JPS60249063A - Laser-doppler anemometer - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed description of the invention [Industrial field of application] The present invention provides a laser light source, a polarizing optical device for at least two partial beams, and a polarizing optical device for focusing at least one of the partial beams onto a measured object. Laser-Doppler-Anemometer for measuring the speed of a moving object, which has a focusing optical device and a detector for scattered light emitted by the moving object.
[Prior art] Laser Doppler anemometers of this type are known, and their measurement principle is based on those of Durst, M.
eiling), White o-(Wh ite
``Principles and Practical of Laser Drabler Wind Speed Measurement'' (Law)
e of La5er-Dopplsr-Anemo
metery) 2nd edition, Academic Zoology L/2 (Ac
academic Pre8@), 1981.

In known Rede-Doppler anemometers, the light beam of a gas laser is split into two partial beams. In the crossed ray method, two partial rays are directed into the flowing medium at different angles, with the
Generates an imaginary interference pattern in the measurement area. Light rays passing directly through the measurement zone are blocked, while light rays scattered from the measurement zone in the direction of the pond are detected by a photomultiplier tube. Since the frequency of the scattered light is related to the speed of the moving object, it is possible to measure the flow velocity.

In the reference ray method, only one partial ray passes through the measurement area. The scattered partial rays are caused to interfere with the reference ray.

This anemometric method has the advantage that it can be applied for practical purposes to moving objects to be measured, for example consisting of flowing media or moving surfaces, without any repercussions. It is sufficient that the moving object to be measured contains light scattering particles.

The particles may be added to the gas or liquid stream prior to measurement.

The drawbacks of conventional wind speed measurement methods are generally as follows. In other words, the structure using gas radar is quite bulky and heavy. In that case, if the deflection optical device is fixed,
Since the laser has to be displaced in order to align the partial beams with the measurement field, expensive laser displacement devices are required. The same applies to the optical device for receiving light.

[Problem that the invention seeks to solve]

The object of the invention is to create a Rede-Doppler anemometer of the type mentioned at the outset, which can be constructed compactly in a small space and which opens up the possibility of complementary applications.

[Means, actions, and effects for solving the problems] Based on the present invention, at least one laser diode is used as a laser light source, and the temperature thereof can be adjusted and kept constant by a temperature control circuit. The above two objectives can be achieved.

In the structure according to the invention, radar diodes are used for the first time in wind speed measurements. The above-mentioned use is possible because the temperature control circuit can maintain the temperature of the laser diode constant. The output frequency of a Raded diode is strongly influenced by the temperature of the Raded diode. In the structure of the anemometer according to the invention, a stable laser frequency suitable for the measurement purpose is obtained by controlling the temperature of the radar diode. The structure according to the invention provides another advantage in that the output frequency of the laser light source is adjustable. This is done according to the invention by a temperature control circuit. By means of a temperature control circuit, the temperature of the laser diode can not only be maintained at a predetermined value, but can also be adjusted to another value, thereby changing the laser frequency.

In order to measure multiple velocity components of a moving object, multiple wind velocity measurement systems simultaneously send partial beams to the object.
Particular benefits are obtained with K as described above in the case of structures in which the scattered light has to be separated from each other again.

In a mechanically particularly advantageous embodiment, the laser diode is mounted on a mount HC, in which a temperature sensor and a current-controlled cold-generating element, preferably a Vertier element, are integrated.

Laser diodes provide simple measurements if they are selected to operate in a single mode manner. In this case, a coherent wavelength is always sufficient to generate the required interference pattern.

The use of a laser diode as a laser light source according to the invention makes it possible to generate the operating current of the laser diode by means of a frequency-controlled modulated oscillator. This design offers the advantage that the measurement frequency can be displaced by the modulation frequency, so that detection can be carried out in the same frequency band for all measurement frequencies and flow rates. This eliminates the need for the use of switchable filters, which were previously required for interference removal.

In a preferred design, due to the small dimensions of the laser diode, the laser diode is placed outside the optical axis, deflecting the light passing diagonally through the measurement field and repassing it at a different angle. By doing so, it is possible to measure the velocity component in the optical axis. In that case, detection can simply be carried out in the direction of the axis to the light. Three laser light sources are provided, two of which are conventionally arranged on the optical axis, the partial beams of which are generated, for example, in a plane rotated by 90° with respect to each other, and the third laser light source is arranged parallel to the optical axis. If arranged outside the optical axis for the measurement of the velocity components, the aforementioned arrangement can perform the measurement of the three velocity components in conjunction with the conventional arrangement for the measurement of the velocity components. In that case, the two laser light sources arranged on the optical wall axis emit at different wavelengths.

Due to the compact arrangement possible according to the invention, the velocities of the two ponds can be measured by constructing a conventional wind speed measuring system with a nine-point axis running obliquely to the optical axis of the laser light source of the two ponds. It is also possible to measure a third velocity component oblique to the component.

As a highly advantageous refinement of the invention, one
Dual laser diodes emitting in 80° opposite directions are used as a radar light source. In this case, a beam splitting device required to split the light from the laser light source into two partial beams is not required, so the fabrication of the structure is It becomes even more compact and simple.

〔Example〕

Next, the present invention will be described in detail based on embodiments shown in the drawings.

In the basic arrangement shown in FIG. 1, the diverging laser beam 16 emerging from the laser diode 1 is focused by a microscope objective or condensing lens 5 and transmitted via a beam splitting device 7 into two parallel beams of equal intensity. It is divided into divided beams a12 and 18.

The split beams 17.degree. 18 are focused by a lens 8 onto a focal point 15. The focal point 15 is the measurement area of the laser drabler anemometer. Measurement area 1 without scattering within split beam 17°18
5 is captured by an optical transformer f (light receiver) 19. Scattered light 20 exiting from the measurement area 15 in the general direction of the optical axis passes through a lens 9 and an aperture 1o and is guided to a photomultiplier tube 1o.

Astigmatism in the beam 16 emerging from the laser diode 1 can be removed by means of a pair of anamorphic prisms 6, if necessary. Alternatively, a crossed cylindrical lens system can be used to obtain anamorphic imaging.

Laser diode 11 is attached to mount 2,
On the other hand, a Bertier element 3 is fixedly mounted on the mount 2. The heat generated by the Beltier element 3 is cooled by the cooling body 4. The temperature control circuit 12 connects the mount 2 and the covered element 3.
is combined with W to provide accurate temperature stabilization and thereby stabilization of the laser diode 10 wavelengths. Since the target temperature value can be set by the temperature control circuit 12, the wavelength of the laser diode I can be tuned. This is because the emitted wavelength is dependent on the temperature of the laser diode 1. The operating current supplied to the laser diode is controlled by a constant current control circuit 13.
and the matching circuit 14 of the laser diode 1
sent to m. In this way, the optical output of the radar diode 1 can be adjusted continuously.

The modulation oscillator 14 is combined with a matching circuit 14m to perform current modulation around the operating point specified by the current control circuit 13, thereby modulating the frequency and intensity of the radar light in the low frequency range and high frequency range. I can do it. This intensity modulation of the laser light causes frequency mixing of the Doppler frequency, which is a measure of the flow velocity, with the frequency of the modulating oscillator 14 in the photomultiplier tube 11 . In this way, a new method for controlling the frequency shift of the door shutter signal is established. This could not be achieved with gas lasers.

Measuring area 15 with a symmetrical intensity distribution that is approximately mouse-shaped
In order to obtain , it is advantageous if the radar diode 1 emits in only one transverse mode.

If you choose a Raded diode with a beam divergence ratio of less than 1:3, it will be anamorphic, f 17, for most applications in flow technology.
It becomes unnecessary to reduce astigmatism due to zoom 6 and other factors.

When using a laser diode 1 that emits in several longitudinal modes, the beam splitting armor 7 used must be path compensated in order to generate coherent partial beams 17.18. Raded diode 1 with only one longitudinal mode
Since this method does not require a beam splitter 7 with optical path compensation and can obtain a large coherent distance of 8 m or more, it is particularly suitable for measuring velocity components along the optical axis, as will be explained in detail with reference to FIG.

For the measurement of the velocity component u3 in the optical axis, a radar diode 1 is arranged outside the optical axis. Laser light 16 passes through the edge area of lens 8 and is focused onto measurement area 15 . The receiver lens 9 directs the light beam parallel to the optical axis again, then it is deflected by 90° each by two prisms 21 and refocused by the receiver lens 9 onto the measurement area 15 . The light beam is lens 8
After passing through, it is blocked by a light drag (light receiver) 19. Detection of scattered light is performed on the optical axis and is not shown in FIG. The structure shown in FIG. 2 can only be realized under extremely difficult conditions using a conventional gas laser. This is because gas lasers usually have a very small coherence distance. By using a laser diode 1 with only one longitudinal mode, a large coherence distance and high optical power are obtained.

FIG. 3 shows the structure for the measurement of three mutually orthogonal velocity components ul+u2 and u3. For this purpose, two laser diodes 1a and 1b are arranged on the optical axis. Laser beams 16& and 16c are separated by beam splitters 7& and 7bK which are rotated by 90 degrees to form a pair of orthogonal parallel beams.
It is divided into partial rays (split rays) of equal intensity. These partial rays are focused by a lens 8 onto a measurement area 15;
After passing through the measurement area 15, it is blocked by the optical transducer 7''19.The velocity components ul and u2, which are orthogonal to each other and perpendicular to the optical axis, can be measured with these beams.

For the measurement of the velocity component u3 located on the optical axis, the arrangement described on the basis of FIG. 2 is used. That is, the radar diode 1c is located outside the optical axis.

Detection of scattered light leaving the measurement area 15 is performed as follows.

a) Similar to the detection method shown in FIG. 1, a lens 9 and a photoelectric detector 11h located on the optical axis for the wavelength of the laser diode 1b are used; b) the scattered light is focused by the lens 9a, and the mirror at any angle to the optical axis by deflecting at 23h and 23b.

A color division is performed by a division device 24, whereby V
- The lights of different frequencies of the dediode 1a and the IC are separated from each other. These light components are detected by photodetectors 11b and 11cK.

C) Scattered light in opposite directions on the optical axis is focused by lens 8 and deflected by mirrors 25h and 25bK. Subsequently, after being focused by the lens 9b'', the wavelengths transmitted by the laser diode 1a and the IC are divided into colors by the dividing device 24h.

These wavelengths are identified by photodetectors 11d and Ile.

FIG. 4 shows an embodiment in which a third velocity component u3, which is not perpendicular to the velocity components u1 and U, is measured.

The arrangement of the laser diodes 1a and 1b and the beam splitters 7 & 7b on the optical axis is the same as in FIG. 3.

Third 1-node diode IC' and beam splitter 7 c
The optical axis for ' is aligned perpendicular to the third velocity component u3. Lens 81 focuses the partial beam onto measurement area 15 . The light receiving lens 9e/ focuses the scattered light, and the scattered light passes through the aperture 10 and reaches the photoelectric detector 11C', but the non-scattered light is blocked by the optical trap 19. The optical axes of the laser diodes 1 and 1b make an angle r smaller than 90° with the optical axis of the laser diode 1c.

FIG. 5 shows an anemometer similar in construction to that of FIG. 1, but with the laser diode 1 replaced by a double radar diode 1'. The dual laser diodes 1' emit in directions rotated by 180° relative to each other. This eliminates the need for the beam splitter 7. This is because two appropriate partial beams 17, 18 are already emitted from the double radar diode 1'. Each of these partial rays passes through a condenser lens 28 and is guided to a lens 8 by a 90° deflection grism 27.
The lens 8 focuses the partial beams 17° 18 onto the measurement area 15. The structure of the pond is similar to that shown in Figure 1. Accordingly, like parts have been given the same reference numerals.

FIG. 6 shows a double laser in which the two partial beams 17, 18 are respectively passed through a condenser lens 28, and the condenser lens 28 and the deflection mirror 29 jointly focus the partial beam 17.18 into the measurement area 151/C. A modified embodiment with a diode 1' is shown.

FIG. 7 shows another arrangement of a laser Doppler anemometer with a double V-the diode 1' for measuring the movement of the surface 30 by the reference beam method. The two diverging partial rays 17, 113 are again deflected parallel by a condenser lens 28. Partial ray 77 then passes through focusing lens 8 . Lens 8 focuses partial beam 17 onto surface 30 . At that time, the semi-transmission fi13 of the partial ray Fi45°
Pass through 1. The semi-transparent mirror 31 passes the light reflected by the moving surface 30 to the photomultiplier tube 1 through the light receiving lens 9 and the aperture 10.
Lead to 1. The scattered light passes through a semi-transparent mirror 32 before the aperture 1o. The second partial ray 18 is formed by two 45° inclined mirrors 33.
The reference beam 18 is directed by a total of 180° (directed by the lens 34 and focused on the photomultiplier tube 11. Since the reference beam 18 is coupled to the measurement beam through the semi-transmissive mirror 32, an interference pattern appears on the photomultiplier tube 1). occurs. Since the scattered waves are generated approximately spherically, the measurement device must use a small aperture in order to obtain a coherent beam.

The construction according to the invention of a laser light source with a laser diode 1.1', In, lb, lc can be added to existing gas sensor-type anemometers designed for the examination of one velocity component, e.g. According to FIG. 3, it is possible to additionally equip two Raded diode anemometers for checking the three velocity components "1+" 2tu3, in which case the Raded light source 1 m may remain as a gas Raded.

According to the invention, therefore, existing gas Rade anemometers can be expanded without significant spatial enlargement for the examination of the three velocity components with Raded diode Rade Doppler anemometers.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram of the structure of a laser Doppler anemometer based on the present invention, in which a laser diode is used as a laser light source and is arranged on the optical axis. Fig. 2 shows a laser diode installed in the optical axis to measure the velocity component. Schematic diagram of the optical path with external pressure on the optical axis, 3rd
The figure is a three-dimensional schematic diagram of an array for testing velocity components perpendicular to each other, Figure 4 is a schematic diagram of an array for measuring velocity components perpendicular to the optical axis and velocity components oblique to the optical axis, and Figure 5 is a schematic diagram of an array for measuring velocity components perpendicular to the optical axis and oblique to the optical axis. 6 is a schematic diagram of an arrangement similar to that of FIG. 1 of "Laser Drabler Wind Velocity" with dual laser diodes as the laser light source; FIG. 6 is a schematic diagram of an arrangement similar to that of FIG. Schematic representation of a variant of the array. FIG. 7 shows a diagrammatic representation of an array of a laser Doppler anemometer according to the invention with dual laser diodes, implementing the reference beam method for the measurement of the velocity of a moving surface. 1.1a, 1b11c...Laser diode, 8.8
'...Condensing lens, 9.9', 9&, 9b. 9 e... Light receiving lens, 11.11*, Ilb. 11c, llc', lld, 11e...photoelectric detector (
photomultiplier tube), 12... temperature control circuit, 15... object to be measured (measurement area), 16, 16 a, 16 b
- Laser light, 17.18... Partial beam (divided beam) 1
9... Light trap (light receiver), 20... Scattered light, 2
4.248...Dividing device, 30...Surface. Applicant's representative Patent attorney Takehiko Suzue, hR/(Director of the Office, Gakudono Shiga), Indication of the case, Patent Application No. 1983-033646, No. 2, Invention name, Laser Tonoshira, Mistake 3 Supplementary market Relationship with the patent applicant case of the Federal Republic of Germany 4, Agent 7, Contents of extraction Follow the attached document

Claims (1)

[Claims] 1) A laser light source (1) and at least two partial beams (
77, 18) and partial beams (17
, 18) as the object to be measured (J5.J(7)
a light condensing optical device (8) for focusing the light on the object, and a detector (1) for the scattered light sent out from the moving object to be measured (15°30).
)) in a laser Doppler anemometer for speed measurement of a moving object to be measured (IS, 30), at least one laser diode (V,
1 a , 1 b , 1 c ), the temperature of which is adjustable via a temperature control circuit (12);
The Wrede-Doppler anemometer is characterized by its ability to maintain constant speed. 2) Attach the L/-ff diode (7) to the T-mount (2), and install the temperature sensor and current-controlled cold heat generating element (
3) The laser Doppler anemometer according to claim 1, wherein the laser Doppler anemometer incorporates: 3) The laser Doppler anemometer according to claim 2, characterized in that a Zeltier element (3) of at least Jm is built into the mount for temperature control of the mount. 4) Laser Doppler anemometer according to any one of claims 1 to 3, characterized in that the Rade light source (1) operates in a single mode manner. 5) Laser Doppler anemometer according to any one of claims 1 to 4, characterized in that the operating current of the laser diode (1) is generated by a frequency-controlled modulation oscillator (14). 6) In order to measure the velocity component (u3) on the optical axis, a radar diode (1c) is placed outside the optical axis, and its light beam is deflected by the condenser lens (8) to the object to be measured. passing through the transparent measurement area (15) diagonally to the light-dark axis,
and through the edge of another condenser lens (9), thereby aligned parallel to the optical axis, and subsequently deflected twice to the opposite edge of another condenser lens and then to the optical axis. Detectors (11d, 11e) of the scattered light that pass obliquely to the measurement area (15) and are subsequently blocked and in the direction of the optical axis.
) is provided, The Rede ψ Dozzoller anemometer according to any one of claims 1 to 5. 7) Three V-the light sources (1a, Ib, 1
c) is provided, and two laser light sources (1a, J b
) form two partial rays running parallel to each other, and the plane connecting the partial rays of one laser light source (1a) is between the plane connecting the partial rays of the other laser light source (1b). Two radar light sources (La, Jb) sandwiching a corner emit laser beams (16m, 16b) of different wavelengths, and the detected scattered light components are divided into three velocity components (ul l ul +
”3), and the third LED light source (IC) and the two V-the light sources (1 m, 1 b
7. The laser Doppler anemometer according to any one of claims 1 to 6, characterized in that at least one of the elements (1) is a radar diode. 8) For the measurement of the velocity component (u3) located on the optical axis, a radar diode (IC) is arranged outside the optical storm axis, and its light beam is deflected by the condensing lens (8) to be measured. passing through a transparent measurement area (15) of the object obliquely to the optical axis;
and passes through the edge of another condenser lens (9), thereby aligned parallel to the optical axis, and is subsequently deflected twice to the opposite edge of another condenser lens and then to the light beam. A detector (Zfd, ll5) of the scattered light passes obliquely to the axis through the measuring region (15) and is subsequently blocked and in the direction of the optical axis.
) are provided, and three types of velocity components (ul + u2
Three laser light sources (la
, 1 b + I C), the light from the two laser light sources (1a, 1b) each forms two partial rays running parallel to each other, and the partial rays from one laser light source (1a) The connecting plane and the plane connecting the partial beams of the other laser light source (1b) sandwich an angle between the two V-za light sources (7a).
, 7b) emit laser beams (16h, 16b) of different wavelengths, and the detected scattered light components are divided into three velocity components ("I
The third laser light source (IC) and the two laser light sources (za
. Doppler anemometer. 9) The third laser light source (1c') and the associated detection system are
The Lehde Doppler anemometer according to claim 7, characterized in that it passes through the measurement area (15) obliquely with respect to the optical axes of the other two V-the light sources (1a, Jb). . 10) Any one of claims 1 to 9, characterized in that a double laser diode (1') emitting in 180° opposite directions on a common substrate is used as a laser light source. Laser Doppler anemometer described in Part 1 0