JPS6047965A - Laser doppler speedometer - Google Patents

Abstract

PURPOSE:To make it possible to measure a particle size and a particle concn. simultaneously with a particle speed, by imparting a particle size analytical analysis to a laser Doppler speedometer. CONSTITUTION:A burst signal is analysed in state separated into a high frequency component and a low frequency component. That is, the high frequency component is analyzed by a frequency analyser 10 while the low frequency component is analyzed by a pulse crest analyser 13 and the synchronism of both signals is discriminated by a signal analyser 14 and, if both signals are synchronous, it is discriminated that both signals are ones generated from one particle which passed a measuring point and both signals are recorded by buffer memory 11. This operation is repeated many times and statistical processing is performed by using a counter 12 to measure a particle size simultaneously with a particle speed. The frequency of a Doppler signal being the flow speed component in the burst signal and the pulse crest value of a pedestal signal being a particle size component are recorded as a pair by the buffer memory 11. The frequency fD of the Doppler signal is converted to the speed V of the particle from this buffer memory 11.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention allows interference fringes generated at the intersection of two laser beams to pass across particles, and the scattered light pulses generated at that time are transmitted to a secondary electron multiplier. Receive light and count it as electrical pulses,
This paper relates to improvements in laser draglar velocimeters for measuring particle velocities in fluids.

[Background of the invention]

A conventional laser-dog dual speed meter has the configuration shown in FIG. That is, a laser beam generated from a laser light source 1 passes through a polarization plane rotator 2 and then passes through a beam sinter 3.
Two beams of equal intensity are formed, and the beam frequency of one of them is shifted by a frequency shifter 4. These two beams pass through a converging lens 5 and form interference fringes at a measurement point 6.

When particles 7 pass through this interference pattern, they generate scattered light pulses. The two beams are blocked by beam stopper 7,
Only the generated scattered light pulses are collected through the condensing lens 8 and converted into electrical signals by the photoelectric converter 9. This electrical signal is called a burst signal as shown in Figure 2.
This is detected by the frequency analyzer 10 as a high frequency component in the burst signal.

The frequency fD of the drag signal was analyzed, and the speed of the particle was calculated from this using the following equation in the calculator 12.

fD・λ.

・・・・・・・・・・・・・・・・・・・・・・・・
...(1) θ 28 River - Here, λ0 is the wavelength of the laser beam, θ is the intersection angle of the laser beam, and ■ is the speed of the particle.

However, conventional systems do not fully utilize the information transmission by burst signals shown in FIG.

The reason for this is thought to be the amplitude Ap of the pedestal signal and the amplitude AsO ratio A p /A s of the dog 2 signal as signals indicating the particle diameter in the burst signal in Fig. 2, and it is necessary to process these simultaneously. This is because this reliability has not been sufficiently obtained.

However, recently, there has been an example in which two types of particles with a certain particle size are entrained in an airflow, and they are separated and measured based on the magnitude of the pedestal signal (Journal of the Japan Society of Mechanical Engineers, vo+ 84. If
x756. P66. (November 1981 issue), but research on particles with a wide distribution is still under way.

In addition, conventionally, laser dragler velocimeters have been used to analyze the movement of airflow, by adding powder with a somewhat uniform particle size to the airflow, and analyzing the movement of the airflow from the velocity of this powder. was. For this reason, the relationship between powder particle size and velocity was not particularly necessary information and did not receive much attention.

[Purpose of the invention]

An object of the present invention is to provide a laser dragura velocimeter that has a particle size analysis function and can measure the total particle concentration in an air stream based on the correlation between particle diameter and particle velocity.

[Summary of the invention]

The present invention is based on the fact that it was thought that the amplitude Ap of the pedestal signal alone, rather than the above-mentioned A p /A s, would be sufficient as a signal indicating the particle diameter, and this was experimentally confirmed.

The experiment was carried out using the system shown in Figure 3. Air at room temperature and pressure was used as the carrier gas, fly ash with an average particle size of 5 μm was entrained into the air, and particles with the same size were attracted to the same level to cause light scattering. Amplitude A of the pedestal signal measured by the method dust monitor and still measured by the laser Doppler method at the same point
The correlation with p was found as shown in Figure 4.

That is, there is a good correlation between the amplitude Ap of the pedestal signal and the particle diameter Dp measured by the light scattering type dust monitor, which is expressed by the following equation.

Ap=C-D, ・・・・・・・・・・・・・・・・・・
(2) Here, C is a coefficient determined by the amplification factor of the secondary electron multiplier, laser beam intensity, etc., and α is a constant determined by the laser optical system.

For the first time, we have found that the particle diameter can be calculated from the amplitude Ap of the pedestal signal using equation (2). Therefore, the particle size and velocity of particles can be measured simultaneously. The results are shown in FIG. This result shows that when air at room temperature and pressure is used as the carrier gas and the gas flow velocity is about 1 m/s, particles of 1 μm or more gradually deviate from the air flow. That is, it has been found that when calculating the speed of airflow, it is sufficient to take the average speed of particles of 1 μm or less.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIG.

The difference between FIG. 3 and FIG. 1 is that the burst signal shown in FIG. 2 is separated into high frequency components and low frequency components for analysis. That is, the high frequency components are analyzed by the frequency analyzer 1O as before, and the low frequency components are analyzed by the pulse wave height value analyzer 1.
3, and the signal analyzer 14 determines whether or not these two signals are synchronized. If they are synchronized, it is determined that both signals are generated from a single particle that passed through the measurement point. and records it in the buffer memory 11. This is repeated many times, and statistical processing is performed using the calculator 12'Th to measure the particle speed and particle diameter.

Next, a method for calculating the particle diameter will be explained with reference to FIG. In the buffer memory 11 of FIG. 3, the frequency of the Doppler signal, which is the flow velocity component in the burst signal, and the pulse height value of the pedestal signal, which is the particle size component, are recorded as a pair. From this buffer memory 11, the frequency fD of the Doppler signal is calculated as 124TL/-the wavelength λ of the laser. The calculation of equation (1) is performed using the intersection angle θ of the laser beam and the velocity V of the particle. On the other hand, the pulse peak value Ap is calculated by the multiplier 2.
1, the coefficients 1/C and l/α are used to calculate the particle diameter Dp using the following equation. The converted particle diameter Dr and particle velocity V are calculated by the computing unit 22 as Dpo+Vo...Dp
m, VB, and their frequencies F calculated by the calculator 23.・
...Dp6 g Vo +Fo as a pair with F
...Recorded as Dp-, V, , Fゎ.

Through the above operations, by separating and analyzing the burst signal of the laser dragler velocimeter into the entire Doppler signal and the pedestal signal, not only the particle velocity V but also the particle diameter Dp at that time can be measured simultaneously.

Furthermore, as shown in FIG. 5, it is clear that particles of 1 μm or less indicate the entire gas flow, whereas particles of 1 μm or more deviate from the gas flow. Therefore, FIG. 7 can be considered as an embodiment that is a further development of FIG. 6.

The example in Figure 7 is the same as Figure 6 and the pulse height value A of the pedestal signal.
Although they are the same up to the part where P is converted to the particle diameter Dp, the subsequent signal processing methods are different. In Fig. 7, the particle diameter D1 is almost equal to the gas flow.If the gas flow velocity is 1 m/s, the particle diameter is compared with 1 μm from Fig. 5 using the calculator 31. Average velocity V(,
Calculate this as the gas flow velocity at all measured points, and furthermore, the cross-sectional area S1 of the intersection of the laser beam facing the flow. This S is the optical system (the size of the laser beam,
The product of Q and the amount of gas passing through the cross-sectional area S is calculated by the multiplier 32. On the other hand, the weight m of the particle having the particle diameter Dp calculated by the calculator 21 is calculated by inputting the specific gravity ρl of the particle and the particle diameter Dp to the calculator 33. This operation is performed for a large number of particle examples, and the calculation unit 34 calculates and outputs the cumulative weight M. Next, by inputting this cumulative weight M and the average gas j&Q at this sampling time, the calculator 34 calculates and outputs the weight W per unit gas amount at that time.

According to the example shown in FIG. 7, in addition to the particle velocity and particle diameter at the measurement point, the particle concentration can also be calculated.

〔Effect of the invention〕

According to the present invention, particle size and particle concentration can be measured simultaneously with particle velocity using a laser draglar velocimeter.

[Brief explanation of the drawing]

Figure 1 is a system diagram of a conventional laser dragler speedometer, Figure 2 is a schematic diagram of a burst signal, Figure 3 is a system diagram of a laser dragler speedometer of the present invention, and Figure 4 is a pulse peak value and particle Diameter calibration curve diagram, Figure 5 is a characteristic diagram of gas flow rate and particle diameter, Figure 6 is a block diagram showing an example of the calculation method of the present invention,
FIG. 7 is a block diagram of another embodiment of the invention. l...Laser light source, 2...Polarization plane rotator, 3...
Beam-"j')tsu1-14...Frequency shifter, 5
... Converging lens, 7... Beam fist stopper, 8...
- Condenser lens, 9... Photoelectric converter, 10... Frequency analyzer, 11... Buffer memory, 12... Calculator, 21... Multiplier, 24... Arithmetic unit, 31 ... Arithmetic unit, 32... Multiplier, quasi-4 diagram #L4 (l DP (pm) Electron S diagram a-manual DP (P-'rrI) Continued from page 1 0 Inventor Kaoru Otsuka Sho Hitachi City Saiwaimachi 3-chome premises

Claims (1)

[Claims] 1. A laser light source, a beam sinter that splits the beam emitted from the laser light source into two beams, an optical system that focuses the two beams, and a A photoelectric converter converts the scattered light generated from particles passing through the intersection of the beams into an electrical signal, and a signal from the photoelectric converter is received.
Among these, the top 2 - a frequency analyzer that measures the frequency of the signal, a pulse peak value analyzer that measures the peak value of the pedestal signal, and a synchronization test that measures the generation times of the Doppler signal and the pedestal signal. a synchronous analyzer,
A laser dragler speedometer comprising a buffer memory that captures the Doppler signal and the pedestal signal when these signals are synchronized, and a calculator that reads data from the buffer memory and calculates the data. . 2. The laser according to claim 1, wherein the particle diameter is calculated from the peak value of the pedestal signal.
dragura speedometer. 3. Ratio M/Q of cumulative weight M of particles and gas amount Q when particles with a particle diameter of 1 μm or less pass through a measurement point in a gas flow
2. The laser draglar velocimeter according to claim 1, wherein: is the particle concentration per unit gas amount at the measurement point.