Fire detector having unheated thermistor, in particular NTC, for detecting thermal fluctuations in region of access opening, and corresponding method

Abstract

The invention relates to a fire detector having an unheated thermistor, in particular an NTC, for detecting thermal fluctuations in the region of an access opening, and to a corresponding method. The fire detector (M) is designed to detect a fire characteristic variable and to output a fire alarm (AL). The fire detector (M) comprises a housing (G) with an inlet opening (OF) and thermistors (T1-T4), in particular NTC, arranged in the region of the inlet opening (OF). The fire detector comprises a control unit (MC) which is connected to a thermistor for detecting temperature measurement signals (S1-S4). The control unit is characterized in that if the signal bandwidth of the signal fluctuations of at least one, preferably all, of the detected temperature measurement signals does not exceed a value of 30 mK, in particular 20 mK, preferably 15 mK, for a minimum time (MZ), the temperature measurement signals are detected by the control unit. If there is no occurrence of ambient air flowing around the at least one thermistor, a warning message (WM) is output. The reason for no thermal fluctuations may be contamination in the area of the access opening or covering the access opening with a protective cover or with an adhesive tape.

Description

Technical Field

[0001] The invention relates to a fire detector, in particular an (optical) smoke detector, for detecting at least one characteristic fire variable in the environment of the fire detector and for outputting a (fire) alarm in the event of a detected fire. The fire detector has a housing with at least one inlet opening, a sensor system for detecting a flow in the area of ​​a sensor system, which is connected to the ambient air via the inlet opening, and a control unit. The control unit is connected to the sensor system for evaluating the suitability of the fire detector. The invention further relates to a corresponding method. Background Art

[0002] Such fire detectors are known, for example, from EP 1 857 989 A1, DE 10 2009 000 393 A1, EP 2 330 577 A1 or EP 2 189 956 A1.

[0003] A fire detector is known from EP 2 624 229 A1, which comprises a housing with a measuring chamber for detecting smoke particles. The fire detector has a flow sensor for detecting a flow rate as a measured variable for evaluating the suitability of the fire detector and an evaluation device adapted therefor. In a preferred embodiment, the flow sensor is designed as a hot wire flow sensor, the functional principle of which is based on the fact that a hot wire cools due to the flow rate. The degree of cooling is a function of the flow velocity and the air temperature. Summary of the invention

[0004] Based on this, one object of the present invention is to specify an improved fire detector.

[0005] A further object of the invention is to specify a fire detector having a more energy-efficient sensor system.

[0006] Finally, it is an object of the present invention to specify a method corresponding to the fire detector according to the invention.

[0007] This object is achieved by the subject matter of the independent claims. Advantageous embodiments of the invention are described in the dependent claims.

[0008] According to the invention, the sensor system has at least one thermistor arranged in the region of at least one of the inlet openings. A thermistor is a passive component with an ohmic resistance value that is temperature-dependent. The thermistor is preferably an NTC (standing for Negative Temperature Coefficient Thermistor) or a PTC (standing for Positive Temperature Coefficient Thermistor), i.e. a thermistor with a negative or positive temperature coefficient. The control unit is connected to at least one thermistor for (exclusively) detecting a corresponding temperature measurement signal. The thermistor is therefore a special temperature sensor.

[0009] According to the invention, the control unit is further configured to output a warning message if the signal bandwidth of the signal fluctuations of at least one of the detected temperature measurement signals, preferably of all the detected temperature measurement signals, does not exceed a value of 30 mK, in particular 20 mK, preferably 15 mK for a minimum time. At least 90% of the detected signal fluctuations, preferably at least 95% of the detected signal fluctuations, extend within this signal bandwidth.

[0010] In other words, the control unit is designed to output a warning message if a signal alternating current component (AC component), i.e. a signal component decoupled from a direct current component (DC component), of at least one of the detected temperature measurement signals, and preferably of all of the temperature measurement signals, has a value of less than 30 mK, in particular less than 20 mK, preferably less than 15 mK, for a minimum time.

[0011] The minimum time is in the range of 1 day to 1 year, in particular in the range of 1 day to 1 month, and preferably in the range of 1 day to 1 week.

[0012] The fire detector can have a timer for detecting the expiration of the minimum time. The timer can be an electronic counter module. The timer can already be integrated in the control unit. Alternatively, the timer can also be implemented as software, which is executed on a processor-assisted control unit, in particular on a microcontroller. The control unit is set up here to first set the counter reading of the timer to a count start value corresponding to the minimum time, and the timer continuously reduces the count start value. If the timer reaches the count value zero, the control unit outputs a warning message. If a signal fluctuation was previously detected by means of the control unit, the timer is set to the count start value again.

[0013] A warning message is output if no ambient air flows around at least one thermistor. Signal fluctuations are caused by thermal fluctuations in the room air, which directly surrounds or washes over the corresponding thermistor from all sides. The absence of ambient air flowing around the at least one thermistor is a sign of contamination in the area of ​​the inlet opening or of an inadmissible covering of the inlet opening with a protective cover or with adhesive tape. In this case, the fire detector can no longer be used. The warning message is therefore a message about the unsuitability of the fire detector.

[0014] The core of the invention is the use of a purely passively operated, i.e. unheated, thermistor for the measurement-technical detection of very small signal changes in the corresponding temperature measurement signal caused by the thermal fluctuations that are almost always present in the environment of the fire detector. If such thermal fluctuations can be detected in the area of ​​the access opening, this is a (reliable) indicator that the access opening is sufficiently transparent for fire detection. At least the access opening is then not completely contaminated or blocked when fluctuations are present, or deliberately covered or shielded. The latter is often the case if the fire detector is deliberately covered by a protective cover due to paint work in order to prevent the fire detector from being accidentally painted. If such a protective cover should not be present, the access opening is often also shielded with the help of corrugated tape or with the help of rubber gloves.

[0015] Thus, studies in measurement technology have shown that thermal fluctuations, i.e. flow fluctuations, are not completely uniform due to their temperature distribution. It is also possible to find that the (average) signal bandwidth of the noise-like signal fluctuations in the corresponding temperature measurement signal, which is typically in the range of about 15 mK, is already a multiple of the pure thermal noise of the thermistor itself. The detection of very small temperature changes is due to the minimum heat input into the thermistor or the minimum heat removal from the thermistor. Since the corresponding thermistor is not heated, there is also no cooling effect that would be caused by thermal fluctuations or flow fluctuations in the case of other heated flow sensors. The level of the cooling effect would then be a measure of the speed of the flow flowing around the flow sensor.

[0016] Such thermal fluctuations in the environment of a fire alarm typically result from the opening and closing of doors, gusts of wind from outside the building blowing against windows that are not completely sealed, air turbulence caused by people or heating equipment, air conditioning equipment, fans or blowers being switched on and off.

[0017] As described above, it can be said that the output of the warning message is suppressed for a duration corresponding to the predefined comparison value. If an air surge with an air temperature slightly different from the temperature of the corresponding thermistor is detected at times during this duration, it can be assumed that the fire detector is not impermissibly contaminated.

[0018] A particular advantage of the invention is that no current- or power-intensive electrical heating of the corresponding thermistor is required. As a result, the fire detector can also advantageously be a (only) battery-assisted fire detector. Its battery can be provided for powering the fire detector alone.

[0019] A further advantage can be seen in that the thermistors used, in particular NTCs, are much more useful as mass products and are also much more compact than dedicated flow sensors.

[0020] Finally, another advantage is that these components can be used together as other fire characteristic variables in fire detectors with overtemperature detection. Thus, the fire detector according to the invention advantageously requires fewer components than a fire detector with a hot wire flow sensor as flow sensor.

[0021] In the case of thermal anemometers, such as hot wire anemometers, sensor elements are used which must be heated electrically and whose resistance depends on the temperature or the cooling effect. Due to the surrounding flow, a heat transfer into the flowing medium occurs which varies with the flow velocity. By measuring the electrical variable, the flow velocity can then be inferred. However, for the operation of such sensors, despite the disadvantageously high current and energy requirements, special electronic systems are additionally disadvantageously required, which regulate the heating current and amplify the sensor signal.

[0022] If the fire detector according to the invention is an optical smoke detector, in particular a scattered light smoke detector, the (characteristic) fire characteristic variable is the smoke concentration, which is measurably correlated to the scattered light level. The smoke concentration is monitored with respect to the exceeding of a minimum smoke concentration, i.e., the minimum scattered light level, measurably. Alternatively or additionally, the smoke concentration or the corresponding scattered light level can also be monitored with respect to an impermissibly rapid increase.

[0023] If the fire detector according to the invention is a heat detector, the (characteristic) fire characteristic variable is the temperature in the immediate vicinity surrounding the fire detector, which is monitored with respect to an exceeding of a minimum temperature. Alternatively or additionally, the temperature can also be monitored with respect to an inadmissibly rapid increase. In this case, the control unit of the fire detector is designed to monitor the corresponding temperature measurement signal with respect to an exceeding of an overtemperature limit value, in particular 54° C., and / or with respect to an exceeding of a rate of temperature rise, in particular 5° C. per minute, preferably 10° C. per minute, as a fire characteristic variable, and to output a fire alarm in the event of a detected fire.

[0024] The fire detector can also be a combination of an optical smoke detector, in particular a scattered light smoke detector and a heat detector. In the simplest case, a fire alarm is triggered as soon as one of the detected fire characteristic variables exceeds an assigned comparison value.

[0025] The control unit of the fire detector is in particular processor-controlled and preferably a microcontroller. On such a microcontroller, via its processor unit, a software program is executed which analyses and evaluates at least one detected fire characteristic variable and outputs a fire alarm in the case of a detected fire, and which outputs a warning message if no thermal fluctuations occur for a predefined minimum time.

[0026] The fire detector is preferably designed as a point detector. The point detector can be connected to a detector line of a fire alarm center with typically a plurality of other fire detectors. Alternatively, the fire detector can be battery-operated.

[0027] According to one specific embodiment, the control unit is designed to continuously convert the corresponding temperature measurement signal into a corresponding digital temperature measurement signal with the aid of an A / D converter at a predetermined sampling period AP, in particular with a sampling period AP in the range of 0.1 to 10 seconds, preferably in the range of 0.5 to 2 seconds. This makes it possible to reliably detect the typically short-lived, sporadic occurrence of flowing air with thermal inhomogeneities. The actual A / D conversion time with the aid of the A / D converter in the microcontroller is typically less than 10 microseconds, in particular less than 2 microseconds.

[0028] According to another embodiment, the control unit is set up to first filter the corresponding detected temperature measurement signal by means of a high-pass filter and then detect signal fluctuations in the corresponding temperature measurement signal. The angular frequency of the high-pass filter, i.e. the filter frequency, is in particular less than 0.1 Hz. As a result, the DC signal component in the corresponding temperature measurement signal is advantageously removed for evaluating the fluctuating AC signal component in the measurement technology in an improved manner. Therefore, the corresponding high-pass filtered signal obtained is partially decoupled from the DC or DC decoupled. The high-pass filter can be an RC element implemented using discrete components, which is connected to the downstream of the corresponding thermistor on the output side or to the downstream of the signal amplifier connected to the downstream of the thermistor on the output side. The aforementioned discrete components may also have been integrated in the control unit. Alternatively, the high-pass filter is a digital high-pass filter.

[0029] According to an alternative embodiment to the previous embodiment, the control unit is configured to first filter the corresponding detected temperature measurement signal by means of a high-pass filter, filter the high-pass filtered signal output by the corresponding high-pass filter by means of a low-pass filter with a filtering time in the range of 1 to 120 minutes, preferably 15 to 60 minutes, and output it as a corresponding filtered output signal. The angular frequency of the high-pass filter, i.e. the filtering frequency, is in particular less than 1 Hz, preferably less than 0.1 Hz. The control unit is configured to output a warning message if, instead of the signal bandwidth of the signal fluctuations in the corresponding temperature measurement signal, at least one filtered output signal, preferably all filtered output signals, does not exceed a predetermined limit value of 5 mK, in particular 3 mK, preferably 1.5 mK for a minimum time. It is thus possible to evaluate the temperature measurement signal more accurately in view of the presence of signal fluctuations.

[0030] According to an alternative embodiment to the two aforementioned embodiments, the control unit is configured to first filter the corresponding detected temperature measurement signal by means of a high-pass filter, filter the high-pass filter signal output by the corresponding high-pass filter by means of a sliding average filter with a predetermined filter time in the range of 1 to 120 minutes, preferably 15 to 60 minutes, in particular by means of a sliding root mean square or arithmetic mean filter, and output it as a corresponding filtered output signal. The angular frequency of the high-pass filter, i.e. the filter frequency, is in particular less than 1 Hz, preferably less than 0.1 Hz. In English technical terminology, such a filter is also called Moving Average Filter. Another name for a root mean square filter is an effective value filter, which is also called an RMS filter in English technical terminology, which stands for Root Mean Square Filter.

[0031] The control unit is designed to output a warning message if, instead of the signal bandwidth of the signal fluctuations in the respective temperature measurement signal, at least one filtered output signal, preferably all filtered output signals, do not exceed a predefined limit value of 5 mK, in particular 3 mK, preferably 1.5 mK for a minimum time. If the sliding mean value filter is a sliding root mean square filter, i.e. a sliding effective value filter or a sliding RMS filter, it is possible here, due to measurement-technical considerations relating to the signal power, to evaluate the temperature measurement signal particularly precisely with regard to the presence of thermal fluctuations.

[0032] The aforementioned high-pass, low-pass and sliding average filters are in particular digital filters, preferably stable FIR filters (FIR stands for Finite Impulse Response), which are implemented as part of a software program on a microcontroller as a control unit. The simplest FIR filter is the classical averaging by summing up the individual successive values ​​and dividing by their number. If this is not performed block by block (digital 1 to digital 10, digital 11 to digital 20, etc.), but rather in an overlapping manner (digital 1 to digital 10, digital 2 to digital 11, digital 3 to digital 12, etc.), a sliding arithmetic mean is obtained. The preferred FIR filter is the averaging by summing up the squares of the individual successive values ​​and dividing by their number together with the subsequent root formation. If this is again not performed block by block, but again in an overlapping manner, a sliding root mean square (sliding RMS) is obtained.

[0033] According to an advantageous embodiment, the predetermined limit value is defined in the range of 1.5 to 10 times, in particular 1.5 to 5 times, a reference value which has been determined by measurement in a flow-free test environment for a new or like-new or overhauled, in particular factory-fresh, fire detector. The measurement determination is typically carried out at a room temperature of 20° C.±2° C. and typically at normal ambient air pressure. The reference value substantially corresponds to the thermal noise or the thermal noise power.

[0034] According to another specific embodiment, the control unit is designed to continuously convert the respective temperature measurement signal into a respective oversampled digital temperature measurement signal by means of an A / D converter by oversampling with a number OVS in the range of 2 to 4096, in particular with a number OVS of 64, 256 or 1024. In this case, the total oversampling time for each conversion of the temperature measurement signal into a mean digital value is less than 50 ms, in particular less than 25 ms, preferably less than 10 ms.

[0035] Oversampling increases the resolution during A / D conversion computationally. The number of "extra" bits follows the relationship 0.5×1d OVS, where 1d is the double logarithm and OVS is the number of oversampling. With a number of 256 oversamplings, the resolution for each converted digital value is increased by 4 bits.

[0036] A particular advantage here is that now a low-cost microcontroller with a 10-bit A / D converter or with a 12-bit A / D converter can be used instead of an expensive microcontroller with a 14-bit A / D converter or a 16-bit A / D converter. In addition, additional signal amplification circuits can be omitted. By increasing the resolution for each converted digital value by an exemplary 4 bits, even the smallest temperature changes in the corresponding temperature measurement signal can be reliably distinguished from the thermal noise of the thermistor.

[0037] According to another specific embodiment, the control unit is designed to control the corresponding thermistor such that for each measured value acquisition the thermistor is heated by less than 0.5 mK, in particular less than 0.1 mK. The corresponding thermistor is thereby operated virtually passively with a negligible temperature rise.

[0038] Alternatively or additionally, the control unit is designed to control the corresponding thermistor such that it consumes a maximum electrical energy of 10 μJ, in particular 5 μJ, preferably 0.5 μJ per measured value acquisition. Even in this case, the corresponding thermistor is actually operated with a negligible temperature rise.

[0039] According to another embodiment, the heat capacity of the corresponding thermistor is measured so that the thermal response time of the corresponding thermistor is a maximum of 3 seconds, in particular 2 seconds, preferably a maximum of 1 second. The "thermal response time" refers to the time interval for the thermistor to detect half of the temperature difference when a sudden temperature difference is applied externally. As a result, even the smallest temperature changes and thus thermal inhomogeneities in the flowing air in the area of ​​the inlet or in the central interior of the measuring chamber can be detected.

[0040] According to another embodiment, a fire detection unit, in particular an optical measuring chamber, which is connected to the ambient air via at least one inlet opening is accommodated or configured in the housing for detecting at least one fire characteristic variable. A grille, in particular an insect screen, is arranged in the area of ​​the respective inlet opening and the fire detection unit.

[0041] In the case of a first embodiment, the grille is arranged in the region of the respective access opening between at least one thermistor and the fire detection unit. In particular, at least one thermistor is arranged radially outside the grille with respect to the main axis of the fire detector. Viewed from the outside, the respective thermistor is located "in front of" the grille. Preferably, at least two thermistors are arranged evenly distributed in the circumferential direction with respect to the main axis of the fire detector. This advantageously makes it possible to carry out particularly reliable monitoring with respect to an impermissible covering of at least one access opening.

[0042] In a second design, at least one thermistor is arranged between the grille and the fire detection unit in the region of the corresponding inlet opening. Compared to the previous design, at least one thermistor is arranged radially inside the grille with respect to the main axis of the fire detector. From the outside, the corresponding thermistor is located "behind" the grille. Further preferably, at least two thermistors are arranged evenly distributed in the circumferential direction relative to the main axis of the fire detector. In the case of an even number of thermistors, these thermistors are arranged radially relative to the main axis. It is thus possible to monitor the grille sections assigned to the corresponding inlet openings in view of increased and ultimately inadmissible high contamination. In addition, it is also possible to monitor in view of an inadmissible covering of at least one inlet opening.

[0043] According to another embodiment, the control unit is configured to start an operating timer of the fire detector when the power supply to the fire detector is started. The control unit is configured to output a covered message or a warning message together with a covered message as an indicator of an impermissible covering of at least one access opening if the signal bandwidth of the signal fluctuations in at least one of the detected temperature measurement signals, preferably in all the temperature measurement signals, does not exceed a value of 30 mK, in particular 20 mK, preferably 15 mK for a minimum waiting time in the range of 1 hour to 3 days, preferably 1 hour to 24 hours, and if in addition the operating time value of the operating timer is less than 2 years, preferably less than 1 year.

[0044] The operating timer can be a counter module with non-volatile electronic memory, such as EEPROM, flash memory or FRAM memory. The operating timer can be a separate electronic component or already integrated in the control unit. Typically, the fire detector is powered by the fire alarm control center via the detector line or via the detector bus when inserted into its detector base. In the case of battery-operated fire detectors, power is supplied when the battery of the fire detector is inserted or switched on.

[0045] In this case, it can be assumed that a fire detector with a short operating life can hardly have any contamination in the area of ​​the inlet opening, so that smoke or combustion gases to be detected cannot flow through the inlet opening into the interior of the fire detector for fire detection. The reason why no fluctuations occur is then with a high probability that the inlet opening is already covered with a protective cover or, due to the lack of such a protective cover, is covered with adhesive tape in order to avoid painting over the fire detector during the pending painting work.

[0046] Advantageously, after reinserting the fire detector into its detector base or when restarting a fire detection system having a plurality of fire detectors according to the invention, a blocked message or a warning message together with a blocked message is output in order to indicate a possible non-operational readiness of the fire detector.

[0047] According to one embodiment, the control unit is configured to output a warning message and / or a masked message directly at the fire detector in an optical and / or acoustic manner, for example by means of a flashing LED or by means of a buzzer. Alternatively or additionally, the warning message and / or the masked message can be output to a superordinate center connected to the fire detector and / or wirelessly via a radio connection to a superordinate center.

[0048] The object of the present invention is also solved by a method for detecting contamination or inadmissible covering of at least one inlet for smoke or combustion gases in the case of a fire detector. Here, at least one (unheated) thermistor is arranged in the area of ​​one of the inlets. Temperature measurement signals are detected by the corresponding thermistor. If a thermal fluctuation with a signal bandwidth of at least 30mK, in particular at least 20mK, preferably at least 15mK is detected in at least one of the temperature measurement signals, a timer is started. Finally, if the (average) signal bandwidth of the signal fluctuation in at least one of the detected temperature measurement signals, preferably in all temperature measurement signals, does not exceed a value of 30mK, in particular 20mK, preferably 15mK for a minimum time, a warning message is output when the ambient air flowing around the corresponding thermistor does not occur. Here, at least 90% of the detected signal fluctuations, preferably at least 95% of the detected signal fluctuations extend within the signal bandwidth.

[0049] The minimum time is in the range of 1 day to 1 year, in particular in the range of 1 day to 1 month, and preferably in the range of 1 day to 1 week.

[0050] For the further description, in order to avoid unnecessary repetitions, it applies that the features and details described in conjunction with the mentioned fire detector and its embodiments also apply in conjunction with and with respect to the corresponding method and vice versa, so that the disclosure regarding the various aspects of the invention always refers to one another or can always refer to one another.

[0051] The features and details described for the fire detector according to the invention, in particular the scattered light smoke detector, such as thermistor, values, temperature values, durations, rates of change, etc., also apply to the corresponding method. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] The present invention and its advantageous embodiments are explained by way of example in the following figure.

[0053] Figure 1 An example of a fire detector according to the invention is shown which has four thermistors which are arranged distributed in the region of the access opening,

[0054] Figure 2 Shown according to Figure 1 The top view of the fire detector in view direction II is drawn in

[0055] Figure 3 A block diagram showing an electronic control unit of a fire detector according to the present invention,

[0056] Figure 4 shows the course of an unfiltered temperature measurement signal of a thermistor arranged in the region of an inlet opening of a fire detector according to the invention,

[0057] Figure 5 The enlarged view shows the Figure 4 The numerical change process of the high-pass filtered signal after filtering the unfiltered temperature measurement signal.

[0058] Figure 6 A greatly enlarged view shows the Figure 5 The change process of the value of the filtered output signal after filtering the high-pass filtered signal. DETAILED DESCRIPTION

[0059] Figure 1 An example of a fire detector M according to the invention is shown, which has four thermistors T1-T4 which are arranged distributed in the region of an inlet opening OF. The housing of the fire detector M is denoted by G, which comprises a base body GG and a cover H. In between, the fire detector M has, by way of example, an inlet opening OF which completely surrounds a main axis A of the fire detector M. The thermistors T1-T4 shown are part of a sensor system for detecting a flow in the region of the sensor system.

[0060] The hood H shown is carried by way of example by a measuring chamber which is accommodated in the interior of the housing G and is connected to the ambient air via at least one inlet opening OF. The optical measuring chamber MK is a preferred embodiment of a fire detection unit MK for detecting at least one characteristic fire variable and is also referred to as a labyrinth. The labyrinth has lamellae, not shown in further detail, in a characteristic manner. The latter are designed to shield the optical measuring chamber MK from ambient light penetrating via the inlet opening OF on the one hand and to be permeable to smoke or combustion gases to be detected on the other hand.

[0061] An insect grid is designated by N, which prevents insects and the like from penetrating into the interior of the measuring chamber MK via the inlet opening OF. In this case, the four thermistors T1-T4 are arranged radially outside the grid N with respect to the main axis A. The grid N is therefore located between the thermistors T1-T4 and the lamellae of the optical measuring chamber MK. If the inlet opening OF is now covered, for example, by means of a protective cap, the thermistors T1-T4 are shielded from the surrounding room air in terms of flow technology.

[0062] In the present example, the optical measuring chamber MK has two light emitting diodes LED of different colors in a known manner, which are each arranged as a photoelectric sensor PD with a scattered light device. In addition, another sensor, for example for detecting toxic gases such as carbon monoxide (CO), or a humidity sensor, for example as a comfort sensor, can be arranged in the measuring chamber MK.

[0063] All the aforementioned sensors and the light emitting diodes LED can be arranged together with a processor-assisted electronic control unit MC of the fire detector M on a circuit carrier PCB of the fire detector M. The control unit MC of the fire detector M is preferably a microcontroller which is set up or programmed to output an alarm AL in the event of a detected fire, symbolically indicated by an arrow. In the present case, an alarm is output if an excessively high level of scattered light or an excessively high CO level of the CO sensor has been detected in the measuring chamber MK.

[0064] according to Figure 1 and Figure 2 In the example of, four thermistors T1-T4 radially located outside the main axis A of the fire detector M are evenly distributed in the circumferential direction. Thermistors T1-T4 are preferably NTCs. The latter are extremely robust, very small in size, and in addition low in cost. In addition to the connecting wires, such NTCs have a maximum size in the range of 1mm to 5mm in three dimensions. Typically, two of the three dimensions are even less than 2mm. This extremely compact configuration with its low thermal capacity guarantees a fast thermal response characteristic of a maximum of 3s, especially a maximum of 2s and preferably a maximum of 1s. Thus, short-term slight temperature changes (thermal fluctuations) in the flowing ambient air are also displayed at the two electrical terminals of the corresponding NTC in the form of corresponding ohmic resistance changes that can be tapped in measurement technology and therefore also in the form of the corresponding electrical temperature measurement signal. The aforementioned thermistors T1-T4 are therefore established or provided for outputting corresponding temperature measurement signals.

[0065] The NTC for the corresponding thermistor T1-T4 can, for example, have an ohmic resistance value of 10kΩ, 20kΩ, 25kΩ, 50kΩ or 100kΩ specified in view of an ambient temperature of 25°C. The corresponding NTC is typically connected in series with a resistor (device) having a constant resistance value. Preferably, the ohmic resistance value of the resistor (component) corresponds to the resistance value of the corresponding NTC at 25°C. The series circuit is connected to a constant voltage difference, such as a voltage difference of 3.0V, which is typically composed of a voltage difference between a reference potential (ground) and a positive constant supply voltage. Then, the center tap of the series circuit is fed to the input of the A / D converter. The A / D converter is usually already integrated in the microcontroller MC. Preferably, the electronic control unit or microcontroller MC is set up or programmed to connect the voltage difference only during the time period of the (queued) A / D conversion. This can be done, for example, by electrically controlling a switching element, such as a transistor, connected in series with the series circuit. This further minimizes the current consumption.

[0066] Alternatively, instead of the ohmic resistor (component), a constant current source can be connected in series with the NTC or usually in series with the thermistor. Alternatively or additionally, a signal amplifier can also be connected between the center taps of the series circuit, the output signal of the signal amplifier being connected to the input of the A / D converter.

[0067] According to the invention disclosure, the control unit MC shown is set up or programmed to output a warning message WM if the (average) signal bandwidth of the signal fluctuations in at least one of the detected temperature measurement signals S1-S4, preferably in all temperature measurement signals S1-S4, does not exceed a value of 30 mK, in particular 20 mK, preferably 15 mK for a minimum time MZ. The minimum time MZ is in particular in the range of 1 day to 1 year, in particular in the range of 1 day to 1 month, and preferably in the range of 1 day to 1 week.

[0068] Figure 3 The block diagram of an electronic control unit MC of a fire detector M according to the invention, which is implemented as a microcontroller, is shown. A software program PRG is executed on the microcontroller MC via its processor unit in order to actuate the associated light-emitting diode LED in the case of a connected optical fire detection unit, to receive a sensor signal from the associated photodiode PD and to analyze it with the aid of an evaluation program and, if necessary, to output a fire alarm AL. The software program PRG is also executed for outputting a warning message WM according to the invention if no ambient air flows around at least one thermistor T1-T4. The absence of thermal fluctuations is an indicator of impermissibly high contamination or blockage of at least one inlet opening.

[0069] like Figure 3As shown, the microcontroller MC has, for this purpose, four integrated A / D converters ADC, which convert the temperature measurement signals S1-S4 from the four thermistors T1-T4 into corresponding digital temperature measurement signals D1-D4. The four digital signals D1-D4 are filtered or converted into corresponding high-pass signals F by means of corresponding high-pass filters HP in a functional block not shown in detail. H1 -F H4 In this example, the four high-pass signals F H1 -F H4 Then it is preferably fed to a corresponding sliding root mean square filter RMS. According to the invention, the filtered output signal F provided at the output is then monitored with regard to the following aspects O1 -F O4 :That is, the filtered output signal F O1 -F O4 Whether at least one of the filter output signal F exceeds a predetermined limit value GW. If this is the case, the count value of the timer TIMER implemented as software in the microcontroller MC is set to a starting count value corresponding to the minimum time and is started for countdown. O1 -F O4 When at least one of the thermistors T1-T4 exceeds the predetermined limit value GW again, the timer TIMER is reset again or restarted with the starting count value. Finally, according to the invention, if the timer TIMER reaches the count value zero, a warning message WM is output for the ambient air flowing around at least one thermistor T1-T4 not occurring.

[0070] Alternatively, the four high-pass signals F H1 -F H4 It can also be fed to a corresponding sliding arithmetic mean filter AVS or a low-pass filter TP. The aforementioned filters HP, RMS, AVS, TP are digital filters, preferably FIR filters. FZ denotes the filter time for the sliding mean filter RMS, AVS or for the low-pass filter TP.

[0071] According to one embodiment, the control unit MC can be connected to an operating timer BZM, which is started when the fire detector is powered on. In this case, the control unit MC is set up or programmed (PRG) to output a covered message COV or a warning message WM together with a covered message COV as an indicator of an impermissible covering (Abdeckung) for at least one access opening if the signal bandwidth of the signal fluctuations in at least one of the detected temperature measurement signals S1-S4, preferably in all temperature measurement signals S1-S4, does not exceed a value of 30 mK, in particular 20 mK, preferably 15 mK for a minimum waiting time WZ in the range of 1 hour to 3 days, preferably 1 hour to 24 hours, and if in addition the operating time value BZW of the operating timer BZM is less than 2 years, preferably less than 1 year.

[0072] Figure 4 The following is a diagram showing the course of an unfiltered temperature measurement signal of a thermistor arranged in the region of an access opening of a fire detector according to the invention. By way of example, the temperature measurement signal has been sampled with a sampling time of 2 seconds and recorded over a period of slightly more than one month (August 28 to October 2) in a non-air-conditioned room in the applicant's development department. The course of the ambient temperature with a respective maximum temperature during the day and a respective minimum temperature at night is reflected in the temperature measurement signal. The maximum temperature interval for this period is approximately 8 degrees Celsius.

[0073] Figure 5 The enlarged view shows the Figure 4 The numerical course of the high-pass filtered signal after filtering the unfiltered temperature measurement signal. The high-pass filter used for decoupling the DC component in the temperature measurement signal has a filtering time of 25 seconds, which corresponds to a filtering frequency of 1 / 25 seconds. The relatively large signal deviations in the form of signal fluctuations with an absolute maximum deviation of approximately 80 mK are shown in a greatly magnified manner in terms of measurement technology until the time when the protective cover is put on (see the two boxes with the text "covering the detector (Abdeckung Melder)"), which occur with the thermal fluctuations of the ambient air. It can be said that these thermal fluctuations wash the direct environment surrounding the measured thermistor from all sides.

[0074] Surprisingly, these signal deviations decrease very quickly with the placement of the protective cover. The reason for this is the shielding effect of the protective cover. In the further course of the change, the value of the filtered temperature measurement signal only still shows signal fluctuations with a deviation of approximately 6 mK at most, which corresponds to a signal bandwidth with a value of twice 12 mK and is therefore approximately one order of magnitude lower than in the time period before the access opening was covered with the protective cover. The high-pass filtering with the absolute temperature difference shown causes the temperature measurement signal to remain above the zero line and correlate with the zero line. Half of the signal bandwidth of the signal fluctuations in the time period when the detector is covered is indicated by the reference symbol B / 2.

[0075] at last, Figure 6 A greatly enlarged view shows the effect of filtering the signal from Figure 5 The process of changing the value of the filtered output signal after filtering the high-pass filtered signal. Figure 6 As shown, the absolute value of the low-pass signal drops sharply from about 5 mK before the protective cover is put on to a value of about 1 mK after the protective cover is put on. The reference symbol GW is used to indicate a limit value with an exemplary value of 1.5 mK, which the absolute value of the low-pass filter signal does not exceed during the period of covering the detector. This very large and stably reproducible signal difference advantageously allows reliable identification of whether the access opening is covered or completely contaminated.

[0076] In summary, the invention relates to a fire detector which is designed to detect a characteristic fire variable and to output a fire alarm. The fire detector comprises a housing with an inlet opening and a thermistor, in particular an NTC, arranged in the region of the inlet opening. The fire detector comprises a control unit which is connected to the thermistor for detecting temperature measurement signals. If the (average) signal bandwidth of the signal fluctuations in at least one of the detected temperature measurement signals, preferably in all temperature measurement signals, does not exceed a value of 30 mK, in particular 20 mK, preferably 15 mK for a minimum time, the control unit is designed in a representative manner for this purpose. The reason why thermal fluctuations do not occur may be contamination in the region of the inlet opening or covering the inlet opening with a protective cover or with adhesive tape.

[0077] Reference numerals list

[0078] A Main axis, axis of symmetry

[0079] ADC A / D Converter

[0080] AL Fire alarm, alarm

[0081] AVS Sliding Arithmetic Mean Filter

[0082] B / 2 half the signal bandwidth

[0083] BZM running timer

[0084] BZW running time value

[0085] COV obscured message

[0086] DET Evaluation Unit

[0087] D1-D4 Digital temperature measurement signal

[0088] F H1 -F H4 High pass filtered signal

[0089] F O1 -F O4 Filter output signal

[0090] FZ filter time

[0091] GG matrix

[0092] GW limit

[0093] H cover, detector cover

[0094] HP High Pass Filter

[0095] LED light emitters, light emitting diodes

[0096] M Fire detectors, smoke detectors

[0097] MC Electronic Control Unit, Microcontroller

[0098] MK Fire Detection Unit, Optical Measuring Chamber

[0099] MZ Minimum Time

[0100] N Insect grilles, nets

[0101] OF inlet, smoke inlet

[0102] PCB circuit carrier

[0103] PD Photo Receiver, Photodiode

[0104] PRG Computer programs, software

[0105] RMS Sliding Root Mean Square Filter

[0106] S1-S4 Temperature measurement signal

[0107] t time, time axis

[0108] T1-T4 Thermistor, NTC

[0109] TIMER Timer, time measurement element

[0110] TP Low Pass Filter

[0111] WM Warning Message, Pollution Message

[0112] WZ minimum waiting time

[0113] Δθ Temperature change

[0114] θ Temperature.

Claims

1. A fire detector for detecting at least one characteristic variable of a fire and for outputting a fire alarm (AL) in the event of a detected fire, wherein the fire detector (M) has a housing (G) with at least one inlet opening (OF), a sensor system for detecting a flow in the area of ​​the sensor system, which is connected to the ambient air via the inlet opening, and a control unit (MC), wherein the control unit (MC) is connected to the sensor system for evaluating the suitability of the fire detector (M), characterized in that the sensor system comprises at least one thermistor (T1-T4), in particular at least one NTC, which is arranged in the region of at least one of the inlet openings (OF), - the control unit (MC) is connected to at least one thermistor (T1-T4) for detecting a corresponding temperature measurement signal (S1-S4), and - The control unit (MC) is designed to output a warning message (WM) if the signal bandwidth of the signal fluctuations of at least one of the detected temperature measurement signals (S1-S4), preferably all of the temperature measurement signals (S1-S4), does not exceed a value of 30 mK, in particular 20 mK, preferably 15 mK for a minimum time (MZ). 2 . The fire detector according to claim 1 , wherein the minimum time is in the range of 1 day to 1 year, in particular in the range of 1 day to 1 month, and preferably in the range of 1 day to 1 week.

3. A fire detector according to claim 1 or 2, wherein the control unit (MC) is configured to continuously convert the corresponding temperature measurement signals (S1-S4) into corresponding digital temperature measurement signals (D1-D4) with the aid of an A / D converter (ADC) with a predetermined sampling period AP, in particular with a sampling period AP in the range of 0.1 to 10 seconds, preferably in the range of 0.5 to 2 seconds.

4. A fire detector according to any one of claims 1 to 3, wherein the control unit (MC) is designed to first filter the corresponding detected temperature measurement signals (S1-S4, D1-D4) by means of a high-pass filter (HP) and then detect signal fluctuations in the corresponding temperature measurement signals (S1-S4, D1-D4).

5. The fire detector according to claim 1 , wherein the control unit (MC) is configured to first filter the respective detected temperature measurement signal (S1-S4, D1-D4) by means of a high-pass filter (HP), and to filter the high-pass filtered signal (F1-S4, D1-D4) output by the respective high-pass filter (HP) by means of a low-pass filter (TP) having a filter time (FZ) in the range of 1 to 120 minutes, preferably 15 to 60 minutes. H1 -F H4 ) is filtered and used as the corresponding filtered output signal (F O1 -F O4 ) output, and wherein the control unit (MC) is configured to replace the signal bandwidth of the signal fluctuations of the corresponding temperature measurement signal (T1-T4) with the at least one filtered output signal (F O1 -F O4 ), preferably all filtered output signals (F O1 -F O4 ) does not exceed a predefined limit value (GW) of 5 mK, in particular 3 mK, preferably 1.5 mK, for a minimum time (MZ), a warning message (WM) is output.

6. The fire detector according to claim 1 , wherein the control unit (MC) is configured to first filter the respective detected temperature measurement signal (S1-S4, D1-D4) by means of a high-pass filter (HP), filtering the high-pass filtered signal (F1-S4, D1-D4) output by the respective high-pass filter by means of a sliding mean value filter with a predefined filter time (FZ) in the range of 1 to 120 minutes, preferably 15 to 60 minutes, in particular by means of a sliding root mean square or arithmetic mean value filter (RMS, AVS). H1 -F H4 ) is filtered and used as the corresponding filtered output signal (F O1 -F O4 ) is output, and the control unit (MC) is designed to output at least one filtered output signal (FO1-FO4), preferably all filtered output signals (F1-F4), if instead of an average signal bandwidth of the signal fluctuations in the corresponding temperature measurement signal (T1-T4), O1 -F O4 ) does not exceed a predefined limit value (GW) of 5 mK, in particular 3 mK, preferably 1.5 mK, for a minimum time (MZ), a warning message (WM) is output.

7. A fire detector according to claim 5 or 6, wherein the predetermined limit value (GW) is specified in the range of 1.5 to 10 times, in particular 1.5 to 5 times, a reference value, which has been determined measurement-technically in a flow-free test environment on a new or like-new or overhauled, in particular factory-fresh, fire detector (M).

8. A fire detector according to any one of claims 3 to 7, wherein the control unit (MC) is designed to continuously convert the corresponding temperature measurement signals (S1-S4) into corresponding oversampled digital temperature measurement signals (D1-D4) by means of an A / D converter (ADC) by oversampling a number OVS in the range of 2 to 4096, in particular with a number OVS of 64, 256 or 1024.

9. A fire detector according to any one of the preceding claims, wherein the control unit (MC) is configured to control the corresponding thermistors (T1-T4) so ​​that the thermistors heat up by less than 0.5 mK, in particular less than 0.1 mK, for each measured value detection, and / or the thermistors consume a maximum electrical energy of 10 μJ, in particular 5 μJ, preferably 0.5 μJ for each measured value detection.

10. The fire detector according to claim 1, wherein the respective thermistor (T1-T4) has a maximum thermal response time of 3 s, in particular 2 s, preferably 1 s.

11. A fire detector according to any one of the preceding claims, - a fire detection unit (MK), in particular an optical measuring chamber, which is connected to the ambient air via at least one inlet opening (OF) for detecting at least one characteristic fire variable is accommodated or constructed in the housing (G), - wherein a grille (N), in particular an insect screen, is arranged in the region of the respective access opening (OF) and the fire detection unit (MK), and - wherein the grid (N) is arranged in the region of the respective inlet opening (OF) between at least one thermistor (T1-T4) and the fire detection unit (MK), or - at least one thermistor (T1-T4) is arranged in the region of the respective inlet opening (OF) between the grille (N) and the fire detection unit (MK).

12. A fire detector according to any of the preceding claims, wherein the control unit (MC) is configured to start an operating timer (BZM) of the fire detector (M) when the fire detector (M) is powered on, wherein the control unit (MC) is configured to output a covered message (COV) or a warning message (WM) together with a covered message (COV) as a flag for impermissible covering of at least one access opening (OF) if the signal bandwidth of the signal fluctuations of at least one of the detected temperature measurement signals (S1-S4), preferably all of the temperature measurement signals (S1-S4), does not exceed a value of 30 mK, in particular 20 mK, preferably 15 mK for a minimum waiting time (WZ) in the range of 1 hour to 3 days, preferably 1 hour to 24 hours, and if in addition the operating time value (BZW) of the operating timer (BZM) is less than 2 years, preferably less than 1 year.

13. A fire detector according to any of the preceding claims, wherein the control unit (MC) is configured to output the warning message (WM) and / or the masked message (COV) directly at the fire detector (M) in an optical and / or acoustic manner and / or to a superior center connected to the fire detector (M) and / or wirelessly via a radio connection to a superior center.

14. A fire detector according to any of the preceding claims, wherein the control unit (MC) is configured to monitor corresponding temperature measurement signals (S1-S4, D1-D4) with regard to exceeding an overtemperature limit value of, in particular, 54°C and / or a temperature rise rate of, in particular, 5°C per minute, preferably 10°C per minute as a fire characteristic parameter and to output a fire alarm (AL) in the event of a detected fire.

15. A method for detecting contamination or inadmissible covering of at least one inlet opening (OF) for smoke or combustion gases in a fire detector (M), - wherein at least one unheated thermistor (T1-T4) is arranged in the region of one of the inlet openings (OF), - wherein the temperature measurement signals (S1-S4) are detected by respective thermistors (T1-T4), and - wherein a warning message (WM) is output for the fact that a flow of ambient air around at least one thermistor (T1-T4) does not occur if the signal bandwidth of the signal fluctuations of at least one of the detected temperature measurement signals (S1-S4), preferably all of the temperature measurement signals (S1-S4), does not exceed a value of 30 mK, in particular 20 mK, preferably 15 mK for a minimum time (MZ).

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