Detector

Abstract

To easily remove a body case from a base part in a detector having a highly airtight housing.SOLUTION: In a detector comprising a housing with a built-in detection circuit having a function for detecting event occurrence of a detection object, it is constituted so that a photodetector for detection is arranged to face an opening provided on a front side of the housing, and a transparent protective cover is provided between the opening and the photodetector for detection, the housing comprises: a lower case to be installed on an installation surface of a building directly or via a mounting base; and a body case having the protective cover to be fitted into the lower case, a fitting part between the lower case and the body case has airtightness, and a pair of tabs which come close to each other at a normal fitting position and the centers of which become a shifted state are formed near the fitting part between the lower case and the body case on each outer peripheral surface of the lower case and the body case.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a detector that detects abnormal events such as flames, and in particular to a technique that is useful when applied to a detector that has a housing with a highly airtight structure for dustproofing and waterproofing. [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, which are capable of detecting specific types of flames and have limited wavelengths of light they can receive so as not to detect sunlight or other heat sources. Furthermore, considering that flame detectors are used outdoors, the housings containing the sensors are sometimes constructed with dustproof and waterproof structures using sealants such as packing. BACKGROUND ART Patent Document 1 describes an invention relating to a flame detector that uses packing for dustproofing and waterproofing.

[0003] On the other hand, flame detectors are sometimes installed by narrowing down the area to be monitored and using an angle adjuster so that the area falls within the detection range. A mounting base for flame detectors that has the ability to adjust the angle around two orthogonal axes, allowing for highly accurate angle adjustment, is described in Patent Document 2, for example. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-71775 [Patent Document 2] Japanese Patent Publication No. 2022-40902 Summary of the Invention [Problem to be solved by the invention]

[0005] Flame detectors installed in monitored areas are often constructed with a main case and a base, with the main case being detachable from the base, which is fixed to a mounting base, to allow access to the interior of the detector by opening the housing during wiring work during installation or during regular maintenance. However, flame detector housings are highly airtight, so a relatively strong force is required to separate the main case from the base. Furthermore, wiring work and maintenance performed during detector installation require the detector to be mounted at a high altitude, and the main case must be separated from the base by removing the bolts and screws that connect the main case, making the work highly difficult. Furthermore, when opening the housing at a high place, there is a risk that the hand will slip and the main body case will fall, losing its grip.

[0006] The present invention has been made in response to the above-mentioned problems, and its purpose is to make it possible to easily remove the main case from the base in a detector whose housing is made up of a main case and a base and has a highly airtight structure. Another object of the present invention is to prevent the main body case from falling even if the hand slips and the main body case fails to be grasped when opening the housing. [Means for solving the problem]

[0007] In order to solve the above problems, the present invention provides: a housing incorporating one or more light-receiving elements for detection that receive light of a predetermined wavelength emitted by a detection target, and a detection circuit having a function of detecting the occurrence of an event in the detection target based on a signal from the light-receiving elements for detection; The detection light receiving element is disposed inside the housing so as to face an opening provided on the front side of the housing, and a transparent protective cover is provided between the opening and the detection light receiving element, The housing includes: a lower case for installation on a surface of a building directly or via a mounting base; and a main body case having the protective cover and fitted to the lower case, The fitting portion between the lower case and the main case is configured to be airtight, A pair of tabs of approximately the same size are formed on the outer periphery of each of the lower case and the main case near the fitting portion between the lower case and the main case, and are close to each other but offset in center when in the correct fitting position.

[0008] In a detector having the above configuration, the tabs formed on the outer peripheral surface of the lower case and the tabs formed on the outer peripheral surface of the main case are positioned so that they do not overlap when viewed from above, so that the main case and the lower case (base portion) can be separated by placing a thumb and index finger on each tab and applying a twisting force. As a result, in a detector whose housing is made up of a main case and a lower case and has a highly airtight structure, the main case can be easily removed from the lower case.

[0009] Preferably, a first alignment mark is provided on the tab formed on the outer peripheral surface of the lower case or the tab formed on the outer peripheral surface of the main case, and a second alignment mark is provided on the tab formed on the outer peripheral surface of the main case or the tab formed on the outer peripheral surface of the lower case. With this configuration, when the main case and the lower case are fitted together so that the first mark and the second mark are aligned, the fitting is automatically aligned, and the main case and the lower case can be easily joined together using the joining screws.

[0010] Preferably, a plurality of pairs of protruding portions are formed on the outer peripheral surfaces of the lower case and the main case at positions different from the positions where the pairs of tabs are formed, the protruding portions protruding outward from the outer peripheral surfaces and facing each other, The overhanging portion is provided with a screw insertion hole and a screw hole whose central axis coincides with that of the corresponding overhanging portion, and the lower case and the main body case are joined together by inserting a screw into the screw insertion hole and threading it into the corresponding screw hole in the overhanging portion, The size of the protruding portion of the main case is set so that the cross section perpendicular to the central axis of the screw insertion hole has a larger area than the cross section of the protruding portion of the lower case perpendicular to the central axis of the screw hole. With this configuration, a step is created at the joint between the protruding portion of the main case and the protruding portion of the lower case, which makes it easier to separate the main case from the lower case by hooking a finger on the step when pulling the main case out from the lower case.

[0011] Furthermore, it is preferable that a pin protruding in the mating direction be provided on the outer peripheral surface of the main case or the outer peripheral surface of the lower case near the mating portion between the main case and the lower case, A rotation range limiting piece having a slit into which the pin is inserted so that the pin can move circumferentially is provided on the outer peripheral surface of the lower case or the outer peripheral surface of the main case in a portion facing the pin. According to this configuration, the rotation of the main body case can be restricted within the range of the slit, thereby preventing damage to the seal member due to friction.

[0012] Preferably, a string-like member for preventing the lower case from falling off is provided, one end of which is fastened to the inner wall surface of the lower case, and the other end of which is fastened to the inner wall surface of the main case. With this configuration, even if the user's hand slips and fails to grasp the main body case when opening the housing, the main body case can be prevented from falling. [Effects of the Invention]

[0013] According to the present invention, in a detector whose housing is composed of a main case and a base and has a highly airtight structure, the main case can be easily removed from the base, and there is an effect that the main case is prevented from falling even if the user's hand slips and fails to grasp the main case when opening the housing. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a perspective view showing an embodiment of a flame detector according to the present invention. [Figure 2] 1 is a perspective view showing a state in which a main body case of a flame detector according to an embodiment is removed from a base portion. FIG. [Figure 3] 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 4] 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

[0015] An embodiment of the present invention applied to a flame detector for detecting hydrogen flames will be described below with reference to the drawings. For convenience of explanation, the side facing the front of the flame detector when installed on a building will be referred to as the upper side, and the rear side will be referred to as the lower side. The flame detector 10 of this embodiment is fixedly installed on a wall such as the ceiling of a building with its back side facing the installation surface by a mounting base 300 with an angle adjustment function, and detects flames in the area in front of it. This flame detector is connected via wiring (sensor line) to a receiver (not shown) that centrally manages multiple flame detectors in the detection area, and when it detects a flame, it transmits a detection signal (alarm signal) to the receiver.

[0016] 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. A recess is provided toward the center on the top surface of the front cover portion 211 of the main body case 210, and a circular opening 211A is formed in the center of the recess. A glass cover 213 serving as a protective cover made of a translucent material such as quartz glass is disposed in this opening 211A so as to cover the upper part of the detection light receiving elements 51, 52A, and 52B described below.

[0017] 3(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 at the bottom 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 FIGS. 1 and 2, protruding parts 210a and 220a are formed on the lower peripheral wall of main body case 210 and the upper peripheral wall of lower case 220, respectively, so as to protrude laterally. Further, a screw insertion hole is formed in the overhanging portion 210a, and a screw hole is formed in the overhanging portion 220a, so that a coupling screw 231 inserted into the screw insertion hole of the overhanging portion 210a is threaded into the screw hole of the overhanging portion 220a and tightened to couple the main body case 210 and the lower case 220. Instead of forming a screw hole in the overhanging portion 220a, a nut may be embedded and the main body case 210 and the lower case 220 may be coupled by the bolt and nut.

[0018] Further, semi-disk-shaped tabs 212a and 221a that protrude outward are provided on the outer peripheral surface of the lower end of cylindrical portion 212 of main case 210 and the outer peripheral surface of the upper end of cylindrical portion 221 of lower case 220. These tabs 212a and 221a are formed at positions that are offset from each other in the circumferential direction by the width of the tabs when lower case 220 of main case 210 is joined at a predetermined position. As a result, with the coupling screw 231 inserted through the protrusions 210a and 220a removed, by placing the thumb on the underside of the tab 212a and the index finger on the top of the tab 221a and applying a twisting force in a clockwise direction, the engagement between the main case 210 and the lower case 220 can be easily released.

[0019] The size of overhanging portion 210a of main body case 210 is set so that the cross-sectional area in the direction perpendicular to the axis of the screw insertion hole is larger than that of overhanging portion 220a of lower case 220, thereby creating a step at the joint between overhanging portions 210a and 220a. This makes it easier to separate main body case 210 from lower case 220 by hooking a finger on the step. Furthermore, if the housing of the flame detector is highly airtight, pulling main case 210 out of lower case 220 can be difficult if a pressure difference occurs between the outside air and the inside of the case, but in the flame detector of this embodiment, the pressure difference between the outside air and the inside of the case is small, and a vent filter 232 (see FIG. 2) that is breathable while also having waterproof and dustproof functions is provided on the bottom wall of lower case 220. This makes it easy to separate lower case 220 and main case 210 even if the housing is highly airtight.

[0020] Furthermore, linear alignment marks M1 and M2 are provided at the center of the upper surface of tab 212a of lower case 220 and at a corresponding portion of the outer circumferential surface of cylindrical portion 212 of main case 210. As a result, when main case 210 and lower case 220 are fitted together so that linear marks M1 and M2 are aligned, protruding portions 210a and 220a automatically align, facilitating the joining operation using joining screws 231. As shown in FIG. 2, a pin 212b for a rotation stopper that protrudes downward is provided at the lower end of the cylindrical portion 212 of the main body case 210, and a rotation range restricting piece 221b having a slit into which the pin 212b can be inserted is provided at the opposing portion of the upper end of the cylindrical portion 221 of the lower case 220.

[0021] Because the housing of the flame detector of this embodiment has a highly airtight structure, when main case 210 is pulled out from (or attached to) lower case 220, it may be pulled out while rotating in the rotational direction, which may cause the packing (O-ring) to twist and be damaged. Therefore, in this embodiment, rotation range limiting piece 221b is provided to prevent excessive rotation in the area where the O-ring on the lower case 220 side comes into contact with the end of main case 210. Furthermore, the slit provided in rotation range restricting piece 221b into which pin 212b can be inserted has a certain width, and the width of this groove allows rotation of main case 210. If main case 210 were configured to be completely unable to rotate, it would be difficult to align the main case 210 when fitting it into lower case 220 while working at height, but by being able to rotate main case 210 to a certain extent, alignment can be carried out safely.

[0022] 2, there is provided wire 225 for preventing it from falling off, one end of which is fixed to the upper surface of the bottom wall of cylindrical portion 221 of lower case 220. Retaining ring 225a is provided at the other end of wire 225, and locking piece 212c is provided on the inner circumferential surface of cylindrical portion 212 of main case 210. By locking retaining ring 225a at the end of wire 225 with locking piece 212c, it is possible to prevent main case 212 from falling even if your hand slips and you fail to grip it when opening the housing.

[0023] 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 and a power line is inserted. The end of the cable inserted into wiring port 224 is connected to terminal 216 on terminal board 215A, which is internally wired to circuit board 214 (see FIG. 3), 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. 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 is fixed to the installation plate 313 of the mounting base 300 by fixing screws 233 inserted into the screw insertion holes 223a.

[0024] The mounting base 300 has a similar configuration to that described in the aforementioned Patent Document 2, and therefore detailed structural illustrations are omitted, but it comprises a base plate 311 which is joined and fixed to a mounting surface such as the wall of a building, a horizontal rotating frame 312 which is connected so as to be rotatable in the left-right direction around an axis (X-axis) which is located approximately in the center of the base plate 311 and is perpendicular to the base plate 311, and a vertical rotating frame 313 which has flanges 313A, 313B joined to the outer surfaces of the left and right flanges 312A, 312B of the horizontal rotating frame 312 and is arranged so as to be tiltable in the front-to-rear direction around an axis (Y-axis) which is parallel to the base plate 311.

[0025] The horizontal rotary frame 312 and the vertical rotary frame 313 each have base portions 312C and 313C that connect a pair of flanges, and are formed so as to form a U-shape in top view. The base plate 311 has joining wing pieces 311A ​​and 311B on both sides that are joined to the mounting surfaces, and has a pedestal portion 311C in the center that is one step higher than the joining wing pieces 311A ​​and 311B. The horizontal rotary frame 312 is attached to this pedestal portion 311C so as to be rotatable about a bolt 314A disposed approximately in the center.

[0026] In addition, two arc-shaped slits 312a for regulating the angle range are formed on the base portion 312C of the horizontal rotary frame 312, one above the other and one below the central bolt 314A as the midpoint, and two arc-shaped slits 312b are formed on the left and right, and bolts 314B are inserted into each of these slits. This allows the horizontal rotary frame 312 to be rotated in a horizontal plane relative to the base plate 311 by loosening the bolt 314B and rotating the entire horizontal rotary frame 312, and the horizontal rotary frame 312 is fixed at a predetermined angular position by tightening the bolt 314B.

[0027] The vertical rotary frame 313 is rotatably mounted to the flanges 312A and 312B of the horizontal rotary frame 312 around a bolt 318A disposed in the center of the left and right flanges 313A and 313B. Although not shown, arc-shaped slits (not shown) are formed in the flanges 313A and 313B, positioned above and below the bolt 318A at the rotation center, and bolts 318B are inserted into these slits. As a result, by loosening the bolt 318B, the vertical rotary frame 313 can be rotated in a vertical plane relative to the left and right flanges 312A, 312B of the horizontal rotary frame 312, and by tightening the bolt 318B, the vertical rotary frame 313 is fixed at a predetermined angular position.

[0028] Next, the internal configuration of the flame detector 10 of this embodiment will be described. The 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. 3A, the ultraviolet sensor 51 is installed approximately in the center of the top surface of the circuit board 214, and the infrared sensors 52A and 52B are installed slightly off-center. As shown in FIG. 3A, the infrared sensors 52A and 52B are arranged parallel to the ultraviolet sensor 51, i.e., in a direction perpendicular to the plane of the paper in FIG. 3A, and one of the sensors is not visible. The circuit board 214 is also equipped with a control circuit that, when it determines that a flame has been detected based on signals from the 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).

[0029] The ultraviolet sensor 51 and the infrared sensors 52A and 52B are sensors that can detect light in different wavelength bands that are appropriately selected so as not to detect sunlight or other heat sources but to 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 is mounted on the circuit board 214 in the same way as the power light 55 and guides the light of an operation indicator light (not shown) that indicates that the detector has detected a flame, and emits the light forward through the glass cover 213.

[0030] 3(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.

[0031] 3(A), a packing (O-ring) 219A is provided as a sealant at the fitting portion between cylindrical portion 212 of main case 210 and cylindrical portion 221 of lower case 220. Packing 219A is housed in a recess formed on the outer periphery of the upper end of cylindrical portion 221 of lower case 220, and is configured to prevent water from entering the case from the fitting portion between main case 210 and lower case 220. As shown in FIG. 3(B), a recess is also provided on the underside of front cover portion 211 of main body case 210, housing gasket (O-ring) 219B as a sealing material, and gasket 219B is configured to prevent water from entering the case through the gap at the joint between the edge of opening 211A of front cover portion 211 and glass cover 213.

[0032] 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 a plurality of screw insertion holes (not shown) provided on the periphery of light guide plate 217, and the screws are 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) 219B is crushed, which makes it adhere tightly to the glass and the aluminum housing, providing excellent sealing properties.

[0033] Next, a means for detecting condensation that has formed on the surface using the dirt detection function that detects dirt adhering to the surface of glass cover 213 will be described with reference to Fig. 4. Fig. 4 shows the cross-sectional structure of the upper part of flame detector 10, i.e., the vicinity of front cover part 211. 4, a light-emitting element 53 and a light-receiving element 54 for detecting dirt are mounted on circuit board 214 at positions facing each other with ultraviolet sensor 51 and infrared sensors 52A and 52B in between. Also, a power light (LED lamp) 55 is provided near infrared sensors 52A and 52B on circuit board 214 to indicate that power is being supplied and the sensors are operating.

[0034] The light-guiding member 56 has a light incident portion 56a with a trapezoidal cross section joined to the bottom surface of the notched recess 211b of the front cover portion 211, and leg portions 56b protruding downward from the lower surface of the light incident portion 56a. The leg portions 56b are inserted into through-holes formed in the front cover portion 211, and their lower end surfaces face the light-receiving surface of the light-receiving element 54. The trapezoidal light incident portion 56a is disposed so that one slant surface faces the center of the glass cover 213. A notched recess is formed in the upper surface of the front cover portion 211, and a light-guiding member 56 made of a translucent material is disposed in the notched recess. A cover piece 57 having a shape corresponding to the notched recess is fitted to cover the upper surface of the light-guiding member 56. A notch (or groove) 57a (see FIG. 1) serving as a light-receiving window is formed in the lower part of the surface of the cover piece 57 facing the center of the glass cover 213.

[0035] Therefore, light emitted from light-emitting element 53 on circuit board 214 obliquely upward toward the center passes through glass cover 213, passes through light-receiving window 57a of cover piece 57, and enters one of the slopes of trapezoidal light incident portion 56a of light-guiding member 56. The light is then reflected by the outer slope of light incident portion 56a, changes direction downward, passes through leg portion 56b, and is incident on light-receiving element 54 and detected. Since the top surface of light-guiding member 56 is covered by cover piece 57, the light incident on light-guiding member 56 is reflected by the top surface and the outer slope of light-guiding member 56 and guided to leg portion 56b, as indicated by dashed-dotted line P in FIG. 4(B). Although FIG. 4(B) depicts the light path as if it were a straight line passing through both the outside and the inside of glass cover 213, in reality, light is refracted when entering and exiting cover glass 213.

[0036] If the surface of glass cover 213 becomes cloudy due to condensation, the light emitted from light-emitting element 53 is diffused and dispersed by the cloudy surface of glass cover 213, resulting in a decrease in the amount of light reaching light-receiving element 54 compared to when there is no condensation. Therefore, by monitoring the signal from light-receiving element 54 with a control circuit comprising a microcomputer or the like on circuit board 214, it is possible to determine that condensation has occurred if the amount of light received decreases significantly over several hours. When the control circuit determines that condensation has occurred, it energizes the heater to generate heat, which in turn raises the temperature of glass cover 213, thereby removing the cloudiness caused by condensation.

[0037] While the present invention has been described above based on the embodiments, the present invention is not limited to the above embodiments and can be modified as appropriate without departing from the spirit and scope of the present invention. For example, the flame detector of the above embodiment is provided with a function for detecting condensation on the glass cover 213 and a function for removing condensation, but these functions may be omitted. Furthermore, the above embodiment has been described using an example in which the flame detector 10 is installed on an installation surface such as a ceiling surface of a building via the mounting base 300, but the flame detector 10 may also be installed directly on the ceiling surface of a building. Furthermore, 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]

[0038] 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) 56 Light guide member 57 Cover Piece 210 Main unit case 210a Overhang 211 Front cover 211A opening 212 Cylindrical part 212a Tab 213 Glass Cover 214 Circuit Board 215A terminal board 215B Back cover 216 connection terminal 217 Light guide plate for operation indicator light 218 Heater 219A O-ring (packing) 219B O-ring (packing) 220 Lower Case 221 Cylindrical part 221a Tab 222 Base 223 Flange 223a Screw insertion hole 224 Wiring port 225 String-like member (wire for preventing falling off) 225a retaining ring 231 Coupling screw 232 Vent Filter 300 Mounting Base 311 base plate 312 Horizontal rotating frame 313 Vertical rotating frame 314A, 318A Rotation center bolt

Claims

1. a housing incorporating one or more light-receiving elements for detection that receive light of a predetermined wavelength emitted by a detection target, and a detection circuit having a function of detecting the occurrence of an event in the detection target based on a signal from the light-receiving elements for detection; The detection light receiving element is disposed inside the housing so as to face an opening provided on the front side of the housing, and a transparent protective cover is provided between the opening and the detection light receiving element, The housing includes: a lower case for installation on a surface of a building directly or via a mounting base; and a main body case having the protective cover and fitted to the lower case, The fitting portion between the lower case and the main case is configured to be airtight, A detector characterized in that a pair of tabs of approximately the same size are formed on each outer peripheral surface of the lower case and the main case near the fitting portion between the lower case and the main case, and are close to each other but have offset centers when in the correct fitting position.

2. 2. The detector of claim 1, wherein the tab formed on the outer peripheral surface of the lower case or the tab formed on the outer peripheral surface of the main case is provided with a first mark for alignment, and the tab formed on the outer peripheral surface of the main case or the tab formed on the outer peripheral surface of the lower case is provided with a second mark for alignment.

3. a plurality of pairs of protruding portions are formed on the outer peripheral surfaces of the lower case and the main case at positions different from the positions where the pairs of tabs are formed, the protruding portions protruding outward from the outer peripheral surfaces so as to face each other; The overhanging portion is provided with a screw insertion hole and a screw hole whose central axis coincides with that of the corresponding overhanging portion, and the lower case and the main body case are joined together by inserting a screw into the screw insertion hole and threading it into the corresponding screw hole in the overhanging portion, The detector described in claim 2, characterized in that the protruding portion of the main body case is sized so that the cross-section perpendicular to the central axis of the screw insertion hole has a larger area than the cross-section of the protruding portion of the lower case in the direction perpendicular to the central axis of the screw hole.

4. a pin protruding in a mating direction is provided on an outer peripheral surface of the main case or an outer peripheral surface of the lower case near a mating portion between the main case and the lower case; A detector as described in claim 3, characterized in that a rotation range limiting piece having a slit into which the pin is inserted so that it can move circumferentially is provided on the outer peripheral surface of the lower case or the outer peripheral surface of the main case, in a portion facing the pin.

5. A detector as described in any one of claims 1 to 4, characterized in that a string-like member for preventing falling off is provided, one end of which is engaged with the inner wall surface of the lower case and the other end of which is engaged with the inner wall surface of the main case.

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