JP6426665B2 - Fluid measurement device - Google Patents

Description

  The present invention relates to a fluid measurement device that measures the flow rate or flow rate of fluid flowing in a flow path using laser light.

  Techniques for measuring the flow rate and flow rate of fluid flowing in a flow path are widely used in the industrial and medical fields. There are various types of devices for measuring the flow rate and the flow rate, such as an electromagnetic flowmeter, a vortex flowmeter, a Coriolis flowmeter, and a laser flowmeter, which are used according to the application. Among them, the laser flowmeter needs to be hygienic because it is possible to measure the flow rate and the flow rate without contacting the fluid flowing in the flow path by using the laser light without contacting the fluid. It is used in applications and applications where the flow meter can not be inserted into the existing flow channel.

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

  When scattered light in such a state is converted into an electrical signal by a photodiode or the like, heterodyne detection is performed and a beat signal is observed. If the frequency spectrum of the beat signal to be observed is calculated and the peak frequency is extracted, the moving speed of the scatterer can be determined. When the flow is a laminar flow, the average flow velocity and the flow rate of the fluid flowing in the flow path in the entire flow path are proportional to the moving speed of the scatterer determined by the above-described one. The flow rate and the flow rate of the fluid can be measured by multiplying and calibrating.

  Although the fluid measurement technique described above has the excellent advantage of being able to measure the absolute value of the moving speed of the scatterer, it requires two beams to be collected 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 size of the apparatus is increased and the cost is increased. In addition, this technique is effective when the concentration of scatterers contained in the fluid is low, and when the concentration of scatterers becomes high, the laser light is multiply scattered by a plurality of scatterers, so that the beat signal is observed. Problem that makes it difficult.

  The speckle method is also used as a velocity measurement method using a laser. The speckle method is a velocity measurement using a random spot pattern (= speckle) generated by interference of irregularly scattered light when a fluid including rough surface or scatterer is irradiated with laser light. It is a law. When the object generating the speckles moves, the speckles also change temporally, so for example, it is possible to obtain a two-dimensional image of the speckles and analyze the movement pattern of the speckles to obtain the movement speed ( Non-Patent Document 1). Since this method requires acquisition and analysis of a two-dimensional image, there is also a problem that the apparatus becomes large and expensive.

  As a method of simplifying the optical system, a method of measuring speckle at one point instead of two dimensions may be considered. In this case, it is known that an irregular signal corresponding to the fluctuation of 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 (see, for example, Patent Document 2).

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

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

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

  The present invention has been made to solve the above problems, and it is an object of the present invention to be able to suppress the decrease in linearity between the measured flow rate and the actual flow rate at high flow rates. Do.

  The fluid measurement device according to the present invention includes a tube in which a fluid containing a plurality of scatterers is made of an elastic body, a bent portion formed in a measurement area, and a curved portion on which the tube is bent A light source disposed on a surface, the scatterer in the fluid flowing through the tube irradiating the scatterer, and the light receiving portion receiving the light scattered by the scatterer contained in the fluid by the irradiation of the coherent light and performing photoelectric conversion And a calculation unit configured to calculate and output the flow rate of the fluid passing through the measurement region based on the electric signal photoelectrically converted by the light reception unit.

  The fluid measurement apparatus includes a base portion for arranging the sensor head in the measurement area on the flat surface, a pipe is disposed in a piping area passing the measurement area on the flat surface, and the sensor head is pushed up in a direction away from the flat surface The bend of the tube is formed by being done.

  In the fluid measurement apparatus, the computing unit extracts a high frequency component of the electric signal photoelectrically converted by the light receiving unit, and a characteristic amount correlated with the flow velocity of the fluid based on the high frequency component extracted by the signal extracting unit. A feature amount calculation unit to calculate, and a calculation unit to calculate at least one of the flow velocity and the flow rate of the fluid from the feature amount.

  As described above, according to the present invention, since the bending portion is formed in the pipe and the sensor head is disposed on the concave side, the linearity between the measured flow velocity and the actual flow velocity at a high flow velocity It is possible to obtain the excellent effect that the reduction of the

FIG. 1 is a configuration diagram showing a configuration of a fluid measurement device according to an embodiment of the present invention. FIG. 2 is a block diagram showing the configuration of the calculation unit 103. As shown in FIG.

  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 measurement device according to an embodiment of the present invention. The fluid measurement device includes a tube 101, a sensor head 102, and a computing unit 103.

  The pipe 101 serves as a flow path, and is made of an elastic body such as vinyl chloride, for example, and a fluid including a plurality of scatterers flows. Moreover, the pipe | tube 101 is bent in the measurement area | region 111, and the bending part 101a is formed.

  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 portion side of the curved portion 101a of the measurement area 111. The light source 121 emits coherent light to scatterers in the fluid flowing through the tube 101. The light source 121 is composed of, for example, a semiconductor laser. The light receiving unit 122 receives the light scattered by the scatterer included in the fluid due to the irradiation of the coherent light, and photoelectrically converts the light. The light receiving unit 122 is, for example, a photodiode.

  The tube 101 and the sensor head 102 are disposed, for example, in a piping area on the flat surface of the base portion 104. The curved portion 101 a of the tube 101 is formed by being pushed up in a direction away from the flat surface by the sensor head 102 on the flat surface of the base 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 side of the base portion 104 by the pressing portion 105 having the opening area in the measurement area 111.

  For example, in the curved portion 101a, the tube 101 is bent at 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 a predetermined curvature B and approaches the side of the base portion 104, and then bends with a curvature A into a state along a flat surface.

  The calculation unit 103 calculates and outputs the flow rate of the fluid passing through the measurement area 111 based on the electric 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 extracting unit 131 extracts the high frequency component of the electrical signal photoelectrically converted by the light receiving unit 122. The feature amount calculation unit 132 calculates a feature amount correlated 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, the light source light (coherent light) having coherence from the light source 121 is applied to the fluid flowing in the curved portion 101a (measurement region 111) of the pipe 101 serving as the flow path. The fluid contains a scatterer that scatters the source light, and the tube 101 is transparent to the source light. When the source light is scattered by scatterers in the fluid, 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, but as the concentration increases, it reaches the light receiving unit 122 through multiple times of scattering. As a result of interference of light scattered in various paths, speckle occurs, and a part of it is observed in the light receiving unit 122.

  Here, assuming that the cross section of the tube 101 is circular and the flow is laminar, the flow velocity distribution at the curved portion 101 a in the tube 101 has a minimum flow velocity at the recess side where the sensor head 102 is disposed. It becomes. Speckles also change from moment to moment as the scatterer moves as the fluid flows. A part of the speckles thus fluctuating is received by the light receiving unit 122 and converted into an electric signal.

  In order to accurately determine the flow rate and the flow velocity, the light received by the light receiving unit 122 may be light directly incident on the light receiving unit 122 from the light source 121 or directly on the light receiving unit 122 from another light source. It is desirable that incident light and light reflected at the surface of the tube 101 and the fluid be as small 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 extracting unit 131 amplifies the signal using an amplification circuit such as a transimpedance amplifier, for example, about 1 V Convert to a manageable level voltage signal.

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

  On the other hand, the output of the amplification circuit further amplifies only the alternating current component by the alternating current amplification circuit and converts it into a digital signal by the ADC circuit to obtain a high frequency digital signal (high frequency component). Assuming that the DC voltage of the output of the amplifier circuit is about 1 V, the AC voltage is usually as small as mV order, so it is amplified by an AC amplifier circuit having a gain of about 10 times to 1000 times to a voltage signal of a manageable level. It is good to do. The faster the sampling frequency of the ADC circuit, the faster the flow rate can be measured. For example, the sampling frequency may be 1 MHz.

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

  Next, a method of calculating a feature amount correlated to the flow velocity of the fluid from the high frequency digital signal will be described. When it is assumed that the fluid flows without gaps in the tube 101 having a constant cross-sectional area, the flow rate and the flow rate are proportional to each other, and thus the feature quantity to be calculated here is a feature quantity correlated with the flow rate. Become.

  The high frequency digital signal represents speckle fluctuation, and there are various known methods for extracting feature quantities correlated with the flow velocity. For example, 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 predetermined time, a method of analyzing a power spectrum and obtaining its inclination. Here, an example is described in which the product sum of the power spectrum power and the frequency is used as a feature quantity for which calibration using an average light reception amount described later functions most effectively.

  In order to calculate the feature quantity 相関 correlated with the flow velocity, first, the high frequency digital signal is subjected to Fourier transform, and the power is calculated to obtain the power spectrum. After the power spectrum is obtained, next, the product sum of the power P (f) and the frequency f is calculated over a predetermined frequency range according to 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 with respect to the actual flow rate. When the flow velocity correlation feature value 算出 calculated by the product sum of the power and the frequency has nonlinearity with respect to the actual flow rate and the average flow velocity, a process of correcting the nonlinearity may be added. As a cause of causing the non-linearity, for example, the frequency characteristic of the amplification circuit may not be flat. As a method of correcting non-linearity, when calculating the product-sum of power and frequency as in the equation of “ν = Σ {P (f) × f × w (f)}”, a weighting coefficient is set for each frequency. There is a method of multiplying by w (f).

For example, when the cutoff frequency of the amplification 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 amplification circuit is canceled by using the following equation for the weighting function, The linearity of relative flow can be improved.

Even if the frequency characteristic of the amplification circuit is more complex, weighting “w (f) = 1 / | H (f) | ² ” when the amplitude characteristic of the transfer function is | H (f) | By using it as a function, it is possible to correct the non-linearity of the relative flow rate depending on the frequency characteristic of the amplification circuit.

In addition, after calculating the product-sum of power and frequency as shown by the formula of "ν = {Σ {P (f) × f}} ^G (G is a real number greater than 0)", power operation is performed to calculate the flow velocity correlation feature The non-linearity of the quantity 補正 may be corrected. Also, as shown by “相関 = {Σ (P (f) × f × f (f))} ^G ”, the power is calculated by multiplying the weighting coefficient w (f) for each frequency, and the flow velocity correlation feature value ν Non-linearity of may be corrected.

  If the plot of the above-mentioned graph is linearly approximated to obtain inclination and offset, and calibration parameters are used, 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 disposed on the concave portion side where the flow velocity is reduced in the curved portion 101a. For this reason, in the measured flow velocity, the decrease in linearity between the measurement flow and the actual flow velocity is suppressed. The correlation between the measured flow velocity value and the actual flow velocity (average flow velocity) is calculated by the flow velocity measurement value obtained by measuring the flow velocity known fluid in advance to obtain the correction value, and the actual measurement is performed using this correction value. By correcting the flow velocity measurement value obtained in, more accurate flow velocity values can be obtained.

  Here, when the amount of bending of the curved portion 101a increases, the average flow velocity in this region is different from the flow velocity in the linear region. Under such conditions, accurate flow velocity and flow rate can not be determined. Therefore, it is important that the bending amount of the local portion 101a be in a range in which the average flow velocity (within the same cross section of the pipe) at the local portion 101a does not change.

  As described above, according to the present invention, since the bend is formed in the pipe and the sensor head is disposed on the concave side, linearity between the measured flow rate and the actual flow rate at a high flow rate is obtained. It will be possible to suppress the decline.

  In the case where the flow velocity is high, the decrease in linearity can be suppressed by obtaining the power spectrum in a wider band, but high performance is required by arithmetic processing, and the apparatus becomes more expensive, but according to the present invention With a very simple configuration, it is possible to suppress the decrease in linearity.

  The present invention is not limited to the embodiments described above, and many modifications and combinations can be made by those skilled in the art within the technical concept of the present invention. It is clear.

  DESCRIPTION OF SYMBOLS 101 ... Tube, 101a ... Curved part, 102 ... Sensor head, 103 ... Calculation part, 104 ... Base part, 105 ... Press part, 111 ... Measurement area, 121 ... Light source, 122 ... Light reception part.

Claims (3)

A tube through which a fluid comprising an elastic body and including a plurality of scatterers flows;
A bend at which the tube formed in the measurement area bends,
A light source disposed on the outer peripheral surface of the tube on the concave side of the curved portion of the measurement area, and irradiating the scatterer in the fluid flowing through the tube with coherent light, and irradiation of coherent light to the fluid A sensor head including a light receiving unit that receives and photoelectrically converts light scattered by the scatterer included;
A calculation unit that calculates and outputs the flow rate of the fluid passing through the measurement area based on the electrical signal photoelectrically converted by the light receiving unit. In the fluid measurement device according to claim 1,
It has a base portion for arranging the sensor head in the measurement area on a flat surface,
The pipe is disposed in a piping area passing through the measurement area on the flat surface;
A fluid measuring device characterized in that the curved portion of the pipe is formed by pushing up the sensor head in a direction away from the flat surface. In the fluid measurement device according to claim 1 or 2,
The arithmetic unit is
A signal extraction unit for extracting a high frequency component of the electric signal photoelectrically converted by the light receiving unit;
A feature amount calculation unit that calculates a feature amount correlated to the flow velocity of the fluid based on the high frequency component extracted by the signal extraction unit;
A calculation unit that calculates at least one of the flow velocity and the flow rate of the fluid from the feature amount.

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