JP7787770B2 - Light-reducing fluid detection device - Google Patents

Description

The present invention relates to a light-reducing fluid detection device that detects fluids present in a monitored space.

An example of a light-attenuating fluid detection device is a light-attenuating smoke density meter.
A dimming smoke density meter consists of an emitter and a receiver, which are placed on opposite sides of the monitored space. The light emitted by the emitter is dimmed by the smoke, and the meter detects the smoke density in the monitored space.

In conventional dimming smoke density meters, smoke could come into contact with the lenses located in front of the light-emitting element of the light-emitting section and the light-receiving element of the light-receiving section, causing the lenses to become soiled by dust and other particles contained in the smoke.
If the lenses of the light emitting unit and the light receiving unit become soiled, the light emitted by the light emitting unit is attenuated due to the soiled lenses, which causes errors in the smoke density measurement.

A method for preventing the above-described lens contamination is disclosed in, for example, Japanese Patent Application Laid-Open No. 2003-222999.
The "dustproof mechanism" of Patent Document 1 prevents the lens from becoming soiled by blowing clean air onto the front surface of the lens.

Japanese Patent Application Laid-Open No. 2017-79396

In the method of Patent Document 1, the dust-proof air blown onto the lens is discharged into the monitored space, which causes a problem that the state of the monitored space is disturbed and changes, making it impossible to accurately detect the true smoke concentration.
Even if no lens is provided in front of the light emitting element and the light receiving element, the light emitting element and the light receiving element can be soiled with dust, resulting in the same problem as above.

The present invention was made to solve these problems, and aims to provide a light-reducing fluid detection device that can accurately detect fluids present in a monitored space, preventing contamination by dust and other particles without affecting the condition of the monitored space.

(1) The light-reducing fluid detection device of the present invention detects fluid present in a monitored space by arranging a light-emitting unit having a light-emitting element and a light-receiving unit having a light-receiving element separated by the monitored space, and is characterized by having a swirling flow generation space in front of the light-emitting element or the light-receiving element that generates a swirling flow of gas, a wall that surrounds the swirling flow generation space, and a first discharge port that is provided in the wall and discharges the gas into the swirling flow generation space to generate a swirling flow.

(2) Furthermore, in the device described in (1) above, a lens is provided in front of the light-emitting element or the light-receiving element, and a second outlet is provided in the wall portion behind the first outlet and ejects gas near the lens.

(3) Furthermore, in the device described in (2) above, the second discharge port is characterized in that it is provided around the entire circumference of the wall portion.

(4) Furthermore, in the device described in (2) or (3) above, a first supply flow path that supplies the gas to the first discharge port and a second supply flow path that supplies the gas to the second discharge port are provided in the wall portion, and the first supply flow path and the second supply flow path are connected to each other.

(5) Furthermore, in any of the above (1) to (3), the first discharge port is characterized in that it is provided near the front end of the wall portion.

This invention includes a swirling flow generation space in front of the light-emitting element or the light-receiving element that generates a swirling flow of gas, and a wall surrounding the swirling flow generation space. The wall has a first outlet that discharges gas into the swirling flow generation space to generate a swirling flow, allowing the gas to be diffused and discharged. Therefore, the discharged gas is less likely to affect the state of the monitored space, allowing the state of the monitored space to be accurately measured.

3 is a cross-sectional view of a light-emitting portion of the light-attenuating fluid detection device according to the embodiment. FIG. 1 is a diagram showing the overall configuration of a light-attenuating fluid detection device according to an embodiment; 2 is an end view taken along the line AA in FIG. 1, showing the shape of a first discharge port. FIG. FIG. 3 is a cross-sectional view taken along line BB in FIG. 2, showing the flow of gas. 2 is a diagram showing a swirling flow generated in the light-emitting section of FIG. 1 and a flow of gas discharged from the light-emitting section. FIG. 10 is a diagram showing the results of fluid analysis of an example of the present invention (gas flow rate: 1 L/mm). FIG. 10 is a diagram showing the results of fluid analysis of an example of the present invention (gas flow rate: 4 L/mm). FIG. 10 is a diagram showing the results of fluid analysis of a comparative example according to an embodiment (gas flow rate: 1 L/mm). 1A and 1B are diagrams illustrating problems with a conventional light-attenuating fluid detection device (part 1). 10A and 10B are diagrams illustrating problems with a conventional light-attenuating fluid detection device (part 2).

Prior to explaining an embodiment of the light-reducing fluid detection device of the present invention, we will first explain conventional light-reducing fluid detection devices and their issues, using a smoke concentration meter, which measures the concentration of smoke in a monitored space, as an example.

A conventional light-reducing fluid detection device, which is a smoke density meter, consists of a light-emitting unit with a light-emitting element and a light-receiving unit with a light-receiving element. The light-emitting unit and the light-receiving unit are positioned opposite each other across the monitored space, and the monitoring light emitted by the light-emitting unit is dimmed by smoke present in the monitored space, thereby detecting the smoke density in the monitored space (optical path length) (see Figure 2).

Figures 9(a) and 9(b) show schematic cross sections of the light-emitting unit 37 of a conventional light-reducing fluid detection device taken along the optical axis. As shown in Figures 9(a) and 9(b), the light-emitting unit 37 includes a lens 9 provided in front of the light-emitting element 39 and a cylindrical hood member 11 provided to surround the lens 9.

In a conventional light-emitting unit 37, as shown in Figure 9(a), when smoke 41 flows into the hood member 11 and comes into contact with the lens 9 provided within the hood member 11, the lens 9 is soiled by dust particles 43 contained in the smoke 41, as shown in Figure 9(b). When the surface of the lens 9 is soiled, the dust particles 43 adhering to the lens 9 dim the monitoring light 45 emitted by the light-emitting element 39, causing errors in smoke concentration measurements.

Therefore, as disclosed in Patent Document 1, a method (air purge) has been used in which clean air or other gas is blown onto the surface of the lens 9 to prevent the adhesion of dust 43.
When air purging is used, as shown in Fig. 10(a), for example, an inlet 31 is provided in the hood member 11 of the light-emitting unit 47 near the lens 9, and purge gas 25 is injected from the inlet 31 toward the lens 9. As a result, as shown in Fig. 10(b), smoke 41 that has flowed into the inside of the hood member 11 is discharged from the hood member 11 together with the purge gas 25, preventing the lens 9 from being soiled.

However, in the case of the light-emitting unit 47 in Figure 10, the purge gas 25 discharged from the hood member 11 flows into the monitored space. As mentioned above, when the purge gas 25 flows into the monitored space, the state of the monitored space is disturbed and changes, resulting in the problem that the actual smoke concentration cannot be accurately detected.

The inventors therefore conducted extensive research into air purging methods that would have minimal impact on the state of the monitored space, and discovered that by diffusing the purge gas so that it is less likely to flow into the monitored space when it is discharged from the hood member, it is possible to reduce the amount of purge gas that flows into the monitored space. The present invention was made based on this discovery, and one embodiment of the present invention will be described in detail below.

2, the light-reducing fluid detection device 1 of this embodiment detects fluid present in a monitored space by arranging a light-emitting unit 3 having a light-emitting element and a light-receiving unit 5 having a light-receiving element across the monitored space. The light-emitting unit 3 and the light-receiving unit 5 are fixed to a fixing plate 7 with their optical axes aligned.
As with the conventional example described above, this embodiment will be described by taking as an example a case where the light-reducing fluid detection device 1 is a smoke concentration meter that measures the concentration of smoke in a monitored space. Note that the present invention can also be applied to a gas concentration meter that measures the concentration of gas, in addition to smoke concentration meters, and the present invention is not limited to this embodiment.

The structure of the light-emitting unit 3 of the light-reducing fluid detection device 1 shown in Figure 2 will be described in detail using Figures 1, 3, and 4. Figure 1 is a cross-sectional view of the light-emitting unit 3 in the optical axis direction. Figure 3 is an end view seen from the arrow A-A in Figure 1, and Figure 4 is a cross-sectional view taken along the line B-B in Figure 3. Note that Figure 4 illustrates a state in which a fourth hood piece 23, which will be described later, has been removed.
In the following description of the light-emitting unit 3, the side facing the light-receiving unit 5 is referred to as the front, and the side opposite the light-receiving unit 5 is referred to as the rear. The light-receiving unit 5 has the same structure as the light-emitting unit 3, and therefore its description will be omitted.

As shown in FIG. 1, the light-emitting unit 3 of the dimming fluid detection device 1 of this embodiment includes a light-emitting element (not shown), a lens 9 provided in front of the light-emitting element, and a cylindrical hood member 11 provided in front of the lens 9 so as to surround it. The hood member 11 corresponds to the wall portion of the present invention, and the internal space of the hood member 11 corresponds to the swirling flow generating space of the present invention.

The hood member 11 is composed of four cylindrical members, which are connected by bolts 13 and attached to the base end 15 where the lens is attached (see Figures 1 and 4). The four members that make up the hood member 11 are, in order from the base end 15 side, a first hood piece 17, a second hood piece 19, a third hood piece 21, and a fourth hood piece 23.

As shown in Figures 3 and 4, the second hood piece 19 and the third hood piece 21 are provided with four bolt holes 27 that axially penetrate the second hood piece 19 and the third hood piece 21 and are spaced equally apart circumferentially. The inner diameter of the bolt holes 27 is larger than the bolt shafts of the bolts 13, and a gap is formed between the bolts 13 and the bolt shafts when the bolts 13 are inserted. This gap serves as a first supply flow path 28 for supplying purge gas 25 to the first discharge port 29, which will be described later. Note that in Figure 3, the bolts 13 are not shown to make the shape of the bolt holes 27 easier to understand. Similarly, in Figure 4, some of the bolts 13 are not shown.

3, four recesses 21a are formed on the front end surface of the third hood piece 21, extending from the bolt holes 27 to the inner surface of the third hood piece 21. When the fourth hood piece 23 is combined with the front end surface of the third hood piece 21, the four recesses 21a form four first discharge ports 29 for discharging the purge gas 25 into the inside of the hood member 11.
3, the direction from the bolt holes 27 in the recess 21a toward the inner surface of the third hood piece 21 is inclined at a predetermined angle θ from the radial direction of the third hood piece 21. As a result, the purge gas 25 is discharged from the four first discharge ports 29 as shown by the dashed arrows in the figure, thereby generating a swirling flow of the purge gas 25 inside the hood member 11.

1, the second hood piece 19 is provided with an injection port 31 for injecting the purge gas 25. In addition, a circular groove portion 19a is provided on the rear end surface of the second hood piece 19, and the groove portion 19a forms a second supply flow path 33 when the first hood piece 17 is combined with the rear end surface of the second hood piece 19.
4, the second supply flow path 33 is connected to the rear end of the bolt hole 27 that forms the first supply flow path 28. Therefore, the first supply flow path 28 communicates with the second supply flow path 33, and the purge gas 25 supplied from the injection port 31 is supplied to the first supply flow path 28 via the second supply flow path 33.

A slit-shaped second discharge port 35 is provided in the side wall of the second supply flow path 33 on the lens 9 side, as shown in the enlarged view of Figure 1, and the purge gas 25 is discharged from the second discharge port 35 near the lens 9.
This slit-shaped second outlet 35 is provided around the entire inner periphery of the hood member 11, so that when the purge gas 25 is discharged from the second outlet 35, the purge gas 25 is sprayed evenly onto the lens 9.
Note that this embodiment does not limit the shape of the second discharge port 35, and any shape may be used as long as it discharges the purge gas 25 near the lens 9. However, a slit shape that is continuous around the entire circumference, such as the second discharge port 35 of this embodiment, or a shape in which a plurality of holes are provided intermittently around the entire circumference is more preferable because it can efficiently prevent contamination of the lens 9.

The flow of purge gas 25 in the light-reducing fluid detection device 1 of this embodiment configured as described above will be explained in detail with reference to Figures 4 and 5. Note that since the light-emitting unit 3 and the light-receiving unit 5 have the same structure, the following explanation will focus on the light-emitting unit 3 as an example. In both Figures 4 and 5, the flow of purge gas 25 is indicated by arrows.

Purge gas 25 injected from inlet 31 (see FIG. 1) of second hood piece 19 is supplied to annular second supply flow path 33 and circulates through second supply flow path 33. Then, as shown in FIG. 4, part of purge gas 25 circulating through second supply flow path 33 flows into first supply flow path 28 (bolt hole 27), and part is discharged from second discharge port 35 to the vicinity of lens 9.
By discharging the purge gas 25 from the second discharge port 35, the purge gas 25 is sprayed all around the lens 9, preventing dust and the like from adhering to the lens 9. Thereafter, the purge gas 25 discharged from the second discharge port 35 flows toward the front of the hood member 11.

Meanwhile, the purge gas 25 that flows into the first supply flow path 28 (bolt hole 27) is discharged from a first discharge port 29 formed near the front end of the hood member 11. The purge gas 25 discharged from the first discharge port 29 forms a swirling flow inside the hood member 11, as indicated by the dark gray arrow in Figure 5.

When the purge gas 25 discharged from the second outlet 35 reaches the vicinity of the front end of the hood member 11, it merges with the swirling flow described above. When the purge gas 25 discharged from the second outlet 35 merges with the swirling flow of the purge gas 25 discharged from the first outlet 29, a twist occurs in the airflow, as shown by the light gray arrow in Figure 5. The twist in the airflow of the purge gas 25 inside the hood member 11 changes the flow direction, which was in the same direction as the optical axis, to a direction that deviates from the optical axis. As a result, the purge gas 25 is discharged from the hood member 11 so as to diffuse radially outward from the hood member 11.

The above-mentioned diffusion effect is enhanced when a swirling flow is generated near the front end of the hood member 11. Therefore, it is preferable that the first outlet port 29 be located near the front end of the hood member 11.

As described above, according to this embodiment, by providing a first discharge port 29 near the front end of the hood member 11 that discharges purge gas 25 to generate a swirling flow, the purge gas 25 can be diffused and discharged away from the optical axis direction. This makes it less likely for the purge gas 25 to flow into the monitored space compared to conventional examples in which the purge gas 25 was discharged in the same direction as the optical axis. Therefore, the purge gas 25 is less likely to affect the state of the monitored space, allowing the original state of the monitored space to be detected correctly.

In this embodiment, the hood member 11 includes a first outlet 29 that discharges purge gas near the front end thereof to generate a swirling flow, and a second outlet 35 that discharges purge gas 25 near the lens 9. However, the present invention is not limited to this configuration, and the hood member 11 may include only the first outlet 29. Even when only the first outlet 29 is provided, an airflow is generated inside the hood member 11, making it difficult for dust to adhere to the surface of the lens 9. Furthermore, the purge gas 25 that forms the swirling flow is also dispersed radially outward from the hood member 11 when discharged from the hood member 11, thereby less likely to affect the state of the monitored space, as in the embodiment. However, when the second outlet 35 is provided behind the first outlet 29 as in the embodiment, an airflow is generated from the rear to the front of the hood member 11, which is preferable because it makes it easier for the purge gas 25 to be discharged from the hood member 11 and makes it difficult for external smoke to enter the hood member 11.
In another aspect, the direction from the bolt hole 27 in the first discharge port 29 toward the inner surface of the third hood piece 21 may be tilted further forward in the axial direction of the third hood piece 21. By tilting the direction in which the purge gas 25 is discharged at a predetermined angle θ with respect to the radial direction of the third hood piece 21 and tilting it forward with respect to the axial direction, the generated swirling flow becomes more likely to flow toward the front end of the hood member 11. This makes it easier for the purge gas 25 to be discharged from the hood member 11 without providing the second discharge port 35, and makes it more difficult for external smoke to flow into the hood member 11.

In addition, in this embodiment, a cylindrical hood member 11 is used to form the swirling flow generating space, but the method of forming the swirling flow generating space is not limited to this. For example, the present invention may be applied to a wall-embedded type in which a lens is installed inside a hole drilled in a concrete wall, etc. In this case, since the internal space of the hole becomes the swirling flow generating space, it is recommended to provide a first outlet and a second outlet on the side wall of the hole and supply purge gas into the hole.

In addition, in this embodiment, the first supply flow path 28 that supplies the purge gas 25 to the first outlet 29 and the second supply flow path 33 that supplies the purge gas 25 to the second outlet 35 are configured to be connected to each other. However, the first supply flow path 28 and the second supply flow path 33 may not be connected to each other, and the purge gas 25 may be injected into each of them.

In the above embodiment, an example was described in which lenses are provided in front of the light-emitting element and the light-receiving element, but the present invention is also effective when lenses are not provided. As mentioned above, even in the case of a dimming fluid detection device in which lenses are not provided in front of the light-emitting element and the light-receiving element, contamination of the light-emitting element and the light-receiving element themselves with dust or the like can cause measurement errors. Applying the present invention can prevent this and achieve the same effects as above.

The effects of the light-reducing fluid detection device of the present invention were specifically confirmed by fluid analysis, and the results will be described below.
As an example of the present invention, the results of fluid analysis when air purging was performed using nitrogen as the purge gas in the light-emitting unit 3 of the dimming fluid detection device 1 described in the embodiment are shown in Figures 6 and 7. Figure 6 shows the results of fluid analysis when the flow rate of the purge gas was 1 L/min, and Figure 7 shows the results when the flow rate of the purge gas was 4 L/min.

8 shows the results of fluid analysis for a comparative example in which no purging gas is discharged from the first discharge port 29, i.e., no swirling flow is generated within the hood member 11. The flow rate of the purging gas in FIG. 8 is 1 L/min, the same as in FIG. 6.
In Figures 6 to 8, the arrows in the figures indicate the direction of gas flow, and the shades of color indicate the mixture ratio of nitrogen, which is the purge gas, to the ambient air, with darker areas indicating a higher concentration of purge gas and lighter areas indicating a lower concentration of purge gas.

In the comparative example shown in Figure 8, the purge gas is discharged from the hood member 11 in the same direction as the optical axis, and it can be seen that the concentration of the purge gas is particularly high near the optical axis, and a large amount of purge gas is flowing into the monitored space.
In contrast, in the example of the present invention shown in Figures 6 and 7, the purge gas discharged from the hood member 11 diffuses radially outward from the hood member 11, and it can be seen that the purge gas is less likely to flow into the monitored space than in the comparative example.
As described above, it has been confirmed that by generating a swirling flow within the hood member 11, it becomes difficult for the purge gas to flow into the monitored space, and the state of the monitored space is less likely to be affected.

Furthermore, comparing Figures 6 and 7, it can be seen that increasing the flow rate of the purge gas causes the discharged purge gas to deviate more from the optical axis. This is because the strength of the swirling flow increases with an increase in the flow rate of the purge gas, thereby increasing the diffusion power of the purge gas. By utilizing this characteristic, measurements can be performed effectively even in poor measurement environments, such as those with strong winds blowing toward the lens surface. When wind blows toward the lens surface, dust is more likely to enter the hood member, so it is necessary to increase the flow rate of the purge gas to counter this. However, increasing the flow rate of the purge gas, as in the conventional example, also increases the adverse impact on the condition of the monitored space.
In this regard, the present invention is suitable for poor measurement environments because increasing the flow rate of the purge gas does not significantly affect the state of the space to be monitored.

REFERENCE SIGNS LIST 1 Light-reducing fluid detection device 3 Light-emitting unit 5 Light-receiving unit 7 Fixing plate 9 Lens 11 Hood member 13 Bolt 15 Base end 17 First hood piece 19 Second hood piece 19a Groove portion 21 Third hood piece 21a Recess 23 Fourth hood piece 25 Purge gas 27 Bolt hole 28 First supply flow path 29 First discharge port 31 Inlet 33 Second supply flow path 35 Second discharge port 37 Light-emitting unit (Prior art example 1)
39 Light-emitting element 41 Smoke 43 Dust 45 Monitoring light 47 Light-emitting part (conventional example 2)

Claims (5)

A light-reducing fluid detection device that detects a fluid present in a monitored space, comprising: a light-emitting unit having a light-emitting element; and a light-receiving unit having a light-receiving element, the light-receiving unit being disposed across the monitored space;
a lens provided in front of the light-emitting element or the light-receiving element; and a wall portion provided to surround the lens and to form a tunnel-shaped swirling flow generating space.
a first discharge port provided near a front end of the wall portion and configured to discharge the gas into the swirl flow generating space to generate a swirl flow;
a second outlet provided in the wall portion rearward of the first outlet for discharging gas near the lens . 2. The light-reducing fluid detection device according to claim 1, wherein the wall portion is formed by a cylindrical hood member or a side wall of a hole formed in the wall portion. 3. The light-reducing fluid detection device according to claim 1 , wherein the direction in which the gas is discharged from the first discharge port is inclined at a predetermined angle with respect to the radial direction of the wall portion and is also inclined forward with respect to the axial direction . The light-reducing fluid detection device according to claim 1 or 2, characterized in that the second discharge port is provided around the entire circumference of the wall portion. The light-reducing fluid detection device according to claim 1 or 2, characterized in that a first supply flow path that supplies the gas to the first outlet and a second supply flow path that supplies the gas to the second outlet are provided in the wall portion, and the first supply flow path and the second supply flow path are connected to each other.