Measurement device and preparation method

Abstract

A measurement device (2) has a piezoelectric sensor (50) and a calculation unit (60). First, the calculation unit (60) acquires an amplitude spectrum by performing a Fourier transform on time-series data of a voltage value which is output by the piezoelectric sensor (50). Next, the calculation unit (60) calculates an integral value of a specific frequency range in the amplitude spectrum. Then, the calculation unit (60) calculates the flow velocity of a fluid on the basis of the integral value. This measurement device (2) can measure the flow velocity with high responsiveness by using the piezoelectric sensor (50). Further, instead of directly converting the voltage value, which is output by the piezoelectric sensor (50), to the flow velocity, the flow velocity of the fluid is calculated on the basis of the integral value of the amplitude spectrum. Thus, the flow velocity can be measured with high accuracy.

Description

Measurement equipment and preparation method

[0001] The present invention relates to a technique for measuring the flow velocity of a fluid.

[0002] Industrial manufacturing equipment may be equipped with a flow meter to measure the flow of gas or liquid. Known measurement methods for flow meters include, for example, a windmill type that converts the rotation of blades into flow velocity, and a hot wire type that converts the temperature change of a metal wire into flow velocity. A conventional flow meter is described, for example, in Patent Document 1.

[0003] Japanese Patent Application Laid-Open No. 2018-087768

[0004] In equipment that requires extremely precise processing, such as semiconductor manufacturing equipment, it is necessary to grasp the flow velocity of gases or liquids in real time. For this reason, a flow meter with excellent responsiveness is required. However, the measurement method of conventional flow meter has limitations in responsiveness.

[0005] To realize a flow meter with excellent response, it is possible to use, for example, a piezoelectric element. A piezoelectric element can instantaneously output a voltage in response to the pressure from the fluid. However, there is no known method for accurately converting the output of a piezoelectric element into a flow velocity.

[0006] Therefore, an object of the present invention is to provide a technique that can measure the flow velocity of a fluid with good responsiveness and accuracy.

[0007] In order to solve the above problem, a first invention of the present application is a measurement device for measuring the flow velocity of a fluid, comprising: a piezoelectric sensor that outputs a voltage value in response to pressure from the fluid; and a calculation unit that calculates the flow velocity of the fluid based on time series data of the voltage value output from the piezoelectric sensor, wherein the calculation unit performs the following processes: a) a process of obtaining an amplitude spectrum by Fourier transforming the time series data; b) a process of calculating an integral value of a specific frequency range in the amplitude spectrum; and c) a process of calculating the flow velocity of the fluid based on the integral value.

[0008] A second aspect of the present invention is the measuring device of the first aspect, wherein the piezoelectric sensor is in the form of a film.

[0009] The third invention of the present application is a measuring device according to the first or second invention, further comprising a memory unit that stores a relational equation showing the correspondence between the integral value and the flow velocity of the fluid, and in step c), the flow velocity is calculated by substituting the integral value calculated in step b) into the relational equation.

[0010] A fourth invention of the present application is a preparation method for measuring the flow velocity of a fluid, comprising the steps of: p) forming a flow of fluid in a space in which a piezoelectric sensor is placed, and acquiring time series data of voltage values ​​output from the piezoelectric sensor for each flow velocity; q) acquiring an amplitude spectrum for each flow velocity by Fourier transforming the time series data; r) calculating an integral value of a specific frequency range in the amplitude spectrum for each flow velocity; and s) calculating a relational expression between the integral value and the flow velocity.

[0011] According to the first to fourth aspects of the present invention, the flow velocity of a fluid can be measured with good responsiveness by using a piezoelectric sensor. Furthermore, the flow velocity of the fluid is calculated based on the integral value of the amplitude spectrum, rather than directly converting the voltage value output from the piezoelectric sensor into the flow velocity. This allows the flow velocity of the fluid to be measured with high accuracy.

[0012] In particular, according to the second aspect of the present invention, the piezoelectric sensor vibrates in response to the pressure from the fluid, thereby making it possible to obtain an amplitude spectrum that corresponds to the flow velocity of the fluid.

[0013] FIG. 1 is a diagram showing the configuration of a preparation device. FIG. 2 is a flowchart showing the flow of a preparation process. FIG. 3 is a diagram showing an example of measurement results of a piezoelectric sensor. FIG. 4 is a diagram showing an example of an amplitude spectrum. FIG. 5 is an example of a graph showing the relationship between an integral value and a flow velocity. FIG. 6 is a diagram showing the configuration of a measurement device. FIG. 7 is a flowchart showing the flow of processing executed by a calculation unit in a measurement process.

[0014] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0015] <1. Preparation Process> First, the preparation process for acquiring the data necessary to measure the flow velocity of a gas fluid will be described. Fig. 1 is a diagram showing the configuration of a preparation device 1 for performing the preparation process. As shown in Fig. 1, the preparation device 1 includes a wind tunnel 10, a current meter 20, a piezoelectric sensor 30, and a calculation unit 40.

[0016] The wind tunnel 10 is a device that generates a gas flow. The wind tunnel 10 has a cylindrical cylinder 11 and a blower 12. The cylinder 11 has an intake port 111 that takes in gas and an exhaust port 112 that exhausts the gas. The blower 12 is disposed inside the cylinder 11. The blower 12 has a motor 121 and a fan 122 that is rotated by the motor 121. When power is supplied to the motor 121, the fan 122 rotates due to the power output from the motor 121. This generates a gas flow from the intake port 111 to the exhaust port 112 inside the cylinder 11. The gas is then exhausted from the exhaust port 112 to a space downstream.

[0017] The current meter 20 is a sensor that measures the flow velocity of the gas. The piezoelectric sensor 30 is a sensor that measures the pressure exerted by the gas. The current meter 20 and the piezoelectric sensor 30 are disposed outside the exhaust port 112 of the wind tunnel 10. When the blower 12 is operated, a gas flow is formed from the exhaust port 112 of the wind tunnel 10 toward the current meter 20 and the piezoelectric sensor 30.

[0018] The current meter 20 and the piezoelectric sensor 30 are electrically connected to the calculation unit 40. The current meter 20 measures the flow velocity of the gas discharged from the wind tunnel 10 and outputs a signal indicating the measurement result to the calculation unit 40. The piezoelectric sensor 30 measures the pressure exerted by the gas discharged from the wind tunnel 10 and outputs a signal indicating the measurement result to the calculation unit 40.

[0019] The flow meter 20 measures the flow velocity of the gas using an existing measurement method. Examples of existing measurement methods include a windmill method that converts the rotation of blades caused by the airflow into flow velocity, and a hot wire method that converts the temperature change of a metal wire caused by the airflow into flow velocity. These existing flow meters 20 can measure flow velocity with high accuracy, but their responsiveness is lower than that of the piezoelectric sensor 30.

[0020] It is desirable that the gas impinges on the flow meter 20 and the piezoelectric sensor 30 at the same flow rate. Therefore, it is desirable that the flow meter 20 and the piezoelectric sensor 30 are disposed adjacent to each other in close proximity. For example, it is desirable that the distance from the exhaust port 112 of the cylinder 11 to the flow meter 20 is the same as the distance from the exhaust port 112 of the cylinder 11 to the piezoelectric sensor 30.

[0021] The calculation unit 40 is a device that performs calculation processing related to the preparation process. The calculation unit 40 is configured, for example, by a computer having a processor 41 such as a CPU, a memory 42 such as a RAM, and a storage unit 43 such as a hard disk drive. The calculation unit 40 may also include an electric circuit board, an oscilloscope, or the like other than a computer.

[0022] The calculation unit 40 is electrically connected to the motor 121, the current meter 20, and the piezoelectric sensor 30. The calculation unit 40 operates the motor 121 and acquires signals output from the current meter 20 and the piezoelectric sensor 30.

[0023] 2 is a flowchart showing the flow of the preparation process for measuring the flow velocity. When the preparation process is performed, first, the operation of the blower 12 is started (step SA1). This causes a gas flow to be formed in the space where the flow meter 20 and the piezoelectric sensor 30 are disposed.

[0024] The piezoelectric sensor 30 outputs a voltage corresponding to the pressure it receives from the gas. The piezoelectric sensor 30 also vibrates in response to the flow of gas. Therefore, the voltage value output from the piezoelectric sensor 30 fluctuates at a minute period corresponding to the vibration of the piezoelectric sensor 30. In particular, the piezoelectric sensor 30 of this embodiment is a film-like piezoelectric element that is flexibly deformable. Therefore, the piezoelectric sensor 30 vibrates well in response to the flow of gas. Therefore, the voltage value output from the piezoelectric sensor 30 can be fluctuated at a frequency corresponding to the flow velocity.

[0025] The voltage output from the piezoelectric sensor 30 is input to the calculation unit 40. The calculation unit 40 stores the voltage value obtained from the piezoelectric sensor 30 together with the time when the voltage value was generated. This provides time-series data of the voltage value that changes over time (step SA2). The calculation unit 40 also obtains the measurement result of the gas flow velocity from the flow meter 20 (step SA3). In step SA3, the blower 12 rotates the fan 122 at a constant speed, so the measurement result of the flow meter 20 is a substantially constant value.

[0026] After step SA3, it is determined whether data covering a sufficient range of flow velocities has been obtained (step SA4). If data covering a sufficient range of flow velocities has not been obtained, the rotation speed of fan 122 driven by blower 12 is changed. This changes the flow velocity of the gas sent from wind tunnel 10 to flow meter 20 and piezoelectric sensor 30 (step SA5). Then, the process returns to steps SA2 and SA3, and the measurement results of piezoelectric sensor 30 and the flow meter are acquired again.

[0027] By repeating steps SA2 to SA4, the calculation unit 40 obtains multiple combinations of the measurement results of the piezoelectric sensor 30 and the measurement results of the flow meter 20. When it is determined in step SA4 that data covering a sufficient range of flow velocities has been obtained, the process proceeds to step SA6 and subsequent steps.

[0028] 3 is a diagram showing an example of the measurement results of the piezoelectric sensor 30. In the example of FIG. 3, a measurement result V1 of the piezoelectric sensor 30 when the measurement result of the current meter 20 is 1.0, a measurement result V2 of the piezoelectric sensor 30 when the measurement result of the current meter 20 is 5.0 m / s, and a measurement result V3 of the piezoelectric sensor 30 when the measurement result of the current meter 20 is 10.0 m / s are shown. The horizontal axis of each graph in FIG. 3 represents time. The vertical axis of each graph in FIG. 3 represents the voltage value output from the piezoelectric sensor 30.

[0029] The calculation unit 40 performs a Fourier transform on each of these measurement results V1 to V3, which are time-series data (step SA6), thereby obtaining a plurality of amplitude spectra corresponding to a plurality of flow velocities.

[0030] Fig. 4 is a diagram showing an example of an amplitude spectrum. In the example of Fig. 4, an amplitude spectrum S1 when the measurement result of the current meter 20 is 1.0 m / s, an amplitude spectrum S2 when the measurement result of the current meter 20 is 5.0 m / s, and an amplitude spectrum S3 when the measurement result of the current meter 20 is 10.0 m / s are shown. The horizontal axis of each graph in Fig. 4 represents the frequency of the voltage value output from the piezoelectric sensor 30. The vertical axis of each graph in Fig. 4 represents the spectrum intensity.

[0031] Next, the calculation unit 40 calculates the integral of the spectral intensity in a predetermined frequency range A for each of the amplitude spectra S1 to S3. This allows the integral of the spectral intensity corresponding to a plurality of flow velocities to be obtained (step SA7). It is desirable to set the frequency range A to a range in which the integral changes significantly depending on the flow velocity. For example, it is desirable to exclude from the integral calculation range A a frequency at which a large peak occurs regardless of the flow velocity, such as at 60 Hz in Figure 4.

[0032] Thereafter, the calculation unit 40 calculates a relational expression between the integral calculated in step SA7 and the corresponding flow velocity (step SA8). FIG. 5 is an example of a graph showing the relationship between the integral and the flow velocity. The horizontal axis of the graph in FIG. 5 represents the integral. The vertical axis of the graph in FIG. 5 represents the flow velocity. In the example of FIG. 5, the relationship between the integral calculated in step SA7 and the corresponding flow velocity is plotted on the graph. In step SA8, the relationship between the integral and the flow velocity is calculated by fitting these plots using, for example, the least squares method. This allows for the calculation of a relational expression for estimating the flow velocity of the gas based on the measurement results of the piezoelectric sensor 30.

[0033] 5, the fitting is performed using a quadratic function, but the function used for fitting may be a linear function or a cubic or higher order function. The calculation unit 40 stores the obtained relational expression in the storage unit 43.

[0034] 2. Measurement Step Next, a description will be given of the measurement step that follows the preparation step and measures the gas flow velocity using the piezoelectric sensor 30. Fig. 6 is a diagram showing the configuration of a measurement device 2 for performing the measurement step. In this measurement step, the gas flow velocity is measured based on the measurement results of the piezoelectric sensor 30 without using a flow meter 20.

[0035] As shown in Fig. 6, the measurement device 2 includes a piezoelectric sensor 50 and a calculation unit 60. The piezoelectric sensor 50 is a sensor that measures the pressure exerted by the gas. The piezoelectric sensor 50 is electrically connected to the calculation unit 60. The piezoelectric sensor 50 measures the pressure exerted by the gas flow and outputs a signal indicating the measurement result to the calculation unit 60.

[0036] As in the preparation process, it is desirable to use a film-shaped piezoelectric element for the piezoelectric sensor 30. It is more desirable to use the piezoelectric sensor 30 used in the preparation process for the piezoelectric sensor 50. However, the piezoelectric sensor 50 does not necessarily have to be the same piezoelectric sensor 30 used in the preparation process. The piezoelectric sensor 50 may be any sensor that has voltage output characteristics and vibration characteristics similar to those of the piezoelectric sensor 30 used in the preparation process.

[0037] The calculation unit 60 is a device that performs calculation processing related to the measurement process. The calculation unit 60 is configured, for example, by a computer having a processor 61 such as a CPU, a memory 62 such as a RAM, and a storage unit 63 such as a hard disk drive. The calculation unit 60 may also include an electric circuit board, an oscilloscope, or the like other than a computer.

[0038] A computer program for performing the measurement process and the relational equation obtained in the preparation process are stored in the storage unit 63 of the calculation unit 60. The calculation unit 60 acquires a signal output from the piezoelectric sensor 50 and processes the acquired signal based on the computer program and the relational equation to calculate the gas flow velocity.

[0039] 7 is a flowchart showing the flow of processing executed by the calculation unit 60 in the measurement process. When a gas flow occurs in the space in which the piezoelectric sensor 50 is disposed, the piezoelectric sensor 50 outputs a voltage corresponding to the pressure exerted by the gas. The piezoelectric sensor 50 also vibrates in response to the gas flow. Therefore, the voltage value output from the piezoelectric sensor 50 fluctuates in a minute cycle corresponding to the vibration of the piezoelectric sensor 50.

[0040] The voltage output from the piezoelectric sensor 50 is input to the calculation unit 60. The calculation unit 60 stores the voltage value obtained from the piezoelectric sensor 50 together with the time at which the voltage value was generated, thereby obtaining time-series data of the voltage value that changes over time (step SB1).

[0041] Next, the calculation unit 40 performs a Fourier transform on the time series data of the voltage values ​​obtained in step SB2 (step SB2), thereby obtaining an amplitude spectrum of the time series data.

[0042] Next, the calculation unit 40 calculates the integral value of the spectral intensity of the obtained amplitude spectrum in a specific frequency range A (step SB3). The frequency range A is the same as the range A used in step SA7 of the above-mentioned preparation process.

[0043] Thereafter, the calculation unit 40 calculates the gas flow velocity based on the integral calculated in step SB3 (step SB4). In step SB4, the flow velocity corresponding to the integral is calculated using the relational expression obtained in step SA8 of the preparation process described above. Specifically, the flow velocity is calculated by reading the relational expression from the storage unit 63 and substituting the integral calculated in step SB3 into the relational expression. This allows an estimated value of the gas flow velocity to be calculated based on the voltage value output from the piezoelectric sensor 50.

[0044] The piezoelectric sensor 50 can output a voltage signal with better response than existing flow meters such as windmill or hot-wire flow meters. Therefore, by using the piezoelectric sensor 50, the gas flow velocity can be measured with better response than conventional methods. Furthermore, the measurement device 2 does not directly convert the voltage value output from the piezoelectric sensor 50 into a flow velocity, but calculates the gas flow velocity based on the integral value of the amplitude spectrum. This allows the gas flow velocity to be measured with high accuracy.

[0045] In particular, as in this embodiment, if a film-shaped piezoelectric element is used as the piezoelectric sensor 50, the piezoelectric sensor 50 can be vibrated in response to the pressure from the gas, thereby making it possible to obtain a good amplitude spectrum that corresponds to the flow velocity of the gas.

[0046] 3. Modifications Although one embodiment of the present invention has been described above, the present invention is not limited to the above embodiment.

[0047] In the above-described embodiments, film-shaped piezoelectric elements are used as the piezoelectric sensors 30 and 50. However, the piezoelectric sensors used in the present invention do not necessarily have to be film-shaped. Any piezoelectric sensor may be used as long as it receives a fluid flow, outputs time-series data of voltage values, and can obtain an amplitude spectrum corresponding to the flow velocity based on the time-series data.

[0048] In the above embodiment, the case of measuring the flow velocity of a gas has been described. However, the flow velocity of a liquid may also be measured using a similar configuration. In other words, the present invention is applicable to any device that measures the flow velocity of a fluid, such as a gas or liquid.

[0049] Furthermore, the elements appearing in the above-described embodiments and modifications may be combined in any manner as long as no contradictions arise.

[0050] 1: Preparation device 2: Measurement device 10: Wind tunnel 11: Cylinder 12: Blower 20: Flow meter 30: Piezoelectric sensor 40: Calculation unit 41: Processor 42: Memory 43: Storage unit 50: Piezoelectric sensor 60: Calculation unit 61: Processor 62: Memory 63: Storage unit 111: Intake port 112: Exhaust port 121: Motor 122: Fan A: Range for integration V1, V2, V3: Measurement results of piezoelectric sensor S1, S2, S3: Amplitude spectrum

Claims

1. A measuring device for measuring the flow velocity of a fluid, comprising: a piezoelectric sensor that outputs a voltage value in response to pressure received from the fluid; and a calculation unit that calculates the flow velocity of the fluid based on time series data of the voltage value output from the piezoelectric sensor, wherein the calculation unit performs the following processes: a) obtaining an amplitude spectrum by Fourier transforming the time series data; b) calculating an integral value of a specific frequency range in the amplitude spectrum; and c) calculating the flow velocity of the fluid based on the integral value.

2. A measuring device according to claim 1, wherein the piezoelectric sensor is in the form of a film.

3. A measuring device according to claim 1 or claim 2, further comprising a memory unit that stores a relational expression showing the correspondence between the integral value and the flow velocity of the fluid, and in step c), the flow velocity is calculated by substituting the integral value calculated in step b) into the relational expression.

4. A preparation method for measuring the flow velocity of a fluid, comprising: p) forming a flow of fluid in a space in which a piezoelectric sensor is placed, and acquiring time series data of voltage values ​​output from the piezoelectric sensor for each flow velocity; q) acquiring an amplitude spectrum for each flow velocity by Fourier transforming the time series data; r) calculating an integral value of a specific frequency range in the amplitude spectrum for each flow velocity; and s) calculating an equation relating the integral value to the flow velocity.

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