EP1005005A2 - Ionisation smoke detector - Google Patents

Abstract

The detector has at least one ionization electrode (4), at least two mutually insulated counter electrodes (1,3), which are components of a measurement chamber and a reference chamber and each contain a gas vol., and at least one power supply. The ionization electrode is made in one piece and extends through the measurement and reference chambers. An Independent claim is also included for a method of operating an ionization smoke detector.

Description

The invention relates to an ionization smoke detector without use radioactive preparations as a radiation source and a method of operation an ionization smoke detector.

Ionization detectors are able to completely independent of their aerosols to detect optical properties. They are also conventional Ionization detectors - i.e. those that contain radioactive preparations for ionization use - able to detect even the presence of very small aerosols to capture. One of the main areas of application for ionization detectors is that Detecting smoke, i.e. its use in fire detection technology. About that In addition, such detectors can also be used for aerosol monitoring of Chambers and rooms are used. Especially in combination with devices for optical aerosol measurement (e.g. absorbance measurement, Scattered light method), particle detection gains a particularly high level Reliability. This can be used in the special fire alarm technology to eliminate delusions and also make statements about to meet the hazardous situation, e.g. B. in which development phase there is a fire, but also to detect the presence of Aerosols, for example in process engineering processes. Ionization detectors also have particularly good properties in relation insensitivity to environmental influences and they are technically very robust.

Due to the different characteristics of many characteristics of smoke, which depend on the specific situation currently existing and which can be made clear by different measuring methods, smoke has the same effect as if there were several different characteristic fire parameters in the conventional sense. The combination of ionization and scattered light chambers already provides excellent information about fire developments.
The wide range of possible uses and the reliability of ionization smoke detectors for fire detection will ensure a wide range of applications in the future.
However, some problems arise from the use of radioactive preparations as a radiation source for generating ions in conventional ionization smoke detectors.
In addition to the general public's reservations about the technical use of radioactivity, there are also problems with the disposal of radioactive substances.
Although these preparations have a very low radiation intensity in modern ionization smoke detectors, it appears advisable to do without radioactive material as an ionization source in the future.
The focus of further development is the construction of chamber systems that are functional without the use of radioactive preparations and that generate the necessary charge carriers for the attachment of the aerosols according to other principles.
Devices with an ionizing effect, which operate on the principle of corona discharge, have proven to be particularly suitable and advantageous.

An ionization smoke detector is known from EP 0 820 045 A2, which has two separate chambers, a reference and a measuring chamber, each with at least one electrode, which is connected to an ionizing device via an electrical energy source. The ions generated by the ionizing device pass partially through openings in the corona space into a measuring and a reference chamber. The ions are generated in the corona space by means of an ionizing electrode which is at high voltage and has the shape of a gold-plated needle.
The ionization electrode generates an inhomogeneous, spatially coherent ion density, the ions of which reach the two counter electrodes arranged in the measuring and reference chamber via the openings mentioned in the corona space.

However, such an ion cloud, generated by high field strengths and impact ionization at an electrode tip, is in principle very inhomogeneous, since the zone of high field strength is very spatially limited (needle tip).
A strong delimitation of zones of high field strength means, however, that all statistical fluctuations of the ionization effects, which are caused by the volume and time-dependent fluctuations in natural radiation around a statistical mean, are not adequately compensated, with disturbing inhomogeneities in the ion distribution in the two chambers is to be expected, which in turn has negative effects on the accuracy of the ionization smoke detector.

The object of the invention is therefore to eliminate the known shortcomings and an ionization smoke detector and a method for its operation create which, using the principle of shock ionization, a homogeneous, time-independent ionization of the in the measurement and Reference chamber located gas volume allows. The essentially homogeneous charge distributions in the measuring and Reference chamber to be proportional to each other.

This object is achieved with the characterizing features of the 1st claim solved. In the subclaims are special preferred embodiments of the invention specified.

Keime" genutzt. Durch ausreichend hohe elektrische Feldstärken werden insbesondere die Elektronen soweit beschleunigt, daß sie an den Gasmolekülen bzw. -atomen Stoßionisierungen hervorrufen können.
Zur Kompensation der Abhängigkeiten der Bildung von Ladungsträgern im Gasraum von Druck, Temperatur und Feuchte ist der erfindungsgemäße Ionisationsrauchmelder als Zwei-Kammersystem aufgebaut, d. h. mit einer Refenzkammer und einer Meßkammer Beide Kammern sind über Ausgleichsöffnungen so verbunden, daß sich in beiden im wesentlichen durch Diffusionsvorgänge gleiche Gasatmosphären ausbilden können.
Ferner wird durch die vorliegende Erfindung gewährleistet, daß in beiden Kammern zur gleichen Zeit ein Referenzstrom ausgeprägt wird, der ohne das Vorhandensein von Aerosolen in der Meßkammer ausschließlich den Zustand der Gasatmosphäre widerspiegelt.
Ausgehend von der natürlichen Ionisierung von Gasen bzw. Gasgemischen, wie z. B. Luft, kann die Anzahl der Ionen je Volumeneinheit durch Stoßionisierungen so weit erhöht werden, daß eine Aerosolmessung analog zu Ionisationskammern, die radioaktive Strahler zur Ionisierung nutzen, möglich ist. According to the invention, homogeneous and proportionally similar relationships with respect to the ionization processes in the reference and in the measurement chamber are obtained if both chambers have a common symmetrical ionization electrode. This arrangement allows the production of homogeneous field conditions of the same type.
In a particularly preferred embodiment of the invention, the ionization electrode is designed as a central wire electrode with a very small diameter which is guided through both chambers. This wire electrode is then surrounded by a two-part, cylindrical electrode system (counter electrodes) that is insulated from one another. The respective counter electrodes are an essential part of the measuring and the reference chamber.
In the principle of exclusive impact ionization preferred here, the natural background ionizations which are produced by the terrestrial and extraterristrial radiation which is constantly present are considered as

Germs ". Sufficiently high electrical field strengths accelerate the electrons in particular to such an extent that they can cause impact ionizations on the gas molecules or atoms.
To compensate for the dependencies of the formation of charge carriers in the gas space on pressure, temperature and humidity, the ionization smoke detector according to the invention is constructed as a two-chamber system, that is to say with a reference chamber and a measuring chamber. Both chambers are connected via compensating openings in such a way that diffusion processes are essentially the same in both Can form gas atmospheres.
Furthermore, the present invention ensures that a reference current is formed in both chambers at the same time, which only reflects the state of the gas atmosphere without the presence of aerosols in the measuring chamber.
Based on the natural ionization of gases or gas mixtures, such as B. air, the number of ions per unit volume can be increased so far by shock ionization that an aerosol measurement analogous to ionization chambers that use radioactive emitters for ionization is possible.

The impact ionization is predominantly carried out by electrons that have been accelerated by high electric fields.
Natural ionization (radiation) is not a continuous and completely even process. Natural ionizations, which fluctuate greatly over time, take place in the individual volume units of a chamber system. The consequences of these temporally and spatially strongly fluctuating ionization processes with regard to the intended impact ionizations and thus the current flow can only be compensated for with regard to the temperature fluctuations and the fluctuations in the gas atmosphere by generating as uniform and extensive a field structure as possible in the entire chamber system. Therefore, the chamber system according to the invention consists of a reference and a measuring chamber, both of which have a common electrode with a strong surface curvature, e.g. B. contain the mentioned wire with a very small diameter. The isolation of the counter electrodes from each other enables the measurement of each chamber current individually. The reference chamber and the measuring chamber are interconnected by equalization openings (diffusion openings) so that the gas atmospheres can be equalized between the two chambers and the gas conditions are the same. Due to the installation position and the special design of the diffusion openings, it can be achieved that aerosols of fire can practically only get into the measuring chamber, which is connected to the external environment through inlet openings.
The current intensity of the ion current flowing between the ionization electrode and the counter electrode in the reference chamber depends only on the state of its gas atmosphere, that of the measuring chamber also on the presence of aerosols. A comparison of both currents allows an assessment of the aerosol concentration in the measuring chamber and thus also in the external environment of the chamber system.
However, it is also conceivable that the ionization electrode is divided in each case for the measuring and the reference chamber, or that the ionization electrodes are arranged separately for both chambers (for example two wires).
In this case, the prerequisite for a uniform field structure in both chambers is the use of ionization electrodes that are the same in all parameters and their common high-voltage regulation.
In a further embodiment, the ionization smoke detector contains, in addition to the chamber system, a complete signal evaluation and conversion unit as well as a unit for generating high voltage. The chamber currents are measured in the signal evaluation and forming unit, compared with one another and the deviations from the normal state obtained in this way are evaluated.
The evaluation results are the parent units, z. B. fire control panels, provided for further processing.
In a preferred embodiment of the invention, this unit takes over the regulation of the reference chamber current. The regulation of the reference chamber current ensures that it is always in the optimum range for the measuring task, fluctuations in the natural ionization rate are compensated for and unwanted flashovers are prevented. The central ionization electrode, which is uniform for both chambers, gives both chambers the same potentials, so that the regulation of the reference current corresponds to a setpoint specification of the basic current in the measuring chamber, ie the current intensity that would occur without aerosols.
Deviations from the normal state can then only be traced back to aerosols in the measuring chamber.

The power supply for the ionization smoke detector according to the invention takes place either via a two-line system which simultaneously serves for the data exchange between the detectors and the central units, or independently, if it is a self-sufficient detector system. Active suction ionization smoke alarm systems, which are connected to central units and, under certain circumstances, are coupled to one another, preferably receive their energy supply from the central units via power supply lines which are routed separately to the data supply lines.
The invention will now be explained in more detail using an exemplary embodiment and FIGS. 1 to 4.

Fig. 1

den einfachen Aufbau eines erfindungsgemäßen zylindrischen Kammersystems mit einer gemeinsamen Ionisierungselektrode in Form eines Drahtes,

Fig. 2

das Kammersystem mit Zwischenelektroden und Schirmelektrode,

Fig. 3

ein Blockschaltbild zur Regelung des Referenzkammerstroms,

Fig. 4

ein Blockschaltbild zur Regelung des Referenzkammerstroms mit unterlagerter Spannungsregelung.

In der in Fig. 1 dargestellten einfachen Ausführungsform läuft die Ionisierungselektrode 4 zentralsymmetrisch durch die Meßkammer 17 und die Referenzkammer 18.
Die Gegenelektroden 1 und 3 sind jeweils hohlzylindrisch um die Ionisierungselektrode 4 angeordnet und durch einen Isolator 2 mit einer Durchgangs- und Ausgleichsöffnung 8 elektrisch isoliert voneinander getrennt.
Der Isolator 2 und der die Grundfläche der zylindrischen Gegenelektrode 1 bildende Isolator 7 schließen gemeinsam mit den zylindrischen Mantelflächen der beiden Gegenelektroden 1 und 3 die Gasvolumina der Meßkammer 17 und der Referenzkammer 18 ein.
Durch die Öffnungen 9 in der zylindrischen Gegenelektrode gelangt die Gasatmosphäre aus der Umgebung des Ionisationsrauchmelders in die Meßkammer 17. Über die Ausgleichsöffnung 8 (Diffusionsöffnung) des Isolators 2, die beide Kammern miteinander verbindet, gelangen die Gasmoleküle der Umgebung über die Meßkammer 17 auch in die Referenzkammer 18.
In beiden Kammern 17 und 18 liegen also durch Gasaustausch gleichartige Gasverhältnisse vor.
Die drahtförmige Ionisierungselektrode 4, welche zur Erzeugung hoher Feldstärken einen sehr geringen Durchmesser aufweist, durchläuft beide Kammern 17 und 18, in diesem Beispiel vorzugsweise genau durch deren Mittelachse. Die Gegenelektroden 1 und 3 sind jeweils über die Anschlüsse 5 und 6 mit einer Versorgungs- und Auswerteschaltung getrennt voneinander verbunden.
Diese Anordnung ermöglicht es, die Ströme für die Meß- und Referenzkammer getrennt zu messen.
Die beide Kammern 17 und 18 gemeinsam durchlaufende Ionisierungselektrode 4 ist mit einem Ende in den Isolator 7 der Meßkammer eingebettet und fixiert. Das andere Ende ist im Grundflächenbereich der zylindrischen Referenzkammer 18 mit der erwähnten Versorgungs- und Auswerteschaltung (Fig. 3 und Fig. 4) kontaktiert. Wenn eine solche Anordnung als punktförmiger Ionisationsrauchmelder zur Raumüberwachung eingesetzt werden soll, wird das Kammersystem um 180° gegenüber der in Fig. 1 angegebenen Darstellung gedreht montiert, so daß die Meßkammer 17 nach unten weist. Durch diese Lage und durch weitere konstruktive Maßnahmen, auf die hier nicht weiter eingegangen werden soll, gelingt es, die Aerosole praktisch von der Referenzkammer 18 fernzuhalten, aber gleichzeitig die Gasatmosphären der Meß- und der Referenzkammer einander und der Umgebung dynamisch ausreichend anzugleichen.
Weitere vorteilhafte Ausführungsformen der Erfindung beziehen sich auf die Möglichkeit, zusätzliche Steuervorgänge durchführen zu können.
Wie in Fig. 2 dargestellt, erlaubt die Anordnung von Zwischenelektroden 10, 14 im Gasvolumen der Meßkammer 17 und der Referenzkammer 18 sowie deren Potentialeinstellung die Beeinflussung der Laufgeschwindigkeit der Ladungsträger (Ionen) zwischen Ionisierungs- 4 und Gegenelektrode 1, 3. Show it:

Fig. 1

the simple construction of a cylindrical chamber system according to the invention with a common ionization electrode in the form of a wire,

Fig. 2

the chamber system with intermediate electrodes and shield electrode,

Fig. 3

a block diagram for controlling the reference chamber current,

Fig. 4

a block diagram for controlling the reference chamber current with subordinate voltage control.

In the simple embodiment shown in FIG. 1, the ionization electrode 4 runs centrally symmetrically through the measuring chamber 17 and the reference chamber 18.
The counter electrodes 1 and 3 are each arranged in a hollow cylindrical manner around the ionization electrode 4 and are electrically insulated from one another by an insulator 2 with a through and compensation opening 8.
The insulator 2 and the insulator 7 forming the base of the cylindrical counter electrode 1 together with the cylindrical outer surfaces of the two counter electrodes 1 and 3 enclose the gas volumes of the measuring chamber 17 and the reference chamber 18.
Through the openings 9 in the cylindrical counterelectrode, the gas atmosphere from the surroundings of the ionization smoke detector enters the measuring chamber 17. Via the compensating opening 8 (diffusion opening) of the insulator 2, which connects the two chambers with one another, the gas molecules in the surroundings also enter the measuring chamber 17 Reference chamber 18.
In both chambers 17 and 18 there are thus similar gas ratios due to gas exchange.
The wire-shaped ionization electrode 4, which has a very small diameter in order to generate high field strengths, passes through both chambers 17 and 18, in this example preferably exactly through its central axis. The counter electrodes 1 and 3 are each connected separately from one another via the connections 5 and 6 to a supply and evaluation circuit.
This arrangement makes it possible to measure the currents for the measuring and reference chamber separately.
One end of the two chambers 17 and 18 passing through ionization electrode 4 is embedded and fixed in the insulator 7 of the measuring chamber. The other end is contacted in the base area of the cylindrical reference chamber 18 with the supply and evaluation circuit mentioned (FIGS. 3 and 4). If such an arrangement is to be used as a point-type ionization smoke detector for room monitoring, the chamber system is mounted rotated by 180 ° with respect to the illustration shown in FIG. 1, so that the measuring chamber 17 points downward. This position and other constructive measures, which will not be discussed further here, make it possible to keep the aerosols practically away from the reference chamber 18, but at the same time to dynamically sufficiently adapt the gas atmospheres of the measuring and reference chambers to one another and the environment.
Further advantageous embodiments of the invention relate to the possibility of being able to carry out additional control processes.
As shown in FIG. 2, the arrangement of intermediate electrodes 10, 14 in the gas volume of the measuring chamber 17 and the reference chamber 18 and their potential setting allow the speed of movement of the charge carriers (ions) between the ionizing 4 and counterelectrode 1, 3.

This can, for. B. can be achieved that only some of the ions, which are formed in the area of high field strengths near the high-voltage ionizing electrode 4, reach the outer chamber walls 17 and 18 formed as counter electrodes 1, 3.
The resulting reduced running speed leads to an even better ability of the ions to attach to existing smoke aerosols.
The intermediate electrodes 10, 14 can also be designed, for example, as a wire mesh or wire mesh.
The entire system can also be covered by an outer, shielding electrode 13, which must be sufficiently perforated for the passage of gas molecules or can also consist of a wire mesh (Fig. 2).

Despite the small cross-section of the ionization electrode 4, low voltages are not sufficient to generate the field strengths required to accelerate the charge carriers sufficiently.
The voltages required for this, which can be between a few hundred and a few thousand volts depending on the shape of the electrode and the chamber structure, are either inductive, e.g. B. generated by means of blocking oscillators, or by means of piezotransformers. The required consumer power is very low because the chamber currents are in the range from pA to nA. The voltages are supplied to the electrodes via a rectifier unit or a modulator circuit.
The regulation of the level of the reference chamber current 24 and the evaluation and correction of its deviations from the normal state are described in principle in FIG. 3.
A predetermined target value 19 of the reference chamber current in FIG. 3 is compared with the actual current of the reference chamber current 24. The difference between the two measured variables is fed to a controller 21, the output signal of which controls the high-voltage generator 16.
The high voltage of the ionization electrode 4 is set in such a way that the actual current of the reference chamber current 24 adapts to the predetermined value. The same high voltage also acts on the measuring chamber 17, so that the adjusted actual current of the measuring chamber current 23 is also set there.
Deviations from the set actual current in the measuring chamber 17 can then essentially only be attributed to the influence of smoke aerosols.

In a further preferred embodiment, the dynamics of the regulation can be further improved by, for example, subordinating the current regulation to a voltage regulation 25. The principle of operation of such an embodiment is described in more detail in FIG. 4. Here, too, a deviation of the reference chamber current 24 is fed to a controller 21.
The output signal of this regulator 21 now forms the setpoint for a subordinate voltage control circuit 25. The image of the high voltage is now compared with this setpoint and the control deviation is fed to a voltage control amplifier 22, the output signal of which causes the high voltage generator 16 to generate a corresponding voltage. Then the images of the two chamber flows 23, 24 are compared again and the deviation from the normal state is analyzed. This principle of regulating the reference chamber current 24 can compensate for temporal fluctuations in the background ionization by changes in the impact ionization capacity.
The arrangement according to the invention of the electrode passing through both chambers allows the ion-generating electric field of both chambers to be formed uniformly. As a result, the natural ionizations which fluctuate strongly in the individual volume units of the chamber systems are better compensated, which leads to a considerable improvement in the measurement accuracy of aerosol particles in the ambient atmosphere to be monitored.

Another advantage of the invention is the regulation of the reference chamber flow 24 by means of a signal evaluation and conversion unit (15 and 20 in FIGS. 3 and 4). As a result, the reference chamber current 24 is always in the optimum range for the measurement task in order to prevent fluctuations in natural ionization or unwanted flashovers.
By arranging an additional intermediate electrode 10, 14, the running speed of the charge carriers can be reduced and an even better attachment of the aerosols can be achieved, which in turn contributes to increasing the sensitivity and measuring accuracy of the ionization smoke detector.

By arranging a correspondingly perforated outer shield electrode can prevent the penetration of ionizing radiation into the gas volume of the two Chambers can be controlled within certain limits.

Reference list

1.

Counter electrode of the measuring chamber

2nd

Isolator with through and compensation opening

3rd

Counter electrode of the reference chamber

4th

Ionizing electrode

5.

Connection for supply and evaluation circuit

6.

Connection for supply and evaluation circuit

7.

Isolator base of the measuring chamber

8th.

Equalization opening (diffusion opening)

9.

Gas inlet openings (aerosols)

10th

Intermediate electrode

11.

Supply circuit intermediate electrode

12th

Supply circuit intermediate electrode

13.

outer shield electrode (perforated)

14.

Intermediate electrode

15.

Power supply circuit

16.

High voltage generator

17th

Measuring chamber

18th

Reference chamber

19th

Target current of the reference chamber current

20th

Voltage control circuit

21.

Current control amplifier

22.

Voltage regulator amplifier

23.

Actual current of the measuring chamber

24th

Actual current of the reference chamber

25th

High voltage regulation

Claims (17)

Ionization smoke detector for aerosol detection with at least one ionization electrode (4) and at least two mutually insulated counter electrodes (1, 3), which are components of the measuring chamber (17) and the reference chamber (18) and each include a gas volume, at least one power supply being provided,
characterized in that
the ionization electrode (4) is made in one piece and runs through the reference chamber (18) and the measuring chamber (17). Ionization smoke detector according to claim 1,
characterized in that
the ionization electrode (4) is wire-shaped and has a strongly curved surface for generating high electric field strengths. Ionization smoke detector according to claim 1 or 2,
characterized in that
the measuring chamber (17) and the reference chamber (18) have a hollow cylindrical shape, the cylinder jacket of both chambers (17, 18) being formed by the counter electrodes (1, 3) which are electrically insulated from one another by means of an insulator (2). Ionization smoke detector according to claim 3,
characterized in that
the insulator (2) is provided with a compensating opening (8) which serves for gas exchange between the reference chamber (18) and the measuring chamber (17) and as a passage for the ionization electrode (4) passing through both chambers (17, 18). Ionization smoke detector according to one or more of the preceding claims, characterized in that
At least one intermediate electrode (10, 14) is arranged between the ionization electrode (4) passing through both chambers (17) and the counter electrodes (1, 3), which can be acted upon with different potential compared to the other electrodes (1, 3). Ionization smoke detector, according to claim 5,
characterized in that
an outer, perforated shield electrode (13) encloses the entire arrangement (1, 2, 3, 4, 5, 6, 7, 10, 11, 14) and with a different one from the other electrodes (1, 3, 10, 14) Potential can be applied. Ionization smoke detector according to one of the preceding claims,
characterized in that
a power supply circuit (15) for controlling the chamber currents (23, 24) is provided, which comprises a current control amplifier (21) and a high voltage generator (16). Ionization smoke detector according to claim 7,
characterized in that
The power supply circuit (15) is subordinated to a voltage control circuit (20) which comprises a high voltage control (25) with a voltage control amplifier (22). Ionization detector according to one of claims 5 to 8,
characterized in that
the high voltage generator (16) for generating the high voltage for the electrodes (1, 3, 4) is designed as a blocking oscillator. Ionization smoke detector according to one of claims 5 to 8,
characterized in that
the high voltage generator (16) for generating the high voltage for the electrodes (1, 3, 4) is designed as a piezotransformer. Method for operating an ionization smoke detector according to one or more of the preceding claims,
characterized in that
the ions necessary for the formation of an ion current in the measuring chamber (17) and the reference chamber (18) are generated by an ionization electrode (4) passing through both chambers (17, 18). A method according to claim 11, characterized in that
the power supply (15) of the reference chamber (18) is regulated in such a way that a predetermined target current (19) is compared with the actual current of the reference chamber current (24) and the difference between the two measured variables is fed to a current control amplifier (21) whose output signal is sent to the high-voltage generator ( 16) which controls the high voltage of the ionization electrode (4) so that the current strength of the reference chamber current (24) matches the predetermined target current strength (19), the same high voltage also acting on the measuring chamber current (23), so that there too adjusts the current strength of the measuring chamber current (23) which is adapted to the target current strength, that is to say the high voltage control variable for both chambers (17, 18) is applied in the same way via the common ionization electrode (4). Method for operating an ionization smoke detector according to claim 12, characterized in that
the power supply circuit (15) is interleaved with an additional voltage regulating circuit (20),
that the output signal of the current control amplifier (21) forms the setpoint for a subordinate voltage control loop (25), the image of the high voltage of the ionization electrode (4) being compared with this setpoint and the control deviation being fed to a voltage regulator amplifier (22), the output signal of which is sent to the high voltage generator (16 ) causes a correspondingly corrected voltage to be generated, the two chamber currents (23, 24) then being compared with one another and the deviation from the normal state being analyzed, with which time fluctuations in the background ionization can be compensated. Method according to one of the preceding claims,
characterized in that
the polarity of the high voltage applied to the electrodes (1, 3, 4), and thus the chamber currents, can be changed; the polarity of the intermediate electrodes (10, 14) and the shield electrode (13) can also be changed. A method according to claim 14, characterized in that
the level of the current strength regulated by means of the power supply (15, 20) is matched to the respective operating conditions of the detector. A method according to claim 13 or 14, characterized in that
the current (23) in the measuring chamber (1) is measured separately from the current (24) in the reference chamber (3). A method according to claim 15, characterized in that
the evaluation of the measurement results of both currents is used for aerosol density measurement.

Images