EP0054680B1 - Smoke detector according to the radiation extinction principle - Google Patents

Abstract

A smoke detector contains two radiation transmitters and two radiation receivers. Each of the radiation transmitters emits in a different spectral region, for instance, one emits above and the other one below 600 nm. One part of the radiation of both radiation transmitters is conducted via a measuring path, which is accessible to smoke, to one of the receivers constituting a measuring radiation receiver, and another part of such radiation is conducted via a comparison path, which is not accessible to smoke, to the other of the receivers constituting a comparison radiation receiver. Connected to both radiation receivers is an evaluation circuit which forms from the measuring radiation intensities prevailing in the two spectral regions and from the comparison radiation intensities prevailing in the same spectral regions a function of the type: <IMAGE> By suitably adjusting or selecting the components of the evaluation circuit, the coefficients a and b are selected such that in the absence of smoke in the measuring path, A becomes zero and in the presence of smoke such is proportional to the smoke density.

Description

The invention relates to a smoke detector based on the radiation extinction principle with radiation transmitters of different wavelengths and radiation receivers, which radiation transmitters transmit rays via a smoke-accessible measurement section to the measurement radiation receiver and rays via a comparison path which is not or less accessible to the comparison radiation receiver, an evaluation circuit arranged downstream of the two receivers sending a signal generated with a certain radiation weakness.

With a smoke detector of this type, a relatively small decrease in the radiation directed from a radiation transmitter onto a radiation receiver must be detected. The disadvantage here is that a decrease in radiation, for example due to aging of the radiation source, dusting optically effective surfaces, or the temperature response of radiation transmitters and receivers can have a similar effect to the presence of smoke in the measuring section, so that a faulty alarm signal is triggered can become, even if there is no smoke, or the smoke detector becomes less sensitive and therefore unusable.

According to US Pat. No. 3,994,603, this disadvantage can be eliminated by providing a comparison beam path which is not or less influenced by smoke, the evaluation circuit using a comparison radiation receiver compensating for the radiation changes not caused by smoke. Although the disadvantages mentioned can largely be avoided in this way, smoke cannot be reliably removed from other types of floating particles, e.g. Distinguish dust particles or mist vapors.

US Pat. No. 3,895,233 describes a device for analyzing S0 ₂ in exhaust gases with solid suspended particles (smoke), in which two alternately actuated radiation transmitters direct their beams of different wavelengths into a measuring section and a comparative section via a radiation splitter, each section contains its own radiation receiver at its end. The disadvantage here is that the solid suspended particles (smoke) have no influence on the measurement result of the analysis, and therefore an extinction of the radiation is excluded.

The object of the invention is to avoid the disadvantages of the prior art and to provide a smoke detector based on the extinction principle which is insensitive to temperature fluctuations, dusting or condensation, aging of the components and other slow changes in properties and which has improved long-term stability and is not susceptible to faults and operates reliably, and the smoke is more reliable from other types of particle that trigger false alarms, e.g. B. dust or fog drops, can distinguish and has a lower susceptibility to false alarms.

The object of the invention is achieved by the features of the characterizing part of patent claim 1.

• Figur 1 zeigt eine Rauchmelder-Anordnung mit Reflektor.
• Figur 2 zeigt eine Rauchmelder-Anordnung mit Strahlungsleiter im Anschluss an die Messstrekke.
• Figur 3 zeigt eine Rauchmelder-Anordnung mit Dispersions-Prisma.
• Figur 4 zeigt eine Rauchmelder-Anordnung mit hintereinander angeordneten Strahlungssendern.
• Figur 5 zeigt eine Rauchmelder-Anordnung mit Strahlungsleitern vor der Messstrecke.
• Figur 6 zeigt eine Rauchmelder-Anordnung mit Mattscheibe.
• Figur 7 zeigt eine Rauchmelder-Anordnung mit Dachkanten-Prisma.
• Figuren 8 und 9 zeigen je eine Auswerteschaltung für einen Rauchmelder.

The invention, as well as expedient developments of the same, are described on the basis of the exemplary embodiments illustrated in the figures.

• Figure 1 shows a smoke detector arrangement with reflector.
• FIG. 2 shows a smoke detector arrangement with a radiation conductor following the measuring section.
• Figure 3 shows a smoke detector arrangement with a dispersion prism.
• FIG. 4 shows a smoke detector arrangement with radiation transmitters arranged one behind the other.
• FIG. 5 shows a smoke detector arrangement with radiation conductors in front of the measuring section.
• Figure 6 shows a smoke detector arrangement with a focusing screen.
• Figure 7 shows a smoke detector arrangement with roof edge prism.
• FIGS. 8 and 9 each show an evaluation circuit for a smoke detector.

In the smoke detector arrangement shown in FIG. 1, two radiation transmitters L, and L _G are arranged in such a way that their main emission directions intersect at an angle of 90 °. A semi-transparent mirror D is arranged at an angle of 45 ° to the two radiation directions. A comparison radiation receiver S _{v is} provided in the direct radiation direction of the one radiation transmitter L. In the radiation direction of the other radiation transmitter L _{G there} is a measuring path M that is accessible to smoke, for example in the length of 10 cm-20 cm. At the end of the measuring section there is a radiation reflector R, which reflects the radiation passing through the measuring section M back to a measuring radiation receiver S _M. This arrangement has the effect that both the radiation from the radiation transmitter L _R , deflected by the semitransparent mirror D, and the portion of the other radiation transmitter L _G transmitted by this mirror D pass the measurement path M and are reflected by the reflector R, by the measurement radiation receiver S _M is recorded. On the other hand, the direct radiation emitted by the radiation transmitter LR after passing through the semi-transparent mirror D and the radiation emitted by the other radiation transmitter L _G and reflected by the semi-transparent mirror D after passing through a comparison path which is not or less accessible to smoke, hits the comparison radiation receiver S _v . This arrangement thus has the effect that the two radiation receivers are acted upon almost identically by the two radiation transmitters in the absence of smoke, but are very different when smoke is present in the measuring section.

The two radiation transmitters L _R and L _G are now designed so that they emit radiation under transmit different wavelength ranges. It has proven expedient to design the one radiation transmitter so that it preferably emits radiation with a wavelength below 600 nm, preferably in the range of green light, while the other radiation transmitter produces radiation above 600 nm, preferably red light or infrared radiation. The wavelength ranges can also be selected so that their mean values are at a distance of at least 50 nm from one another. With the choice of the wavelength ranges, the different extinction properties of different suspended particles can be used to distinguish smoke, since it has been shown that the difference in absorption in the two spectral ranges mentioned has a characteristic value for different types of particles. If, as explained later, the evaluation circuit connected to the two radiation receivers is matched to this difference, it can be achieved that smoke particles deliver a particularly large output signal, while other particle types, e.g. dust or fog droplets, have a significantly lower influence, so that an alarm signal is essentially caused by smoke, but not by other types of particles. Broadband emitters, e.g. B. incandescent lamps, with appropriate upstream color filters. The use of light-emitting diodes, which are aimed at the emission of radiation in certain wavelength ranges, has proven particularly expedient. To focus the radiation on the measurement path M, the use of a collimator lens K is recommended in order to avoid radiation losses. Such a collimator lens can, however, be dispensed with if the radiation sources are designed as LASER diodes. The two radiation receiver S _v and S _m are expediently adapted to the radiation of the two radiation transmitters L _G and L _R, that is, they are expediently designed so that they are sensitive to the spectral ranges of both Strahiungssender L _G and L _R.

The partial ratio of the semi-transparent mirror D can, but need not, be 1: 1. If radiation transmitters L _R and L _G with very different intensities or radiation receivers S, and S _v with very different sensitivity are used, it is expedient to choose a different ratio, if necessary up to 50: 1, in order to achieve that the receivers Emit approximately the same output signal in both spectral ranges.

Instead of a single reflector R, several reflector elements can also be provided, with which the measuring section M is folded several times, e.g. in a star shape (DE 2 856 259).

FIG. 2 shows a modified embodiment of a smoke detector arrangement in which a separate collimator lens K ₁ and K _{2 is} provided for each of the two radiation transmitters L _G and L. In contrast to the first example, the radiation is not reflected after passing through the measurement section M, but is returned to the measurement radiation receiver S _M using a radiation guide F (fiber optics). In this exemplary embodiment, measurement radiation receiver S and comparison radiation receiver S _v can be arranged directly adjacent to one another, or in a further development of the invention, can be designed as a dual radiation receiver. This makes the connection to the evaluation circuit considerably easier, and the same optical properties and the same temperature response are achieved.

Figure 3 shows a smoke detector arrangement with directly adjacent radiation transmitters L _G and L _R. In order to ensure that the measurement beams of both radiation transmitters run parallel to one another in such an arrangement, the dispersion of a prism P is used. The radiation from the two radiation transmitters L _R and L _G is first aligned by a collimator K and passes through the same prism P. If light is refracted less than shorter-wave light, the angle of the main radiation directions is compensated and both beams M emerge from the prism parallel to one another. This ensures that the measurement beam paths largely agree for both wavelengths or spectral ranges and are subject to the same influences. The comparison radiation can be taken in front of or behind the prism at a suitable point.

FIG. 4 shows a further smoke detector arrangement with a matching measuring beam M in both spectral areas. In this example, this is achieved in that the two radiation sources L _R and L _G are arranged one behind the other on the same axis. In this case, for example, a green-emitting LED chip can be mounted on an infrared-emitting chip, so that the radiation emitted by the infrared chip radiates through the green chip. The two types of radiation are directed in parallel by a collimator K and pass through the measuring section M in identical ways. In this case, a semitransparent mirror D is provided in front of or behind the collimator K, which directs a portion of the radiation onto the comparison radiation receiver S _v . This ensures complete compensation for all intensity fluctuations and misalignments.

As shown in FIG. 5, the radiation from the two radiation transmitters L _G and L _{R can} also be combined by means of radiation-conducting elements F ₁ , F ₂ (fiber optics) and a collimator K at the output of the elements to form the measuring beam M.

According to FIG. 6, the two radiation transmitters L _G , L _{R can} also irradiate the same focusing screen element MS, the radiation emanating from this being guided into the measuring path M by means of the collimator K.

According to Figure 7, the in slightly different Chen directions emitted radiation of the two radiation transmitters L _R , L _{G can} also be directed in the same direction of the measuring path M by means of a roof edge prism DP. A more uniform illumination of the aperture can still be achieved if an entire array (side by side arrangement) of narrow roof edge prisms is used instead of the one roof edge prism (Fresnel prism).

If the two radiation transmitters are installed one behind the other, their light can be combined into the measuring section by using a bifocal Fresnel lens. Every second ring of this Fresnel lens maps one radiation transmitter to a point (which can also be at infinity), while the other rings map the other radiation transmitter to the same point. If the two radiation transmitters are mounted next to each other, they can be imaged on the same pixel using a cylindrical bifocal Fresnel lens.

A complete identity of the measuring section for the two spectral areas can moreover be achieved by the two radiation transmitters being connected to a spectrally variable radiation source, e.g. an incandescent lamp with an optical filter that can be switched to two different spectral regions or a tunable light-emitting diode.

FIG. 8 shows a suitable evaluation circuit which can be connected to the radiation receivers S _m and S _v and can be used to operate the radiation transmitters L _R and L _G.

In this circuit, the comparison radiation receiver S _{v is connected} to the negative input of an operational amplifier C ₁ of the MC 34002 type, the positive input of which is grounded and the output of which is coupled to the negative input via a resistor R ₁ . The output of the operational amplifier C ₁ is connected to a controllable switch S _w , for example a FET switch MC 14066, which is periodically switched from one initial position to the other by an oscillator OS. Both outputs of the switching device SW are each connected to a driver channel for the two radiation transmitters L _G and LR. The oscillator has the effect that the two radiation transmitters emit radiation alternately, either adjoining one another or with intermediate times, ie in the form of alternating radiation pulses. In principle, both channels can be constructed identically or, taking into account different properties of the radiation transmitters, can be constructed at least analogously. In the following description, the analog components are placed in parentheses. The two outputs of the switching device SW are connected to earth via a resistor R ₃ (R ₇ ) and are simultaneously connected to the negative input of an operational amplifier C ₃ (C ₄ ) of the type MC 34002, the positive input of which is at the tap of a voltage divider R ₄ , R _s (R _a , R ₉ ). The output of the operational amplifier C ₃ (C ₄ ) operates the associated radiation transmitter L _G (L _R ) via a resistor R ₆ (R ₁₀ ). A resistance of the voltage divider, for example resistance R ₄ (R ₈ ), can expediently be set or exchanged in order to be able to set the control level for the intensity of the two radiation sources.

The circuit described has the effect that the intensity of the two radiation transmitters L _G and L _{R is} automatically regulated to a specific intensity level depending on the intensity of the reference radiation received by the reference radiation receiver S _v , so that intensity fluctuations due to aging, temperature changes and similar effects are automatically compensated for.

The measuring radiation receiver S _M is also connected to the negative input of an operational amplifier C _{2 of} the type MC 34002, the positive input of which is in turn grounded and the output of which is coupled through a resistor R ₂ to the negative input. The output of this operational amplifier C ₂ is connected to an AC amplifier AC, at the output of which there is an alarm circuit A.

dabei sind a und b Faktoren, die sich aus den Eigenschaften der Komponenten speziell im Spannungsteilerverhältnis R₄/R₅ (R₈/R₉) ergeben. Durch geeignete Einstellung des Widerstandes R₄ (R_s) kann dabei erreicht werden, dass das Wechselspannungssignal A Null wird, wenn kein Rauch in der Messstrecke M vorhanden ist. Das Ausgangssignal A wird dabei unmittelbar abhängig von der Rauchdichte, und die Alarmschaltung kann so eingerichtet werden, dass ein Alarmsignal ausgelöst oder weitergegeben wird, sobald das Ausgangssignal A einen vorgegebenen Schwellenwert übersteigt. Da in diesem Fall die Abweichung von Null als Kriterium zur Auslösung eines Alarmsignales dient, werden die Schwierigkeiten vorbekannter, nach dem Extinktionsprinzip arbeitende Rauchmelder, bei denen eine kleine Abweichung von einem grossen und schwierig zu stabilisierenden Wert bestimmt werden musste, von Vornherein vermieden.The amplitude of the output signal of the AC voltage amplifier AC supplied to the alarm circuit thus depends in the following manner on the radiation intensities I _G and I _R recorded by the measurement radiation receiver S _M in the two spectral ranges and on the reference radiation intensities I _Rv and I _Gv recorded by the reference radiation receiver S _v in the same spectral ranges from:

a and b are factors that result from the properties of the components, especially in the voltage divider ratio R ₄ / R ₅ (R ₈ / R ₉ ). By suitably setting the resistance R ₄ (R _s ) it can be achieved that the AC voltage signal A becomes zero when there is no smoke in the measuring section M. The output signal A becomes directly dependent on the smoke density, and the alarm circuit can be set up in such a way that an alarm signal is triggered or passed on as soon as the output signal A exceeds a predetermined threshold value. Since in this case the deviation from zero serves as a criterion for triggering an alarm signal, the difficulties of previously known extinguishing smoke detectors, in which a small deviation from a large and difficult to stabilize value had to be determined, are avoided from the outset.

oder

oder

zu bilden und als Alarmkriterium auszuwerten. Sie sind ebenfalls ein Mass für die Rauchdichte.There is also the possibility of one of the sizes

or

or

to form and evaluate as an alarm criterion. They are also a measure of smoke density.

werden.An alarm signal is triggered when one of the sizes A, B / a, C / b or 2D / a exceeds a value between 0.01 (due to the stability of the smoke detector) and 0.2 (due to the length of the measuring section) , where a and b are chosen such that

will.

oder

die von der Rauchart abhängen und die einen Schluss darauf zulassen, welche Art von Rauch vorliegt.The circuit can be developed in such a way that additional parameters are formed, for example

or

which depend on the type of smoke and which allow a conclusion to be drawn about the type of smoke.

gebildet werden,
welche ebenfalls, in Kombination mit dem Hauptkriterium A, B, C oder D, dazu verwendet werden können, die Unterschiede im Ansprechverhalten für verschiedene Feuerarten zu verändern. Eine Zusatzauswertung einer der Grössen E, F, G, oder H kann auch verwendet werden, um noch schärfer zwischen Rauch und Störgrössen wie Staub oder Betauung zu unterscheiden.It can also

be formed
which, in combination with the main criteria A, B, C or D, can also be used to change the response differences for different types of fire. An additional evaluation of one of the sizes E, F, G, or H can also be used to distinguish between smoke and disturbance variables such as dust or condensation.

The smoke development can be tracked if the time differential quotient dA / dt, dB / dt, dC / dt or dD / dt of the output signal A, B, C or D is also formed.

The stability of the smoke detector can be significantly increased if you suppress the small and slow changes in the output signal and only evaluate signals that are at least as fast as can be generated by a fire. This can be achieved either by slowly changing at least one of the factors a, b, c, d, e, f, g or h in order to compensate for these fluctuations or by comparing the output signal with its moving average.

Another evaluation circuit is recorded in FIG. 9. The signal of the measurement radiation receiver S _M as well as the signal of the comparison radiation receiver S _v is integrated in time (A ₂ , C ₂ , S ₂ or A ₁ , C ₁ , S,). The comparator K compares the integral of the comparison radiation receiver with a predetermined value, which is determined by the voltage divider E3, R ₄ , and opens the switch S _{3 of} the sample and hold amplifier (S ₃ , C ₃ , A ₃ ) at that time which the integration value exceeds the specified value. An alarm circuit A is located at the output of the amplifier A _3. The oscillator OS controls the repetition of the integration process and switches between the two radiation transmitters L _G and L _R with the aid of the flip-flop FF.

The smoke detectors described have significantly improved stability, even over longer periods, as well as improved functional reliability and greater susceptibility to faults. Changes due to dust and changes in the properties of the components are automatically compensated for without the risk of an incorrect alarm triggering and without loss of sensitivity. By appropriately selecting the spectral ranges used, it can also be achieved that the smoke detectors described preferably react to smoke particles, but not or only weakly to other types of particles.

Claims (24)

1. Smoke detector according to the radiation- extinction principle, having two radiation transmitters (L_R, L_G) of different wave length which are to be actuated in a time sequence, said radiation transmitters (L_R, L_G) transmitting a radiation (I_R, I_G) over a smoke-accessible measurement path (M) to a measurement radiation receiver (S_M) and a radiation (I_RV, I_GV) over a no or less smoke-accessible comparison path (V) to a comparison radiation receiver (S_v) whereby an evaluation circuit subordinated to the two receivers generates an output-signal which, at a certain radiation weakness of the radiation (I_R, I_G) across the measurement path (M), causes an alarm release, characterized in that the evaluation circuit generates, from the radiation intensity I_R, I_G of the radiation received successively from the two radiation transmitters (L_R, L_G) after passage of the measurement path (M) and from the radiation intensity I_Rv, I_GV of the radiation received from the two radiation transmitters after passage of the comparison path (V), the output signal

a, b being predetermined coefficients which are set by means of circuit components of the evaluation circuit or are programmed in said evaluation circuit. (figs. 8, 9)

2. Smoke detector according to claim 1, characterized in that the evaluation circuit generates, from the radiation (I_R, I_G) received after passage of the measurement path (M) and from the radiation (I_RV, I_GV) received after passage of the comparison path (V), the output

or

or

a, b being predetermined coefficients that are programmed in the evaluation circuit. (fig. 9)

3. Smoke detektor according to claim 1, characterized in that circuit components of the evaluation circuit, preferable, resistors (R₄, R₈) in voltage dividers (R₄, R_s; R_e, Rg), are selected in such a way that the output A is zero when there is no smoke in the measurement path. (fig. 8)

4. Smoke detector according to one of claims 1 or 2, characterized in that the evaluation circuit in addition selectively generates the output signal

or

c, d, e and f being predetermined coefficients and programmed in the evaluation circuit. (fig. 9)

5. Smoke detector according to one of claims 1, 2, 4, characterized in that in the evaluation circuit additionally the output signal

is selectively generated, g and h being predetermined coefficients and programmed in the evaluation circuit. (fig. 9)

6. Smoke detector according to one of claims 1 to 5, characterized in that the evaluation circuit is formed such that at least one of the coefficients a, b, c, d, e, f, g or h can be slowly varied. (figs. 8, 9)

7. Smoke detector according to one of claims 1 to 6, characterized in that the evaluation circuit compares the instant values of at least one of the output signals A, B, C, D, E, F, G or H with the shifting average value of the selected output signal or signals. (figs. 8, 9)

8. Smoke detector according to claims 1 and 2 or one of claims 4 to 6, characterized in that the evaluation circuit generates, in addition to at least one of the output signals, the time differential quotient of this or another output signal. (figs. 8, 9)

9. Smoke detector according to one of claims 1, 3, 6, 7, 8, characterized in that the evaluation circuit comprises a current circuit (AC) in which the alternate part of the output signal of the measurement radiation receiver (S_M) is generated as a criterion for relaising the alarm. (fig. 8)

10. Smoke detector according to one of claims 1, 3, 6, 7, 8, 9, characterized in that the evaluation circuit comprises control means (R₁, C₁, R₃, R4, C₃, R₆; R₁, C₁, R₇, R_s, Rg, C₄, R₁₀) that controls the radiation intensity of the two radiation transmitters (L_G, L_R) onto a predetermined level in response to the received radiation intensity (I_GV, I_RV) within the corresponding wave length field. (fig. 8)

11. Smoke detector according to claim 10, characterized in that the control level (R₄, R_s; R₈, Rg) for the radiation within the two wave length fields is adjustable. (fig. 8)

12. Smoke detector according to one of claims 1, 2, 4, 5, 6, 7, 8, characterized in that the evaluation circuit comprises at least one integration stage (S₁, C₁, A₁; S₂, C₂, A₂) which carries out a time integration of the signal of at least one of the two radiation receivers (S_M, S_v). (fig. 9)

13. Smoke detector according to claim 12, characterized in that the evaluation circuit comprising a comparator (K) and a current circuit (S₃) evaluates the integration value of the signal of the measurement radiation receiver (S_M) in that moment in which the integral of the signal of the comparison receiver (S_v) reaches a predetermined level. (fig. 9)

14. Smoke detector according to claim 2, characterized in that the evaluation circuit generates an alarm signal when one of the coefficients A, B/a, C/b or 2D/a exceeds a value being within 0,01 and 0,2 whereby the coefficients a, b are selected such that

if there is no smoke in the measurement path (M). (figs. 8, 9)

15. Smoke detector according to one of claims 1-14, characterized in that the two radiation transmitters (L_R, L_G) on one hand, for parallely conducting their rays (I_R, I_G, I_RV, I_RG), and/or the two radiation receivers (S_M, S_v) on the other hand, for compensating their temperatures, are arranged in close vicinity to each other and that the two radiation emitters are triggered by the evaluation circuit in such a manner that they give alternating rays onto the radiation receivers.

16. Smoke detector according to claim 15, characterized in that a prism (P) is arranged between the radiation transmitters (L_R, L_G) and the measuring path (M) which, by means of its dispersion, deviates the rays (I_R, I_G) in such a manner that the measuring path is nearly equal for the two wave lengths. (fig. 3)

17. Smoke detector according to claim 15, characterized in that the two radiation transmitters (L_R, L_G) are disposed on behind the other in the radiating direction so that the radiation of one radiation transmitter (L_R) penetrates the other radiation transmitter (L_G). (fig. 4)

18. Smoke detector according to claim 15, characterized in that the two radiation transmitters (L_R, L_G) are disposed one behind the other or side by side in the radiating direction and that a bifocal Fresnel lens is provided that depicts the radiation of the two radiation transmitters (L_R, L_G) on the same viewpoint.

19. Smoke detector according to claim 15, characterized in that the two radiating transmitters (L_R, L_G) are disposed such that they radiate onto a focussing screen (MS), whereby the radiation emanating from the radiated surface of the focussing screen is conducted into the measuring path (M). (fig. 6)

20. Smoke detector according to claim 15, characterized in that there is provided a greater number of roof edge prisms which each combine the radiation of the two radiating transmitters (L_R, L_G) toward the measuring path (M). (fig. 7)

21. Smoke detector according to one of claims 15-20, characterized in that each radiating transmitter (L_R, L_G) is made up as a wide-band radiation source having an optic filter which is in front with it.

22. Smoke detector according to one of claims 15 to 21, characterized in that the two radiation transmitters (L_R, L_G) are made up as a wide-band radiation source having an optic filter in front with it whose passband is variable by means of electric signals.

23. Smoke detector according to one of claims 15-20, characterized in that the radiation transmitters (L_R, L_G) are made up as an entirely tuneable light emitting diode.

24. Smoke detector according to claim 15, characterized in that the measuring radiation receiver (S_M) and the comparison radiation receiver (S_v) are combined to a dual radiation receiver.

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