EP1549916A1

EP1549916A1 - Device for the determination of flow parameters for a fluid and method for operating such a device

Info

Publication number: EP1549916A1
Application number: EP03807809A
Authority: EP
Inventors: Lutz Burkhardt
Original assignee: Wagner Alarm- und Sicherungssysteme GmbH
Current assignee: Wagner Group GmbH
Priority date: 2002-10-07
Filing date: 2003-08-28
Publication date: 2005-07-06
Also published as: US20060074569A1; AU2003258682B2; US7162374B2; AU2003258682C1; WO2004034001A1; JP2006502392A; AU2003258682A1

Abstract

The invention relates to a device for the determination of flow parameters of a fluid, in particular, the temperature and flow speed and changes therein, in a fluid flow for monitoring, a method for operating such a device, a determination method itself and a fire recognition or oxygen measuring device provided with such a device. The aim of the invention is the recognition of a slow or sudden blockage, crack or break in a pipe system (13) of an aspirative fire recognition device by means of a measurement technique, whereby an air flow sensor (1), operated with a constant excess temperature, is combined with a regulation algorithm, running in a microprocessor (4), for monitoring the fluid flow or the flow resistance in the pipe system (13). The required resistance of the air flow sensor (1) can thus be calculated according to an exact sensor calibration curve and a precise control loop (3) formed. The measured values recorded by the air flow sensor (1) are thus extremely reliable, such that changes in condition for the flow parameters provide information about the state of the pipe system (13) or the intake system.

Description

DEVICE FOR DETERMINING THE FLOW RATE OF A FLUID AND METHOD FOR

OPERATION OF SUCH A DEVICE

The present invention relates to a device for determining flow variables, in particular the temperature, the flow rate and its change, in a fluid flow to be monitored, in particular in smoke and gas suction detectors, with a thermoelectric and air temperature sensor operated in constant temperature mode, a thermoelectric temperature sensor and a control circuit for setting an excess temperature ΔT at the air flow sensor, as well as a method for operating such a device, a corresponding working method and a fire detection or oxygen measuring device equipped with such a device.

Devices for determining flow variables of the type mentioned at the outset and corresponding methods for operating such devices are known in particular from hot wire anemometry. A heated wire is placed in a flowing fluid; Based on the amount of heat dissipated by the fluid, statements about various flow sizes can be obtained.

There are two basic operating modes for hot wire anemometry: constant current mode and constant temperature mode, which is used in most cases because, among other things, the thermal inertia of the

Hot wire bypassed (probe) and thus a higher accuracy of the probe is achieved.

The basic idea of constant temperature operation. consists in reducing the influence of the thermal inertia of the probe by keeping the hot wire constant Temperature (resistance) is maintained and the heating current required for this is used as a measure of the flow velocity of the fluid. For this purpose, a Wheatstone bridge circuit is generally used, so that the resistance and thus the temperature of the hot wire always maintains a constant value through feedback. In thermal equilibrium, the heat loss from the probe must be equal to the electrical power supplied. From the point of view of anemometry, the relationship between fluid velocity and electrical power is of primary interest. This connection is extremely complex, not linear and can only be described by means of an empirical law (King) that has to be modified according to the given circumstances. The use of a linear generator is therefore necessary for the evaluation.

Fig. 1 shows the basic circuit diagram of a constant temperature anemometer. In the equilibrium state, there is a certain voltage on the vertical diagonal C-D of the bridge, which voltage is supplied by a servo amplifier 15. If the convective cooling on the probe 18 changes, a small voltage will arise on the horizontal diagonal A-B, which - often amplified - is fed back to the vertical diagonal C-D of the bridge. The polarity of this feedback voltage is chosen so that the bridge adjusts itself automatically.

In addition to the complex relationship between the fluid velocity and the electrical power recorded as a measured variable, there is a further problem in that the probe responds to any change in the heat dissipation, which can also be caused, for example, by a change in the temperature or the pressure of the flow medium. This is particularly problematic if the method is used continuously in order to be able to reliably draw conclusions based on changes in the measured flow parameters, for example on the state of the pipeline system in which the fluid flows. - 5 -

The oxygen measuring device serves to set the basic level of inertization in the target area. If a threshold value of the oxygen concentration is exceeded - for example due to a leak in the target area - the control issues a command to a special system for introducing inert gas into the room, so that the oxygen content is reduced. The oxygen measuring device signals when the threshold value of the basic inerting level has been reached again. The location of the basic level of inerting depends on the properties of the room.

In a preferred application, an aspirative fire detection system is combined with an inert gas device for fire prevention and / or extinguishing. The oxygen measuring device and the fire detection device of the inert gas device are integrated in the aspirative fire detection system. This then takes on the task of providing the controller with the data required for monitoring the target area from the air sample taken in.

In order to guarantee that an aspirative device functions properly and as maintenance-free as possible, it is necessary to continuously monitor the volume flow of the air sample supplied to the detector. However, the volume flow depends on the mass flow and the density of the added air sample, which in turn is a function of the air pressure and the temperature. Therefore, monitoring the volume flow proves to be a complicated measurement task. In order to be able to reliably detect blockages or damage to the intake pipe system or the intake openings, high measurement accuracy is required with regard to volume flow monitoring. This also includes compensation, -., Fire detection devices are used in particular wherever the smallest and barely perceptible fire parameters are to be detected and are used in particular for object or room monitoring, for example of IT systems or server rooms.

In enclosed rooms, the facilities of which react sensitively to the effects of water, such as IT areas, electrical control and distribution rooms or storage areas with high-quality goods, so-called inerting processes are increasingly being used to reduce the risk and extinguish fires. The extinguishing effect resulting from these processes is based on the principle of oxygen displacement. As is known, normal ambient air consists of 21% by volume of oxygen, 78% by volume of nitrogen and 1% by volume. composed of other gases. To extinguish and prevent fires, the introduction of an oxygen-displacing inert gas, such as pure nitrogen, increases the inert gas concentration in the room in question and reduces the oxygen content. Many substances no longer burn when the oxygen content falls below 15 - 18 vol .-%. Depending on the combustible materials present in the room in question, a further decrease in the oxygen content to, for example, 12% by volume may be necessary.

Such an inert gas device for carrying out the aforementioned inerting process essentially has the following components: an oxygen measuring device for measuring the oxygen content in the target area to be monitored; a fire detection device for detecting a fire parameter in the room air of the target room; a controller for evaluating the data of the oxygen measuring device and the fire parameter detector and for sequence control of the inerting process; and a plant for the production and sudden inputs' ^~ passing an inert gas into the target area. - 3 -

In particular for air flow monitoring in intake pipe systems in the case of aspirative fire detection or oxygen measuring devices, it is important that a blockage or a pipe break in the intake pipe system is reliably detected in order to ensure a fault-free operation

To guarantee operation of the fire detection or oxygen measuring device. Here, an aspirative fire detection device is understood to be a device that actively draws in a representative part of the room air from a room to be monitored via a pipeline or duct system at a plurality of points and these parts then a detector for detecting a fire parameter or for detecting Gasses in the air, especially oxygen.

An aspirative fire detection system essentially consists of an intake pipe system with individual small intake openings, a fan that sucks an air sample from the target area via the intake openings of the intake pipe system, and a detector in which fire parameters are then determined in the intake air sample. Since an aspirative fire detection device actively draws in air samples from the target area and thus any existing fire parameters, such devices react much faster and more sensitively to fires than conventional solutions. This provides the best possible opportunity for intervention.

The term fire parameter is understood to mean physical quantities that are subject to measurable changes in the vicinity of an incipient fire. e.g. the ambient temperature, the solid or liquid or gas content in the ambient air (formation of smoke in the form of particles or eros, oils or steam) or the ambient radiation - an aspirative the influence of air density or air pressure in the measurement technology used for volume flow monitoring.

The present invention is the _. Problem based on the fact that to monitor the volume flow in intake pipe systems of aspirative fire detection devices, the measurement techniques used to date are too uncertain or only consider the volume flow and not the flow resistance in order to be able to make reliable statements about the condition of the intake pipe system. One of the reasons for the uncertainties is that the sensors used are dependent on the temperature of the fluid flow and on the air pressure or density of the fluid and are therefore unsuitable for continuous and adjustment-free use. The reliable monitoring of the volume flow in intake pipe systems also requires the most accurate evaluation of the measurement data.

Furthermore, it is problematic with the solution known from the prior art that only long-lasting changes in volume flow in intake pipe systems are to be assessed. It is customary to compare these changes with threshold values, and an airflow fault is reported when the threshold value is exceeded. To avoid malfunction reports due to environmental influences (air pressure, temperature), however, relatively large threshold values are selected. However, long pipes have a high flow resistance, so that a pipe break at the end of the pipe only results in a small change in air flow. This relatively small change in air flow is generally not detectable with the devices and methods known from the prior art.

On the basis of the problem outlined, the present invention is based on the object of one of the aforementioned? Type, in particular in smoke and gas suction detectors, of a device for air flow monitoring that is used in this way. form that a continuous and maintenance-free recording of flow parameters is possible, which are sufficiently precise to be able to make reliable statements about the condition of the intake pipe system, and to specify a corresponding method for operating such a device and a corresponding working method.

This object is achieved according to the invention in a device of the type mentioned at the outset by a control algorithm implemented in a microprocessor which is in the control loop of the

Device is included, and the excess temperature ΔT is kept constant at the airflow sensor.

The advantages of the invention are, in particular, that the control circuit contains a control algorithm implemented in a microprocessor, by means of which the excess temperature ΔT at the air flow sensor is kept constant. As a result, the air flow sensor is set exactly in its working point or working temperature, which is independent of fluctuations or changes in the fluid temperature. As a result, the amount of heat dissipated from the thermoelectric airflow sensor actually only corresponds to the amount of heat dissipated from the fluid. In this embodiment, the electrical current flowing through the air flow sensor or the electrical power dissipated by the air flow sensor advantageously actually does just that

It is a measure of the flow size to be measured (speed, mass flow, etc.) and is not subject to the uncertainties caused by fluctuations in the fluid temperature.

The object on which the invention is based is further achieved by a method for operating such a device, in which the air flow sensor is briefly increased to a temperature peak value.

The technical problem underlying the present invention is further solved by a method for determining Flow variables, in particular the temperature T, the flow velocity w and their change Δw, in a fluid stream to be monitored, in particular in smoke and gas suction detectors, are solved according to the invention by the following method steps: the fluid temperature T is determined by means of a thermoelectric temperature sensor; The overtemperature ΔT set on a thermoelectric air flow sensor operated in constant temperature mode is regulated to a constant value as a function of the fluid temperature T; the amount of heat dissipated by the thermal air flow sensor is determined; and flow quantities, in particular the temperature, the flow velocity, the flow resistance and its change, are calculated on the basis of the amount of heat removed by means of an evaluation algorithm implemented in a microprocessor.

The advantages of the invention are, in particular, that a very effective method for determining flow variables, in particular in smoke and gas suction detectors, for optimizing the air flow monitoring in the piping system can be achieved. In particular, because the overtemperature ΔT at the thermoelectric airflow sensor assumes a constant value irrespective of the fluid temperature T, it can be achieved that the thermoelectric airflow sensor is used exactly in its previously determined working point or working temperature and thus the electric power dissipated actually only by depends on the fluid flow. The measurement error is significantly reduced due to the method according to the invention. In the thermoelectric air flow sensor according to the invention, the quantity of heat Q removed by the heated sensor through the fluid flow is the measure of the flow quantities to be determined. Since the overtemperature ΔT of the sensor assumes a constant value here, the amount of heat Q removed is identical to the heating power P supplied to the sensor. The heating power P depends on the heating current I according to the following equation ^' (1): p = r R (1)

Here R denotes the internal resistance of the sensor. The amount of heat Q dissipated by the sensor can then be described by equation (2) as follows:

Q = [A + B • (p • V) ^{1 / n} ] • (ΔT - T) (2)

Here, A, B and n are sensor-specific constants, which are experimental before commissioning the sensor, i.e. by means of a calibration, and p represents the fluid density. From equations (1) and (2) it follows that the volume flow V and the mass flow (p • V) of the fluid flow can be determined via the heating power P and the temperature T.

From equations (1) and (2) it follows that the volume flow V and the mass flow N = p • V of the fluid flow can be determined via the heating power P and the temperature T. The flow resistance F _w in the pipe depends on the flow velocity w as follows:

F _w = 0.5 • cApw ² (3)

Since the volume flow V according to the flow velocity w and the cross section A of the pipe

V = A-w (4)

depends, follows for the flow resistance F _w in the pipe:

F _w = 0.5 • cpA ^ -V ² (5) It follows from equation (5) that the flow resistance F _w in the piping system and its changes can be determined via the volume flow V.

It is also conceivable, based on these measured values, to detect the change in the flow resistance in the pipeline system. To do this, it would be necessary to compare the current measured values with initial measured values, which were recorded and stored, for example, when the system was started up. Furthermore, the method according to the invention is suitable for detecting changes in the flow resistance in the intake pipe system. In addition to an accurate volume flow measurement, this also involves compensation for the influence of the air or fluid density p in order to be able to reliably assess the flow resistance. A correction factor is determined from a table created for this purpose on the basis of stored initial values of the airflow and temperature sensors as well as the current temperature and, if appropriate, the current absolute air pressure. This table is necessary because different intake pipe systems and different intake powers of the fan require different correction factors would be to record the current absolute air pressure, for example, via a separately designed sensor for air pressure measurement, but other embodiments are of course also conceivable here.

Finally, the object on which the invention is based is also achieved by an aspirative fire detection device which continuously takes room or device cooling air samples from a room or device to be monitored and feeds them to a detector for detecting a fire parameter via a pipeline system, and with a device for determining flow variables described above is equipped.

With the device according to the invention, one possibility is given for carrying out the method described above. Preferred developments of the invention are with regard to the determination device in subclaims 2 to 5, with regard to the operating method in subclaim 7, with regard to the determination method in subclaims 9 and 10, and with reference to the aspirative fire detection and / or oxygen measurement device in subclaims 12 and 13 specified.

It is thus provided for the device that the microprocessor further comprises an evaluation algorithm for calculating flow quantities on the basis of the electrical heating power P of the air flow sensor, in particular for calculating the mass flow N, the flow velocity w and the temperature T of the fluid flow. The advantage of this embodiment according to the invention lies in the fact that in the control algorithm implemented in the microprocessor, the target resistance of the thermoelectric air flow sensor can be calculated according to the exact sensor characteristic curve and an exact control loop (eg PI controller) can be formed. The voltage at the thermoelectric temperature sensor can be measured with an AD converter, for example, and then filtered to eliminate noise and other disturbances. The temperature of the fluid flow To is calculated on the basis of the measured voltage. The desired constant overtemperature ΔT (for example 40 ° C.) is added to the fluid temperature To. The result is the target temperature T _s0 n of the _{thermoelectric} air flow _sensor . The target resistance of the airflow sensor is determined from this in the evaluation algorithm of the microprocessor based on the exact sensor characteristic. The controller regulates the voltage on the hot wire of the airflow sensor in order to set the actual value of the resistance of the airflow sensor to the setpoint. In this way, according to the invention, the overtemperature ΔT is kept constant. The electrical voltage and the electrical current at or through the thermoelectric air flow sensor are measured by means of an AD converter and then filtered. From this, the electrical power P is calculated, which is also a measure of the air flow. In a particularly advantageous embodiment of the device according to the invention, it is provided that the evaluation algorithm includes the detection of small abrupt flow changes, in particular changes in volume flow, of the fluid flow. For this purpose, in addition to the exact volume flow measurement, the influence of the air density is also compensated in order to be able to assess the flow resistance in this way. With the help of stored initial values of the air flow and temperature sensors as well as the current temperature and, if applicable, the current air pressure, even small, sudden changes in the air flow can be detected. The basic idea here is that changes due to disruptive environmental influences (air pressure, temperature) are generally slower than a pipe break. The evaluation of small, sudden changes thus also enables the detection of sudden blockages in a single suction opening, which occurs, for example, in the event of vandalism or when a box is placed in a high rack in front of a suction opening.

In a particularly advantageous embodiment, it is provided that the evaluation algorithm includes the compensation of a temperature and / or pressure-dependent change in density of the fluid flow. The advantage of this embodiment is in particular that, by taking into account the temperature or pressure-dependent change in density of the fluid flow, the electrical power dissipated by the fluid flow is independent of fluctuations in the change in density of the fluid flow. As a result, the accuracy of the flow variables determined by means of the present invention, in particular the flow resistance, is significantly improved.

A possible implementation of the determination device according to the invention provides that the microprocessor contains a memory for storing initial values of the flow quantities. The advantage of this embodiment lies in the fact that the evaluation algorithm does not only flow values with a high accuracy can be calculated, but also long-term changes in the state of the flow quantities can be demonstrated. Since the calculation of the gradient of the flow variables is based on the precise air flow values, the measurement of the changes in the pipe system of a smoke and gas intake detector is advantageously possible in this embodiment, for example. Such changes can occur due to slow or sudden constipation, cracks or breaks. Since the overtemperature .DELTA.T at the airflow sensor is kept constant by the invention, the gradient of the airflow variables is not subject to any temperature-related or other-related shift. A repeated adjustment of the air flow sensor is also advantageously omitted.

In one possible implementation, the airflow sensor is advantageously designed such that it can be briefly increased to a temperature peak. This has the particular advantage that the airflow sensor is characterized by its particularly high durability.

The air flow sensor is preferably so for the operation of such a determination device _. designed so that it can be briefly increased to a peak temperature of up to 500 ° C. As a result, the air flow sensor is particularly effectively freed from impurities due to the short-term operation at a greatly increased temperature. The entire heating output is used to burn or loosen the dirt particles adhering to the airflow sensor. During this time, the fan of the aspirative fire detection device is advantageously switched off in order to avoid any cooling of the airflow sensor. This cleaning ensures that no dirt particles are deposited or deposited on the airflow sensor even in continuous use, so that the sensitivity of the sensor is always unchanged. A possible implementation of the invention consists in that the device according to the invention for determining flow variables in an aspirative fire detection and / or oxygen measuring device, which continuously takes room or device cooling air samples from a room or device to be monitored and via a piping system to a detector Recognize a fire parameter that is integrated. The advantage of this embodiment is in particular that the air flow in the pipe system can be monitored precisely and also changes in the pipe system, which may occur due to slow or sudden blockage, cracks or breaks, can be reliably detected. As a result, the aspirative fire detection and / or oxygen measuring device can be used particularly reliably and maintenance-free.

In a further advantageous embodiment it is provided that the air flow sensor or the temperature sensor of the device according to the invention is integrated in the center, in particular, in the air inlet channel of a detector for fire parameters of an aspirative fire detection and / or oxygen measuring device. The advantage of this embodiment is that all electrical components of the aspirative fire detection device are combined in one unit. As a result, the construction of such a fire detection and / or oxygen measuring device is particularly easy to carry out.

Finally, it is preferably provided that the air flow sensor at a position in the air inlet duct of the detector of the aspirative device according to the invention which is narrowed in cross section

Fire detection and / or oxygen measuring device is arranged. With this arrangement, the air flow sensor is in a position in which the flow velocity is increased due to the narrowing of the cross section. This will make the dynami. the airflow sensor also increased. This means that extremely small changes in the flow parameters can be detected and get ranked. This advantageously increases the sensitivity of the device according to the invention for determining flow variables. At the same time, the monitoring of aspirative fire detection and / or oxygen measurement devices can be optimized. Of course, other embodiments are also conceivable here.

Preferred exemplary embodiments of the invention are explained in more detail below with reference to the drawings.

Show it:

1: a basic circuit diagram of a constant

State-of-the-art temperature anemometers;

Fig. 2: a block diagram of the invention

Device for determining flow quantities in accordance with a preferred exemplary embodiment;

3 shows a schematic illustration of a preferred embodiment of the aspirative fire detection device according to the invention;

4a: a longitudinal section through a detector for fire parameters from the exemplary embodiment according to FIG. 3; and

4b: a cross section through the detector for

Fire parameters from the exemplary embodiment according to FIG. 3.

Fig. 1 shows a schematic diagram of a constant temperature __ anemometer according to the prior art. The basic idea of ^" constant temperature mode of operation is to to reduce the flow of thermal inertia of a hot wire probe 18 by keeping the sensing element 18 at a constant temperature (resistance) and using the heating current required as a measure of the flow rate. For this purpose, a Wheatstone bridge circuit is used, the resistance and thus the temperature of the hot wire 18 being kept constant by feedback. In the state of equilibrium there is a certain voltage on the vertical diagonal of the bridge CD, which is supplied by the servo amplifier 15. If the convective cooling on the probe 18 changes, a small voltage will arise on the horizontal diagonal AB, which - amplified many times - is fed back onto the vertical diagonal CD of the bridge. The polarity of this feedback voltage is selected so that the bridge adjusts itself automatically. The relationship between the flow velocity of the fluid and the anemometer voltage is not linear, so that the use of a linear generator is necessary for further evaluation. A direct calibration curve is usually used after linearization to determine the flow velocity from the anemometer voltage. In general, the probe 18 in the circuit shown in FIG. 1 responds to any change in heat dissipation. This can also be caused, for example, by changing the temperature or pressure of the fluid. However, these variables must also be taken into account in order to carry out a highly precise measurement of flow parameters. Furthermore, the basic circuit diagram of the constant temperature anemometer according to the prior art shown in FIG. 1 does not take into account the fluctuation in the fluid temperature in relation to the excess temperature set on the probe 18. To carry out a measurement that is as accurate as possible, it makes sense to set a constant temperature difference or excess temperature in the probe 18.

2 shows a block diagram of the device according to the invention for determining flow variables according to a preferred one Embodiment. The device according to the invention comprises a thermoelectric air flow sensor 1 operated in constant temperature mode and a temperature sensor 2. Both sensors are embedded in the flow to be measured. The control or reading out of the sensors 1, 2 takes place via a control circuit 3. This contains a control algorithm implemented in a microprocessor 4, by means of which the overtemperature ΔT at the air flow sensor 1 is kept constant. It is thus possible to calculate the target resistance of the thermoelectric airflow sensor 1 according to the exact sensor characteristic curve and to form an exact control loop. For this purpose, the voltage Uo at the temperature sensor 2 is first measured using an AD converter 5. A filter 6 is then applied to eliminate noise and other disturbances. The air temperature To is calculated therefrom in an evaluation unit 7. The previously determined constant overtemperature ΔT is added to the air temperature o in a further step. The result is the target temperature T _So iι of the thermoelectric air flow sensor 1. Based on the exact sensor characteristic curve, the target resistance of the sensor 1 is calculated in the microprocessor 4. The controller 3 then regulates the voltage at the airflow sensor 1 in order to set the actual value of the resistance to the previously calculated target value. As a result, the overtemperature ΔT at the airflow sensor 1 is kept constant.

When the flow velocity is recorded, the voltage Ui and the current Ii at the thermoelectric airflow sensor 1 are measured by means of an AD converter 5 and then filtered with a filter 6. In a further evaluation unit 7, the electrical power P and the actual value of the resistance of the air flow sensor 1 are calculated. The electrical power P required to keep the excess temperature ΔT constant is a measure of the air flow. The exemplary embodiment of the device according to the invention for determining flow variables shown in FIG. 2 makes it possible to measure the flow parameter almost without errors, so that changes in the state of the flow variables, in particular the flow resistance, can also be calculated. For this purpose, initial values of the flow quantities are stored in a memory (not explicitly shown) integrated in the microprocessor 4. The gradient of the flow variables is then continuously calculated using the evaluation algorithm. By means of this embodiment it is thus possible to detect changes in the fluid flow which occur, for example, due to slow or sudden blockage, cracks or rupture of the flow channel.

If the density of the air changes due to a change in temperature and / or air pressure, the detected volume flow of the fluid also changes, although the pipe system is unchanged. A necessary compensation of the change in air density is carried out in the microprocessor 4. The compensation factor is determined on the basis of the initial values (temperature, air flow) and the current temperature. An absolute air pressure sensor is optionally used to measure the air pressure (not explicitly shown).

3 shows a schematic illustration of a preferred embodiment of the aspirative fire detection or oxygen measuring device according to the invention. A suction pipe system 13 for sucking air samples through various suction openings is arranged in a target space 12. The suction pipe system 13 is equipped with a suction detector, in which the air samples from the target space 12 include a detector 8 for detecting fire parameters or for measuring oxygen and others Gases are supplied. Furthermore, a fan 14 is provided, which serves to suck in the air sample from the target area via the pipeline system. The suction power of the fan 14 is adapted to the associated intake pipe system. In order to To ensure that the illustrated aspirative fire detection or oxygen measuring device functions properly, it is necessary to continuously monitor the air flow supplied to the detector 8 via the intake pipe system 13 and to detect a malfunction during intake in good time. For this purpose, the device according to the invention for determining flow variables is located in the suction detector of the aspirative fire detection or oxygen measuring device.

4a and 4b show a longitudinal section or cross section through the detector 8 for fire parameters or for gases from the exemplary embodiment according to FIG. 3. The section line is indicated as a dashed line in FIG. 4a. In the detector shown, the thermoelectric air flow or temperature sensor 1, 2 is integrated in the smoke and / or gas measuring cell of the suction detector. Both sensors 1, 2 are positioned centrally in the air inlet duct 9. At the level of the air flow sensor 1, the cross section is narrowed in order to increase the flow speed. This increases the dynamics of the airflow sensor 1.

In a further development of the invention, the air flow sensor 1 is freed of impurities by brief operation at a greatly increased temperature. During this time the fan 14 is switched off in order to avoid any cooling. The entire heating power is used to burn or loosen the dirt particles adhering to the air flow sensor 1. There is no airflow evaluation during this time. Cleaning is either done automatically at regular intervals or manually controlled. This cleaning ensures that the sensitivity of the airflow sensor 1 is not reduced even by prolonged operation due to the accumulation of dirt particles. Reference sign of the components

1 airflow sensor

2 temperature sensor

3 control loop

4 microprocessor

5 AD converters 6 filters

7 evaluation unit

8 detector

9 air inlet duct

10 gas sensor or smoke sensor 11 gas sensor or smoke sensor

12 target area

13 Intake pipe system

14 fans

15 servo amplifier 16 resistor

17 potentiometers

18 hot wire probe

19 sources of tension

Name of the physical quantities

P electrical power

I sensor heating current u sensor voltage

R sensor resistance

V volume flow

W flow velocity

Fw flow resistance c drag coefficient

P fluid density

N mass flow

T fluid temperature

Q dissipated amount of heat

A cross section of the pipe

Claims

1. Device for determining flow quantities, in particular the temperature, the flow velocity, the

Flow resistance and its change, in a fluid flow to be monitored, in particular in smoke and gas suction detectors, with a thermoelectric air flow sensor (1), 10 a thermoelectric temperature sensor (2) and a thermoelectric temperature sensor

Control circuit (3) for setting an excess temperature ΔT on the air flow sensor (1), so that the control circuit (3) contains a control algorithm implemented in a microprocessor (4), via which the

Overtemperature ΔT at the air flow sensor (1) is kept constant.

2. The device according to claim 1, wherein the microprocessor (4) further comprises an evaluation algorithm for calculating flow quantities on the basis of the electrical heating power P of the air flow sensor (1), in particular for calculating the mass flow N, the flow rate

25 speed w, the volume flow V, the flow resistance F _{w of} an intake pipe system (13) and the temperature T of the fluid flow.

3. Device according to claim 1 or 2,

30 d a d u r c h g e k e n n e c i n that the evaluation algorithm includes the compensation of a temperature and / or pressure-dependent change in density of the fluid flow.

35

4. Device according to one of the preceding claims, that the microprocessor (4) contains a memory for storing initial values of the flow quantities for calculating changes in the state of the flow quantities in the evaluation algorithm.

5. Device according to one of the preceding claims, d a d u r c h g e k e n n z e i c h n e t that the evaluation algorithm includes the detection of small sudden flow changes, in particular volume flow changes, of the fluid flow.

6. A method of operating a device according to one of the preceding claims, that the air flow sensor (1) is briefly increased to a peak temperature value.

7. The method according to claim 6, d a d u r c h g e k e n n z e i c h n e t that the temperature is 500 ° C.

8.- A method for determining flow quantities, in particular the temperature T of the flow velocity w and- whose change .DELTA.w in a fluid stream to be monitored, in particular ^¬ sondere in smoke and Gasansaugmeldern, comprising the steps of:

a) determining the fluid temperature T by means of a thermoelectric temperature sensor (2);

b) regulation of the constant overtemperature ΔT set on a thermoelectric air flow sensor (1) operated in constant temperature mode as a function of the fluid temperature T; c) determining the amount of heat Q discharged by the thermoelectric air flow sensor (1); and

d) calculating flow variables, in particular the

Temperature T, the flow velocity w, the flow resistance F "and its change ΔF _W , based on the amount of heat Q removed by means of an evaluation algorithm implemented in a microprocessor (4).

9. The method according to claim 8 with the following further method steps after method step d):

e) compensation of the temperature and / or pressure-dependent change in fluid density in the flow variables determined in method step d).

10. The method according to claim 8 or 9, with the following further process step after step e):

f) Determination of changes over time, in particular of small sudden changes in volume flow, of the flow variables determined under point d).

11. Aspirative fire detection and / or oxygen measuring device, which constantly takes room or device cooling air samples from a room or device (12) to be monitored and, via a piping system (13), a detector (8) for detecting a fire parameter and / or other gases, in particular oxygen , supplies, characterized by a device for determining flow variables according to one of claims 1 to 4.

12. Aspirative fire detection and / or oxygen measuring device according to claim 11, characterized in that the air flow sensor (1) and / or the temperature sensor (2) in the detector (8), in particular centrally in the air inlet channel (9) of the detector (8), integrated are.

13. The apparatus of claim 11 or 12, so that the airflow sensor (1) is arranged at a position in the air inlet duct (9) of the detector (8) that is narrowed in cross section.