signal pulse is input to the upstream ultrasonic transmission / reception unit 2a. At this time, SW1, SW7, and SW8 are turned on, and SW3, 4, and 5 are also turned on. On the other hand, SW2, SW6 and SW9 are turned off. As a result, the upstream ultrasonic transmission / reception unit 2a is vibrated and excited at the drive terminal 43a, and a drive monitor waveform appears at the monitor terminal 44a after the delay time described above. This waveform is input from the amplifying unit 7 to the zero cross comparator 9 via the monitor line MNT (SW7), and as described above, the zero cross point of the predetermined rank wave is specified, and the propagation time detection signal is output to the time measuring circuit 10. . The time measurement circuit 10 measures the time from the input timing of the drive signal to the zero cross point of the monitor waveform as a delay time t0 (FIG. 7).

  As will be described later, in the present invention, the measurement frequency of the delay time t0 is reduced, for example, once every six months. Then, the delay time t0 is stored. When normal flow rate measurement is performed, the drive signal pulse is input to the upstream ultrasonic transmission / reception unit 2a, the switch is switched, and the time tx until the zero cross signal is detected from the downstream ultrasonic transmission / reception unit 2b is measured. Tx−t0 is calculated. Then, the flow rate is measured using this value.

  This will be described in more detail. After the drive signal pulse is input to the upstream ultrasonic transmission / reception unit 2a, since the ultrasonic wave is emitted into the medium to be measured, the SW7 before the waveform reaches the downstream ultrasonic transmission / reception unit 2b. , SW8 is turned off, and SW2 and SW6 are turned on (SW1, 3, 4, and 5 are kept in the ON state and SW9 is kept in the OFF state). As a result, the received waveform of the downstream ultrasonic wave transmitting / receiving unit 2b is input to the zero cross comparator 9 from the amplifying unit 7 via the drive line MNT (SW6), the zero cross point of the predetermined rank wave is specified, and the propagation time detection signal is time-measured. It is output to the circuit 10. The time measuring circuit 10 measures the time from the input timing of the drive signal to the zero cross point of the received waveform as the original measurement time tx (FIG. 7). Thereby, the final forward propagation time can be calculated as tx−t0.

  Subsequently, the same measurement is performed by exchanging the transmission / reception relationship between the upstream ultrasonic transmission / reception unit 2a and the downstream ultrasonic transmission / reception unit 2b. That is, since the drive signal pulse is input to the downstream ultrasonic wave transmitting / receiving unit 2b, SW2, SW7, SW9 are turned on, and SW3, 4, 5 are also turned on. On the other hand, SW1, SW6 and SW8 are turned off. As a result, the downstream ultrasonic transmission / reception unit 2b is excited by vibration at the drive terminal 43b, the zero-cross point of the predetermined-order wave is specified as described above, and the propagation time detection signal is output to the time measurement circuit 10. The time measuring circuit 10 measures the time t0 'from the input timing of the drive signal to the zero cross point of the monitor waveform. Next, SW7 and SW9 are turned OFF and SW1, SW2 and SW6 are turned ON (SW2, 3, 4, and 5 are in the ON state, and SW8 is kept in the OFF state). As a result, the zero cross point of the received waveform of the upstream ultrasonic transmission / reception unit 2 a is specified, and the propagation time detection signal is output to the time measurement circuit 10. The time measuring circuit 10 measures a time tx ′ from the input timing of the drive signal to the zero cross point of the received waveform. Thereby, the final backward propagation time can be calculated as tx′−t0 ′. Then, the flow velocity (or flow rate) can be calculated by a well-known method using the aforementioned forward propagation time tx−t0 together. Thereby, even when the ultrasonic element deteriorates with time and the delay time t0 changes, the time tx-t0 in which the ultrasonic beam SW actually propagates can be accurately measured. Therefore, the flow rate can be measured accurately.

  As described above, in this embodiment, the measurement of the delay time t0 is not performed every time the gas flow rate is measured, but is stored in a storage device (for example, the RAM 113 (see FIG. 26) of the calculation unit 11) to measure the flow rate. At this time, tx−t0 is calculated using the stored value. In this way, since it is not necessary to frequently measure the delay time t0, the power consumption of the circuit can be reduced and the number of times of switch switching can be reduced, so that the frequency of measuring the gas flow rate is increased. Is also possible.

  Further, since the delay time t0 drifts over time, as shown in FIG. 15, when a predetermined number of days have passed after shipment from the factory and the predetermined time has elapsed, the delay time t0 is measured and the stored value is updated. Good. Since the value of the delay time t0 of the ultrasonic transmission / reception unit 2 varies depending on the temperature, the measurement is desirably performed when the ultrasonic transmission / reception unit 2 reaches a predetermined reference temperature Ta.

  More specifically, the propagation time correction unit 11 (see FIG. 1) includes a delay time storage unit 113 (FIG. 26) that stores a delay time t0 measured at a predetermined reference temperature, and a propagation time measurement. As the time measuring unit 1E measures and acquires the original measurement time tx, it includes a propagation time correction calculating unit that reads the delay time t0 from the delay time storage unit 113 and corrects and calculates the propagation time as tx−t0. Further, the fluid temperature measuring means 80 for measuring the temperature of the fluid GF to be measured, and the delay time t0 ′ is measured as the predetermined calibration timing at which the temperature measured by the temperature measuring means reaches the reference temperature comes. Delay time measuring means. Then, delay time updating means for updating the stored contents of the delay time storage means 113 with the measured and acquired delay time t0 'is provided. In this way, the delay time t0 'can be measured periodically to update the value, so that accurate flow measurement can be performed over many years.

  The calibration timing may be determined so as to arrive at a lower frequency than the flow rate measurement timing by the propagation time measuring means 1E. That is, the frequency of measuring the delay time t0 may be less than the frequency of measuring the flow rate (frequency of measuring the ultrasonic propagation time). For example, the delay time t0 is measured once every six months or once a year. As a result, it is not necessary to frequently measure the delay time t0, which leads to lower power consumption of the ultrasonic flowmeter 1.

Further, in the embodiment of FIG. 15, only one reference temperature is determined, and the delay time storage means 113 stores the delay time measured at the reference temperature, and further stores the delay time in advance. A delay time calibration line is determined on the basis of the temperature coefficient α. For example, equations (1) and (2) in FIG. 15 are determined as the delay time calibration line. Here, the expression (1) satisfies t1 ₀ = αTa + β1, and the expression (2) satisfies t2 ₀ = αTa + β2. Equation (1) corresponds to the upstream ultrasonic transmission / reception unit 2a, and equation (2) corresponds to the downstream ultrasonic transmission / reception unit 2b. On the other hand, the propagation time measuring means 1E performs the propagation time measurement at an arbitrary temperature, reads the delay time t0 corresponding to the measured temperature at which the propagation time is measured from the delay time calibration line, and uses this to determine the propagation time tx− t0 is calculated. In this way, even when the temperature at which the flow rate measurement is performed is different from the reference temperature at which the delay time t0 is measured, the delay time t0 is read from the delay time calibration line and the propagation time is calculated (tx−t0). Can be used. As a result, it is possible to correct the change in the delay time t0 of the ultrasonic element due to temperature and perform accurate flow measurement.

  For example, the temperature coefficient α is measured for each ultrasonic flowmeter at the time of factory shipment, and the value is stored. In this way, even if there is an individual difference in the temperature coefficient α, it is possible to accurately obtain the delay time t0. When there is not much individual difference of the temperature coefficient α at the time of factory shipment, the representative average value may be stored. The temperature coefficient α and the intercept β are stored in the temperature coefficient storage area 113a and the intercept storage area 113b of the RAM 113 (see FIG. 26), respectively. The measurement data of the delay time t0 is stored in the measurement data storage area 113c. The

  FIG. 21 shows a flowchart for measuring the delay time t0. First, in step S1, it is determined whether or not a predetermined number of days have passed since the factory shipment or the previous measurement. When it determines with No here, it progresses to a return. If it is determined as Yes, the process proceeds to S2, and it is determined whether or not the measured value of the temperature sensor 80 is in the temperature range of the representative temperature Ta ± ΔT. When it determines with Yes here, it moves to S3, delay time t0 of each ultrasonic element 2a, 2b is measured, and a memory | storage value is updated. Thereafter, the delay time calibration line described above is updated.

  FIG. 25 shows a flowchart for measuring the gas flow rate. First, in step S18, a drive signal is input to the upstream ultrasonic transmission / reception unit 2a. Thereafter, the switch is switched in S19, and the process proceeds to S20. In S20, a time tx1 from when the drive signal is input to when the zero-cross signal of the downstream ultrasonic wave transmitting / receiving unit 2b is detected is detected. Thereafter, the delay time t0 corresponding to the current temperature is calculated using the delay time calibration line (S22), and t1 = tx1-t0 is calculated (S22). Next, in S23 to S26, the same processing is performed for the downstream ultrasonic wave transmitting / receiving unit 2b to calculate t2 = tx2-t0. In S27, the gas flow rate is calculated from t1 and t2.

  Next, as shown in FIG. 17, the delay time t0 may be measured at a plurality of different reference temperatures Ta1, Ta2, and Ta3, and the delay time calibration line may be determined from these measured values. In this way, since the delay time t0 is measured and stored at a plurality of points, the relationship between the temperature and the delay time t0 (delay time calibration line) can be accurately determined as compared with the case where only one point is measured. .

  FIG. 22 shows a flowchart for measuring the delay time at a plurality of reference temperatures. First, in step S5, it is determined whether or not a predetermined number of days have elapsed since the previous measurement. When it determines with No here, it progresses to a return, and when it determines with Yes, it progresses to S6. In S6, it is determined whether or not the measured value of the temperature sensor 80 is in the temperature range of the representative temperature Ta1 ± ΔT. When it determines with Yes here, it progresses to S7, the transmission delay time t0 is measured about Ta1, and a memory | storage value is updated. Next, in S8, it is determined whether or not the measured value of the temperature sensor 80 is in the temperature range of the representative temperature Ta2 ± ΔT. When it determines with Yes by S8, it progresses to S9, the transmission delay time t0 is measured about Ta2, and a memory | storage value is updated. Then, it progresses to S10 and S11 and performs the same process about representative temperature Ta3.

  Next, a method for determining a delay time calibration line when delay times are measured at a plurality of reference temperatures will be described with reference to FIG. In FIG. 23, the delay time calibration straight line indicated by a broken line is based on old data, and the straight line is based on new data. First, an old delay time calibration straight line indicated by a broken line is defined by equation (0). Here, when the delay time t0 is newly measured at any one of the reference temperatures Ta1, Ta2, and Ta3 and the stored value is updated, the delay time calibration line is updated to the equation (1). For example, when the first measurement point (Ta1, t01) is measured, the equation (1) uses the temperature coefficient α1 of the equation (0) as the temperature coefficient as it is, and uses the first measurement point (Ta1, t01) as it is. Defined as a straight line through. Thereafter, when the second measurement point (Ta2, t02) is measured, the delay time calibration straight line is updated to Equation (2). Equation (2) is defined as a straight line passing through the first and second measurement points. Next, when the third measurement point (Ta3, t03) is measured, the delay time calibration line is updated to equation (3). Equation (3) is defined by the least square method using these three measurement points.

  FIG. 24 shows a flowchart for determining the delay time calibration line. First, in S12, it is determined whether or not the first measurement value is obtained among the reference temperatures Ta1, Ta2, and Ta3. When it determines with No here, it progresses to a return. On the other hand, if it is determined Yes, the process proceeds to S13, and the delay time calibration straight line is updated to equation (1). Next, proceeding to S14, it is determined whether or not the second measurement value has been obtained. When it determines with Yes here, it progresses to S15 and a delay time calibration straight line is updated to (2) Formula. Next, the process proceeds to S16, and when the third measurement value is obtained, the process proceeds to S17, and the delay time update straight line is updated to the expression (3).

Next, another embodiment of the present invention is shown in FIG. In the embodiment of FIG. 16, a pulsed driving voltage is continuously applied to the ultrasonic transmission / reception unit 2 a plurality of times during one flow rate measurement. Further, the correction information generation means 8 (see FIG. 1) averages the occurrence timings of a plurality of zero-cross points generated in the monitor output voltage waveform derived from a plurality of pulsed drive voltages, and determines them as measurement reference points. . For example, the delay time t1 ′ ₀ of the upstream ultrasonic transmission / reception unit 2a is defined by (t11 ₀ + t21 ₀ + t31 ₀ ) / 3. In this way, since the pulsed drive voltage is continuously applied to the ultrasonic transmission / reception unit 2 a plurality of times, the vibration of the ultrasonic transmission / reception unit 2 can be stabilized.

  In addition, a driving voltage can be applied as shown in FIG. In this embodiment, a pulsed driving voltage is continuously applied to the ultrasonic transmission / reception unit 2 a plurality of times in one flow measurement, and the last of the plurality of pulsed driving voltages is applied to this. It is applied as a marker pulse having a pulse voltage amplitude larger than the preceding remaining one. If it does in this way, vibration of an ultrasonic transceiver part can be stabilized.

Next, calculation formulas for measuring the gas flow rate will be described with reference to FIGS. FIG. 28 is a schematic diagram of a case where an ultrasonic beam is transmitted from the ultrasonic transmission / reception unit 2a and received by the ultrasonic transmission / reception unit 2b (hereinafter also referred to as “during forward measurement”). The meaning of each symbol is shown below.
tx: Original measurement time (time from when a drive pulse is input to the ultrasonic transmission / reception unit 2a until a zero cross signal is generated in the ultrasonic transmission / reception unit 2b);
t01: Delay time (time from when a drive pulse is input to the ultrasonic transmission / reception unit 2a until a zero cross signal is generated at a partial electrode of the ultrasonic transmission / reception unit 2a);
T01: Actual propagation time (after the ultrasonic wave escapes the piezoelectric ceramic diaphragm of the ultrasonic transmission / reception unit 2a, it passes through the acoustic impedance matching layer and the fluid to be measured, and is detected as a specific zero-cross point by the ultrasonic transmission / reception unit 2b. Time to be)
γa: The amount of change in the delay time t01 on the ultrasonic transmission / reception unit 2a side due to secular change.

FIG. 29 is a schematic diagram when an ultrasonic beam is transmitted from the ultrasonic transmission / reception unit 2b by switching between the transmission side and the reception side (hereinafter also referred to as “reverse direction measurement”). The meaning of each symbol is shown below.
ty: Original measurement time (time from when a drive pulse is input to the ultrasonic transmission / reception unit 2b until a zero cross signal is generated in the ultrasonic transmission / reception unit 2a);
t02: Delay time (time from when a drive pulse is input to the ultrasonic transmission / reception unit 2b until a zero cross signal is generated at a partial electrode of the ultrasonic transmission / reception unit 2b);
T02: Actual propagation time (after the ultrasonic wave escapes the piezoelectric ceramic diaphragm of the ultrasonic transmission / reception unit 2b, it passes through the acoustic impedance matching layer and the fluid to be measured, and is detected as a specific zero cross point by the ultrasonic transmission / reception unit 2a. Time to be)
γb: An amount of change in the delay time t02 on the ultrasonic transmission / reception unit 2b side due to secular change.

As shown in FIGS. 28 and 29, the original measurement times tx and ty, the delay times t01 and t02, and the actual propagation times T01 and T02 are connected by the following relationship.
T01 = tx−t01 (1)
T02 = ty−t02 (2)
Or
tx = T01 + t01 (1) ′
ty = T02 + t02 (2) ′
It is. On the other hand, in the ultrasonic transmission / reception unit 2a and the ultrasonic transmission / reception unit 2b, the delay times t01 and t02 change by γa and γb, respectively, due to the aging of the piezoelectric ceramic diaphragm,
t′01 = t01 + γa (3)
t′02 = t02 + γb (4)
It becomes.

In the conventional ultrasonic flowmeter, the original measurement times tx and ty themselves are adopted as the propagation time for flow rate calculation, but the equations (3) and (4) are zero points of the propagation time used for flow rate calculation. Means drifting by γa or γb due to aging of the element. On the other hand, as a factor that may affect the original measurement times tx and ty, aging degradation of the acoustic impedance layer may be considered, but both influence on the delay times t01 and t02 due to aging degradation of the piezoelectric ceramic diaphragm. It is considered to be much smaller than. That is, in (1) ′ and (2) ′, the actual propagation times T01 and T02 can be regarded as almost unchanged as compared with the delay times t01 and t02, so the original measurement time tx ′ after the deterioration with time and the original measurement time The amount of change in ty ′ is also substantially equal to γa and γb, which are the amounts of change in delay times t01 and t02. That is,
t′x = tx + γa (5)
t′y = ty + γb (6)

In the present invention, the actual propagation times T01 and T02 obtained by subtracting the delay times t01 and t02 from the original measurement times tx and ty are used as the propagation times for flow rate calculation. Therefore, the effect of the zero point drift due to the aging deterioration is effective. Can be eliminated. That is, the propagation length of the ultrasonic beam is L, the propagation speed of the ultrasonic beam in the gas is K, the flow velocity of the gas is v, the transmission angle of the ultrasonic beam (see FIG. 1) is θ, and the cross-sectional area of the flow path 3 is S, where Q is the passing volume of gas per unit time,
T01 = L / (K + v · cos θ) (7)
T02 = L / (Kv · cos θ) (8)
And the gas flow velocity v is
v = (L / 2 cos θ) × (1 / T01-1 / T02) (9)
From (1), (2), (9),
v = (L / 2 cos θ)
X {1 / (tx-t01) -1 / (ty-t02)} (10)
The flow rate Q is
Q = S · v (11)
As required.

Next, the gas flow rate v ′ after deterioration with time is
v ′ = (L / 2 cos θ) × (1 / T′01−1 / T′02)
= (L / 2 cos θ)
X {1 / (tx'-t'01) -1 / (ty'-t'02)} (12)
It becomes. However, from (3), (4), (5), (6), (12)
v ′ = (L / 2 cos θ)
× {1 / ((tx + γa) − (t01 + γa))
−1 / ((ty + γb) − (t02 + γb))}
= (L / 2 cos θ)
X {1 / (tx-t01) -1 / (ty-t02)}
= V (before deterioration over time) (13)
Thus, it is clear that the flow velocity measurement value v ′ is hardly affected by the deterioration with time.

  That is, even if the original measurement times tx and ty change as shown in (5) and (6) due to deterioration with time and the zero point drifts, the actual propagation time T01 obtained by subtracting the delay times t01 and t02 responsible for most of the drift contribution. , T02, the influence of the included amounts of change γa, γb is always subtracted out and accurate flow rate measurement becomes possible. In this case, as a zero point drift correction method, in the equation (10), the delay times t01 and t02 which are subtraction terms from the original measurement times tx and ty are updated with new measured values each time, Any of the methods of using the delay times t01 and t02 at the time of shipment as the reference values and then using the reference values while correcting the change amounts γa and γb obtained from the measured delay times may be employed.

  Next, returning to FIG. 2, the cross-sectional structure of the ultrasonic transmission / reception unit 2 will be described. The ultrasonic transmission / reception unit 2 includes a piezoelectric ceramic vibration plate 21 whose main part (vibration driving unit) is polarized in the thickness direction, and covers each main surface of the piezoelectric ceramic vibration plate 21. A main electrode pair 22 and 23 which are formed to face each other with a plate 21 and to which a drive voltage for ultrasonically vibrating the piezoelectric ceramic vibration plate 21 is applied, and the main electrode pair 22 and 23 are both insulated and separated. A monitoring partial electrode 24 is formed on the piezoelectric ceramic diaphragm 21 and takes out a piezoelectric monitoring signal of ultrasonic vibration generated in the piezoelectric ceramic diaphragm 21 when a drive voltage is applied.

  The piezoelectric ceramic vibrating plate 21 is made of a perovskite ferroelectric ceramic such as lead zirconate titanate (PZT), barium titanate, lead titanate, lanthanum zirconate titanate, and the like in the thickness direction. Polarized. Each electrode 22, 23, 34 is made of a metal vapor deposition film such as Cu.

  The main electrode pair 22, 23 is connected to the ground electrode 22 (connected to the GND side) covering the first main surface of the piezoelectric ceramic diaphragm 21 and the drive electrode 23 (connected to the drive power source side) covering the second main surface. ). The monitor partial electrode 24 is formed to have a smaller covering area with respect to the piezoelectric ceramic diaphragm 21 than both the ground electrode 22 and the drive electrode 23. The electrode drive electrode 23 is set to have a smaller covering area with respect to the piezoelectric ceramic diaphragm 21 than the ground electrode 22, and the monitor partial electrode is formed in the remaining area not covered by the drive electrode 23 on the second main surface of the piezoelectric ceramic diaphragm 21. 24 is formed.

  The monitor partial electrode 24 is formed in the outer peripheral area of the second main surface of the piezoelectric ceramic diaphragm 21. Specifically, the piezoelectric ceramic diaphragm 21 is formed in a disc shape, and the drive electrode 23 has a circular outer peripheral shape along the outer peripheral edge of the piezoelectric ceramic diaphragm 21. Then, a part of the drive electrode 23 is cut out so that a part of the circular outer peripheral edge is recessed inward in the radial direction, and a monitor partial electrode 24 is formed inside the cutout region 23c. . The outer peripheral edge on the drive electrode 23 side is adjacent to the monitor partial electrode 24 so that a gap 20 having a predetermined width is formed between the drive electrode 23 and the monitor partial electrode 24. It is formed in a shape that follows the outer peripheral edge of the electrode 24. The width w of the gap 20 formed between the drive electrode 23 and the monitor partial electrode 24 is adjusted to 0.5 mm or more and 2.5 mm or less.

  The form of formation of the monitor partial electrode 24 is not limited to the one described above. For example, as shown in FIG. 12, the drive electrode 23 is cut out by a linear gap 20 to form an arcuate monitor partial electrode. It is also possible to form 24.

  Further, as shown in FIG. 13, the polarization processing of the piezoelectric ceramic diaphragm 21 is performed by patterning the monitor partial electrode 24 and the drive electrode 23, and polarization blocks 71 and 72 that are insulated and separated in a form corresponding to these electrodes. And a polarization block on the ground electrode 22 side, and a high polarization voltage is applied from the polarization power source 74. On the other hand, as shown in FIG. 14, the monitor partial electrode 24 and the drive electrode 23 are formed as an integrated electrode 23G, and a non-separated polarization block 72 corresponding to the integrated electrode 23G and a polarization block on the ground electrode 22 side It is also possible to employ a method of patterning the integrated electrode 23G after performing the polarization process with being sandwiched therebetween.

Returning to FIG. 2, the piezoelectric ceramic diaphragm 21 is disposed in the casing 29 such that the second main surface side on which the drive electrode 23 and the monitor partial electrode 24 are formed faces the inner surface of the bottom portion 28 of the casing 29. Yes. A drive terminal 43 and a monitor terminal 44 project from the back surface of the bottom portion 28 of the casing 29, and the drive electrode 23 and the monitor partial electrode 24 are connected to the drive terminal 43 and the monitor terminal 44, respectively.

  The side wall 30 of the casing 29 is made of, for example, a metal material having excellent corrosion resistance, such as stainless steel or aluminum alloy, engineering plastic, or the like, and has an opening on the back side in a shape in which the end on the bottom side of the inner peripheral surface is expanded into a stepped shape. Forming part. A substrate 27 having the drive terminal 43, the ground terminal 41, and the monitor terminal 44 standing on the back side is fitted into the opening on the back side, and a polymer material such as epoxy resin or silicone resin is filled from the back side. A bottom portion 28 is formed. The drive terminal 43, the ground terminal 41, and the monitor terminal 44 extend through the bottom 28 to the back side.

  The piezoelectric ceramic diaphragm 21 is disposed at a desired position in the opening opposite to the bottom 28 of the casing 29. An acoustic impedance matching layer 25 is provided so as to close the opening and in close contact with the ground electrode 22 formed on the second main surface of the piezoelectric ceramic diaphragm 21. The acoustic impedance matching layer 25 is formed in a disc shape from a composite material in which a resin material such as an epoxy resin is used as a matrix and a gap forming filler (for example, glass balloon) is dispersed, and the piezoelectric ceramic diaphragm 21 is formed. An ultrasonic emission surface is formed on the main surface opposite to the contact side. In order to improve the transmission efficiency of ultrasonic waves, the volume mixing ratio of the void forming filler of the acoustic impedance matching layer 25 is an intermediate acoustic impedance value between the piezoelectric ceramic diaphragm 21 and the fluid to be measured (here, city gas). (For example, the geometric average value of both is set as a target value). In order to obtain a target acoustic impedance value, the acoustic matching layer 15 may be made of a resin material that does not contain a void forming filler.

  Next, an insulating layer 26 made of silicone resin is disposed between the piezoelectric ceramic diaphragm 21 and the bottom 28 of the casing 29. The drive terminal 43, the drive electrode 23, the monitor terminal 44, and the monitor partial electrode 24 are bonded by soldering with individual wires 33 and 34 that penetrate the insulating layer 26.

Further, the conduction path 31 to the ground electrode 22 is formed so as to go from the second main surface side of the piezoelectric ceramic diaphragm 21 to the first main surface side through the side peripheral surface of the piezoelectric ceramic diaphragm 21. The ground electrode 22 is connected via a conduction path 31 to a ground terminal 41 that protrudes from the bottom surface of the bottom portion 28 of the casing 29. In FIG. 2, the conduction path 31 is a wire 31 whose one end is soldered to the ground electrode 22 on the first main surface side of the piezoelectric ceramic diaphragm 21. A concave portion 25 c that accommodates the soldered portion 31 s of the wire 31 is formed on the surface of the acoustic impedance matching layer 25 that faces the ground electrode 22.

  Returning to FIG. 1, the ultrasonic drive mechanism 4 and the peripheral circuit blocks 7 to 11 are provided in the control circuit unit 1E. The ultrasonic drive mechanism 4 includes a transmission unit 5, a reception unit 6, and a switching unit 4s. The transmission unit 5 is a circuit for inputting drive signals to the ultrasonic transmission / reception units 2a and 2b. The receiving unit 6 includes a switch or the like, and the drive mode is switched by switching the switch. The switching control of the receiving unit 6 is performed by the switching unit 4s. The amplifying unit 7 amplifies the ultrasonic wave received by the receiving unit 6 with a predetermined amplification factor and inputs the amplified ultrasonic wave to the zero cross point detecting unit 9. The zero cross point detector 9 detects a zero cross point of a specific rank wave (for example, a third wave) included in the received ultrasonic waveform. The time measuring unit 10 includes a forward propagation time until the ultrasonic beam SW transmitted from the upstream ultrasonic transmission / reception unit 2a reaches the downstream ultrasonic transmission / reception unit 2b, and the second drive in the first drive mode. In this mode, the backward propagation time until the ultrasonic beam SW transmitted from the downstream ultrasonic transmission / reception unit 2b reaches the upstream ultrasonic transmission / reception unit 2a is measured. Moreover, the calculating part 11 calculates the average flow velocity and flow volume of the fluid under measurement which flow through a flow path from the time difference between said forward propagation time and reverse propagation time.

  Hereinafter, various modifications of the ultrasonic transmission / reception unit 2 will be described. In the embodiment of FIG. 3A, only one drive pulse is input. However, in order to equalize and stabilize the drive waveform, a plurality of drive pulses are continuously input as shown in FIG. 3B. May be.

  Further, as shown in FIG. 8, it is also possible to provide a switch SW10 that integrates the monitor terminal with the drive terminal 43 and switches the drive electrode 23 and the monitor partial electrode 25 between conductive connection / insulation separation. In this configuration, by switching the drive of the switch SW10 so that the drive electrode 23 and the monitor partial electrode 25 are conductively connected at the time of drive input, the monitor partial electrode 25 can also bear the application of the drive voltage. The drive voltage can be applied to the plate 21 more uniformly. By immediately switching the switch SW10 after driving, the drive electrode 23 and the monitor partial electrode 25 can be insulated and separated, and the vibration waveform of the piezoelectric ceramic diaphragm 21 can be monitored more clearly via the monitor partial electrode 25. FIG. 9 shows a circuit configuration example in this case. The switches SW8 and SW9 in FIG. 4 are omitted, and a part of the drive line INP is shared by the monitor line MNT.

  When a drive signal pulse is input to the upstream ultrasonic transmitting / receiving unit 2a, SW1, SW7, SW10 are turned on, and SW3, 4, 5 are also turned on. On the other hand, SW2, SW6 and SW11 are turned off. At the time of reception, SW7, SW1, and SW10 are turned off, and SW2, SW6, and SW11 are turned on. When a drive signal pulse is input to the flow side ultrasonic wave transmitting / receiving unit 2b, SW2, SW7 and SW11 are turned on, and SW3, 4 and 5 are also turned on. On the other hand, SW1 and SW6 are turned off. At the time of reception, SW7, SW2 and SW11 are turned OFF and SW1, SW6 and SW10 are turned ON (SW3, 4 and 5 are kept ON).

  In the configuration of FIG. 10, the first main surface of the piezoelectric ceramic diaphragm 21 is configured such that one end of the ground wiring portion is connected to the ground electrode 22 and insulated from both the drive electrode 23 and the monitor partial electrode 24. The ground lead layer 31a formed on the peripheral side surface of the piezoelectric ceramic diaphragm 21 in such a manner that the other end is connected to the ground connection pad 3p formed on the other end, and the other end is soldered to the ground connection pad 3p. Is formed of a wire 31b soldered to the ground terminal 41. Note that the ground connection pad 3p and the monitor partial electrode 24 take the geometrical balance of the vibration drive distribution by the drive electrode 22 into consideration (the geometric center of gravity) of the first main surface of the piezoelectric ceramic diaphragm 21. ) It is arranged in a substantially point-symmetrical positional relationship with respect to the position.

In the configuration of FIG. 7, the casing 29 is electrically connected to the bottom portion 28, the side wall portion 30 that rises from the periphery of the bottom portion 28, and the top surface portion 29 t that closes the opening on the opposite side of the bottom portion 28 of the side wall portion 30. The metal member can be formed. On the inner surface of the top surface portion 29t, the ground electrode 22 covering the first main surface of the piezoelectric ceramic diaphragm 21 is disposed in close contact with the conductive adhesive layer 46, and the ground electrode 22 is grounded through the casing 29. It has become. In addition, an acoustic impedance matching layer 25 in which an ultrasonic emission surface is formed on the main surface opposite to the contact side with the top surface portion 29t is disposed in close contact with the outer main surface of the top surface portion 29t. A rubber insulating ring is fitted on the inner peripheral surface of the side wall portion 30, and the gap between the piezoelectric ceramic diaphragm 21 and the bottom portion 28 is filled with a gel-like polymer material such as silicone. The ground terminal 41 is formed so as to be integrated with the bottom portion 28.

  In addition, as shown in FIG. 20, it is also possible to measure a flow rate by using the ultrasonic transmission / reception unit 2 that does not have a monitor partial electrode. A block diagram of the ultrasonic flowmeter 1 in this case is shown in FIG. For example, when transmitting an ultrasonic wave from the upper-side ultrasonic transmission / reception unit 2a, SW8 is turned on, SW1 is turned off, and SW7 is turned off. After a pulsed drive signal is input to the drive terminal 43a, before the ultrasonic beam is output, SW8 is turned off, SW1 is turned on, and SW7 is turned on. When the piezoelectric ceramic diaphragm 21 of the ultrasonic transmission / reception unit 2 is acoustically vibrated, a piezoelectric monitoring signal is taken out from the drive terminal 43 a and can be detected by amplifying it with the amplifier 7.

  Next, the time measuring unit 10 will be described with reference to FIG. A clock signal having a predetermined cycle is input to the time measuring unit 10. Further, when measuring the gas flow rate, a timing start signal is input at the same timing as the drive signal applied to the ultrasonic transmission / reception unit 2. Time measurement is started by the input of the timing start signal. Next, the zero cross signal from the receiving side ultrasonic element 2 is input, and the time measurement is completed. Then, the time from the input of the timing start signal to the input of the zero cross signal is output to the calculation unit 11.

The schematic diagram which shows the whole structure of the ultrasonic flowmeter used as the application object of this invention. The longitudinal cross-sectional view which shows one Embodiment of the ultrasonic transmission / reception element of this invention. Explanatory drawing which shows the electrode form of the ultrasonic transmission / reception element of FIG. 1 with the drive example. Explanatory drawing which similarly shows the 1st modification of a drive example. The figure which shows the detail of the circuit part of FIG. FIG. 5 is a circuit diagram showing a configuration example of a zero cross comparator circuit in FIG. 4. FIG. 6 is a timing chart showing an operation sequence of the zero cross comparator circuit of FIG. 5. Operation | movement explanatory drawing of the ultrasonic flowmeter of FIG. Explanatory drawing which shows the modification of the terminal connection form which concerns on the ultrasonic transmission / reception element of FIG. 1 with a drive example. The figure which shows the circuit modification corresponding to FIG. Explanatory drawing which shows the 1st modification of the ultrasonic transmission / reception element of FIG. Explanatory drawing which similarly shows a 2nd modification. The figure which shows the modification of an electrode formation form. Explanatory drawing which shows the 1st example of the polarization process of a piezoelectric ceramic diaphragm. Explanatory drawing which similarly shows a 2nd example. An example of an acoustic vibration waveform when a driving pulse is hit once. An example of an acoustic vibration waveform when a driving pulse is applied a plurality of times. An example of measuring transmission delay time at multiple reference temperatures. Acoustic vibration waveform when marker pulse is applied. The modification of the block diagram of an ultrasonic flowmeter. An example of an ultrasonic element without a partial electrode. The flowchart at the time of measuring transmission delay time. The flowchart at the time of measuring delay time in several reference temperature. Explanatory drawing in the case of determining a delay time calibration straight line. The flowchart in the case of determining a delay time calibration straight line. The flowchart for measuring a gas flow rate. The detailed block diagram of a calculating part. FIG. 3 is a detailed view of a time measurement unit and a calculation unit. Flow calculation explanatory drawing (the 1). Flow calculation explanatory drawing (the 2).

Explanation of symbols

3p Ground connection pad 20 Gap 21 Piezoelectric ceramic diaphragm 22, 23 Main electrode pair 22 Ground electrode 23c Notch area 24 Monitor partial electrode 25 Acoustic impedance matching layer 25c Concave portion 26 Insulating layer 28 Bottom 29 Casing 29t Top surface 30 Side wall Part 31 Wire (conduction path)
31b Wire 31a Grounding lead layer 31s Soldering part 41 Grounding terminal 43 Drive terminal 46 Conductive adhesive layer

Claims (22)

A flow path forming section for forming a flow path of the fluid to be measured;
A piezoelectric ceramic diaphragm which is provided at different positions in the flow direction of the fluid to be measured with respect to the flow path forming portion and is polarized in the plate thickness direction; and an electrode formed on the piezoelectric ceramic diaphragm. The ultrasonic transmitter / receiver is provided, and one side functions as a measurement ultrasonic wave transmission side to the fluid to be measured and the other functions as a measurement ultrasonic wave reception side. A pair of ultrasonic transmission / reception units capable of transmitting an ultrasonic beam having directivity in a predetermined direction;
Driving voltage applying means for applying a pulsed driving voltage to the ultrasonic wave transmitting and receiving unit;
Propagation time measuring means for measuring the propagation time from when the ultrasonic beam transmitted from the ultrasonic transmission / reception unit on the transmission side reaches the ultrasonic transmission / reception unit on the reception side after being transmitted from the ultrasonic transmission / reception unit When,
Based on the measured the propagation time anda flow rate calculating means for calculating the flow rate of the fluid to be measured,
The propagation time measuring means includes
A monitor output voltage for acquiring an acoustic vibration waveform generated in the piezoelectric ceramic diaphragm of the ultrasonic transmission / reception unit as a monitor output voltage waveform generated in the electrode when the drive voltage is applied to the transmission / reception ultrasonic transmission / reception unit Waveform acquisition means;
Correction information generating means for generating correction information of the propagation time based on the acquired monitor output voltage waveform;
A propagation time correcting means for correcting the measured propagation time based on the correction information;
Equipped with a,
The correction information generation means determines a zero-cross point in a predetermined order generated in the monitor output voltage waveform as a measurement reference point, that is, the correction information, measures a delay time t0 from the drive voltage application timing to the measurement reference point, The time from the application timing of the drive voltage measured by the propagation time measuring means to the zero-cross point of the predetermined order of the arrival waveform generated in the ultrasonic transmission / reception unit on the receiving side is defined as the original measurement time tx, and the propagation time is tx. Calculated as -t0,
The propagation time correction means includes
Delay time storage means for storing the delay time t0 measured at a predetermined reference temperature;
Propagation time correction that reads the delay time t0 from the delay time storage means and corrects and calculates the propagation time as tx-t0 as the propagation time measuring means measures and acquires the original measurement time tx for flow rate measurement. A calculation means;
Fluid temperature measuring means for measuring the temperature of the fluid to be measured;
A delay time measuring means for measuring the delay time t0 ′ as a predetermined calibration timing arrives when the temperature measured by the temperature measuring means reaches the reference temperature;
Delay time updating means for updating the stored contents of the delay time storage means with the measured and acquired delay time t0 ′;
An ultrasonic flowmeter comprising: The ultrasonic flowmeter according to claim 1, wherein the calibration timing is determined so as to arrive at a lower frequency than the flow rate measurement timing by the propagation time measurement unit . In the propagation time correction means, only one point of the reference temperature is determined, and the delay time storage means stores the delay time measured at the reference temperature. Having a delay time calibration line determining means for determining a delay time calibration line based on the stored temperature coefficient;
The propagation time measuring means measures the propagation time at an arbitrary temperature, reads a delay time corresponding to the measured temperature at which the propagation time is measured from the delay time calibration line, and uses the delay time to measure the propagation time. The ultrasonic flowmeter according to claim 1 or 2, wherein the time is calculated . In the propagation time correction means, the reference temperatures are determined at a plurality of different points, and the delay time storage means stores delay times respectively measured at the plurality of reference temperatures, and further, the delay A delay time calibration curve determining means for determining a delay time calibration curve based on the plurality of reference temperatures stored in the time storage means;
The propagation time measuring means measures the propagation time at an arbitrary temperature, reads a delay time corresponding to the measured temperature at which the propagation time was measured from the delay time calibration curve, and uses the delay time to measure the propagation time. The ultrasonic flowmeter according to claim 1 or 2, wherein the time is calculated . The drive voltage application means continuously applies the pulsed drive voltage to the ultrasonic transmission / reception unit a plurality of times during one flow measurement,
5. The correction information generation means averages the generation timings of a plurality of zero cross points generated in a monitor output voltage waveform derived from the plurality of pulsed drive voltages, and determines the average as a measurement reference point. The ultrasonic flowmeter according to any one of the above. The ultrasonic transmitting / receiving element is:
A main electrode pair that is formed oppositely across the piezoelectric ceramic diaphragm so as to cover each main surface of the piezoelectric ceramic diaphragm, and to which the drive voltage is applied to ultrasonically vibrate the piezoelectric ceramic diaphragm;
A monitoring portion formed on the piezoelectric ceramic diaphragm so as to be insulated and separated from any of the main electrode pairs, and for extracting a piezoelectric monitoring signal of ultrasonic vibration generated in the piezoelectric ceramic diaphragm upon application of the drive voltage With electrodes,
The ultrasonic flowmeter according to claim 1, wherein the monitor output voltage waveform acquisition unit extracts the piezoelectric monitoring signal of the monitoring partial electrode as the monitor output voltage waveform . The main electrode pair includes a ground electrode that covers the first main surface of the piezoelectric ceramic diaphragm and a drive electrode that also covers the second main surface, and the monitor partial electrode is any of the ground electrode and the drive electrode. The ultrasonic flowmeter according to claim 6, wherein a covering area of the piezoelectric ceramic diaphragm is smaller than that of the piezoelectric ceramic diaphragm . The drive electrode is formed to have a smaller covering area with respect to the piezoelectric ceramic diaphragm than the ground electrode, and the monitor partial electrode is formed in a remaining area of the piezoelectric ceramic diaphragm that is not covered with the drive electrode. The ultrasonic flowmeter according to claim 7, wherein: The ultrasonic flowmeter according to claim 8, wherein the monitoring partial electrode is formed in an outer peripheral area of the second main surface of the piezoelectric ceramic diaphragm . The piezoelectric ceramic diaphragm is formed in a disk shape, and the drive electrode has a circular outer peripheral edge shape along the outer peripheral edge of the piezoelectric ceramic diaphragm, and a part of the circular outer peripheral edge is radially inward. The ultrasonic flowmeter according to claim 9, wherein a part of the drive electrode is cut out so as to be recessed in a concave shape, and the monitoring partial electrode is formed inside the cutout region . The outer peripheral edge on the drive electrode side is formed at a position adjacent to the monitor partial electrode by forming a gap with a predetermined width between the drive electrode and the monitor partial electrode. The ultrasonic flowmeter according to claim 9 or 10, wherein the ultrasonic flowmeter is formed in a shape that follows the periphery . The ultrasonic flowmeter according to claim 11 , wherein a width of the gap formed between the drive electrode and the monitor partial electrode is 0.5 mm or more and 2.5 mm or less . The piezoelectric ceramic diaphragm is disposed in the casing such that the second main surface side on which the drive electrode and the partial electrode for monitoring are formed faces the inner surface of the bottom of the casing,
The ultrasonic wave according to any one of claims 7 to 12, wherein the drive electrode and the monitor partial electrode are respectively connected to a drive terminal and a monitor terminal which are formed to protrude from a bottom rear surface of the casing. Flowmeter. An insulating layer is disposed between the piezoelectric ceramic diaphragm and the bottom of the casing, and the drive terminal, the drive electrode, the monitor terminal, and the monitor partial electrode are respectively separated by individual wires that penetrate the insulating layer. The ultrasonic flowmeter according to claim 13 , which is bonded . A conduction path to the ground electrode is formed from the second main surface side of the piezoelectric ceramic diaphragm to the first main surface side through the side peripheral surface of the piezoelectric ceramic diaphragm, and the bottom rear surface of the casing The ultrasonic flowmeter according to claim 13 or 14, wherein the ground electrode is connected to a ground terminal projecting from the ground terminal via the conduction path . The piezoelectric ceramic diaphragm is disposed at a desired position in the opening opposite to the bottom of the casing, and ultrasonic waves are emitted to the main surface opposite to the contact side with the piezoelectric ceramic diaphragm so as to close the opening. The ultrasonic flowmeter according to claim 15, wherein an acoustic impedance matching layer having a surface is provided in close contact with the ground electrode formed on the first main surface of the piezoelectric ceramic diaphragm . The conduction path is a wire whose one end is soldered to the ground electrode on the first main surface side of the piezoelectric ceramic diaphragm, and the wire is disposed on a surface of the acoustic impedance matching layer facing the ground electrode. The ultrasonic flowmeter according to claim 16, wherein a concave portion that accommodates the soldering portion is formed . One end of the conduction path is connected to the ground electrode, and the ground connection pad is formed on the first main surface of the piezoelectric ceramic diaphragm so as to be insulated from both the drive electrode and the monitor partial electrode. The other end of the piezoelectric ceramic diaphragm is connected to the ground lead layer formed on the peripheral side surface, one end is soldered to the ground connection pad, and the other end is soldered to the ground terminal. Consisting of wires,
The ultrasonic flowmeter according to claim 16 , wherein the acoustic impedance matching layer is closely disposed over the entire surface of the ground electrode . The casing is formed of a metal member in which a bottom portion of the casing, a side wall portion rising from a peripheral edge of the bottom portion, and a top surface portion closing the opening on the opposite side of the side wall portion are electrically connected to each other, and the top surface portion The grounding electrode that covers the first main surface of the piezoelectric ceramic diaphragm is disposed in close contact with the inner surface of the piezoelectric ceramic diaphragm via a conductive adhesive layer, and the driving voltage is grounded through the casing. The ultrasonic flowmeter described in 1. The ultrasonic flow rate according to claim 19, wherein an acoustic impedance matching layer having an ultrasonic emission surface formed on a main surface opposite to a contact side with the top surface portion is disposed in close contact with the outer main surface of the top surface portion. Total. 21. The ultrasonic flowmeter according to claim 6, wherein the drive voltage applying unit applies the drive voltage to the main electrode pair without applying the drive voltage to the monitoring partial electrode . The drive voltage applying means applies the pulsed drive voltage to the ultrasonic transmission / reception unit a plurality of times in a single flow rate measurement, and the last of the plurality of pulsed drive voltages. The ultrasonic flowmeter according to any one of claims 1 to 21, wherein the ultrasonic flowmeter is applied as a marker pulse having a pulse voltage amplitude larger than that of the remaining one preceding it .

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