JP2013217888A - Ultrasonic level meter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ultrasonic level meter capable of measuring a liquid position of a container having various environments.SOLUTION: To a piezoelectric element 3 of an ultrasonic vibration body 1, a sine-wave pulse of 50 Vp-p with applied voltage of 500 KHz is applied. As a result, an ultrasonic wave propagates through a carbon fiber composite material 2 and a stainless steel container 6 and propagates to a liquid of about 150°C; and most of it reflects on an inner surface of the opposing stainless steel container 6 and propagates again to the liquid of about 150°C, and propagates through the stainless steel container 6, propagates through the carbon fiber composite material 2 and propagates to the piezoelectric element 3. By measuring a time difference between the time when the sine-wave pulse is applied and the time when the received propagation waveform is detected, the existence of a liquid in the stainless steel container 6 is confirmed. As for a method of measuring the time difference, a trigger method is used. If liquid does not exist, a received waveform does not exist in a position of a time difference for propagating through liquid, so it can be confirmed that liquid does not exist in the position.

Description

  The present invention relates to an ultrasonic level meter provided with an ultrasonic transducer for measuring a liquid level in a container using ultrasonic propagation time.

  The ultrasonic level meter measures the position of the liquid surface in the container, and there are a method for transmitting and receiving ultrasonic waves parallel to the liquid surface and a method for transmitting and receiving ultrasonic waves perpendicular to the liquid surface. . In either method, the shape of the received waveform is important in order to detect liquid. The received waveform is preferably one that can be measured by a simple time difference measuring circuit using a trigger method, and for this purpose, a waveform shape that rises sharply is good.

  Patent Document 1 describes the configuration of an ultrasonic flowmeter that increases the S / N that indicates the sensitivity of the reception sensitivity and improves the rising characteristics of the waveform that indicates the ease of triggering. The thickness of the matching layer is not less than 0.18λ and not more than 0.22λ, preferably 0, of the wavelength λ (m) of the matching layer material obtained from the acoustic velocity (m / s) of the matching layer and the ultrasonic frequency (Hz). .2λ.

  Patent Document 2 describes a propagation time difference type ultrasonic flow meter using both a trigger method and a correlation method. Among them, the trigger method is capable of measuring with high accuracy because it obtains the time difference directly from the received waveform. On the other hand, the trigger method can measure when the received waveform is disturbed by foreign matter or bubbles mixed in the fluid. There is a drawback that it is easy to disappear. However, since the correlation method obtains both waveforms from the correlated waveforms, it can be measured even if a certain amount of foreign matter, bubbles, etc. are mixed in, but it is described that it has the disadvantage of not being as accurate as the trigger method. .

  Patent Documents 3 and 4 describe piezoelectric vibrators that suppress acoustic vibration in the orientation direction of high-elasticity fibers in a fiber composite material and preferentially transmit acoustic vibrations in a direction orthogonal to the high-elasticity fibers. ing.

  JP 2001-330485 A   JP 2010-38667 A   Japanese Patent Laid-Open No. 7-284198   WO2004 / 075753

  Ultrasonic Handbook Editorial Committee, “Ultrasonic Handbook”, Maruzen Co., Ltd., August 1999, p346-347   Tadashi Shiogama, “Manufacture and Application of New Piezoelectric Materials”, CMC Corporation, December 1987, p99-109

  However, in the case of a material having a small vibration loss (a mechanical quality factor is large), for example, a metal material such as stainless steel, the method described in Patent Document 1 does not sufficiently raise the received ultrasonic vibration.

  Further, even in the method using the propagation time difference formula that uses the trigger method and the correlation method in combination with Patent Document 2, if the rising of the received waveform is bad, the correlation method is always used and a highly accurate propagation time difference cannot be obtained. There is a point.

  Furthermore, even if the fiber composite material which is a matching material which is one of the materials having the best matching characteristics is used, the fiber is arranged in a direction orthogonal to the fibers in the fiber composite material in the propagation direction of the ultrasonic wave. There are cases where the rising of the received waveform is not sufficient, and there is a problem that the ultrasonic wave propagation loss is large and sufficient sensitivity cannot be obtained.

  When the temperature of the fluid to be measured exceeds 100 ° C., the ultrasonic vibrator is always in a high temperature near the temperature of the fluid, and the ultrasonic vibrator may be deteriorated. Further, there are many problems in the ultrasonic wave propagation waveform due to the temperature characteristics of the ultrasonic vibrator.

  Therefore, in order to improve the reception waveform even when the temperature of the fluid to be measured exceeds 100 ° C., a method for solving the above-described problems by changing the method of using the fiber composite material from the conventional method is devised. did.

  The present invention provides an ultrasonic vibrator for an ultrasonic level meter, in which a plurality of high elastic fibers having a tensile elastic modulus of 100 GPa or more are oriented in the same direction in a base material made of a resin or a carbonized resin, and the high elasticity An ultrasonic vibrating body is used in which a fiber composite material having a fiber orientation direction perpendicular to a bonding surface with a piezoelectric element and a piezoelectric element are bonded.

  The present invention also uses an ultrasonic vibrator in which a cylindrical fiber composite material orients fibers in the column direction and the length in the column direction is larger than the diameter as an ultrasonic transducer of an ultrasonic level meter. is there.

  The present invention also provides an ultrasonic transducer in which a polygonal columnar fiber composite material orients fibers in the column direction and the length in the column direction is larger than the length of the side of the polygon as an ultrasonic transducer of an ultrasonic level meter. A vibrating body is used.

  The present invention also provides an ultrasonic vibration for an ultrasonic transducer for an ultrasonic level meter, in which fibers are oriented in a columnar fiber composite material in the column direction and the length in the column direction is less than the diameter and longer than 0.2 mm. It uses the body.

  The present invention is also an ultrasonic vibrator of an ultrasonic level meter, orienting fibers in the column direction of a polygonal columnar fiber composite material, and the length in the column direction is equal to or less than the length of the side of the polygon, An ultrasonic vibrator that is longer than 0.2 mm is used.

  The present invention also uses an ultrasonic vibrator in which a high elastic fiber is a carbon fiber or a carbon-containing fiber as an ultrasonic vibrator of an ultrasonic level meter.

  According to the ultrasonic vibrator of the present invention, even when the temperature of the fluid to be measured exceeds 100 ° C., the reception waveform is good and the propagation loss of the ultrasonic vibration is small, so the trigger method is used to make the stainless steel container. The level of the liquid level inside can be measured with high accuracy, or the presence or absence of liquid can be measured with high reliability.

It is the structure which evaluates the ultrasonic vibrating body by this invention. It is a received waveform of the ultrasonic wave which propagated the ultrasonic vibrating body of FIG. It is the sound speed calculated | required from the received waveform of FIG. 2 is a graph showing the relationship between the length of an ultrasonic vibrator and a detection voltage in the configuration of FIG. It is the top view which attached the ultrasonic transducer | vibrator to the stainless steel container. FIG. 6 is a side view of FIG. 5. It is a top view which shows the ultrasonic transducer | vibrator using a carbon fiber composite material. It is a figure which shows the cross section in the AA in FIG. 6 is a received waveform in the configuration of FIG. It is sectional drawing which shows having attached the ultrasonic transducer | vibrator using the ultrasonic vibrating body of this invention to the PFA container. It is a received waveform in the structure in FIG. It is a figure explaining the orientation of the carbon fiber of a carbon fiber composite material. It is sectional drawing which attached the ultrasonic vibrating body of this invention to the stainless steel container side surface.

  A basic configuration which is an embodiment of the present invention will be described with reference to the perspective view of FIG. Although the present invention has the configuration of FIG. 1A, the configurations of FIG. 1B, FIG. 1C, and FIG. In FIG. 1A, the piezoelectric elements 3a and 3b having a diameter of 10 mm and a thickness of 1 mm are bonded to both sides of the carbon fiber composite material 2 in the ultrasonic wave propagation direction by an epoxy resin 7. The carbon fiber composite material 2 has a length of 40 mm, a width of 10 mm, and a height of 10 mm. The carbon fibers are oriented in the same direction as the ultrasonic propagation direction of the carbon fiber composite material 2 (two-dot chain line in the figure). FIG. 1A will be described using the coordinate axes X, Y, and Z shown in the drawing. The carbon fiber composite material 2 has a length in the X direction of 40 mm, a length in the Y direction of 10 mm, and a length in the Z direction of 10 mm. Then, the piezoelectric elements 3a and 3b having a diameter of 10 mm and a thickness of 1 mm are bonded to both sides of the carbon fiber composite material 2 in the X direction by the epoxy resin 7. The carbon fibers of the carbon fiber composite material 2 are oriented in the X direction.

  The piezoelectric element 3 is a lead-based piezoelectric ceramic, and is a LowQ material having a mechanical quality factor Qm of about 80. Silver electrodes are provided on both sides by baking. It is polarized in a direction perpendicular to the silver electrode surface.

  Here, a method for observing ultrasonic propagation in the carbon fiber composite material 2 will be described. First, a sine wave pulse of 2 MHz and 10 Vp-p is applied to the piezoelectric element 3a. The ultrasonic wave propagates in the same direction as the carbon fiber direction in the carbon fiber composite material 2, propagates to the piezoelectric element 3b, and generates a voltage by the piezoelectric effect. Waves are observed by measuring this voltage with an oscilloscope. And the observed waveform is shown in FIG. Here, the maximum voltage was the second wave, which was about 1.12 Vp-p.

  FIG. 1B will be described using X, Y, and Z. The carbon fiber composite material 2 has a length in the X direction of 40 mm, a length in the Y direction of 10 mm, and a length in the Z direction of 10 mm. Then, the piezoelectric elements 3a and 3b having a diameter of 10 mm and a thickness of 1 mm are bonded to both sides of the carbon fiber composite material 2 in the X direction by the epoxy resin 7. The carbon fibers in the carbon fiber composite material 2 are oriented in the Y direction. The ultrasonic wave propagation direction and the orientation direction of the carbon fibers in the carbon fiber composite material 2 are orthogonal to each other. The piezoelectric element 3 is a lead-based piezoelectric ceramic, and is a LowQ material having a mechanical quality factor Qm of about 80. Silver electrodes are provided on both sides by baking. It is polarized in a direction perpendicular to the silver electrode surface.

  Here, a method for observing ultrasonic propagation in the carbon fiber composite material 2 will be described. First, a sine wave pulse of 2 MHz and 10 Vp-p is applied to the piezoelectric element 3a. The ultrasonic wave propagates in a direction orthogonal to the carbon fiber direction in the carbon fiber composite material 2, propagates to the piezoelectric element 3b, and generates a voltage by the piezoelectric effect. Waves are observed by measuring this voltage with an oscilloscope. The observed waveform is shown in FIG. Here, the maximum voltage was the third wave, which was about 0.039 Vp-p.

  FIG. 1C will be described using X, Y, and Z. The carbon fiber composite material 2 has a length in the X direction of 40 mm, a length in the Y direction of 10 mm, and a length in the Z direction of 10 mm. Then, the piezoelectric elements 3a and 3b having a diameter of 10 mm and a thickness of 1 mm are bonded to both sides of the carbon fiber composite material 2 in the X direction by the epoxy resin 7. The carbon fibers in the carbon fiber composite material 2 are oriented in two directions, the X direction and the Y direction. The ultrasonic propagation direction and the orientation direction of the carbon fibers oriented in the X direction in the carbon fiber composite material 2 are the same, and the ultrasonic propagation direction and the orientation direction of the carbon fibers oriented in the Y direction in the carbon fiber composite material 2 Are orthogonal.

  The piezoelectric element is a lead-based piezoelectric ceramic, and is a LowQ material having a mechanical quality factor Qm of about 80. Silver electrodes are provided on both sides by baking. It is polarized in a direction perpendicular to the silver electrode surface.

  Here, a method for observing ultrasonic propagation in the carbon fiber composite material 2 will be described. First, a sine wave pulse of 2 MHz and 10 Vp-p is applied to the piezoelectric element 3a. The ultrasonic wave propagates in the carbon fiber composite material 2, propagates to the piezoelectric element 3b, and generates a voltage due to the piezoelectric effect. Waves are observed by measuring this voltage with an oscilloscope. And the observed waveform is shown in FIG. Here, the maximum voltage was the fifth wave, which was about 0.146 Vp-p. Moreover, although the waveform is disordered, this is because the orientation direction of the carbon fiber in the carbon fiber composite material 2 is oriented in the same direction as the propagation direction of the ultrasonic wave and the perpendicular direction exists. It is thought to be a thing.

  FIG. 1D will be described using X, Y, and Z. The carbon fiber composite material 2 has a length in the X direction of 40 mm, a length in the Y direction of 10 mm, and a length in the Z direction of 10 mm. Then, the piezoelectric elements 3a and 3b having a diameter of 10 mm and a length of 1 mm are bonded to both sides of the carbon fiber composite material 2 in the X direction by the epoxy resin 7. The carbon fibers in the carbon fiber composite material 2 are oriented in two directions, the Y direction and the Z direction. The ultrasonic propagation direction and the orientation direction of the carbon fibers oriented in the Y and Z directions in the carbon fiber composite material 2 are orthogonal to each other.

  The piezoelectric element is a lead-based piezoelectric ceramic, and is a LowQ material having a mechanical quality factor Qm of about 80. Silver electrodes are provided on both sides by baking. It is polarized in a direction perpendicular to the silver electrode surface.

  Here, a method for observing ultrasonic propagation in the carbon fiber composite material 2 will be described. First, a sine wave pulse of 2 MHz and 10 Vp-p is applied to the piezoelectric element 3a. The ultrasonic wave propagates in the direction perpendicular to the carbon fiber direction in the carbon fiber composite material 2, propagates to the piezoelectric element 3b, and generates a voltage by the piezoelectric effect. Waves are observed by measuring this voltage with an oscilloscope. FIG. 2D shows the observed waveform. Here, the maximum voltage was the third wave, which was about 0.051 Vp-p.

  Here, the physical properties of the carbon fiber composite material 2 are shown in Table 1. One direction means that carbon fibers are arranged only in the X direction in the carbon fiber composite material 2. The term “perpendicular” means that carbon fibers are arranged only in the Y direction and the Z direction in the carbon fiber composite material 2.

  2 (a), FIG. 2 (b), FIG. 2 (c) and FIG. 2 (d) show the propagation time and speed of the ultrasonic wave, the received wave number having the maximum peak in the received waveform and the peak value in Table 2. Summarized. The reason why the reception waveform is 10 waves or less is related to the trigger method. The speed of sound is, for example, the graph of FIG. 3 is created by measuring the propagation time by adding 5 mm, 10 mm, 20 mm, and 30 mm to the length of the carbon fiber composite material 2 in the configuration of FIG. Was calculated.

  Non-Patent Document 1 describes that a propagation time can be accurately measured to the ns order by measuring a zero cross point using a trigger wave as a method for measuring a propagation time.

ここでＵＬとは図１（ａ）の構成、ＵＴは図１（ｂ）の構成、ＬＴは図１（ｃ）の構成、ＴＴは図１（ｄ）の構成を示すものである。

Here, UL indicates the configuration of FIG. 1A, UT indicates the configuration of FIG. 1B, LT indicates the configuration of FIG. 1C, and TT indicates the configuration of FIG. 1D.

  From the above results, the material with small attenuation of ultrasonic vibration has the same carbon fiber direction as the ultrasonic propagation direction, and the material with the carbon fiber orientation direction orthogonal to the ultrasonic propagation direction has high attenuation. Therefore, only when the ultrasonic wave propagation direction and the orientation direction of the carbon fibers in the carbon fiber composite material 2 are the same, a material with a small attenuation of ultrasonic vibration is obtained.

  The carbon fiber is preferably continuous in the carbon fiber composite material 2. This is because if not continuous, the resin penetrates between the carbon fibers and attenuates the ultrasonic vibration.

  Here, the rising edge of the received waveform is expressed by the wave number that is the maximum peak of the received waveform. As shown in Table 2, when the ultrasonic wave propagation direction and the orientation direction of the carbon fibers in the carbon fiber composite material 2 are the same, the voltage value at the peak of the second wave is the maximum. The other UT and TT are the third wave, and the LT is the fifth wave. LT is a fiber in the carbon fiber composite material 2 oriented in a direction orthogonal to the fiber oriented in the same direction as the ultrasonic wave propagation direction. As a result, the propagation path becomes complicated and the received waveform is considered to be disturbed. The fact that there is no maximum peak by the 10th wave is a waveform with a bad rise, so it can be determined that a waveform having no maximum peak by the 10th wave cannot be used for the trigger method.

  As described above, both the low loss of ultrasonic propagation and the rise of the received waveform are good because the carbon fibers in the anisotropic fiber composite are oriented only in the ultrasonic propagation direction. It turns out that it is only.

  And in the shape of carbon fiber composite material 2, when it is a cylinder, it is desirable that length is larger than a diameter. This is to make the fundamental vibration a vibration mode in the length direction. By doing so, the characteristics of the carbon fiber composite material 2 can be further enhanced by matching the characteristics of the carbon fiber composite material 2 with those of the fiber direction and shape. In the case of a polygonal columnar shape, the fundamental vibration is changed to a vibration mode in the column length direction by increasing the column length from the maximum side length. Further, in the case of a polygonal columnar shape, the fundamental vibration can be more surely set to the vibration mode in the length direction of the column by increasing the length of the column than the maximum length of the diagonal line in the case of a square or more.

  FIG. 4 shows the relationship between the ultrasonic propagation length and the detection voltage in the configuration of FIG. 1, but the UL is compared with other UTs, LTs, and TTs when the length of the carbon fiber composite material 2 is 10 mm or more. A detection voltage twice or more can be obtained, and the difference from others increases as the detection voltage becomes longer. This is considered to be due to the addition of the shape effect to the material propagation loss.

  Therefore, in the case of a cylinder, the influence of the shape of the carbon fiber composite material 2 is considered to be different at a position where the column length and the diameter are equal. In the case of a polygonal column, it is considered that the side length or the diagonal length and the column length are different at a boundary. That is, in the case of a cylinder, since the vibration in the length direction of the column becomes a fundamental mode when the length of the column is larger than the diameter, the ultrasonic wave propagates in the length direction of the column. Since the carbon fibers are oriented in the column direction, the vibration loss in the column direction of the carbon fiber composite material 2 is reduced. Due to the synergistic effect of the above two points, only this configuration is considered to be an extremely excellent ultrasonic transducer.

  When the length of the cylinder is equal to or less than the size of the diameter, the fundamental vibration mode is vibration in the radial direction and is orthogonal to the direction of the carbon fiber. Therefore, it is thought that only the effect of carbon fiber appears strongly. It is conceivable that the rise of the waveform is improved due to the effect that carbon fiber is highly elastic.

  The same applies to a polygonal column. When the column length is larger than the size of a side or a diagonal line, it is considered that the propagation waveform is good and the reception sensitivity is also high. When the length of the column is equal to or smaller than the size of the side or the diagonal, it is conceivable that the rising of the waveform is improved by the effect of the high elastic fiber.

  Next, the ultrasonic propagation characteristics from the ultrasonic transducer in which the piezoelectric element 3 and the carbon fiber composite material 2 are joined to stainless steel will be described. Usually, in order to improve the propagation characteristics, the matching layer is set to a length of 1/4 of the wavelength of the vibration to propagate. However, here, the concept of matching is not used, and it is based on a new concept of propagating ultrasonic waves. Therefore, the length of the carbon fiber composite material 2 constituting the ultrasonic vibrator is in a wide range from 0.21 mm to 40 mm. Observe the waveform and sensitivity.

  This will be described with reference to the plan view of FIG. 5 and the side view of FIG. The dimensions of the stainless steel container 6 are 100 mm in length, 70 mm in width and 100 mm in height, and the thickness of the stainless steel container 6 is 6 mm. Pure water 9 is located at a height of about 80 mm from the bottom of the container.

  The ultrasonic vibrator 1 will be described with reference to a plan view of FIG. 7 and FIG. 8 showing a cross section taken along line AA of FIG. The carbon fiber composite material 2 has a size of 10 mm square and a length of 0.21 mm to 40 mm. The carbon fibers are oriented in the length direction perpendicular to the surface. That is, the carbon fibers are oriented in the same direction as the ultrasonic wave propagation direction. Then, the piezoelectric element 3 is bonded to one surface of the carbon fiber composite material 2 by the epoxy resin 7 to constitute the ultrasonic vibrator 1.

  The piezoelectric element 3 has a diameter of 10 mm and a thickness of 1 mm. The material is a lead-based piezoelectric ceramic, and is a LowQ material having a mechanical quality factor Qm of about 80. The carbon fiber composite material 2 and the piezoelectric element 3 are joined by the epoxy resin 7 with the centers of the respective surfaces being aligned as shown in FIGS. The structure in which the carbon fiber composite material 2 and the piezoelectric element 3 are joined is the ultrasonic vibrator 1.

  The carbon fiber composite material 2 side of the ultrasonic vibrator 1 described above was brought into contact with the side surface of the stainless steel container 6 via silicon grease as a contact medium. The central axis position of the ultrasonic vibrator 1 is set to a height of about 40 mm from the bottom surface of the stainless steel container 6.

  Next, a sin wave pulse having an applied voltage of 2 MHz and 10 Vp-p is applied to the piezoelectric element 3 of the ultrasonic vibrator 1. As a result, the ultrasonic wave propagates through the carbon fiber composite material 2 and the stainless steel container 6, propagates to the pure water 9, almost reflects off the inner surface of the opposing stainless steel container 6, and propagates again into the pure water 9. , Propagates through the carbon fiber composite material 2 and propagates to the piezoelectric element 3.

  Due to the ultrasonic vibration propagated to the piezoelectric element 3, a voltage is generated in the piezoelectric element 3, and the received waveform shown in FIG. 9 is obtained. FIG. 9a shows a received waveform in which the thickness of the carbon fiber composite material 2 is 0.21 mm, FIG. 9b shows a received waveform of 0.43 mm, and FIG. 9c shows 40 mm. FIG. 8d shows a received waveform when the piezoelectric element 3 is directly brought into contact with the stainless steel container 6 through silicon-based grease without using the carbon fiber composite material 2.

  Actually, the received waveform was observed with the thickness of the carbon fiber composite material 2, 0.21 mm, 0.43 mm, 0.86 mm, 1.72 mm, 3.42 mm, 5.14 mm, 6.85 mm, 8.58 mm. There are 14 types: 10.3 mm, 12.0 mm, 13.7 mm, 20 mm, 30 mm, and 40 mm. It is a received waveform when the piezoelectric element 3 is directly brought into contact with the stainless steel container 6 via silicon grease without using the carbon fiber composite material 2.

  When the piezoelectric element 3 (diameter 10 mm, thickness 1 mm) is directly contacted with a stainless steel container via silicon grease without using the carbon fiber composite material 2, the received waveform has a positive peak voltage of 17.8 mV. there were. Compared with this, the reception waveform when the thickness of the carbon fiber composite material 2 was 0.21 mm was almost the same, and the peak voltage on the plus side was 8.38 mV. Therefore, the carbon fiber composite material 2 having a thickness of 0.21 mm is merely a load and does not act as an ultrasonic wave propagation body. The action of the ultrasonic wave propagating body may be that the rising of the received waveform is improved as compared with the conventional material, the receiving sensitivity is increased, or of course both.

  In the received waveform in which the thickness of the carbon fiber composite material 2 is 0.43 mm, the first peak voltage on the plus side is 15.8 mV at the third wave, and the second peak voltage on the plus side is 20 at the seventh wave. .4 mV. The carbon fiber composite material 2 having a thickness of 0.43 mm has a reception voltage equal to or higher than that, and has a peak that can be triggered in the third wave. Therefore, there exists an effect | action as an ultrasonic vibration body.

  Further, the reception waveform of the carbon fiber composite material 2 having a length of 40 mm has a positive peak voltage in the second wave and is 10.7 mV. The waveform is suitable for the trigger method. Since the signal-to-noise ratio is good, it becomes a more suitable waveform by amplifying the received waveform. As another means for increasing the reception voltage, the drive voltage is increased. For example, the applied voltage is a 2 MHz, 30 Vp-p sine wave pulse.

  The state described below is suitable for the trigger method. It is important to compare the peak voltage value of a wave with a higher voltage value than the preceding and following waves, not only the magnitude of the voltage value of the previous waveform, but also the peak voltage value and the largest voltage value of the previous wave. is there. For the trigger method, since the voltage value of the previous wave can be considered as noise, it can be handled in the same manner as the S / N ratio. Therefore, both the peak voltage value and the large voltage ratio compared to the previous wave are desired.

  Therefore, if the S / N ratio of the waveform is high, a waveform suitable for the trigger method can be obtained by electrically amplifying the waveform.

  For comparison, a piezoelectric rod 3 having a diameter of 10 mm and a thickness of 1 mm was joined to one end of a stainless rod 10 mmφ 40 mm in length with an epoxy resin 7 and the received waveform was observed in the same manner as above. A small received waveform could not be confirmed due to large noise propagating through the.

  For comparison, the piezoelectric element 3 having a diameter of 10 mm and a thickness of 1 mm was joined to one end of an acrylic rod 10 mmφ 40 mm in length with an epoxy resin 7 and the received waveform was observed in the same manner as above. A waveform that becomes a very small signal is placed on a large low-frequency received waveform that propagates through the acrylic, and the trigger method cannot be used.

  Therefore, the reception waveform having a length of 40 mm of the carbon fiber composite material 2 has an improved rising of the reception waveform and higher reception sensitivity than the conventional material. There is an effect of.

  The fact that the carbon fiber composite material 2 can be used for transmission / reception of ultrasonic waves even when the length of the carbon fiber composite material 2 is 40 mm is very effective as the ultrasonic vibrator 1 in contact with a container containing a fluid at 200 ° C. Even if the temperature of the carbon fiber composite material 2 in contact with the container is 200 ° C., the temperature of the carbon fiber composite material 2 in contact with the piezoelectric element 3 becomes considerably low, so that the normal piezoelectric element 3 can be used. Moreover, since the temperature change of the piezoelectric element 3 becomes small, the measurement accuracy can be increased. Such high-temperature applications include an ultrasonic flow meter and an ultrasonic level meter. In addition, when used at a higher temperature, the heat resistance of the carbon fiber composite material 2 is obtained by carbonizing or partially carbonizing the organic material that is the base material of the carbon fiber composite material 2 by heat treatment in an inert atmosphere. Increase sex.

  It was confirmed that the rising characteristics could be improved by the effect of the carbon fiber in the carbon fiber composite material 2 with a length of 10 mm or less that does not consider the action of the shape of the carbon fiber composite material 2. The length was 0.42 mm, but could not be confirmed at 0.21 mm. Therefore, it became clear that a length greater than 0.2 mm was necessary with a thickness of 10 mm or less without considering the effect of the shape.

  The rise characteristic can be improved by the effect of the carbon fiber in the carbon fiber composite material 2 at a thickness of 10 mm or more that the action of the shape of the carbon fiber composite material 2 can be used, and the reception sensitivity can be increased. confirmed. Its length was 40 mm. The upper limit is a problem in actual use. Actually, the length of the carbon fiber composite material 2 was measured in the same manner as 60 mm. As a result, the second wave had a plus-side peak voltage of 14.8 mV. The waveform was even better than 40 mm.

  Furthermore, the ultrasonic propagation characteristics from the carbon fiber composite material 2 of the ultrasonic vibrator 1 to the PFA will be described. Usually, in order to improve the propagation characteristics, the matching layer is set to a length of 1/4 of the wavelength of the vibration to propagate. However, since the concept of matching is not used here, it is based on a new concept of propagating ultrasonic waves, so the waveform and sensitivity of the carbon fiber composite material 2 are observed over a wide range from 0.21 mm to 40 mm. To do.

  This will be described with reference to the cross-sectional view of FIG. The whole shown in FIG. The dimensions of a circular tube made of PFA (polytetrafluoroethylene) are an inner diameter of 4 mm, an outer diameter of 16 mm, and a length for transmitting and receiving ultrasonic waves of about 60 mm. The length of the PFA between the ultrasonic vibrator 1 and the fluid is 3 mm. And the distance of the surface which contact | connects the carbon fiber composite material 2 is 92 mm. The fluid in the circular pipe is pure water 9.

  Similarly to the above, the carbon fiber composite material 2 has a length of 10 mm square and a thickness of 0.21 mm to 40 mm. The carbon fibers are oriented in the same direction as the ultrasonic wave propagation direction. In the ultrasonic vibrator 1, the piezoelectric element 3 was bonded to one surface of the carbon fiber composite material 2 with an epoxy resin 7.

  The piezoelectric element 3 has a diameter of 10 mm and a thickness of 1 mm. The material is a lead-based piezoelectric ceramic, and is a LowQ material having a mechanical quality factor Qm of about 80. As shown in the figure, the ultrasonic vibration body 1 was prepared by bonding the carbon fiber composite material 2 and the piezoelectric element 3 with an epoxy resin 7.

  The ultrasonic vibrating body 1 described above was brought into contact with PFA as a carbon fiber composite material 2 through silicon-based grease as a contact medium.

  Next, a sin wave pulse with an applied voltage of 2 MHz and 10 Vp-p is applied to the piezoelectric element 3 a of the ultrasonic vibrator 1. As a result, the ultrasonic wave propagates through the carbon fiber composite material 2 and PFA, propagates to the pure water 9, propagates to the opposing PFA surface, propagates through the carbon fiber composite material 2, and propagates to the piezoelectric element 3b.

  Due to the ultrasonic vibration propagated to the piezoelectric element 3b, a voltage is generated in the piezoelectric element 3b, and the received waveform shown in FIG. 11 is obtained. 11a shows that the thickness of the carbon fiber composite material 2 is 0.21 mm, FIG. 11b shows 0.43 mm, FIG. 11c shows 40 mm, and FIG. 11d shows that the piezoelectric elements 3a and 3b are directly used without using the carbon fiber composite material 2. It is a received waveform when making it contact with PFA via a silicon-type grease.

  Here, in the received waveform when the piezoelectric elements 3a and 3b are directly brought into contact with the PFA via the silicon-based grease without using the carbon fiber composite material 2, there is a positive peak at the seventh wave, and the voltage is 7.10 mV. Met. Compared with this, the reception waveform when the length of the carbon fiber composite material 2 is 0.21 mm is substantially the same, but the fourth wave has a plus-side peak, and the plus-side peak voltage is 10.8 mV. Since the increase in the voltage of the fourth wave having the peak voltage from the first wave is gentle, the waveform is not suitable for the trigger method. Although the carbon fiber composite material 2 having a length of 0.21 mm is slightly improved, it does not have a noticeable effect as an ultrasonic wave propagation body.

  The received waveform with the carbon fiber composite material 2 having a thickness of 0.43 mm has a positive peak voltage of 9.38 mV in the third wave. Therefore, the carbon fiber composite material 2 having a thickness of 0.43 mm has a reception voltage equal to or higher than that obtained when the piezoelectric elements 3a and 3b are directly brought into contact with the PFA via silicon grease without using the carbon fiber composite material 2. The third wave has a peak that can be triggered. Therefore, there exists an effect | action as an ultrasonic vibration body.

  The reception waveform of the carbon fiber composite material 2 having a length of 40 mm has a positive peak voltage in the third wave and is 5.2 mV. The waveform is suitable for the trigger method. Since the signal-to-noise ratio is good, it becomes a more suitable waveform by amplifying the received waveform. As another means for increasing the reception voltage, the drive voltage is increased. For example, the applied voltage is a 2 MHz, 30 Vp-p sine wave pulse.

  For comparison, a piezoelectric rod 3 having a diameter of 10 mm and a thickness of 1 mm was joined to one end of a stainless steel rod 10 mmφ 40 mm in length with an epoxy resin 7 and the received waveform was observed in the same manner as above. The received waveform could not be confirmed.

  For comparison, the piezoelectric element 3 having a diameter of 10 mm and a thickness of 1 mm was joined to one end of an acrylic rod 10 mmφ 40 mm in length with an epoxy resin 7 and the received waveform was observed in the same manner as above. The received waveform could hardly be confirmed.

  Therefore, the reception waveform having a length of 40 mm of the carbon fiber composite material 2 has an improved rising of the reception waveform and higher reception sensitivity than the conventional material. There is an effect of.

  It was confirmed that the rising characteristics could be improved by the effect of the carbon fiber in the carbon fiber composite material 2 with a length of 10 mm or less that does not consider the action of the shape of the carbon fiber composite material 2. The length was 0.42 mm, but could not be confirmed sufficiently at 0.21 mm. Therefore, it became clear that a length greater than 0.2 mm was necessary with a thickness of 10 mm or less without considering the effect of the shape.

  The rise characteristic can be improved by the effect of the carbon fiber in the carbon fiber composite material 2 at a thickness of 10 mm or more that the action of the shape of the carbon fiber composite material 2 can be used, and the reception sensitivity can be increased. confirmed. Its length was 40 mm. The upper limit is a problem in actual use.

  Here, the orientation direction of the carbon fibers in the carbon fiber composite material 2 will be described with reference to FIG. The broken arrow in FIG. 12A indicates the ultrasonic wave propagation direction. The orientation direction 10a of the fibers in the carbon fiber composite material is the same as the ultrasonic wave propagation direction and is the 0 degree orientation direction. The orientation direction 10b of the fiber is 5 degrees with respect to the ultrasonic wave propagation direction, and is an orientation direction of 5 degrees. The fiber orientation direction 10c has an angle of 30 degrees with respect to the ultrasonic wave propagation direction, and is an orientation direction of 30 degrees.

  The carbon fiber composite material with 0 degree orientation is prepared by laminating prepreg sheets with the same fiber direction and curing the resin. The carbon fiber composite material oriented at 5 degrees is formed by alternately laminating the prepreg sheets of FIGS. 12B and 12C and curing the resin. The produced carbon fiber composite material has carbon fibers having orientation directions of +5 degrees and -5 degrees with respect to the ultrasonic wave propagation direction. Since the carbon fiber composite material with 30 degree orientation is produced in the same manner as described above, the produced carbon fiber composite material has carbon fibers with orientation directions of +30 degrees and −30 degrees with respect to the ultrasonic wave propagation direction. .

  Since the ultrasonic propagation of the carbon fiber composite material propagates in the fiber direction, the sound speed of the carbon fiber composite material with 0 degree orientation is 13700 m / s, and the sound speed of the carbon fiber composite material with 90 degree orientation is 2650 m / s. there were. From this, when the orientation direction of the carbon fiber is 45 degrees, it is considered that the influence of the matrix is about half, so that the effect of the fiber cannot be sufficiently exhibited. Therefore, an orientation direction of 40 degrees or less is desirable for exerting the fiber effect. More preferably, it is within 30 degrees, and of course, the largest received signal is in the orientation direction of the carbon fiber at 0 degrees.

  The performance of the ultrasonic level meter can be greatly improved by using the characteristics of the carbon fiber composite material described above. An ultrasonic level meter using a carbon fiber composite material will be described below.

  Further, FIG. 13 showing a cross section of a part of the stainless steel container 6 and the ultrasonic vibration body shows an example in which the ultrasonic vibration body 1 is attached to the side surface of the stainless steel container 6 as an ultrasonic level meter. First, a stainless steel mounting base 11 is attached to the outer surface of the stainless steel container 6 with an epoxy resin having a maximum operating temperature of about 200 ° C. A female screw is provided at the center of the cylindrical mounting base 11.

  A taper is provided at the tip of the columnar carbon fiber composite material 2 in which the carbon fibers are oriented in the direction of the arrow, and the disc-shaped silicon gel 11 is joined to the tip of which the tip is tapered. The diameter of the tip narrowed by the taper is preferably 70% or less and 20% or more of the original diameter. If it is 70% or less, the tip area is about half or less, so that ultrasonic waves with more uniform phases can be propagated. Further, since the heat transfer area is also reduced, the heat transfer from the stainless steel container 6 can be reduced. Furthermore, the contact pressure between the carbon fiber composite material 2 and the stainless steel container 6 through the silicon gel 11 can be increased by about twice or more. The reason why 20% or more is preferable is that when the area is 20% or less, the tip area becomes 4% or less, and the contact area becomes too small to sufficiently propagate the ultrasonic wave to the stainless steel container 6. The silicon gel 11 is a contact medium that improves the adhesion between the carbon fiber composite material 2 and the stainless steel container 6, and can reduce the ultrasonic propagation loss between the carbon fiber composite material 2 and the stainless steel container 6.

  The reception waveform is improved by providing a taper at the tip of the carbon fiber composite material 2. This is considered to be due to the fact that uniform phase information can be obtained by reducing the contact area when there are portions with different phases on the contact surface. Further, since the contact surface with the stainless steel container 6 is reduced by providing a taper at the tip, for example, when the stainless steel container 6 is at a high temperature exceeding 100 ° C., the heat transfer to the carbon fiber composite material 2 can be reduced. Therefore, the temperature rise of the piezoelectric element 3 can be reduced.

  A male screw is provided on the side surface of the carbon fiber composite material 2. This is for mounting on the mounting base 11. Further, the male screw on the side surface of the carbon fiber composite material 2 is carbon if the smallest diameter reduced by the male screw with respect to the diameter of the carbon fiber composite material 2 is 70% or more of the diameter of the original carbon fiber composite material 2. The ultrasonic wave propagating through the fiber composite material 2 is not so affected.

  Furthermore, the heat of the carbon fiber composite material 2 can be efficiently released into the outside air by joining the heat sink 13 for heat dissipation to the side surface portion of the carbon fiber composite material 2. Thereby, since the temperature of the carbon fiber composite material 2 can be reduced, the temperature rise of the piezoelectric element can be reduced. And even if the heat sink 13 for heat dissipation was joined to the side surface portion of the carbon fiber composite material 2, the ultrasonic wave propagated was hardly affected. It is considered that this does not affect the propagation of ultrasonic waves because the carbon fiber in the carbon fiber composite material 2 is not bent or cut.

  A piezoelectric element is bonded to the rear portion of the carbon fiber composite material 2 using an epoxy resin. The piezoelectric element is a composite piezoelectric element, and the composite piezoelectric element is described in detail in Non-Patent Document 2, for example. When the composite piezoelectric element is used, since the composite piezoelectric element is a composite material made of an organic material such as a piezoelectric ceramic and an epoxy resin, it is desirable that the temperature be used as close to room temperature as possible. In particular, it cannot be used at temperatures exceeding the heat resistance temperature of epoxy resin.

  The ultrasonic vibrator 1 is attached to the stainless steel container 6. By screwing the male screw of the side surface portion of the carbon fiber composite material 2 into the female screw of the mounting base 12 attached to the stainless steel container 6 with a heat-resistant grade epoxy resin, the tip of the carbon fiber composite material 2 is attached to the stainless steel container 6 through the silicon gel. It can be reliably contacted. If the contact is insufficient, the ultrasonic wave does not sufficiently propagate to the stainless steel container 6 and therefore does not sufficiently propagate to the liquid in the stainless steel container 6.

  Next, a method for measuring whether or not a liquid exists at a position where the ultrasonic vibrator 1 is attached to the stainless steel container 6 will be described using the configuration of FIG.

  For example, a sin wave pulse with an applied voltage of 500 KHz and 50 Vp-p is applied to the piezoelectric element 3 of the ultrasonic vibrator 1. As a result, the ultrasonic wave propagates through the carbon fiber composite material 2 and the stainless steel container 6, propagates to the liquid at about 150 ° C., is mostly reflected by the inner surface of the opposing stainless steel container 6, and again enters the liquid at about 150 ° C. Propagate, propagate through the stainless steel container 6, propagate through the carbon fiber composite material 2, and propagate to the piezoelectric element 3.

  The presence of the liquid in the stainless steel container 6 is confirmed by measuring the time difference from the time when the received propagation waveform is detected from the time when the sin wave pulse is applied. The trigger method was used as a method for measuring the time difference. If there is no liquid, it can be confirmed that there is no liquid at that position because the received waveform does not exist at the position of the time difference in which the liquid propagates.

  Further, a method for attaching the ultrasonic vibrator 1 to the bottom surface of the stainless steel container 6 and measuring the position of the liquid in the stainless steel container 6 will be described. Here, the ultrasonic vibrator 1 is attached so that ultrasonic waves are transmitted and received perpendicular to the liquid level in the stainless steel container 6.

  Then, for example, a sin wave pulse with an applied voltage of 700 KHz and 50 Vp-p is applied to the piezoelectric element 3 of the ultrasonic vibrator 1. As a result, the ultrasonic wave propagates through the carbon fiber composite material 2 and the stainless steel container 6, propagates to the liquid at about 150 ° C., almost reflects off the liquid surface, and propagates again into the liquid at about 150 ° C. Propagate, propagate through the carbon fiber composite material 2, and propagate to the piezoelectric element 3.

  The position of the liquid surface of the stainless steel container 6 is measured by measuring the time difference from the time when the received propagation waveform is detected from the time when the sin wave pulse is applied. The trigger method was used as a method for measuring the time difference.

  Although the carbon fiber composite material has been described above, the high elastic fiber having a tensile elastic modulus exceeding 100 Gpa is not limited to the carbon fiber, for example, SiC fiber, alumina fiber, para-aramid fiber, PBO fiber, ultrahigh molecular weight polyethylene fiber, poly There are arylate fibers. Therefore, composite materials other than carbon fibers can also be used.

  In the above, a composite piezoelectric element is used as the piezoelectric element, but a piezoelectric single crystal such as lithium niobate, an organic piezoelectric material such as PVDF, and a piezoelectric ceramic can also be used.

  As described above, the ultrasonic vibrator of the present invention can be suitably used for an ultrasonic level meter.

DESCRIPTION OF SYMBOLS 1 Ultrasonic vibrator 2 Carbon fiber composite material 3 Piezoelectric element 4 Carbon fiber 5 Received waveform 6 Stainless steel container 7 Epoxy resin 8 PFA container 9 Pure water 10 Fiber orientation direction 11 Silicon gel 12 Mounting base 13 Heat sink

Claims (6)

  A plurality of high elastic fibers having a tensile modulus of 100 GPa or more are oriented in the same direction in a base material made of resin or a carbonized product of the resin, and the orientation direction of the high elastic fibers is perpendicular to the bonding surface with the piezoelectric element. An ultrasonic level meter having an ultrasonic vibrator formed by bonding a fiber composite material and a piezoelectric element.   2. The ultrasonic level meter having an ultrasonic vibrator according to claim 1, wherein the cylindrical fiber composite material has fibers oriented in the column direction, and the length in the column direction is larger than the diameter.   2. The ultrasonic vibrator according to claim 1, wherein the fiber composite material in the shape of a polygonal column has fibers oriented in the column direction, and the length in the column direction is larger than the length of the side of the polygon. Sonic level meter.   2. The ultrasonic wave having an ultrasonic vibrator according to claim 1, wherein the cylindrical fiber composite material has fibers oriented in a column direction, and a length in the column direction is equal to or less than a diameter and longer than 0.2 mm. Level meter.   The polygonal columnar fiber composite material has fibers oriented in the column direction, and the length in the column direction is equal to or less than the length of the side of the polygon and longer than 0.2 mm. An ultrasonic level meter having the ultrasonic vibrator according to Item 2.   The ultrasonic level meter having an ultrasonic vibrator according to claim 1, wherein the highly elastic fiber is a carbon fiber or a carbon-containing fiber.

Images