JP2003050202A - Smoke density measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To facilitate the adjustment of an optical system and to accurately measure smoke with low density in a light transmission type smoke density measuring device. SOLUTION: Thin film mirrors 5A and 5B are formed on the outer peripheral surface of a transparent glass pipe 3 symmetrically about the center of the pipe. A light source part 10 radiates light from the side. The light is focused in a surface vertical to a cylindrical axis by a cylindrical lens 14 so as to focus light to a point closest to the center to be reflected multiplexly. The smoke is guided into the glass pipe 3 to form a measuring region, and multiplexly reflected laser beams are received. Smoke density is measured based on a light receiving level.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a smoke density measuring device using a light transmission method.

[0002]

2. Description of the Related Art Conventionally, a light transmission type smoke concentration measuring device (smoke meter) has been known for measuring the concentration of particulate matter discharged from a combustion engine or airborne particulate matter. The conventional light transmission type smoke concentration measuring device is arranged so that the light source and the light receiving part face each other, the light path from the light source to the light receiving part is intersected with the smoke path, and the smoke density in the light path is measured from the attenuation rate of the transmitted light. To do. In such a light transmission type measurement device, since the smoke concentration is measured from the attenuation rate of light that has been transmitted through the sample smoke only once, the intersection (measurement area) between the optical path and the sample smoke path is measured. And the sensitivity to low concentrations was low. If an attempt is made to increase the measurement area in order to eliminate this drawback, the size of the device will be increased. In addition, since the crossing portion is small, there is a drawback that the temperature and density of smoke vary greatly with time and the output value of the measuring device is not stable.

In addition, the present inventor, in Japanese Patent Application Laid-Open No. 8-43305, performs vapor deposition on the circumferential portion of a cylindrical glass tube and slightly displaces it from the central axis thereof so that the cylindrical glass tube is perpendicular to the central axis. We have proposed a smoke concentration measuring device that measures the smoke concentration by irradiating parallel laser light from the side and reflecting it multiple times in the measurement area. The number of reflections by this cylindrical glass tube is a function of the distance of the closest point of laser light from the center of the cylindrical glass tube. According to this device, the optical path length becomes long and the smoke density can be measured with high sensitivity.

[0004]

In such a conventional device, if the ideal thin parallel light can be directed to the glass tube, the light can be transmitted through the measurement region any number of times. You can However, in reality, since the incident light has a certain beam width, the distance from the cylindrical axis side of the glass tube to the outer portion of the beam differs from the respective portions to the center of the cylindrical axis. Therefore, as the number of reflections increases, the reflection point on the mirror shifts due to the laser beam portion, and light with different numbers of reflections eventually overlaps and enters the light receiving portion. Therefore, there is a problem in that light with a small number of reflections and a short optical path length is also received, which causes a decrease in sensitivity. Therefore, the number of practical reflections was about 7.

The present invention has been made in view of the above-mentioned conventional problems, and by increasing the number of reflections, it is possible to measure the smoke density with high sensitivity and low density. The purpose is to provide a device.

[0006]

According to a first aspect of the present invention, a cylindrical glass is formed in which a reflection film is formed at a position symmetrical with respect to a central axis of an outer peripheral surface and smoke to be measured is introduced. A tube, and a light source unit that allows light that does not pass through the center point of the glass tube to enter from a side of the glass tube toward a reflective film,
A light receiving unit that receives reflected light that is incident from the light source unit and is multiple-reflected from the reflective film of the glass tube, wherein the light source unit is a surface perpendicular to the central axis of the glass tube. It is characterized in that it comprises a cylindrical lens which is focused inside and the focusing point on the optical axis is located at the shortest position from the central axis of the glass tube.

According to a second aspect of the invention of the present application, in the smoke concentration measuring apparatus according to the first aspect, the light source section is a laser light source which has a predetermined deviation from the diameter of the glass tube and which emits laser light. It is characterized in that it has a deviation setting means for setting the deviation of the laser light of the light source section.

According to the present invention having such characteristics,
A reflecting film is formed on the cylindrical glass tube symmetrically with respect to its center axis, and smoke to be measured is introduced into the glass tube. Also, light is incident from the side of this glass tube from the light source. This incident light does not pass through the center of the glass tube only in the plane perpendicular to the cylindrical axis by the cylindrical lens, and is converged at a point closest to the center to make the light incident and irradiate the reflective film. Then, the light is multiply reflected by the reflecting film a number of times according to the deviation from the center point, and the light is attenuated according to the concentration of smoke passing through the glass tube. The light receiving section receives the reflected light and calculates the concentration of smoke passing through the glass tube based on the received light level.

[0009]

1 is a horizontal sectional view of a smoke concentration measuring apparatus according to an embodiment of the present invention, and FIG. 2 is a vertical sectional view thereof. As shown in these drawings, the smoke concentration measuring device has a duct 1 to which smoke as a sample, for example, exhaust gas of a diesel engine or the like is added, and its tip end is opened as a nozzle 2. A transparent glass tube 3 covering the outer peripheral portion of the nozzle 2 is provided, and a suction duct 4 for sucking smoke passing through the nozzle 2 is further provided. Here, the glass tube 3 is transparent and has an accurate cylindrical shape, and a thin film is formed as a reflective film on a part thereof.
As shown in FIG. 2, in this thin film mirror, thin film mirrors 5A and 5B are formed symmetrically with respect to the center of the glass tube in a range of 1/4 of each circumference. It is assumed that these thin film mirrors 5 are formed in a band shape from the outer circumference of the glass tube 3 within a constant width D. The suction duct 4 may be omitted when it is discharged directly to the atmosphere.

A light source section 10 is provided on the side of the glass tube 3 as shown in FIGS. The light source unit 10 includes, for example, a laser diode 11 and the laser diode 11
It has the drive part 12 which drives. Then, a collimator lens 13 for converting this laser light into parallel laser light
Also, a cylindrical lens 14 is provided near the glass tube 3. The cylindrical lens 14 is focused only in the plane perpendicular to the cylindrical axis of FIG. 2 (parallel to the paper surface), and is focused at the shortest point from the central axis of the glass tube 3. In this way, the thin film mirror 5 of the glass tube 3 repeatedly reflects the light as described later, and the light is emitted from the glass tube. The beam emitted from the glass tube 3 is transmitted to the light receiving section by the lens 15.

The light receiving portion is a focusing lens 1 for focusing the emitted light.
5 and a photoelectric converter for receiving the focused laser light and converting it into an electric signal, for example, a photodiode 16. The output of the photodiode 16 is given to the latch unit 18 and the divider 19 via the amplifier 17. The latch unit 18 is a sample hold circuit that holds the amplified output, and its output is given to the divider 19. The divider 19 divides these inputs and outputs the output from the concentration calculator 20.
Give to. The concentration calculation unit 20 calculates the concentration from the table based on this ratio calculation power. The deviation setting unit 2
1 is to move the light source unit 10 in the vertical direction in FIG. 2 and set a deviation d _X described later to an arbitrary value.

Next, the operation of this embodiment will be described. First, the driving unit 12 drives the laser diode 11 to emit laser light. And collimating lens 1
3. The cylindrical lens 14 irradiates a measurement area in the glass tube 3 with a laser beam having a diameter sufficiently smaller than the cylindrical curvature. At this time, smoke is not guided to the duct 1. In this way, even if the laser light passes through the measurement area, it will not be attenuated by smoke or dust. Here slightly lower than the center point of the glass tube 3 showing laser beam by a one-dot chain line, it is irradiated toward the thin-film mirror 5B to focus with a predetermined deviation d _x at a point closest to the center point. In this way, the focal points are formed at the same distance from the center point, and the light enters the glass tube 3 at substantially symmetrical positions. The light is reflected again from this point, and the same point data is focused and reflected again from the center point. Thus, the reflection position is gradually changed and the same operation is repeated. Further, since the curvature of the glass tube does not affect in the direction perpendicular to the paper surface, the light beam is repeatedly reflected as shown in the drawing by changing the focusing position around the central axis.

Here, the deviation between the diameter 3a of the glass tube 3 and the incident laser beam is d _X. Here, when the radius of the outer diameter of the glass tube 3 is r ₁ and the radius of the nozzle 2 is r ₂ , the one-time measurement optical path length d _{M of} the light beam and the reflection angle θ are expressed by the following equations. d _M = 2 × √ (r ₂ ² −d _X ² ) θ = sin ⁻¹ (d _X / r ₁ ) And the number of reflections can be arbitrarily selected by changing the deviation d _X. The number of passages N when light passes through the measurement region is the number of reflections +1 and is represented by the following equation. N = INT {(π / 2−θ) / 4θ} × 2 + 1 Further, the total optical path length L of light is expressed by the following equation. L = N · d _M

In this way, the light beam inside the glass tube does not gradually spread even if reflection is repeated, and the number of reflections can be practically 20 or more. For example, if the outer diameter r ₁ of the glass tube is 79 mm and the deviation d _X is 1.6 mm, the thin film mirrors 5A and 5B of the mirrors are as shown in FIG.
Is reflected 19 times and reflected upward from the lower thin film mirror 5B. This reflected light has passed through the measurement region 20 times, and this light is received by the photodiode 16, the level of the reflected light is amplified and held in the latch section 17.

Here, the received light level is expressed by the following equation. I = I ₀ exp (Lβ) L is the total optical path length, and β is a function proportional to the particle concentration. I ₀ is the incident light intensity.

Next, a sample smoke is introduced into the duct 1 and sucked from the suction duct 4 side to pass through the measurement area. In this state, the measurement area is similarly irradiated with laser light. In this way, the laser light passes through the measurement region 20 times, and the laser light is attenuated according to the smoke density. Therefore, the smoke density can be calculated by measuring the degree of this attenuation. If it is assumed that smoke such as dust is passing through this measurement region, this laser light will be attenuated according to the concentration of dust.
That is, the divider 19 calculates the ratio with the intensity of the laser light in a state where the smoke held in the latch portion 18 does not pass. By performing the division, the influence of the intensity I ₀ of the laser light is removed, and the smoke density can be calculated. Further, since the optical path length L is constant, β can be calculated from the split calculation force. The particle concentration may be held in advance as a table in the concentration calculator with respect to the divided value, and the value may be output, or the concentration may be directly calculated from this function.

Here, in the present embodiment, the incident light is deviated from the horizontal diameter 3a of the glass tube 3 by a deviation d _X (here, 1.6 mm).
Although the laser light has a deviation from the center only, the incident angle θ is changed by changing the value of the deviation d _X ,
The change in the incident angle θ changes the number of passes N. The total optical path length L also changes as shown in FIG. By appropriately changing the deviation d _{X of the} incident light, the total optical path length L can be significantly changed. Therefore, by setting the deviation d _X corresponding to the smoke density by the deviation setting unit 20,
The total optical path length can be appropriately selected, which enables accurate concentration measurement. Particularly when the density is low, the density can be measured with high accuracy by increasing the total optical path length L.

In this embodiment, as shown in FIG. 2, 1/4 thin film mirrors of the entire circumference are respectively formed at two points where the center of the glass tube 3 is point-symmetrical. Not limited to the range,
It is sufficient to form a thin film mirror with the center of the glass tube being point-symmetric. Therefore, the thin film mirror may be formed in more or less area. Further, the thin film mirror may be intermittently formed only in a portion where light is actually incident and reflected.

[0019]

As described in detail above, according to the present invention, by using a cylindrical lens, it is possible to increase the measurement optical path length in a measurement region where multiple reflections and smoke pass. Therefore, it becomes possible to measure with high accuracy even when the sensitivity is increased and the smoke density is low. Further, by using a glass tube having an accurate shape, the reflective film can be accurately formed. Therefore, the number of reflections can be significantly increased as compared with the conventional smoke density measuring device, and the measurement can be performed with high sensitivity. Further, by appropriately changing the number of reflections, it is possible to obtain an effect that the smoke density from low density to high density can be measured with high accuracy by one measuring device.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a smoke concentration measuring device according to an embodiment of the present invention.

FIG. 2 is a vertical sectional view of an optical axis portion of a smoke concentration measuring device according to an embodiment of the present invention.

FIG. 3 is a diagram showing a state of multiple reflection on a glass tube.

[Explanation of symbols]

1 duct 2 nozzles 3 glass tubes 4 suction duct 5,5A, 5B Thin film mirror 10 light source 11 Laser diode 12 Drive 13 Collimating lens 14 Cylindrical lens 15 Focusing lens 16 photodiode 18 Latch 19 Divider 20 Concentration calculator 21 Deviation setting section

Claims (2)

[Claims] 1. A cylindrical glass tube in which a reflection film is formed at a position symmetrical with respect to the central axis of the outer peripheral surface, into which smoke to be measured is introduced, and light which does not pass through the center point of the glass tube. A light source section which is incident from the side of the glass tube toward a reflective film, and a light receiving section which is incident from the light source section and receives reflected light which is multiple-reflected from the reflective film of the glass tube, The light source unit includes a cylindrical lens that focuses the light from the light source in a plane perpendicular to the central axis of the glass tube and has a focal point on the optical axis as the shortest position from the central axis of the glass tube. A smoke concentration measuring device characterized by the above. 2. The light source unit is a laser light source that emits laser light with a predetermined deviation from the diameter of the glass tube, and has deviation setting means for setting the deviation of the laser light of the light source unit. The smoke concentration measuring device according to claim 1, wherein: