Fire detector with a self-monitoring module

Abstract

Fire detector (1) with a light transmitter device (5) for emitting a measuring light (M) into a measuring area (6), with a sensor device (7) for measuring the measuring light (M) from the measuring area (6) and for generating a sensor signal, with an evaluation device (11) for detecting a fire on the basis of the sensor signal, with a self-monitoring module (13) for detecting electromagnetic interference in the sensor signal, characterized in that the self-monitoring module (13) is designed to use a dark signal, which is designed as the sensor signal when the light transmitter device (5) is deactivated, to detect the electromagnetic interference, and the self-monitoring module (13) is designed to detect the electromagnetic interference in the dark signal using a statistical analysis and / or on the basis of a frequency analysis.

Description

State of the art

[0001] Automatic fire alarm systems are commonly used for the early detection of fires in public or private premises. Such fire alarm systems typically include at least one fire detector, which can detect a fire in its surroundings early and trigger an alarm based on fire-specific parameters such as smoke, soot particles, temperature, or gas concentrations.

[0002] For example, EP 0 903 708 A1 discloses a fire detector having an event memory that permanently stores data on the fire detector's functional parameters in the event of a fault or alarm event. As an example, it is also stated that messages regarding the registration of a fluctuation in a fire detector's measurement signal are stored, with the occurrence of a fluctuation indicating that an electromagnetic disturbance may have occurred.

[0003] A compact particle sensor is known from US 2001 / 0 038 338 A1. US 3 982 130 A discloses a smoke detector based on ultraviolet wavelengths. EP 0 903 708 A1 discloses an automatic fire detector for detecting one or more fire parameters. Disclosure of the invention

[0004] Within the scope of the invention, a fire detector having the features of claim 1 is proposed. Preferred or advantageous embodiments of the invention emerge from the subclaims, the following description and the attached figures.

[0005] Within the scope of the invention, a fire detector is presented which is suitable and / or designed for detecting a fire. In particular, the fire detector is designed as an automatic fire detector. In its design, the fire detector can be integrated into a housing which can particularly preferably be attached to a ceiling or a wall. The fire detector can be designed as a surface-mounted fire detector or as a flush-mounted fire detector. In particular, the fire detector comprises at least one alarm device for outputting an alarm signal upon detection of a fire. Alternatively or additionally, the fire detector can also have a data interface, wherein the fire detector is designed to output the alarm signal for detecting the fire via the interface to a data network and, for example, to a fire alarm control center or to rescue services. The fire detector is particularly preferably designed to be energy self-sufficient.In particular, it is implemented as a stand-alone system which can be operated independently of energy by means of an integrated energy storage device, such as a battery or accumulator.

[0006] The fire detector comprises a light transmitter device for emitting a measuring light into a measuring area and a sensor device for measuring the measuring light from the measuring area and for generating a sensor signal. The light transmitter device is particularly preferably designed as a light-emitting diode (LED). In particular, it is a blue light-emitting diode, a UV light-emitting diode, or an infrared light-emitting diode. The sensor device is oriented relative to the measuring area such that it can receive at least part of the measuring light from the measuring area. In particular, the sensor device comprises a sensor element for detecting the measuring light and a circuit for generating the sensor signal.

[0007] For example, the light transmitter device and sensor device can together form an absorption measuring section, wherein an absorption of the measuring light can be measured as a function of a turbidity of the air in the measuring area, so that a fire can be concluded.

[0008] Alternatively, and particularly preferably, the fire detector is designed as a scattered light sensor, wherein the sensor device is arranged such that it receives exclusively scattered light from the measuring light in the measuring area. With this measuring method, the measuring light scattered by smoke particles or other particles in the ambient air in the measuring area is detected, and a fire is determined based on the height or intensity of the scattered light. The measuring area is openly connected to the environment surrounding the fire detector, allowing ambient air to circulate into or through the measuring area.

[0009] The fire detector also includes an evaluation unit for detecting a fire based on the sensor signal. For example, a fire is detected when the height or intensity of the measured light falls below a predefined threshold during an absorption measurement, or when the scattered light exceeds a predefined threshold during a scattered light measurement.

[0010] The fire detector further comprises a self-monitoring module designed to detect electromagnetic interference in the sensor signal. The self-monitoring module can be a separate module or formed as part of the evaluation device. Such electromagnetic interference can, in particular, be transmitted in a field-bound manner and received there, for example, by a conductor of the sensor device acting as an antenna. The electromagnetic interference is generated by a mostly unknown interference source, with the sensor device forming the interference sink. The coupling path between the interference source and the interference sink is, in particular, non-conductive. In particular, the coupling can involve capacitive coupling, inductive coupling, or radiation coupling between the interference source and the interference sink.

[0011] Within the scope of the invention, it is proposed that the self-monitoring module be configured to use a dark signal as the sensor signal to detect electromagnetic interference. The fire detector, in particular the evaluation device, is configured to deactivate the light transmitter device to generate the dark signal. Thus, the dark signal is configured as a sensor signal when the light transmitter device is deactivated. In particular, a measuring light measurement is performed by the sensor device while the light transmitter device is not emitting any measuring light, and the result of the measuring light measurement is passed on to the self-monitoring module as a dark signal.

[0012] The inventive design has the advantage that, by deactivating the light transmitter device, all interference that may be caused by the light transmitter device or by the transmission path via the measuring area to the sensor device are excluded. For example, errors in the driver of the light transmitter unit are excluded, as are interference caused by contamination in the measuring area and the resulting poor transmission of the measuring light. By using the dark signal instead of a sensor signal with an activated light transmitter device, a measurement environment for detecting electromagnetic interference can be provided that is largely free of interference. This makes the detection of electromagnetic interference significantly more reliable than when using the sensor signal with an activated light transmitter device.

[0013] In a preferred development of the invention, the measuring area and / or the sensor device, in particular the sensor element of the sensor device, is arranged in a labyrinth, in particular an optical labyrinth, so that the measuring space and / or the sensor device or the sensor element are optically shielded from ambient light from the environment of the fire detector. In particular, the labyrinth is designed such that there is no straight, open connection from the sensor device, in particular from the sensor element, to the environment. Preferably, at least one, at least two, and in particular at least three reflections are necessary in order to be able to bring ambient light onto the sensor element in the labyrinth. In contrast, the labyrinth is fluidically open to the environment so that ambient air can circulate through the measuring space.

[0014] Particularly preferably, the sensor device comprises at least one photodiode as the sensor element. Such photodiodes are highly reliable and measure even the lowest light outputs.

[0015] According to the invention, the self-monitoring module is designed to detect the electromagnetic interference using a statistical analysis, in particular a frequency analysis, and / or on the basis of a frequency analysis.

[0016] Electromagnetic interference that impairs the function of the fire detector primarily occurs in an interference frequency range between 1 kHz and 10 kHz. Therefore, it is particularly advantageous to monitor the dark signal for electromagnetic interference in this frequency range. This is preferably achieved using an analog filter circuit that filters out signal components with non-critical frequencies, i.e., signal components with frequencies outside the interference frequency range, from the dark signal.

[0017] Preferably, the dark signal is not sampled continuously, but rather a measured value is determined at longer intervals, for example once per second or more. If the correlation between the dark signal and the sample is not maintained over this period, which is long compared to the interference frequency range, it can always be assumed that the sample was taken at a random point in time during the course of the interference wave. If, for example, more than 20 measured values are sampled in a common measurement window, they are randomly distributed across the interference wave, which is assumed to be constant. These 20 measured values are sufficient to determine the amplitude of the interference wave. This determination is independent of the actual frequency of the interference wave.

[0018] Another method is to calculate a frequency distribution of the measured values and use this to directly evaluate the influence on the smoke measurement of the fire detector. The evaluation can be designed in particular as a prediction for a false alarm or as a probability of a real alarm. If, for example, an interference amplitude greater than a predefined first limit value, e.g. greater than 100 mV, is measured over a period of 3 hours for more than 20 minutes, reliable smoke detection can no longer be guaranteed. So that when an alarm is triggered, the probability that the alarm is a real alarm and not a false alarm is low. If, under the same conditions, an interference amplitude greater than a second limit value, e.g. greater than 300 mV, is measured, a false alarm must be expected within the next day, so that a prediction of a false alarm can be issued for the second limit value.

[0019] Using the measured or estimated amplitude of the interference wave, it is possible to calculate the probability with which a smoke measurement deviates from the undisturbed measurement by a certain absolute value. Based on this probability, the probability of a false alarm can be calculated. The latter probability depends not only on the specific interference amplitude, but also on its variance over a longer period of time (e.g., over 3 hours).

[0020] In particular, the self-monitoring module is designed to issue a warning message locally upon detection of electromagnetic interference or, for example, to forward it to a control center via the data interface. In these configurations, it is possible for the warning message to be perceived locally or further processed at the control center, so that the cause of the electromagnetic interference can be remedied without delay.

[0021] In a possible further development of the invention, the self-monitoring module is configured to transmit at least one characteristic of the electromagnetic interference to the evaluation device, wherein the evaluation device is configured to take the electromagnetic interference into account when detecting the fire based on the sensor signal. For example, the sensitivity of the fire detector can be reduced upon detection of the electromagnetic interference.

[0022] Further features, advantages, and effects of the invention will become apparent from the following description of a preferred embodiment of the invention and the accompanying figures. These show: Fig. 1 a schematic representation of a fire detector as an embodiment of the invention 1.

[0023] The Fig.Figure 1 shows a highly schematic representation of a fire detector 1 as an embodiment of the invention. The fire detector 1 is arranged on a ceiling 2 and serves to detect smoke particles 3 or other fire characteristics in the ambient air of the environment U of the fire detector 1. The fire detector 1 is arranged in a housing 4, which is screwed, for example, to the ceiling 2.

[0024] The fire detector 1 operates according to the so-called scattered light principle, whereby a light emitting device 5, in this case designed as an LED, radiates a measuring light M into a measuring area 6. The fire detector 1 further comprises a sensor device 7 with a sensor element 10, which is arranged such that it does not receive any direct measuring light M from the light emitting device 5. For example, a measuring direction R of the sensor device 7 forms an included angle alpha between 100° and 30° with respect to the main beam direction H. The sensor device 7 is thus designed to receive exclusively scattered, in particular retroreflected, measuring light from the measuring space 6. The scattered light principle is based on the idea that, when the ambient air in the measuring area 6 is unpolluted, the measuring light M is not scattered, so that no measuring light M is received by the sensor device 7.In the event that the ambient air in the measuring area 6 contains smoke particles 3 or other fire characteristics, the measuring light M is scattered or reflected and returned to the sensor device 7, where this portion of the measuring light M is measured. The sensor element 10 is designed, for example, as a photodiode.

[0025] In order to be able to carry out the scattered light measurement without interference, the measuring area 6 is arranged in a labyrinth 8, which on the one hand enables a fluidic coupling of the measuring area 6 with the environment 3, but on the other hand prevents ambient light from directly radiating into the measuring area 6. For example, the labyrinth 8 has a plurality of ambient openings 9 through which ambient air can circulate in the measuring area. The labyrinth 8 is constructed such that ambient light entering through the ambient opening 9 would have to be reflected at least once, preferably at least twice, to reach the measuring area 6. Alternatively or additionally, the labyrinth 8 is implemented such that ambient light entering through the ambient opening 9 would have to be reflected at least once, preferably at least twice, to impinge on a sensor element 10 of the sensor device 7.

[0026] The fire detector 1 comprises an evaluation device 11, which receives the sensor signal from the sensor device 7 and detects a fire based on the sensor signal. For example, it detects whether the portion of the measuring light M scattered in the measuring area 6, which was recorded by the sensor element 10, is above a predeterminable limit value. For example, the evaluation device 11 is designed as a microcontroller or as another data processing device.

[0027] Optionally, the fire detector 1 additionally comprises an alarm device 12, which is designed to emit a visual or acoustic alarm upon detection of a fire. Furthermore, the fire detector 1 optionally comprises a battery (not shown) for powering the fire detector 1.

[0028] The fire detector 1 has a self-monitoring module 13 for detecting electromagnetic interference (EMC) in the sensor signal of the sensor device 7. Thus, the sensor signal is routed to both the monitoring device 11 and the self-monitoring module 13. The self-monitoring module 13 can also form a component of the evaluation device 11. In particular, the self-monitoring module can be implemented as a program or a subprogram in the evaluation device 11.

[0029] For the purpose of detecting electromagnetic interference in the sensor signal, the fire detector 1 is designed to deactivate the light transmitter device 5 during the detection of the sensor signal by the self-monitoring module 13, so that the measuring room 6 is darkened. For example, the control is handled by the evaluation device 11. It should be noted that due to the labyrinth 8, the measuring room 6 is already shielded from ambient light, so that the darkening is very reliable. The sensor signal picked up by the sensor device 7 from the darkened measuring room 6 is referred to as the dark signal.

[0030] The self-monitoring module 13 is designed to examine the dark signal for indications or characteristics of electromagnetic interference.

[0031] This is achieved in a first exemplary implementation by filtering out signal components with frequencies that do not correspond to an interference frequency range, e.g., analogically. The resulting filtered dark signal thus contains only signal components in the interference frequency range, e.g., 1 kHz to 10 kHz. In a very simple implementation, the energy of this filtered dark signal range could be determined and used as a measure of electromagnetic interference.

[0032] Alternatively, the amplitude of the electromagnetic interference wave is determined, in particular measured or estimated. This is achieved by sampling the filtered dark-field signal at a frequency lower than the frequencies in the interference wave frequency range. For example, a frequency of 1 Hz or lower is used. Sampling is uncorrelated or free-running with the electromagnetic interference waves. From a plurality of consecutive measured values, e.g., more than 20, the amplitude or at least an amplitude reference value is determined by frequency analysis or estimation.

[0033] If the self-monitoring module 13 detects electromagnetic interference, it can issue a warning message to a control center or technical service via a communication module 14. The warning message can either trigger the deployment of service personnel or change the reliability level of the fire detector, with the reliability level being lowered if electromagnetic interference is present. Alternatively or additionally, a visual or acoustic warning message can be issued locally via a signaling device 15.

[0034] Alternatively or additionally, the self-monitoring module 13 can transmit at least one characteristic of the detected electromagnetic interference to the evaluation device 11, wherein the evaluation device 11 is configured to take the at least one characteristic of the electromagnetic interference into account when detecting the fire. This can be implemented, on the one hand, by raising a trigger threshold for an alarm. On the other hand, this can be implemented by outputting a probability that the alarm is a real alarm and not a false alarm and transmitting it to the control center.

Claims

[1] Fire detector (1) with a light transmitter device (5) for emitting a measuring light (M) into a measuring area (6), with a sensor device (7) for measuring the measuring light (M) from the measuring area (6) and for generating a sensor signal, with an evaluation device (11) for detecting a fire on the basis of the sensor signal, with a self-monitoring module (13) for detecting electromagnetic interference in the sensor signal, characterized by , that the self-monitoring module (13) is designed to use a dark signal, which is designed as the sensor signal when the light transmitter device (5) is deactivated, to detect the electromagnetic interference, and the self-monitoring module (13) is designed to detect the electromagnetic interference in the dark signal using a statistical analysis and / or on the basis of a frequency analysis. [2] Fire detector (1) according to claim 1, characterized by that the fire detector (1) is designed as a scattered light sensor. [3] Fire detector (1) according to claim 1 or 2, characterized by that the measuring area (6) and / or the sensor device (7) is arranged in a labyrinth (8). [4] Fire detector (1) according to one of the preceding claims, characterized by that the sensor device (7) comprises at least one photodiode as a sensor element (10). [5] Fire detector (1) according to one of the preceding claims, characterized by that the self-monitoring module (13) is designed to detect the dark signal with a measuring frequency of less than 100 Hz, preferably less than 10 Hz and in particular less than 1 Hz. [6] Fire detector (1) according to claim 5, characterized bythat the self-monitoring module (13) is designed to detect the electromagnetic interference in the dark signal using more than 20, preferably more than 30 measured values with the measuring frequency in a measuring window. [7] Fire detector (1) according to claim 6, characterized by that the self-monitoring module (13) is designed to estimate an amplitude and / or an energy of the electromagnetic interference on the basis of the measured values in the measuring window. [8] Fire detector (1) according to one of the preceding claims, characterized by that the self-monitoring module (13) is designed to issue a warning message locally or to forward it to a control center when electromagnetic interference is detected. [9] Fire detector (1) according to one of the preceding claims, characterized bythat the self-monitoring module (13) is designed to transfer at least one characteristic of the electromagnetic interference to the evaluation device (11), wherein the evaluation device (11) is designed to take the electromagnetic interference into account when detecting the fire on the basis of the sensor signal.

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