EP0449761A2 - Method for signalling fire in a thatched roof and fire alarm for thatched roofs - Google Patents

Abstract

The fire alarm system uses 2 or more heat-sensitive optical fibres, positioned immediately above or below the thatch, or incorporated within it. The fire alarm signal is activated when the light propagation along at least 2 optical fibres exhibits a variation, with a fault signal supplied when the light propagation exhibits a variation along a single optical fibre. Pref. a control device supplies each successive optical fibre with a light intensity varied periodically between 0 and a max. value.

Description

The invention relates to a method for reporting fire in a thatched roof and a fire alarm for thatched roofs.

Thatched roofs burn very easily and quickly. The straw (the thatch) is usually tied to the roof battens with coconut yarn that burns quickly so that the burning roofing material falls off the roof. This often blocks the escape routes for people in the building. In order to save lives, a fire detector for thatched roofs must be triggered very quickly after a roof fire has started. Rapid fire alarms can of course also save the building and the inventory. This is particularly important for historic buildings worth preserving.

Remote monitoring of a large number of thatched buildings for fire strives for the greatest possible reliability of the fire report - false reports are not only valuable because of the unsuccessful use of crew and material, but also reduce trust in the monitoring system, which in the worst case can lead to the fact that a correct message is ignored.

It is difficult to achieve both rapid and reliable fire detection for thatched roofs, and this ultimately results from the roof being too high and too high on the house. Smoke or fire detectors that detect ions or smoke particles are usually intended for indoor use. The smoke gases from an outside roof fire (which is the most common case) rise freely. The fire is not reported until the roof has blown enough to allow smoke to enter the building, and that is usually too late. The installation of such fire detectors on the outside requires special designs, can disfigure the roof and leads to false reports due to atmospheric influences, for example smoke from chimneys. Special, highly sensitive fire detectors installed on the inside also often give false reports due to tobacco smoke or dust.

It is also known to unclamp heat sensitive wires on the outside of the roof. The electrical resistance of the wires changes when heated by a fire and triggers the fire alarm. The biggest problem with this solution is to make the fire detector sufficiently resistant to lightning strikes, which in turn are a very common cause of fire in thatched roofs. Conversely, a message cannot be allowed for every lightning strike or every major electrical impulse that occurs on the heat-sensitive wires, because this would result in a false alarm rate that is far too high.

A fire detector with an optical fiber is known from European laid-open publication No. 1 113 046, the light conduction of which is reduced by the action of heat. This fire detector has a transmitter for irradiating light into one end of the fiber, a control unit for generating an intensity control signal for the transmitter and a receiver for signaling the intensity of light received which is emitted from the other end of the fiber. In the event of fire, the effect of heat reduces the light conduction of the fiber, so that the received light intensity falls, which triggers the fire alarm. To ensure that the fire message is not suppressed by light from the fire that is radiated into the fiber after it has burned through, the irradiated light is sent in a modulated form and the fire message is triggered unless this modulation is in the light is recovered, which may be received from the other end of the fiber. A similar fire alarm is known from U.S. Patent No. 4,712,096.

The aim of the invention is to provide a method and a fire alarm for quickly and reliably reporting a fire specify in a thatched roof, and an improved method for equipping a thatched roof with a fire alarm.

As is apparent from claims 1 and 3, this aim is achieved in that light is passed through two or more optical fibers, the light conduction of which is reduced by the action of heat, and which are stretched out directly under, in or on the thatched roof, in particular in close proximity to one another, and that fire is reported when the light conduction is reduced by at least two fibers.

According to the invention, the fire alarm occurs quickly and reliably because the fibers are directly influenced by the heat generated by the fire and do not, like smoke detectors, detect such an unpredictable phenomenon as the smoke gases. Reliability is increased by only reporting fire if at least two fibers are affected. Damage to just one fiber, for example mechanical damage, does not trigger a fire alarm. There can be many reasons why only one fiber is damaged. It can be torn or kinked by larger birds, gnawed by rodents, or kinked by objects thrown on the roof. Insignificant phenomena such as tobacco smoke and dust are of course completely prevented from triggering fire reports.

According to the invention, excellent resistance to lightning strikes and other electrical discharges which act on the roof is also achieved, since optical fibers are electrically insulating.

As indicated in claims 2 and 4, an error can be reported if the light conduction is reduced by only one of the fibers. The active elements of the fire alarm, the fibers, are continuously monitored for correct function. This is a very essential self-monitoring function, which considerably increases operational safety and reliability. This function is particularly important in remote monitoring systems in which the error message can be used to call a maintenance technician.

The fire alarm according to the invention can advantageously be provided with a common control unit (for example a microprocessor or a one-chip microcomputer) for all fibers (claim 5), which controls an alternating radiation of light into the fibers. With this solution, the function of the signaling circuit can also be transferred to the control unit. The signal processing is thus centralized and can be carried out digitally under the control of a multi-fiber program. This results in great savings in the circuit design of the fire alarm.

The continuous monitoring of each fiber can be carried out by means of a dynamic measurement, as stated in claim 6. The main purpose is of course to report a fire if there are two fibers that do not produce a satisfactory output signal when exposed to maximum intensity. In addition, however, as stated in claim 7, it can be determined how high the irradiated intensity must be in order to obtain a satisfactory output signal. In this way it can be determined whether the fiber is aging, i.e. whether their light conductivity decreases over time and report an error if a predetermined aging limit is exceeded.

By performing the dynamic measurement as specified in claim 8, the energy consumption of the measurement is reduced. The transmitter is turned on in intensity and thus in terms of energy consumption only as little as is necessary to obtain a satisfactory output signal from the fiber, and is then switched off. Only when the fiber is burned out or damaged in any other way is the transmitter turned on to the maximum intensity. The minimal energy consumption results in a long operating time in battery operation, for example in the event of a power failure due to lightning strikes near a monitored thatched roof. Especially in thunderstorms, one is interested in the fire alarm working reliably.

The fact that the measurement is carried out as specified in claim 9 avoids having to digitize intensity values. One measures how far one has to increase in intensity in order to obtain a satisfactory output signal by measuring the time from the start of an intensity ramp. Incidentally, the shape of the ramp signal is not particularly important. It can be linear or have another curve shape, and it can be generated by an analog circuit, for example an RC element, so that it is continuous, or it can be specified by the control unit in discrete steps, for example via a digital-analog Converter.

The invention also includes the method specified in claim 10 for equipping a thatched roof with a fire alarm. Practical experience shows that a fire in a thatched roof will very quickly run from the point of ignition to the back of the roof, after which it will spread more slowly to the sides. The fibers are therefore preferably attached in pairs close to the roof back so that two fibers always burn through at approximately the same time.

The invention is described in more detail below with reference to the accompanying drawings, which show various exemplary embodiments.

1 shows a block diagram of a fire alarm according to the invention.

Fig. 2 shows a block diagram of an inventive Fire alarm, in which all functions are controlled by a computer.

Fig. 3 shows a transmitter circuit for 2 fibers, which can be connected to two output ports of a computer.

Fig. 4 shows a receiver circuit for 2 fibers, which can be connected to an input port of a computer.

Fig. 5 illustrates the attachment of the optical fibers of the fire alarm on a thatched roof.

6 shows a simplified flow diagram of a program routine for alternately measuring the light conduction of two fibers.

1 has two optical fibers 1, in which both the core and the cladding are made of plastic and are surrounded by a protective cap, also made of plastic, with a total diameter of 2-6 mm, which corresponds approximately to the diameter of thatch.

In this context, optical fibers of the plastic type have the advantage that they burn out quickly. Where longer fiber lengths are required, for example in very large buildings, fibers with glass or quartz core and sheathing made of plastic or glass could also be used because of the lower transmission attenuation, since they will blow under all circumstances, but with a certain delay compared to one Plastic-plastic fiber.

Each fiber 1 is connected by means of a plug connection to a transmitter 2 and a receiver 3 with connection elements 4 and 5. The connector 4 of the transmitter is normal a light-emitting or laser diode, while the connection element 5 of the receiver is typically a phototransistor. With the help of the optoelectronic elements 4 and 5, a light signal is sent from each end 1 from one end to the other end. The transmitters 2 are controlled by an output signal from a signal generator 6. A notification circuit 7 receives both the output signal of the signal generator and the output signals of the two receivers 3.

In the signaling circuit 7, the control signal for the irradiation of light in one end of the fibers is compared with the signal which is produced when light is received from the other end of the fibers. As long as these two signals coincide within predetermined limits, both fibers are intact and no fire alarm is given.

If one of the fibers 1 is damaged, so that the light conduction is reduced by it, there is a deviation in its output signal. As long as the other light guide 1 is intact, this leads to an error message being sent to a downstream signal transmitter 8 in order to call a technician for checking and possible repair. If both light guides 1 are damaged, for example burn out, the signal deviation for both light guides is determined, and the signaling circuit reports fire to the signal transmitter 8 connected downstream.

A larger signaling center with a larger number of light guides can be constructed using modular technology, for example with a transmitter-receiver module for each light guide and a common control and signaling circuit etc. A fire detector of this type is shown in FIG. 2, but still only with 2 fibers. The circuits 6, 7 and 8 according to FIG. 1 are replaced in FIG. 2 by a computer 14 with output gates 12 and input gates 13. The computer may be a one-chip instrument controller type of general, general is used to control devices.

3 shows a transmitter circuit for two optical fibers, which can be connected to the output gates of such a computer. The circuit has two channels, each with a light-emitting diode 4, which is driven by an enhancement-type MOSFET transistor 16. The gate electrode of the transistor is connected to the output gate 12 of the computer via an RC element 17, 18. A common current-limiting resistor 19 is connected in series with the transistors and the light-emitting diodes. The resistor 17 in the RC element is decoupled with a diode 20 in order to be able to quickly discharge the capacitor 18. As long as the gates 12 are at ground potential (logic 0), the transistors 16 are switched off and the diodes 4 do not emit any light. When the gates 12 are set to high potential (logical 1), the capacitors 18 are slowly charged via the resistors 17. The resulting ramp-shaped voltage rise at the gate electrodes is converted by the transistors and the light-emitting diodes into a light signal with a ramp-shaped intensity curve, which is radiated into the fibers 1.

Fig. 4 shows a receiver circuit for two optical fibers, which can be connected to an input port 13 of a microcomputer. The circuit does not entirely correspond to FIG. 2, since it only has a common output for both fibers. This circuit requires the light to be transmitted alternately through the fibers, i.e. that the two output gates 12 in Fig. 3 are alternately set to logic 1.

The receiver circuit of FIG. 4 simply consists of a phototransistor 5 for each fiber, which is connected to the supply voltage via a common load resistor 21. When one of the phototransistors receives light from a fiber 1, the potential at the output terminal 13 of the circuit drops in proportion to the received light intensity. This potential reduction can be done by the microcomputer be demonstrated at its entrance gate 13. In practice, the potential must fall below a threshold, which depends on the design of the computer, so that signal reception can be demonstrated. The resulting sensitivity of the circuit can therefore be adjusted by a suitable choice of the resistor 21.

FIG. 6 shows a simplified flow diagram of a program routine in the microcomputer 14, which uses the circuits according to FIGS. 3 and 4 to carry out an alternate measurement of the light conduction through the fibers. The principle of the program routine is that it introduces light into a fiber via one of the gates 12. The light radiation has a ramp-shaped intensity as described in connection with FIG. 3. While the ramp is running, the entrance gate 13 is continuously read to determine whether the light reception from the other end of the fiber has exceeded the threshold set by the resistor 21. The running time from the start of the ramp until the threshold is exceeded is a measure of the optical conductivity of the fiber. If the ramp has to run too long before light is received enough from the fiber, this can form the basis for an error message (reduced light conduction, aged fiber) or an alarm (no light conduction).

After calling the routine in step 30, both transmitter diodes 4 are switched off in step 31 by connecting the output gates 12 to ground, the capacitors 18 being quickly discharged via the diodes 20. A ramp time counter (an internal register) in the computer is loaded with a maximum ramp time. It is then checked in step 32 whether light is already being received from the last measured fiber, although no light is radiated into it. In this case, the cause must be light from a fire shining into the blown fiber, and this fact is noted in step 33 by zeroing the ramp time counter. This will continue explained in more detail below.

Normally, no light is received if there is no transmission. In step 34, the new fiber is therefore selected which is to be measured (the fiber is changed), after which its transmitter is switched on in step 35/36. It is also noted that the next time the routine is called, it is the other fiber's turn. A loop 37 is then run through, in which the output signal from the receiver 3 is continuously queried on the input gate 13 of the computer, while the ramp time counter is counted down (decremented), step 38.

If loop 37 is exited, either because light enough has been received from the fiber or the ramp time counter has been counted down to zero, the transmitter is turned off in step 39 (both transmitters for the sake of simplicity). In step 40 it is then checked whether the ramp has been running for so long that the transmission of the fiber must be reduced. If this is the case, a maintenance error is noted in step 41 by setting an internal mark in the computer. The maintenance error is reported externally by another routine, which does not require any description here.

After checking for maintenance errors, it is checked in step 42 whether a flag for an alarm from the other fiber has been set in the computer from an earlier run of the routine because of a lack of light conduction. This check is also carried out after step 33, which was described above. If the alarm flag is set for the other fiber, a check is carried out in step 43 to determine whether the current fiber is interrupted (no light is conducting) by examining whether the ramp time counter has been counted down to zero. If this is the case, then no light conduction has been detected during the course of the irradiation ramp - or light conduction has been determined without irradiation, see step 33. In this case, both fibers are defective and the Step 44 is reported by setting an internal mark in the fire computer. The light measuring routine then frees up space for subsequent routines in step 45.

If there is no alarm from the other fiber, it is checked in step 46 whether the ramp time counter has been counted down to zero, i.e. whether there is a lack of light conduction in the current fiber. If there is insufficient light conduction, an alarm for the current fiber is set in step 47 for use in the next run of the routine, and the routine is exited in step 45. If light has been received, the routine is also exited at step 45, but without setting an alarm. This also applies if the light guide is so bad that a maintenance error was set in step 41.

The diagram in Fig. 6 is simplified since one will normally count alarms for both fibers a few times before a fire alarm is triggered to be quite sure of the alarm. It would also pose no difficulty for a person skilled in the art to extend the principle to more than two fibers and, moreover, to change both the circuit examples shown and the signal treatment discussed here as required.

Fig. 5 shows a section of a thatched roof with two optical fibers 1, which are mounted as a fire sensor. It can be seen that the fibers are attached directly under the roof back, which is completed with a turf covering 9. The fibers 1 are inserted from the roof space outwards and led around the entire roof on the outside, where they are sewn with coconut yarn 11 of the same type that is otherwise used for the thatched roof. This type of installation close to the back of the roof results in the shortest fiber length when the roof is fully monitored. It is shown in practice that a fire in a thatched roof runs very quickly from the point of ignition to the back of the roof, while it lasts longer needs to spread out to the sides.

The installation of the fibers on the roof can also be adapted to any emerging need, for example, a fire of fibers arising from the roof space can be reported on the inside of the roof, and fibers can be attached wherever a particularly early notification is desired , for example over the windows of bedrooms or children's rooms etc.

Claims (10)

A method of reporting fire in a thatched roof, characterized in that light is passed through two or more optical fibers, the light transmission of which is reduced by the action of heat, and which are stretched out directly under, in or on the thatched roof, in particular in close proximity to one another, and in that fire is reported when the light conduction is reduced by at least two of the fibers. A method according to claim 1, characterized in that an error is reported when the light conduction is reduced by only one of the fibers. Fire detector with an optical fiber, the light conduction of which is reduced by the action of heat, with a transmitter for irradiating light into one end of the fiber, a control unit for generating an intensity control signal for the transmitter and a receiver for signaling the intensity of light received from the other end of the fiber is emitted, characterized in that the fire detector comprises two or more fibers for attachment to a thatched roof as well as a transmitter coupled to the control unit and a receiver for each fiber and a detection circuit coupled to the receiver for reporting fire when the light line through at least two of the fibers decreased. Fire detector according to claim 3, characterized in that the detection circuit is set up to report an error if the light conduction is reduced by only one of the fibers. Fire alarm according to claim 3 or 4, characterized in that the control unit is common to all fibers and is set up to effect an alternating light irradiation into the fibers. Fire detector according to one of Claims 3-5, characterized in that the control unit is set up to vary the light intensity radiated into each fiber repeatedly and with intermediate values between 0 and a maximum value set in advance or vice versa, and in that the detection circuit is set up to Report fire if it is found in at least two fibers that the light intensity radiated into the fiber has been a predetermined number of times above the maximum value without the light intensity radiated from the fiber exceeding a predetermined threshold value. Fire detector according to claim 6, characterized in that the detection circuit is set up to report a reduced fiber quality, a system fault or the like, if it is found in at least one fiber that the light intensity radiated into the fiber is a predetermined number of times over an im predefined error limit must be less than the maximum value to cause the light intensity emitted from the fiber to be above the threshold. Fire alarm according to Claim 6 or 7, characterized in that the control unit is set up to let the light intensity radiated into each fiber rise with intermediate values from 0 to the maximum value and to switch off the transmitter as soon as the light intensity emitted from the fiber exceeds the threshold value. Fire detector according to Claim 8, characterized in that the control unit is set up to emit the intensity control signal in the form of a ramp signal at a predetermined rate of increase, so that the detection circuit is coupled to the receiver Contains detector circuit which emits an indicator signal when the light intensity emitted from the fiber is above the threshold value, that the signaling circuit contains a time measuring circuit which measures the time from the start of the ramp signal to the occurrence of the indicator signal, and that the signaling circuit is set up to fire or report errors, depending on whether the measured time has exceeded a predetermined number of times a predetermined maximum value or has exceeded a predetermined number of times a predetermined error limit. Method for equipping a thatched roof with a fire alarm, characterized in that a fire alarm is used with at least two fire sensors in the form of optical fibers, the light conduction of which is reduced by the action of heat, in particular a fire alarm according to one of claims 3 - 9, and in that the fibers are stretched out immediately be mounted under, in or on the thatched roof, preferably in pairs close to each other and preferably above half the roof height, especially close to the roof back.

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