JP2009004916

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DESCRIPTION JP2009004916
PROBLEM TO BE SOLVED: To provide an ultrasonic output device capable of rapidly attenuating
a reverberation vibration output of a piezoelectric ceramic diaphragm from which a drive signal
input is cut off and improving an S / N ratio at a receiving side. SOLUTION: A partial electrode 24
is provided on a first main surface of a piezoelectric ceramic diaphragm so as to be insulated and
separated from a first main electrode 23 serving as an input side of a driving voltage. The
reverberation vibration signal appearing on the detection-side electrode is phase-reversed after
one of the detection-side electrode and the other is the input-side electrode and the input of the
measurement drive signal to the main electrode pair is cut off. It is feedback input to the input
side electrode as a reverberation suppression signal for reducing the vibration. The reverberation
vibration can be actively canceled by the antiphase vibration input of the reverberation vibration
signal itself. [Selected figure] Figure 8
Ultrasonic output device
[0001]
The present invention relates to an ultrasound output device.
[0002]
Unexamined-Japanese-Patent No. 2004-251653
[0003]
04-05-2019
1
Conventionally, ultrasonic flowmeters for measuring the flow rate of city gas, water, etc. are
known.
As a measurement principle at that time, generally, the "propagation time difference method" is
used.
This is provided with a pair of ultrasonic wave transmitting / receiving units on the upstream
side and downstream side in the fluid flow direction of the flow path, alternately switching the
ultrasonic wave transmitting / receiving direction between the ultrasonic wave transmitting /
receiving units and transmitting from the upstream ultrasonic wave transmitting / receiving unit
The time until the transmitted ultrasonic beam reaches the downstream ultrasonic transmitting
and receiving unit (forward propagation time) and the ultrasonic beam transmitted from the
downstream ultrasonic transmitting and receiving unit reaches the upstream ultrasonic
transmitting and receiving unit The time (reverse direction propagation time) is measured, and
the average flow velocity and the flow rate of the fluid flowing in the flow path are obtained from
the time difference between the two (for example, Patent Document 1).
[0004]
The ultrasonic drive unit (ultrasonic transducer) used in the flow meter as described above has a
vibration drive unit made of a piezoelectric ceramic diaphragm, and is stopped after transmitting
an ultrasonic beam by the drive voltage input for measurement. , Will wait until the next
measurement. However, since the piezoelectric ceramic diaphragm has the characteristics as a
mechanical vibrator, the vibration does not stop immediately but continues the reverberation
vibration output even if the driving voltage input to the ultrasonic transmitting / receiving unit is
stopped. It may be a factor of the S / N ratio drop on the receiving side.
[0005]
An object of the present invention is to provide an ultrasonic output apparatus capable of rapidly
attenuating the reverberation vibration output of the piezoelectric ceramic diaphragm from
which the drive signal input is blocked, and improving the S / N ratio at the receiving side.
Means for Solving the Problems and Effects of the Invention
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[0006]
In order to solve the above-mentioned problems, an ultrasonic output device according to the
present invention comprises: a piezoelectric ceramic vibration plate polarized in a plate thickness
direction; and a piezoelectric ceramic vibration plate interposed between the piezoelectric
ceramic vibration plate and the piezoelectric ceramic vibration plate. A first main electrode
covering the first main surface and a second main electrode also covering the second main
surface, and the first main electrode and the insulation on the first main surface of the
piezoelectric ceramic diaphragm. A partial electrode provided in a separated form, Measurement
drive signal input means for inputting a measurement drive signal for generating ultrasonic
vibration for measurement to a piezoelectric ceramic diaphragm to a main electrode pair, a first
main electrode and a partial electrode The reverberation vibration signal appearing on the
detection side electrode is phase-reversed after one of the detection side electrode and the other
as the input side electrode, and the input of the measurement drive signal to the main electrode
pair is interrupted. Reduce vibration Characterized by comprising a reverberation suppressed
signal input means having an inverting feedback circuit for feeding back to the input side
electrode as because of the reverberation suppressed signal.
[0007]
According to the ultrasonic output apparatus of the present invention, the partial electrodes are
provided on the first main surface of the piezoelectric ceramic diaphragm in a form insulated and
separated from the first main electrode serving as the drive voltage input side, With one of the
partial electrodes as the detection side electrode and the other as the input side electrode, the
reverberation vibration signal appearing on the detection side electrode is phase inverted after
blocking the input of the measurement drive signal to the main electrode pair, and this is left in
the piezoelectric ceramic diaphragm Since the feedback input is made to the input side electrode
as a reverberation suppressing signal for reducing the reverberation vibration, the reverberation
vibration can be actively canceled by the reverse phase vibration input of the reverberation
vibration signal itself.
As a result, reverberation vibration can be attenuated quickly and efficiently, and the S / N ratio
at the receiving side can be improved.
In addition, since the reverberation suppression signal to be input to the same piezoelectric
ceramic diaphragm is generated based on the reverberation vibration signal derived from the
same piezoelectric ceramic diaphragm, the temperature characteristic of the piezoelectric
ceramic diaphragm, the electrodes, etc. There is also the advantage that the trends are the same
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and less susceptible.
[0008]
In the ultrasonic output apparatus of the present invention, since the piezoelectric ceramic
diaphragm which is an electromechanical conversion element is adopted as a vibration drive unit,
when an ultrasonic wave emitted from another ultrasonic output apparatus is received, The
mechanical vibration of the piezoelectric ceramic diaphragm in which the ultrasonic waves are
excited can be extracted from the first main electrode as an electric signal waveform, and can be
used as an ultrasonic wave receiving element.
[0009]
The reverse feedback circuit can be integrated into a sensor module in which the piezoelectric
ceramic diaphragm, the pair of main electrodes and the partial electrodes, and the input / output
wiring to those electrodes are integrated.
As a result, the main parts of the device can be made compact, the structure can be complicated
by wiring, and the wiring distance to the reverse feedback circuit and each electrode can be
shortened, so that the noise resistance can be improved. it can.
[0010]
On the other hand, a reverse feedback formed separately from the sensor module at the terminal
portion of the input / output wiring of the sensor module in which the piezoelectric ceramic
diaphragm, the main electrode pair and the partial electrodes, and the input / output wiring to
those electrodes are integrated. It is also possible to connect the circuit externally. This makes it
possible to miniaturize the sensor module attached to the structure to be measured, and by
externalizing the inverting feedback circuit, it is easy to multifunctionalize the control circuit
configuration of the inverting feedback circuit, etc. It can correspond to
[0011]
The partial electrode can be formed in a smaller area than the first main electrode. Thereby, a
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large area of the first main electrode responsible for vibration drive for measurement can be
secured on the first main surface of the piezoelectric ceramic diaphragm, and the vibration
driving characteristics of the piezoelectric ceramic diaphragm by the main electrode pair can be
favorably secured. it can. In this case, if the partial electrode is used as a detection side electrode,
the reverberation suppression signal can also be input to the piezoelectric ceramic diaphragm
through the first main electrode having a large area, so that the damping effect of the
reverberation vibration can be greatly enhanced.
[0012]
In this case, the reverse feedback circuit can be provided on the short circuit path which shorts
the partial electrode and the first main electrode. And, on the output side of the reverberation
suppression signal of the inversion feedback circuit on the short circuit path, a reverberation
suppression signal input switch for switching the short circuit path between conduction and
interruption, and an input period of the measurement drive signal to the first main electrode A
reverberation suppression signal input switch control means can be provided which switches and
controls the reverberation suppression signal input switch so that the short circuit path is in a
conduction state after the short circuit path is in a cutoff state and the measurement drive signal
is in an interruption state. In this configuration, by switching control of the reverberation
suppression signal input switch, the input of the measurement drive signal and the generation of
the reverberation suppression signal and the feedback input can be smoothly switched by a
simple circuit configuration.
[0013]
The inverting feedback circuit can be configured as an inverting amplifier circuit. It is easy to set
the input level of the reverberation suppression signal to an appropriate value by the
amplification factor (gain) of the inverting amplification circuit. When the partial electrode is
formed to have a smaller area than the first main electrode, and the partial electrode is used as a
detection-side electrode, the inverting amplification circuit generates a signal voltage of
reverberation vibration appearing in the partial electrode measured with the short circuit path
cut off. The signal voltage of the reverberation vibration appearing on the partial electrodes is
inverted and amplified at an amplification factor greater than 1 in the direction in which the
difference between the amplitude of the signal vibration of the reverberation vibration appearing
on the first main electrode similarly decreases. It can be configured to be input to the main
electrode. That is, even if the detection voltage level of the reverberation lowers due to the
reduction of the area of the partial electrode, a reverberation suppression signal of a sufficient
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voltage level can be generated by setting the gain of the inverting amplification circuit large, and
thus the reverberation oscillation is rapidly Can be attenuated.
[0014]
In addition, the above-mentioned inverting amplification circuit can be configured to be variably
adjustable within a predetermined range of amplification factor. Even if the appropriate level of
the reverberation suppression signal changes due to temperature change or deterioration with
time of the piezoelectric ceramic diaphragm or the electrode, this can be easily coped with by
changing the amplification factor of the inversion amplification circuit.
[0015]
On the other hand, the inverting feedback circuit can also be configured as an inverting buffer
circuit (inverter circuit). The inverting feedback circuit can be configured by an inexpensive
inverter IC, and the circuit cost can be reduced. In this case, a plurality of inversion buffer circuits
are inserted in parallel in the short circuit path, and an inversion buffer circuit connection switch
mechanism is provided to switch the number of connection to the short circuit path of the
inversion buffer circuit, thereby outputting the reverberation suppression signal by the inversion
buffer circuits. And the input level of the reverberation suppression signal can be made variable.
[0016]
The input path of the measurement drive signal can then be distributed between the first main
electrode and the partial electrodes. In this case, the measurement drive signal can be
simultaneously applied to the first main electrode and the partial electrode through the input
path, and the vibration drive efficiency of the piezoelectric ceramic diaphragm can be further
enhanced. In this case, the distribution path to the partial electrode side of the input path is
always in a conductive state, while the distribution path to the first main electrode side of the
input path is a main for inputting the measurement drive signal to the first main electrode
Further branches into a path and a sub path formed in parallel with the main path and provided
with an inverting feedback circuit, and the reverberation suppression signal input switch can
switch one of the main path and the sub path exclusively to the input path. Can be configured to
connect to Then, the reverberation suppression signal input switch control means causes the
main path to conduct with the input path and the sub path to be disconnected from the input
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path during the input period of the measurement drive signal to the first main electrode, while
the input of the measurement drive signal After the cutoff, the main path is cut off from the input
path, and the dereverberation signal input switch can be switched and controlled so that the sub
path is electrically connected to the input path. As a result, generation and input of the
reverberation suppression signal can be performed without any problem while simultaneously
vibrating and driving the first main electrode and the partial electrode.
[0017]
On the other hand, the partial electrode can also be used as a monitoring electrode for extracting
a piezoelectric monitoring signal of ultrasonic vibration generated in the piezoelectric ceramic
diaphragm with the application of the measurement drive signal. Thus, the vibration waveform of
the piezoelectric ceramic diaphragm to which the drive signal is input can be monitored in real
time.
[0018]
For example, after the drive signal is input, it is necessary to know when ultrasonic vibration
actually occurred in the piezoelectric ceramic diaphragm by monitoring the waveform of this
partial electrode, including the delay in the piezoelectric ceramic diaphragm. Can. Therefore, if
the time from the input timing of the drive signal to the appearance of the vibration waveform at
the output of the partial electrode is measured, 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 can be accurately
grasped. . In particular, even when the delay time fluctuates with the time deterioration of the
vibration drive unit, by specifying the delay time by monitoring the output of the partial
electrode, the measurement standard of the ultrasonic wave propagation time is the ultrasonic
wave to be measured fluid. The actual emission timing can be approached, and the zero point
flow rate of the ultrasonic output device becomes less susceptible to the time-dependent drift. Of
course, it is also possible to detect the timing at which a specific vibration waveform appears at
the output of the partial electrode and use this as a measurement standard of ultrasonic wave
propagation time. In this case, it is not always necessary to specify the delay time itself by
measurement.
[0019]
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In this case, the dereverberation signal input means detects a predetermined timing reference
point in the waveform of the piezoelectric monitoring signal generated in the partial electrode
after blocking the input of the measurement drive signal to the main electrode pair, and detects
the timing reference point. It can be configured to determine the input timing of the
dereverberation suppression signal based on it. Thereby, the input timing of the reverberation
suppression signal can be accurately adjusted to the appropriate timing (the ideal timing is that
the phase of the reverberation suppression signal is 180 ° out of phase with the reverberation
vibration). In this case, if the measurement drive signal is simultaneously applied to the first main
electrode and the partial electrode through the input path, voltage monitoring of the partial
electrode after the measurement drive signal is cut off can be performed without switching the
switch. The input timing of the suppression signal can be adjusted with higher accuracy.
[0020]
Next, the reverberation suppression signal input means can be configured to be capable of
variably adjusting the input time of the reverberation suppression signal. Thereby, the input time
of the reverberation suppression signal can be easily adjusted to a value convenient for
optimizing the attenuation suppression of the reverberation vibration.
[0021]
The reverberation suppression signal input means can be configured to divide and input the
reverberation suppression signal into a plurality of input periods separated from each other by
the input cutoff period. By dividing and inputting the reverberation suppression signal in this
manner, even if some phase shift (deviation from 180 °) occurs between the reverberation
vibration and the reverberation suppression signal generated based on this, the reverberation
The influence of the in-phase component included in the suppression signal can be reduced.
[0022]
Also, the reverberation suppression signal input means can be configured to be capable of
variably adjusting the input voltage level of the reverberation suppression signal. As a result, the
input voltage level of the reverberation suppression signal can be easily adjusted to a value
convenient for optimizing the attenuation suppression of the reverberation vibration. Also, the
dereverberation signal can be input so that the voltage level gradually decreases. Even if a slight
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phase shift (a shift from 180 °) occurs between the reverberation vibration and the
reverberation suppression signal generated based on this, the influence of the in-phase
component contained in the reverberation suppression signal is reduced. Can.
[0023]
Next, a partial area of the first main electrode and the second main electrode can be cut out in
the first main surface of the piezoelectric ceramic diaphragm, and a partial electrode can be
formed in the cut-out area. Thereby, there is an advantage that the first main electrode or the
second main electrode covering the main surface of the piezoelectric ceramic diaphragm and the
partial electrode can be formed collectively by a known electrode patterning method (for
example, photolithography).
[0024]
In addition, since it is necessary to give the voltage reference at the time of output extraction also
to the ground for the partial electrode, the configuration in which the second main electrode is
shared by the first main electrode and the partial electrode simplifies the structure of the
vibration drive unit It is also convenient for Specifically, the first main electrode has a smaller
covering area for the piezoelectric ceramic diaphragm than the second main electrode, and the
remaining area not covered by the first main electrode of the second main surface of the
piezoelectric ceramic diaphragm. It is preferable to form a partial electrode on the
[0025]
In this case, when the partial electrodes are formed in the outer peripheral region of the second
main surface of the piezoelectric ceramic diaphragm, the influence of the partial electrodes on
the vibration drive characteristics of the piezoelectric ceramic diaphragm can be reduced.
[0026]
When the piezoelectric ceramic diaphragm is formed in a disk shape, the first main electrode can
be formed to have a circular outer peripheral shape along the outer peripheral edge of the
piezoelectric ceramic diaphragm.
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In this case, a part of the first main electrode can be cut out by recessing a part of the circular
outer peripheral edge in a radially inward concave manner, and a partial electrode can be formed
inside the cutout area. In this way, it is possible to easily form a wire for output extraction and a
soldered portion while sufficiently reducing the formation area of the partial electrode.
[0027]
In addition, the outer peripheral edge on the first main electrode side is formed on the outer
peripheral edge of the partial electrode so as to form a gap of a predetermined width between
the first main electrode and the partial electrode at a position adjacent to the partial electrode. It
can be formed in a shape to be copied. Thus, while ensuring insulation between the first main
electrode and the partial electrode, the exposed portion between the first main electrode and the
partial electrode, which is a dead area on vibration drive of the piezoelectric ceramic diaphragm,
is minimized. be able to. The width of the gap formed between the first main electrode and the
partial electrode is preferably 0.5 mm or more and 2.5 mm or less. If it is 0.5 mm or less, the
insulation between the first main electrode and the partial electrode may not be sufficiently
secured (for example, poor plating or bridging due to adhesion of conductive foreign matter), and
if it is 2.5 mm or less, the piezoelectric ceramic diaphragm The dead area on the vibration drive
increases too much, which leads to the problem that the drive efficiency of ultrasonic vibration
decreases.
[0028]
An embodiment of the ultrasonic output apparatus of the present invention will be described
with reference to the drawings, taking the case of application to an ultrasonic flow meter as an
example. FIG. 1 is a basic configuration of an embodiment of an ultrasonic flowmeter used as a
general residential gas meter or the like. The ultrasonic flowmeter 1 is provided at a position
different from each other in the flow direction O of the measurement fluid GF with respect to the
flow passage formation portion 3 forming the flow passage of the measurement fluid GF and the
flow passage formation portion 3 Is the sending side of the measurement ultrasonic wave to the
fluid GF to be measured, and the other is the receiving side of the measurement ultrasonic wave,
and the directivity to the predetermined direction as the measurement ultrasonic wave
respectively. And an ultrasonic transmission / reception unit 2a, 2b that can transmit an
ultrasonic beam SW. The flow path forming unit 3 and the ultrasonic transmitting / receiving
units 2a and 2b constitute a flowmeter main body 1M, and the flowmeter main body 1M and the
control circuit unit 1E constitute the whole ultrasonic flowmeter 1. The ultrasonic transmitting
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and receiving units 2a and 2b constitute the main part of the ultrasonic output apparatus.
[0029]
The flow path forming unit 3 is made of metal, for example. When the object to be measured is a
gas, the axial cross-sectional shape of the flow path forming portion 3 may be any as long as it
forms a space closed by the wall portion 3J, for example, any of circular, elliptical, square and
rectangular May be adopted. In the present embodiment, the flow path forming unit 3 is formed
to have a rectangular flow path cross section, and the upper wall portion 3Ja has the upstream
ultrasonic transmission / reception portion 2a, and the lower wall portion 3jb has the
downstream ultrasonic transmission / reception portion 2b is attached. That is, the ultrasonic
transmitting and receiving units 2a and 2b which make a pair are distributed and arranged in a
form in which the flow path is sandwiched.
[0030]
The ultrasonic transmitting and receiving units 2a and 2b are ultrasonic transducers having an
ultrasonic transducer. Both of them are configured as the ultrasonic wave output device of the
present invention, and an ultrasonic wave transmission function of transmitting an ultrasonic
wave beam by application of a driving voltage and an ultrasonic wave reception function of
outputting an electric signal (reception signal) by reception of an ultrasonic wave beam. And a
combination of All of them have the same structure, and therefore will be described as being
represented by one of them (hereinafter, represented by reference numeral "2").
[0031]
FIG. 2 shows an example of the cross-sectional structure of the ultrasonic transmission /
reception unit 2 (ultrasonic output apparatus). The ultrasonic transmission / reception unit 2 is
formed so that the main part (vibration drive unit) is opposed to the piezoelectric ceramic
vibration plate 21 polarized in the plate thickness direction with the piezoelectric ceramic
vibration plate 21 interposed therebetween. A main electrode pair comprising a first main
electrode 23 covering the first main surface of the plate 21 and a second main electrode 46 also
covering the second main surface, and a first main surface of the piezoelectric ceramic
diaphragm 21 One main electrode 23 and a partial electrode 24 provided in an insulated manner
are provided.
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[0032]
The piezoelectric ceramic vibrating plate 21 is made of, for example, a perovskite-type
ferroelectric ceramic such as lead zirconate titanate (PZT), barium titanate, lead titanate, lead
lanthanum zirconate titanate, etc. It is polarized. Each of the electrodes 22, 23, 24 is formed of a
metal vapor deposition film of Cu or the like.
[0033]
In the main electrode pair 22, 23, the second main electrode 22 covering the second main
surface of the piezoelectric ceramic diaphragm 21 is connected to the ground (GND) side, and the
first main electrode 23 covering the first main surface is also for measurement Connected to the
drive power supply of The partial electrode 24 is formed to have a smaller covering area for the
piezoelectric ceramic diaphragm 21 than any of the second main electrode 22 and the first main
electrode 23. As shown in FIG. 8, the first main electrode on the first main surface of the
piezoelectric ceramic diaphragm 21 is set such that the covering area for the piezoelectric
ceramic diaphragm 21 is smaller than that of the second main electrode 22. The partial electrode
24 is formed in the remaining area not covered by the numeral 23.
[0034]
The partial electrodes 24 are formed in the outer peripheral region of the first main surface of
the piezoelectric ceramic diaphragm 21. Specifically, the piezoelectric ceramic diaphragm 21 is
formed in a disk shape, and the first main electrode 23 has a circular outer peripheral shape
along the outer peripheral edge of the piezoelectric ceramic diaphragm 21. Then, a part of the
first main electrode 23 is notched in such a manner that a part of the circular outer peripheral
edge is recessed in a radially inward direction, and the partial electrode 24 is formed inside the
notched area 23c. . The outer peripheral edge on the first main electrode 23 side forms a gap 20
of a predetermined width between the first main electrode 23 and the partial electrode 24 at a
position adjacent to the partial electrode 24. It is formed in the shape which imitates the outer
periphery of. The width w of the gap 20 formed between the first main electrode 23 and the
partial electrode 24 is adjusted to 0.5 mm or more and 2.5 mm or less.
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[0035]
Returning to FIG. 2, the piezoelectric ceramic diaphragm 21 is disposed in the casing 29 such
that the first main surface side on which the first main electrode 23 and the partial electrode 24
are formed faces the inner surface of the bottom 28 of the casing 29 There is. A drive terminal
43 and a monitor terminal 44 are formed to protrude from the back surface of the bottom
portion 28 of the casing 29, and the first main electrode 23 and the partial electrode 24 are
connected to the drive terminal 43 and the monitor terminal 44 respectively. The drive terminal
43 is connected to an output circuit of a measurement drive signal for causing the piezoelectric
ceramic diaphragm 21 to generate ultrasonic vibration for measurement, and a measurement
drive signal input unit for inputting the measurement drive signal to the main electrode pair
Configure.
[0036]
Next, as shown in FIG. 8, with the partial electrode 24 as the detection side electrode and the first
main electrode 23 as the input side electrode, a reverberation vibration signal that appears on
the detection side electrode after blocking the input of the measurement drive signal to the main
electrode pair. And a feedback circuit 100 for feedback-inputting this signal to the input side
electrode as a reverberation suppression signal for reducing reverberation vibration remaining in
the piezoelectric ceramic diaphragm 21. The reverse feedback circuit 100 forms the main part of
the reverberation suppression signal input means, and in the present embodiment, as shown in
FIG. 2, the reverse feedback circuit 100 is mounted on the substrate 100S, and the piezoelectric
ceramic diaphragm 21, main The sensor unit integrated with the electrode pair and the partial
electrode 24 and the input / output wiring to the electrodes, that is, integrated into an ultrasonic
transmitting / receiving unit 2 (hereinafter also referred to as a sensor module 2).
[0037]
As shown in FIG. 8, the inversion feedback circuit 100 is provided on a short circuit path which
shorts the partial electrode 24 and the first main electrode 23, and the reverberation suppression
signal of the inversion feedback circuit 100 is formed on the short circuit path. A reverberation
suppression signal input switch SWM is provided on the output side to switch the short circuit
path between conduction and cutoff. In the reverberation suppression signal input switch SWM,
the short circuit path is cut off during the measurement drive signal input period to the first main
electrode 23 by the microcomputer 11 described later, and the short circuit path is turned on
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after the measurement drive signal input is cut off. It is controlled to switch to That is, the
microcomputer 11 constitutes an essential part of the function of the reverberation reduction
signal input means.
[0038]
In FIG. 8, the inverting feedback circuit 100 is configured as an inverting amplifier circuit.
Specifically, the inverting amplification circuit comprises an operational amplifier IC0 and
resistors R1 and R2 for determining gain, and the reverberation vibration signal detected by the
partial electrode 24 is inputted to the inverting input terminal of the operational amplifier IC0.
The noninverting input terminal of the operational amplifier IC0 is grounded. As described above,
the partial electrode 24 to be the detection side electrode is formed to have a smaller area than
the first main electrode 23, and the above-mentioned inverting amplifier circuit is used for
reverberation vibration appearing in the partial electrode 24 measured with the short circuit
path cut off. In the direction in which the difference between the amplitude of the signal voltage
and the amplitude of the signal voltage of the reverberation vibration similarly appearing in the
first main electrode 23 decreases, the signal voltage of the reverberation vibration appearing in
the partial electrode 24 is inverted and amplified at an amplification factor greater than 1 Each
value of the resistors R1 and R2 for gain determination is determined so as to be input to the
first main electrode 23.
[0039]
Returning to FIG. 2, the casing 29 is a metal member in which the bottom portion 28, the side
wall portion 30 rising from the periphery of the bottom portion 28, and the top surface portion
29 t closing the opening on the opposite side of the bottom portion 28 of the side wall portion
30 are mutually conductive. It is formed. The second main electrode 22 covering the second
main surface of the piezoelectric ceramic diaphragm 21 is closely disposed on the inner surface
of the top surface portion 29t via the conductive adhesive layer 46, and the second main
electrode 22 is grounded via the casing 29. It is supposed to be The drive terminal 43 and the
monitor terminal 44 extend through the bottom 28 to the back side. Further, the ground terminal
41 is formed so as to protrude integrally with the bottom portion 28. Further, the substrate 100S
on which the inversion feedback circuit 100 is mounted is fixed on the bottom portion 28. The
power supply terminal 45 of the reverberation suppression signal input switch SWM (FIG. 8) and
the power supply terminal 46 of the operational amplifier IC0 (FIG. 8) mounted on the substrate
100S also penetrate the bottom 28 and extend to the back side. ing.
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[0040]
In addition, since the metal casing 29 doubles as the ground conductor, the ground terminal is
omitted as shown in FIG. 3, and the ground connection portion (here, the flow path forming
portion in FIG. A mounting screw portion 41th may be formed to be screwed with a mounting
screw hole formed in the wall portion 3.
[0041]
Next, as shown in FIG. 2, 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 closely attached to the outer main surface of the top surface portion 29t. It is
arranged.
The acoustic impedance matching layer 25 is formed in a disc shape, for example, of a composite
material in which a resin material such as epoxy resin is used as a matrix and a filler for void
formation (for example, a glass balloon) is dispersed. On the other hand, an insulating ring made
of rubber is fitted on the inner peripheral surface of the side wall 30, and the space between the
piezoelectric ceramic diaphragm 21 and the bottom 28 is filled with a gel polymer material 26
such as silicone, Is covered by an insulator 47 such as resin. In order to improve the transmission
efficiency of ultrasonic waves, the volume compounding ratio of the filler for void formation of
the acoustic impedance matching layer 25 is an acoustic impedance value intermediate between
the piezoelectric ceramic diaphragm 21 and the fluid to be measured (here, city gas). (For
example, the geometric mean value of both is set as the target value). In addition, in order to
obtain the target acoustic impedance value, the acoustic matching layer 25 may be formed of a
resin material which does not mix the filler for void formation.
[0042]
Returning to FIG. 1, the control circuit unit 1E is provided with the above-described ultrasonic
drive mechanism 4 and peripheral circuit blocks 7-11. The ultrasonic drive mechanism 4 has a
transmitting unit 5, a receiving unit 6, and a switching unit 4s. The transmitting unit 5 is a circuit
for inputting a drive signal to the ultrasonic transmitting and receiving units 2a and 2b. The
receiving unit 6 is composed of a switch or the like, and switching of the switch makes it possible
to switch the above-mentioned drive mode. The switching control of the receiving unit 6 is
performed by the switching unit 4s. The amplification unit 7 amplifies the ultrasonic waves
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received by the reception unit 6 at a predetermined amplification factor, and inputs the amplified
ultrasonic waves to the zero cross point detection unit 9. The zero cross point detection unit 9
detects a zero cross point of a specific order wave (for example, the third wave) included in the
received ultrasonic waveform. The time measurement unit 10 has a second propagation time
until the ultrasonic beam SW transmitted from the upstream ultrasonic transmission / reception
unit 2a reaches the downstream ultrasonic transmission / reception unit 2b in the first drive
mode, and the second drive In this mode, the backward propagation time until the ultrasonic
beam SW transmitted from the downstream ultrasonic transmitting / receiving unit 2b in the
mode reaches the upstream ultrasonic transmitting / receiving unit 2a is measured. Further, the
microcomputer 11 calculates the average flow velocity and the flow rate of the fluid to be
measured flowing in the flow path from the time difference between the forward propagation
time and the backward propagation time described above.
[0043]
As shown in FIG. 7, the ultrasonic transmitting / receiving unit 2 receives a drive signal from the
outside, so that the signal is converted into mechanical vibration by the piezoelectric ceramic
vibration plate, and is further propagated through the acoustic impedance matching layer 25 to
be Since the radiation to the measurement fluid occurs, there is a certain delay time from the
input timing of the drive signal to the time when the ultrasonic wave is emitted to the fluid to be
measured. Then, in the conventional flow rate measurement (FIG. 7: (3)), the input timing of the
drive signal is regarded as equivalent to the emission timing of the ultrasonic wave to the fluid to
be measured, and this is used as the measurement starting point of the ultrasonic wave
propagation time. . However, in this measurement method, it is clear that the delay time is
included as a measurement error in the ultrasonic wave propagation time as described above,
and the delay time is the time degradation of the vibration drive unit and the reverse direction to
the forward direction measurement. If it fluctuates due to the asymmetry to temperature change
etc. between the time of measurement (Fig. 7: (1)), the error of the delay time to the original
ultrasonic wave propagation time (Fig. 7: (2)) The contribution rate also fluctuates, and there is a
problem that measurement correction of ultrasonic wave propagation time becomes impossible.
[0044]
However, the configuration of the ultrasonic wave output device 2 in the present embodiment,
that is, the piezoelectric ceramic diaphragm 21 concerned with the application of the drive
voltage to the piezoelectric ceramic diaphragm 21 which constitutes the main part of the
vibration drive unit By adopting a configuration provided with a partial electrode 24 for taking
out a piezoelectric monitoring signal of ultrasonic vibration generated in 21, the vibration
waveform of the piezoelectric ceramic diaphragm to which the drive signal is input can be
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monitored in real time.
[0045]
That is, as shown by the broken line in FIG. 7, after the drive signal is input, when ultrasonic
vibration actually occurs in the piezoelectric ceramic diaphragm 21 in a form including the delay
of the piezoelectric ceramic diaphragm, It can be known by monitoring the waveform of the
partial electrode 24.
Therefore, if the time from the input timing of the drive signal to the appearance of the vibration
waveform in the output of the partial electrode 24 is measured, the delay time from the input
timing of the drive signal to the discharge timing of the ultrasonic wave to the fluid to be
measured can be grasped. As a result, even if the delay time fluctuates due to the deterioration
with time of the vibration drive unit, by specifying the delay time by monitoring the output of the
partial electrode 24, the measurement standard of ultrasonic wave propagation time can be
measured fluid of ultrasonic waves. It is possible to approximate the actual release timing to (Fig.
7: (4)) and to reduce the measurement error.
[0046]
FIG. 4 shows a detailed example of the circuit configuration of FIG. The ground terminals 41a and
41b of the two ultrasonic transmitting and receiving units 2a and 2b are connected to the ground
line GND via the individual switches SW3 and SW4. The ground line GND is switchable between
ground conduction and float by starting switch SW5. On the other hand, the drive terminals 43a
and 43b are connected selectively switchably to the drive input line INP by the switches SW1
and SW2. The monitor terminals 44a and 44b are alternatively connected to the monitor line
MNT by switches SW8 and SW9. Furthermore, the drive input line INP and the monitor line MNT
are selectively connected to the amplification unit 7 by switches SW6 and SW7.
[0047]
Note that, on the drive input line INP, a bootstrap circuit 51 for impedance conversion, which is a
pair of parallel bidirectional diodes, is provided. Further, an overvoltage protection circuit 52
consisting of a parallel bidirectional diode pair is disposed between the monitor line MNT and the
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ground line GND. Furthermore, a resistor R2 is inserted between the drive input line INP and the
ground line GND in order to improve noise resistance and stabilize the drive input voltage.
Further, on the monitor line MNT, a resistor R1 for adjusting the input impedance to the
amplification unit 7 is inserted. The amplifying unit 7 has a charge amplifier 71 for converting
the change in charge amount generated in the piezoelectric ceramic diaphragm from the input
upper stage side, and an inverting amplification unit 72 for inverting and amplifying the output
voltage of the charge amplifier 71. Note that, instead of the charge amplifier 71, a voltage
amplifier that uses an electrode voltage of a piezoelectric ceramic diaphragm may be used.
[0048]
FIG. 5 shows an example of the circuit configuration of the zero cross comparator unit 9. The
input signal of the waveform output of the amplification unit 7 has the same lower limit
amplitude as the first comparator 91 that squares the input signal with respect to GND. It is
distributed and input to a second comparator 92 that square-waves 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, and the output of the second comparator 92 is also
input to the reset terminal. The output change edge of the set / reset flip flop (RSFF) circuit 93
The zero cross point pulse generation circuit 94 configured of a monostable circuit detects a
pulse waveform corresponding to a zero cross point due to a half wave exceeding the amplitude
Vs among the input waveform from the amplification unit 7 in a form triggered by Output as a
signal. 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 outputs a
detection signal of propagation time by counting a prescribed number of pulse inputs.
[0049]
FIG. 6 is a timing chart showing the operation sequence of each part. The amplified output (Va)
of the vibration waveform excited by the input of the drive pulse (measurement drive signal) is
squared by the first comparator 91 while the (Vb1) second comparator 92 is inverted with the
amplitude Vs as a threshold The vibration waveform is squared by the waveform. Thereby, 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 this embodiment, it is
recognized from the zero crossing point of the predetermined order wave of the initial vibration
waveform whose amplitude gradually increases (here, the zero crossing point of the second
positive half wave (that is, the third zero crossing point from the waveform start point). , And the
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amplitude threshold of the second comparator 92 is determined.
[0050]
The circuit of FIG. 4 operates as follows. The repeat drive of each switch is controlled by the
microcomputer 11 of FIG. 1 executing a predetermined control program. First, a drive signal
pulse is input to the upstream ultrasonic transmitting and receiving unit 2a. このとき、
SW1,SW7,SW8がONとなり、SW3,4,5もONとなる。 On the other hand, SW2,
SW6 and SW9 are turned off. As a result, the upstream ultrasonic transmitting and receiving unit
2a is vibrated and excited at the drive terminal 43a, and the drive monitor waveform appears at
the monitor terminal 44a after the above-mentioned delay time. This waveform is input from the
amplification unit 7 to the zero cross comparator 9 through the monitor line MNT (SW7), 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 a time t0 (FIG. 7) to the zero cross point of the monitor waveform
starting from the input timing of the drive signal.
[0051]
Since the ultrasonic wave based on the drive input is emitted from the upstream ultrasonic
transmitting and receiving unit 2a into the medium to be measured, the SW7 and SW8 are set
until the waveform reaches the downstream ultrasonic transmitting and receiving unit 2b. The
switch SW2 and the switch SW6 are turned on as OFF (SW1, SW3, SW4, SW5 are ON). SW9
continues to be in the OFF state). Thereby, the reception waveform of the downstream ultrasonic
transmission / reception unit 2b is input from the amplification unit 7 to the zero cross
comparator 9 through the drive line MNT (SW 6), the zero cross point of the predetermined
order wave is specified, and the propagation time detection signal is timed It is output to the
circuit 10. The time measuring circuit 10 measures the time tx (FIG. 7) to the above-mentioned
zero crossing point of the received waveform, starting from the input timing of the drive signal.
Thereby, the final forward propagation time can be calculated as tx−t0.
[0052]
Subsequently, the transmission / reception relationship between the upstream ultrasonic
transmission / reception unit 2a and the downstream ultrasonic transmission / reception unit 2b
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is exchanged and the same measurement is performed. That is, in order to input a drive signal
pulse to the downstream ultrasonic transmission / reception unit 2b, SW2, SW7 and SW9 are
turned ON, and SW3, 4 and 5 are also turned ON. On the other hand, SW1, SW6 and SW8 are
turned off. As a result, the downstream ultrasonic transmitting and receiving unit 2b is
vibrationally excited at the drive terminal 43b, the zero crossing point of the predetermined
order wave is specified as described above, and the propagation time detection signal is output to
the time measuring circuit 10. The time measuring circuit 10 measures a time t0 'up to the zero
cross point of the monitor waveform starting from the input timing of the drive signal. Next, the
switches SW7 and SW9 are turned OFF and the switches SW1, SW2 and SW6 are turned ON
(SW2, SW3, SW4, SW5 are in the ON state. SW8 continues to be in the OFF state). As a result, the
zero cross point of the reception waveform of the upstream ultrasonic wave transmission /
reception unit 2a 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 'up to the abovementioned zero crossing point of the received waveform starting from the input timing of the
drive signal. Thereby, the final backward propagation time can be calculated as tx'-t0 '. Then, the
flow velocity (or flow rate) can be calculated by a known method using the above-mentioned
forward propagation time tx-t0.
[0053]
Here, in any of the ultrasonic transmitting / receiving units 2a and 2b, after the input of the
measurement drive signal to the main electrode pair is interrupted, the reverberation vibration
signal is detected by the partial electrode 24 which is the detection side electrode, and the
inversion of FIG. The signal is inverted and amplified by the feedback circuit 100, and is feedback
input to the first main electrode 23, which is an input side electrode, as a reverberation
suppression signal. That is, the reverberation vibration can be actively canceled by the reverse
phase vibration input of the reverberation vibration signal itself, and the reverberation vibration
can be damped quickly and efficiently, and the S / N ratio at the receiving side can be improved.
[0054]
Specifically, the zero cross point detection signal (see FIG. 4) is output as a timing reference point
on the waveform of the piezoelectric monitoring signal generated in the partial electrode 24 after
the input drive to the main electrode pair of the measurement drive signal is interrupted. 6) is
distributed to the microcomputer 11. The microcomputer 11 regards the period until receiving
the zero cross point detection signal as the input period of the measurement drive signal, and in
the meanwhile, the reverse feedback circuit 100 is provided with the reverberation reduction
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signal input switch SWM of FIG. 8 turned off (opened). The short circuit path is cut off. As a
result, the output of the inverting feedback circuit 100 is not input to the first main electrode 23,
and interference with the measurement drive signal input is avoided. On the other hand, when
the zero cross point detection signal is detected, the microcomputer 11 immediately turns on
(closes) the reverberation reduction signal input switch SWM to make the short circuit path
provided with the inversion feedback circuit 100 conductive. Then, the reverberation
suppression signal output of the inversion feedback circuit 100 is input to the first main
electrode 23, and the reverberation vibration is canceled. The reverberation reduction signal
input switch SWM is returned to the OFF state within a period until the ultrasonic transmission /
reception unit is operated and driven as the reception side.
[0055]
As described above, the partial electrode 24 is formed in a smaller area than the first main
electrode 23, and as shown in the timing diagram of FIG. The amplitude of the signal voltage of
the reverberation vibration appearing on the partial electrode 24 (in the absence of a feedback
input to the main electrode 23) is smaller than the amplitude of the signal voltage of the
reverberation vibration appearing on the first main electrode 23 as well. However, since the
inverting feedback circuit 100 inversely amplifies and amplifies this at an amplification factor
greater than 1 and inputs it to the first main electrode 23, the detection voltage level of the
reverberation vibration is lowered by the area reduction of the partial electrode 24. In spite of
that, a reverberation suppression signal of a sufficient voltage level can be generated, and thus
reverberation oscillation can be rapidly attenuated.
[0056]
Hereinafter, various modified examples of the present invention will be described. In the circuit
configuration of FIG. 8, the insertion direction of the inversion feedback circuit 100 in the short
circuit path is determined such that the partial electrode 24 is the detection side electrode and
the first main electrode 23 is the input side electrode. It is also possible to replace and configure
both as shown in FIG.
[0057]
Further, as shown in FIG. 11, the microcomputer 11 controls the reverberation reduction signal
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to be input at once by continuously closing the reverberation reduction signal input switch SWM
in a single period (T0). However, as shown in FIG. 12 and FIG. 13, the input can be divided into a
plurality of input periods (T1 ′, T2 ′,...) Separated from each other by the switch interruption
period. In FIG. 12, the input periods T1 ', T2',... Are set to be equal to each other, while in FIG. 13,
the input periods T1 ', T2',. There is. Further, the total input time of the reverberation reduction
signal may be variably settable by the adjustment control of the ON duration time of the
reverberation reduction signal input switch SWM by the microcomputer 11.
[0058]
Next, as shown in FIG. 14, the inverting amplification circuit constituting the inverting feedback
circuit 100 can variably configure its output gain. In the embodiment of FIG. 14, gain adjustment
is performed by variably configuring the value of the negative feedback resistor. Specifically, the
resistor arrays R51, R52,..., Rn constituting negative feedback resistors are connected /
disconnected by switching control of the switch arrays SW51, SW52,. The combined resistance
value can be varied according to the number of connections.
[0059]
Therefore, even if the reverberation vibration input level to the detection side electrode is the
same, the input voltage level of the reverberation reduction signal can be variably adjusted by
changing the gain (amplification factor) of the inverting amplification circuit. For example, as
shown in FIG. 11, the reverberation reduction signal input switch SWM is continuously closed in
a single period (T0) to collectively input the reverberation reduction signal. Can be input with
time so that the voltage level decreases gradually. Also, as shown in FIG. 12 and FIG. 13, when
the reverberation reduction signal is input by being divided into a plurality of input periods (T 1
′, T 2 ′,...) Separated from each other by the switch cutoff period, time series By setting the
gain smaller for an input period located later, the reverberation reduction signal can be input so
that the voltage level gradually decreases.
[0060]
In FIG. 14, the substrate of the inversion feedback circuit 100 ′ formed separately from the
sensor module 2 is externally connected to the terminal portions (41, 43, 44) of the input /
output wiring of the sensor module 2. Configured. As a result, as shown in FIG. 15, the sensor
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module 2 ′ does not need to incorporate the substrate of the inverting feedback circuit, and the
configuration is simplified (specifically, the terminal 45 and the associated terminal of the
inverting feedback circuit 100 ′) 46 is omitted).
[0061]
Next, in the embodiment shown in FIG. 16, the inverting feedback circuit 100 is configured by an
inverting buffer circuit (inverter IC1). In the configuration of FIG. 16, the input path of the
measurement drive signal is distributed to the first main electrode 23 and the partial electrode
24, and the distribution path to the partial electrode 24 side of the input path is always in the
conductive state. . On the other hand, the distribution path to the first main electrode 23 side of
the input path includes a main path for inputting a measurement drive signal to the first main
electrode 23, and a sub path formed in parallel with the main path and provided with the
inverting feedback circuit 100. Further, it branches into a path, and one of the main path and the
sub path is connected to the input path exclusively and switchably by the reverberation
reduction signal input switches SW0 and SW1. In this embodiment, the reverberation reduction
signal input switch is configured by a set of SPST switches SW0 and SW1 individually provided
for the main path and the sub path, but it is also possible to configure this with one SPDT switch.
It is possible.
[0062]
Also here, while the microcomputer 11 operates as a reverberation reduction signal input switch
control means, the main path conducts with the input path and the sub path is cut off from the
input path during the input period of the measurement drive signal to the first main electrode 23
(SW0 is ON, SW1 is OFF), the main path is cut off from the input path after the input of the
measurement drive signal is cut off, and the sub path is conducted with the input path (SW0 is
OFF, SW1 is ON). The switches SW0 and SW1 are switched and controlled. By this operation, as
shown at the bottom of FIG. 16, an input sequence of the reverberation reduced signal similar to
that of FIG. 10 is realized.
[0063]
As shown in FIG. 17, a plurality of inversion buffer circuits IC1, IC2,. An inversion buffer circuit
connection switch mechanism (SW1, SW2,..., SWn) 105 can also be provided. The sink current of
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the reverberation reduction signal output can be variably adjusted according to the number of
connected inverting buffer circuits. Then, if the reverberation vibration input level to the
detection side electrode is the same, variably adjust the input voltage level of the reverberation
reduction signal by changing the sink current value of the reverberation reduction signal output
(that is, the number of connected inverting buffer circuits). Can.
[0064]
Further, in the configurations of FIG. 18 and FIG. 19, this is an example in which a pair of
inversion buffer circuits IC1 and IC2 whose connection directions are opposite to each other are
provided in parallel. The configuration of FIG. 18 is an example in which the substrate of the
inversion feedback circuit 100 is incorporated in the sensor module 2. In this case, although the
external appearance terminal structure of the sensor module 2 is substantially the same as the
configuration of FIG. 2, as shown in FIG. · Drive terminal 43 → Power supply terminal 43 'of
inversion buffer circuit IC1 · Monitor terminal 44 → Drive terminal 44' · Power supply terminal
45 of switch SWM → Power supply terminal 45 of switch SW0 · Power supply terminal 46 of
operational amplifier IC0 → Power supply of switch SW1 Terminal 46 '
[0065]
The above configuration further stabilizes the vibration phase control when the area S2 of the
partial electrode 24 becomes larger than a certain value with respect to the electrode area S1 of
the first main electrode 23 (for example, when 3 ≦ S1 / S2 ≦ 10). It can be used effectively if
you want to Specifically, when the switch SW1 is opened and the switch SW2 is closed in a state
where the switch SW0 is opened, vibration is detected on the partial electrode 24 side and input
to the first main electrode 23 while being reverse buffered by the inverter IC2. (1st reverberation
suppression input). On the other hand, when the switch SW2 is opened and the switch SW1 is
closed, vibration is detected on the side of the first main electrode 23, and input to the partial
electrode 24 while being phase-inverted by the inverter IC1 (second reverberation suppression
input). The first main electrode 23 on the large area side is vibration-suppressed by the first
reverberation suppression input, and the control to the vibration suppression drive of the smallarea side electrode 24 is alternately repeated by the second reverberation suppression input. The
phase shift of the reverberation reduction signal can be reduced, and more effective
reverberation suppression can be achieved.
[0066]
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Further, FIG. 19 shows an embodiment in which the circuit configuration is equivalent to that of
FIG. 18, but only the inversion buffer circuit connection switch mechanism 105 is separated from
the sensor module 2 as the external mounting substrate 102. The sensor module 2 and the
external mounting board 102 are connected by a connector 101.
[0067]
BRIEF DESCRIPTION OF THE DRAWINGS The schematic diagram which shows the whole
structure of the ultrasonic flowmeter which becomes an application object of this invention. The
longitudinal cross-sectional view which shows one Embodiment of the sensor module used for
the ultrasonic output apparatus of this invention. The longitudinal cross-sectional view which
shows the modification of FIG. FIG. 2 shows the details of the circuit part of FIG. 1; FIG. 5 is a
circuit diagram showing a configuration example of the zero cross comparator circuit of 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. The circuit
diagram which shows 1st embodiment which concerns on the summary of this invention of the
ultrasound output apparatus of FIG. FIG. 9 is a timing chart showing an operation sequence of
the circuit of FIG. 8; FIG. 9 is a circuit diagram showing a modification of FIG. 8; The timing chart
which shows the 1st example of the input sequence of a reverberation reduction signal. The
timing chart which similarly shows a 2nd example. The timing diagram which similarly shows a
3rd example. The circuit diagram which shows 2nd embodiment which concerns on the summary
of this invention of the ultrasonic wave output apparatus of FIG. The longitudinal cross-sectional
view which shows one structural example of the sensor module in the case of setting it as the
circuit structure of FIG. FIG. 7 is a circuit diagram showing a second embodiment of the
ultrasonic output apparatus of FIG. 1 according to the present invention, together with a timing
chart showing an input sequence of a reverberation reduction signal. FIG. 17 is a circuit diagram
showing a first modified example of FIG. 16; FIG. 17 is a circuit diagram showing a second
modification of FIG. 16 together with a timing chart showing an input sequence of a
reverberation reduction signal. FIG. 17 is a circuit diagram showing a third modification of FIG.
16;
Explanation of sign
[0068]
DESCRIPTION OF SYMBOLS 1 ultrasonic flow meter 2 ultrasonic transmission / reception part
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(sensor module) 11 microcomputer (measurement drive signal input means, reverberation
suppression signal input means, reverberation suppression signal input switch control means) 21
piezoelectric ceramic diaphragm 22, 23 main electrode pair 22 first Two main electrodes 23
First main electrode 24 Partial electrodes 100, 100 'Inverted feedback circuit SWM, SW0, SW1
Reverberation suppression signal input switch
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