EP1638062A1 - Aspirating smoke detector and method of its operation - Google Patents

Abstract

A fire alarm box (61) sucks air in via a system (64) of pipes for rooms and equipment to be monitored and examines this air for parameters which are characteristic of a fire. Volume flow in the system of pipes and the fire alarm box is measured and, after adjustment, is examined for a disconnection or obstructions by comparison with upper and lower limiting values (614). Preferably a correction value is determined for every detector with respect to temperature, air pressure, humidity and hermeticity. An independent claim is also included for a fire alarm box with a detector for the parameters of a fire for carrying out the method of the present invention.

Description

Technical area

The invention relates to a method for detecting blockages and

Interruptions in a pipe system of a fire detector, which draws the air through the pipe system from one or more monitoring rooms or electrical equipment, and monitors for fire characteristics. The invention further relates to a fire detection system for carrying out the method, comprising at least one fire detector for detecting at least one fire characteristic to which a representative amount of room or equipment air is supplied via said pipe system and a device for determining a flow value, based on which the state of the pipe system is judged.

State of the art

Such methods are known, for example, from DE 33 31 203 A1, DE 44 28 694 A1 and EP 1 056 062 B1. Systems using such methods consist of at least one fan, which sucks in ambient air from a pipe system from the rooms or devices to be monitored and supplies at least one detector for fire parameters. As fire characteristics are in ansaugenden fire alarm systems mostly smoke and combustion gases such. As hydrogen and carbon monoxide detected to detect a fire as early as possible in the formation phase of the same. The piping systems used in this case can consist, for example, of an elongated pipe to which holes for sucking in the air are attached at suitable locations. Suitable locations are, for example, the outlets of appliance cooling air or in the middle of a smaller space to be monitored. The suction holes can also follow each other at regular intervals, which makes sense, especially in large halls or high-bay warehouses. As a rule, the suction holes are dimensioned so that each hole sucks in as much air as possible. In addition to the I-pipes just mentioned pipe systems with multiple branches find especially U and H systems Use. In order to ensure a fire detection in all monitoring areas, it is necessary to detect blockages of individual holes or breaks in the pipeline. Since a monitoring area can be allocated to each hole, this area will no longer be able to be monitored for blockage of the hole. Even with an interruption of a pipe, no more air will be sucked from the interruption following holes, which can no longer monitor the areas associated with these holes. To detect such pipe changes, it is customary to monitor the mass flow or volume flow within the pipe system. An increase in volume flow indicates an interruption and a decrease in constipation. Usually, interruption and blockage are detected by comparing the flow values with upper and lower limit values, whereby an exceeding of the upper limit value is interpreted as an interruption and the falling below the lower limit value as a blockage. In DE 33 31 203 A1, a temperature-compensated thermal anemometer is used for air flow monitoring. In one possible mode of operation, these anemometers heat an electrical temperature resistor to a constant temperature and measure the power required for it. Particles flowing past this resistance cool the resistance. The cooling depends on the temperature difference between the particles and the resistance and the amount of particles flowing per unit time. Here, the measured power serves as a measure of the mass flow. Now, if the mass flow is used to detect blockages or interruptions, it may happen that the mass flow is already affected by changes in air pressure and temperature and the measured value exceeds the thresholds mentioned even though there is no obstruction or interruption. For example, as the pressure increases, the density of the air increases, so more particles pass through the sensor per time and therefore cool it more. To circumvent this problem would make the windows formed from the thresholds correspondingly large, but in turn the sensitivity to constipation and

Minimizes interruption. Therefore, DE 44 28 694 A1 uses an additional pressure sensor to perform a pressure compensation of the measured value in addition to the temperature compensation known from DE 33 31 203 A1. In other words, in DE 44 28 694 A1, just as is customary in volumetric flow measurements, the volume flow is determined from the measured values for the mass flow, the temperature and the pressure according to the following formula. $$V\left(t\right)=\frac{m\left(t\right)*R_L*T}{p}=\frac{m\left(t\right)}{\rho }$$

In which: V (t) is the volume flow, m (t) the mass flow, T the temperature of the air flow, R _L the specific gas constant of the air, p the air pressure and ρ the density of the air.

In EP 1 056 062 B1, a value representing the air flow is determined from the rotational speed and the power consumption of the fan. What can be dispensed with an additional air flow sensor. EP 1 056 062 B1 also describes that by observing the fan speed and the power consumption of the driving engine a density change of the air can be detected and that a corresponding correction factor can be determined by means of a trend detection. As a result, the pressure sensor used in DE 44 28 694 A1 is dispensable. The method of the correction values determined by a trend, however, has the disadvantage that a device using this method can not cope with the density changes during a longer phase in the switched-off state and may, under certain circumstances, start from false assumptions regarding the prevailing density ,

However, none of the above-described methods or systems describes that a density change of the air also affects the flow properties of the pipe system itself and thus a blockage or a

Interruption can be feigned without such a change has actually taken place.

Object of the invention

This problem is addressed by the present invention, the object of which is to provide a method and a fire master of the type described above that are even more sensitive with regard to the detection of blockages and

Interruptions are as the previously described methods and systems.

Description of the invention

The object is achieved according to the preamble and the characterizing features of claim 1 and claim 10 and will be described in more detail below. Advantageous preferred embodiments are described in subclaims 2-9 and 1-13.

The invention is based on the finding that changes in the density of the air not only affect the measured values of the airflow sensors, but also change the fan and rawcharacteristics and thus affect the overall system of fan and intake manifold. This will be shown using the example of a temperature-related density change. Fig. 1 shows the characteristics of a fan and a pipe system with predominantly laminar flow at two different temperatures, in which the volume flow on the X-axis and on the Y-axis of the differential pressure, is softer generated by the fan and applied via the pipe system drops. The solid dark curves, each labeled with b, correspond to a low temperature and the dashed (light) characteristic curves of higher temperature, respectively marked with a. The air density is known to increase when switching from a higher to a lower temperature, which is also caused by an increase in pressure. It can clearly be seen that the fan duct shifts at high temperature (2a) at a constant speed with a temperature drop from bottom to top to the characteristic curve at low temperature (2b). At the same time, the pipe characteristic shifts to the right at high temperature (1 a) to the characteristic curve at low temperature (1b). Thus, the high temperature operating point (3a) is also shifted to the low temperature operating point (3b). It can be clearly seen that this also entails an increase in the volumetric flow and it becomes clear that an upper volumetric flow limit value can be exceeded even if the temperature decrease is superimposed with an increasing pressure and an interruption is simulated. The reverse direction, an increase in temperature with decreasing pressure at the same time can simulate pipe blockage without actually having such changes to the pipe system. The Flg.1 can also be seen that the power absorbed by the fan increases with decreasing temperature, which causes an increase in density. If, instead, the fan power is left constant, which will be discussed again later, this results in a comparable situation, since in this case with increasing Density is accompanied by a falling speed and also results in a new fan characteristic.

In Fig. 2, in addition to the pipe system shown in Fig. 1 further characteristics (5a, 5b, 6a, 6b) are shown for other pipe systems using the same fan. Here, too, the volume flow is plotted on the X axis and the differential pressure is plotted on the Y axis, and the characteristic curves labeled b in each case designate a tube or fan bel low temperature and the characteristic curves a the same tube or fan at a higher temperature. It can be clearly seen that the density-related changes in the volume flow also depend on the pipe system used.

To this hitherto unknown influence on the system of fan and

In the method according to the invention, correction values are determined which represent the changes in the properties of the system consisting of the intake pipe and the fan, which are based on changes in the density of the air or changes in at least one environmental parameter affecting the air density, and for the correction of the mass flow. and / or volumetric flow and / or used to adjust the limits.

It is also within the meaning of the invention, not always all influencing variables on the air density for correction zoom in, since it can be dispensed with additional expensive sensors such as pressure sensors in cases where lower demands on sensitivity, and still remains sensitive enough Clogging and interruptions Reliable detection in the pipe system. Only in cases where highest accuracy is required, all factors influencing air density are used for correction. In addition to the above-mentioned temperature and air pressure, these factors include the air humidity whose influence on the air density can be deduced from the following formula: $$\rho =\frac{p}{R_L*T}\left(1-0.377\phi \frac{p_d}{p}\right)$$

Where ρ is the density of the air, p the pressure, p _d the saturation vapor pressure, φ the relative humidity, T the temperature in Kelvin and R _L the specific gas constant of the dry air.

In a preferred embodiment of the method according to the invention, a correction value is therefore determined for each temperature occurring during operation of the fire detector, which represents the changes in the properties of the system consisting of the intake pipe and fan, which are based on changes in temperature of the air and when reaching the respective temperature for correction of the mass and / or volumetric flow measured value and / or for adapting the limit values.

In a further preferred embodiment of the method according to the invention, a correction value is determined for each air pressure occurring during operation of the fire detector, which represents the changes in the properties of the system consisting of the intake pipe and fan, which are based on air pressure changes of the air and for correction of the respective pressure the mass and / or volumetric flow measured value and / or to adapt the limit values is applied.

In a further preferred embodiment of the method according to the invention, a correction value is determined for each occurring in the operation des.Brandmelders humidity, which represents the changes der.Eigenschaften existing from the intake manifold and fan system based on changes in humidity of the air and upon reaching the respective humidity is used to correct the mass and / or volumetric flow measured value and / or to adapt the limit values.

In a further preferred embodiment of the method according to the invention, a correction value is determined for each occurring during operation of the Brandmeiders temperature and each air pressure occurring during operation of the fire detector, which represents the changes in the properties of the system consisting of the intake manifold and fan on temperature or Pressure changes of the air are based and upon reaching the respective temperature and the respective pressure for the correction of the mass and / or volumetric flow measured value and / or to adapt the limit values is applied.

In a further preferred embodiment of the method according to the invention for each occurring during operation of the Brandmeiders temperature, each occurring during operation of the Brandmeiders air humidity and each occurring during operation of the fire alarm air pressure ever a correction value is determined, the changes in the properties of the existing of the intake manifold and fan Systems that respond to temperature, density, or pressure changes of the

Are based on air and when reaching the respective temperature, humidity and the respective air pressure to correct the mass and / or volumetric flow measurement and / or to adjust the limits is applied.

In a further preferred embodiment of the method according to the invention, a correction value is determined for each occurring in the operation of the fire detector air density, which represents the changes in the properties of the system consisting of the intake manifold and fan, based on density changes of the air and upon reaching the respective air density Correction of the mass and / or volumetric flow measured value and / or to adapt the limit values is applied.

In a further preferred embodiment of the method according to the invention, the correction values for temperature, air pressure and air humidity or the air density derived therefrom are determined by measurement for each fan pipe system and stored in a table.

In a further preferred embodiment of the method according to the invention, only supporting values for individual regions of the temperature and / or the air pressure and / or the air humidity and / or the air density derived therefrom are stored in the table, from which the respective correction values are determined by interpolation.

Since it is not possible to create and store any number of tables for all conceivable combinations of fans and pipe systems, this process is limited to a few standard systems or must be measured separately for each system.

In order nevertheless to remain flexible in the dimensioning of the pipe systems and to avoid costly measurements, in a further preferred embodiment of the method according to the invention the correction values representing the changes in the characteristics of the system consisting of the intake pipe and fan, which are based on temperature, and / or pressure, and / or humidity, and / or density changes of the air based, for temperature and / or air pressure and / or humidity or the air density derived therefrom, independently determined by the fire detector during operation and entered in a table provided for in the further course of the operation always to resort to it and to correct the current air flow values.

A fire prevention device according to the invention therefore contains at least one fire characteristic detector, a fan with a pipe system connected thereto, which sucks air from one or more monitoring rooms or electrical appliances and supplies it to the detector and furthermore a device for detecting a mass and / or volumetric flow Comparing means comparing a current flow value with upper and lower limits and at least one or more sensors for environmental parameters from the group consisting of the temperature, the air pressure and the humidity, and further a memory in which correction values are stored containing the Changes in the characteristics of the system consisting of the intake manifold and fan, which represents changes in at least one of the environmental parameters from the group consisting of the temperature, the atmospheric pressure and the humidity and / or the density change of the Lu derived therefrom ft, and a correction device which applies the correction values to the current measured values of the mass and / or volumetric flow and / or to the limit values.

A preferred fire alarm device according to the invention additionally contains a correction value calculation unit which determines the correction values from the current mass and / or volumetric flow measured value and a stored reference or a clogging / interrupt value,

Another preferred fire cutting apparatus according to the invention comprises a test unit which checks whether a change in the mass and / or volumetric flow measured value is based on a pipe change (blockage / interruption) or changes one or more of the environmental parameters and / or the resulting air density change.

Another preferred fire alarm device according to the invention includes an air density calculator.

Description of the embodiments

Fig.1

shows characteristics of a fan. Tube system at two different temperatures (air densities) at constant fan speed.

Fig. 2

shows the same as Fig. 1 but with further pipe characteristics.

Fig. 3

shows characteristics of a fan pipe system bel two different temperatures (air densities) at constant fan power.

Fig. 4

shows a table with correction parameters for environmental parameters.

Fig. 5

shows a table with correction values for the air density

Fig. 6

shows a fire detector according to the invention

Fig. 7

shows another embodiment of a fire detector according to the invention

In the following the invention will now be explained in more detail with reference to the drawings. In the various drawings, labels are retained when like things are referred to. The designation "a" in connection with a digit means a high temperature and the designation "b" always means a low temperature and the axes of FIGS. 1-3 each show the volume flow (X axis) and the pressure difference (Y axis) ,

As already stated above, changes in the density of the air not only affect the measured value of an airflow sensor, but also the system itself and the actual flow rate, which are formed by the fan and intake manifold. It has already been shown with reference to Fig. 1 that with an increase in air density, the e.g. caused by a drop in temperature, the actual volume flow increased, without causing a change in the tube has taken place. The high temperature, low density (3a) operating point migrates to the low temperature, high density operating point as the temperature falls (Figure 3b). 1 and 2, this system behavior is shown at a fixed speed, wherein in Fig. 2, several pipe systems are shown in comparison, Fig. 3 shows the characteristics of a system of fan and pipe system, in which the fan performance is recorded and the Speed remains variable. Here it can be seen that the fan characteristic at high temperature and low density (2a) shifts downwards to the fan characteristic at low temperature and high density (2b) as the temperature drops. In this case, in contrast to the systems shown in FIGS. 1 and 2, the volume flow decreases. This is explained by the higher density of air at which the fan has to work more, is braked and thus can promote less flow.

From these considerations it becomes clear that even the temperature- and pressure compensated measured value of a mass flow sensor as described in DE 44 28 694 A1 is still subject to fluctuations that are not due to a blockage or an interruption of the pipe systems but based on the interactions between density changes of the air and the system formed by fan and pipe system.

Therefore, in a method according to the invention, the volumetric flows of different fan duct systems are measured at different temperatures and / or air pressures and or humidities, and the deviations are determined to a corresponding desired value, which is e.g. corresponds to the volume flow values under normal conditions (273.15 K and 101325 Pa). These deviations are now stored in a table in the fire detector. During the detection operation, the current values for temperature and / or pressure and / or humidity are measured with a temperature and / or pressure and / or humidity sensor and, if appropriate, the current air density is calculated therefrom. Subsequently, for each of these measured values and / or the calculated air density, the correction value is taken from the table and added or subtracted to the current, mass or volumeric current value. If, for example, the temperature reaches 30 ° C, the fire detector removes the corresponding correction value from the table and adds or subtracts it from the current volume flow value or the optionally compensated mass flow value. In the same way, corrections are made for pressure and humidity changes. Although the air flow value thus obtained no longer corresponds to the current mass flow or. Volume flow value, but changes only due to actual changes in the pipe system such as blockages and interruption and is therefore ideally suited for their monitoring. Especially if all variables which influence the air density are used for the correction, the limits for interruption and blockage can be set very close to the set value of the air flow. Which means a significant increase in sensitivity over the prior art.

As an alternative to correcting the air flow value, it is also conceivable to adapt the limits for interruption and blockage to the density changes in the respective fan tube system.

However, in order not to have to store an infinite number of correction values in the tables, the correction values are preferably stored in the table for a few support values. All other intermediate correction values are determined therefrom by an interpolation for each temperature and / or pressure and / or humidity and / or the air density determined therefrom. A such exemplary table can be seen in Fig. 4. It shows from left to right: the temperature in ° C, a corresponding digital temperature correction value, the air pressure in hectopascals, a corresponding digital pressure correction value, the humidity in% and a corresponding digital humidity correction value.

Since, however, with the method described above, it is restricted to a few systems predetermined in terms of their dimensioning or each system has to be measured individually, in a particularly preferred embodiment of the method according to the invention the table is created by the fire detector itself during operation. This means that the fire detector can automatically adjust itself to all possible connected fan pipe systems and otherwise necessary costly measurements can be omitted.

For this purpose, the fire detector detects the current mass and / or volumetric flow value and the current environmental data such as temperature and / or air pressure and / or humidity corresponding to the system expansion with the aid of appropriate sensors or by means of fan characteristics. At this time, one can assume that the pipe system is not subject to change. For safety, however, the specialist who starts up the fire detector should be convinced of the proper condition of the system. The fire detector now saves the measured mass and volume flow value, possibly compensated for temperature and pressure, as commissioning value and enters the measured environmental data in the table. The correction factor 0 is now entered permanently in the table for these measured values. If one of the recorded environmental parameters such as temperature, air pressure or humidity changes, the airflow value will also change. Because changes to the piping system now occur either within a few seconds, such as an interruption or tampering caused by tampering, or within several weeks or months of normal clogging, and changes in environmental parameters within several minutes or even hours air flow changes caused by a change in the pipe, which are caused by changes in the environmental parameters can be well distinguished. This distinction can be made either by means of a time criterion or the rate of change of the air flow value taking into account the rate of change of the Environmental parameters or a combination of both. Once it has been determined that the airflow change is due to the changed environmental parameters, the correction value is determined. When changing only one

The parameter is simply determined. The difference to the commissioning value is entered as a correction value.

ohne Berücksichtigung der Feuchte und $$\rho =\frac{p}{R_L\ast T}\left(1-\mathrm{0,377}\phi \frac{p_d}{p}\right)$$

unter Berücksichtigung der FeuchteIf several parameters change at the same time, either the parameters with the lower change can be ignored, and the difference between the current air flow value and the commissioning value is only saved to the parameter with the greater density change than the provisional correction value. Another possibility is to use the following formulas to determine a proportionality factor for each parameter with which the determined difference to the commissioning value is weighted: $$\rho =\frac{p}{R_{L}T}$$

without consideration of the humidity and $$\rho =\frac{p}{R_L*T}\left(1-0.377\phi \frac{p_d}{p}\right)$$

taking into account the humidity

Where ρ is the density of the air, p is the pressure, p _{d is} the saturation vapor pressure, φ is the relative humidity, T is the temperature in Kelvin and R _{L is the} specific gas constant of the dry air.

The selected difference is now entered as the correction value for the respective parameter. To simplify this, the influence of moisture can be neglected.

Another possibility for determining correction values is not to determine individual correction values for the various environmental parameters, but to calculate the respective density of the air on the basis of the measured environmental parameters such as temperature, pressure and possibly humidity with the above-mentioned formulas and the difference from the Enter the commissioning value and the current airflow value as a correction value for the respective density. A table of how to obtain them is shown by way of example in FIG. Therein, the air density in kg / m ³ is entered in the left column and the corresponding digital correction value in the right column. The gray shaded fields store the values that were valid during commissioning.

It can now be assumed that the density or environmental parameter values which are adjacent to the values during commissioning can already be achieved within the next few days after commissioning. Significant blockages are not yet to be assumed at this time, which is why the correction values then determined are still considered faultless. In addition, already known density or environmental parameter values are repeatedly achieved. If the corrected airflow value deviates from the commissioning value in an already known range, then this deviation is due to an incipient blockage or a creeping interruption and is taken into account in the determination of further correction values. Even if the density, temperature, pressure and humidity do not change over a longer period of time, changes in the air flow value during this time can be attributed to changes in the pipe system and are taken into account in the later introduction of new correction values.

Fig. 6 shows a fire alarm device according to the invention, which is indicated as a whole by 61. It contains at least one detector (62) for fire characteristics such as smoke or combustion gases. A fan (63) having a pipe system (64) connected thereto, which sucks air from one or more monitoring rooms or electrical equipment and supplies it to the detector. The fire detection, which is not the subject of the invention will not be further described here. Furthermore, the fire detector (61) includes a sensor (65) for detecting a mass and / or flow and at least one further environmental sensor (67,68, 69), from the group consisting of a temperature, pressure, and humidity sensor is formed. The outputs of this at least one environmental sensor are connected via an optional airtightness calculator (610) to a first memory (611) in which a correction value table is stored and connected to a first input of a test unit (612). At a second input of the test unit is the signal of the mass or volume flow sensor (65). The test unit now checks whether a change in the mass or volume flow to a change in environmental parameters from the sensors (67, 68, 69) or a change in the pipe (64) baruht and outputs a corresponding signal at its control output. The control output of the test unit (612) is provided with a respective control input of the memory (611), a correction value calculation unit (613) and an optional second memory (614) for a clogging / interruption value connected. The correction value calculation unit (613) obtains the data necessary for calculating the correction values from the mass and / or volume flow sensor (65), a third memory (615) containing reference values and the environmental parameter scores (67, 68, 69). From the latter, the correction value calculation unit (613) receives the data either via the table pointer (B11) or its own direct connection line, not shown for the sake of clarity. The correction value calculation unit (613) constantly calculates a new correction value from the incoming data. If the test unit (612) has determined that there is no pipe change (clogging / interruption) and there are no final correction values for the current environmental parameters, the new correction value, together with the environmental parameters and / or the air density, is transferred to the table in the first memory ( 611). As soon as preliminary or final correction values are available for current environmental parameters and / or air densities, they are provided, if appropriate, after an interpolation operation, which is not shown here, at a first input of a correction device (616). At a second input of the correction device (616) is the current signal of the mass or volume flow sensor (65). The correction device (616) adds or subtracts the measured value of the sensor (65) with the correction value from the table memory (811) and provides the corrected airflow signal at a first input of the comparison device (66). The comparator (66) compares the corrected airflow value with upper and lower limits stored in a fourth memory (617). If this comparison is a. Indicates interruption or tube clogging, then the comparator (66) outputs a corresponding signal at its output (618). Furthermore, the comparison device (66) can determine the difference between the corrected airflow value from the correction device (616) with the value at startup, which is stored in a fifth memory (619), a clogging / interruption value. If the tester (612) has determined that there are pipe changes, that value is taken over into the fifth memory (614) and can be used for more recent correction value calculations.

Fig. 7 shows an alternative embodiment In which, in contrast to Fig. 6, the mass flow sensor (65 in Fig. 6) has been replaced by an air flow calculation unit (700) which outputs an air flow value the operating data such as power consumption and fan speed. For a more precise calculation of the air flow, the air flow calculation unit (700) can additionally use one or more of the environmental measured values of the sensors (67, 68, 69). The necessary. Connection is not shown here. Incidentally, FIG. 7 corresponds to FIG. 6.

Claims (13)

Method for detecting obstructions and interruptions in the piping system of an aspirating fire detector that draws the air via the pipe system from one or more monitoring rooms or electrical equipment, and monitors for fire characteristics and the one with an air flow sensor and / or based on current fan data mass and / or volumetric flow monitored by comparison with predetermined limit values, characterized in that a correction value is determined which represents changes in the properties of the system consisting of the intake manifold and the fan, which are based on changes in the density of the air and / or at least one environmental parameter causing an air density change, and which is used to correct the mass and / or volumetric flow measured value and / or to adapt the limit values. A method according to claim 1, characterized in that a correction value is determined for each temperature occurring during operation of the fire detector. A method according to claim 1 or 2, characterized in that a correction value is determined for each occurring during operation of the fire detector air pressure. A method according to claim 1 2 or 3, characterized in that a correction value is determined for each occurring during operation of the fire detector air humidity. Method according to one or more of the preceding claims, characterized in that a correction value is determined for each air density occurring during operation of the fire detector. Method according to one or more of the preceding claims, characterized in that for each combination of fan and pipe system, a table is created which contains the environmental parameter values and / or air density values and the associated correction values. A method according to claim 6, characterized in that in the table, only some support values are stored and the remaining correction values are determined by interpolation for each prevailing environmental parameters and / or air density. A method according to claim 6 or 7, characterized in that the fire detector creates the table itself during operation and determines the necessary correction values even during operation A method according to claim 8, characterized in that the fire detector between interruption and blockage caused mass and / or volume flow change on the one hand and an environmental parameters related mass and / or volumetric flow change on the other hand by observing the change rates of mass and / or volume flow and the environmental parameters and / or by applying a time criterion, Fire detector for carrying out the method according to one of claims 1 to 9 with at least one detector (62) for fire characteristics, with a fan (63) with a connected pipe system (64), the air from one or more monitoring rooms or electrical equipment sucks and the Detector (62) supplies, and with a device for detecting a mass and / or volume flow (65 700) and with one or more sensors (67, 68, 69) for environmental parameters from the group consisting of a temperature Pressure and a humidity sensor is formed and further with a comparison device (66), in the flow values with upper and lower limits (617) are compared, characterized in that the fire detector includes a memory (611) with a table, stored in the correction values which represent changes in the characteristics of the system consisting of the intake manifold and fan, which are based on density changes of the air and or at least one environmental parameter that causes an air density change, and a correction device (66) which corrects the current mass and / or volumetric flow values with the correction values. Fire detector according to Claim 10, characterized in that the fire detector contains a correction value calculation unit (613) which determines the correction values from the current mass and / or volumetric flow measured value and a stored reference (615) or a clogging / interruption value (614). Fire detector according to claim 10 or 11, characterized in that the fire detector contains a test unit (612) which checks whether a change in the mass and / or volumetric flow measured value to a pipe change (blockage / interruption) or changes in the Umweitparameter and / or resulting air density change is based. Fire detector according to one or more of claims 10 to 12, characterized in that the fire detector includes an air density calculation member (610).

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