JP2018009920A - Fluid measurement apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent deterioration in linearity between flow velocity measured at high-speed flow velocity and actual flow velocity.SOLUTION: A tube 101 becomes a flow channel in which fluid containing a plurality of scatterers flows and has a bent part 101a formed by being bent at a measurement area 111. A sensor head 102 including a light source 121 and a light reception part 122, is provided on an outer peripheral surface of the tube 101 on a recess side of the bent part 101a in the measurement area 111. The light source 121 irradiates the scatterers in the fluid flowing in the tube 101 with coherent light. The light reception part 122 receives light scattered by the scatterers contained in the fluid by radiation of the coherent light to perform photoelectric conversion.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a fluid measuring device that measures the flow rate and flow velocity of a fluid flowing through a flow path using laser light.

  Techniques for measuring the flow rate and flow velocity of a fluid flowing through a channel are widely used in the industrial and medical fields. There are various types of devices for measuring flow rate and flow velocity, such as electromagnetic flowmeters, vortex flowmeters, Coriolis flowmeters, and laser flowmeters. Among these, the laser flowmeter needs to be hygienic because it can measure the flow rate and flow velocity without contact with the fluid flowing through the flow path by using laser light. It is used in applications and applications where a flow meter cannot be inserted into an existing flow path.

  As a laser flow meter, there is a two-beam laser Doppler flow meter (see Patent Document 1). In this flow meter, first, the laser beam emitted from the light source is split into two beams by a half mirror, one of the branched beams is reflected by the mirror, and the two beams are condensed at one point in the flow path. When the scatterer included in the fluid in the flow path passes through the condensing point, the light is scattered, but the scattered light from the two beams undergoes different Doppler shifts.

  When the scattered light in such a state is converted into an electric signal by a photodiode or the like, a heterodyne detection is performed and a beat signal is observed. By calculating the frequency spectrum of the observed beat signal and extracting the peak frequency, the moving speed of the scatterer can be obtained. When the flow is a laminar flow, the average flow velocity and flow rate of the fluid flowing through the flow channel are proportional to the moving speed of the scatterer obtained as described above, and therefore a proportional constant according to the flow channel. By multiplying and calibrating, the flow velocity and flow rate of the fluid can be measured.

  The fluid measurement technique described above has an excellent advantage of being able to measure the absolute value of the moving speed of the scatterer, but requires two beams focused at one point in order to perform heterodyne detection. For this reason, a plurality of optical components and their highly accurate alignment are required, and there is a problem that the apparatus is increased in size and cost. This technique is effective when the concentration of scatterers contained in the fluid is low. When the concentration of scatterers is high, the laser light is multiple-scattered by multiple scatterers, so the beat signal is observed. There is a problem that becomes difficult.

  A speckle method is also used as a speed measurement method using a laser. The speckle method uses a random speckle pattern (= speckle) that is generated by interference of irregularly scattered light when laser light is irradiated onto a fluid containing a rough surface or a scatterer. Is the law. When an object that generates speckles moves, speckles also vary with time. For example, a two-dimensional image of speckles is acquired, and a moving speed can be obtained by analyzing speckle movement patterns ( Non-patent document 1). Since this method requires acquisition and analysis of a two-dimensional image, there is still a problem that the apparatus becomes large and expensive.

  As a method for simplifying the optical system, a method of measuring speckles at one point instead of two dimensions is also conceivable. In this case, an irregular signal corresponding to speckle fluctuation is observed, and the time correlation length calculated from the autocorrelation function of the observed signal is known to be inversely proportional to the moving speed of the scatterer. . Also, the slope of the power spectrum of the signal can be used instead of the time correlation length. This principle is used for analyzing Brownian motion of particles and measuring skin blood flow in a living body (see, for example, Patent Document 2).

JP-A-57-059173 Japanese Patent Application Laid-Open No. 07-92184

Yoshinori Aizu et al., “Basics of Laser Measurement I: Velocity Measurement”, Laser Research, Vol. 27, No. 8, 572-578, 1999.

  By the way, in the technique for obtaining the flow rate / flow velocity using the power spectrum of the signal obtained by measuring speckles at one point, the linearity between the measured flow velocity and the actual flow velocity decreases as the flow velocity increases. There is a problem.

  The present invention has been made to solve the above-described problems, and an object thereof is to suppress a decrease in linearity between a measured flow velocity and an actual flow velocity at a high flow velocity. To do.

  The fluid measurement device according to the present invention includes a tube made of an elastic material through which a fluid including a plurality of scatterers flows, a curved portion where the tube formed in the measurement region is bent, and an outer periphery of the tube on the concave side of the curved portion of the measurement region. A light source that radiates coherent light to a scatterer in a fluid flowing through a pipe, and a light receiving unit that receives light scattered by the scatterer included in the fluid by irradiation of the coherent light and photoelectrically converts the light A sensor head, and a calculation unit that calculates and outputs a flow rate of the fluid that passes through the measurement region based on an electrical signal photoelectrically converted by the light receiving unit.

  The fluid measuring device includes a base portion that places the sensor head in a measurement region on a flat surface, a pipe is disposed in a piping region that passes through the measurement region on the flat surface, and is pushed up in a direction away from the flat surface. As a result, a curved portion of the tube is formed.

  In the fluid measuring apparatus, the calculation unit includes a signal extraction unit that extracts a high-frequency component of the electrical signal photoelectrically converted by the light-receiving unit, and a feature quantity that correlates with the fluid flow velocity based on the high-frequency component extracted by the signal extraction unit. A feature amount calculation unit to calculate, and a calculation unit to calculate at least one of the flow velocity and flow rate of the fluid from the feature amount.

  As described above, according to the present invention, since the bent portion is formed in the tube and the sensor head is arranged on the concave portion side, the linearity between the measured flow velocity at the high flow velocity and the actual flow velocity. An excellent effect is obtained that the decrease in the thickness can be suppressed.

FIG. 1 is a configuration diagram showing the configuration of the fluid measuring device according to the embodiment of the present invention. FIG. 2 is a configuration diagram illustrating a configuration of the calculation unit 103.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a configuration diagram showing the configuration of the fluid measuring device according to the embodiment of the present invention. This fluid measuring device includes a tube 101, a sensor head 102, and a calculation unit 103.

  The tube 101 serves as a flow path, is made of an elastic body such as vinyl chloride, and a fluid containing a plurality of scatterers flows. The tube 101 is bent in the measurement region 111 to form a curved portion 101a.

  The sensor head 102 includes a light source 121 and a light receiving unit 122, and is disposed on the outer peripheral surface of the tube 101 on the concave side of the curved portion 101 a of the measurement region 111. The light source 121 irradiates the scatterer in the fluid flowing through the tube 101 with coherent light. The light source 121 is composed of, for example, a semiconductor laser. The light receiving unit 122 receives light scattered by a scatterer included in the fluid by irradiation with coherent light, and performs photoelectric conversion. The light receiving unit 122 is, for example, a photodiode.

  For example, the pipe 101 and the sensor head 102 are disposed in a piping region on the flat surface of the base body 104. A curved portion 101 a of the tube 101 is formed by being pushed up by the sensor head 102 in a direction away from the flat surface on the flat surface of the base body portion 104. The local portion 101a may be formed by pressing the tube 101 disposed on the flat surface of the base portion 104 to the base portion 104 side by a pressing portion 105 having an opening region in the measurement region 111.

  For example, in the bent portion 101a, the tube 101 bends with a predetermined curvature A in a direction away from the base portion 104 on a plane perpendicular to the flat portion of the base portion 104 including the axis of the tube 101, and then makes a U-turn. It bends with the predetermined curvature B, approaches the base portion 104 side, and then bends with the curvature A in a state along the flat surface.

  The calculation unit 103 calculates and outputs the flow rate of the fluid passing through the measurement region 111 based on the electrical signal photoelectrically converted by the light receiving unit 122. For example, as illustrated in FIG. 2, the calculation unit 103 includes a signal extraction unit 131, a feature amount calculation unit 132, and a calculation unit 133. The signal extraction unit 131 extracts a high frequency component of the electric signal photoelectrically converted by the light receiving unit 122. The feature amount calculation unit 132 calculates a feature amount that correlates with the flow velocity of the fluid flowing through the pipe 101 based on each high-frequency component extracted by the signal extraction unit 131.

  First, light source light (coherent light) having coherence from the light source 121 is irradiated to the fluid flowing through the curved portion 101a (measurement region 111) of the tube 101 serving as a flow path. The fluid includes a scatterer that scatters the light source light, and the tube 101 is transmissive to the light source light. When the light source light is scattered by the scatterer in the fluid, a part of the light is received by the light receiving unit 122. When the concentration of the scatterer is low, most of the scattered light is single-scattered. However, as the concentration increases, the scattered light reaches the light receiving unit 122 through multiple scattering. As a result of interference of the light scattered in various paths, speckle is generated, and a part of the speckle is observed in the light receiving unit 122.

  Here, assuming that the cross section of the tube 101 is circular and the flow is a laminar flow, the flow velocity distribution in the curved portion 101a in the tube 101 has a minimum flow velocity on the concave side where the sensor head 102 is disposed. It becomes. As the scatterer moves as the fluid flows, the speckles change from moment to moment. A part of the speckle that fluctuates in this way is received by the light receiving unit 122 and converted into an electrical signal.

  In order to obtain the flow rate and flow velocity with high accuracy, the light received by the light receiving unit 122 includes light directly incident on the light receiving unit 122 from the light source 121 or directly from the other light sources to the light receiving unit 122. It is desirable that incident light and light reflected on the surface of the tube 101 and the fluid are not included as much as possible.

  Since the electric signal output from the light receiving unit 122 is usually weak and the output current of the light receiving unit 122 is on the order of μA, the signal extraction unit 131 amplifies the signal using an amplifier circuit such as a transimpedance amplifier. Convert the voltage signal to a level that is easy to handle.

  Next, in the signal extraction unit 131, only the low frequency component of the signal is extracted through a low-pass filter, converted into a digital signal by an ADC circuit, and a low frequency digital signal is acquired. The cut-off frequency of the low-pass filter may be about 1 Hz, for example. The sampling frequency of the ADC circuit may be set to about 1 to 100 Hz, for example, in accordance with the update rate of the measured flow rate or flow velocity value.

  On the other hand, only the alternating current component is further amplified by the alternating current amplifier circuit and converted into a digital signal by the ADC circuit to obtain a high frequency digital signal (high frequency component). Assuming that the output DC voltage of the amplifier circuit is about 1V, the AC voltage is usually as small as mV. Therefore, it is amplified by an AC amplifier circuit having a gain of about 10 to 1000 times to obtain a voltage signal that is easy to handle. Good. The higher the sampling frequency of the ADC circuit, the faster the flow rate can be measured. For example, the sampling frequency may be 1 MHz.

  From the high-frequency digital signal acquired as described above, the feature amount is calculated by digital signal processing by the feature amount calculation unit 132, and the flow velocity and flow rate of the fluid are calculated by digital signal processing by the calculation unit 133 from the calculated feature amount.

  Next, a method for calculating a feature quantity correlated with the fluid flow velocity from the high-frequency digital signal will be described. Note that when it is assumed that the fluid flows through the tube 101 having a constant cross-sectional area without any gap, the flow velocity and the flow rate are in a proportional relationship, and thus the feature amount obtained here is a feature amount that also correlates with the flow rate. Become.

  The high-frequency digital signal represents speckle fluctuation, and there are various known methods for extracting a feature quantity correlated with the flow velocity from here. For example, there are a method for calculating a time correlation length from an autocorrelation function of a high-frequency digital signal, a method for determining the number of times a signal crosses a reference potential within a certain time, and a method for determining a slope by analyzing a power spectrum. Here, an example is shown in which the product sum of the power and the frequency of the power spectrum is used as the feature quantity for which the calibration using the average received light quantity described later functions most effectively.

  In order to calculate the feature quantity ν correlated with the flow velocity, first, a high-frequency digital signal is Fourier-transformed, and a power spectrum is obtained by calculating its power. Once the power spectrum is obtained, the product sum of the power P (f) and the frequency f is calculated over a predetermined frequency range by the following equation.

  A graph can be created by plotting the result of calculating the product sum of power and frequency calculated as described above against the actual flow rate. In addition, when the flow velocity correlation characteristic amount ν calculated by the product sum of power and frequency has nonlinearity with respect to the actual flow rate and the average flow velocity, processing for correcting the nonlinearity may be added. As the cause of the non-linearity, for example, the frequency characteristic of the amplifier circuit may not be flat. As a non-linearity correction method, a weighting coefficient is calculated for each frequency when calculating the sum of products of power and frequency as in the formula of “ν = Σ {P (f) × f × w (f)}”. There is a method of multiplying w (f).

For example, when the cutoff frequency of the amplifier circuit in the signal extraction unit 131 is f _cut [Hz] and has a first-order low-pass filter characteristic, the attenuation characteristic of the amplifier circuit is canceled by using the following equation for the weighting function: The linearity of the relative flow rate can be improved.

Even if the frequency characteristic of the amplifier circuit is more complicated, if the amplitude characteristic of the transfer function is | H (f) |, “w (f) = 1 / | H (f) | ² ” is weighted. By using it as a function, it is possible to correct the nonlinearity of the relative flow rate depending on the frequency characteristics of the amplifier circuit.

Further, as shown in the equation “ν = {Σ {P (f) × f}} ^G (G is a real number larger than 0)”, after calculating the sum of products of power and frequency, the power is calculated and the flow velocity correlation feature The nonlinearity of the quantity ν may be corrected. In addition, as in “ν = {Σ (P (f) × f × w (f))} ^G ”, power calculation is performed in a state where the weighting coefficient w (f) is multiplied for each frequency, and the flow velocity correlation feature amount ν. The non-linearity may be corrected.

  By calculating the slope and offset by linearly approximating the plot of the graph described above and using it as a calibration parameter, it is possible to convert the calculated feature quantity into a flow rate.

  In the embodiment, as described above, the flow velocity measurement is performed by the sensor head 102 arranged on the concave portion where the flow velocity becomes slower in the curved portion 101a. For this reason, in the measured flow velocity, the linearity fall between the actual flow velocity of a measurement location is suppressed. Calculate the correlation between the flow velocity measurement value and the actual flow velocity (average flow velocity) from the flow velocity measurement value obtained by measuring the fluid with a known flow velocity in advance, and use this correction value to determine the actual measurement. If the flow velocity measurement value obtained in step 1 is corrected, a more accurate flow velocity value can be obtained.

  Here, when the bending amount of the curved portion 101a is increased, the average flow velocity in this region becomes different from the flow velocity in the linear region. In such a state, an accurate flow rate and flow rate are not required. Therefore, it is important that the amount of bending of the local portion 101a is within a range in which the average flow velocity in the local portion 101a (within the same cross section of the pipe) does not change.

  As described above, in the present invention, since the bent portion is formed in the tube and the sensor head is disposed on the concave side, the linearity between the measured flow velocity at the high flow velocity and the actual flow velocity is obtained. The decrease can be suppressed.

  In the case where the flow velocity is fast, by obtaining the power spectrum in a wider band, the decrease in linearity can be suppressed, but high performance is required by the arithmetic processing, and the device becomes more expensive. It is possible to suppress a decrease in linearity with a very simple configuration.

  The present invention is not limited to the embodiment described above, and many modifications and combinations can be implemented by those having ordinary knowledge in the art within the technical idea of the present invention. It is obvious.

  DESCRIPTION OF SYMBOLS 101 ... Tube, 101a ... Curve part, 102 ... Sensor head, 103 ... Calculation part, 104 ... Base | substrate part, 105 ... Holding | suppressing part, 111 ... Measurement area | region, 121 ... Light source, 122 ... Light-receiving part.

Claims (3)

A tube made of an elastic material through which a fluid containing a plurality of scatterers flows;
A curved portion where the tube formed in the measurement region bends;
A light source that is disposed on the outer peripheral surface of the tube on the concave side of the curved portion of the measurement region and that irradiates the scatterer in the fluid flowing through the tube with coherent light, and irradiates the fluid with coherent light. A sensor head including a light receiving unit that receives and photoelectrically converts light scattered by the included scatterer;
A fluid measuring device comprising: an arithmetic unit that calculates and outputs a flow rate of the fluid passing through the measurement region based on an electrical signal photoelectrically converted by the light receiving unit. The fluid measurement device according to claim 1,
A base portion for disposing the sensor head in the measurement area on a flat surface;
The pipe is disposed in a piping region passing through the measurement region on the flat surface;
The fluid measuring device, wherein the curved portion of the tube is formed by being pushed up by the sensor head in a direction away from the flat surface. The fluid measuring device according to claim 1 or 2,
The computing unit is
A signal extraction unit for extracting a high-frequency component of the electrical signal photoelectrically converted by the light receiving unit;
A feature amount calculation unit that calculates a feature amount correlated with the flow velocity of the fluid based on the high-frequency component extracted by the signal extraction unit;
A fluid measurement device comprising: a calculation unit that calculates at least one of a flow velocity and a flow rate of the fluid from the feature amount.

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