JP3053694B2 - Flow velocity measuring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flow velocity measuring device for detecting a velocity based on scattered light from fine particles.

[0002]

2. Description of the Related Art As a conventional light scattering type measuring apparatus, for example, as shown in JP-B-63-25285, two laser beams are irradiated so as to intersect in a measurement area, and the laser beams intersect. There is known an apparatus which forms an interference fringe in a measured area and measures the velocity and the diameter of the particle based on scattered light from fine particles passing through the measured area.

[0003]

However, in such a conventional measuring apparatus, not only is the configuration of the optical system complicated and large, but also it has directivity to particles and the speed of a specific directional component. However, there is a drawback that it can only be detected.

The present invention has been made in view of the above-mentioned problems of the conventional velocity measuring apparatus, and is small in size, non-contact, omnidirectional, and capable of measuring particle velocity regardless of particle direction. It is an object to provide a measuring device.

[0005]

SUMMARY OF THE INVENTION The present invention provides a clock oscillator for periodically oscillating a clock signal, a light source driven by a clock output of the clock oscillator to generate a light beam having a predetermined intensity distribution and beam diameter, and a light source. Optical means for converging the light beam in the measurement area, and the light beam and the light receiving axis of the scattered light intersect at a substantially right angle to collect the scattered light from particles passing through the measurement area, and the intensity distribution of the light source Light receiving means for converting an electric signal with the same sensitivity distribution as above, and a pulse train holding means for holding a pulse train of a predetermined number or more of scattered light levels from the output of the light receiving means periodically obtained in response to the clock of the clock oscillator. Based on the envelope waveform formed by the pulse train held by the pulse train holding means ,
An envelope estimating means for estimating a normalized envelope waveform with a constant peak, and an envelope estimated by the envelope estimating means.
Set a predetermined threshold for the normalized envelope waveform and
A time measuring means for measuring a time of exceeding the threshold level of the structured envelope waveform, and a speed converting means for converting the time measured by the time measuring means into speed information. .

[0006]

According to the present invention having the above features, the light source is periodically driven by the clock oscillator, and the light beam is focused on the measurement area by the optical means. If there are fine particles passing through the measurement area, the scattered light is received by the light receiving means. Therefore, while the light source is intermittently driven, a plurality of light receiving signals are obtained while passing through the measurement area, and the levels thereof are held by a predetermined number or more by the pulse train holding means. Then, based on the pulse train, an envelope waveform of the pulse wave with the peak value being a predetermined value is estimated from the intensity distribution of the light source and the sensitivity distribution of the light receiving means. Then, a predetermined threshold value is set for the estimated envelope signal, and the time during which the threshold value is exceeded is measured. In this way, it is possible to always treat the measurement area as having passed through the central portion even when passing through any point. Therefore, this time is converted into a speed signal corresponding to the measurement area and output.

[0007]

FIG. 1 is a block diagram showing the overall configuration of a flow velocity measuring apparatus according to one embodiment of the present invention. In FIG. 1, a clock oscillator 1 is an oscillator that periodically generates a pulse train, and is configured such that its cycle can be continuously changed by a frequency variable circuit 2 connected to the outside. This clock signal is provided to the LD drive circuit 3. The LD drive circuit 3 drives the laser diode 4 as a light source intermittently according to a clock frequency. The light beam generated by the laser diode 4 is converted into a parallel light beam by a collimator lens 5 and further focused by a focusing lens 6 to a predetermined beam diameter in a measurement area. Here, the collimator lens 5 and the focusing lens 6 constitute optical means for focusing the light beam of the light source on the measurement area.

A condenser lens 7 for condensing scattered light in a direction substantially perpendicular to the light beam is provided. Behind the condenser lens 7, a beam intensity correction element 8 is disposed, which maximizes the amount of transmission at the center of the light receiving axis and continuously reduces the amount of transmission around the center, and corrects the intensity of the received scattered light. You. Furthermore, a collimator lens 9 for collecting scattered light is provided behind the collimator lens. A light receiving element 10 is provided at the focal position of the collimator lens 9. Here, for ease of explanation, it is assumed that the light receiving element 10 receives a signal in the range through a minute aperture near the center, for example, and the sensitivity distribution is constant in the light receiving range. Condensing lens 7
The light receiving element 10 constitutes light receiving means for receiving scattered light with a predetermined sensitivity distribution (for example, Gaussian distribution).

The light receiving element 10 converts the scattered light into an electric signal corresponding to the level of the scattered light, and the output is supplied to an A / D converter 12 via an amplifier 11. A / D
The converter 12 is supplied with a sampling signal at the timing of the clock of the clock oscillator 1, and A / D-converts the output of the amplifier 11 at each timing.
The A / D conversion output is provided to the arithmetic processing unit 14 via the input interface 13. The arithmetic processing unit 14 includes a CPU, a ROM for storing its program, a RAM for temporarily storing data, and the like. The arithmetic processing unit 14 estimates the envelope by holding the continuously obtained pulse train, measures the time corresponding to the envelope, and converts the time into a speed. The output is provided to a display 15 for displaying speed information.

Next, the operation of this embodiment will be described with reference to waveform diagrams and flowcharts. When the operation is started, first, the clock oscillator 1 oscillates a clock signal at a cycle initially set by the frequency variable circuit 2, and the laser diode 4 is driven at that timing. Therefore, the light beam is focused at a predetermined period in the measurement area. When minute particles pass through this measurement area, scattered light is obtained on the light receiving element 10 via the condenser lens 7, the beam intensity correction element 8, and the collimator lens 9.

In the present invention, as shown in FIG.
The light projecting axis of the light beam 21 and the light receiving axis of the scattered light receiving range 22 are arranged so as to be substantially at right angles. Light beam 2
The right end of 1 shows the intensity distribution of the light beam, and the lower end of the light receiving range 22 shows the sensitivity distribution including the light receiving element 10. Then, as shown in the enlarged view of the measurement portion in FIG. 2B, since the cross section of the light beam 21 and the cross section of the light receiving range 22 are both circular, the light receiving region 23 is a complete sphere.

In addition to this, the light intensity distribution of the laser diode 4 is usually a Gaussian distribution as shown in FIG.
The distribution I of light intensity with respect to a distance X perpendicular to the axis is represented by the following equation. ^{I = (exp (-x 2/} 2)) 2 typically is in the range of level, i.e. the light beam level 13.5% of exp (-2) relative to the peak value. The diameter d of the sphere in the measurement area 23 is given by the following equation, where f is the focal length of each of the lenses 6 and 7, λ is the wavelength of light, and D is the diameter of the light beam expanded by the collimator lens 5. . d = 4fλ / πD

Also, the sensitivity distribution of the light receiving means is set to be the same, that is, a Gaussian distribution. In this way, the same scattering intensity can be obtained regardless of the direction in which the light passes through the center of the measurement region 23 in any direction.

When the fine particles pass through the center of the sphere in the measurement area 23 in an arbitrary direction, a signal shown in FIG. 3 (a1) is obtained. This pulse train is a pulse along an envelope waveform A1 determined by the intensity distribution of the laser diode 4 as the light source and the sensitivity distribution of the light receiving means, and is a signal having a lighting timing level. When the particles pass not at the center but around the measurement area 23 at the same speed, a low-level signal shown in FIG. 3 (b1) is obtained. Also, when a particle smaller than this passes through the center, a low signal of the same level is obtained. However, each of them has an envelope waveform A2 determined by the intensity distribution of the laser diode 4 and the sensitivity distribution of the light receiving means. When fine particles having a higher speed pass through the center of the measurement area 23, the envelope waveform A is increased as shown in FIG.
It becomes a pulse train along the envelope waveform A3 obtained by shortening 1 on the time axis.

When the operation of the arithmetic processing unit 14 is started, first in step 31 shown in FIG.
It is checked whether there is an A / D conversion input from the input interface 2 through the input interface 13. If there is an A / D conversion input, the process proceeds to step 32 to store it in the memory in the arithmetic processing means, and proceeds to step 33 to check whether the pulse is continuous. Step if continuous
Returning to step 31, the same processing is repeated while waiting for the A / D conversion input. If the pulses do not continue, the process proceeds to step 34 to check whether the number of pulses stored in the memory is a predetermined number, for example, four or more. If it is four or more, the routine proceeds to routine 35, where a distribution curve that matches this data sequence is estimated. This curve is a curve shown in equation (1), and the variable x is an arbitrary value. (A2) of FIG. 3 is a result of normalizing the waveform of (a1) to calculate an envelope, and (b2) and (c2) estimate the envelopes of the input pulses of (b1) and (c1), respectively. The peak value is normalized so as to be constant. Then, the routine proceeds to a routine 36, in which a certain level with respect to the peak value is set as a threshold value, as shown in FIGS. 3 (a2), (b2) and (c2).
As shown in (2), the time exceeding the threshold value Vth of the envelope waveform is calculated.

Then, as shown in FIG. 3, not only when the fine particles pass through the center of the measurement area 23 but also when they pass therearound, if the same velocity is obtained by normalization, all the same envelopes are obtained. It becomes a linear waveform, and the time can be measured. And the light diameter D of the collimator lenses 5 and 9
Is known in advance, and the size d of the measurement area 23 is also known, so that the velocity of the particles can be measured based on the time T1 or T2 passing through the area. In this case, no matter what direction the particles pass,
It is not necessary to pass through the center of the vehicle, and the speed can be detected even when the periphery of the vehicle is grazed. So routine
At 37, the time is converted into a speed signal and displayed on the display 15 (step 38).

Here, the microcomputer 14 has achieved the function of the pulse train holding means 16 for holding the pulse train obtained continuously through the input interface B in the memory in the steps 31 to 33, and thus obtained in the routine 35. The function of the envelope estimating means 17 for estimating the envelope waveform based on the pulse train is achieved. The functions of a time measuring means 18 for calculating a time exceeding a predetermined threshold based on the envelopes estimated in the routines 36 and 37, respectively, and a speed converting means 19 for converting this time into a speed based on the cycle of the clock oscillator 1 Have achieved.

If the number of pulses obtained in step 34 is less than 4, the process proceeds to step 39 to clear the memory. Then, the process proceeds to step 40, where the clock frequency of the clock oscillator 1 is changed. For example, when the particle speed is high and the number of pulses is less than 4, the required number of clocks is obtained by shortening the clock cycle. In this way, by returning to step 31 and repeating the same processing, the required number of pulses can be obtained by passing the particles. Thereafter, by performing the same processing, the velocity of the particles can be calculated. Here microcomputer 1
4 achieves the function of the cycle adjusting means 20 for changing the cycle of the clock oscillator when the number of pulses is small in steps 39 and 40. This makes it possible to detect the velocity of the particles without contacting the detection area. Therefore, it is possible to measure the flow velocity of a fluid containing particles, for example, the flow velocity of an air flow or the flow velocity of a liquid such as water.

In this embodiment, the intensity distribution of the laser diode 4 and the sensitivity distribution of the light receiving means are Gaussian distributions.
Light sources and light receiving means having other intensity distributions may be used. In this embodiment, the light receiving element 10 itself has no sensitivity distribution, and the sensitivity distribution is made Gaussian distribution by the beam intensity correcting element 8. However, if the light receiving element 10 itself has a Gaussian distribution, the beam intensity correcting element 8 is unnecessary. Becomes Further, the correction element 8 for correcting the beam intensity is not limited to the Gaussian distribution, but may be any element. In these cases, it is necessary to estimate the envelope of the characteristic corresponding to the intensity distribution.

[0020]

As described above in detail, according to the present invention, the measurement area is spherical, and the velocity can be detected when the particle passes in any direction. Therefore, it is possible to provide a non-contact and non-directional flow rate measuring device. In addition, compared with a conventional flow velocity measuring device in which a light beam intersects in a measurement region, an effect that the device can be realized with a relatively simple configuration can be obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an overall configuration of a particle measuring device according to one embodiment of the present invention.

FIG. 2A is a diagram illustrating a relationship between the optical system of the present embodiment, a light beam, and scattered light, and FIG. 2B is an enlarged view of a measurement region.

FIGS. 3 (a1), (b1), and (c1) are diagrams showing changes in the light receiving signal level obtained according to the present embodiment.
(B2) and (c2) are diagrams showing estimated waveforms of the envelope corresponding to the level.

FIG. 4 is a flowchart illustrating the operation of the present embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Clock oscillator 2 Frequency variable circuit 3 LD drive circuit 4 Laser diode 5, 9 Collimator lens 6 Focusing lens 7 Condensing lens 8 Beam intensity correction element 10 Light receiving element 12 A / D converter 14 Operation processing unit 16 Pulse train holding means 17 Envelope Line estimation means 18 Time measurement means 19 Speed conversion means 20 Period adjustment means 21 Light beam 22 Light receiving range 23 Measurement area

Claims (3)

(57) [Claims] 1. A clock oscillator that periodically oscillates a clock signal, a light source driven by a clock output of the clock oscillator to generate a light beam having a predetermined intensity distribution and a beam diameter, and measuring a light beam of the light source Optical means for focusing in a region, the light beam and the light receiving axis of the scattered light intersect at a substantially right angle, and scattered light from particles passing through the measurement region is collected, and the same as the intensity distribution of the light source. Light receiving means for converting an electric signal with a sensitivity distribution of; and a pulse train holding means for holding a pulse train of a predetermined number or more of scattered light levels from an output of the light receiving means periodically obtained in response to a clock of the clock oscillator. Formed by a pulse train held by the pulse train holding means
Based on the envelope waveform
An envelope estimating means for estimating a-normalized envelope waveform, the normalized envelope waveform the estimated by envelope estimating means
, A predetermined threshold value is set for the normalized envelope waveform.
A flow velocity measuring device, comprising: a time measuring means for measuring a time exceeding a threshold level; and a speed converting means for converting the time measured by the time measuring means into speed information. 2. The flow velocity measuring apparatus according to claim 1, further comprising a period adjusting means for changing a period of said clock oscillator to be shorter when a continuous pulse train is equal to or less than a predetermined number. 3. The flow velocity according to claim 1, wherein the light receiving means includes a beam intensity correction element for correcting the beam intensity so that the center of the light receiving axis of the scattered light is strong and the periphery is weak. measuring device.