JPH0755827A - Current meter - Google Patents

Abstract

PURPOSE:To provide a small current meter excellent in mobility and portability by which the current can be measured accurately and easily. CONSTITUTION:A laser beam emitted from a laser light source 11 is split into two and one of them is further split into two to produce three laser beams 15a, 15b, 15c which are condensed substantially linearly, at a predetermined interval, within a measuring region 4 by means of an optical system comprising spectrometers 13a, 13b, a reflector 14, a lens 16, etc. The current meter also comprises a photoelectric conversion element 18 for receiving the light scattered on microparticles 6 contained in a fluid 5 to be measured flowing through the vicinity of each focus of three laser beams in the measuring region 4, and a signal processing circuit 19 for detecting a normal signal based on the sequence and time interval of output pulses from the photoelectric conversion element 18 and determining the velocity of the fluid 5 based on the time interval of pulse and the distance between focuses of laser beams.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a velocity meter constructed to measure the flow velocity of a fluid to be measured by measuring the velocity of fine particles in the fluid to be measured using laser light.

[0002]

2. Description of the Related Art Conventionally, a Pitot tube, a hot-wire anemometer or the like has been used as a means for measuring a flow velocity, and recently, a laser anemometer using a gas laser or a semiconductor laser as a light source has been developed.

A conventional anemometer utilizing such laser light is shown in FIG. This anemometer has a gas laser 1 that oscillates a laser beam, and the laser beam from this gas laser 1 is split by a beam splitter 2 into two parallel laser beams. The laser light from the beam splitter 2 is condensed by the focus lens 3 and forms interference fringes in the measurement area 4. The direction of the scattered light reflected from the fine particles 6 contained in the fluid to be measured 5 flowing in the measurement region 4 is changed by the mirror 7, and this scattered light is condensed by the lens 8 and the condensed scattering is carried out. The light is received by the photomultiplier tube 9 and outputs an electric signal according to the scattered light. The output of the photomultiplier tube 9 is calculated by the signal processing unit 10.

The conventional anemometer constructed in this way is divided into two beams of equal intensity and the same phase by the beam splitter 2.
An interference fringe is formed in the measurement area 4 by the two laser beams. By flowing the fluid to be measured 5 into the measurement area 4, the fine particles 6 existing in the fluid to be measured 5 also pass through the measurement area 4, that is, the interference fringes at the same speed. When passing through the interference fringes, the fine particles 6 emit scattered light that changes in intensity depending on the interference fringes. The scattered light is condensed on the photomultiplier tube 9 through the lens 8. Then, the photomultiplier tube 9 outputs a signal corresponding to the scattered light that changes strongly, that is, a Doppler signal to the signal processing unit 10. In the signal processing unit 10, the velocity of the fine particles 6 is calculated based on the known interval of interference fringes and the time of the Doppler signal. Since the calculated velocity is also the flow velocity of the fluid to be measured 5 that flows at the same velocity as the fine particles 6, by arranging the measurement region 4 in advance so that the interference fringes are perpendicular to the flow direction of the fluid to be measured 5, The flow velocity of the measurement fluid 5 can be measured.

Since the optical system of the conventional laser Doppler velocimeter as described above is of the backscattering type, the amount of light received and emitted by the photomultiplier tube 9 is 1/100 of the amount of light of the commonly used forward scattering type. It is the following. Therefore, an argon ion laser having a large output is used, the entire apparatus becomes large, the mobility of the measurement is poor, and the portability is poor.

In order to solve such a problem, it is considered to use a small red semiconductor laser in place of the gas laser 1 and a small semiconductor light receiving element such as an avalanche photodiode in place of the photomultiplier tube 9. . However, the output of the red semiconductor laser is much lower than that of the gas laser 1, and the amplification factor of the avalanche photodiode is 1/1000 or less of that of the photomultiplier tube 9. Therefore, as the current laser Doppler velocimeter, It does not work and cannot be realized as it is.

[0007]

As described above, the conventional laser Doppler velocimeter uses an argon ion laser having a large output in order to obtain a large output, and the entire apparatus becomes large, resulting in poor measurement mobility. However, there is a problem that it is not portable.

In order to solve such a problem, use of a small red semiconductor laser and a small semiconductor light receiving element, such as an avalanche photodiode, has been considered, but the red semiconductor laser outputs as compared with a gas laser. Is extremely low, and the amplification factor of the avalanche photodiode is less than 1/1000 of that of the photomultiplier tube 9, so it does not operate as the current laser Doppler anemometer.
It cannot be realized as it is.

The present invention has been made in view of the above situation, and its object is to obtain a large amount of reflected light, to be small in size, to be excellent in maneuverability and portability for measurement, and to accurately measure a flow velocity. The object is to provide a velocity meter that is simple and easy to perform.

[0010]

A velocity meter according to the present invention comprises a laser light source and a laser beam emitted from the laser light source.
An optical system that splits the three laser beams obtained by splitting one of the laser beams into two, and linearly focuses the laser beams in the measurement region at a predetermined interval, and the optical system that converges the laser beams in the measurement region. One of the light receiving elements for receiving scattered light sequentially scattered from the fluid to be measured passing near each focus of one laser beam, the output sequence of each output pulse from this light receiving element, and the time interval of the pulses It is characterized by further comprising: arithmetic means for detecting what is determined as a signal and for obtaining the flow velocity of the fluid to be measured based on the time interval of the pulse and the focal length of the laser light.

[0011]

According to the anemometer constructed as described above, the laser beam from the laser light source is focused on the three focal points forming the measurement area, and thus the laser doppler anemometer forming the interference fringes is formed. A large amount of light can be received, and an S / N ratio sufficient for signal processing can be obtained. In addition, since the amount of light is sufficient to use a semiconductor element for both the laser light source and the light receiving element, the anemometer can be configured in a small size, which increases maneuverability and facilitates setting for measurement. In addition to simple and easy measurement, it has a long service life and easy maintenance.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the velocity meter of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram according to an embodiment of a velocity meter of the present invention, and the same or corresponding portions as those of the conventional FIG.

In FIG. 1, the velocity meter of the present invention has, for example, a red semiconductor laser 11 as a laser light source, and this semiconductor laser 11 is driven by a power source (not shown). A collimator lens 12 is provided on the optical axis of the laser 11, and the collimator lens 12 reduces the divergence angle of the laser light to form parallel laser light. A first spectroscope 13a and a second spectroscope 13a are provided on the output side of the collimator lens 12.
A spectroscope 13b and a reflecting mirror 14 are provided, and the laser light from the laser light source 11 is divided into three divided lights 15a and 1a.
It is divided into 5b and 15c, and the light amount ratio thereof is approximately 2: 1: 1.

On the output side of the first spectroscope 13a, the second spectroscope 13b, and the reflecting mirror 14, the lens 1 for converging three laser beams into the measurement area 4 as three focal points.
6, the focal points of the split lights 15a, 15b, and 15c are arranged in a substantially straight line at equal intervals in the measurement area 4, and then expanded again. By flowing the fluid to be measured 5 into the measurement area 4, the fine particles 6 present in the fluid to be measured 5 are also measured at the same speed in the measurement area 4,
That is, it passes through the three focal points. When the fine particles 6 sequentially pass through the three focal points, the laser light is scattered,
This scattered light becomes parallel light by the lens 16, and this parallel light is condensed by the lens 17 and converted into an electric signal by the photoelectric conversion element 18. As the photoelectric conversion element 18, for example, a semiconductor light receiving element can be used.

The output of the photoelectric conversion element 18 is 3 particles.
Since the laser light is scattered light when passing through respective focal portions, it has a pulse-like waveform having three peaks as shown in FIG. The signal processing unit 19 measures the pulse time interval, and divides the inter-focal distance by this time interval only when a regular signal is input to obtain the flow velocity of the fluid to be measured.

Next, a method of determining whether the signal is a regular signal in the signal processing section 19 will be described. Photoelectric conversion element 1
The output from 8 is evenly spaced in time as shown in FIG. 3 when one fine particle 6 sequentially passes through the three focal points of the measurement region 4, and the magnitude of the output is equal to the divided light quantity ratio 2. :
It corresponds to 1: 1. On the other hand, when a plurality of fine particles 6 pass through the measurement region 4 at the same time, or when the fine particles 6 pass through the measurement region 4 obliquely and pass through only two of the three focal points or only one focal point. For example, as shown in FIG. 4, the output pulses of the photoelectric conversion element 18 are not evenly spaced in time. The signal processing unit 19 discriminates both by measuring the magnitude and time interval of the output pulse,
The flow velocity is calculated as a normal signal only when one particle 6 sequentially passes through the three focal points of the measurement area 4.

Next, an example of a specific discriminating method will be described with reference to FIG. FIG. 5 is a block diagram showing the functions of the signal processing unit 19. The output of the photoelectric conversion element 18 is the comparator 2
0a is input to the comparator 20b. The comparator 20a compares it with the reference voltage from the reference voltage signal generation circuit 21, and the comparator 20b generates a reference voltage that is ½ of the reference voltage 21 and the ½ reference voltage from the ½ reference voltage signal generation circuit 22. The timing circuit 23 compares the voltage with a predetermined voltage while the voltage is higher than a predetermined voltage.
Outputs a square wave to. The timing circuit 23 temporarily clears the timer 24 with the rectangular wave from the comparator 20a and starts time measurement.

Next, the time data of the timer 24 is held in the memory 25 by the first rectangular wave from the comparator 20b, and the timer 24 is cleared again to start the second time measurement. Further, the comparison unit 26 compares the second time data of the timer 24 with the first time data held in the memory 25 by the second rectangular wave from the comparator 20b. The time data held in the memory 25 as being measured is input to the speed calculator 27 to calculate the speed.

In this way, the timing circuit 23 determines whether the output from the comparator is sequentially output,
The timer 24, the memory 25, and the comparison unit 26 determine whether or not the output pulses are at equal intervals in combination with the timing circuit 23. By both of the determination functions, it is determined whether the light received by the photoelectric conversion element 18 is the regular scattered light from the fine particles 6. In the above embodiment in which the laser light is focused at equal intervals, it is determined whether the output pulses are at equal intervals. However, the laser light is set at any given interval even if it is not at equal intervals. May be determined.

When comparing both time data in the comparison unit 26, in order to have a range of time difference in which they are equal to each other, for example, if the time data is 12 bits, only the upper 8 bits are compared, and the lower 8 bits are compared. By ignoring the 4 bits of, it can be judged as normal when the deviation is within ± 0.4%.

As described above, in the signal processing unit 19, the rectangular wave from the comparator 20a is input, and then the comparator 2
Only when two rectangular waves from 0b are continuously input at equal intervals, the flow velocity is calculated as being determined to be normal. On the other hand, when the rectangular wave from the comparator 20a is continuous, when only one output from the comparator 20b is output, or when three or more are continuous, the signal is truncated as an error signal.

When the flow direction of the fine particles 6 in the measurement region 4 is opposite to the above description, the output pulse of the photoelectric conversion element 18 is also opposite to the above description, and therefore it can be comprehensively determined. If so, the mobility is further improved.

As described above, according to the above-described embodiment, the laser beam from the semiconductor laser is focused on the three focal points forming the measurement area to form interference fringes for measurement. The amount of reflected light is larger than that of a velocity meter, and an S / N ratio sufficient for signal processing can be obtained. In addition, since a semiconductor laser can be used as a light source and a semiconductor light receiving element can be used for a photoelectric conversion element, the device can be downsized, the mobility of the measurement can be improved, and the setting for the measurement can be facilitated. Makes maintenance easier. Furthermore, since the measurement of the flow velocity is performed by one particle passing through the measurement area,
It is possible to measure the flow velocity at that moment rather than the average flow velocity for a certain period of time, and it is possible to detect a change in flow velocity in a short time. In addition,
The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the scope of the invention.

[0024]

As described in detail above, according to the present invention, a sufficiently large amount of light can be received by the light receiving element, so that an S / N ratio sufficient for signal processing can be obtained. Therefore, the semiconductor laser and the semiconductor light receiving element can be used for the light source and the light receiving element, and they are small and have excellent measurement mobility and portability,
It is possible to provide a flow velocity meter that can easily and easily perform accurate flow velocity measurement.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment of a measurement system of a velocity meter according to the present invention.

FIG. 2 is a schematic diagram showing a state of laser light in a measurement region of the anemometer of the present invention.

FIG. 3 is an output waveform diagram when the light receiving element is irradiated with normal scattered light in the anemometer of the present invention.

FIG. 4 is an output waveform diagram showing an example when the light receiving element is irradiated with abnormal scattered light in the anemometer of the present invention.

FIG. 5 is a schematic configuration diagram showing a function of a signal processing unit of the velocity meter of the present invention.

FIG. 6 is a schematic configuration diagram showing a conventional anemometer.

[Explanation of symbols]

 4 measurement area 5 fluid to be measured 6 fine particles 11 semiconductor laser (light source) 12 collimator lens 13 spectroscope (optical system) 14 reflecting mirror (optical system) 18 photoelectric conversion element (light receiving element) 19 signal processing unit (arithmetic means)

Claims (1)

[Claims] 1. A laser light source and a laser light emitted from the laser light source are divided into two, and one of the laser light is further divided into two, and three laser lights obtained are predetermined substantially linearly in a measurement region. An optical system for collecting light at intervals, a light receiving element for receiving scattered light scattered from a fluid to be measured passing near each focus of the three laser lights collected in the measurement region, and What is judged to be a normal signal is detected from the output sequence of each output pulse from the light receiving element and the time interval of the pulse, and the object is detected based on the time interval of the pulse and the focal length of the laser light. An anemometer which is provided with a calculating means for obtaining a flow velocity of a measurement fluid.