JP6737621B2 - Fluid measuring device - Google Patents

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.

The technology for measuring the flow rate and flow velocity of a fluid flowing through a flow channel is widely used in the industrial and medical fields. There are various types of devices for measuring the flow rate and the flow velocity, such as an electromagnetic flow meter, a vortex flow meter, a Coriolis type flow meter, and a laser flow meter, and they are used properly according to the application. Among them, the laser flow meter needs to be hygienic because it is possible to measure the flow rate and the flow velocity without contacting the fluid flowing through the flow path by using laser light without contacting the fluid. It is used for 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 type laser Doppler flow meter (see Patent Document 1). As shown in FIG. 16A, this flow meter includes a light source 601, a half mirror 602, a mirror 603, a lens 604, and a light receiving unit 605. The laser light emitted from the light source 601 is split by a half mirror into two beams, one of the split beams is reflected by the mirror 603, and the two beams are condensed at one point in the flow path 606. Light is scattered when the scatterer 607 contained in the fluid in the flow path 606 passes through the converging point, but the scattered light from the two beams undergoes different Doppler shifts.

When the scattered light in such a state is condensed using the lens 604 and converted into an electric signal by the light receiving unit 605 such as a photodiode, heterodyne detection is performed, and a beat signal as shown in FIG. 16B is observed. It As shown in FIG. 16C, the moving speed of the scatterer 607 can be obtained by calculating the frequency spectrum of the beat signal and extracting the peak frequency.

When the flow is a laminar flow, the average flow velocity and the flow rate of the fluid flowing in the flow channel 606 are proportional to the moving speed of the scatterer 607 obtained as described above, and therefore the proportional constant corresponding to the flow channel 606 is set. 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 it requires two beams to be condensed at one point in order to perform the heterodyne detection. For this reason, a plurality of optical components and their highly accurate alignment are required, and there is a problem that the device becomes large and the cost becomes high. Also, this technique is effective when the concentration of scatterers contained in the fluid is low, and when the concentration of scatterers becomes high, multiple scatterings of the laser light are caused by multiple scatterers. There is a problem that it becomes difficult.

A speckle method is also used as a speed measurement method using a laser. The speckle method is a velocity measurement using a random speckle pattern (= speckle) that is generated by the interference of randomly scattered light when irradiating a laser beam on a fluid containing rough surfaces or scatterers. Is the law. When an object that generates speckles moves, the speckles also fluctuate with time. Therefore, for example, a two-dimensional image of the speckles is acquired, and the movement speed of the speckles can be obtained by analyzing the movement pattern of the speckles ( Non-Patent Document 1). Since this method requires acquisition and analysis of a two-dimensional image, it also has a problem that the device becomes large and expensive.

As a method of simplifying the optical system, a method of measuring speckle at one point instead of two-dimensionally can be considered. In this case, it is known that an irregular signal according to the fluctuation of the speckle is observed, and the time correlation length calculated from the autocorrelation function of the observed signal is in inverse proportion to the moving speed of the scatterer. .. Also, instead of the time correlation length, the slope of the power spectrum of the signal can be used. This principle is used for analysis of Brownian motion of particles and measurement of skin blood flow of a living body (for example, refer to Patent Document 2).

However, when trying to apply the above-mentioned principle to the measurement of a fluid flowing through a flow channel, the characteristic quantities such as the time correlation length and the slope of the power spectrum depend on the absorption coefficient and scattering coefficient of the fluid, the shape of the flow channel, etc. There is a problem that it will change. It is difficult to measure the flow velocity and the flow rate with high accuracy because the measured feature amount changes greatly even if the concentration of the fluid changes.

JP-A-57-059173 JP, 07-92184, A

Aizu Yoshinaga et al., "Basics of Laser Measurement I: Velocity Measurement", Laser Research, Vol. 27, No. 8, pp. 572-578, 1999.

As described above, the two-beam type laser Doppler flowmeter and the speckle method using a two-dimensional image have a problem that the device becomes large in size and expensive. Further, in the method using the time variation information of the speckle at one point, the calculated feature amount varies with the change of the absorption coefficient and the scattering coefficient of the fluid, so that the flow rate and the flow velocity cannot be accurately measured. There was a problem that it was difficult.

The present invention has been made to solve the above problems, and an object of the present invention is to make it possible to accurately measure a flow velocity and a flow rate by using a small-sized, low-cost and simple optical system.

A fluid measuring device according to the present invention receives a light source that irradiates a fluid including a plurality of scatterers with coherent light, and receives the light scattered by the scatterers contained in the fluid by the irradiation of the coherent light and performs photoelectric conversion. The light receiving unit, the signal extracting unit that extracts the low-frequency component and the high-frequency component of the electrical signal photoelectrically converted by the light receiving unit, and the feature amount that correlates with the flow velocity of the fluid based on the high-frequency component that the signal extracting unit extracts A feature amount calculation unit, a calibration value calculation unit that calculates a calibration parameter based on the low frequency component extracted by the signal extraction unit, and a feature amount is calibrated with the calibration parameter to calculate at least one of a fluid flow velocity and a flow rate. And a calibration unit for

In the above fluid measurement device, the calibration parameters include an offset calibration parameter and a gain calibration parameter, and the calibration value calculation unit calculates the average received light amount <I> and the coefficient parameters A and B (A>) obtained from the average value of the low frequency components. 0, B≧0), the offset calibration parameter is obtained by A×<I>+B, and the average received light amount <I> and coefficient parameters C, D, E, F (C>0, D≧0, E>0) , F>0) to obtain the gain calibration parameter by F/(C×<I> ^E −D), and the calibration unit multiplies the gain calibration parameter by a value obtained by subtracting the offset calibration parameter from the feature amount.

In the above fluid measurement device, the feature amount calculation unit sets the feature amount to ν, and sets the power P(f) of the power spectrum of the electric signal, the frequency f, the frequency weighting w(f), and the non-linearity correction coefficient G. It is calculated by using ν={Σ(P(f)×f×w(f))} ^G.

In the fluid measuring device, the light receiving section, from a position directly reflected light is maximum in the light receiving surface of the light receiving portion of the fluid, that are spaced apart over a distance L which is calculated by the following equation (1).

In the above fluid measuring device, it is preferable to include a light shielding portion that shields the light directly incident on the light receiving portion from the light source.

As described above, according to the present invention, it is possible to obtain an excellent effect that the flow velocity and the flow rate can be accurately measured using a small-sized, low-cost and simple optical system.

FIG. 1 is a configuration diagram showing a configuration of a fluid measuring device according to an embodiment of the present invention. FIG. 2 is a configuration diagram showing another configuration of the fluid measuring device according to the embodiment of the present invention. FIG. 3 is a characteristic diagram showing a waveform example of a high-frequency digital signal in the fluid measuring device described with reference to FIG. FIG. 4 is an explanatory diagram for explaining the operation of the signal processing circuit 207 in the fluid measurement device described with reference to FIG. FIG. 5 is a characteristic diagram showing an example of a frequency spectrum of a high frequency digital signal in the fluid measuring device described with reference to FIG. FIG. 6 is a characteristic diagram showing a relative flow rate calculation result when milk is measured as a fluid. FIG. 7 is a characteristic diagram showing a relative flow rate calculation result in the case of measuring concentrated milk added with India ink as a fluid. FIG. 8 is a characteristic diagram showing the concentration dependency (a) of the offset and slope of the relative flow rate and the concentration dependency (b) of the average amount of received light when measured with concentrated milk added with India ink as a fluid. FIG. 9 is a characteristic diagram showing the dependence of the offset and the slope of the relative flow rate on the average amount of received light when measured with concentrated milk added with India ink as a fluid. FIG. 10 is a characteristic diagram showing the average light receiving amount dependency of the offset and the slope of the relative flow rate when milk is measured as the fluid. FIG. 11 is a characteristic diagram showing an example of calculating an actual flow rate for concentrated milk added with India ink as a fluid. FIG. 12 is a configuration diagram showing a partial configuration of the fluid measuring device according to the embodiment of the present invention. FIG. 13 is a characteristic diagram showing the analysis result of the direct reflected light intensity and the scattered light intensity using the ray analysis simulator. FIG. 14 is a configuration diagram showing another configuration of the fluid measurement device according to the embodiment of the present invention. FIG. 15 is a configuration diagram showing another configuration of the fluid measurement device according to the embodiment of the present invention. FIG. 16A is a configuration diagram showing a configuration of a two-beam type laser Doppler flowmeter. FIG. 16B is a characteristic diagram showing a measurement waveform example measured by the two-beam type laser Doppler flowmeter. FIG. 16C is a characteristic diagram showing a measurement waveform example measured by a two-beam type laser Doppler flowmeter.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a configuration diagram showing a configuration of a fluid measuring device according to an embodiment of the present invention. This fluid measurement device includes a light source 101, a light receiving unit 102, a signal extraction unit 103, a feature amount calculation unit 104, a calibration value calculation unit 105, and a calibration unit 106.

The light source 101 irradiates the fluid 122 to be measured flowing in the flow channel 121 with light. The light receiving unit 102 receives the light scattered by the scatterer 123 included in the fluid 122 by the irradiation of the coherent light and photoelectrically converts the light. The signal extracting unit 103 extracts the low frequency component and the high frequency component of the electric signal photoelectrically converted by the light receiving unit 102.

The characteristic amount calculation unit 104 calculates a characteristic amount that correlates with the flow velocity of the fluid 122 based on the high frequency component extracted by the signal extraction unit 103. The calibration value calculation unit 105 calculates a calibration parameter based on the low frequency component extracted by the signal extraction unit 103. The calibration unit 106 calibrates the characteristic amount with the calibration parameter and calculates at least one of the flow velocity and the flow rate of the fluid 122.

The fluid measuring device having the above-described configuration can be realized by, for example, the device shown in FIG. This device includes a light source 101 that is a laser that emits single-mode laser light, a drive circuit 201 that drives the light source 101, a light receiving unit 102 that is a photodiode, and an amplifier circuit 202 that amplifies the output current of the light receiving unit 102. With. The light source 101 may be, for example, a vertical cavity surface emitting laser. In addition, the laser light may have a wavelength that has high transparency to the flow channel 121 and the fluid 122 to be measured.

This device also includes a low-pass filter 203, an analog-digital conversion circuit (ADC circuit) 204 that converts a low-frequency component of the signal extracted by the low-pass filter 203 into a digital signal, an AC amplification circuit 205, and an AC amplification circuit 205. And an ADC circuit 206 for converting the amplified AC component into a digital signal. The amplification circuit 202, the low-pass filter 203, the ADC circuit 204, the AC amplification circuit 205, and the ADC circuit 206 correspond to the signal extraction unit 103. Further, a signal processing circuit 207 for calculating the flow velocity and the flow rate of the fluid 122 by inputting the low frequency component converted into a digital signal and the AC component converted into a digital signal is provided. The signal processing circuit 207 includes a feature amount calculation unit 104, a calibration value calculation unit 105, and a calibration unit 106.

First, the drive circuit 201 drives the light source 101 (laser) to irradiate the fluid 122 flowing through the flow path 121 with light from the light source having coherence. The fluid 122 needs to include a scatterer 123 that scatters the light from the light source, and the flow channel 121 needs to be transparent to the light from the light source. 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 (photodiode). When the concentration of the scatterer 123 is low, most of the scattered light becomes single scattering, but as the concentration increases, the scattered light reaches the photodiode through multiple times of 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 photodiode.

Here, assuming that the flow channel 121 has a circular cross section and the flow is a laminar flow, it is known that the flow velocity distribution in the flow channel 121 is as shown in FIG. 2B. .. The flow velocity becomes maximum at the center of the flow channel 121, and decreases as it approaches the circumferential portion of the flow channel 121. As the scatterer 123 moves along with the flow of the fluid 122, the speckle also changes moment by moment. Part of the speckle that fluctuates in this way is received by the photodiode and converted into an electrical signal.

In order to accurately obtain the flow rate and the flow velocity, the light received by the photodiode is reflected by the light directly incident on the photodiode from the laser or the surface of the flow channel 121 and the fluid 122. It is desirable that light is not included as much as possible. The configuration of the optical system for this will be described later.

Since the electric signal output from the photodiode is usually weak and the output current of the photodiode is on the order of μA, it is amplified by using an amplifier circuit 202 such as a transimpedance amplifier, and a voltage signal of a manageable level of, for example, about 1V. Convert to.

Next, only the low frequency component of the signal is extracted through the low pass filter 203, converted into a digital signal by the ADC circuit 204, and the low frequency digital signal is acquired. The cutoff frequency of the low-pass filter 203 may be, for example, about 1 Hz. The sampling frequency of the ADC circuit 204 may be, for example, about 1 to 100 Hz in accordance with the update rate of the measured flow rate or flow velocity value.

On the other hand, in the output of the amplifier circuit 202, a high frequency digital signal (high frequency component) is obtained by further amplifying only the AC component by the AC amplifier circuit 205 and converting it into a digital signal by the ADC circuit 206. If the DC voltage of the output of the amplifier circuit 202 is about 1V, the AC voltage is usually small on the order of mV, so that the AC voltage is amplified by the AC amplifier circuit 205 having a gain of about 10 to 1000 times, and a voltage at a level easy to handle. Good signal.

If the ADC circuit 206 has high performance and sufficient accuracy can be obtained even with a weak AC voltage, the AC amplifier circuit 205 can be omitted. The higher the sampling frequency of the ADC circuit 206, the faster the flow velocity can be measured. Here, as an example, the sampling frequency is 1 MHz.

In the device described with reference to FIG. 2, the output of the amplification circuit 202 is separated into a low frequency component that passes through the low pass filter 203 and a high frequency component that passes through the AC amplification circuit 205. When a high-performance ADC circuit can be used, the output of the amplifier circuit 202 may be directly converted into a digital signal by the ADC circuit without branching. In this case, the DC component of the digital signal may be treated as a low frequency digital signal and the AC component may be treated as a high frequency digital signal.

FIG. 3 shows an example of the high frequency digital signal acquired as described above. The waveform of FIG. 3 represents the time variation of the speckle generated by the scatterer 123 moving with the fluid 122, and the velocity and flow rate of the fluid 122 can be calculated by the digital signal processing of the signal processing circuit 207 described below. You can

The flow of digital signal processing will be described with reference to FIG. For the low frequency digital signal, a low pass filter (digital low pass filter) is further applied by digital processing, and an average value is calculated. As the digital low pass filter, a known method such as a moving average method, an IIR filter, an FIR filter can be used. Note that the digital low-pass filter can be omitted when the noise can be sufficiently reduced by the low-pass filter 203 in the analog circuit. The average value obtained here is a value corresponding to the average received light amount of scattered light received by the photodiode. In the present invention, the calibration parameter for obtaining the flow rate and the flow velocity of the fluid 122 is calculated based on the average received light amount obtained from the low frequency component. This method will be described later.

Next, a method of calculating the feature amount that correlates with the flow velocity of the fluid from the high frequency digital signal will be described. Note that, assuming that the fluid 122 flows through the flow passage 121 having a constant cross-sectional area without a gap, the flow velocity and the flow rate have a proportional relationship, and thus the feature amount obtained here is a feature that correlates with the flow rate as well. It becomes the amount.

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

In order to calculate the feature amount ν correlated with the flow velocity, first, the high frequency digital signal is Fourier transformed and the power thereof is calculated to obtain a power spectrum.

As an example, FIG. 5 shows an example in which the power spectrum is calculated for the milk to be measured that flows through the flow path made of a transparent material. In the milk, fat globules are dispersed in an emulsion state, and the fat globules serve as scatterers. In this case, since scattered light is detected by the homodyne method that does not use reference light, it directly corresponds to the moving speed of the scatterer unlike the two-beam laser Doppler flowmeter that realized heterodyne detection using reference light. No beat frequency is observed.

Instead, the light scattered multiply by the scatterers moving in the fluid interferes with each other, resulting in an exponential decrease in power with increasing frequency. It is shown that the higher the frequency is, the faster the scatterer 123 is included. When comparing the flow rate of 100 ml/min and the flow rate of 300 ml/min, the case of 300 ml/min is It can be confirmed that the power shifts to the high frequency side and is distributed. In the case of 0 ml/min, the power is concentrated on the low frequency side. In this state, the fluid is stopped as a whole, but the individual scatterers 123 continue a random motion due to Brownian motion without stopping, and the motion of the scatterers 123 is observed as a low-frequency component. ing.

When such a power spectrum is obtained, the product sum of the power P(f) and the frequency f is then calculated over a predetermined frequency range by the formula shown below.

FIG. 6 is a graph in which the result of calculating the product sum of the power and the frequency calculated as described above is plotted against the actual flow rate. As a frequency range for calculating the sum of products, the lower limit is 1 kHz and the upper limit is 500 kHz. The plot is also shown when the concentration of commercially available milk in the initial state is 100% and the concentration of milk is diluted to 60% and 20% by dilution with water. As shown in FIG. 6, at each concentration, a result having a high linearity with respect to the actual flow rate is obtained, and the feature amount correlated with the flow velocity can be extracted from the power spectrum by the above-described calculation. I can confirm.

When the flow velocity correlation feature amount ν calculated by the product sum of power and frequency has non-linearity with respect to the actual flow rate and the average flow velocity, a process of correcting the non-linearity may be added. The cause of the non-linearity may be that the frequency characteristic of the amplifier circuit 202 is not flat. As a method of correcting the non-linearity, a weighting coefficient w for each frequency is used when calculating the product sum of power and frequency, as in the formula of “ν=Σ{P(f)×f×w(f)}”. There is a method of multiplying by (f).

For example, when the cut-off frequency of the amplifier circuit 202 is f _cut [Hz] and it has a first-order low-pass filter 203 characteristic, the attenuation characteristic of the amplifier circuit 202 is canceled by using the following equation for the weighting function, and the relative flow rate is The linearity of can be improved.

Even if the frequency characteristic of the amplifier circuit 202 is more complicated, if the amplitude characteristic of the transfer function is |H(f)|, then “w(f)=1/|H(f)| ² ” By using it as a weighting function, it is possible to correct the nonlinearity of the relative flow rate depending on the frequency characteristic of the amplifier circuit 202.

In addition, as in the formula of “ν={Σ{P(f)×f}} ^G (G is a real number greater than 0)”, the product sum of power and frequency is calculated, and then the power calculation is performed to calculate the power flow correlation feature. The non-linearity of the quantity ν may be corrected. Further, as in “ν={Σ(P(f)×f×w(f))} ^G ”, a power calculation is performed by multiplying the weighting coefficient w(f) for each frequency, and the flow velocity correlation feature amount ν May be corrected.

If the slope and offset are obtained by linearly approximating the plot of FIG. 6 and used as calibration parameters, the calculated feature amount can be converted into the flow rate, but if the concentration is different, the slope and offset become different values. Therefore, the same correction coefficient cannot be used for fluids having various concentration states.

Further, FIG. 7 is a graph in which the result of calculating the product sum of the power and the frequency obtained in the same manner as above is plotted against the actual flow rate with the concentrated milk added with India ink as the measurement target. In this case, a characteristic amount having high linearity with respect to the actual flow rate is obtained at each concentration, but the slope and offset of the straight line differ depending on the concentration.

In the case of normal milk, the offset and slope of the straight line decreased monotonically as the concentration decreased, whereas in the case of concentrated milk containing India ink, the slope of the straight line becomes the most when the concentration is 60%. When the density is large and the concentration is 100% or 20%, the slope is reduced. This is because the concentration of the scatterer 123 contained in the milk is increased and the scattering coefficient is increased by concentrating the milk, and that the absorption coefficient is increased by the addition of India ink. It is thought to be an influence.

As described above, in the method for performing homodyne detection of speckle fluctuation, the obtained feature amount exhibits various behaviors depending on the type and number of scatterers contained in the fluid, the difference in absorption coefficient with respect to the wavelength of light used for measurement, and the like.

In contrast to the behavior of the above-described characteristic amount, in the present invention, the value of the average amount of received light obtained from the low frequency component is used to correct the intercept of the straight line and the slope that differ for each density. Hereinafter, this method will be described.

FIG. 8A is a graph in which the approximate straight line of the plot for each concentration in FIG. 7 is obtained by the least squares method, and the slope and offset of the obtained approximate straight line are plotted for each concentration. It should be noted that data of densities of 80% and 40%, which are omitted in FIG. 7, are added in FIG. 8A. As shown in FIG. 8A, the slope and offset of the approximate straight line show the maximum value at the density of 40%, and it can be confirmed that the density and the density decrease even if the density is lower or higher.

Next, FIG. 8B is a plot of the values of the average amount of received light for each density. The average received light amount also shows the maximum value at a density of 40%, and it can be seen that the density dependence of the average received light amount is similar to the density dependence of the offset and the slope.

FIG. 9 is a graph in which the horizontal axis represents the average amount of received light and the vertical axis represents the slope and offset. Further, FIG. 10 is a graph in which the same plot is made for normal milk. From these graphs, it can be seen that the offset changes linearly with respect to the average received light amount, and the slope is proportional to the power of the average received light amount. Further, in the case shown in FIG. 9, since the variation range of the average received light amount is relatively narrow, it is possible to linearly approximate the inclination.

The inventors diligently investigated the dependence of the slope and the offset on the average amount of received light for various fluids and flow paths. As a result, the flow rate correlation feature ν and the average amount of received light <I It was found that the actual flow rate Flow can be approximately calculated based on

[Calibration calculation 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 that satisfy A>0, B>=0, C>0, D>=0, E>0, F>0)

In the case of the concentrated milk supplemented with India ink shown in FIG. 9, suitable coefficient parameters are, for example, A=0.514, B=64.96, C=1.24e-6, D=0, E= 2.46 and F=1. Further, when the dependence of the slope on the average received light amount is linearly approximated instead of power, A=0.514, B=64.96, C=0.0103, D=1.57, E=1, F = 1.

FIG. 11 is a result of converting the flow velocity correlation feature amount ν into an actual flow rate using the latter coefficient parameter. It can be seen that even if the concentrations greatly differ from 20% to 100%, the same coefficient parameter can be used to calculate a value close to the actual flow rate.

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

By the way, in the above method, in order to correct the density dependence, not the density value but the average amount of received light is used. As is clear from the example of concentrated milk added with India ink, the average amount of received light does not necessarily increase monotonically with increasing concentration. Therefore, it is not possible to uniquely obtain the density from the average received light amount, but by using the phenomenon that the appropriate offset calibration parameter and gain calibration parameter are almost the same for the same average received light amount, the flow velocity correlation feature It is possible to calculate the flow rate and average flow velocity from ν.

In order to perform such calibration accurately using the average amount of received light, the light received by the photodiode that is not scattered by the scatterers contained in the fluid (that is, from the laser directly to the photodiode) It is important to keep the ratio of incident light, light reflected from the surface of the flow path, light reflected by the interface between the flow path and the fluid, etc. small.

At least, the amount of reflected light received by the photodiode should be smaller than the amount of scattered light received. More preferably, the amount of reflected light received is 1 of the amount of scattered light received. It is preferably /10 or less.

If this condition is not satisfied, the average amount of received light does not change much even if the concentration of the fluid changes and the flow velocity correlation feature amount ν changes, so the calibration accuracy decreases.

FIG. 12 shows a configuration example for reducing the proportion of light that is not scattered by the scatterer. The photodiode (PD) is surrounded by a light shielding structure 151 made of a material having a light shielding property with respect to the wavelength of the light from the light source, whereby the laser (LD) directly changes to the photodiode (PD). It blocks incoming light. Further, in order to prevent the directly reflected light reflected on the surface of the flow path 121 or the fluid from entering the photodiode (PD), the photodiode (PD) is arranged at a position deviated from the reflection center position of the directly reflected light. ing.

FIG. 13 shows an example in which the distribution of the intensity of the direct reflected light and the scattered light is analyzed using a ray analysis simulator. The direct reflected light has a strong intensity at the reflection center position, but the intensity sharply increases when deviated from the center position. Decrease. On the other hand, scattered light is diffused by a large number of scatterers and spreads, so that the peak intensity is small and widely distributed. Therefore, by disposing the photodiode (PD) at a position displaced from the reflection center position, the ratio of the scattered light intensity to the direct reflected light intensity can be increased.

Specifically, the light emitted from the laser (LD) with the beam diameter ω ₀ has the beam diameter shown by the following equation at the position of the propagation distance z.

Assuming a Gaussian beam, and letting the distance from the reflection center position be L, the reflected light intensity distribution ratio I(L) is expressed by the following equation, and the reflected light intensity distribution ratio decreases exponentially as L increases. ..

In the example of FIG. 13, if the photodiode (PD) is arranged in a region where the reflected light intensity distribution ratio of the directly reflected light is less than −30 dB, the directly reflected light intensity can be made 1/10 of the scattered light intensity.

Although the intensity ratio of the direct reflected light and scattered light changes to some extent depending on the measurement target, if the reflected light intensity distribution ratio of the direct reflection light is below -40 dB, there is a margin for various measurement targets and direct reflection is performed. It is possible to satisfy the condition that the light intensity is sufficiently smaller than the scattered light intensity.

Let d _{1 be} the distance from the laser (LD) to the surface of the flow channel 121 and d ₂ be the distance from the flow channel 121 surface to the photodiode (PD), and z=d ₁ +d ₂ and I(L)=10 ⁻⁴ Substituting into the above equation gives the following equation.

The photodiode (PD) may be arranged at a position that satisfies this formula. For example, the wavelength λ of the laser (LD) is 800 nm, the distance d ₁ from the laser (LD) to the surface of the flow channel 121 and the distance from the surface of the flow channel 121 to the photodiode (PD) are both 1 mm, and the beam of the laser (LD) is When the above equation is calculated assuming that the diameter ω ₀ is 2 μm, L>=0.55 mm, and it can be seen that the laser (LD) and the photodiode (PD) should be separated by 0.55 mm or more.

Note that in the example of FIG. 12, the center position of the reflected light coincides with the center position of the laser (LD), but when the light source light is obliquely incident on the reflection surface of the flow channel 121, the center position of the reflected light. Is displaced from the center position of the laser (LD). In this case, the photodiode (PD) may be arranged at a position separated from the laser (LD) center by a position where the reflected light intensity reaches a peak, not by the center position of the laser (LD). ..

As described above, according to the present invention, even when the scattering coefficient or the absorption coefficient of a fluid changes due to a change in concentration, the average light receiving amount is used to calibrate the flow velocity correlation feature amount ν, It is possible to measure the average flow velocity.

Next, a fluid measuring device capable of measuring the flow rate and the flow velocity of the fluid when the type of the fluid or the shape of the flow path is changed will be described with reference to FIG. FIG. 14 is a configuration diagram showing a configuration of another 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, a drive circuit 201, an amplification circuit 202, a low pass filter 203, an ADC circuit 204, an AC amplification circuit 205, an ADC circuit 206, a signal processing circuit 207, a storage unit 401, and a selection unit. And 402. The light source 101, the light receiving unit 102, the drive circuit 201, the amplification circuit 202, the low-pass filter 203, the ADC circuit 204, the AC amplification circuit 205, the ADC circuit 206, and the signal processing circuit 207 are the same as those described above, and detailed description thereof will be omitted.

In this fluid measuring apparatus, a storage unit 401 that stores a set of calibration parameters for a plurality of channels and combinations of fluids is provided, and a coefficient parameter to be used can be selected by a user operation of the selection unit 402.

As a method of selection, a number may be assigned to each coefficient parameter set and the number of the parameter set to be used may be designated, or a list of measurable flow paths and fluid combinations may be displayed and selected by the user. You may allow it. This makes it possible to measure various flow paths and the flow rates and flow velocities of fluids using a single fluid measuring device.

Alternatively, some or all of the coefficient parameters may be directly input from outside the fluid measurement device. As a result, the flow rate and flow velocity can be measured by the user by inputting appropriate coefficient parameters even for combinations of channels and fluids that are not stored in advance.

Further, instead of inputting the coefficient parameter itself, as shown in FIG. 15, the actual flow rate information can be input from the input section 501, and based on the relative flow rate calculated by the calculation section 502 and the actual flow rate information, An appropriate coefficient parameter may be calculated. Also in this device, the light source 101, the light receiving unit 102, the drive circuit 201, the amplification circuit 202, the low-pass filter 203, the ADC circuit 204, the AC amplification circuit 205, the ADC circuit 206, and the signal processing circuit 207 are the same as those described above. Detailed description is omitted.

Specifically, for example, the user sets the flow path to be measured and the fluid in the fluid measuring device, sets the actual flow rate to 0 mL/min, and informs the fluid measuring device that the current flow rate is 0 mL/min. input. The input unit 501 may be allowed to input the actual flow rate numerically, or may be provided with a button for inputting flag information indicating that the flow rate is 0 mL/min. With this input, the fluid measurement device measures the low-frequency digital signal and the high-frequency digital signal, calculates the values of the average received light amount and the relative flow rate, and stores them in the storage unit 503.

Next, the flow rate is set to 200 mL/min, and information indicating that the current flow rate is 200 mL/min is input to the fluid measurement device by a user operation or the like. Similarly to the above, the input unit 501 may be allowed to input the actual flow rate numerically, and may be provided with a button or the like for transmitting flag information that the flow rate is 200 mL/min.

With this input, the fluid measurement device measures the low-frequency digital signal and the high-frequency digital signal, calculates the values of the average amount of received light and the relative flow rate, and stores them in the storage unit 503. When the relative flow rates at these two points are obtained, it is possible to obtain the offset and slope at a certain average received light amount by performing regression analysis assuming that the relative flow rate changes linearly with respect to the actual flow rate. In addition, in the measurement of these two points, the value of the average amount of received light is usually constant even if only the flow rate changes, so either one of the values of the average amount of received light may be adopted, or the value of the average amount of received light may be adopted. You may make it use the average value of average light-receiving amount.

Next, by a user's operation, the fluid is diluted with water so as to have different concentrations. At this time, it is not necessary to grasp the specific density value, but it is desirable to change the density to the extent that the average amount of received light changes. In this state, by measuring the state of 0 mL/min and the state of 200 mL/min again, it is possible to obtain the offset and the inclination in the state where the average light receiving amounts are different.

When these data are gathered, the simultaneous equations are solved by linearly approximating the dependence of the slope on the average received light amount, and the coefficient parameters E=1 and F=1 are solved to specify the remaining parameters A to D. You can Further, by adding measurements at different concentrations, it becomes possible to determine the coefficient parameter in consideration of the non-linearity of the average light receiving amount dependency of the slope.

When optimizing the coefficient parameters for a combination of a channel and a fluid, some coefficient parameters of which are already known, it is not always necessary to perform a plurality of measurements as described above. You may reduce the number of conditions to measure according to the number of.

As described above, according to the present invention, based on the high frequency component of the electric signal obtained by photoelectrically converting the light scattered by the scatterer contained in the fluid by the irradiation of the coherent light in the light receiving unit. The feature amount that correlates with the flow velocity of the fluid is calculated, the calibration parameter is calculated based on the low frequency component of the obtained electric signal, and the feature amount is calibrated with the calibration parameter, so it is small and low-cost and simple. It becomes possible to measure the flow velocity and flow rate with high precision using various optical systems.

The present invention is not limited to the embodiments described above, and many modifications and combinations can be implemented by a person having ordinary knowledge in the field within the technical idea of the present invention. That is clear.

101... Light source, 102... Light receiving part, 103... Signal extracting part, 104... Feature amount calculating part, 105... Calibration value calculating part, 106... Calibration part, 121... Flow path, 122... Fluid, 123... Scatterer.

Claims (2)

A light source for irradiating a fluid containing a plurality of scatterers with coherent light,
A light receiving unit that receives light scattered by the scatterer contained in the fluid by irradiation of coherent light and performs photoelectric conversion,
A signal extraction unit for extracting a low frequency component and a high frequency component of the electric signal photoelectrically converted by the light receiving unit,
A characteristic amount calculation unit that calculates a characteristic amount that correlates with the flow velocity of the fluid based on the high-frequency component extracted by the signal extraction unit;
A calibration value calculation unit that calculates a calibration parameter based on the low-frequency component extracted by the signal extraction unit,
A calibration unit that calibrates the characteristic amount with the calibration parameter to calculate at least one of a flow velocity and a flow rate of the fluid,
The calibration parameters include offset calibration parameters and gain calibration parameters,
The calibration value calculation unit,
Using the average received light amount <I> obtained from the average value of the low frequency components and the coefficient parameters A and B (A>0, B≧0), the offset calibration parameter is obtained by A×<I>+B,
Using the average received light amount <I> and the coefficient parameters C, D, E, F (C>0, D≧0, E>0, F>0), F/(C×<I> ^E −D) Find the gain calibration parameters,
The fluid measuring device, wherein the calibration unit multiplies the gain calibration parameter by a value obtained by subtracting the offset calibration parameter from the feature amount. The fluid measuring apparatus according to claim 1 Symbol placement,
A fluid measuring device comprising: a light-shielding portion that shields light that directly enters the light-receiving portion from the light source.