JP2003339092A - Ultrasonic wave sensor, and ultrasonic wave flowmeter employing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ultrasonic wave sensor for ensuring an always stable detection accuracy over a wide temperature range. <P>SOLUTION: The ultrasonic wave sensor 2 is provided with a pair of piezoelectric vibrators 5a, 5b for mutually transmitting/receiving an ultrasonic wave, and one of the piezoelectric vibrators 5a, 5b (e.g. 5a) is provided with a static capacitance adjustment section 17 for adjusting the static capacitance of a piezoelectric substance 6 of the vibrator 5a to be nearly in matching with the static capacitance of a piezoelectric substance 6 of the other piezoelectric vibrator (e.g. 5b). The static capacitance adjustment section 17 is formed by trimming at least either of a piezoelectric substrate 14 configuring the piezoelectric vibrators 5a, 5b or a pair of electrodes 15 clamping the piezoelectric substrate 15. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic sensor and an ultrasonic flowmeter using the ultrasonic sensor.

[0002]

2. Description of the Related Art Generally, as shown in FIG. 11, an ultrasonic flowmeter is constructed by providing an ultrasonic sensor A in a flow path through which a fluid such as gas or liquid flows. This ultrasonic sensor A
Is provided with, for example, a pair of piezoelectric vibrators B1 and B2, one piezoelectric vibrator B1 is located upstream (left side in the figure) and the other piezoelectric vibrator B2 is located downstream (right side in the figure) by a predetermined distance L. They are arranged so as to face each other. The piezoelectric vibrators B1 and B2 in this case have both functions of transmitting and receiving ultrasonic waves.

Here, assuming that the fluid is flowing at a constant speed, ultrasonic waves are transmitted from the piezoelectric vibrators B1 and B2. At this time, the time required for the ultrasonic wave transmitted from the upstream piezoelectric vibrator B1 to be received by the downstream piezoelectric vibrator B2 is t1, and the ultrasonic wave transmitted from the downstream piezoelectric vibrator B2. Let t2 be the time required for the piezoelectric transducer B1 on the upstream side to receive the signal, t1 <t2, and the difference Δt (= t2-t1) between both times t1 and t2 is proportional to the flow velocity v of the fluid. There is.

Therefore, the flow velocity v of the fluid can be measured by detecting the difference Δt in time required for the ultrasonic waves to reach the piezoelectric vibrators B1 and B2, and the cross-sectional area of the flow path can be known. Thus, the flow rate can be measured from the flow velocity v.

[0005]

In the above ultrasonic flowmeter, when the flow of fluid is stopped and the flow rate is zero, the above-mentioned time difference Δt detected by the ultrasonic sensor A is detected.
Should be zero. However, in reality, each piezoelectric vibrator B1, which constitutes the ultrasonic sensor A,
In B2, there is a slight difference in response time until the received ultrasonic wave is converted into an electric signal and is output. Similarly, when converting an electric signal into an ultrasonic wave and outputting the ultrasonic wave, there is a difference in response time.

Therefore, even when the flow rate is zero, the above time difference Δt does not become zero and an error occurs. Hereinafter, such an error is referred to as a time error Δte. Moreover, this time error Δ
te has temperature dependency as shown in FIG. 12, and tends to increase as the temperature increases, for example.

Each piezoelectric vibrator B constituting the ultrasonic sensor A
If such a time error Δte occurs due to variations in the responsiveness of 1 and B2, the flow rate of the fluid cannot be accurately measured. Therefore, such a time error Δte
Need to be prevented. To that end, for example, characteristic data indicating the temperature dependence of the time error Δte as shown in FIG. 12 is stored in advance in a memory or the like inside the apparatus, and when the time difference Δt is detected as described above, this time difference Δt is detected. Time error Δte corresponding to temperature from Δt
It is conceivable to remove the influence of the time error Δte by performing the correction for subtracting.

However, it is extremely troublesome to individually measure and register the characteristic data as shown in FIG. 12 in each memory for each ultrasonic sensor A constituting the ultrasonic flowmeter. The circuit for performing the correction signal processing also becomes complicated and expensive.

The present invention has been made to solve the above-mentioned problems, and it is possible to easily and effectively eliminate the time error caused by the variation in the responsiveness between the piezoelectric vibrators, so that the wide range of temperature can be achieved. An object of the present invention is to provide an ultrasonic sensor that always ensures stable detection accuracy, and an ultrasonic flowmeter using the ultrasonic sensor.

[0010]

Before describing the concrete means for solving the problems of the present invention, the basic concept of the present invention will be explained.

The present inventor has made extensive studies as to the cause of variations in responsiveness among the piezoelectric vibrators constituting the ultrasonic sensor, and has obtained the following findings.

Now, for example, 2 which constitutes an ultrasonic sensor
When attention is paid to one piezoelectric vibrator, it is assumed that the electrostatic capacities C1 and C2 of the piezoelectric bodies forming each piezoelectric vibrator are different from each other. Then, the piezoelectric vibrators having piezoelectric bodies having different capacitances C1 and C2 are arranged at an equal distance from one sound source, and the ultrasonic waves generated by the sound source are received by the respective piezoelectric vibrators. It shall be.

In this case, as shown in FIG. 1, the response time required for converting the ultrasonic waves received by each piezoelectric vibrator into an electric signal and outputting the electric signal is different from each other due to the difference in the capacitances C1 and C2. Moreover, the response time has temperature dependency, and the difference in response time increases as the temperature rises (in the example of FIG. 1, a time error of Δtea occurs at the temperature Ta). Therefore, a temperature-dependent time error Δte occurs between both piezoelectric vibrators, as shown in FIG.

FIG. 2 examines the relationship between the difference ΔC between the capacitance of each of the other piezoelectric vibrators and the corresponding time error Δte with reference to one piezoelectric vibrator at a constant temperature. It shows the result. As can be seen from this result, it can be seen that the larger the difference ΔC in capacitance between the piezoelectric vibrators, the larger the time error Δte.

From the above, it is considered that the cause of the variation in responsiveness among the piezoelectric vibrators constituting the ultrasonic sensor is mainly due to the difference in the electrostatic capacitance of the piezoelectric vibrators. Therefore, as shown in FIG. 3, the electrostatic capacitances C1, which are held by the respective piezoelectric vibrators constituting the ultrasonic sensor,
If C2 is adjusted in advance so as to substantially match each other, the response times of the respective piezoelectric vibrators show the same temperature change characteristics, and therefore, as shown in FIG. Can be eliminated, resulting in a time error Δte
Can be extremely small.

The present invention has been made on the basis of the above findings, and has the following features to solve the conventional problems. That is, the ultrasonic sensor of the present invention according to claim 1 has a plurality of piezoelectric vibrators that receive ultrasonic waves from transmitting devices that are the same sound source and a plurality of piezoelectric vibrators that transmit ultrasonic waves received by the same receiving device. And a piezoelectric vibrator that transmits and receives ultrasonic waves to and from each other, wherein at least one of the piezoelectric vibrators has the piezoelectric vibrator. It is characterized in that a capacitance adjustment unit is provided which adjusts the capacitance held therein so as to be substantially equal to the capacitance held by another piezoelectric vibrator.

The ultrasonic sensor according to a second aspect of the present invention is the ultrasonic sensor according to the first aspect of the present invention, wherein the capacitance adjusting section includes a piezoelectric substrate forming the piezoelectric vibrator or a pair of piezoelectric substrates sandwiching the piezoelectric substrate. It is characterized in that at least one of the electrodes is trimmed.

Further, in the ultrasonic sensor according to a third aspect of the present invention, in the configuration of the first aspect of the invention, the capacitance adjusting section is provided between a pair of signal lines connected to the electrodes of the piezoelectric vibrator. It is characterized in that a capacitive element is connected in parallel to the.

An ultrasonic flowmeter according to a fourth aspect of the invention is such that the ultrasonic sensor according to any one of the first to third aspects is arranged in a fluid pipe through which a fluid whose flow rate is to be detected flows. It is characterized by becoming.

With this configuration, it is possible to easily and effectively eliminate the influence of a time error caused by the difference in electrostatic capacitance between the piezoelectric vibrators. for that reason,
It is possible to obtain an ultrasonic sensor and an ultrasonic flowmeter using the ultrasonic sensor that always ensure stable detection accuracy over a wide temperature range.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 5 is a configuration diagram of an ultrasonic flowmeter according to an embodiment of the present invention, and FIG. 6 is a front view showing a cutaway portion of a piezoelectric vibrator that constitutes an ultrasonic sensor used in the ultrasonic flowmeter. is there.

The ultrasonic flowmeter 1 of this embodiment is shown in FIG.
As shown in FIG. 3, the ultrasonic sensor 2 and the drive detection unit 3 are provided. The ultrasonic sensor 2 is arranged in a fluid pipe 4 through which a fluid such as gas or liquid flows, and the drive detection unit 3 drives the ultrasonic sensor 2 and based on the detection output from the sensor 2. It outputs a signal corresponding to the flow rate of the fluid.

The ultrasonic sensor 2 includes a pair of piezoelectric vibrators 5.
a (1) (on the left side in the drawing), the piezoelectric vibrator 5a on the upstream side of the fluid pipe 4 and the other (on the right side) the piezoelectric vibrator 5b on the downstream side of the fluid pipe 4 Are attached to each other so as to face each other with a predetermined distance therebetween. In this case, the piezoelectric vibrators 5a and 5b are
It has both ultrasonic wave transmission and reception functions.

As shown in FIG. 6, each of the piezoelectric vibrators 5a and 5b is provided with a piezoelectric body 6, a cap 7 for forming an acoustic matching layer is capped on the piezoelectric body 6, and the cap 7 is provided. A cylindrical case 8 is fixed to the bottom of the case 8.
One end of the cable 9 extended from the drive detection unit 3 is drawn therein. Each signal line 10 of the cable 9 is electrically connected to the piezoelectric body 6. The inside of the cap 7 and the case 8 is sealed with a sealing material 11 such as resin.

As shown in FIG. 7A, the piezoelectric body 6 is formed by forming electrodes 15 on both upper and lower surfaces of a disk-shaped piezoelectric substrate 14, and the above-mentioned signal lines are formed on the upper and lower electrodes 15, respectively. 10 are connected to each other.

In the ultrasonic flowmeter 1 having the above structure, when measuring the flow rate of a fluid such as gas or liquid flowing in the fluid pipe 4, the drive detection unit 3 outputs a start signal as in the conventional case. To excite each piezoelectric vibrator 5a, 5b. Then, the drive detection unit 3 transmits the ultrasonic wave transmitted from the upstream piezoelectric vibrator 5a, the time t1 required for the ultrasonic wave transmitted from the upstream piezoelectric vibrator 5a to be received by the downstream piezoelectric vibrator 5b, and the transmission time from the downstream piezoelectric vibrator 5b. The time t2 required until the generated ultrasonic wave is received by the piezoelectric vibrator 5a on the upstream side is detected, and the flow rate is measured based on the difference Δt (= t2-t1) between the two times.

Here, when the values of the electrostatic capacities held by the piezoelectric vibrators 5a and 5b are different from each other, the time difference detected does not become zero even when the flow rate in the fluid pipe 4 is zero, and the time error Δ.
te may occur. Each piezoelectric vibrator 5a, 5
The difference in capacitance of b is caused by that the capacitance between the electrodes 15 provided on both surfaces of each piezoelectric substrate 14 in the piezoelectric body 6 shown in FIG.

Therefore, in the case of this embodiment, of the pair of piezoelectric vibrators 5a and 5b, for example, one piezoelectric vibrator 5a, as shown in FIG. By trimming a part of the outer peripheral portion of the electrode 15, the capacitance is adjusted so as to be substantially equal to the electrostatic capacity of the piezoelectric body 6 constituting the other piezoelectric vibrator 5b. The trimmed portion is secured as the capacitance adjusting unit 17. The trimming of the piezoelectric body 6 in this case is adjusted in advance before assembling the piezoelectric vibrators 5a and 5b.

Incidentally, in order to secure the capacitance adjusting section 17 for making the capacitances between the piezoelectric bodies 6 constituting the piezoelectric vibrators 5a and 5b substantially equal to each other, a method other than that shown in FIG. 7B is required. As shown in FIG. 7C, the central part of the electrode 15 may be trimmed, or the outer peripheral part of the electrode 15 may be trimmed uniformly over the entire circumference as shown in FIG. 7D. Further, as shown in FIG. 7E, instead of trimming the electrode 15, a part of the outer circumference of the piezoelectric substrate 14 may be trimmed.

In this way, the capacitance adjusting section 17 is secured in the piezoelectric body 6 which constitutes the piezoelectric vibrators 5a and 5b, and the capacitances between the piezoelectric vibrators 5a and 5b are adjusted in advance so that they are substantially the same. Then, as shown in FIG. 3, the responsiveness of the piezoelectric vibrators 5a and 5b shows the same temperature change tendency. As a result, as shown in FIG.
Since there is no variation in responsiveness between a and 5b, the time error Δte can be made extremely small.

Therefore, since the ultrasonic flowmeter 1 equipped with the ultrasonic sensor 2 produces almost no time error, it is possible to always perform stable and accurate flow measurement over a wide temperature range.

The following modifications and applications to the above embodiment can be considered. (1) In the above embodiment, the pair of piezoelectric vibrators 5
The capacitance adjusting unit 17 is secured to one of the piezoelectric vibrators 5a or 5b of a and 5b.
By providing the capacitance adjusting unit 17 on both a and 5b,
It is also possible that the electrostatic capacities of a and 5b are substantially the same.

(2) In the above embodiment, the capacitance adjusting portion 17 is formed by trimming a part of the electrode 15 of the piezoelectric body 6 constituting the piezoelectric vibrators 5a and 5b or the piezoelectric substrate 14.
However, instead of processing the piezoelectric body 6, for example, as shown in FIG. 8, at the location where the cable 9 extended from the drive detection unit 3 is drawn into the case 8, the signal line 10 of the cable 9 is secured. It is also possible to connect a capacitor 18 as a capacitance element in parallel between the two and to use this capacitor 18 as an electrostatic capacity adjusting section.

In this case, the capacitance value of the capacitor 18 is adjusted according to the electrostatic capacitance of the piezoelectric body 6 or the electrostatic capacitance of the piezoelectric vibrators 5a and 5b during the assembly of the piezoelectric vibrators 5a and 5b. At this time, if a variable capacitance type capacitor is used as the capacitor 18, it is not necessary to select the capacitors 18 having various capacitance values, and therefore the capacitance can be adjusted more easily.

As described above, even when the capacitor 18 as the capacitance adjusting unit is connected between the pair of signal lines 10, the piezoelectric body 6 and the capacitor 18 are always at the same temperature, and each piezoelectric vibrator. Since the electrostatic capacities of 5a and 5b are substantially the same, it is possible to eliminate variations in responsiveness between the piezoelectric vibrators 5a and 5b. Moreover, since the capacitor 18 can be added later even during or after assembly, it is convenient because adjustment can be performed including variations in responsiveness due to differences in electrostatic capacitance that occur during assembly.

(3) In FIG. 8, the capacitor 18 is directly connected in parallel between the pair of signal lines 10, but as shown in FIG. 9, the relay substrate 20 is provided in the case 8 of the piezoelectric vibrators 5a and 5b. A pair of relay electrode patterns 21a and 21b are formed on the relay substrate 20, and the capacitor 1 is arranged in parallel between the relay electrode patterns 21a and 21b.
8 are connected to each of the relay electrode patterns 21a and 21b.
Alternatively, the signal line 10 of the cable 9 and the lead wire 22, one end of which is connected to each electrode 15 of the piezoelectric body 6, may be connected together. In the case of this configuration, the capacitor 18 can be stably and reliably attached to the relay board 20. Moreover, by adjusting the tendency (inclination) of the temperature dependency of the capacitance of the capacitor 18 and the capacitance of the piezoelectric body 6 to be connected, it is possible to accurately adjust over a wide temperature range.

Although the capacitor 18 is connected between the signal lines 10 of the cable 9 located on the piezoelectric vibrators 5a and 5b side, instead of the capacitor 18, the capacitor 18 is connected between the signal lines of the cable 9 located on the drive detection unit 3 side. A configuration in which 18 is connected is also possible.

(4) In the above embodiment, the pair of piezoelectric vibrators 5a and 5b constituting the ultrasonic sensor 2 transmit and receive ultrasonic waves to each other, but the ultrasonic sensor 2 of the present invention is not limited to this. The configuration is not limited to such a configuration, and a configuration as shown in FIG.

That is, in the ultrasonic sensor shown in FIG. 10A, the directions of the fluid flowing through the pair of piezoelectric vibrators 5a and 5b are opposite to each other with respect to the single transmitting device 23 serving as the ultrasonic sound source. The ultrasonic waves transmitted from the transmission device 23 are arranged facing each other at an equal distance to each of the piezoelectric vibrators 5.
It is configured to receive by a and 5b. In this case, the electrostatic capacities held by the piezoelectric vibrators 5a and 5b on the receiving side are adjusted to be substantially the same.

The ultrasonic sensor shown in FIG. 10 (b) has a single transmitting device 23 which serves as a sound source of ultrasonic waves.
The pair of piezoelectric vibrators 5a and 5b are arranged in the same direction with respect to the flowing direction of the fluid and separated from each other by different distances, and the ultrasonic waves transmitted from the transmitter 23 are transmitted to the respective piezoelectric vibrators 5a and
5b is used for receiving. In this case, the electrostatic capacities held by the piezoelectric vibrators 5a and 5b on the receiving side are adjusted to be substantially the same.

Further, in the ultrasonic sensor shown in FIG. 10 (c), a pair of piezoelectric vibrators 5a and 5b are provided as a single receiving device 24.
Are arranged opposite to each other at equal distances in the opposite directions with respect to the direction of fluid flow, and ultrasonic waves transmitted simultaneously from the respective piezoelectric vibrators 5a and 5b are received by the same receiving device 24. In this case, the electrostatic capacities held by the piezoelectric vibrators 5a and 5b on the transmission side are adjusted to be substantially the same.

Furthermore, in the ultrasonic sensor shown in FIG. 10 (d), a pair of piezoelectric vibrators 5a and 5b are arranged in the same direction and different distances from the single receiving device 24 in the same direction. The receiving device 24 receives the ultrasonic waves simultaneously transmitted from the piezoelectric vibrators 5a and 5b. In this case, the electrostatic capacities held by the piezoelectric vibrators 5a and 5b on the transmission side are adjusted to be substantially the same.

In the above description, the ultrasonic sensor is 2
Although the piezoelectric vibrators 5a and 5b are provided, the present invention can be applied to the piezoelectric vibrators having three or more piezoelectric vibrators.

[0044]

The present invention has the following effects. (1) According to the ultrasonic sensor of the first aspect of the present invention, it is possible to effectively eliminate the variation in responsiveness due to the difference in the capacitance of each piezoelectric vibrator, and to make the time error extremely small. You can Therefore, it is possible to obtain an ultrasonic sensor that always ensures stable detection accuracy over a wide temperature range.

(2) According to the ultrasonic sensor of the invention of claim 2, in addition to the effect of the invention of claim 1,
The variation in response of each piezoelectric vibrator can be removed by an extremely simple operation of trimming at least one of the piezoelectric substrate or the electrodes sandwiching the piezoelectric substrate, which constitutes the piezoelectric vibrator, and the cost can be reduced.

(3) According to the ultrasonic sensor of the invention of claim 3, in addition to the effect of the invention of claim 1,
The variation in response of each piezoelectric vibrator can be eliminated by a simple work of connecting a capacitive element in parallel between a pair of signal terminals connected to the electrodes of the piezoelectric vibrator. Moreover,
Since a capacitive element can be added later during assembly or after completion, there is an advantage that the capacitance value can be adjusted including variations in responsiveness due to differences in electrostatic capacitance that occur during assembly.

(4) According to the ultrasonic flowmeter of the invention described in claim 4, it is possible to always perform stable and accurate flowrate measurement over a wide temperature range.

[Brief description of drawings]

FIG. 1 is a characteristic diagram showing temperature dependence of responsiveness of each piezoelectric vibrator during ultrasonic wave transmission / reception, which is caused by a difference in electrostatic capacity held by each piezoelectric vibrator forming an ultrasonic sensor.

FIG. 2 is a difference ΔC in electrostatic capacitance between other piezoelectric vibrators based on a certain piezoelectric vibrator and a time error Δ corresponding thereto.
It is a characteristic view which shows the result of having investigated the relationship with te.

FIG. 3 is a characteristic showing the temperature dependence of the response time of ultrasonic wave transmission / reception of each piezoelectric vibrator when the electrostatic capacities of the piezoelectric vibrators constituting the ultrasonic sensor are adjusted to be substantially equal to each other. It is a figure.

FIG. 4 is a characteristic diagram showing the temperature dependence of the time error Δte when the electrostatic capacities of the respective piezoelectric vibrators constituting the ultrasonic sensor are substantially matched.

FIG. 5 is a configuration diagram of an ultrasonic flowmeter according to an embodiment of the present invention.

FIG. 6 is a front view showing a part of a piezoelectric vibrator, which constitutes an ultrasonic sensor used in the ultrasonic flowmeter of FIG.

7A and 7B are diagrams showing a piezoelectric body used in the piezoelectric vibrator of FIG. 6 and various examples in which a capacitance adjusting unit is provided on the piezoelectric body.

FIG. 8 is an explanatory diagram showing an example of a case where a capacitor as a capacitance adjusting unit is provided in a piezoelectric vibrator that constitutes an ultrasonic sensor.

FIG. 9 is an explanatory diagram showing another example of a case where a capacitor as a capacitance adjusting unit is provided on a piezoelectric vibrator that constitutes an ultrasonic sensor.

FIG. 10 is an explanatory diagram showing various configuration examples of the ultrasonic sensor.

FIG. 11 is an explanatory diagram in the case of measuring the flow rate of fluid using an ultrasonic flow meter.

FIG. 12 is a characteristic diagram showing temperature dependence of a time error Δte caused by variation in response of piezoelectric vibrators constituting an ultrasonic sensor.

[Explanation of symbols]

1 Ultrasonic flow meter 2 Ultrasonic sensor 3 Drive detector 4 fluid pipe 5a, 5b Piezoelectric vibrator 6 Piezoelectric body 10 signal lines 14 electrodes 15 Piezoelectric substrate 17 Trimming part (capacitance adjustment part) 18 Capacitor (Capacitance adjuster)

Claims (4)

[Claims] 1. A plurality of piezoelectric vibrators that receive ultrasonic waves from a transmitter that serves as the same sound source, a plurality of piezoelectric vibrators that transmit ultrasonic waves that are received by the same receiver, and mutually transmit ultrasonic waves. An ultrasonic sensor comprising any one of a plurality of piezoelectric vibrators for transmitting and receiving, wherein at least one of the piezoelectric vibrators has a capacitance held by the piezoelectric vibrator, An ultrasonic sensor, comprising: a capacitance adjusting unit that is adjusted to substantially match the capacitance of a piezoelectric vibrator. 2. The ultrasonic wave according to claim 1, wherein the capacitance adjusting unit is formed by trimming at least one of a piezoelectric substrate forming the piezoelectric vibrator or a pair of electrodes sandwiching the piezoelectric substrate. Sensor. 3. The ultrasonic sensor according to claim 1, wherein the capacitance adjusting unit includes a capacitive element connected in parallel between a pair of signal lines connected to the electrodes of the piezoelectric vibrator. . 4. An ultrasonic flowmeter, wherein the ultrasonic sensor according to any one of claims 1 to 3 is arranged in a fluid pipe through which a fluid whose flow rate is to be detected flows.