JP4078878B2 - Ultrasonic sensor and ultrasonic flow meter using the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an ultrasonic sensor and an ultrasonic flowmeter using the same.
[0002]
[Prior art]
In general, as shown in FIG. 11, the ultrasonic flowmeter is configured by providing an ultrasonic sensor A in a flow path through which a fluid such as gas or liquid flows. The ultrasonic sensor A includes, for example, a pair of piezoelectric vibrators B1 and B2, with one piezoelectric vibrator B1 on the upstream side (left side in the figure) and the other piezoelectric vibrator B2 on the downstream side (right side in the figure). They are arranged opposite to each other with a predetermined distance L apart. In this case, the piezoelectric vibrators B1 and B2 have both functions of transmitting and receiving ultrasonic waves.
[0003]
Here, when the fluid is flowing at a constant speed, ultrasonic waves are transmitted from the piezoelectric vibrators B1 and B2. At that 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 Is t2 <t2, and the difference Δt (= t2−t1) between the times t1 and t2 is proportional to the flow velocity v of the fluid. Yes.
[0004]
Therefore, the flow velocity v of the fluid can be measured by detecting the time difference Δt required for the ultrasonic waves to reach the piezoelectric vibrators B1 and B2, and if the cross-sectional area of the flow path is known, the flow velocity The flow rate can be measured from v.
[0005]
[Problems to be solved by the invention]
By the way, in the above-described ultrasonic flowmeter, when the flow of fluid is stopped and the flow rate is zero, the time difference Δt detected by the ultrasonic sensor A should be zero. However, actually, each piezoelectric vibrator B1 and B2 constituting the ultrasonic sensor A has a slight difference in response time until the received ultrasonic wave is converted into an electric signal and output. Similarly, there is a difference in response time when an electrical signal is converted into an ultrasonic wave and output.
[0006]
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. In addition, the time error Δte has temperature dependence as shown in FIG. 12, and tends to increase as the temperature increases, for example.
[0007]
If such a time error Δte occurs due to variations in responsiveness of the piezoelectric vibrators B1 and B2 constituting the ultrasonic sensor A, the flow rate of the fluid cannot be accurately measured. Therefore, it is necessary to prevent such a time error Δte from occurring. For this purpose, 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 in the apparatus, and when the time difference Δt is detected as described above, this time difference is detected. It is conceivable to eliminate the influence of the time error Δte by performing correction by subtracting the time error Δte corresponding to the temperature from Δt.
[0008]
However, for each ultrasonic sensor A constituting the ultrasonic flowmeter, it is extremely troublesome to individually measure and register the characteristic data as shown in FIG. 12 in the memory. The circuit for doing this also becomes complicated and expensive.
[0009]
The present invention has been made in order to solve the above-described problems, and it is possible to easily and effectively eliminate time errors caused by variations in responsiveness between the piezoelectric vibrators, so that it is always stable over a wide temperature range. An object of the present invention is to provide an ultrasonic sensor that ensures detection accuracy, and an ultrasonic flowmeter using the ultrasonic sensor.
[0010]
[Means for Solving the Problems]
Before describing the specific problem solving means of the present invention, the basic concept of the present invention will be described.
[0011]
The present inventor diligently studied the cause of variation in responsiveness among the piezoelectric vibrators constituting the ultrasonic sensor, and obtained the following knowledge.
[0012]
For example, when attention is paid to two piezoelectric vibrators constituting an ultrasonic sensor, it is assumed that the capacitances C1 and C2 of the piezoelectric bodies constituting the piezoelectric vibrators are different from one another. The piezoelectric vibrators having piezoelectric bodies having different capacitances C1 and C2 as described above are arranged at an equal distance from one sound source, and the ultrasonic waves generated by the sound sources are received by the respective piezoelectric vibrators. It shall be.
[0013]
In this case, as shown in FIG. 1, the response time until the ultrasonic wave received by each piezoelectric vibrator is converted into an electrical signal and output is different from each other due to the difference in capacitances C1 and C2, and The response time depends on temperature, and for example, the difference in response time increases as the temperature increases (in the example of FIG. 1, a time error of Δtea occurs at the temperature Ta). For this reason, as shown in FIG. 12, a time error Δte having temperature dependency occurs between the two piezoelectric vibrators.
[0014]
FIG. 2 shows the result of examining the relationship between the difference ΔC from the capacitance of each of the other piezoelectric vibrators and the corresponding time error Δte with a certain piezoelectric vibrator as a reference at a constant temperature. It is shown. As can be seen from this result, the time error Δte increases as the capacitance difference ΔC of the piezoelectric vibrator increases.
[0015]
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 capacitance of the piezoelectric vibrators. Therefore, as shown in FIG. 3, if the capacitances C1 and C2 possessed by the piezoelectric vibrators constituting the ultrasonic sensor are adjusted in advance so as to substantially coincide with each other, the response time of each piezoelectric vibrator is set. Since they exhibit the same temperature change characteristics, as shown in FIG. 4, variations in responsiveness among the piezoelectric vibrators can be eliminated, and as a result, the time error Δte can be extremely reduced.
[0016]
The present invention has been made on the basis of the above-described knowledge, and is performed as follows in order to solve the conventional problems.
That is, the ultrasonic sensor according to the first aspect of the present invention includes a plurality of piezoelectric vibrators that receive ultrasonic waves from a transmission device that is the same sound source, and a plurality of ultrasonic waves that are received by the same reception device. Ultrasonic flowmeter for measuring the flow rate of fluid by detecting the time required for transmitting and receiving ultrasonic waves A sonic sensor , wherein at least one of the piezoelectric vibrators is adjusted so that a capacitance held by the piezoelectric vibrator is substantially equal to a capacitance held by another piezoelectric vibrator. The capacitance adjusting unit is provided.
[0017]
The ultrasonic sensor according to a second aspect of the present invention is the ultrasonic sensor according to the first aspect, wherein the capacitance adjusting unit includes a piezoelectric substrate constituting the piezoelectric vibrator or a pair of electrodes sandwiching the piezoelectric substrate. It is characterized by trimming at least one of them.
[0018]
According to a third aspect of the present invention, there is provided the ultrasonic sensor according to the first aspect, wherein the capacitance adjustment section is a capacitive element between a pair of signal lines connected to the electrodes of the piezoelectric vibrator. It is characterized by being connected in parallel.
[0019]
According to a fourth aspect of the present invention, there is provided an ultrasonic flowmeter in which the ultrasonic sensor according to any one of the first to third aspects is disposed in a fluid pipe through which a fluid as a flow rate detection target flows. It is a feature.
[0020]
With this configuration, it is possible to easily and effectively eliminate the influence of time errors caused by the difference in capacitance between the piezoelectric vibrators. For this 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]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 5 is a configuration diagram of the ultrasonic flowmeter according to the embodiment of the present invention, and FIG. 6 is a front view showing a part of the piezoelectric vibrator constituting the ultrasonic sensor used in the ultrasonic flowmeter by cutting away. is there.
[0022]
The ultrasonic flow meter 1 of this embodiment includes an ultrasonic sensor 2 and a drive detection unit 3 as shown in FIG. The ultrasonic sensor 2 is disposed 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. Thus, a signal corresponding to the flow rate of the fluid is output.
[0023]
The ultrasonic sensor 2 includes a pair of piezoelectric vibrators 5a and 5b. One (left side in the figure) piezoelectric vibrator 5a is provided on the upstream inner wall of the fluid pipe 4, and the other (right side in the figure) piezoelectric vibration. The child 5b is attached to the inner wall on the downstream side of the fluid pipe 4 so as to face each other with a predetermined distance therebetween. In this case, each of the piezoelectric vibrators 5a and 5b has both functions of transmitting and receiving ultrasonic waves.
[0024]
As shown in FIG. 6, each of the piezoelectric vibrators 5 a and 5 b includes a piezoelectric body 6, and a cap 7 that forms an acoustic matching layer is crowned on the piezoelectric body 6. A cylindrical case 8 is fixed, and one end of a cable 9 extended from the drive detection unit 3 is drawn into the case 8. Each signal line 10 of the cable 9 is electrically connected to the piezoelectric body 6. The cap 7 and the case 8 are sealed with a sealing material 11 such as a resin.
[0025]
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-described signal lines 10 are respectively connected to the upper and lower electrodes 15. It is connected.
[0026]
In the ultrasonic flowmeter 1 configured as described above, when measuring the flow rate of a fluid such as a gas or a liquid flowing in the fluid pipe 4, an activation signal is output from the drive detection unit 3 as in the conventional case, and each piezoelectric The vibrators 5a and 5b are excited. Then, the drive detection unit 3 transmits the time t1 required until the ultrasonic wave transmitted from the upstream piezoelectric vibrator 5a is received by the downstream piezoelectric vibrator 5b and the downstream piezoelectric vibrator 5b. The time t2 required for the received ultrasonic wave to be received by the upstream piezoelectric vibrator 5a is detected, and the flow rate is measured based on the difference Δt (= t2−t1) between the two times.
[0027]
Here, if the capacitance values of the piezoelectric vibrators 5a and 5b are different from each other, the detected time difference may not be zero even when the flow rate in the fluid pipe 4 is zero, and a time error Δte may occur. There is. The difference in capacitance between the piezoelectric vibrators 5a and 5b is that the capacitance between the electrodes 15 provided on both surfaces of each piezoelectric substrate 14 in the piezoelectric body 6 shown in FIG. Due to the different.
[0028]
Therefore, in the case of this embodiment, for example, one piezoelectric vibrator 5a of the pair of piezoelectric vibrators 5a and 5b, as shown in FIG. 7B, the electrode 15 on the upper surface side of the piezoelectric body 6 is used. By trimming a part of the outer peripheral portion of the piezoelectric vibrator 5b, adjustment is made so as to substantially match the capacitance of the piezoelectric body 6 constituting the other piezoelectric vibrator 5b. The trimmed portion is secured as the capacitance adjustment unit 17. Trimming of the piezoelectric body 6 in this case is adjusted in advance before assembling the piezoelectric vibrators 5a and 5b.
[0029]
In order to secure the capacitance adjusting unit 17 that substantially matches the capacitance between the piezoelectric bodies 6 constituting the piezoelectric vibrators 5a and 5b, in addition to the configuration shown in FIG. As shown in FIG. 7C, the central portion of the electrode 15 may be trimmed, or the outer peripheral portion of the electrode 15 may be uniformly trimmed over the entire circumference as shown in FIG. Furthermore, as shown in FIG. 7E, instead of trimming the electrode 15, a part of the outer periphery of the piezoelectric substrate 14 may be trimmed.
[0030]
As described above, the capacitance adjusting unit 17 is secured in the piezoelectric body 6 constituting the piezoelectric vibrators 5a and 5b, and the piezoelectric vibrators 5a and 5b are adjusted in advance so that the electrostatic capacitances substantially coincide with each other. For example, as shown in FIG. 3, the responsiveness of each of the piezoelectric vibrators 5a and 5b shows the same temperature change tendency. As a result, as shown in FIG. 4, since there is no variation in the responsiveness between the piezoelectric vibrators 5a and 5b, the time error Δte can be made extremely small.
[0031]
Therefore, since the ultrasonic flowmeter 1 provided with the ultrasonic sensor 2 hardly generates a time error, it is possible to always perform a stable and accurate flow rate measurement over a wide temperature range.
[0032]
The following modifications and application examples can be considered for the above embodiment.
(1) In the above embodiment, the capacitance adjusting unit 17 is secured in one of the pair of piezoelectric vibrators 5a and 5b, but the piezoelectric vibrators 5a and 5b. It is also possible to provide a capacitance adjusting unit 17 on both of them so that the capacitances of the two 5a and 5b substantially coincide.
[0033]
(2) In the above embodiment, the capacitance adjusting unit 17 is secured by trimming the electrode 15 or part of the piezoelectric substrate 14 of the piezoelectric body 6 constituting the piezoelectric vibrators 5a and 5b. For example, as shown in FIG. 8, a capacitor as a capacitive element is provided between the signal lines 10 of the cable 9 at a place where the cable 9 extended from the drive detection unit 3 is drawn into the case 8 as shown in FIG. 8. 18 may be connected in parallel, and the capacitor 18 may be used as a capacitance adjusting unit.
[0034]
In this case, the capacitance value of the capacitor 18 is adjusted according to the capacitance of the piezoelectric body 6 or the capacitance of the piezoelectric vibrators 5a and 5b in the course of assembling 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 a capacitor 18 having various capacitance values, so that the capacitance adjustment can be performed more easily.
[0035]
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 the piezoelectric vibrators 5a and 5b. Therefore, 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 assembly or after completion, it is convenient that adjustment including the variation in responsiveness caused by the difference in electrostatic capacitance occurring during assembly is possible.
[0036]
(3) Although the capacitor 18 is directly connected in parallel between the pair of signal lines 10 in FIG. 8, a relay substrate 20 is provided in the case 8 of the piezoelectric vibrators 5a and 5b as shown in FIG. A pair of relay electrode patterns 21a and 21b are formed on the relay substrate 20, and a capacitor 18 is connected in parallel between the relay electrode patterns 21a and 21b, and a cable is connected to each relay electrode pattern 21a and 21b. The other end of each lead wire 22 having one end connected to each signal line 10 and 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 securely attached to the relay substrate 20. In addition, by adjusting the temperature dependence tendency (inclination) of the capacitance of the capacitor 18 and the piezoelectric body 6 to be connected, it is possible to accurately adjust over a wide temperature range.
[0037]
Although the capacitor 18 is connected between the signal lines 10 of the cable 9 located on the piezoelectric vibrators 5a and 5b side, the capacitor 18 is connected between the signal lines of the cable 9 located on the drive detection unit 3 side instead. It is also possible to adopt the configuration described above.
[0038]
(4) In the above-described embodiment, the pair of piezoelectric vibrators 5a and 5b constituting the ultrasonic sensor 2 transmit / receive ultrasonic waves to / from each other. The configuration is not limited to that shown in FIG.
[0039]
That is, the ultrasonic sensor shown in FIG. 10A is equidistant from the single transmission device 23 serving as an ultrasonic sound source in a direction opposite to each other with respect to the direction in which the fluid flows through the pair of piezoelectric vibrators 5a and 5b. The ultrasonic waves transmitted from the transmitter 23 are received by the respective piezoelectric vibrators 5a and 5b. In this case, the capacitances of the piezoelectric vibrators 5a and 5b on the receiving side are adjusted so as to substantially match.
[0040]
Further, the ultrasonic sensor shown in FIG. 10B is different in the same direction with respect to the direction in which the fluid flows through the pair of piezoelectric vibrators 5a and 5b with respect to the single transmission device 23 serving as an ultrasonic sound source. The ultrasonic waves transmitted from the transmitter 23 are received by the piezoelectric vibrators 5a and 5b. In this case, the capacitances of the piezoelectric vibrators 5a and 5b on the receiving side are adjusted so as to substantially match.
[0041]
Furthermore, in the ultrasonic sensor shown in FIG. 10C, the pair of piezoelectric vibrators 5a and 5b are arranged opposite to each other by an equal distance in the opposite directions with respect to the direction of fluid flow from the single receiving device 24. The ultrasonic wave transmitted simultaneously from the piezoelectric vibrators 5a and 5b is received by the same receiving device 24. In this case, the capacitances of the piezoelectric vibrators 5a and 5b on the transmission side are adjusted so as to substantially match.
[0042]
Furthermore, in the ultrasonic sensor shown in FIG. 10 (d), a pair of piezoelectric vibrators 5a and 5b are arranged away from each other by a different distance in the same direction with respect to the direction of fluid flow from a single receiving device 24. The receiving device 24 receives the ultrasonic waves transmitted simultaneously from the transducers 5a and 5b. In this case, the capacitances of the piezoelectric vibrators 5a and 5b on the transmission side are adjusted so as to substantially match.
[0043]
In the above description, the ultrasonic sensor includes the two piezoelectric vibrators 5a and 5b. However, the present invention can be applied to a sensor including three or more piezoelectric vibrators.
[0044]
【The invention's effect】
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 variations in responsiveness due to the difference in capacitance between the piezoelectric vibrators, and extremely reduce the time error. Can do. Therefore, it is possible to obtain an ultrasonic sensor that ensures stable detection accuracy over a wide temperature range.
[0045]
(2) According to the ultrasonic sensor of the second aspect of the invention, in addition to the effect of the first aspect of the invention, the piezoelectric substrate constituting the piezoelectric vibrator or at least one of the electrodes sandwiching the piezoelectric substrate is trimmed. With such an extremely simple operation, variations in the responsiveness of each piezoelectric vibrator can be eliminated, and the operation can be carried out at a low cost.
[0046]
(3) According to the ultrasonic sensor of the invention described in claim 3, in addition to the effect of the invention described in claim 1, a capacitive element is connected in parallel between a pair of signal terminals connected to the electrodes of the piezoelectric vibrator. It is possible to eliminate variations in the responsiveness of the piezoelectric vibrators with a simple operation. Moreover, since the capacitive element can be added later even during assembly or after completion, there is an advantage that the capacitance value can be adjusted including variations in responsiveness caused by the difference in capacitance that occurs during assembly. is there.
[0047]
(4) According to the ultrasonic flowmeter of the invention described in claim 4, it is possible to perform stable and accurate flow rate measurement over a wide temperature range.
[Brief description of the drawings]
FIG. 1 is a characteristic diagram showing temperature dependence of responsiveness at the time of ultrasonic wave transmission / reception of each piezoelectric vibrator due to a difference in capacitance held by each piezoelectric vibrator constituting an ultrasonic sensor.
FIG. 2 is a characteristic diagram showing a result of examining a relationship between a capacitance difference ΔC of each of the other piezoelectric vibrators and a corresponding time error Δte using one piezoelectric vibrator as a reference.
FIG. 3 is a characteristic showing the temperature dependence of the response time at the time of ultrasonic wave transmission / reception of each piezoelectric vibrator when the capacitance between the piezoelectric vibrators constituting the ultrasonic sensor is adjusted so as to substantially match each other. FIG.
FIG. 4 is a characteristic diagram showing the temperature dependence of the time error Δte when the capacitances between the 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.
6 is a front view showing a part of a piezoelectric vibrator constituting an ultrasonic sensor used in the ultrasonic flowmeter of FIG.
7 is a diagram showing various examples when a piezoelectric body used in the piezoelectric vibrator of FIG. 6 and a capacitance adjusting unit are provided on the piezoelectric body.
FIG. 8 is an explanatory diagram illustrating an example in which a capacitor as a capacitance adjusting unit is provided in the piezoelectric vibrator constituting the ultrasonic sensor.
FIG. 9 is an explanatory diagram showing another example when a capacitor as a capacitance adjusting unit is provided in the piezoelectric vibrator constituting the ultrasonic sensor.
FIG. 10 is an explanatory diagram illustrating various configuration examples of an ultrasonic sensor.
FIG. 11 is an explanatory diagram in the case of measuring the flow rate of a 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]
DESCRIPTION OF SYMBOLS 1 Ultrasonic flowmeter 2 Ultrasonic sensor 3 Drive detection part 4 Fluid pipe | tube 5a, 5b Piezoelectric vibrator 6 Piezoelectric body 10 Signal line 14 Electrode 15 Piezoelectric substrate 17 Trimming part (capacitance adjustment part)
18 Capacitor (Capacitance adjuster)

Claims (4)

A plurality of piezoelectric vibrators that receive ultrasonic waves from a transmitter that is the same sound source, a plurality of piezoelectric vibrators that transmit ultrasonic waves received by the same receiver, and a plurality of piezoelectric elements that transmit and receive ultrasonic waves to each other An ultrasonic sensor for an ultrasonic flowmeter that includes any of the vibrators , detects the time required to transmit and receive ultrasonic waves, and measures the flow rate of the fluid ,
At least one of the piezoelectric vibrators has a capacitance adjusting unit that adjusts the capacitance held by the piezoelectric vibrator so as to substantially match the capacitance held by the other piezoelectric vibrators. An ultrasonic sensor is provided.   The ultrasonic sensor according to claim 1, wherein the capacitance adjusting unit is formed by trimming at least one of a piezoelectric substrate constituting the piezoelectric vibrator or a pair of electrodes sandwiching the piezoelectric substrate.   The ultrasonic sensor according to claim 1, wherein the capacitance adjusting unit is formed by connecting a capacitive element in parallel between a pair of signal lines connected to electrodes of the piezoelectric vibrator.   An ultrasonic flowmeter, wherein the ultrasonic sensor according to any one of claims 1 to 3 is disposed in a fluid pipe through which a fluid as a flow rate detection target flows.

Images