JP2014006231A - Coriolis flowmeter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a coriolis flowmeter having high measurement accuracy.SOLUTION: A coriolis flowmeter 1 whose flow tube 2 is linear is constituted of the linear stainless-steel flow tube 2, a vibrating body 3, and support bodies 5. The vibrating body 3 is constituted by joining, with epoxy resin, a piezoelectric element 4 to a stainless-steel elastic body 6 into which semicircles and straight lines are combined and integrated in a ring shape. The integrated, ring-like, stainless-steel elastic body 6 constituting the vibrating body 3 has a through-hole as shown in Figs. The through-hole becomes a flow tube 2b. Stainless-steel flow tubes 2a, 2c on both sides of the flow tube are positionally adjusted and welded with the through-hole (flow tube 2b) of the elastic body 6 to make the flow tube 2 completed. The flow tube 2a is welded with the support body 5a. The flow tube 2c is welded with the support body 5b.

Description

  The present invention relates to a mass flow meter or a density meter using Coriolis force.

  The Coriolis flow meter that directly determines the mass flow rate is a direct mass flow meter that utilizes the fact that the Coriolis force acting on the vibrating measurement fluid is proportional to the mass flow rate when vibration is applied to the measurement fluid flowing in the flow tube. However, since the Coriolis force is a slight force with respect to the excitation force, the Coriolis flowmeter requires a highly sensitive and stable force measuring means.

  Normally, Coriolis force is detected as elastic deformation or strain of the flow tube due to Coriolis force. For this reason, conventionally, the flow tube has a curved shape with a large amount of deformation. Since the curved Coriolis flowmeter is curved in a U shape, there is a problem in that pressure loss due to the shape of the sensor tube tends to occur when the fluid to be measured passes through the sensor tube. In addition, the curved Coriolis flowmeter generally has a drawback that the shape becomes large. When the fluid to be measured is slurry, the U-shaped curved portion may be clogged with powder in the slurry. For this reason, straight pipe type Coriolis flowmeters having a straight pipe shape have been developed.

  There are two types of straight Coriolis flowmeters, one that uses a single flow tube as the flow tube to be vibrated and the other that has a plurality of straight tubes arranged in parallel. In any case, it has a drive means that supports both ends of the straight pipe and vibrates the flow pipe at the middle part, and a means for detecting minute displacement or strain due to Coriolis force between the drive means and the support part. ing.

  The straight pipe type flow tube having such a configuration is normally driven in a bending fundamental vibration mode in which a support portion is a node portion by a driving means. When this frequency is ω, the flow velocity is v, and the mass per unit volume is m, the Coriolis force F is proportional to the vector product of the frequency ω and the flow velocity v, and is expressed as −2 m [ω] × [v]. Here, [ω] and [v] are vectors. The above is described in detail in Non-Patent Document 1.

Japan Measuring Instruments Manufacturers Association, "Flow Measurement AtoZ", Industrial Technology Co., Ltd., November 1995, p161-172 Izumi Igarashi et al., “Si Micromachining Advanced Technology”, Science Forum, Inc., March 1992, p87-143

  However, a flow tube having nodes at both ends generates a vibration in the bending secondary vibration mode by the Coriolis force at the frequency of the bending fundamental vibration mode. Therefore, the drive vibration mode can be excited greatly, but the detection vibration of the secondary vibration mode of the detection mode, which has a natural frequency that is usually twice or more higher than the natural frequency of the bending fundamental vibration mode, has a small vibration displacement. turn into.

  Moreover, in order to improve the measurement accuracy of the Coriolis flowmeter, it is necessary not to leak the vibration of the flow tube for measuring the flow rate to the outside. Therefore, in order to prevent the vibration from leaking to the outside, a counter tube that vibrates in the opposite phase to the vibration of the flow tube is provided, so that the vibrations of the flow tube and the counter tube are canceled and the vibration is not leaked to the outside. However, fluid needs to flow through both the flow tube and the counter tube, and fluid must be equally distributed through both the flow tube and the counter tube, but it is difficult to accurately distribute the fluid.

  The present invention provides a Coriolis flowmeter in which a vibrating body that applies vibration to a flow tube through which a fluid flows has a drive source in an elastic body and has a space in the center of the vibrating body.

  In the present invention, the vibrating body that applies vibration to the flow tube that flows the fluid joins the flow tube and the elastic body, and the flow tube or the elastic body has a drive source, and a space is provided at the center of the vibrating body. A Coriolis flowmeter with a

  In the above Coriolis flowmeter, the flow tube is made straight.

  The flow tube is bent in the above Coriolis flowmeter.

  The Coriolis flowmeter is configured such that the drive vibration mode by the vibration generator that applies vibration to the flow tube through which the fluid flows is the same as the detection vibration mode of the vibration caused by the flow of the fluid caused by the Coriolis force.

  The Coriolis flowmeter is different in driving vibration mode and detection vibration mode from each other by a quarter wavelength.

  The straight tubular Coriolis flowmeter of the present invention can measure the mass flow rate of fluid with high accuracy.

It is a perspective view of the Coriolis flow meter of a 1st embodiment of the present invention. It is a perspective view of the used piezoelectric element of FIG. It is a figure explaining the drive vibration mode and detection vibration mode of the Coriolis flowmeter shown in FIG. It is a top view of the Coriolis flow meter of a 2nd embodiment of the present invention. It is a side view of the Coriolis flow meter of the 2nd embodiment of the present invention. It is a figure explaining the drive vibration mode and detection vibration mode of the Coriolis flowmeter shown in FIG. It is a top view of the Coriolis flow meter of a 3rd embodiment of the present invention. It is a side view of the Coriolis flow meter of the 3rd embodiment of the present invention. It is a top view of the Coriolis flow meter of a 4th embodiment of the present invention.

  A basic configuration according to the first embodiment will be described with reference to the perspective view of FIG.

  The Coriolis flow meter 1 in which the flow tube 2 is linear includes a flow tube 2 made of stainless steel, a vibrating body 3, and a support portion 5. The vibrating body 3 has a ring-shaped integral stainless steel elastic body 6 combining a semicircle and a straight line, and the piezoelectric element 4 joined to the integral stainless steel elastic body 6 with an epoxy resin.

  The integral ring-shaped stainless steel elastic body 6 constituting the vibrating body 3 has a through-hole as shown in the figure. This penetrating hole becomes the flow tube 2b. Then, the stainless steel flow tubes 2a and 2c on both sides become a flow tube 2 completed by welding together with the position of the hole (flow tube 2b) through which the elastic body 6 passes.

  The flow tube 2a is welded and joined to the support portion 5a. The support portion 5a is provided with a through-hole that matches the inner diameter of the flow tube 2a. The flow tube 2c is welded and joined to the support portion 5b. The support portion 5b is provided with a through-hole that matches the inner diameter of the flow tube 2c.

  The piezoelectric element 4 joined to the stainless steel elastic body 6 will be described. The piezoelectric element 4 is a lead-based piezoelectric ceramic and is polarized in the thickness direction. The piezoelectric element 4 will be described in detail with reference to the perspective view of FIG. FIG. 2A shows a driving piezoelectric element 4 a for vibrating the flow tube 2. The arrow indicates the polarization direction, and the diagonal line indicates the electrode 7a. For example, the piezoelectric element 4a is prepared by providing an electrode 7a after bonding a piece divided into three for each polarization with an epoxy resin.

  FIG. 2B shows a piezoelectric element 4b that detects vibration of the flow tube 2 due to Coriolis force. Arrows indicate the direction of polarization. The oblique lines indicate the electrodes 7b and 7c. The electrode 7b and the electrode 7c are separated. The piezoelectric elements 4a and 4b are the same as the front side in a state where the front side in FIG. 4 is joined to the elastic body 6 made of stainless steel. In the above description, the piezoelectric element 4 has been described as a lead-based piezoelectric ceramic.

  Next, the drive vibration mode and the detection vibration mode of the Coriolis flow meter 1 will be described with reference to FIG. The drive mode is indicated by a solid line written in the figure. The vibrating body is a vibration mode in which bending vibrations for a total of 6 wavelengths are excited in a direction parallel to the paper surface because there are two 1.5 wavelengths in the straight part and 1.5 wavelengths in the semicircular part as shown by the solid line. is there.

  Next, the detection vibration mode of the Coriolis flow meter 1 will be described with reference to FIG. The detection mode is indicated by a two-dot chain line written in the vibrating body 3 and the flow tube 2 in the figure. The vibrating body 3 is a vibration mode in which bending vibrations for a total of six wavelengths are excited in a direction parallel to the paper surface as indicated by a two-dot chain line.

  The vibration modes of the drive mode and the detection mode are the same, and the drive vibration mode and the detection vibration mode have a difference in position of vibration nodes or vibration antinodes by a quarter wavelength. The drive vibration mode and the detection vibration mode have a temporal phase difference of vibration by a quarter wavelength.

  Here, the flow measurement of the Coriolis flow meter 1 will be described. In order to excite 6-wave bending vibration to the vibrating body 3, a voltage having a natural frequency of 6-wave bending vibration is applied between the electrodes of the piezoelectric element 4a through a lead wire. Further, the density of the fluid can be measured by detecting the natural frequency of the driving vibration mode.

  When the fluid flows in the flow tube 2 that vibrates in the bending vibration mode of 6 wavelengths indicated by the solid line in FIG. 3, Coriolis force is generated in the fluid, and vibration in the detection mode is generated. The detected vibration mode is the same as the drive vibration mode, and the detected vibration mode has a difference in position of the vibration node or vibration antinode by 1/4 wavelength from the drive vibration mode. Further, the drive vibration mode and the detection vibration mode have a temporal phase difference of vibration by a quarter wavelength.

  In order to detect vibration in the detection mode, the piezoelectric element 4b is joined in accordance with the position of the detection vibration mode. In order to detect the vibration in the detection mode indicated by the two-dot chain line in FIG. 3, the voltage between the electrode 7b of the piezoelectric element 4b and the lead wire connected to the electrode 7c and the ground wire is measured.

  Since the polarization direction of the piezoelectric element 4b is the same and the vibration directions of the electrode 7b and the electrode 7c are opposite, the voltage in the detection mode is obtained by subtracting the voltage generated in the electrode 7c from the voltage generated in the electrode 7b. The mass flow rate is detected by measuring. Further, since the vibration phase is the same in the driving vibration mode at the positions of the electrode 7b and the electrode 7c, the generated voltage in the driving mode is canceled by subtracting the generated voltage in the electrode 7c from the generated voltage in the electrode 7b. can do. As a result, the SN ratio of the detection voltage can be increased.

  In addition, since the piezoelectric element for detecting distortion can be generally reduced in size and weight as compared with an electromagnetic pickup composed of a coil and a magnet, the phenomenon of mechanical Q of the flow tube 2 when attached to the flow tube 2 can be reduced. In addition, since the coil and the magnet are not divided into two parts, the structure is simple and the problem that the detection signal is distorted by the leakage magnetic field does not occur.

  In the piezoelectric element, a signal proportional to the bending moment of the flow tube 2 is obtained. Therefore, a phase difference (time difference) proportional to the mass flow rate, which is different from the electromagnetic pickup that detects the speed, is detected. When a straight tubular flow tube 2 having a simple support structure at both ends is used as a vibration detecting means of a mass flow meter, a phase difference (time difference) proportional to the obtained mass flow rate is larger than that of an electromagnetic pickup. Become. Therefore, the accuracy of flow rate measurement can be increased.

  As described above, since the drive vibration mode and the detection vibration mode are the same, a mass flow with high sensitivity can be measured. Further, since the detected signal is configured not to detect the drive vibration mode, the SN ratio becomes high. Furthermore, since the vibration is confined in the ring-shaped vibrating body, vibration leakage to the outside is reduced.

  A basic configuration according to the second embodiment will be described with reference to a plan view of FIG. 4 and a side view of FIG.

  The Coriolis flow meter 1 having a curved flow tube 2 includes a vibrating body 3 formed by joining piezoelectric elements 4 with an epoxy resin on the top and bottom of a titanium alloy flow tube 2, and a support portion 5 to which the vibrating body 3 is welded. Consists of. Here, the piezoelectric elements 4a and 4b are for driving, and the piezoelectric elements 4c and 4d and the piezoelectric elements 4e and 4f are for detection.

  In order to excite the bending vibration, when one of the piezoelectric elements 4a and 4b is extended, the other is contracted. In this way, bending vibration is excited. Similarly, when one of the piezoelectric elements 4c and 4d and the piezoelectric elements 4e and 4f are extended, the other is contracted.

  The flow tube 2 is a curved tube. Compared to a straight pipe, the sensitivity increases because the ratio of the Coriolis force acting on the flow pipe 2 is large.

  The drive vibration mode of the Coriolis flow meter 1 will be described with reference to FIG. The drive vibration mode is indicated by a solid line in the figure. The solid line indicates that the outside of the center line of the ring-shaped vibrating body 3 is displaced vertically upward with respect to the paper surface. A solid line indicates that the inner side of the center line of the ring-shaped vibrating body 3 is displaced vertically downward with respect to the paper surface. That is, it is a third-order bending vibration mode in a direction perpendicular to the paper surface.

  Next, the detection vibration mode of the Coriolis flow meter 1 will be described with reference to FIG. The detected vibration mode is indicated by a dotted line in the figure. The dotted line indicates that the outer side of the center line of the ring-shaped vibrating body 3 is displaced vertically upward with respect to the paper surface. The dotted line indicates that the inner side of the center line of the ring-shaped vibrating body 3 is displaced vertically downward with respect to the paper surface. That is, it is a third-order bending vibration mode in a direction perpendicular to the paper surface.

  The driving vibration mode and the detection vibration mode are the same, and the third bending vibration mode is perpendicular to the paper surface. The drive vibration mode and the detection vibration mode are different in the vibration phase by a quarter wavelength.

  Here, the flow measurement of the Coriolis flow meter 1 will be described. In order to excite the three-wave bending vibration to the vibrating body 3, a voltage having a natural frequency of the three-wave bending vibration is applied between the electrodes of the piezoelectric element 4a through the lead wire. Further, the density of the fluid can be measured by detecting the natural frequency of the driving vibration mode.

  When the fluid flows through the flow tube 2 that vibrates in the bending vibration mode of the three wavelengths indicated by the solid line in FIG. 6, a Coriolis force is generated in the fluid, and the detection mode vibration indicated by the dotted line in FIG. 6 is generated. The detected vibration mode is the same as the drive vibration mode, and the detected vibration mode has a difference in position of the vibration node or vibration antinode by 1/4 wavelength from the drive vibration mode. Further, the drive vibration mode and the detection vibration mode have a temporal phase difference of vibration by a quarter wavelength.

  In order to excite the vibration of the drive mode shown by the solid line in FIG. 6, a voltage is applied to the lead wire and the ground wire connected to the electrodes of the piezoelectric elements 4a and 4b. In order to detect vibration in the detection mode, the piezoelectric elements 4c and 4d and the piezoelectric elements 4e and 4f are joined in accordance with the position of the detection vibration mode.

  The piezoelectric elements 4c and 4d and the piezoelectric elements 4e and 4f are arranged so as to generate voltages having the same phase if the directions of bending vibration are the same. Therefore, the piezoelectric elements 4c and 4d and the piezoelectric elements 4e and 4f are obtained by measuring the difference between the generated voltages of the piezoelectric elements 4e and 4f from the generated voltages of the piezoelectric elements 4c and 4d in the detection mode in which the bending vibration directions are different. Measure voltage in detection mode. To measure the mass flow rate. Further, since the vibration phase is in phase in the drive vibration mode, the voltage generated in the drive mode can be canceled by measuring the difference between the voltage generated in the piezoelectric elements 4e and 4f from the voltage generated in the piezoelectric elements 4c and 4d. .

  As described above, since the drive vibration mode and the detection vibration mode are the same, a mass flow with high sensitivity can be measured. Further, since the detected signal is configured not to detect the drive vibration mode, the SN ratio is increased. Furthermore, since the vibration is confined in the ring-shaped vibrating body, vibration leakage to the outside is reduced. And sensitivity can be raised by making a flow pipe into a curved pipe.

  A basic configuration according to the third embodiment will be described with reference to a plan view of FIG. 7 and a side view of FIG. Up to now, the example using the piezoelectric element as the vibration generating means and the vibration detecting means has been described, but other means may be used, for example, an electromagnetic effect using a magnet and a coil can be used. A first embodiment in which an electromagnetic effect is used for vibration generating means and vibration detecting means will be described with reference to a plan view of FIG. 7 and a side view of FIG.

  The configuration of the Coriolis flow meter 1 is the same as in FIG. 1 except for the vibration generating means and the vibration detecting means. The vibration generating means is composed of drive magnets 8a, 8b, 8c and drive coils 9a, 9b, 9c. The driving magnet 8b and the driving coil 9b, the driving magnets 8a and 8c, and the driving coils 9a and 9c generate vibrations having opposite phases.

  The vibration detection means includes detection magnets 8d and 8e and detection coils 9d and 9e. The mass flow rate is measured by measuring the difference between the voltage or current generated by the detection coil 9d and the voltage or current generated by the detection coil 9e.

  A fourth embodiment in which an electrostatic effect is used for vibration generating means and vibration detecting means will be described with reference to the plan view of FIG. Those using the electrostatic effect are suitable for small-sized ones.

  The configuration of the Coriolis flow meter 1 having a straight flow tube 2 is created by etching and bonding a silicon substrate. The processing method and bonding method of the silicon substrate 10 are described in detail in Non-Patent Document 2.

  The configuration of the Coriolis flow meter 1 having a straight flow tube 2 is the same as that shown in FIG. 1, and uses an electrostatic effect for vibration generating means and vibration detecting means. In order to simplify the drawing, the vibration generating means and the vibration detecting means are omitted.

  As described above, a desired drive mode and detection mode can be realized using the electromagnetic effect and the electrostatic effect.

DESCRIPTION OF SYMBOLS 1 Coriolis flow meter 2 Flow pipe 3 Vibrating body 4 Piezoelectric element 5 Support part 6 Elastic body 7 Electrode 8 Magnet 9 Coil 10 Silicon substrate

Claims (6)

  A Coriolis flowmeter characterized in that the vibration generating means for applying vibration to a flow tube through which a fluid flows has a structure having a space in the center of the vibrating body.   A Coriolis flowmeter characterized in that the vibration generating means for applying vibration to a flow tube for flowing a fluid has a structure having a space at the center of the vibrating body by joining the flow tube and an elastic body.   The Coriolis flowmeter according to claim 1 or 2, wherein a flow pipe for flowing a fluid is linear.   The Coriolis flowmeter according to claim 1 or 2, wherein a flow pipe for flowing a fluid is curved.   The drive vibration mode by the vibration generating means for applying vibration to the flow tube through which the fluid flows is the same as the detection vibration mode of the vibration caused by the fluid flowing due to the Coriolis force. 2. Coriolis flow meter according to 2.   6. The Coriolis flow meter according to claim 5, wherein the driving vibration mode and the detection vibration mode are different from each other by a quarter wavelength.

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