JP2018009919A - Fluid measurement apparatus and method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To further improve measurement accuracy while preventing increase of power consumption in velocity measurement using a speckle.SOLUTION: A light source 101 is provided around a tube 121 being a flow channel and irradiates fluid 122, which contains a plurality of scatterers 123, flowing in the tube 121 with coherent light at a predetermined irradiation angle. A light reception part 102 is provided around the tube 121 and receives light (scattering light) scattering by the scatterers contained in the fluid flowing in the tube 121 to perform photoelectric conversion by radiation of the coherent light from the light source 101. The light source 101 radiates the coherent light at an irradiation angle θ in the state in which light intensity (scattering light intensity) that the light reception part 102 receives light becomes maximum.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a fluid measuring apparatus and method for measuring 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.

  However, in the speed measurement method using the speckle described above, the intensity of scattered light received is smaller than the intensity of the laser light, and the laser light intensity is increased in order to increase the measurement accuracy. For this reason, there exists a problem that the power consumption in a measurement will increase.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to increase the measurement accuracy by suppressing an increase in power consumption in speed measurement using speckles.

  A fluid measurement apparatus according to the present invention includes a tube through which a fluid to be measured including a plurality of scatterers flows, a light source that radiates coherent light at a predetermined irradiation angle on a fluid that is disposed around the tube and flows through the tube, A light receiving unit that is arranged around the tube and receives light scattered by a scatterer included in the fluid by irradiation of coherent light from a light source and photoelectrically converts it, and an electric signal photoelectrically converted by the light receiving unit The light source emits coherent light at an irradiation angle in which the intensity of the scattered light received by the light receiving unit is maximized. To do.

  In the fluid measuring device, it is preferable to provide a light shielding unit that blocks reflected light reflected and scattered by the surface of the tube from being received by the light receiving unit.

  The fluid measurement method according to the present invention includes a first step of irradiating coherent light from a light source from the periphery of a tube through which a fluid to be measured including a plurality of scatterers flows, and a light receiving unit disposed around the tube. A second step of receiving and photoelectrically converting light scattered by a scatterer included in the fluid by irradiation of coherent light from a light source, and intensity of the scattered light received by the light receiving unit with respect to the irradiation angle of the coherent light A third step of setting the optimum state in which the maximum is maximized, and a fourth step of calculating and outputting at least one of the flow velocity and the flow rate of the fluid based on the electrical signal photoelectrically converted by the light receiving unit in the optimum state, and Is provided.

  In the fluid measuring method, in the third step and the fourth step, it is preferable that the reflected light reflected / scattered on the surface of the tube is blocked from being received by the light receiving unit.

  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, the irradiation angle of coherent light is set to an optimum state in which the intensity of scattered light received by the light receiving unit is maximized, and the light source receives the light intensity received by the light receiving unit. Because the coherent light is irradiated at the irradiation angle in the state where the maximum is, in the speed measurement using the speckle, the excellent effect that the increase in power consumption can be suppressed and the measurement accuracy can be further improved. can get.

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 flowchart for explaining a fluid measuring method using the fluid measuring device according to the embodiment of the present invention. FIG. 3 is an explanatory diagram for explaining the irradiation angle. FIG. 4 is a configuration diagram illustrating the configuration of the calculation unit 103. FIG. 5 is a configuration diagram showing the configuration of another fluid measuring device according to the embodiment of the present invention.

  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 light source 101, a light receiving unit 102, and a calculation unit 103.

  The light source 101 is disposed around the tube 121 serving as a flow path, and irradiates the fluid flowing through the tube 121 including a plurality of scatterers with coherent light at a predetermined irradiation angle. The light source 101 is composed of, for example, a semiconductor laser. The tube 121 is made of a material that is transparent to the light source light. The tube 121 is made of, for example, vinyl chloride. In FIG. 1, the pipe 121 shows a cross section parallel to the flow path direction of the pipe 121.

  The light receiving unit 102 is arranged around the tube 121, receives light (scattered light) scattered by the scatterer 123 included in the fluid 122 flowing through the tube 121 by irradiation of coherent light from the light source 101, and photoelectrically receives the light. Convert. The light receiving unit 102 is, for example, a photodiode. The calculation unit 103 calculates and outputs at least one of the flow velocity and the flow rate of the fluid 122 based on the electrical signal photoelectrically converted by the light receiving unit 102.

  In the fluid measuring apparatus according to the embodiment, the light source 101 irradiates the coherent light at the irradiation angle θ in a state where the Doppler shifted scattered light intensity received by the light receiving unit 102 is maximized. The light scattered and Doppler shifted in the measurement object is emitted around the incident position. For this reason, many Doppler shifted scattered light can be acquired by arrange | positioning in the distance close | similar from the position where light injected into the measuring object. Further, for example, light reflected or scattered on the skin surface is preferably not received as much as possible because it does not undergo Doppler shift. For this reason, as shown in FIG. 3, the light source 101 is tilted with respect to the measurement target so that light is obliquely incident, and the light receiving unit 102 is disposed in the normal direction of the measurement target from the position where the light is incident, thereby performing the Doppler shift. The reflected / scattered light 101b can be reduced with the intensity of the scattered light 101c having been maximized.

  Next, a fluid measuring method using the above-described fluid measuring device will be described with reference to the flowchart of FIG. First, in step S201, coherent light is emitted from the light source 101 from around the tube 121 through which the fluid 122 to be measured including the plurality of scatterers 123 flows (first step).

  Next, in step S202, the light scattered by the scatterer 123 contained in the fluid 122 due to the irradiation of the coherent light from the light source 101 by the light receiving unit 102 arranged around the tube 121 is received and subjected to photoelectric conversion (first step). 2 steps).

  Next, in step S203, the irradiation angle of the coherent light is set to an optimum state in which the Doppler-shifted scattered light intensity received by the light receiving unit 102 is maximized (third step). As shown in FIG. 3, the beam 101 a emitted from the light source 101 is incident on the measurement region with an inclination from a state parallel and perpendicular to the axial direction (flow channel direction) of the tube 121. The light receiving surface of the light receiving unit 102 is disposed in parallel with the axial direction (flow channel direction) of the tube 121. By making the beam 101a tilted as described above, the directly reflected light (reflected / scattered light) 101b reflected by the surface of the tube 121 is not received by the light receiving unit 102, and in addition, is received by the light receiving unit 102. The irradiation angle θ and each arrangement are determined so that the intensity of the scattered light 101c to be maximized.

  Next, in step S204, at least one of the flow velocity and the flow rate of the fluid 122 is calculated and output based on the electric signal photoelectrically converted by the light receiving unit 102 in the set optimum state (fourth step).

  As illustrated in FIG. 4, the calculation unit 103 includes a signal extraction unit 131, a feature amount calculation unit 132, a calibration value calculation unit 133, and a calibration unit 134. The signal extraction unit 131 extracts a low frequency component and a high frequency component of the electric signal photoelectrically converted by the light receiving unit 102.

  The feature amount calculation unit 132 calculates a feature amount that correlates with the flow velocity of the fluid 122 flowing through the pipe 121 based on the high-frequency component extracted by the signal extraction unit 131. The calibration value calculation unit 133 calculates a calibration parameter based on the low frequency component extracted by the signal extraction unit 131. The calibration unit 134 calibrates the feature amount with the calibration parameter and calculates at least one of the flow velocity and the flow rate of the fluid 122.

  First, light source light having coherence from the light source 101 is irradiated to the fluid 122 flowing through the pipe 121 serving as a flow path. The fluid 122 includes a scatterer 123 that scatters the light source light, and the tube 121 is transmissive to the light source light. When the light source light is scattered by the scatterer 123 in the fluid 122, a part of the light is received by the light receiving unit 102. When the concentration of the scatterer 123 is low, most of the scattered light is single-scattered, but as the concentration increases, the light reaches the photodiode through multiple scattering. As a result of interference of light scattered in various paths, speckle is generated, and a part of the speckle is observed in the light receiving unit 102.

  Here, assuming that the cross section of the pipe 121 is circular and the flow is a laminar flow, the flow velocity distribution in the pipe 121 has a maximum flow velocity at the center of the pipe 121 and approaches the circumferential portion of the pipe 121. As the flow rate decreases, the flow rate decreases. As the scatterer 123 moves in accordance with the flow of the fluid 122, the speckle also changes every moment. A part of the speckle that fluctuates in this way is received by the light receiving unit 102 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 102 is reflected directly on the light receiving unit 102 from the light source 101 or on the surfaces of the tube 121 and the fluid 122. It is desirable that the generated light (directly reflected light) is not included as much as possible.

  For example, as shown in FIG. 5, it is preferable to provide a light shielding unit 104 that blocks the direct reflection light reflected / scattered from the surface of the tube 121 from being received by the light receiving unit 102. When the scattered light is received by the light receiving unit 102 and the optimum state in which the Doppler shifted scattered light intensity is maximized, the direct reflected light reflected from the surface of the tube 121 is blocked from being received by the light receiving unit 102. State. Even when the directly reflected light is received by a part of the light receiving surface of the light receiving unit 102, it is possible to prevent the directly reflected light from being received by the light receiving unit 102. This makes it possible to widen the selection range in which the scattered light intensity is maximum.

  The electrical signal output from the light receiving unit 102 is usually weak, and the output current of the light receiving unit 102 is on the order of μA. For this reason, as described above, the measurement is performed after setting the irradiation angle of the coherent light to the optimum state in which the intensity of the scattered light received by the light receiving unit 102 is maximized. In the optimum state, the signal extraction unit 131 amplifies the signal using an amplifier circuit such as a transimpedance amplifier, and converts it into a voltage signal having a level that is easy to handle, for example, about 1V.

  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 flow rate and flow rate of the fluid 122 are calculated by digital signal processing by the feature amount calculation unit 132, the calibration value calculation unit 133, and the calibration unit 134.

  For the low frequency digital signal, a low pass filter (digital low pass filter) is further applied by digital processing to calculate an average value. As the digital low-pass filter, a known method such as a moving average method, an IIR filter, or an FIR filter can be used. The average value obtained here is a value corresponding to the average amount of scattered light received by the light receiving unit 102. Based on the average amount of light received from the low frequency component, a calibration parameter for obtaining the flow rate and flow velocity of the fluid 122 is calculated. This method will be described later.

  Next, a method for calculating the feature quantity correlated with the flow velocity of the fluid 122 from the high-frequency digital signal will be described. Note that when it is assumed that the fluid 122 flows through the pipe 121 having a constant cross-sectional area without a 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. It becomes.

  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 value into a flow rate.However, if the concentration is different, the slope and offset will be different. Therefore, the same correction coefficient cannot be used for the fluid 122 having various concentrations. In the method of homodyne detection of speckle fluctuations, the obtained feature quantity exhibits various behaviors depending on the type and number of scatterers 123 included in the fluid 122, the difference in absorption coefficient with respect to the wavelength of light used for measurement, and the like.

  For the behavior of the above-described feature amount, by using the value of the average received light amount obtained from the low frequency component, the straight line intercept and the slope that are different for each density are corrected. Hereinafter, this method will be described.

  As a result of intensive investigations by the inventors on the average received light amount dependency of inclination and offset for various fluids 122 and flow paths, by performing calibration using the following formula, the flow velocity correlation feature value ν and the average received light amount < Based on I>, it has been found that the actual flow rate Flow can be calculated approximately.

[Calibration formula]
Offset calibration parameter: Offset = A × <I> + B
Gain calibration parameter: Gain = F / (C × <I> ^E− D)
Flow rate or flow rate: Flow = Gain × (ν−Offset)
(The coefficient parameters A to F are real numbers satisfying A> 0, B> = 0, C> 0, D> = 0, E> 0, F> 0)

It is also possible to convert the flow velocity correlation feature quantity ν into an average flow velocity using the above calibration calculation formula. As described above, when it is assumed that the fluid 122 flows in a state where a flow path having a specific cross-sectional area is satisfied, the flow rate and the average flow velocity are proportional to each other, and the average flow velocity is obtained by dividing the flow rate by the cross-sectional area of the flow channel. . For example, when the cross-sectional area of the flow path is 10 mm ² , the coefficient for converting the flow rate [mL / min] to the average flow velocity [mm / sec] is “1000 [mm ³ / mL] / 60 [sec / min]. ] / 10 [mm ² ] ≈1.67 ”, and among the coefficient parameters described above, by setting F to 1.67, the flow velocity correlation feature quantity ν can be converted into an average flow velocity.

  By the way, in the above method, in order to correct the density dependency, the average received light amount is used instead of the density value. The average amount of received light does not necessarily increase monotonously with increasing density. Therefore, it is not possible to uniquely determine the density from the average received light amount, but for the same average received light amount, by using the phenomenon that the appropriate offset calibration parameter and gain calibration parameter are almost the same, the flow velocity correlation feature amount It is possible to calculate the flow rate and average flow velocity from ν.

  As described above, according to the present invention, the irradiation angle of coherent light is set to an optimum state in which the intensity of scattered light received by the light receiving unit is maximized, and the light source is scattered by the light receiving unit. Since the coherent light is irradiated at the irradiation angle in a state where the intensity of the emitted light is maximized, in the speed measurement using the speckle, the increase in power consumption can be suppressed and the measurement accuracy can be further increased. . Since the received light intensity of scattered light is increased, the signal-to-noise ratio can be further increased, and the amount of light emitted from the light source can be further reduced, so that power consumption can be suppressed.

  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 ... Light source, 101a ... Beam, 101b ... Directly reflected light, 101c ... Scattered light, 102 ... Light-receiving part, 103 ... Calculation part, 121 ... Tube, 122 ... Fluid, 123 ... Scattering body.

Claims (5)

A first step of irradiating coherent light from a light source from around a tube through which a fluid to be measured including a plurality of scatterers flows;
A second step of receiving and photoelectrically converting light scattered by the scatterer included in the fluid by irradiation of coherent light from the light source at a light receiving unit disposed around the tube;
A third step of setting the irradiation angle of the coherent light to an optimum state in which the intensity of the scattered light received by the light receiving unit is maximized;
And a fourth step of calculating and outputting at least one of a flow velocity and a flow rate of the fluid based on an electrical signal photoelectrically converted by the light receiving unit in the optimum state. The fluid measurement method according to claim 1,
In the third step and the fourth step, the fluid measurement method is characterized in that the reflected light reflected and scattered by the surface of the tube is blocked from being received by the light receiving unit. A tube through which a fluid to be measured including a plurality of scatterers flows;
A light source disposed around the tube and irradiating the fluid flowing through the tube with coherent light at a predetermined irradiation angle;
A light receiving unit that is arranged around the tube and receives and photoelectrically converts light scattered by the scatterers included in the fluid by irradiation of coherent light from the light source;
A calculation unit that calculates and outputs at least one of a flow velocity and a flow rate of the fluid based on an electrical signal photoelectrically converted by the light receiving unit, and
The fluid measurement apparatus, wherein the light source irradiates the coherent light at an irradiation angle in a state where the intensity of the scattered light received by the light receiving unit is maximized. The fluid measuring device according to claim 3, wherein
A fluid measuring apparatus comprising: a light shielding unit that blocks reflected light reflected / scattered on a surface of the tube from being received by the light receiving unit. The fluid measuring device according to claim 3 or 4,
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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