Heating means control method of detector, and detector

Abstract

To provide a detector having dirt detecting means for a glass cover, to detect dew condensation of the glass cover without augmenting the number of components, and thus suppress an increase in cost.SOLUTION: A heating means control method for a detector including a detection light receiving element, a transparent protective cover disposed near the detection light receiving element, dirt detection means capable of detecting dirt of the protective cover, heating means brought into contact with an internal surface of the protective cover, and a control circuit that determines a degree of dirt of the protective cover on the basis of a signal sent from the dirt detecting means, and controls or turns on or off the heating means, includes a step at which the control circuit determines the degree of dirt of the protective cover on the basis of the signal sent from the dirt detecting means, and a step at which, when the degree of dirt of the protective cover exceeds a predetermined value, actuates the heating means over only a predesignated predetermined period.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to a detector that detects abnormal events such as flames, and in particular to a heating means control method that is useful when applied to a detector equipped with a heating means (heater) that removes condensation from a glass cover that covers the front side of the sensor. [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 that can be received so as not to detect sunlight or other heat sources. In addition, flame detectors are designed to be dustproof and waterproof for outdoor use, and some have a glass cover on the front side of the sensor located in the center of the case.

[0003] In flame detectors that have a glass cover in front of the sensor, changes in temperature and humidity in the installation environment can cause condensation on the surface of the glass cover, which can interfere with light reception and prevent the sensor from performing its normal detection function.To prevent this, a heater is installed on the inside of the glass cover to remove the fogging caused by condensation, and by passing electricity through the heater, the glass cover is warmed and the water on the surface evaporates, preventing any interference with light reception. Furthermore, in flame detectors, if the glass cover (light receiving glass) becomes dirty with dust or the like, the flame detection function will be reduced, so a dirt detection function may be provided.

[0004] Conventionally, there is an invention relating to a fire detector that is provided with a sensor for detecting condensation, and when condensation is detected, a moisture detection signal is used to prevent the output of a fire detection signal or to display a condensation detection indication (Patent Document 1). Furthermore, Patent Documents 2 and 3 disclose inventions relating to flame detectors equipped with a function for detecting dirt on a glass cover (light-receiving glass). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 57-123490 [Patent Document 2] Japanese Patent Application Laid-Open No. 2002-298242 [Patent Document 3] Japanese Patent Publication No. 2022-40664 Summary of the Invention [Problem to be solved by the invention]

[0006] Because heaters consume a large amount of electricity, there is a desire to minimize operating time in order to reduce power consumption. To achieve this, it is effective to install a sensor that detects condensation and turns on the heater when condensation is detected. However, providing a sensor to detect condensation on the glass cover increases the number of components in the flame detector, leading to increased costs and making it difficult to reduce the size.

[0007] Furthermore, in recent years, demand for hydrogen energy has increased, and hydrogen vehicles are now being driven around town. Hydrogen vehicles are refueled at hydrogen stations, but there is a risk of hydrogen leaks during the refueling process. However, because hydrogen gas and the hydrogen flames that occur when it ignites are invisible, it can take a while to notice 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.

[0008] The present invention was made with an eye on the above-mentioned problems, and its purpose is to detect condensation on a glass cover in a detector equipped with a means for detecting dirt on the glass cover that covers the front side of the sensor without increasing the number of parts, thereby suppressing cost increases. Another object of the present invention is to reduce the power consumption of a heater for removing condensation and improve power efficiency. [Means for solving the problem]

[0009] In order to solve the above problems, the present invention provides: a housing incorporating a circuit board having a function of detecting an event to be detected; 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 dirt detection means capable of detecting dirt on the protective cover; a heating means provided in contact with the inner surface of the protective cover; a control circuit mounted on the circuit board, which determines the degree of contamination of the protective cover based on a signal from the contamination detection means and controls the heating means to be turned on and off; A method for controlling a heating means in a detector comprising: The control circuit a first step of determining a degree of dirt on the protective cover based on a signal from the dirt detection means; a second step of operating the heating means for a predetermined time when it is determined that the degree of contamination of the protective cover has exceeded a predetermined value; This is designed to execute the following.

[0010] According to the control method described above, when condensation occurs on the glass cover (protective cover) that covers the front side of the sensor (detection light receiving element), the amount of light that passes through the glass cover decreases in the same way as dirt, so in a detector equipped with a means for detecting dirt on the glass cover, it is possible to detect fogging due to condensation on the glass cover and activate a heater as heating means to remove the condensation without increasing the number of parts. This eliminates the need to provide a separate condensation detection sensor, suppressing cost increases, and because the heater as heating means is activated only when necessary, it is possible to reduce power consumption by the heater and improve power efficiency.

[0011] Here, preferably, after the second step, a third step of determining whether or not the degree of contamination of the protective cover has fallen below a predetermined value is included. a fourth step of notifying the user that the protective cover is dirty when it is determined in the third step that the degree of dirt on the protective cover is not below a predetermined value, If it is determined in the third step that the degree of contamination of the protective cover has fallen below a predetermined value, the fourth step is not executed, and the operation of the heating means is stopped after the predetermined time has elapsed. This method makes it possible to distinguish between condensation and dirt on the glass cover and to execute appropriate processing for each. Also, if the control circuit is configured with a program-controlled microcomputer, a single program can detect and remove condensation on the glass cover, and detect and notify of dirt, thereby shortening the time required for processing.

[0012] Preferably, the contamination detection means is configured such that a light-emitting element disposed inside the housing emits light toward the protective cover, and a light-guiding member is disposed so as to receive the test light emitted from the light-emitting element through a light-receiving window on the outside of the protective cover, and the test light is guided to a light-receiving element disposed inside the housing, The control circuit In the first step, a contamination value of the protective cover is calculated based on the amount of light received by the light receiving element, In the second step, when it is determined that the contamination value exceeds a predetermined threshold value, the heating means is operated for a predetermined time. According to this method, the glass cover dirt detection means can be configured with a small number of parts, and condensation formed on the glass cover can be detected and removed, and dirt can be detected and reported efficiently and accurately.

[0013] Another invention of the present application is: a housing incorporating a circuit board having a function of detecting an event to be detected; 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 dirt detection means capable of detecting dirt on the protective cover; a heating means provided in contact with the inner surface of the protective cover; a control circuit mounted on the circuit board, which determines the degree of contamination of the protective cover based on a signal from the contamination detection means and controls the heating means to be turned on and off; In a detector comprising: The control circuit a function of determining the degree of dirt on the protective cover based on a signal from the dirt detection means; a function of operating the heating means for a predetermined time when it is determined that the degree of contamination of the protective cover has exceeded a predetermined value; The present invention is designed to have the following. According to the above detector, there is no need to provide a condensation detection sensor in addition to the means for detecting dirt on the glass cover, which prevents an increase in costs and reduces the power consumption of the heater, thereby improving power efficiency. [Effects of the Invention]

[0014] According to the detector and the method for controlling the heating means of the detector of the present invention, in a detector equipped with a means for detecting dirt on the glass cover covering the front side of the sensor, condensation on the glass cover can be detected without increasing the number of parts, thereby suppressing cost increases and reducing power consumption by the heater. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a perspective view showing an embodiment of a flame detector according to the present invention. [Figure 2]1A is a perspective view of a central cross section showing the internal structure of a flame detector according to an embodiment, and FIG. 1B is an enlarged cross section showing a portion surrounded by a dashed line B in FIG. 1A. [Figure 3] FIG. 2 is a cross-sectional plan view showing the internal structure of the flame detector according to the embodiment. [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 according to the embodiment, and FIG. 1B is an explanatory diagram showing the path of light emitted from a light-emitting element for detecting condensation. [Figure 5] 1 is a perspective view showing a state in which a cover piece covering a light guide member in the flame detector of the embodiment is removed. FIG. [Figure 6] 10 is a flowchart illustrating an example of a procedure for a detection window monitoring process performed by a control circuit in the flame detector of the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0016] 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. Flame detectors are generally fixedly installed on the wall of a building with their backs facing the mounting surface, either directly or using an angle adjuster as a base, and detect flames in the area directly in front of them. Such flame detectors are connected via wiring (detector lines) to a monitoring panel (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 monitoring panel.

[0017] 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.

[0018] 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.

[0019] 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 at the bottom of main body case 210, and the upper end part of lower case 220 is fitted inside main body case 210. As shown in FIG. 1, main body case 210 and lower case 220 are joined together by screws 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.

[0020] 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 directly or via a mounting base 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 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. 2), which is provided inside main body case 210, on which elements and ICs constituting a circuit having a flame detection function are mounted, and on which wiring connecting the elements and ICs is formed.

[0021] 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, and 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 offset from the 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. Circuit board 214 is also provided with a circuit that has the function of transmitting a detection signal (alarm signal) to a monitoring panel (not shown) when it is determined that a flame has been detected based on signals from sensors 51, 52A, and 52B.

[0022] 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 passes through 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 provided separately from the power light 55 described below and guides light from operation indicator lights (LED lamps) 58A, 58B that indicate that the detector has detected a flame, and emits the light forward through the glass cover 213.

[0023] 2(B), the central side of light guide plate 217 is formed one step lower so as not to come into contact with glass cover 213, and corresponding to this one step lower portion, thin planar heater 218 is disposed so as to come into contact with the underside of glass cover 213. This 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 central side, removing condensation from the entire glass cover 213.

[0024] 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 from 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.

[0025] 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. 2 shows grooves 211a with semicircular cross sections, but the cross sections of grooves 211a may be inverted V-shaped, rectangular, or the like. The number of grooves 211a is not limited to three and may be one, two, four, or more. Grooves 211a may be continuous in the circumferential direction along the edge of opening 211A, or may be formed intermittently. Instead of providing grooves, multiple hemispherical or polygonal pyramidal depressions may be formed and arranged in a dot pattern.

[0026] 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, allowing glass cover 213 to be heated efficiently and preventing a slower rate of temperature rise and a longer time required to remove condensation. This shortens the time required to remove condensation from the surface of glass cover 213, preventing a prolonged state in which normal detection function cannot be performed (off-alert time) and reducing power consumption. Furthermore, if front cover part 211 is made of a metal with high thermal conductivity and has a recess that houses packing 219, it is possible to prevent heat from being transferred to packing 219 and causing deterioration. Furthermore, groove 211a for reducing heat transfer also contributes to reducing the weight of main body case 211.

[0027] 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 Figures 4 and 5. Figure 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.

[0028] Light-emitting element 53 is mounted in a position facing slightly upward and to the side, and light-receiving element 54 is mounted in a position facing straight up. Also, above light-receiving element 54 and at the bottom of notched recess 211b formed in the upper surface of front cover portion 211, light-guiding member 56 made of a light-transmitting material is disposed, as shown in Fig. 5, and cover piece 57 having a shape corresponding to notched recess 211b is fitted into notched recess 211b so as to cover the upper surface of light-guiding member 56 (see Fig. 2).

[0029] In other words, the front cover portion 211 has a ring-shaped bulge portion that is formed so that the central side where the opening 211A is located is recessed and that bulges forward around it, and a part of this bulge portion is cut out to form the recess 211b, and the light-guiding member 56 is arranged at the bottom of the recess 211b, and the light-guiding member 56 is covered by a cover piece 57 that has a shape that complements the recess 211b of the bulge portion and is fitted into the recess 211b. With this configuration, even if the light-guiding member 56, which also functions as a condensation detection means, is provided on the front cover portion 211, the apparent shape of the front cover portion 211 does not change, and the light-guiding member 56 can be made inconspicuous, which has the advantage of not compromising the design of the detector.

[0030] The light guide 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, with the leg portions 56b being inserted into through holes formed in the front cover portion 211 and with their lower end surfaces facing the light receiving surface of the light receiving element 54. The trapezoidal light incident portion 56a is disposed so that one inclined surface faces the center of the front cover portion 211. In addition, 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.

[0031] Therefore, the test light emitted from the light-emitting element 53 on the circuit board 214 diagonally upward toward the center passes through the glass cover 213, passes through the light-receiving window 57a of the cover piece 57, and enters one of the slopes of the trapezoidal light incident portion 56a of the light-guiding member 56. The light then reflects off the outer slope of the light incident portion 56a, turns downward, passes through the leg portion 56b, and is incident on the light-receiving element 54 and detected. At this time, the upper surface of the light-guiding member 56 is covered by the cover piece 57, and the light that enters the light-guiding member 56 is reflected off the upper surface and the outer slope of the light-guiding member 56 and guided to the leg portion 56b, as indicated by the dashed-dotted line P in FIG. 4(B). Note that while FIG. 4(B) depicts the light path as if it passes through both the outside and the inside of the glass cover 213 in a straight line, in reality, the light is refracted when entering and exiting the glass cover 213.

[0032] If condensation occurs on the surface of glass cover 213, the light emitted from dirt detection light-emitting element 53 is diffused and dispersed by the condensation on the surface of glass cover 213, and the amount of light reaching dirt detection light-receiving element 54 is reduced compared to when there is no condensation. Therefore, a decrease in the amount of light received due to condensation can be detected by monitoring the signal of dirt detection light-receiving element 54 with a control circuit comprising a microcomputer or the like on circuit board 214. However, since it is not possible to distinguish between condensation and dirt from the signal of light-receiving element 54 alone, it is not possible to immediately determine that condensation has occurred based on a decrease in the amount of light received by light-receiving element 54. Therefore, if the amount of received light decreases, it is determined that condensation has occurred and the heater 218 is made to generate heat to raise the temperature of the glass cover 213.If condensation has occurred, it can be removed by heating, so if the decrease in the amount of received light does not resolve after a predetermined time has passed, it is determined that dirt has occurred.

[0033] Next, an example of a specific procedure for the detection window monitoring process of glass cover (detection window) 213 by the control circuit on circuit board 214 will be described using the flowchart in Fig. 6. The detection window monitoring process can be repeatedly executed periodically, for example, by a timer interrupt. In the following description, the state in which dirt on the surface of glass cover 213 cannot be distinguished from condensation will be referred to as "fogging." When the control circuit starts the detection window monitoring process, it first causes the dirt detection light emitting element (LED) 53 to emit light (step S1), and then measures the amount of light received based on the signal from the dirt detection light receiving element 54 (step S2).

[0034] Thereafter, the control circuit calculates a contamination value representing the degree of contamination from the measured value and an initial value previously stored in memory (step S3), and determines whether the calculated contamination value exceeds a preset threshold value (step S4). If it determines that the contamination value does not exceed the threshold value (NO), the control circuit ends the detection window monitoring process. On the other hand, if the control circuit determines in step S4 that the contamination level exceeds the threshold value (YES), it proceeds to step S5, where it turns on the heater 218 to generate heat. Next, it starts a timer (condensation detection timer) that measures a predetermined time (step S6), and when the predetermined time has elapsed, it proceeds to step S7.

[0035] In step S7, the amount of light received is measured based on the signal from the dirt detection light-receiving element 54, and a dirt value is calculated. Then, it is determined whether the calculated dirt value is below a preset threshold value (step S8). If it is determined that the dirt value is not below the threshold value (NO), the process proceeds to step S9, where an occurrence of a dirt abnormality is notified, for example, by flashing the operation indicator lights 58A, 58B or the power light 55, and the heater 218 is turned off, and the process ends (step S10). On the other hand, if it is determined in step S8 that the contamination value is below the threshold value (YES), it is highly likely that the "cloudiness" was due to condensation, so step S9 is skipped and the process proceeds to step S10, where the heater 218 is turned off and the process ends. Note that in step 9, a separate algorithm may be provided to determine whether or not to issue a contamination alarm.

[0036] By having the control circuit execute the above-described process, the flame detector of this embodiment can detect fogging on the glass cover using the dirt detection means provided for detecting dirt on the glass cover. Therefore, if fogging is detected, the heater is turned on to generate heat. If condensation is the cause of the fogging on the glass cover, the condensation can be removed and the heater is not turned on more than necessary, thereby reducing power consumption. Furthermore, since there is no need for a condensation detection means, the number of parts can be reduced and costs can be avoided compared to when a dirt detection means and a condensation detection means are provided separately.

[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 of the present invention. For example, in the above embodiment, a trapezoidal block-shaped light-guiding member 56 is provided to guide light emitted from the light-emitting element 53 in an oblique direction intersecting with the glass cover 213 toward the mounting position of the light-receiving element 54, but this light-guiding member 56 may be a single optical fiber or a bundle of multiple optical fibers.

[0038] 6 is executed periodically, the control circuit may be provided with a clock function so that the detection window monitoring process is executed only during times when condensation is likely to occur (e.g., early morning).Furthermore, the flame detector 10 may be provided with a temperature sensor, humidity sensor, etc. so that the detection window monitoring process is executed when a preset condensation occurrence condition is met. Furthermore, although the above embodiment describes the application of the present invention to a flame detector, 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]

[0039] 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 56a Light incidence part 56b Legs 57 Cover Piece 57a Light receiving window (notch) 210 Main unit case 210a Overhang 211 Front cover 211A opening 211a Groove 211b Notched recess 212 Cylindrical part 213 Glass Cover 214 Circuit Board 215A terminal board 215B Back cover 216 connection terminal 217 Light guide plate 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 Joining screws

Claims

1. a housing incorporating a circuit board having a function of detecting an event to be detected; 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 dirt detection means capable of detecting dirt on the protective cover; a heating means provided in contact with the inner surface of the protective cover; a control circuit mounted on the circuit board, which determines the degree of contamination of the protective cover based on a signal from the contamination detection means and controls the heating means to be turned on and off; A method for controlling a heating means in a detector comprising: The control circuit a first step of determining a degree of dirt on the protective cover based on a signal from the dirt detection means; a second step of operating the heating means for a predetermined time when it is determined that the degree of contamination of the protective cover has exceeded a predetermined value; A method for controlling a heating means of a detector, comprising:

2. a third step of determining whether or not the degree of contamination of the protective cover has fallen below a predetermined value after the second step; a fourth step of notifying the user that the protective cover is dirty when it is determined in the third step that the degree of dirt on the protective cover is not below a predetermined value, 2. The method for controlling the heating means of a detector according to claim 1, wherein if it is determined in the third step that the degree of contamination of the protective cover has fallen below a predetermined value, the fourth step is not executed and operation of the heating means is stopped after the predetermined time has elapsed.

3. The contamination detection means is configured to guide the test light to a light-receiving element disposed inside the housing by a light-emitting element disposed inside the housing and emitting light toward the protective cover, and a light-guiding member disposed so as to receive the test light emitted from the light-emitting element through a light-receiving window on the outside of the protective cover, The control circuit In the first step, a contamination value of the protective cover is calculated based on the amount of light received by the light receiving element, 3. The method for controlling a heating means of a detector according to claim 1, wherein in the second step, if it is determined that the contamination value exceeds a predetermined threshold value, the heating means is operated for a predetermined time.

4. a housing incorporating a circuit board having a function of detecting an event to be detected; 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 dirt detection means capable of detecting dirt on the protective cover; a heating means provided in contact with the inner surface of the protective cover; a control circuit mounted on the circuit board, which determines the degree of contamination of the protective cover based on a signal from the contamination detection means and controls the heating means to be turned on and off; A detector comprising: The control circuit a function of determining the degree of dirt on the protective cover based on a signal from the dirt detection means; a function of operating the heating means for a predetermined time when it is determined that the degree of contamination of the protective cover has exceeded a predetermined value; A detector comprising:

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