Detector

Abstract

To make indication by an actuation indicator easily visible in a detector provided with an actuation indicator.SOLUTION: Provided is a detector comprising: a housing having within it a circuit board where a detection circuit having the function to detect an event to be detected is formed; one or more light-receiving elements for detection that are disposed inside the housing so as to face an opening provided on the front side of the housing and receive light of a prescribed wavelength emanated from a detection object; and a transparent protective cover provided between the opening and the one or more light-receiving elements for detection. An actuation indicator for notifying that an event as the detection object has been detected by the detection circuit, on the basis of a signal from the one or more light-receiving elements for detection is mounted on the circuit board, and a light-guide plate is included that is disposed between the protective cover and the circuit board and attached to the housing, for causing light from the actuation indicator to be ejected from the protective cover.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a detector that detects an abnormal event such as a flame, and more particularly to a detector that is provided with an indicator light (operation indicator light) that indicates that a flame or the like has been detected. [Background technology]

[0002] Flame detectors are one type of fire detector used in fire alarm systems installed inside and outside buildings. Flame detectors use ultraviolet and infrared sensors that can detect specific types of flames and have limited wavelengths of light they can receive so as not to detect sunlight or other heat sources. Considering their outdoor use, flame detectors are dustproof and waterproof, with a cover glass in front of the sensor located in the center of the case. Furthermore, flame detectors may be equipped with an operation indicator light that indicates when a flame is detected.

[0003] Conventionally, inventions relating to flame detectors equipped with an operation indicator lamp are disclosed in Patent Documents 1 and 2. Of these, the flame detector described in Patent Document 1 has a light-emitting element that functions as an operation indicator light disposed on the back of the flame-detecting element (UVtron), and the light-emitting element flashes when a flame is detected. Also, the flame detector described in Patent Document 2 has a flame-detecting element disposed facing a light-transmitting window (cover glass) disposed in an opening in the front center of the main body case, and an operation indicator light having a ring-shaped light-emitting portion that surrounds the light-transmitting window. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 4832037 [Patent Document 2] Japanese Patent Application Laid-Open No. 2016-71775 Summary of the Invention [Problem to be solved by the invention]

[0005] The flame detector described in Patent Document 1 has an operation indicator light disposed on the back of the element that detects flames, which has the advantage of making the indicator light less noticeable, but has the problem that the display of the operation indicator light is difficult to see when the flame detector is installed in a high place. On the other hand, the flame detector described in Patent Document 2 has an operation indicator light disposed on the front of the main body case, which has the advantage of making the display of the operation indicator light easy to see, but has the problem that assembling the parts is tedious and the space available to install other parts, such as an element for detecting dirt on the cover glass, is limited when it is desired to install other parts.

[0006] In recent years, demand for hydrogen energy has increased, and hydrogen vehicles are now being used on city streets. Hydrogen vehicles are refueled at hydrogen stations, but there is a risk of hydrogen leaks during the refueling process. However, because both gaseous hydrogen and the hydrogen flames that appear when hydrogen is applied are invisible, it can take a while to detect a leak, which can lead to a hydrogen fire or explosion. For this reason, flame detectors that can detect hydrogen flames are becoming increasingly important in order to detect and warn of flames caused by ignition of leaked hydrogen.

[0007] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to make the indication by the operation indicator light in a detector equipped with the operation indicator light more visible. Another object of the present invention is to provide a detector equipped with an operation indicator light that allows for easy assembly of parts and avoids limiting the space available for installing other parts on the front of the detector's main body case. [Means for solving the problem]

[0008] In order to solve the above problems, the present invention provides: a housing incorporating a circuit board on which a detection circuit having a function of detecting an event to be detected is formed; one or more light-receiving elements for detection, which are disposed inside the housing so as to face an opening provided on the front side of the housing and receive light of a predetermined wavelength emitted by a detection target; a transparent protective cover provided between the opening and the one or more detection light receiving elements; In a detector comprising: an operation indicator light is mounted on the circuit board to notify that the detection circuit has detected a target event; The light guiding plate is disposed between the protective cover and the circuit board, and is attached to the housing to allow light from the operation indicator lamp to be emitted from the protective cover.

[0009] With a detector having the above-described configuration, the light guide plate disposed between the protective cover and the circuit board functions as a member that emits light from the operation indicator light, making the display by the operation indicator light easier to see. Furthermore, because the light guide plate that emits light from the operation indicator light is located inside the protective cover, there is no need to provide a member that emits light from the operation indicator light on the front surface of the detector's main body case, which simplifies the front surface of the main body case and avoids limiting the space available for installing other components, such as condensation detection means, if desired.

[0010] Preferably, the light guide plate has a size larger than that of the protective cover, The operation indicator light is disposed on the circuit board at a position outside the opening and inside the light guide plate. With this configuration, since the light guide plate is large, the light emitted from the light guide plate can be emitted from the entire protective cover, making the display by the operation indicator lamp easier to see. In addition, it is possible to prevent the light emitted from the operation indicator lamp from being directly seen through the opening in the front of the main body case, and it is possible to allow almost all of the light emitted from the operation indicator lamp to enter the light guide plate.

[0011] Preferably, a groove and / or a slit is formed in a portion of the light guide plate corresponding to the edge of the opening, in a form that follows a part of the edge of the opening. With this configuration, the light incident on the light guide plate from the operation indicator light can be prevented from spreading beyond the area where the grooves or slits are formed. Therefore, when the size of the light guide plate is set large to make it easier to assemble parts, it is possible to avoid a reduction in the amount of light emitted from the required areas due to light being deflected to unnecessary areas.

[0012] Furthermore, preferably, a light incident portion having a light incident surface facing the operation indicator light is provided at a portion of the light guide plate corresponding to the operation indicator light, The groove and / or slit provided in the vicinity of the light incident portion is formed so as to pass outside the light incident portion and partially surround the light incident portion. With this configuration, more light incident on the light guide plate from the operation indicator lamp can be guided toward the opening on the front surface of the main body case, making the indication by the operation indicator lamp easier to see.

[0013] Furthermore, preferably, the light guide plate has a plurality of screw insertion holes formed in a region outside the area in which the grooves and / or slits are formed, and is fixed to the inner wall of the housing with a plurality of screws inserted into the plurality of screw insertion holes, sandwiching the protective cover between the light guide plate and the edge of the opening of the housing. With this configuration, the protective cover is fixed by being sandwiched between the light guide plate and the inner wall of the housing, making it easy to assemble the parts. Furthermore, since a plurality of screw insertion holes for inserting screws to fix the light guide plate are formed in a portion outside the area where the grooves and / or slits are formed, there is no need for excessive heat loss caused by the fixing screws or for the light emission of the detector operation indicator visible through the cover glass to be obstructed, thereby realizing efficient heating and an easy-to-read display.

[0014] Preferably, the front or rear surface of the light guide plate in the area corresponding to the opening is textured and / or micro-processed. According to this configuration, by adjusting the density and size of the grain and microstructure on the surface of the light guide plate, the distribution of light emitted from the light guide plate can be made more uniform, making the display by the operation indicator light easier to see. [Effects of the Invention]

[0015] According to the present invention, in a detector equipped with an operation indicator light, the display by the operation indicator light can be made easily visible. Furthermore, the assembly of parts can be simplified, and the installation space for other parts on the front surface of the detector body case can be prevented from being limited. Furthermore, when the size of the light guide plate is set large to make the display of the operation indicator light easily visible and simplify the assembly of parts, it is possible to prevent the amount of light emitted from the required parts from being reduced due to light being deflected to unnecessary parts. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a perspective view showing an embodiment of a flame detector according to the present invention. [Figure 2] 1A is a central cross-sectional perspective view showing the internal structure of a flame detector according to an embodiment, and FIG. 1B is an enlarged cross-sectional view showing a part of the internal structure (a portion surrounded by a dashed line) in an enlarged manner. [Figure 3] 1A is a plan view showing the shape of the light guide plate and the arrangement of sensors inside the main body case of the flame detector of the embodiment, and FIG. 1B is a cross-sectional side view showing the cross-sectional structure of the light guide plate and the circuit board along line B-B' in FIG. [Figure 4] FIG. 2 is a perspective view showing an example of a specific structure of a light-guiding member in the flame detector of the embodiment. [Figure 5] 1A is a cross-sectional front view showing the internal structure of the upper part of the main body case of the flame detector of the embodiment, and FIG. 1B is a partially enlarged cross-sectional view showing the shape of the incident part of the light emitted from the operation indicator light of the light-guiding member. DETAILED DESCRIPTION OF THE INVENTION

[0017] An embodiment of the present invention applied to a flame detector for detecting hydrogen flames will be described below with reference to the drawings. Fig. 1 is a perspective view of a flame detector 10 of this embodiment, Fig. 2 is a central cross-sectional perspective view and a partially enlarged cross-sectional view showing the internal structure, and Fig. 3 is a plan view showing the internal structure of the flame detector of this embodiment and a cross-sectional front view showing the structure of the upper part of the detector. For convenience of explanation, in the following description, the side that faces the front when the flame detector is installed in a building will be referred to as the upper side, and the back side will be referred to as the lower side. Flame detectors are generally installed with their backs facing the mounting surface, either directly on the wall of a building or fixed to a base such as an angle adjuster, and detect flames in the area directly in front of them. Such flame detectors are connected via wiring (sensor lines) to a receiver (not shown) that centrally manages multiple flame detectors within the detection area, and when they detect a flame, they send a detection signal (alarm signal) to the receiver.

[0018] 1, the flame detector 10 of this embodiment includes a housing made up of a main body case 210 having a front cover portion 211 and a cylindrical portion 212, and a lower case 220 having a cylindrical portion 221 and a base portion 222 and coupled to the rear side of the main body case 210 and fixed to an installation location. Although not particularly limited, in this embodiment, the main body case 210 and the lower case 220 are formed from aluminum castings.

[0019] A recess is provided toward the center on the top surface of the front cover portion 211 of the main body case 210, and as shown in FIG. 1, a circular opening 211A is formed in the center of the recess, and a glass cover 213 serving as a protective cover made of a translucent material such as quartz glass is arranged in this opening 211A so as to cover the upper part of the detection light receiving elements 51, 52A, and 52B described below.

[0020] 2(A), the lower part of cylindrical part 212 of main body case 210 is a cylinder having an outer diameter slightly larger than that of cylindrical part 221 of lower case 220, and the upper end part of lower case 220 is inserted into an opening in the lower part of main body case 210, and the upper end part of lower case 220 is fitted inside main body case 210. Then, as shown in FIG. 1, main body case 210 and lower case 220 are configured to be joined by bolts 231 inserted into protruding parts 210a and 220a formed so as to protrude laterally from the lower peripheral wall of main body case 210 and the upper peripheral wall of lower case 220.

[0021] In addition, wing-shaped flange portions 223 are formed at the four corners of the base portion 222 of the lower case 220, and screw insertion holes 223a are formed in the flange portions 223 so that the lower case 220 can be fixed to an installation surface such as a ceiling surface by inserting screws (not shown) into the screw insertion holes 223a. Furthermore, a cylindrical wiring port 224 is provided on the outer peripheral surface of cylindrical portion 221 of lower case 220, through which an end of a cable (not shown) having wiring such as a signal line or a power line is inserted. The end of the cable inserted into wiring port 224 is connected to a terminal on terminal board 215A which is internally wired to circuit board 214 (see FIG. 2) which is provided inside main body case 210, has elements and ICs mounted thereon that constitute a circuit having a flame detection function, and has wiring that connects the elements and ICs together.

[0022] Flame detector 10 of this embodiment is equipped with one ultraviolet sensor 51 and two infrared sensors 52A and 52B to detect a hydrogen flame. As shown in FIG. 2(A), ultraviolet sensor 51 is installed approximately in the center of the top surface of circuit board 214, and infrared sensors 52A and 52B are installed slightly off-center. Of these, infrared sensors 52A and 52B are arranged parallel to ultraviolet sensor 51, i.e., in a direction perpendicular to the plane of the paper in FIG. 2(A), as shown in FIG. 3(A). Circuit board 214 is also provided with a control circuit that, when it determines that a flame has been detected based on signals from sensors 51, 52A, and 52B, transmits a detection signal (alert signal) to a receiver (not shown) and turns on an operation indicator light (described below).

[0023] The ultraviolet sensor 51 and the infrared sensors 52A and 52B are sensors capable of detecting light in different wavelength bands that are appropriately selected so as to detect sunlight and other heat sources and also detect light with wavelengths specific to hydrogen flames. In addition, below the circuit board 214, a terminal board 215A and a back cover 215B are arranged parallel to each other with a predetermined distance between them, and a connection terminal 216 to which the end of the cable (wiring) is connected is mounted facing downward in the center of the underside of the terminal board 215A, and is exposed by penetrating the back cover 215B. On the other hand, above the circuit board 214, a light guide plate 217 made of a light-transmitting resin is arranged so as to contact the peripheral edge of the underside of the glass cover 213. The light guide plate 217 guides light from operation indicator lights (LED lamps) 58A, 58B (described later) which are provided separately from the power light 55 (described later) and which indicate that the detector has detected a flame, and emits the light forward through the glass cover 213.

[0024] 2(B), the central portion of light guide plate 217 is formed one step lower so as not to come into contact with glass cover 213, corresponding to the edge of opening 211A on the front surface of main body case 210, and corresponding to this lowered portion, thin, planar heater 218 is disposed so as to come into contact with the underside of glass cover 213. Heater 218 has an annular shape when viewed from above, and heats the peripheral portion of glass cover 213. The heat imparted from heater 218 to glass cover 213 is transferred from the peripheral portion of glass cover 213 to the center, removing condensation from the entire glass cover 213.

[0025] 2(B), a recess that houses packing (O-ring) 219 as a sealing material is provided on the underside of front cover portion 211 of main body case 210, and packing 219 is configured to prevent water from entering the case through a gap at the joint between the edge of opening 211A of front cover portion 211 and glass cover 213. A sealing material is also provided at the fitting portion between cylindrical portion 212 of main body case 210 and cylindrical portion 221 of lower case 220.

[0026] In the flame detector of this embodiment, glass cover 213 is formed to be slightly larger than opening 211A. Light guide plate 217 is formed to be slightly larger than glass cover 213. Then, with glass cover 213 and packing 219 sandwiched between light guide plate 217 and the edge of the opening of front cover portion 211, screws are inserted from below into multiple screw insertion holes 217d provided on the periphery of light guide plate 217, and screwed into screw holes provided in corresponding locations on front cover portion 211. As a result, when attaching the light guide plate 217 to the front cover part 211, the glass cover 213 can be fixed at the same time, which makes it easy to assemble the parts, and also the packing (O-ring) 219 is crushed, which allows it to adhere tightly to the glass and aluminum housing, providing excellent sealing properties.

[0027] Furthermore, in flame detector 10 of the present embodiment, three heat insulating grooves 211a are formed on the underside of the edge of opening 211A of front cover part 211. Grooves 211a are formed over the entire circumferential direction of front cover part 211 so as to form a circle when viewed from above. As described above, the formation of multiple grooves 211a reduces the contact area between front cover portion 211 and glass cover 213, reducing the transfer of heat from heater 218 to glass cover 213 to front cover portion 211, and efficiently heating glass cover 213, thereby preventing the rate of temperature rise from slowing down and the time required to remove condensation from increasing. Note that to prevent the heater temperature from rising higher than necessary, which could cause thermal damage to other parts or unnecessary power consumption, a temperature sensor may be provided near the glass cover surface, and heater 218 may be feedback-controlled based on the detected temperature.

[0028] Next, the structure and operation of the light guide plate 217 that functions as a light emitting member that emits light from the operation indicator lamp forward will be described with reference to FIGS. 3(A) shows the shape of light guide plate 217 and the arrangement of sensors 51, 52A, and 52B inside main body case 210, and Fig. 3(B) shows the cross-sectional structure of light guide plate 217 and circuit board 214 taken along line B-B' in (A). Fig. 4 is a partially enlarged view showing the detailed structure of light guide plate 217, and Fig. 5 is a cross-sectional view and partially enlarged view showing the internal structure of the upper part of main body case 210 including light guide plate 217, which is a main component of the present invention.

[0029] 3(A), the elements denoted by the reference symbols 58A and 58B are LED lamps serving as operation indicators that emit visible light. These operation indicators 58A and 58B are mounted facing upward below light guide plate 217 and outside opening 211A of glass cover 213 on circuit board 214. Light guide plate 217 is configured so that light emitted from operation indicators 58A and 58B enters light guide plate 217 and spreads out in a planar form. 3(A), the operation indicator lights 58A and 58B are installed at positions spaced approximately 120 degrees apart, but they may be installed at positions spaced 180 degrees or at other angles. Also, the number of operation indicator lights is not limited to two, and may be one or three or more.

[0030] 3, reference numerals 53 and 54 denote a light-emitting element (LED) and a light-receiving element for detecting dirt on the protective cover 213, and the light-emitting element 53 and the light-receiving element 54 are disposed in opposing positions with the sensors 51, 52A, and 52B in between. Light emitted obliquely upward from the light-emitting element 53 passes through the protective cover 213, is introduced into a light-guiding member disposed on the edge of the front cover portion 211, changes direction downward, and is received by the light-receiving element 54, and the degree of dirt on the protective cover 213 is determined from the decrease in the amount of received light. Note that this dirt detection function is not essential to the present invention, so a detailed description thereof will be omitted.

[0031] 3(B), light guide plate 217 is disposed parallel to and above circuit board 214 at a predetermined distance. To prevent light detection by sensors 51, 52A, and 52B and light emitted from light emitting element 53 for detecting dirt from being obstructed, light guide plate 217 has openings formed therein corresponding to sensors 51, 52A, and 52B and light emitting element 53, as shown in FIG. 3(A). Furthermore, power lights (LED lamps) 55 are provided near infrared sensors 52A and 52B on circuit board 214 to indicate that power is being supplied and the sensors are operating.

[0032] Next, the detailed structure of the light guide plate 217 that functions as the light emitting portion of the operation indicator lamp will be described. As described above, glass cover 213 is larger than the size of central opening 211A of front cover portion 211, and light guide plate 217 is formed to be even larger than glass cover 213. Therefore, when light incident from two fan-shaped light entrance portions 217a provided corresponding to operation indicator lights 58A, 58B spreads over the entire light guide plate 217, the light that reaches the area outside opening 211A is wasted because it cannot be seen from the front of the flame detector, and the amount of light emitted from opening 211A is reduced accordingly, resulting in poor efficiency.

[0033] 3(A), in this embodiment, multiple (three in the figure) arc-shaped grooves 217b that follow the edge of opening 211A and two V-shaped slits 217c that connect grooves 217b and surround the outside of light entrance portion 217a are formed in light guide plate 217, so that incident light does not spread to the outer edge. Here, the direction of the straight line portions of the two V-shaped slits 217c is the tangent direction of arc-shaped grooves 217b. The cross-sectional shape of grooves 217b can be any shape, such as a U-shape, a V-shape, a U-shape, or a modified form thereof.

[0034] Groove 217b may be on the upper or lower surface of light guide plate 217. Alternatively, a groove may be formed in the portion of slit 217c shown in FIG. 3(A), and a slit may be formed in the portion of groove 217b. FIG. 4 shows the specific structure of groove 217b and slit 217c provided in light guide plate 217. Note that if groove 217b were eliminated and the entire surface were slits, the inner region of light guide plate 217 would be separated from the outer region, so groove 217b is necessary. As can be seen from FIG. 4, light guide plate 217 has unevenness and slopes formed on the front and back surfaces in addition to groove 217b and slit 217c, but is generally flat overall.

[0035] Furthermore, in this embodiment, the shape of light incident portion 217a of light guide plate 217 is devised. The shape of light incident portion 217a is shown in Fig. 5. Fig. 5(A) shows a cross-sectional structure of the upper part of front cover portion 211 of main body case 210 taken along line A-A' shown in Fig. 3(A). Fig. 5(B) shows an enlarged view of a portion of Fig. 5(A). As shown in FIG. 5(B), the operation indicator light 58A (58B) is mounted on the circuit board 214 with its light emitting surface facing upward, and the light incident portion 217a has a shape such that a portion of the light guide plate 217, which is generally almost flat, is curved downward, and an incident surface IF facing the operation indicator light 58A (58B) is formed at the tip of the curved light incident portion 217a.

[0036] Furthermore, in order to achieve the above-described shape, a gap S continuous with the slit 217c is provided above the curved portion of the light incident portion 217a, and the upper surface of the light incident portion 217a facing this gap S is curved. As a result, light that enters the incident surface IF from below is reflected by the curved surface and changes direction toward the center of the opening 211A, and proceeds into the flat region at the center of the light guide plate 217. Note that, in this embodiment, the upper side of the light incident portion 217a, i.e., the portion facing the glass cover 213, is curved, but it may also be formed as an inclined surface having a predetermined inclination angle.

[0037] 5, the inner portion of the light incident portion 217a is formed as a tapered surface. The angle of this tapered surface is set so that its extension is outside the edge of the opening 211A. This allows a portion of the light incident at an angle from the operation indicator light 58A (58B) onto the incident surface IF of the light incident portion 217a to pass through the light incident portion 217a and exit from the flat upper surface of the light incident portion 217a and be emitted from the opening 211A, thereby preventing the light of the operation indicator lights 58A and 58B from being directly visible. Instead of a tapered surface, a curved surface may be formed on the inner side of the light incident portion 217a.

[0038] Furthermore, in this embodiment, the surface of the flat portion on the central side of light guide plate 217, particularly the portion facing opening 211A, is textured, so that light that has traveled along the flat portion hits the textured pattern and is emitted toward the surface side. This makes it possible to make the flat portion on the central side of light guide plate 217 shine almost uniformly as a whole, and to prevent components located inside light guide plate 217 from being seen through protective cover 213. Also, because light guide plate 217, which serves as an apparent operation indicator, is located inside main body case 210 rather than on the front side of the case, it is possible to avoid limiting the installation space for other components on the front side of the main body case.

[0039] The texture on the surface of light guide plate 217 may be uniform, or the intensity of the texture (height and density of the unevenness) may gradually increase from the outside toward the center, or may be gradually changed to form multiple circles. Instead of applying a textured finish to the flat surface at the center of light guide plate 217, fine processing may be applied to impart a V-shaped cross-section, or the surface may be formed into a triangular prism shape, or a combination of these processes may be applied. As a result, when the operation indicator light is turned on, opening 211A on the front surface of main body case 210 becomes bright overall, allowing users to recognize that the indicator light is on. Furthermore, since the indicator light is non-directional, it can be seen from any direction, improving visibility. Furthermore, the textured finish prevents components on the surface of circuit board 214 from being visible from the outside, improving the design of the detector.

[0040] While the present invention has been described above based on the embodiments, it is not limited to the above embodiments and can be modified as appropriate without departing from the spirit of the present invention. For example, in the above embodiments, slits 217c are formed in light guide plate 217. However, a metal film serving as a reflective layer may be provided on the inner surface of slits 217c to reflect more light and prevent it from diffusing to the outside. Furthermore, the cover glass 213 side of circuit board 214 may be colored white to increase the reflection of light emitted downward from light guide member 217 and assist in light emission to the outside. In addition, in the above embodiment, the present invention is described as being applied to a flame detector, but the present invention can also be applied to human presence sensors and other detectors that use pyroelectric elements as infrared sensors to detect human bodies. [Explanation of symbols]

[0041] 10 Flame detector 51 Ultraviolet sensor (light-receiving element for flame detection) 52A, 52B Infrared sensor (light-receiving element for flame detection) 53 Light-emitting element for detecting dirt 54 Dirt detection light receiving element 55 Power light (LED lamp) 58A, 58B Operation indicator light (LED lamp) 210 Main unit case 210a Overhang 211 Front cover 211A opening 211a Groove 212 Cylindrical part 213 Glass Cover 214 Circuit Board 215A terminal board 215B Back cover 216 connection terminal 217 Light guide plate for operation indicator light 217a Light incidence part 217b Groove 217c Slit 217d Screw insertion hole 218 Heater 219 Sealing material (O-ring) 220 Lower Case 220a Overhang 221 Cylindrical part 222 Base 223 Flange 223a Screw insertion hole 224 Wiring port 231 Connecting bolt

Claims

1. a housing incorporating a circuit board on which a detection circuit having a function of detecting an event to be detected is formed; one or more light-receiving elements for detection, which are disposed inside the housing so as to face an opening provided on the front side of the housing and receive light of a predetermined wavelength emitted by a detection target; a transparent protective cover provided between the opening and the one or more detection light receiving elements; A detector comprising: an operation indicator light is mounted on the circuit board to notify that the detection circuit has detected an event to be detected based on a signal from the one or more detection light-receiving elements; a light guide plate disposed between said protective cover and said circuit board, said light guide plate allowing light from said operation indicator light to be emitted from said protective cover;

2. the light guide plate has a size larger than the protective cover, 2. The detector according to claim 1, wherein the operation indicator light is disposed outside the opening on the circuit board and inside the light guide plate.

3. 3. The detector according to claim 2, wherein a groove and / or a slit is formed in a portion of the light guide plate corresponding to the edge of the opening, the groove and / or slit being formed in a shape that follows a portion of the edge of the opening.

4. a light incident portion having a light incident surface facing the operation indicator light is provided at a portion of the light guide plate corresponding to the operation indicator light, 4. The detector according to claim 3, wherein the groove and / or slit provided in the vicinity of the light incident portion is formed so as to pass outside the light incident portion and partially surround the light incident portion.

5. The detector described in claim 4, characterized in that a plurality of screw insertion holes are formed in the light guide plate in a region outside the area in which the grooves and / or slits are formed, and the light guide plate is fixed to the inner wall of the housing with a plurality of screws inserted into the plurality of screw insertion holes, sandwiching the protective cover between the light guide plate and the edge of the opening of the housing.

6. 6. A detector according to claim 1, wherein the front or rear surface of the area of ​​the light guide plate corresponding to the opening is textured and / or micro-processed.

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