JP5187674B2 - Sensor head for gas detection - Google Patents

Description

  The present invention relates to a gas detection sensor head that reduces detection delay.

  Conventionally, the concentration of various gases present in the atmosphere has been detected using a gas absorption phenomenon such as infrared absorption. The light source light and the gas transmitted light are transmitted from the detection device to the target atmosphere location via an optical fiber so that the detection device can operate at a location remote from the target atmosphere location where gas detection is performed. A gas detection sensor head (hereinafter simply referred to as a sensor head) is installed that performs spatial light propagation only for a certain distance where a phenomenon is desired.

  As shown in FIG. 7, the conventional sensor head 71 is configured such that the inner shell 73 that surrounds the light propagation space 72 and the light incident disposed at a position facing each other across the light propagation space 72 of the inner shell 73. Portion 74 and light emitting portion 75, gas inlet 76 disposed in inner shell 73, dustproof waterproof filter 79 covering the outer periphery of inner shell 73, and end portion of dustproof waterproof filter 79 is closed and light emitting portion An end cap (not shown) that accommodates 75 optical fibers is provided.

  In general, in the sensor head 71, the inner shell 73 is formed in a cylindrical shape, the light incident portion 74 and the light emitting portion 75 are disposed at both ends of the inner shell 73, and spatial propagation from the light incident portion 74 toward the light emitting portion 75. The optical axis of the transmitted light is parallel to the central axis of the inner shell 73. In the illustrated example, the light incident portion 74 and the light emitting portion 75 are arranged on the centers of both ends of the inner shell 73, that is, on the central axis of the cylindrical inner shell 73. Therefore, the optical axis coincides with the central axis.

  On the other hand, the gas inlet 76 is disposed on the side surface of the inner shell 73. The gas inlet 76 is also disposed opposite to the opposite side surface of the inner shell 73. The gas flows into the light propagation space 72 through the gas inlet 76 from the outside of the sensor head 71 that is the target atmosphere.

  The dustproof and waterproof filter 79 is for removing dust and moisture between the target atmosphere and the gas inlet 76. The dustproof and waterproof filter 79 is made of a filter material that allows gas to pass therethrough and does not allow dust and moisture to pass therethrough. The dustproof and waterproof filter 79 is designed to maintain long-term reliability.

  In the conventional sensor head 71, the size of the dustproof / waterproof filter 79 and the inner shell 73 is determined in consideration of the ease of attachment of the dustproof / waterproof filter 79 and the inner shell 73 or the ease of installation in the target atmosphere. ing.

JP-A-5-256769 Japanese Patent Laying-Open No. 2005-61992

  The conventional sensor head 71 shown in FIG. 7 has a problem that the speed at which the gas in the target atmosphere reaches the optical axis at the center of the light propagation space 72 is slow (it takes time). For example, in a facility that produces and distributes fuel gas, when the sensor head 71 is installed around the facility to monitor gas leakage from the facility, the rate at which the gas reaches the optical axis from the target atmosphere is slow. The gas concentration change cannot be known quickly.

  The JIS M 7626 stationary flammable gas detection alarm specifies the detection delay and its test method, and the detection delay must be within 30 seconds.

  In order to meet this requirement, in order to quickly detect a change in gas concentration, it is necessary to increase the speed at which the gas reaches the optical axis from the target atmosphere.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a gas detection sensor head that solves the above-described problems and shortens the detection delay.

In order to achieve the above object, the present invention includes an inner shell that surrounds a light propagation space, and a light incident portion and a light emission portion that are disposed at positions opposed to each other across the light propagation space of the inner shell. A gas inlet disposed in the inner shell, a dustproof waterproof filter that covers the outer periphery of the inner shell, and an end cap that closes the end of the dustproof waterproof filter and accommodates the optical fiber of the light emitting portion. The gas inlet is formed in a shape that is long in one direction and short in the other direction, and is disposed opposite to both sides of the optical axis that connects the light incident part and the light emitting part. The outer diameter of the filter is 20 to 40 mm, the gap between the inner shell and the dustproof and waterproof filter is 0.4 to 0.6 mm, the area of the outer periphery of the dustproof and waterproof filter is A, and the dustproof and waterproof Filter and end cap volume is V When the ratio V / A is 0.71 der less is, the light propagation space is small gas detection sensor head than the minor axis of the gas inlet.

The major axis of the gas inlet may be parallel to the optical axis connecting the light incident part and the light emitting part.

The inner shell may be cylindrical , the light incident portion and the light emitting portion may be disposed on both end faces of the inner shell, and the gas inlet may be disposed on a side surface of the inner shell.

  The present invention exhibits the following excellent effects.

  (1) The detection delay can be shortened.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

  As shown in FIG. 1, a gas detection sensor head 1 according to the present invention opposes an inner shell 3 surrounding a light propagation space 2 with the light propagation space 2 of the inner shell 3 interposed therebetween. A light incident part 4 and a light emission part 5 arranged at positions, a plurality of gas inlets 6 arranged in the inner shell 3, a dustproof waterproof filter 9 covering the outer periphery of the inner shell, and the dustproof waterproof filter 9 and an end cap (not shown) for accommodating the optical fiber of the light emitting portion, and the outer diameter of the dustproof and waterproof filter 9 is 20 to 40 mm. When the clearance between the dustproof and waterproof filter 9 is 0.4 to 0.6 mm, the area of the outer periphery of the dustproof and waterproof filter 9 is A, and the volume in the dustproof and waterproof filter 9 and the end cap is V The ratio V / A is 0.71 or less.

  The inner shell 3 is preferably formed into a cylindrical shape such as a cylinder or a rectangular tube (polygonal cylinder). In the present embodiment, the inner shell 3 is formed into a cylindrical shape. The inner shell 3 is formed by forming a material having a predetermined thickness (SUS in the present embodiment) into a cylindrical shape having a predetermined outer diameter.

  The light incident portion 4 and the light emitting portion 5 may be disposed anywhere on the inner shell 3 as long as they face each other. However, in this embodiment, the inner shell 3 is cylindrical and both end surfaces thereof are parallel to each other. Therefore, the light incident part 4 and the light emitting part 5 are arranged on both end faces of the inner shell 3. In particular, here, the light incident part 4 and the light emitting part 5 are arranged at the centers of both end faces of the inner shell 3, and the optical axes coincide with the central axis of the inner shell 3.

  The light incident part 4 and the light emitting part 5 are provided with a lens 8 at the tip of an optical fiber 7 and the lens 8 is penetrated from the outer end face of the inner shell 3 to the light propagation space 2. The lens 8 is polished obliquely to prevent light interference. The optical fiber 7 of the light emitting portion 5 is folded in a loop shape within the space surrounded by the end caps and wired side by side with the optical fiber 7 of the light incident portion 4.

  The gas inlet 6 may be disposed anywhere on the inner shell 3, but in this embodiment, gas flowing from the target atmosphere into the light propagation space 2 of the inner shell 3 flows at right angles to the optical axis. Thus, the gas inlet 6 is disposed so as to face the side surface of the inner shell 3 and the side surface on the opposite side. The gas flows easily from the gas inlet 6 to the gas inlet 6 on the opposite side to the optical axis, thereby facilitating the gas flow and shortening the time for the gas to flow into the light propagation space 2 from the target atmosphere. can do.

  In the present embodiment, the gas inlet 6 has a shape that is long in one direction and short in the other direction, such as an ellipse, an ellipse, a rectangle, and a flat hexagon. The longer opening diameter is called the major axis, and the shorter opening diameter is called the minor axis. In the illustrated example, the gas inlet 6 is formed in a flat octagon having two sides parallel to the major axis and another two sides parallel to the minor axis.

  In the present embodiment, the gas inlet 6 has a short axis directed in the circumferential direction of the inner shell 3 and a long axis directed in the axial direction of the inner shell 3. Therefore, the major axis of the gas inlet 6 is parallel to the optical axis connecting the light incident part 4 and the light emitting part 5.

  In the present embodiment, the gas inlets 6 are arranged in a line so that the long axes of the plurality of gas inlets 6 are on the same straight line.

  The dustproof / waterproof filter 9 is for removing dust and moisture, and is composed of, for example, a sintered metal filter. The dustproof / waterproof filter 9 is formed by forming a filter material having a predetermined thickness into a cylindrical shape having a predetermined inner diameter, and fixing flanges (not shown) at both ends to an end cap and an optical fiber housing portion described later. is there.

As shown in FIG. 2, one end of the gas detection sensor head 1 is attached to an optical connector 26 that accommodates an optical connector connected to the optical fiber 7 of the light incident portion 4 and an extra length of the optical fiber 7. An end cap 27 is attached to the other end of the gas detection sensor head 1.
The end cap 27 has a space communicating with the light propagation space 2 surrounded by the inner shell 3 and has a closed end. The optical fiber 7 of the light emitting portion 5 of the gas detection sensor head 1 is looped back in the end cap 27 and returns to the optical fiber housing portion 26 through the outside of the inner shell 3 and is connected to the optical connector. The optical fiber cable 24 connects the light source unit, the gas concentration detection unit, and the optical fiber housing unit 26.

  As shown in FIG. 3, the gas concentration detection device 31 detects the gas concentration by receiving the light source unit 32 that provides the light source light to the gas detection sensor head 1 and the light transmitted through the gas detection sensor head 1. And a gas concentration detector 33.

  The light source unit 32 includes a triangular wave generator 321 that generates a triangular wave that defines the sweep width and sweep period of the modulation center wavelength, a bias power source 322 that outputs a bias voltage based on the triangular wave, an inductor 323 that cuts off an AC component, and a modulation frequency. An oscillator 324 that generates a sine wave voltage that defines an amplitude, a capacitor 325 that cuts off a direct current component, a frequency multiplier 326 that doubles the sine wave, and a laser light emitting element to which a bias voltage and a sine wave voltage are applied in a superimposed manner 327, a Peltier element 328 for heating and cooling the laser light emitting element 327, and a temperature control power source 329 for driving the Peltier element to control the temperature of the laser light emitting element 327.

  The gas concentration detection unit 33 includes a light receiving element 331 that receives the transmitted light from the gas detection sensor head 1, a phase detection circuit 332 that performs phase sensitive detection on the received light signal based on the signal A of the oscillator and the signal B of the multiplier, A signal storage unit 333 that stores the detected signal as a time series, and a signal processing unit 334 that calculates a gas concentration by performing arithmetic processing on the time series are provided.

  In the gas concentration detection system 31, the gas detection sensor head 1 can be used for multipoint measurement by inserting an arbitrary number in series or in parallel into the optical fiber 7 extending from the light source unit 32 to the gas concentration detection unit 33. it can.

  Since the gas concentration detection method in the gas concentration detection system 31 is a well-known and commonly used technique, a description thereof will be omitted.

  Since the gas concentration detection system 31 performs transmission by light and information processing by an electronic device, if the gas flows into the light propagation space 2 of the gas detection sensor head 1, the gas concentration can be detected immediately. Therefore, the detection delay defined in JIS depends on the speed at which the gas reaches the optical axis from the target atmosphere.

  The effects of the gas detection sensor head 1 of FIG. 1 will be described.

In the gas detection sensor head 1 of FIG. 1, the area (hereinafter referred to as a surface area) of the outer periphery of the dustproof / waterproof filter 9 is A, and the volume of the space in the dustproof / waterproof filter 9 and the end cap 27 (hereinafter referred to as the internal volume). When V is V), the ratio V / A is 0.71 or less. To compare this feature with the prior art, reference is made to FIG.

As shown in FIG. 4A, when the outer diameter of the dustproof and waterproof filter 9 is 30 mm, the surface area A is
2 × π × 1.5 cm × 10 cm≈94 cm ²
(The dimension shown in the drawing is mm, but the calculation formula is cm; the same applies hereinafter).

Since the volume of the cylindrical space surrounded by the dustproof / waterproof filter 9 (the inner shell 3 is removed) V1 (volume of the dustproof / waterproof filter 9 alone) V1 is φ26,
V1 = π × 1.3 cm ² × 10 cm = 53 cm ³
It is.

Since the volume of the cylindrical space surrounded by the end cap 27 (volume of the end cap 27) V2 has an inner diameter of 44 mm and a length of 36 mm,
V2 = π × 2.2 cm ² × 3.6 cm≈55 cm ³
It is.

As shown in FIG. 4B, the volume V3 of the conventional inner shell 73 has an outer diameter of φ20 mm and a length of 100 mm.
V3 = π × 1.0 cm ² × 10 cm≈31 cm ³
It is.

Assuming that there are 10 spaces (referred to as gas inlet portions) formed between the opposing gas inlets 76 by arranging five gas inlets 76 on each side surface and five on each side. The total volume V4 of the gas inlet port has a diameter of φ10 mm and a depth equal to the outer diameter of the inner shell 73 of 20 mm.
V4 = π × 0.5 cm ² × 2 × 10 ≈16 cm ³
It is.

At this time, when the inner shell 73 is accommodated in the dustproof waterproof filter 9, the volume V3 of the inner shell 73 is removed from the sum of the volume V1 of the dustproof waterproof filter 9 and the volume V2 of the end cap 27. The internal volume V is obtained by adding the total volume V4 of the gas inlet 76. That is, the internal volume V is
V = V1 + V2-V3 + V4
= 53 + 55-31 + 16 = 93
It becomes. Here, since the volume of the light propagation space 72 is small, it is excluded from the calculation.

Therefore, the ratio V / A is
V / A = 93/94 ≒ 1
It becomes.

FIG. 4C is a first embodiment of the present invention, in which the outer diameter of the inner shell 3 is increased. Since the volume V3 of the inner shell 3 of the present invention has an outer diameter of φ25 mm and a length of 100 mm,
V3 = π × 1.25 m ² × 10 cm≈49 cm ³
It is.

There are two spaces (gas inlet portions) formed between opposing gas inlets 6 by arranging one elliptical gas inlet 6 on each side and one on the upper and lower sides. Assuming that the total volume V4 of the gas inlet portion is 2.5 mm in width, R is 1.25 mm, and the depth is equal to the outer diameter 25 mm of the inner shell 3,
V4 = (5.75 cm × 0.25 cm + π × 0.125 ² cm ² )
× 2.5cm × 2 pieces
≒ 7.4cm ³
It is.

At this time, when the inner shell 3 is accommodated in the dustproof and waterproof filter 9, the internal volume V is
V = V1 + V2-V3 + V4
= 53 + 55-49 + 7.4 = 66.4
It becomes. Here, since the volume of the light propagation space 2 is small, it is excluded from the calculation.

Therefore, the ratio V / A is
V / A = 66.4 / 94≈0.71
It becomes.

  In the prior art of FIG. 4B, the ratio V / A is 1, and at this time, the detection delay is 30 seconds. Although this value satisfies the JIS standard, it cannot be said that it is sufficiently fast because there is no margin. In the present invention shown in FIG. 4C, the ratio V / A is 0.71, the detection delay is 20 seconds, and the detection delay can be shortened compared to the conventional case.

  Thus, in the present invention, the ratio V / A is reduced by increasing the outer diameter of the inner shell 3 and reducing the gap with the dustproof / waterproof filter 9 (0.5 mm in the above embodiment). The detection response is made faster. The ratio V / A can be arbitrarily set by changing the dimensions of the dustproof and waterproof filter and the inner shell. However, considering the installation in the target atmosphere, a suitable value for the outer diameter of the dustproof and waterproof filter 9 is φ20 to 40 mm. Therefore, it is desirable to select the dimensions of the dustproof and waterproof filter and the inner shell so that the ratio V / A is 0.71 or less within the range of this preferable value. The gap between the inner shell 3 and the dustproof / waterproof filter 9 is preferably small, and 0.4 to 0.6 mm is a preferable value in consideration of its mounting property.

  As can be seen from FIG. 4A, the space in the end cap 27 communicates with the space in the dustproof and waterproof filter 9 and occupies a part of the internal volume V. Therefore, the internal volume V can be changed by changing the end cap 27. FIG. 4D shows another embodiment of the present invention, in which the inner diameter and length of the end cap 27 are reduced and applied to the gas detection sensor head 1 of the first embodiment of the present invention.

Since the volume of the cylindrical space surrounded by the end cap 27 (volume of the end cap 27) V2 has an inner diameter of φ26 mm and a length of 20 mm,
V2 = π × 1.3 cm ² × 2 cm≈11 cm ³
It is.

Therefore, the internal volume V is
V = V1 + V2-V3 + V4
= 53 + 11-49 + 7.4 = 22.4
It becomes.

Therefore, the ratio V / A is
V / A = 22.4 / 94≈0.24
It becomes. The detection delay is 8 seconds.

  Thus, the ratio V / A can also be reduced by reducing the inner diameter or length of the end cap 27. However, since the optical fiber 7 is folded and accommodated in the end cap 27, it is desirable to secure the space in the end cap 27 to the extent that the curvature of the optical fiber 7 does not increase.

  FIG. 5 shows the relationship between the ratio V / A and the detection delay. By setting the ratio V / A to 0.71 or less, the detection delay can be set to 20 seconds or less, and the detection delay within 30 seconds of the JIS standard can be achieved.

  Other features of the present invention will be described.

  As shown in FIG. 1, the opening area can be increased without impairing the mechanical strength of the inner shell 3 by making the gas inlet 6 long in one direction and short in the other direction. By increasing the opening area, it is possible to improve the speed at which the gas is introduced. If the gas inlet 76 is circular as in the conventional sensor head 71, the opening area of the gas inlet 76 can only be increased by increasing the opening diameter uniformly in all directions. The mechanical strength of 73 decreases. In that respect, the gas inlet 6 of the gas detection sensor head 1 of the present invention does not extend the short axis, but can increase the opening area by extending the long axis. In this case, the mechanical strength of the inner shell 3 is increased. Does not drop.

  The direction in which the gas inlet 6 is lengthened is not limited to the direction parallel to the optical axis, and may be arbitrary in the circumferential direction or the oblique direction of the inner shell 3 so long as the mechanical strength is not reduced.

  The gas detection sensor head 1 of the present invention can shorten the time during which gas flows from the target atmosphere into the light propagation space 2 by increasing the opening area of the gas inlet 6. Therefore, by using the gas detection sensor head 1 for the gas concentration detection system 21, a change in the gas concentration of the target atmosphere can be detected quickly.

  Next, the sensor head 61 for gas detection shown in FIG. 6 has gas inlets 6 arranged alternately. That is, in the gas detection sensor head 1 of FIG. 1, the long axes of the plurality of gas inlets 6 are aligned in a line so that they are on the same straight line. However, in the gas detection sensor head 61 of FIG. The gas inlets 6 are arranged at different positions in the circumferential direction of the inner shell 3 so that the long axes of the gas inlets 6 adjacent to each other in the axial direction are not on the same straight line. The gas inlets 6 that are separated from each other are not limited to this, and the major axes may be on the same straight line.

  In the present embodiment, a plurality of gas inlets 6 are also arranged in the circumferential direction of the inner shell 3. As a result, the number of gas inlets 6 is greater than that of the gas detection sensor head 1.

  Since the gas detection sensor head 61 has the gas inlets 6 arranged alternately, the mechanical strength of the inner shell 3 can be further ensured and the vibration resistance can be improved.

  Further, since the gas detection sensor head 61 has the gas inlets 6 arranged alternately, the number of the gas inlets 6 can be increased without impairing the mechanical strength of the inner shell 3.

It is sectional drawing along the side surface of a gas detection sensor head which shows one Embodiment of this invention, a fracture | rupture side surface, and a central axis. It is an external view of the sensor head for gas detection. It is a schematic block diagram of a gas concentration detection apparatus. It is a figure which shows the definition and specific example dimension of the surface area A and the internal volume V, (a) is a dust-proof waterproof filter and end cap, (b) is a conventional inner shell, (c) is an inner shell of the present invention, ( d) shows the end cap of the present invention. It is a detection delay characteristic figure with respect to ratio V / A in the sensor head for gas detection. It is sectional drawing along the central axis of the sensor head for gas detection which shows one Embodiment of this invention. It is sectional drawing along the side surface, fracture | rupture side surface, and central axis of the conventional sensor head for gas detection.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Gas detection sensor head 2 Light propagation space 3 Inner shell 4 Light incident part 5 Light emission part 6 Gas inflow port 7 Optical fiber 8 Lens 9 Dust-proof waterproof filter 27 End cap

Claims (3)

An inner shell that surrounds the light propagation space, a light incident portion and a light emission portion that are disposed opposite to each other across the light propagation space of the inner shell, and a gas inflow port that is disposed in the inner shell And a dustproof waterproof filter that covers the outer periphery of the inner shell, and an end cap that closes the end of the dustproof waterproof filter and accommodates the optical fiber of the light emitting portion, and the gas inlet is in one direction. It is formed in a long and short shape in the other direction and is disposed opposite to both sides of the optical axis connecting the light incident part and the light emitting part, and the outer diameter of the dustproof and waterproof filter is 20 to 40 mm, The clearance between the inner shell and the dustproof waterproof filter is 0.4 to 0.6 mm, the area of the outer periphery of the dustproof waterproof filter is A, and the volume inside the dustproof waterproof filter and end cap is V. when it, the ratio V / a is der 0.71 below The gas detection sensor head the light propagation space being less than the minor axis of the gas inlet.   2. The gas detection sensor head according to claim 1, wherein a major axis of the gas inlet is parallel to an optical axis connecting the light incident part and the light emitting part.   The inner shell is cylindrical, the light incident portion and the light emitting portion are disposed on both end faces of the inner shell, and the gas inlet is disposed on a side surface of the inner shell. 3. A gas detection sensor head according to 1 or 2.

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