JP5111846B2 - Ultrasonic output element - Google Patents

Description

  The present invention relates to an ultrasonic output element.

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 monitor a vibration waveform of a piezoelectric ceramic diaphragm to which a drive signal is input in real time, for example, to grasp a delay time from an input timing of a drive signal to a discharge timing of ultrasonic waves to a fluid to be measured. It is an object of the present invention to provide an ultrasonic output element having the above-mentioned advantageous structure.

Means for Solving the Problems and Effects of the Invention

In order to solve the above problems, the ultrasonic output element of the present invention is:
A piezoelectric ceramic diaphragm polarized in the plate thickness direction;
A main electrode pair formed so as to oppose the piezoelectric ceramic diaphragm so as to cover each main surface of the piezoelectric ceramic diaphragm, and to which a driving voltage for ultrasonically vibrating the piezoelectric ceramic diaphragm is applied;
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; Assuming that

  According to the configuration of the ultrasonic output element of the present invention, in addition to the driving electrode, the ultrasonic wave generated in the piezoelectric ceramic diaphragm upon application of the driving voltage to the piezoelectric ceramic diaphragm forming the main part of the vibration driving unit. Since the monitoring partial electrode for taking out the piezoelectric monitoring signal of vibration is provided, the vibration waveform of the piezoelectric ceramic diaphragm to which the drive signal is input can be monitored in real time.

  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.

  The ultrasonic output element of the present invention employs a piezoelectric ceramic diaphragm as an electromechanical conversion element as a vibration drive unit, so when receiving an ultrasonic wave emitted from another ultrasonic output element, The mechanical vibration of the piezoelectric ceramic diaphragm excited by ultrasonic waves can be extracted from the drive electrode as an electric signal waveform, and can also be used as an ultrasonic receiving element.

  In the ultrasonic output element of the present invention, the main electrode pair includes a ground electrode (connected to the GND side) covering the first main surface of the piezoelectric ceramic diaphragm and a drive electrode (drive power source) covering the second main surface. Connected to the side). It is desirable that the monitoring partial electrode be formed so that the covering area of the piezoelectric ceramic diaphragm is smaller than any of the ground electrode and the drive electrode so that the vibration driving of the piezoelectric ceramic diaphragm by the main electrode pair is not hindered.

  In this case, it is preferable to cut out a partial region of either the drive electrode or the ground electrode that covers both main surfaces of the piezoelectric ceramic diaphragm and form a monitor partial electrode in the cut-out region. Accordingly, there is an advantage that the drive electrode or the ground electrode and the monitor partial electrode covering the main surface of the piezoelectric ceramic diaphragm can be collectively formed by a well-known electrode patterning technique (for example, photolithography).

  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 is formed to have a smaller covering area on the piezoelectric ceramic diaphragm than the ground electrode, and the monitor partial electrode is provided in the remaining area not covered by the drive electrode on the second main surface of the piezoelectric ceramic diaphragm. It is good to form.

  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 grounding path is formed on the first main surface of the piezoelectric ceramic diaphragm so that the conduction path is connected to the ground electrode at one end and insulated from both the drive electrode and the monitor partial electrode. 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.

  An embodiment of an ultrasonic output element of the present invention will be described with reference to the drawings, taking as an example a case where the ultrasonic output element is applied to an ultrasonic flowmeter. FIG. 1 shows the basic configuration of an embodiment of an ultrasonic flow meter used as a general residential gas meter or the like. The ultrasonic flowmeter 1 is provided with a flow path forming portion 3 that forms a flow path of the fluid GF to be measured and a position different from each other in the flow direction O of the fluid GF to be measured with respect to the flow path forming portion 3. Functions as the transmission side of the measurement ultrasonic wave to the fluid GF to be measured and the other as the reception side of the measurement ultrasonic wave, and the directivity in a predetermined direction as each measurement ultrasonic wave And a pair of ultrasonic transmission / reception units 2a and 2b capable of transmitting an ultrasonic beam SW. 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. Both are configured as an ultrasonic output element of the present invention, an ultrasonic transmission function for transmitting an ultrasonic beam by applying a drive voltage, and an ultrasonic reception function for outputting an electric signal (reception signal) by receiving an ultrasonic beam And a composite. Since they all have the same structure, they will be described as representatives (hereinafter represented by reference numeral “2”).

  FIG. 2 shows an example of a cross-sectional structure of the ultrasonic transmission / reception unit 2 (ultrasonic output element). 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 first 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.

  As already described with reference to FIG. 7, the ultrasonic transmission / reception unit 2 receives a driving signal from the outside, so that the signal is converted into mechanical vibration by the piezoelectric ceramic vibration plate and further propagates through the acoustic impedance matching layer 25. 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 (FIG. 7: (3)), the input timing of the drive signal is regarded as equivalent to the timing at which the ultrasonic wave is released to the fluid to be measured, and this is used as the starting point for measuring the ultrasonic propagation time. . However, in this measurement method, it is clear that the delay time is included in the ultrasonic propagation time as a measurement error, and the delay time is in the reverse direction from the time degradation of the vibration drive unit or the forward measurement. If it fluctuates with the non-objectivity with respect to the temperature change during the measurement (FIG. 7: (1)), the error of the delay time to the original ultrasonic propagation time (FIG. 7: (2)) The contribution rate also fluctuates, and there is a problem that measurement correction of the ultrasonic propagation time becomes impossible.

  However, the configuration of the ultrasonic output element 2 of the present invention, that is, the piezoelectric ceramic diaphragm 21 constituting the main part of the vibration driving unit, in addition to the driving electrode, the piezoelectric ceramic diaphragm according to the application of the driving voltage. By adopting the configuration in which the monitoring partial electrode 24 for taking out the piezoelectric monitoring signal of the ultrasonic vibration generated in 21 is employed, the vibration waveform of the piezoelectric ceramic diaphragm to which the drive signal is input can be monitored in real time.

  That is, as indicated by a broken line in FIG. 7, when the drive signal is input, the time when the ultrasonic vibration is actually generated in the piezoelectric ceramic diaphragm 21 in a form including the delay of the piezoelectric ceramic diaphragm is determined. This can be known by monitoring the waveform of the monitoring partial electrode 24. Therefore, if the time from the input timing of the drive signal to the time when the vibration waveform appears at the output of the monitor partial electrode 24 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 grasped. it can. As a result, even when the delay time fluctuates with the aging deterioration of the vibration drive unit, by specifying the delay time by monitoring the output of the monitoring partial electrode 24, the ultrasonic propagation time measurement standard can be changed. The actual release timing to the measurement fluid can be approached (FIG. 7: (4)), and the measurement error can be reduced.

  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 (configured by a microcomputer) of FIG. 1 executing a predetermined control program). 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 measuring circuit 10 measures the time t0 (FIG. 7) from the input timing of the drive signal to the zero cross point of the monitor waveform.

  Since the ultrasonic wave based on the driving input is emitted from the upstream ultrasonic transmission / reception unit 2a into the medium to be measured, SW7 and SW8 are changed until this waveform reaches the downstream ultrasonic transmission / reception unit 2b. Switching off is performed by turning SW2 and SW6 on (SW1, 3, 4, and 5 are in the ON state, and SW9 is 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 tx (FIG. 7) from the input timing of the drive signal to the zero cross point of the received waveform. 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.

Hereinafter, various modifications of the present invention 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. 11, 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 of the side wall portion 30 opposite to the bottom portion 28. 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.

The schematic diagram which shows the whole structure of the ultrasonic flowmeter used as the application object of this invention. 1 is a longitudinal sectional view showing an embodiment of an ultrasonic output element of the present invention. Explanatory drawing which shows the electrode form of the ultrasonic output element of FIG. 1 with the example of a drive. 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 output element of FIG. The figure which shows the circuit modification corresponding to FIG. Explanatory drawing which shows the 1st modification of the ultrasonic output 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.

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 (15)

A piezoelectric ceramic diaphragm polarized in the plate thickness direction;
A main electrode pair formed so as to oppose the piezoelectric ceramic diaphragm so as to cover each main surface of the piezoelectric ceramic diaphragm, and to which a driving voltage for ultrasonically vibrating the piezoelectric ceramic diaphragm is applied;
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 Electrodes,
Equipped with a,
There is provided a changeover switch for connecting the partial electrode for monitoring to either the power supply line of the driving voltage or the output line of the piezoelectric monitoring signal,
By connecting the monitoring partial electrode to the power supply line, the drive voltage is applied to the monitoring partial electrode together with the main electrode pair, and then the changeover switch is switched to the output line side of the piezoelectric monitoring signal. An ultrasonic output element that extracts the piezoelectric monitoring signal . 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. ultrasonic output device according to claim 1, covering the area with respect to the piezoelectric ceramic diaphragm is formed smaller than. 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 electrode is provided in a remaining area of the piezoelectric ceramic diaphragm that is not covered with the drive electrode. ultrasonic output device according to claim 2 in which partial electrodes are formed. Ultrasonic output device according to claim 3 wherein the monitor portion electrode is formed on the outer peripheral edge region of said 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. ultrasonic output device according to a part of the drive electrodes in the form of retracting the concave is cut, in claim 4, wherein the monitor portion electrode inside of the cutout area is formed. 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. ultrasonic output device according to claim 4 or claim 5 is formed in a shape imitating the periphery. Ultrasonic output device according to claim 6, the width of the gap formed between the drive electrode and the monitor part electrode is a 0.5mm or 2.5mm 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,
To the bottom drive terminal and the monitor terminal is protruded on the back surface of the casing, ultrasound according to any one of claims 2 to 7 wherein the drive electrode and the monitor portion electrodes are respectively connected Output element. 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 output element according to claim 8 , 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 of the casing ultrasonic output device according to claim 8 or claim 9 wherein the ground electrode to a ground terminal formed projecting on the rear surface is connected via a conductor passing 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 output element according to claim 10, 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. ultrasonic output device according to claim 11, the concave portion is formed for accommodating the soldering portion of the. 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,
Ultrasonic output device according to claim 11, wherein the acoustic impedance matching layer over the entire surface of the ground electrode is disposed in close contact. 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 10. The ground electrode covering 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 drive voltage is grounded via the casing. The ultrasonic output element according to 1. The outer main surface of the top portion, the ultrasonic output according to claim 14, the acoustic impedance matching layer ultrasonic emitting surface on the main surface opposite to the contact side with the top face portion is formed is disposed in close contact element.

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