JPH0677024B2 - Velocity measurement probe - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a laser Doppler probe for measuring a flow velocity of a fluid based on a change in frequency difference caused by a Doppler effect exerted by the fluid between laser light beams irradiated on the fluid. Regarding the probe for flow velocity measurement used in the rosimeter (LDV), in particular, the simple construction that eliminates the use of problematic optical fibers makes assembly and handling extremely easy, and the flow velocity of fluid can be measured stably and accurately even in the field. It's something I got to get.

(Prior art and its problems) Regarding the observation of water flow, instead of mechanical methods such as propeller anemometers and electrical methods such as hot-wire anemometers, which have been used for a long time,
Recently, an optical method has been introduced, and various improvements have been made from the viewpoint of hydraulic research. A laser Doppler velocimeter (LDV) newly developed as an optical measurement method of such a flow velocity is an optical precision measurement of the flow velocity by the Doppler effect of the flow velocity on the laser light. The planer velocimeter has many problems because it aims at completely non-contact velocity measurement, and it is inferior to the heat ray velocity meter in terms of its ease of use, and it has hindered its popularization along with the problem of price.

The present inventor eliminates the drawbacks of the conventional laser Doppler velociometer (LDV) and introduces a laser beam having an extremely good coherence to the optical method of the fluid flow velocity to enable the precise measurement of the flow velocity. By introducing an optical fiber to the laser Doppler velociometer, the conventional LDV probe was made significantly smaller, and it was difficult to measure in the past.
JP-A-59 has made it possible to measure the flow velocity near the boundary surface where the density suddenly changes, and the flow velocity of the plasma flow that handles a minute fluid space.
The probe for flow velocity measurement described in Japanese Patent No. 193362 was first developed.

However, the above-mentioned flow velocity measuring probe using the optical fiber has various problems as described below.

(1) Conventionally, as a method of injecting a laser beam from a light source arranged apart from a light source into a measurement probe, a diffused light emitted from a light source is collected and an optical fiber is collected at the collected point. Although the laser beam emitted from the light source was used as effectively as possible by accurately locating the incident aperture end of the, the aperture end face of the core area of the optical fiber was extremely small, so only a part of the emitted laser beam was emitted. It could not be injected into the core region, and the amount of lost light was considerably large. Also, if the position of the optical fiber deviates even slightly due to vibration or shock when the measuring instrument moves, it becomes difficult to maintain the injection state of the laser light, and it took a lot of time to restore the accurate injection position. .

(2) On the other hand, in order to receive a laser beam having a Doppler frequency component corresponding to the flow velocity of the fluid, the reference light beam that has passed through the fluid flow velocity measurement point to generate the Doppler effect, and the reference light beam It is necessary to receive light by the photoelectric conversion element that is placed apart from the scattered light of the intersecting measurement light beam, and for that purpose, the open end of the core area of the receiving optical fiber must be precisely aligned with the optical axis of the reference light beam. It was necessary to match exactly. However, since the light-receiving end face of the optical fiber is extremely small, as in the case of (1), there is a problem that the amount of received scattered light is particularly small and the light-receiving optical fiber is displaced.

(3) As described above, a gas laser element has been conventionally used as a laser light source in the visible region for accurately injecting the light required for the flow velocity measuring probe into the optical fiber. However, the gas laser element is resistant to vibration and shock. It was weak and not suitable for outdoor use, nor was it suitable for outdoor use because it required a high-voltage power supply.

(4) Further, as described above, even a slight displacement of the mounting position of the optical fiber causes a state in which measurement is not possible, so that it is necessary to set the mounting position precisely, and vibration and shock are likely to occur. When using it outdoors, extreme care was required in handling the measuring instruments.

(Object of the present invention) An object of the present invention is to provide a semiconductor laser light source element incorporated without using an optical fiber for introducing light, which is the root of the above-mentioned conventional problems, and has a simple structure with low loss. , Providing a probe for flow velocity measurement suitable for outdoor use.

(Means for Solving the Problems) In order to solve the above-mentioned problems, the probe for measuring the flow velocity of the present invention includes a semiconductor laser element, a spherical lens, and a spherical convex lens surrounding the spherical lens close to the front and rear of the spherical lens. A focusing optical system for focusing a laser diverging from the semiconductor laser device to form a laser light beam, and a half parallel to each other formed by both surfaces of a transparent flat plate inclined with respect to the optical axis of the laser light beam. A split refracting optical system configured by a mirror and a mirror for splitting the laser light beams and refracting the laser light beams at substantially right angles to form a pair of parallel laser light beams having mutually different intensities, and a flow velocity of the pair of parallel laser light beams. A condensing optical system for converging light at a measurement point and intersecting each other, and a laser light beam of the one of the parallel laser light beams having the weaker intensity. A photoelectric conversion element that receives the laser light beam that has passed through the flow velocity measurement point and is located on the axis of the beam, and the fluid at the flow velocity measurement point due to the Doppler effect of the laser light beam that has passed through the flow velocity measurement point. It is characterized by being configured so that the flow velocity can be measured.

That is, first, unlike the gas laser element in the above-described conventional probe, the semiconductor laser element is arranged in the flow velocity measuring probe itself so that the optical fiber for light transmission is unnecessary and the laser beam is injected into the optical fiber. It solves all the problems caused by this. Next, the focusing optical system focuses the diffused light emitted from the semiconductor laser element to form a laser light beam for effective use, and for example, has a convex lens, a spherical lens and a convex lens. , Diffuse light into parallel light, focus the parallel light at a close position, shape the focused light into a thin light beam, and, if necessary, have a pinhole on the optical axis of the lens system. An optical mask is provided to limit the light beam that has passed through the lens system to only the pinhole portion.
Next, the split-refractive optical system is, for example, an optical glass plate having a smooth surface and a perfectly reflective bottom surface and arranged at an angle of 45 ° to the optical axis of the focusing optical system. With the mirror formed by the reflection bottom surface, one laser light beam that has passed through the pinhole is split into two laser light beams, and the two laser light beams are refracted at a substantially right angle to form a parallel laser light beam. Further, of the two flat light laser light beams, the laser light beam reflected and refracted by the half mirror having the smooth surface is made weaker than the laser light beam reflected and broken by the mirror having the perfect reflection bottom surface, for example, the intensity ratio thereof. Is set to about 3: 7, the laser light beam from the half mirror is used as reference light, and the laser light beam from the mirror is used later as scattered light. Next, the condensing optical system is composed of, for example, a convex lens, and condenses the two parallel laser light beams from the split refracting optical system at the flow velocity measuring point to intersect with each other. Next, the photoelectric conversion element is composed of, for example, a photodiode in front of which an optical mask having a pinhole is provided, and only the reference light and the scattered light within the same solid angle as the reference light are received by the photodiode through the pinhole. Then, it is converted into an electric signal according to the amount of received light and taken out as a flow velocity measurement output.

(Operation of the Present Invention) The flow velocity measuring probe of the present invention configured as described above has the following operations.

(1) By incorporating a semiconductor laser device that serves as a light source for measurement into the LDV probe, the optical fiber that was conventionally used to connect to the outside is no longer needed, so the light generated when injecting light into the optical fiber is eliminated. There is no loss,
The precision adjustment required for setting the position of the optical fiber is no longer necessary.

(2) Since the conventional purpose was to measure the flow velocity two-dimensionally, an optical mask having three pinholes was used to form two laser light beams eccentric to the reference light beam at right angles. Was there. Therefore, the light out of the pinhole was not used, but the LDV probe of the present invention was able to perform the one-dimensional measurement, and the laser light beam was divided into two by the Hoof mirror, so that the loss of the light quantity was remarkably reduced. .

(3) Since the photoelectric conversion element is built into the light receiving part of the LDV probe, the outer diameter of the probe itself is increased to about 12 mm, which is a little unsuitable for measuring the ultrafine structure of a fluid, but Also, because it was housed in an outer casing with an outer diameter of about 13 mm in order to secure the mechanical strength to withstand insertion of the probe in the fluid, there is no deterioration in performance in terms of shape and dimension,
Since the light-receiving optical mask can be used without using the light-receiving optical fiber, it is possible to easily dispose the probe for light reception and increase the amount of light received.

(4) As described above, the precision of the arrangement of the optical system is relaxed by not using the optical fiber, and even if the optical system is displaced due to some vibration or shock, accurate signal detection can be performed, and it can be used outdoors. Measurement of the fluid flow velocity was easy.

(5) Since the loss of light quantity that has conventionally occurred in each part can be significantly reduced, the quantity of light that can be directly used for measurement is greatly increased, which facilitates signal detection of measurement results. With the increase of, it becomes possible to clearly detect and measure the change in light intensity due to the Toppler effect even for fluids containing few scattering particles, such as fresh water, and the signal processing in turbid water flow velocity measurement can be performed with small signal amplification. , Easy and natsu.

(6) Since the laser light source used has been changed from a conventional gas laser element to a semiconductor laser element, the high voltage power source conventionally used for driving the gas laser element is not required, and the power consumption can be reduced accordingly, and the gas laser is weak against shocks and the like. By not using the element, a flow velocity measuring probe suitable for measurement in the field can be obtained.

In particular, the flow velocity measuring probe of the present invention is remarkably superior to the conventional one for the field measurement in the following points.

(7) Since the LDV probe according to the present invention is not in contact with the flow velocity measurement point in the fluid, the desired flow velocity can be precisely performed in the field without substantially disturbing the state of the fluid flow.

(8) The probe of the present invention is also capable of measuring the instantaneous flow velocity, which is the principle feature of the laser Doppler-perosimeter (LDV), and therefore can also measure the flow velocity of turbulent flow generated in a river or the like.

(9) Since the probe of the present invention performs absolute measurement of the flow velocity in principle, there is no fear of deterioration of measurement accuracy due to flow conditions or wear of measuring equipment.

(Example) Hereinafter, the present invention will be described in detail with reference to the drawings.

First, the configuration of the entire fluid flow velocity measuring system using the flow velocity measuring probe of the present invention will be described with reference to FIG.

In the overall configuration shown in the figure, among the probes for flow velocity measurement of the present invention, the probe 23 for light transmission is a
It is integrally formed with the light-receiving probe 24 that is opposed via 20 and is connected to each component of the external measurement system. That is, after the two laser light beams emitted from the laser light source built in the measurement probe supplied with the power supply voltage 22 from the laser light source 21 are focused on the measurement point P in the fluid 20, Of the laser light beams B ₁ and B ₂ , the reference light beam B ₁
The light component incident on the photoelectric conversion element 8 in the light receiving probe 24 located in the straight traveling direction is a beat frequency component generated based on the Doppler effect of the flow velocity of the fluid on the mutual interference between the reference light and the scattered light. The electric signal 25 of the photoelectric conversion output of the incident light component is amplified by the amplifier 26, only the beat frequency component due to the Doppler effect is extracted by the band filter 27, and the beat-frequency converter 28 beats the beat frequency component. A voltage signal proportional to the beat frequency of the frequency component is taken out and the required flow velocity measurement data is calculated by the calculator 29.

Next, the detailed configuration and operation of the probe for flow velocity measurement of the present invention, which is a main part of the fluid flow velocity measurement system described above, will be described in detail with reference to FIG. Of the probe for measuring the flow velocity of the present invention whose main part is schematically shown in FIG. 1, in the light-transmitting probe 23, the diffused light emitted from the semiconductor laser element 2 which is driven by supplying the power source voltage 1 from the external power source is used. The lens system 3 configured as described later focuses in parallel to form a thin light beam. Such a thin light beam is arranged in the optical path by inclining a half mirror 4 and a mirror 5 on the bottom surface, which are parallel to each other and have a bottom surface of a transparent glass plate as a mirror surface, to the incident light beam by about 45 °. By doing so, the light beams are converted into two parallel light beams that are parallel to each other, and are further condensed by the condensing lens system 6 so as to intersect each other at the flow velocity measurement point P in the fluid 20, and the flow velocity of the fluid 20 due to the Doppler effect. Prepare for measurement.

Among the light-transmitting probes having the above-described basic structure, the lens system 3 that converges the diffused light from the semiconductor laser element 2 into a laser light beam includes, for example, as shown in FIG. It can be configured by combining the spherical lens 10 and the convex lens 11, the convex lens 9 reduces the diffusion angle of the diffused light from the light source, the spherical lens 10 focuses the diffused light to the nearest distance, and the convex lens 11 Make focused light parallel light. With the lens system 3 having such a configuration, the light amount of diffused light from the semiconductor laser element 2 serving as a light source is concentrated and extracted in a thin light beam.

Next, the half mirror 4 and the mirror 5 convert the above-mentioned one laser light beam into two parallel light beams having mutually different amounts of light and refracting the traveling directions thereof at substantially right angles. There is. The half mirror 4 and the mirror 5 which perform such an action, for example, have a bottom surface of a glass plate having a thickness of 3.5 mm having a smooth surface having an appropriate transmittance as a mirror surface, and reflect the reflectance and the transmittance of the surface and the total reflection of the bottom surface. Depending on the combination, the half mirror 4 formed by the surface and the mirror 5 formed by the bottom surface
Although the light quantity ratio of the two laser light beams formed respectively can be appropriately set by, the reflection beam from the half mirror 4 is usually weaker.

Half mirrors 4 configured in parallel with each other as described above
As shown in FIG. 3, the mirror 5 and the mirror 5 are arranged at an angle of 45 ° with respect to the incident light beam, and the incident light beam is weakly refracted at a right angle. ₁ and a remarkably strong light beam B ₂ from the mirror 5. The latter light beam B ₂ is used to irradiate and scatter the fluid 20 and to take out a part of the scattered measurement light beam B ₂ together with the reference light beam B ₁ to measure the flow velocity by the Doppler effect.

That is, as shown in FIG. 4, when a light beam having a frequency f ₁ is incident almost at right angles to the flow direction of a fluid having a flow velocity u, the flow velocity u of the fluid exerts a Doppler effect on the light beam, The frequency of the light component that travels straight in the incident direction is
The frequency of the scattered light that remains the same frequency f ₁ as the incident light but goes to another direction after being scattered by the fluid becomes another frequency f ₂ that changes according to the angle between the incident direction and the traveling direction.

Therefore, as shown in FIG. 5, when the reference light beam B ₁ and the measurement light beam B ₂ both having the frequency f ₁ cross each other and are incident on the measurement point P in the fluid, the reference light beam B ₁ The light component that travels in the incident direction has a frequency f ₁ that travels straight in the incident direction.
Of the reference light B ₁ and a scattered light component having a frequency f ₂ according to the crossing angle θ and the flow velocity u in the measurement light beam B ₂ that advances from the incident direction by an angle θ and proceeds in the incident direction of the reference light beam. Is the combined light component of. When such frequency f _1, f ₂ frequency difference f ₁ ~f ₂ is sufficiently smaller than the, during the combined beam components,
The beat frequency component corresponding to the absolute value of the frequency difference | f ₁ −f ₂ | is included, and the flow velocity u of the fluid can be calculated from this bead frequency.

Explaining the Doppler effect, when a moving particle is irradiated, the light scattered in the traveling direction of the measurement light beam B ₂ and the scattering scattered from the traveling direction of the measurement light beam B ₂ as shown in FIG. The emitted light appears (this scattering is called Mie scattering). The light beam is scattered in the traveling direction of these measuring light beam B ₂ has the same frequency as the measuring light beam B _2, does not depend on the velocity of the particle P. However, the other light beams undergo a change in frequency depending on the angle θ formed by the traveling direction of the measurement light beam B ₂ and the speed (including the speed and direction) of P. This phenomenon is the Doppler effect.

Accordingly, the reference light beams B ₁ toward the optical mask 7 is not caused any frequency change, the measuring light beam B ₂ of the scattered light toward the optical mask 7 light beam frequency frequency of the original measurement beam B ₂ (Hence the frequency of B ₁ ). As a result, the absolute value of the difference between the frequency f ₂ of the light beam output from the photoelectric change element 8 toward the optical mask of the frequency f ₁ of the reference light beams B ₁ measuring light beam B ₂ of the scattered light, | f ₁ It corresponds to a change in light intensity at a frequency corresponding to −f ₂ | (this is called the beat frequency or Doppler shift). And | f ₁
Since −f ₂ | is completely proportional to the flow velocity at point P, the flow velocity can be measured after all. However, as described above, if the intensities of the light beams directed to the optical mask 7 among the scattered lights of the reference light beam B ₁ and the measurement light beam B ₂ are not substantially equal to | f
It becomes difficult to detect ₁ −f ₂ |. Reference light beams B ₁ and the measuring light beam B ₂ and is better one measurement light beam B ₂ is always larger. In the present invention, it is preferable that the ratio of the reference light beam B ₁ and the measurement light beam B ₂ is, for example, B ₁ : B ₂ = 3: 7.

Next, as described above, only the combined light component directed from the flow velocity measuring point P in the straight traveling direction of the reference light beam B ₁ is passed through the optical mask 7 having appropriate apertures as shown in FIG. It is extracted and supplemented by the photoelectric conversion element 8 composed of a photodiode, for example, and converted into an electric signal.

In the light receiving probe of the conventional flow velocity measuring probe, the above-mentioned combined light component is received by the opening end face of the optical fiber and guided to the external photomultiplier, but the opening diameter of the optical fiber is about 50 to 200 μm. It is extremely small and requires extremely precise position adjustment to position it so that it can accurately capture the reference light beam, and measurement is not possible if the position of the receiving optical fiber deviates even slightly due to vibration or shock. Was coming. Further, at the opening end face of the optical fiber, incident light is reflected depending on the incident angle of light and cannot be captured.Therefore, the optical axes of the receiving optical fiber and the reference optical beam must be accurately aligned. Yes, higher precision is required to adjust the position of the optical fiber. In contrast to the configuration of such a conventional light-receiving probe, when a photoelectric conversion element, for example, a photodiode is directly incorporated as described above and a required light-receiving component is extracted by an optical mask having a pinhole, an optical mask By arranging the photodiode 8 immediately after 7, it is possible to set the diameter of the pinhole of the optical mask 7 to be sufficiently large within the required flow velocity measurement accuracy, which not only simplifies the configuration but also the position of the component. The adjustment becomes much easier, and there is no possibility that the flow velocity cannot be measured due to a slight displacement or deformation due to vibration or thermal expansion.

Next, the performance of the probe for flow velocity measurement of the present invention will be examined with comparison with the conventional flow velocity meter in the indoor water channel and the result of actual measurement in an actual river.

Since the Pete frequency generated in the fluid-transmitted light by the Doppler effect exerted by the fluid flow velocity on the frequency of the incident light, which is the operating principle of the probe for measuring the velocity of the present invention, is equal to the Doppler shift amount νo, the flow velocity U is the wavelength λ of the incident light. , With respect to the refractive index n of the medium and the crossing angle θ of the incident light beams, It is expressed by

On the other hand, a hot film anemometer (HFV) conventionally used to measure the fluid flow velocity, that is, the amount of heat generated by the current and the amount of heat released by the flow and the equilibrium temperature when heating is performed by passing an electric current through a thin metal wire spread in the fluid Velocity meters, which determine the flow velocity based on the resistance change due to the cooling action of the flow of thin metal wires, are capable of point measurement in a wide measurement range from low flow velocity to high flow velocity and have excellent frequency response. It is widely used for measuring fluids, but it is said that it is not suitable for measuring actual rivers because it is vulnerable to dirt, the heating current cord cannot be lengthened, and bubbles easily occur due to heat generation. In the indoor water channel, the flow velocity fluctuation was measured at the same time for the same fluid using the probe for flow velocity measurement of the present invention and the hot film anemometer, and the results are shown in FIGS. 7 (a) and 7 (b), respectively. The measured results are shown in FIGS. 8 (a) and 8 (b), respectively. As is clear from FIG. 7, both flow velocity fluctuation measurement results are in good agreement, but the power spectra are in good agreement in the low and middle frequency regions, but appear in the vicinity of 2.0 Hz by the probe of the present invention. The peaks in the high frequency region are not significantly shown by the hot film velocimeter, and while the probe of the present invention provides a sufficient level of electric output, the hot film velocimeter has a weak electric output. Therefore, the signal-to-noise ratio deteriorates, and it is considered that the difference is the result of the error in the measurement in the high frequency region. From the above comparison results, it is apparent that the probe for flow velocity measurement of the present invention has the required frequency response characteristic required for flow velocity measurement in the indoor water channel.

On the other hand, a comparison with a CM-2 type electric anemometer, which has been commonly used in the past, that is, an anemometer that indicates the power generation output based on the rotation by the flow of a propeller located in the fluid as the velocity value is measured in a real river. As for the result,
Using the probe of the present invention and the CM-2 type electric velocimeter, the results of measuring the flow velocity fluctuation in the low flow velocity region at the same time for the same fluid are shown in FIGS. 9 (a) and 9 (b), respectively. Fig. 10 (a) shows the result of measuring the power spectrum of
And (b) respectively, and the results of measurement of flow velocity fluctuations in the high flow velocity region are shown in Fig. 11 (a) and (b), respectively, and the result of measurement of the power spectrum in the high flow velocity region is also shown in Fig. 11 (a) and (b). It is shown in FIGS. 12 (a) and 12 (b), respectively.

In addition, describing the preparation conditions of FIGS. 8, 10, and 12, FIGS. 8, 10, and 12 are spectrum diagrams of FIG. 7, FIG. 9, and FIG. 11, respectively. .

FIG. 7 shows a hot film anemometer and the present invention in which a uniform flow flowing through a water channel is given a surface wave with an irregular small amplitude to create a flow including turbulence (however, no backflow occurs). 1 cm
These are the results of measurements that were placed separately in the flow and measured. It happens that the peak of the wave appeared in the spectrum because the wave component also included a wave with a period of 2 seconds.

9A and 9B are measured in an actual river with a gentle flow, where FIG. 9A shows the measurement result according to the present invention, and FIG. 9B shows the measurement result by the propeller anemometer (CM-2). Comparing those spectrum diagrams (a) and (b) of FIG.
-It can be seen that turbulence with a frequency much higher than that of the -2 anemometer can be measured. Further, the slope (-5) of the spectral gradient (-5/3), which is a general property of turbulence, can also be found for (a), and it can be seen that the present invention has performance as a turbulence measuring instrument.

Fig. 11 shows the result of the same measurement as Fig. 9 in an actual river with a rather fast flow. In this case, since the flow is fast, the amplitude of turbulence is large, and turbulence of high frequency is also included. Also in this case, the result (a) according to the present invention can measure a higher frequency than the result (b) by the CM-2, and the gradient of -5/3, which is common to the spectrum of turbulence, is clarified. You can see that it is done.

From the above results, the present invention has the same measurement accuracy as the hot film anemometer (currently said to have the highest accuracy).
It can be said that it has significantly higher accuracy than the conventional measuring instruments described above for field observation.

To compare the respective measurement results, FIG. 9 (a),
The flow velocity fluctuations in the low flow velocity region shown in (b) are almost the same, but the power spectra in the low flow velocity region shown in FIGS. 10 (a) and 10 (b) are not very common between the two. However, the attenuation of the latter is remarkable in the frequency range higher than 0.2 Hz. On the other hand, the flow velocity fluctuations in the high flow velocity region shown in FIGS. 11 (a) and 11 (b) are almost the same, but in the high flow velocity region shown in FIGS. 12 (a) and 12 (b). Regarding the power spectrum, all the peaks present in the latter are present in the former, but the peaks in the high frequency region of 0.5 Hz or higher present in the former do not appear in the latter, and the spectrum of the latter in the high frequency region is It shows a sharp decrease. The former, that is, the measurement result by the probe of the present invention, shows that the level does not decrease up to around 1 Hz, and that the power spectrum is close to the theoretical −5/3 power law.

From the above results, it is recognized that the CM-2 type electric velocity meter cannot follow the short period velocity fluctuation due to the rotation of the propeller or the like, whereas the probe of the present invention covers a wide frequency range. It is clear that accurate flow velocity measurements can be made.

According to the result of measuring the flow velocity profile in the actual river by sequentially changing the installation depth of the probe for measuring the current velocity of the present invention, the characteristics of the flow field in the actual river can be grasped almost faithfully by the probe of the present invention. Recognized as something.
That is, the conventional anemometer is difficult to catch the short-term velocity fluctuation, and there is a considerable limit to the elucidation of the periodic characteristics of the river turbulence, whereas the present velocity probe It was possible to confirm the existence from a short cycle of about 0.4 seconds to a long cycle velocity fluctuation of several tens of seconds.

(Effects of the Invention) As is apparent from the above description, according to the present invention, the flow velocity measuring probe for measuring the fluid flow velocity based on the Doppler effect by the laser light beam has a significantly simpler structure than the conventional one. It can be easily manufactured without requiring precise adjustment of the mounting position of each component as in the past, and it is widely used for measuring fluid flow velocity in indoor waterways and actual rivers. A particular effect is obtained in that the measurement of the fluid flow velocity over the frequency range and the measurement of the flow velocity fluctuation over a wide period range can be performed extremely faithfully.

[Brief description of drawings]

FIG. 1 is a diagram schematically showing a configuration example of a probe for measuring a flow velocity of the present invention, and FIG. 2 is a diagram schematically showing a configuration example of a focusing optical system in the light transmission probe, and FIG. Is also a diagram schematically showing an example of the constitution of the split refracting optical system in the light transmission probe, FIG. 4 is a diagram schematically showing the principle of fluid velocity measurement based on the Doppler effect, and FIG. FIG. 7 is a diagram schematically showing a mode of fluid velocity measurement based on the Doppler effect by the invention probe, FIG. 6 is a diagram schematically showing an example of the overall configuration of a fluid velocity measurement system using the probe of the invention, FIG. (A) and (b) are characteristic curve diagrams showing the measurement results of the flow velocity fluctuation by the probe of the present invention and the conventional hot film anemometer, respectively, and FIGS. 8 (a) and (b) show the measurement results of the power spectrum thereof. Characteristic curves shown in Fig. 9 (a) And (b) are characteristic curve diagrams showing measurement results of flow velocity fluctuations in a low frequency range by the probe of the present invention and a conventional CM-2 type flow velocity measuring device, respectively, and FIGS. 11 (a) and 11 (b) are characteristic curve diagrams showing the measurement results of the power spectrum of the high frequency region, respectively, and FIG. 11 (a) and 11 (b) are the characteristic curve diagrams showing the measurement results of the flow velocity fluctuation in the high frequency region, respectively. Similarly, (b) is a characteristic curve showing the measurement result of the power spectrum in the high frequency region, and FIG. 13 is an operation explanatory diagram. 1 ... Power supply voltage, 2 ... Semiconductor laser element 3,6 ... Lens system, 4 ... Half mirror 5 ... Mirror, 7 ... Optical mask 8 ... Photoelectric conversion element, 9, 11 ... Convex lens 10 ... … Spherical lens 20 …… Fluid, 21 …… Laser light source power supply 22 …… Power supply voltage, 23 …… Optical transmission probe 24 …… Receiving probe, 25 …… Electrical signal 26 …… Amplifier, 27 …… Band filter 28 …… Frequency-voltage converter 29 …… Computer

Claims (1)

[Claims] 1. A semiconductor laser device, a spherical lens, and a spherical convex lens that surrounds and surrounds the spherical lens in front of and behind the spherical lens, respectively, and focuses laser light emitted from the semiconductor laser device to form a laser light beam. A focusing optical system and a half mirror and a mirror that are parallel to each other and are formed on both sides of a transparent plate that is inclined with respect to the optical axis of the laser light beam, and divide the laser light beam and refract it at substantially right angles. Split refracting optical system for forming a pair of parallel laser light beams having mutually different intensities, a condensing optical system for converging the pair of parallel laser light beams at a flow velocity measurement point and crossing each other, and the parallel laser light beam Light that receives the laser light beam that has passed through the flow velocity measurement point and is located on the axis of the weaker laser light beam A probe for flow velocity measurement, comprising an electric conversion element, and configured so that the flow velocity of the fluid at the flow velocity measurement point can be measured by the Doppler effect of the laser light beam that has passed through the flow velocity measurement point.