Fire detector and a method for detecting an interfering object

Abstract

Fire detector (1) with a housing (2), wherein the housing (2) can be arranged on a wall and / or on a ceiling (3) of a room, with a sensor system for detecting a fire, wherein the sensor system is arranged in or on the housing (2), with at least one radiation transmitter section (4) for emitting transmitted light radiation (L1) into an environment of the fire detector (1), with at least one radiation receiver section, wherein the at least one radiation receiver section is designed to detect a received light radiation (L2) which is formed by the emitted transmitted light radiation (L1) reflected by an interfering object (5), with an evaluation device, wherein the evaluation device is designed to detect the interfering object (5) by means of the detected received light radiation (L2), characterized by a receiver light-emitting diode (6) which is designed to emit light radiation and comprises the at least one radiation receiver section, and a control device which is designed to trigger and / or output a fault message when the interfering object (5) is detected by the evaluation device.

Description

State of the art

[0001] The invention relates to a fire detector with a housing, wherein the housing can be arranged on a wall and / or on a ceiling of a room, with a sensor system for detecting a fire, wherein the sensor system is arranged in or on the housing, with at least one radiation transmitter section for emitting transmitted light radiation of a limited spectral range into an environment of the fire detector, with at least one radiation receiver section, wherein the at least one radiation receiver section is designed to detect received light radiation which is formed by the emitted transmitted light radiation reflected by an interfering object, with an evaluation device, wherein the evaluation device is designed to detect the interfering object based on the detected received light radiation. The invention also relates to a method for detecting an interfering object.

[0002] Fire detectors are used for automatic early fire detection and are usually installed in residential or office spaces or public buildings in order to alert people in the vicinity to a dangerous situation.

[0003] DE 10 2004 001 699 A1, which arguably represents the closest prior art, describes a fire detector with three radiation emitters and three radiation receivers, whose beam paths form at least two spatially spaced scattering volumes. Because at least one of several scattering volumes encompasses at least a portion of a cover plate enclosing the fire detector, contamination of the cover plate is detected.

[0004] A smoke detector is known from US 2010 / 0 238 036 A1. The smoke detector includes a smoke detection circuit for detecting smoke and generating a detection signal. A proximity detection circuit generates a proximity detection signal in response to the detection of an object at a selected distance from the smoke detector.

[0005] US 2001 / 0 038 337 A1 discloses a smoke detector which may be hard-wired or battery-operated and has a circuit for providing an audio-visual alarm upon detection of smoke.

[0006] DE 10 2007 053 400 A1 discloses a method for detecting the approach of a vehicle to an object, comprising the steps described below. After emitting light using an existing light source on the vehicle, light reflected from the object is detected. The detected reflected light is evaluated to detect the approach of the vehicle to the object.

[0007] EP 0 120 881 B1 discloses a scattered radiation smoke detector which can be connected to an evaluation unit by means of radiation-conducting elements.

[0008] A lighting device is known from DE 102 27 487 A1.

[0009] DE 20 2008 018 087 U1 discloses a radiation protection element for protecting against the escape of radiation from a radiation source from a room.

[0010] DE 10 2009 056 268 A1 discloses a hazard detector and a method for detecting objects in the vicinity of the hazard detector. Disclosure of the invention

[0011] Within the scope of the invention, a fire detector having the features of claim 1 and a method having the features of claim 11 are disclosed. Preferred or advantageous embodiments of the invention emerge from the subclaims, the following description and the attached figures.

[0012] The invention thus relates to a fire detector. The fire detector comprises a housing, which can be arranged on a wall and / or ceiling of a room. The arrangement can be flush with the ceiling or wall or mounted on the ceiling or wall. For example, the fire detector can be connected to one or more fire detectors installed in rooms and / or to a fire alarm control panel. Optionally, the fire detector comprises a siren for emitting an audible fire warning. For example, the fire detector has an integrated power supply; in particular, the fire detector is battery-operated.

[0013] The fire detector comprises a sensor system for detecting a fire. The sensor system is designed, in particular, to record fire-specific measurement parameters, by means of which the fire can be detected. For example, the fire-specific measurement parameters are smoke particles and / or fire gases. The sensor system is particularly preferably arranged in the housing, in particular in a measuring chamber of the housing. However, it can also be provided that the sensor system is arranged on the housing, in particular on the outside, visible to a person.

[0014] The fire detector comprises at least one radiation transmitter section for emitting transmitted light radiation into the surroundings of the fire detector. The surroundings are understood to mean, in particular, the room or a sub-area of ​​the room in which the fire detector is to be arranged. The radiation transmitter section is preferably arranged on the outside of the housing, so that the emission of the transmitted light radiation is converted into the surroundings. The transmitted light radiation of the at least one radiation transmitter section preferably reaches a range of at least 10 cm, in particular of at least 50 cm, and especially of at least 100 cm.

[0015] The fire detector has at least one radiation receiver section, wherein the at least one radiation receiver section is designed to detect received light radiation formed by the emitted transmitted light radiation reflected by an interfering object. In particular, the transmitted light radiation is at least partially scattered from the interfering object to the radiation receiver section as received light radiation and is thus reflected. In particular, the radiation transmitter section and the radiation receiver section are arranged relative to one another such that the transmitted light radiation from the radiation transmitter section does not directly strike the radiation receiver section. If the transmitted light radiation is reflected by the interfering object to the radiation receiver section, the interfering object is positioned relative to the fire detector in such a way that the detection of the fire-specific measurement parameters and consequently the detection of the fire is not ensured.In particular, the interfering object prevents or reduces airflow to the fire detector, so that fire-specific measurement parameters, such as smoke particles in the airflow, are not or insufficiently conveyed to the fire detector. The interfering object is, in particular, a piece of furniture, e.g., a cabinet. The radiation receiver section is preferably arranged on the outside of the housing.

[0016] The fire detector comprises an evaluation device. The sensor system for transmitting the recorded fire-specific measurement parameters is preferably coupled to the evaluation device, wherein the evaluation device is configured to detect the fire based on the transmitted fire-specific measurement parameters.

[0017] The evaluation device is designed to detect the interfering object using the detected received light radiation. In particular, the at least one radiation receiver section is coupled to the evaluation device in order to transmit the received light radiation detected by the radiation receiver section as a signal to the evaluation device. For example, the evaluation device sets a light intensity limit for the detected received light radiation, and the evaluation device detects the interfering object if the light intensity limit is exceeded. The evaluation device is arranged, for example, in the housing.

[0018] According to the invention, the fire detector comprises a control device configured to trigger and / or output a fault message upon detection of the interfering object by the evaluation device. The fault message may be a visual message, e.g., a flashing light, and / or an acoustic message, e.g., a siren.

[0019] Within the scope of the invention, it is proposed that the fire detector comprises a receiver light-emitting diode which is designed to emit light radiation and comprises the at least one radiation receiver section, and wherein it is provided in particular that the radiation receiver section forms a subsection of the receiver light-emitting diode.

[0020] In the embodiment according to the invention, a component that is usually only used to emit light radiation is used as the radiation receiver section. This eliminates the need for components and their integration into the fire detector. Furthermore, fewer openings or receptacles are required in the housing for radiation transmitter sections and radiation receiver sections, since the function of detecting the received light radiation and emitting light radiation, in particular the transmitted light radiation, can be implemented by the same component. The receiver LED nevertheless enables the reliable detection of interfering objects. Due to the extremely compact design of LEDs, the receiver LED can be arranged unobtrusively on the housing. Given the long service life of LEDs, long-term reliable detection of interfering objects is achieved.

[0021] The receiver LED is designed, for example, as an SMD (surface-mounted device) LED, but preferably as a PIN LED. The at least one receiver LED is made, for example, from the semiconductor material aluminum gallium arsenide (AlGaAs), gallium arsenide phosphide (GaAsP), aluminum indium gallium phosphide (AlInGaP), gallium phosphide (GaP), silicon carbide (SiC), zinc selenide (ZnSe), indium gallium nitride (InGaN), and / or gallium nitride (GaN).

[0022] In particular, the transmitted light radiation is modulated with a specific identification frequency assigned to the addressed receiver LED. Preferably, the at least one radiation transmitter section is configured to emit modulated transmitted light radiation using a frequency that does not match the frequency of the ambient light of the fire detector. The modulated transmitted light radiation at least largely prevents the ambient light of the fire detector from being detected as stray light, thus preventing, in particular, an erroneous fault message.

[0023] Particularly preferably, the receiver LED is configured to detect the received light radiation exclusively within a limited spectral range of the emitted transmitted light radiation of the radiation transmitter section. For example, the at least one receiver LED is configured to detect the received light radiation exclusively within a spectral range between 220 and 400 nm, within a spectral range between 400 and 450 nm, within a spectral range between 450 and 500 nm, within a spectral range between 500 and 570 nm, within a spectral range between 570 and 590 nm, within a spectral range between 590 and 610 nm, within a spectral range between 610 and 760 nm, and / or within a spectral range between 760 and 800 nm.In particular, the at least one receiver light-emitting diode is designed to detect the received light radiation exclusively in an ultraviolet, a blue, a green, a yellow, an orange, a red and / or an infrared spectral range.

[0024] A preferred structural implementation of the invention provides that the receiver LED comprises the at least one radiation transmitter section. In particular, the same semiconductor region of the receiver LED is used by the radiation transmitter section and the light receiver section. For example, the receiver LED with the at least one radiation transmitter section is designed to emit the transmitted light radiation in a spectral range between 220 and 400 nm, in a spectral range between 400 and 450 nm, in a spectral range between 450 and 500 nm, in a spectral range between 500 and 570 nm, in a spectral range between 570 and 590 nm, in a spectral range between 590 and 610 nm, in a spectral range between 610 and 760 nm, and / or in a spectral range between 760 and 800 nm.In particular, the receiver LED with the at least one radiation transmitter section is designed to emit the transmitted light radiation in an ultraviolet, blue, green, yellow, orange, red, and / or infrared spectral range. In particular, the at least one or exactly one receiver LED is designed to detect the reflected received light radiation of the specifically emitted transmitted light radiation. By designing the receiver LED with the at least one radiation transmitter section, a small number of components and consequently a space-saving design for detecting interfering objects are implemented.

[0025] Particularly preferably, the fire detector comprises at least or exactly two receiver LEDs with the radiation transmitter sections. Preferably, the at least or exactly two receiver LEDs are designed to detect the received light radiation of the specifically emitted transmitted light radiation reflected by the interfering object. The light radiation characteristics detected by the at least or exactly two receiver LEDs are, for example, evaluated independently of one another by the evaluation device. Alternatively, the detected light radiation characteristics can be correlated by the evaluation device in order to perform mutual referencing to avoid an erroneous fault report. For example, the at least or exactly two receiver LEDs with the radiation transmitter sections are arranged on the housing at a distance of at least 3 cm and / or at most 10 cm from one another.

[0026] As an alternative or optional addition to detecting the received light radiation of the emitted transmitted light radiation, at least one of the at least two or exactly two receiver LEDs is configured to detect the received light radiation of the emitted transmitted light radiation of the other receiver LED(s) reflected by the interfering object. Mutual transmission and reception of the transmitted and received light radiation is thus implemented.

[0027] In a preferred development, it is provided that the at least or exactly two receiver LEDs are alternately activated as radiation transmitter sections in a periodic time sequence. This means that one of the at least or exactly two receiver LEDs emits the transmitted light radiation, while another of the receiver LEDs is activated as a radiation receiver section until a switchover occurs. To activate the receiver LED as a radiation transmitter section, it is preferably switched in the forward direction. If the receiver LED is activated as a radiation receiver section, it is preferred that the receiver LED not emit any transmitted light radiation in order to avoid the detection of its own transmitted light radiation. The control device is preferably designed to control the receiver LEDs alternately as radiation transmitter sections in the periodic time sequence.

[0028] It is possible for the at least two or exactly two receiver LEDs to be configured to emit transmitted light radiation in a different spectral range. For example, at least one of the receiver LEDs is configured as a red LED, and the at least one other of the receiver LEDs is configured as a blue LED. In a particularly preferred embodiment, the at least two or exactly two radiation transmitter sections are configured to emit the transmitted light radiation in the same limited spectral range. For example, the at least two or exactly two receiver LEDs are each configured as a red LED.

[0029] The interfering object is preferably detected at a distance of at least 1 cm and / or at most 50 cm from the at least one receiver LED or from at least one of the receiver LEDs. Within this distance, the receiver LED detects, in particular, a received light radiation intensity that exceeds the light intensity limit defined by the evaluation device, so that the interfering object is detected.

[0030] In a preferred embodiment of the invention, the functionality of the fire detector is signaled by the emitted light radiation of the at least one radiation transmitter section. The at least one radiation transmitter section thus serves as an optical signaling means that indicates to the user the correct and / or faulty operation of the fire detector. The radiation transmitter section therefore serves, on the one hand, to indicate the functionality of the fire detector, and, on the other hand, to detect interfering objects via the receiver LED. For example, functionality is signaled by the flashing of the at least one radiation transmitter section. If the correct operation of the fire detector can no longer be guaranteed, e.g., due to a low battery, the at least one radiation transmitter section can be provided to flash at a different interval than during correct operation.Optionally, the output of a signal tone can be provided.

[0031] In one possible implementation, the control device is configured to control the emission of the transmitted light radiation from the at least one radiation transmitter section or from at least one of the radiation transmitter sections in continuous light mode. Alternatively, the control device can be configured to control the at least one radiation transmitter section or at least one of the radiation transmitter sections to emit the transmitted light radiation in flashing light mode.

[0032] For example, the fire detector is designed as a scattered light detector, a fire gas detector, a heat detector, a humidity detector, an ionization fire detector, or a multi-criteria detector. In the scattered light detector, the sensors are designed specifically for detecting smoke particles; in the fire gas detector, they are designed specifically for detecting fire gases; in the heat detector, they are designed for detecting an ambient temperature; in the humidity detector, they are designed for detecting an ambient humidity; in the ionization fire detector, they are designed for detecting an electrical quantity; and in the multi-criteria detector, they are designed for detecting several fire-specific measurement parameters.

[0033] A further subject matter of the invention relates to a method for detecting an interfering object for a fire detector, preferably according to the preceding description. The at least one radiation transmitter section emits transmitted light radiation of a limited spectral range into the environment of the fire detector, wherein at least one receiver LED, which is designed to emit light radiation, detects received light radiation formed by the emitted transmitted light radiation reflected by the interfering object. The receiver LED comprises at least one radiation receiver section. In particular, the receiver LED comprises the at least one radiation transmitter section. An evaluation device detects the interfering object based on the detected received light radiation, wherein upon detection of the interfering object, a fault message is triggered and / or output.

[0034] Further features, advantages, and effects of the invention will become apparent from the following description of preferred embodiments of the invention. These show: Fig. 1 shows a fire detector with a receiver LED as a first embodiment of the invention; Fig. 2 the fire detector with two receiver LEDs as a second embodiment of the invention; Fig. 3 turn off the fire alarm Fig. 2 with an interfering object, wherein one of the two receiver LEDs detects the received light radiation of the specially emitted transmitted light radiation reflected by an interfering object; Fig. 4 turn off the fire alarm Fig. 2 with the interfering object, wherein one of the receiver LEDs detects the received light radiation of the emitted transmitted light radiation reflected at the interfering object from the other receiver LED.

[0035] Corresponding or identical parts are provided with the same reference numerals in the figures.

[0036] Fig. Figure 1 shows a fire detector 1 as a first embodiment of the invention. The fire detector 1 is designed, for example, as a scattered light, a fire gas, a heat, a humidity, an ionization, or a multi-criteria detector. For example, the fire detector 1 is connected to one or more fire detectors and / or to a monitoring center. The fire detector 1 is powered by an internal power supply, for example, via batteries, or via an external power supply.

[0037] The fire detector 1 has a housing 2 with a base 2a, wherein the fire detector 1 is arranged via the base 2a on a ceiling 3 of a room. The fire detector 1 is arranged as a surface-mounted detector on the ceiling 3, but it can also be provided, for example, as a flush-mounted detector on the ceiling 3. The fire detector 1 has a sensor system for detecting a fire. The sensor system records fire-specific measurement parameters, such as smoke particles, to detect the fire. The housing 2 has a measuring chamber housing section 2b in which the sensor system is arranged. The fire detector 1 also comprises an evaluation device, which is arranged, for example, in the measuring chamber housing section 2b. The sensor system is connected to the evaluation device for transmitting the recorded fire-specific measurement parameters, wherein the evaluation device detects the fire based on the transmitted fire-specific measurement parameters.For example, the fire detector 1 includes a control device that triggers an alarm upon fire detection. The control device is arranged, for example, in the measuring chamber housing section 2b.

[0038] An interfering object 5 is shown, which is arranged relative to the fire detector 1 in such a way that the airflow to the fire detector 1 is prevented or at least reduced, so that the airflow containing the fire-specific measurement parameters is insufficiently directed to the fire detector 1. Thus, the interfering object 5 prevents the recording of the fire-specific measurement parameters and consequently the detection of the fire. The interfering object 5 is, for example, a piece of furniture such as a cupboard, a chest of drawers, a shelf, a houseplant, or other interfering objects, such as stacked boxes.

[0039] In this exemplary embodiment, the fire detector 1 comprises precisely one radiation transmitter section 4 for detecting the interfering object 5. The radiation transmitter section 4 is designed to emit transmitted light radiation L1 of a limited spectral range into the surroundings of the fire detector 1. The radiation transmitter section 4 is arranged on the outside of the measuring chamber housing section 2b in such a way that the emitted transmitted light radiation L1 of the radiation transmitter section 4 is emitted toward a floor of the room in which the fire detector 1 is arranged. The emitted transmitted light radiation L1 of the radiation transmitter section 4 is reflected back by the interfering object 5 to the radiation transmitter section 4 as received light radiation L2. A receiver light-emitting diode 6 comprises the radiation transmitter section 4 and detects the received light radiation L2. The receiver light-emitting diode 6 is designed, for example, as a PIN light-emitting diode.

[0040] The fire detector 1 comprises a printed circuit board on which electronic circuits are formed, for example for controlling the receiver LED 6.

[0041] The detected received light radiation L2 is transmitted to the evaluation device, which detects the interfering object 5 based on the detected received light radiation L2. For example, upon detection of the interfering object 4 by the evaluation device, the control device issues a command to output a visual and / or acoustic fault signal to alert a user to the interfering object 4. The receiver LED 6 with the radiation transmitter section 4 enables a compact design for detecting interfering objects 5.

[0042] For example, the radiation transmitter section 4 is configured to emit modulated transmitted light radiation L1 using a frequency that does not match the frequency of the ambient light of the fire detector 1. For example, the radiation transmitter section 4 is configured as an infrared light-emitting diode. The receiver light-emitting diode 6 is, for example, receptive exclusively to the spectral range of the modulated transmitted light radiation L1.

[0043] For example, the radiation emitter section 4 indicates the functionality of the fire detector 1. For example, the radiation emitter section 4 is activated by flashing when the fire detector 1 is operating properly, while it is activated as a continuous light in the event of faulty operation, e.g., a sensor failure. In this way, the functionality of the fire detector 1 is always visible to a person.

[0044] Fig. 2 shows a Fig. 1 alternative embodiment of the fire detector 1. The fire detector 1 comprises two receiver LEDs 6, which comprise radiation transmitter sections 4. However, it can also be provided to arrange three, four, or more receiver LEDs 6, which comprise radiation transmitter sections 4. Furthermore, it is possible to arrange radiation transmitter sections 4 that are designed exclusively as radiation transmitter sections 4. For example, the two receiver LEDs 6 are designed as infrared LEDs. The two receiver LEDs 6 with the radiation transmitter sections 4 are arranged on the base 2a of the housing 2 such that the transmitted light radiation L1 is emitted toward the floor of the room in which the fire detector 1 is arranged. In particular, the two receiver LEDs 6 reduce the risk of a misinterpreted fault.

[0045] Fig. 3 shows the fire detector 1 from Fig. 2. The receiver LEDs 6 with the radiation transmitter sections 4 are designed to detect the received light radiation L2 of the specifically emitted transmitted light radiation L1, as shown for one of the two receiver LEDs 6. The receiver LEDs 6 are, for example, exclusively receptive to the spectral range of the specifically emitted transmitted light radiation. For example, the radiation transmitter sections 4 are each designed to emit modulated light radiation using a frequency that does not match the frequency of the ambient light of the fire detector 1 and / or the frequency of the other radiation transmitter section 4.

[0046] As in Fig. 4, it can alternatively or optionally be provided that the receiver light-emitting diodes 6 are designed to detect the received light radiation L2 of the emitted transmitted light radiation L1 of the other radiation transmitter section 4 reflected at the interfering object 5.

[0047] For example, the receiver LEDs 6 are alternately activated as a radiation receiver section. Thus, the transmitted light radiation L1 is emitted by only one of the two receiver LEDs 6, while the other of the two receiver LEDs 6 is connected as the radiation receiver section and is thus designed to detect the received light radiation L2. The activation of the receiver LED 6 as a radiation transmitter section 4, and vice versa, is controlled, for example, by the control device of the fire detector 1. If one of the receiver LEDs 6 is connected as a radiation transmitter section 4, it does not emit any transmitted light radiation L1.

[0048] For example, the switched receiver LED 6 is controlled in continuous light mode. Alternatively, it is possible for the switched receiver LED 6 to be controlled in flashing light mode. In this case, it can be provided that the activation of one receiver LED 6 occurs as the radiation transmitter section 4, and vice versa, after a flashing light is emitted by the respective switched receiver LED 6 as the radiation transmitter section 4.

[0049] For example, at least one of the two radiation transmitter sections 4 indicates the functionality of the fire detector 1. For example, at least one of the radiation transmitter sections 4 is activated by flashing when the fire detector 1 is operating properly and by a continuous light when the fire detector 1 is operating incorrectly, e.g., in the event of a sensor failure.

Claims

[1] Fire detector (1) with a housing (2), wherein the housing (2) can be arranged on a wall and / or on a ceiling (3) of a room, with a sensor system for detecting a fire, wherein the sensor system is arranged in or on the housing (2), with at least one radiation transmitter section (4) for emitting transmitted light radiation (L1) into an environment of the fire detector (1), with at least one radiation receiver section, wherein the at least one radiation receiver section is designed to detect a received light radiation (L2) which is formed by the emitted transmitted light radiation (L1) reflected by an interfering object (5), with an evaluation device, wherein the evaluation device is designed to detect the interfering object (5) by means of the detected received light radiation (L2), characterized by a receiver light-emitting diode (6) which is designed to emit light radiation and comprises the at least one radiation receiver section, and a control device which is designed to trigger and / or output a fault message when the interfering object (5) is detected by the evaluation device. [2] Fire detector (1) according to claim 1, characterized by that the at least one receiver light-emitting diode (6) is designed to detect the received light radiation (L2) exclusively in a limited spectral range of the emitted transmitted light radiation (L1) of the radiation transmitter section (4). [3] Fire detector (1) according to claim 1 or 2, characterized by that the receiver light-emitting diode (6) comprises the at least one radiation transmitter section (4). [4] Fire detector (1) according to claim 3, characterized bythat the receiver light-emitting diode (6) with the at least one radiation transmitter section (4) is designed to emit the transmitted light radiation (L1) in an ultraviolet, a blue, a green, a yellow, an orange, a red and / or an infrared spectral range. [5] Fire detector (1) according to claim 3 or 4, characterized by that the fire detector (1) has at least or exactly two receiver light-emitting diodes (6) with the radiation transmitter sections (4), wherein the at least or exactly two receiver light-emitting diodes (6) are designed to detect the received light radiation (L2) of the specifically emitted transmitted light radiation (L1) reflected at the interfering object (5) and / or the received light radiation (L2) of the emitted transmitted light radiation (L1) of the other receiver light-emitting diode(s) (6) reflected at the interfering object (5). [6] Fire detector (1) according to claim 5, characterized bythat the at least or exactly two receiver light-emitting diodes (6) are designed to emit the transmitted light radiation (L1) in the same limited spectral range. [7] Fire detector (1) according to one of the preceding claims, characterized by that the control device is designed to control the emission of the transmitted light radiation (L1) of the at least one radiation transmitter section (4) in flashing light mode. [8] Fire detector (1) according to one of the preceding claims, characterized by that the functionality of the fire detector (1) is signaled by the transmitted light radiation (L1) of the at least one radiation transmitter section (4). [9] Fire detector (1) according to one of the preceding claims, characterized by that the detection of the interfering object (5) takes place at a distance of the interfering object (5) from the at least one receiver LED (6) of at least 1 cm and / or of at most 50 cm. [10] Fire detector (1) according to one of the preceding claims, characterized by that the fire detector (1) is designed as a scattered light smoke detector, as a fire gas detector, as a heat detector and / or as an ionization fire detector. [11] Method for detecting an interfering object (5) for a fire detector (1), characterized byin that at least one radiation transmitter section (4) emits transmitted light radiation (L1) of a limited spectral range into an environment of the fire detector (1), wherein at least one receiver light-emitting diode (6), which is designed to emit light radiation, detects received light radiation (L2) which is formed by the emitted transmitted light radiation (L1) reflected by the interfering object (5), wherein the receiver light-emitting diode (6) comprises at least one radiation receiver section, wherein an evaluation device detects the interfering object (5) by means of the detected received light radiation (L2), and wherein a fault message is triggered and / or output upon detection of the interfering object (5).

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