EP0772852B1 - Improvements relating to optical smoke detectors - Google Patents

Description

The invention relates to devices intended detecting the presence of smoke, in particular with a view to carrying out surveillance of a premises with regard to risks fire and, for this purpose, to automatically trigger an alarm, particularly an audible one, when the density of smoke detected exceeds a predetermined threshold.

It aims more particularly, among these detectors, those that implement an optical effect by using, using an appropriate detector, the reflection of a relatively intense light brush on some of the particles making up the smoke to be checked, fumes circulating in a dark room which contains said detector.

Given the intensity of the light brush, if it was continuously issued, power consumption resulting from the device would be very important.

To avoid this drawback, it has already been proposed to emit said brush in the form of pulses short-lived lights t spaced from each other of identical periods T much longer, the durations t being for example of the order of a millisecond or 100 microseconds and periods T, of the order of 5 to 10 seconds, the detection then being carried out on the basis electric response signals produced by the detector only during durations t, the values of these signals being compared in turn to a value representative of the above threshold so as to trigger the alarm in case of overshoot.

To create said pulses of duration t, we preferably operates as follows: charging during periods T a capacitor using an electric current of low intensity, then we discharge this capacitor at the end of each of said periods for times t and the pulses are applied to a light source of duration t thus generated, which are translate by light pulses of the same duration forming the light brush.

In general, to avoid triggers nuisance alarms that could be caused by sudden lighting of the detector, due for example to scanning of the device by an intense light beam itself created directly from a manual torch or indirectly by reflection of the sun on a surface glass moved at the sight of the device, it does not trigger an alarm signifying a fire risk only after having checked that the trigger threshold programmed in advance remains exceeded for several light pulses successive (see document EP-A-0 011 205).

If the difference between said light pulses successive reaches or exceeds 5 or 10 seconds, the duration of such a security check may reach the half a minute or more, which is prohibitive.

The invention aims, above all, to remove this disadvantage while benefiting from the great savings due to the formation of the light brush used for the detection using short spaced pulses in the time.

For this purpose, smoke detection devices of the kind in question according to the invention still include means for forming the incident light brush of control using current pulses also spaced out in time, and they're basically characterized in that they further comprise means to automatically increase the transmission frequency said impulses from the first manifestation of a detection representative of a threshold being exceeded predetermined by the density of the smoke to be controlled, the possible triggering of an alarm being then commanded according to the signals produced by the detector in response to several of the successive pulses sent to the increased frequency, said means then being at again neutralized if examination of said signals reveals a back to normal and only in this case.

• les moyens pour émettre les impulsions lumineuses constitutives du pinceau incident comprennent une source de courant continu et une source lumineuse branchée aux bornes de la source de courant par l'intermédiaire d'au moins un interrupteur électronique et les moyens pour augmenter la fréquence des impulsions lors des dépassements du seuil prédéterminé par le signal de réponse du détecteur comprennent un amplificateur de ce signal de réponse, un convertisseur analogique-numérique, un microprocesseur comprenant le seuil enregistré dans une mémoire appropriée, et un circuit, associé au microprocesseur et éventuellement intégré à celui-ci, propre à augmenter la fréquence d'actionnement de l'interrupteur dès dépassement du seuil par le signal de réponse et tant que dure ce dépassement,
• le microprocesseur comprend des moyens pour détecter, notamment par un calcul de dérivée, le sens de l'évolution des amplitudes des signaux de réponse du détecteur correspondant aux impulsions successives émises à la fréquence augmentée, et des moyens pour déclencher l'alarme si ce sens est croissant et seulement dans ce cas,
• l'ensemble constitué par le microprocesseur et le circuit de commande de la fréquence d'émission des impulsions constitutives du pinceau lumineux incident est agencé de façon telle que les amplitudes de celles, de ces impulsions, qui sont émises à la fréquence augmentée croissent dans le temps,
• l'ensemble du microprocesseur et du circuit de commande de la fréquence d'émission des impulsions constitutives du pinceau lumineux incident est agencé de façon telle que les largeurs et/ou amplitudes de celles, de ces impulsions, qui sont émises à la fréquence augmentée soient supérieures à celles des impulsions qui étaient émises auparavant à fréquence normale.

In preferred embodiments, use is also made of one and / or the other of the following arrangements:

• the means for emitting the light pulses constituting the incident brush comprise a direct current source and a light source connected to the terminals of the current source by means of at least one electronic switch and the means for increasing the frequency of the pulses during exceedances of the threshold predetermined by the response signal of the detector include an amplifier of this response signal, an analog-digital converter, a microprocessor comprising the threshold recorded in an appropriate memory, and a circuit, associated with the microprocessor and possibly integrated with that here, suitable for increasing the actuation frequency of the switch as soon as the threshold is exceeded by the response signal and as long as this excess lasts,
• the microprocessor comprises means for detecting, in particular by a derivative calculation, the direction of the evolution of the amplitudes of the detector response signals corresponding to the successive pulses emitted at the increased frequency, and means for triggering the alarm if this direction is increasing and only in this case,
• the assembly constituted by the microprocessor and the circuit for controlling the frequency of emission of the pulses constituting the incident light brush is arranged in such a way that the amplitudes of those, of these pulses, which are emitted at the increased frequency increase in the time,
• the assembly of the microprocessor and of the circuit for controlling the frequency of emission of the pulses constituting the incident light brush is arranged in such a way that the widths and / or amplitudes of those of these pulses which are emitted at the increased frequency are higher than those of the pulses which were previously emitted at normal frequency.

The invention includes, apart from these arrangements main, certain other provisions which preferably used at the same time and which will be more explicitly question below.

In the following, we will describe some modes preferred embodiments of the invention with reference to drawing attached hereto in a manner which is of course not limiting.

Figure 1 of this drawing shows very schematically the component, an established detection device according to the invention, in which the detection is carried out optics proper.

Figure 2 is a simplified diagram of the assembly of the detection device according to the invention.

Figure 3 shows in more detail a other component of this device, namely its circuit pulse frequency control bright.

Figures 4, 5 and 6 are diagrams showing each appear, on the one hand at the top, the impulses incident light and, on the other hand at the bottom, the signals detector response for three situations respectively different.

In a manner known per se, the detector comprises a housing 1 mounted on a base 2 and pierced with windows 3 able to give way to smoke F to be checked.

These windows 3 are associated with baffles (not shown) to prohibit the maximum introductions of light into the housing and so form inside this case a dark room.

The housing contains a clean light source L to emit a light brush P in the dark room, and a detector D placed in a shadow area of this room opposite the source L.

If no smoke is present in the housing when the incident brush P is emitted, it is not practically not reflected towards detector D and the response of the latter is very weak, even practically nothing.

If, on the contrary, the box contains smoke, the X particles making up this smoke constitute small mirrors suitable for reflecting light: some rays thus reflected reach detector D and the intensity of the latter's response is all the more high that the density of the smoke considered is itself higher.

As said above, the incident light brush P is not emitted continuously, but in the form of pulses I (Figure 4) whose durations t are relatively small, especially of the order of 100 microseconds at 1 millisecond, the periods T which elapse between the successive I pulses being themselves relatively long, and in particular of the order of 5 to 10 seconds.

With such duration relationships, we can generate, by successive charges and discharges, using a switch, of a resistance circuit R-capacity C suitable (figure 3), circuit whose capacitor C is mounted at the terminals of the light source L to be excited, 1 Amp current pulses from current charging medium whose intensity is only 100 microamps or even lower.

This way you get a very significant consumption of detectors considered, the ratio of this reduction exceeding usually 5000.

As also said above, to avoid any nuisance alarm, each overshoot should be threshold detected on the basis of a light pulse incident be confirmed on several subsequent pulses and such a check may turn out to be too long in practice: saving a minute or even half a minute, can be extremely valuable to extinguish the start of a fire.

The invention makes it possible to benefit from both considerable savings due to light emission under the form of brief pulses repeated at a rhythm relatively slow and the security of a response delivered only after a multiple verification, while limiting to a very small duration, which may be of the order of the second, getting that answer.

To this end, according to the invention, one increases automatically transmit pulse frequency bright as soon as an abnormal threshold crossing has been detected on the basis of an incident pulse sent to the normal low frequency.

The above-mentioned multiplied verification is then carried out using the pulses emitted at the increased frequency: this verification is therefore much faster than before and can lift much faster the uncertainty regarding the origin of the anomaly; the response of the device detection is therefore much faster without the reliability of this response is in no way diminished.

We schematized in Figure 2 a device allowing to obtain such a result.

• un amplificateur 4 recueillant la sortie du détecteur D,
• l'ensemble constitué par un microprocesseur 5 et un convertisseur d'entrée analogique-numérique 6, ensemble recevant la sortie de l'amplificateur 4 et comprenant, enregistré dans une mémoire, le seuil S dont le dépassement par le signal sortant du détecteur D et amplifié par l'amplificateur 4 signifie une densité dangereuse de fumée F,
• un circuit 7 recevant la sortie de l'ensemble 5-6 et propre à commander la fréquence d'émission des impulsions lumineuses émises par la source L, circuit qui peut faire partie au moins partiellement dudit ensemble 5-6,
• et une source de courant électrique 8 alimentant les différents composants ci-dessus.

This device includes:

• an amplifier 4 collecting the output of the detector D,
• the assembly constituted by a microprocessor 5 and an analog-to-digital input converter 6, assembly receiving the output of the amplifier 4 and comprising, recorded in a memory, the threshold S whose exceeding by the signal leaving the detector D and amplified by amplifier 4 means a dangerous density of smoke F,
• a circuit 7 receiving the output of the assembly 5-6 and suitable for controlling the frequency of emission of the light pulses emitted by the source L, a circuit which can be at least partially part of the said assembly 5-6,
• and a source of electric current 8 supplying the various components above.

• le condensateur C ci-dessus, monté aux bornes de la source de courant 8 par l'intermédiaire de la résistance R ci-dessus de façon à être progressivement chargé par cette source, avec une vitesse et à un niveau dépendant de la valeur de ladite résistance,
• et un circuit 9 connectant la source lumineuse L aux bornes du condensateur C par l'intermédiaire d'un interrupteur électronique 10 et d'une résistance 11.

The circuit 7 for controlling the frequency of transmission of the pulses I comprises for its part (see FIG. 3), in a manner known per se:

• the capacitor C above, mounted at the terminals of the current source 8 via the resistor R above so as to be gradually charged by this source, with a speed and at a level dependent on the value of said resistance,
• and a circuit 9 connecting the light source L to the terminals of the capacitor C via an electronic switch 10 and a resistor 11.

• montées en parallèle sur la résistance R, au moins une autre résistance 12 de valeur inférieure à celle de cette résistance R, ladite autre résistance 12 pouvant même se limiter à un simple conducteur 13 de faible résistance, la mise en circuit à volonté de l'une ou l'autre des résistances en parallèle (R, 12, 13...) étant commandée par un commutateur électronique 14,
• et des liaisons électriques symbolisées par les flèches 15 et 16 et associées à des moyens de commande appropriés pour transformer les instructions élaborées par le microprocesseur 5 en commandes correspondantes, soit du commutateur 14 seul, soit de ce commutateur et de l'interrupteur 10, dans l'hypothèse où ce dernier ne serait pas organisé de façon à se fermer automatiquement pendant une courte durée chaque fois que la charge du condensateur C dépasse un seuil prédéterminé.

Said circuit 7 further includes here:

• mounted in parallel on the resistor R, at least one other resistor 12 of value lower than that of this resistor R, said other resistor 12 can even be limited to a single conductor 13 of low resistance, switching on at will either of the resistors in parallel (R, 12, 13 ...) being controlled by an electronic switch 14,
• and electrical connections symbolized by the arrows 15 and 16 and associated with appropriate control means for transforming the instructions prepared by the microprocessor 5 into corresponding commands, either of the switch 14 alone, or of this switch and of the switch 10, in the hypothesis that the latter would not be organized so as to close automatically for a short time each time the charge of the capacitor C exceeds a predetermined threshold.

The operation of the assembly is as follows.

Normally, i.e. in the absence of smoke F in the housing 1, the light source L emits light pulses I spaced by identical periods T and relatively long (Figure 4) which are generated by chronic automatic discharges from capacitor C, which is gradually loaded continuously by the power source 8.

These light pulses translate to the output of detector D by voltage signals V (figure 4) very low amplitude: this amplitude remains lower than the threshold S recorded in the microprocessor 5 (taking into account, of course, the coefficient amplification imposed by the amplifier 4) so that this microprocessor does not generate any outputs 15, 16 control signal likely to disturb the succession normal standby cycles.

As soon as a sufficiently dense puff of smoke F has penetrated into the housing 1, the emission of a light pulse, called I ₀ , by the source L is reflected, due to the reflection of certain light rays composing this pulse on particles X of this smoke, by development by the detector D of a voltage pulse V ₀ (FIG. 5).

If this voltage V ₀ is greater than the threshold S, the microprocessor immediately delivers on its outputs 15, 16 an order of increase in the frequency of emission of the light pulses, this frequency being for example multiplied by a coefficient of the order of 10.

This increase is obtained by modifying the position of switch 14 so as to replace in the circuit RC resistance R by one of the resistors plus small 12, 13 or others.

Each of the subsequent pulses I ₁ , I ₂ , I ₃ ... which then succeed at an accelerated frequency the incident pulse I ₀ corresponds to a voltage response V ₁ , V ₂ , V ₃ ...

Examining the values of these responses is crucial to determine if the threshold exceeded observed during from the emission of the incident pulse Io was fleeting and would therefore have given rise to a false alarm if it had only taken into consideration or if, on the contrary, it it was indeed the beginning of a fire which should give rise to when an alarm is issued.

For the first case, in fact, said values successive go down and go back quickly below the threshold S: in this case, the microprocessor 5 develops instructions to return the switch 14 in its initial standby position.

In the second case, the successive values in increasing question: this is a confirmation of the danger initially detected and the microprocessor is arranged so as to excite an alarm of any desirable nature, especially sound.

The direction of the evolution of the successive values above can be determined by calculating a derivative in the microprocessor.

If said successive values V ₁ , V ₂ ... remain constant, the ambiguity may remain longer.

Several solutions can then be envisaged to remove this ambiguity.

According to a first solution, the decision to trigger the alarm or to return to the standby state is postponed until a change in the controlled amplitudes of the responses V _{n is} detected in one or the other direction.

According to another solution, the alarm is automatically triggered after a minimum duration T _a which can itself have a value all the greater as the difference between the constant value of the response pulses V _n and the threshold S is smaller.

According to yet another variant intended to refine the response of the set, the incident pulses I ' ₁ , I' ₂ ... are given values which are themselves increasing: experience indeed shows that the resulting variation in the amplitudes of the corresponding response signals V ' ₁ , V' ₂ ... is greater than the variation of the amplitudes of the incident pulses.

This is what has been shown in FIG. 6.

We could also, for the same purpose, give the durations and / or the individual amplitudes of the pulses values still constant, but greater than those of pulses I emitted at low rate during each normal sleep period.

Each of the two switches 10 and 14 above described is advantageously constituted by a transistor or by a semiconductor with three electrodes including the electrode is connected to the corresponding output (16 or 15) of microprocessor 5, said transistors or analogs which can even be integrated into this microprocessor, as well as the resistances (11, 12, R) to which they are associated.

This constitution, or better still this integration, makes it possible to act in a particularly fine manner on the values of the frequencies and / or amplitudes of the pulses I ₁ , I ₂ ... to be generated.

Likewise, to accurately determine the instants of discharge of capacitor C, provision is made advantageously a circuit suitable for measuring the voltage real at each instant across said capacitor, circuit can also be part of the whole 5-6 : this voltage measurement makes it possible to get rid of errors that could result from the aging of circuits.

As a result of what, and whatever the mode of adopted implementation, we finally obtain a device optical smoke detection whose constitution and operation result sufficiently from the above.

This device presents compared to those currently known many advantages and in particular that of a fast reliable response, without practically no increase in average current consumption electric, which remains extremely weak.

As it goes without saying, and as it results from elsewhere already from the above, the invention is in no way limited to those of its modes of application and embodiment which have been more specifically considered; she embraces it, on the contrary, all the variants having all the characteristics of claim 1, in particular those where part of microprocessor 5 above would be replaced by a comparator (not shown) receiving on one of its inputs the output of amplifier 4 and on its other input, an electrical signal representative of the threshold S, the output of this comparator then being applied to circuit 7, preferably via the assembly constituted by a microprocessor and by a analog-to-digital converter, assembly allowing particularly simple signal processing and efficient.

Claims (5)

1. A device for detecting the presence of smoke (F), the device comprising a dark chamber (1) that receives the smoke to be detected, a source (L) suitable for emitting into said chamber a light pencil (P) formed by short duration pulses that are spaced apart by identical much longer periods, a detector (D) suitable for generating response signals (V) associated with the successive light pulses being reflected partially by certain particles (X) making up the smoke contained in the chamber, and means for comparing said response signals with a predetermined threshold (S) and for triggering an alarm in the event of such threshold being exceeded by a plurality of said successive response signals, the device being characterized in that it further comprises means for automatically increasing the frequency at which said pulses are emitted on the first occasion it is detected that the smoke density has exceeded the predetermined threshold; an alarm then possibly being triggered as a function of the signals (V) generated by the detector in response to a plurality of successive pulses emitted at a higher frequency, said means then being returned to normal if, and only if, examination of said signals indicates that the situation has returned to normal.
2. A detector device according to claim 1, characterized in that the means for emitting the light pulses constituting the incident pencil (P) comprise a DC source (8, C) and a light source (L) connected across the terminals of the DC source via at least one electronic switch (10, 14) and in that the means for increasing the frequency of the pulses in the event of the predetermined threshold (S) being exceeded by the response signal (V) from the detector (D) comprise an amplifier (4) for amplifying said response signal, an analog-to-digital converter (6), a microprocessor (5) including the threshold recorded in a suitable memory, and a circuit (7, 15, 16) associated with the microprocessor and optionally integrated therein, suitable for increasing the frequency at which the switch is actuated as soon as the threshold is exceeded by the response signal and so long as it continues to exceed the threshold.
3. A detector device according to claim 2, characterized in that the microprocessor (5) includes means for detecting the direction of variation of the amplitudes of the response signals (V) from the detector (D) corresponding to successive pulses emitted at the increased frequency, in particular by calculating a derivative, and means for triggering an alarm if, and only if, said direction is increasing.
4. A detector device according to claim 2 or 3, characterized in that the assembly constituted by the microprocessor (5) and the circuit (7, 15, 16) for controlling the frequency at which the pulses constituting the incident light pencil (P) are emitted is organized in such a manner that the amplitudes of those pulses which are emitted at the higher frequency increase over time.
5. A detector device according to claim 2 or 3, characterized in that the assembly comprising the microprocessor (5) and the circuit (7, 15, 16) for controlling the frequency at which the pulses constituting the incident light pencil (P) are emitted is organized in such a manner that the width and/or the amplitudes of the pulses emitted at the higher frequency are greater than of the pulses which were previously emitted at the normal frequency.

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