WO2009080581A1

WO2009080581A1 - A fire detecting system and method for early detection of fire

Info

Publication number: WO2009080581A1
Application number: PCT/EP2008/067509
Authority: WO
Inventors: Sune Sebastian Gyltner; Kristian Stetter
Original assignee: Intes A/S
Priority date: 2007-12-21
Filing date: 2008-12-15
Publication date: 2009-07-02
Also published as: DK200701861A; EP2235703A1; EP2235703B1; DK176996B1

Abstract

A fire detecting system (16) and method serves for early detection of fire. The system is of the kind comprising a first radiation sensitive semi-conductor (22a, 35a) for measuring a first radiation intensity at a first wavelength and emitted from an area susceptible of fire and creating a first output signal representing the first radiation intensity and at least one second radiation sensitive semi-conductor (22b, 22c, 35b, 35c) for measuring at least one second radiation intensity at at least one second wavelength and emitted from the area susceptible of fire and creating a second output signal representing the second radiation intensity. The fire detecting system (16) comprises, that the first radiation sensitive semi-conductor (22a, 35a) and the at least one second radiation sensitive semi-conductor (22b, 22c, 35b, 35c) are arranged in a predefined pattern, that the fire detecting system (16) has means for converting the first output signal into a first temperature indicating signal and the at least second output signal to at least one second temperature indicating signal, processor means for comparing the first temperature indicating signal with the at least second temperature indicating signal, serving as a control for the first temperature indication signal, a database (21) including ignitibility data of materials on a susceptible fire target, and compare means for comparing the temperature indication signals with the database.

Description

A fire detecting system and method for early detection of fire

The present invention relates to a fire detecting system of the kind comprising a first radiation sensitive semi-conductor for measuring a first radiation intensity at a first wavelength and emitted from an area susceptible of fire and creating a first output signal representing the first radiation intensity, and at least one second radiation sensitive semi-conductor for measuring at least one second radiation intensity at at least one second wavelength and emitted from the area susceptible of fire, and creating at least one second output signal representing the second radiation intensity.

Fires starts when both flammable and/or combustible material with an adequate supply of oxygen or another oxidizer is subjected to enough heat. Some common fire-causing sources of heat include e.g. a spark, another fire, e.g. an explosion, a cigarette or a lit match, thermal radiation, e.g. sun light, a flue, incandescent light bulb or a radiant heater.

Mechanical and electrical machinery may cause fire if combustible materials used on or located near the equipment are exposed to intense heat. Fire may propagate to an uncontrolled level and cause great damage to and destruct human life, animals plants and property. Hence, a fire can be of considerably costs, detrimental to environment and society and should be discovered as early as possible to avoid and ward off such damages and adverse effects.

Often hot-spots are not recognised before it is too late and the fire develops to the above mentioned stages in which considerable damage takes place.

Conventionally used technologies to recognise the early onset on fire include live video from the fire and exact temperature measurement over long distances, to save time and increase the reliability and safety in early fire detection.

Almost all objects or surfaces emit electromagnetic radiation, which intensity and spectral distribution depends on the body's temperature. Detectors for the near-infrared (NIR) spectral range of 750nm to 3000nm can detect thermal radiation from temperatures of approx. 300⁰C on surfaces. NIR radiation is reflected by most surfaces, and direct view on the flames is not necessary. For example NIR radiation is reflected or scattered by aerosols such as fog, smoke and dust. Therefore in many situations open fires can be localized through smoke.

This temperature is far below the limit at which the human eye can see radiation, the visible light (VIS) spectral range within about 400nm to 750nm of the electromagnetic spectrum to which the retina is sensitive. Open fire also emits in this range, and low-cost alarm systems for late detection are easy to realize in this wavelength range.

To look at wavelengths even longer than the NIR spectral range like the mid infrared (MIR) 3μm to 30μm makes it possible to register even lower temperatures. In this way potential fire sources can be detected long before they burst into open flames.

When using known camera-based fire surveillance based on NIR video images and processing, every pixel of an image is identified and used for precise localization of the potential fire source. Thermography in the NIR is used to provide temperature measurement of each single pixel within the video image. The shown object is displayed with precise temperature values for each point on the surface, and these information help to detect origins of fire before the flashpoint temperature is reached and therefore to prevent fire. The image acquisition takes place in a wavelength range invisible for the human eye and the image is transferred into a black and white video. Areas of unusual activity that may give reason to alarm are highlighted with certain colours, to simplify the situation judgment immense. For the detection of aerosols, the skilled observer can decide whether it is smoke, fog or dust based on the development over time. Based on the video images precise localization within a 3D room is possible. In case of a known topography the distance to the observed surface can be determined, as the direction of each pixel within the viewing angle is known. With a fixed installation of the surveillance system only one camera is necessary for an exact localization. This is mandatory for a targeted situation judgment and initiation of fire fighting activities. Is the fire source detected by two cameras at the same time, the precise localization is possible without further information. Therefore localization in three dimensions is possible even with moving objects within the surveillance area when multiple cameras are used.

The use of thermography combined with video images has many advantages. It ensures clear sight through dense smoke and allows search and rescue of humans as well as safe temperature measurement of objects close to the fire, however the technique requires continuous day-and-night surveillance to spot abnormalities and deviation from standard conditions, to safely distinguish between false temperature fluctuations and movements. If the observing person is inattentive just for at short period or is not sufficiently qualified to read the images the fire may develop anyway.

Artificial light, sunlight, controlled fire sources like lighters or Bunsen burners, industrial ovens, welding arcs, etc emits in the IR-range and may cause false-alarms.

US Patent No. 6,927,394 discloses a method for detecting flames. The method uses that false-alarm sources emit radiation in both the infrared and the visible wavelength ranges while potential fire sources emit in the visible wavelength range only. If radiation is found in both the infrared spectral range and in the visible spectral range, it is interpreted as a false alarm. The method involves comparison of the measured frequency spectra and known reference spectra from potential fire sources and radiation from false-alarm sources. The method monitors potential fire sources in a zone in a general manner and activate uncritical an extinguisher system, which e.g. sprinkles extinguishant all over the zone. In addition all machinery are turned off resulting in unnecessary great damage to the machines, longer closedown times of production resulting in high costs. Only the temperature is measured and this known method does not provide any measurements providing sufficient knowledge to enable target-directed and specific early fire extinguishing using fire extinguishants particularly suited for the purpose.

Hence, there is a need within the art of fire detection to provide alternative and safe measures to early fire detection.

In a first aspect according to the present invention is provided an early fire detection method and system of the kind mentioned in the opening paragraph by means of which enhanced security and huge costs savings can be obtained.

In a second aspect according to the present invention is provided an early fire detection method and system of the kind mentioned in the opening paragraph providing a high level of identification accuracy of the flammable and/or combustible material .

In a third aspect according to the present invention is provided an early fire detection method and system of the kind mentioned in the opening paragraph by means of which false alarms can be excluded to a higher degree than hitherto known. In a fourth aspect according to the present invention is provided an early fire detection method and system of the kind mentioned in the opening paragraph which can be tailored to a specific environment based on prior knowledge of the compositions of the materials used the environment.

In a fifth aspect according to the present invention is provided an early fire detection method and system of the kind mentioned in the opening paragraph wherein counteractive measures towards a fire can be initialized faster and much more targeted than hitherto known.

In a sixth aspect according to the present invention is provided an early fire detection method and system in which information of the material on fire is provided to the fire fighters prior to initiating extinguishing the fire.

The novel and unique features whereby this is achieved according to the present invention consists in that the fire detecting system comprises that the first radiation sensitive semi-conductor and the at least one second radiation sensitive semi-conductor are arranged in a predefined pattern, that the fire detecting system has means for converting the first output signal into a first temperature indicating signal and the at least second output signal to at least one second temperature indicating signals, processor means for comparing the first temperature indicating signal with the at least second temperature indicating signal, to provide a control for the first temperature indication signal, a database including ignitibility data of materials on a susceptible fire target, and compare means for comparing the temperature indication signals with the database. An optical system reproduces the zone on the radiation sensitive semi-conductors so that each area in the zone corresponds to one radiation sensitive semi-conductor or more.

Since the position of the radiation sensitive semi-conductors according to the present invention is arranged in a defined pattern the areas which the radiation sensitive semi-conductors monitor are also well-defined. Two radiation sensitive semiconductors are selected to monitor and register at two different wavelengths radiated from the same area and the results are compared to confirm if the registration are either a false alarm or a true alarm. Two radiation sensitive semiconductors situated at different spots in the pattern will monitor different areas in e.g. a room or an open place. When a potential fire source turns up in the area within a monitoring zone of one of the radiation sensitive semi-conductors it will send an alarm signal so that the extinguisher system can focus its resources in that area only. If e.g. extinguishant is sprinkled it is only sprinkled in that area and only electricity and heat sources, like machines, in that area are turned off. In this inventive way damages and tidying-up operations can be considerably reduced compared to a situation in which extinguishant is sprinkled all over an assembly of machinery. The production can be resumed early, cost of repair is low, and reduction of income is kept at a minimum. It is even possible to have the production line going in spite of the incident in one part of the zone that is not close to the incident, which further minimizes economical loss.

Within the scope of the present invention in the following the term black body means an object that absorbs all electromagnetic radiation that falls onto it. No radiation passes through it and none is reflected, which make black bodies ideal sources of thermal radiation. The amount and spectrum of electromagnetic radiation they emit is directly related to their temperature. Black bodies below around 43O⁰C produce very little radiation at visible wavelengths and appear black. Black bodies above this temperature produce radiation at visible wavelengths starting at red, going through orange, yellow, and white before ending up at blue as the temperature increases.

Hence, a body emits broadband radiation due to its temperature, so-called blackbody radiation, the hotter the object the higher the radiation. The centre of the radiation is also blue shifted with higher temperature of the blackbody. The intensity of a radiation sensitive semi-conductor, which responds to a known wavelength from a blackbody can be transformed to a temperature that is the temperature of the blackbody. A second radiation sensitive semi-conductor measuring at another wavelength will register another intensity but when transformed into temperature will indicate the same temperature, unless the registered radiation is not from a blackbody or there is some fault in the fire detecting system.

The air absorbs radiation at some IR wavelength ranges. This must be considered when selecting the measuring wavelengths, i.e. the first wavelength and the at least one second wavelength. A radiation sensitive semi-conductor that measures the radiation from an object at a wavelength where air absorbs will return an output signal corresponding to a too low temperature. Therefore, the wavelengths where the radiation sensitive semi-conductors respond should be chosen to be in the ranges where the gas molecules in air do not absorb.

If the two radiation sensitive semi-conductors indicate the same temperature, the temperature is compared with the known ignitibility temperature of the material in the monitored zone, area or room. A temperature, e.g. 200⁰C, is critical if the object is paper while there is no need to send an alarm signal if a piece of metal have reached that temperature. In an advantageously embodiment of the present invention the pattern can be selected from the group comprising a 2- dimensional array, a 3-dimensional array, concentric circles, polygons or arbitrary order. How the radiation sensitive semi- conductors are organised is less important as long as their positions within the pattern are known together with information of from which area each radiation sensitive semiconductors detects radiation.

In a preferred embodiment of the invention the radiation sensitive semi-conductors can be selected from the group comprising photo diodes, PIN diodes, CMOS circuits, bolometer or CCD chips and combination of these. Anything that is photosensitive could be used as e.g. photodiodes like PIN diodes. In a photosensitive CMOS the photodiodes are prearranged in a defined array where the amount of radiation that reaches each photodiode can be read out. If a very high detecting level is required a liquid nitrogen cooled CCD chip is especially preferred.

The inventive fire detecting system is particularly suited to use radiation sensitive semi-conductors that can measure in the wavelength range from about 200nm to about 3,500nm. To detect the potential fire source early, the MIR spectral range from 3μm to 30μm is best suited. But to avoid that the air absorbs some of the radiation it is better to measure in the wavelength range between 8μm and 14μm. There are other sources that emit radiation in this spectral range without being potential fire sources, such as artificial light, sunlight, lighters or Bunsen burners, industrial ovens, welding arcs, etc. In addition these potential fire sources also emit radiation in the visible spectral range. A detector responding to a wavelength in the visible spectral range from 400nm to 750nm can determine that it is not a potential fire source since it emits in both the MIR and visible range. If the fire detecting system is to monitor a very well illuminated zone or an outdoor place during a sunny day visible radiation from a false-alarm source is drowned by the background visible radiation. To sort out a welding arc as a false-alarm source it is better to use a radiation sensitive semi-conductor that responds to a wavelength in the ultraviolet (UV) spectral range from 200nm to 400nm since such an arc is a strong UV radiation emitter. In many factory zones fluorescent lamps are used as illumination. They emit relatively little radiation in the infrared range. In a zone very illuminated with fluorescent lamps the radiation sensitive semi-conductors used for reference and control can advantageously be chosen to respond to radiation in the NIR spectral range from 750nm to 3000nm.

The means for converting an output signal into a temperature indicating signal, the processor means and the compare means preferably may expediently include a control unit in the form of e.g. a microprocessor, a field-programmable gate array (FPGA) or a programmable logic controller (PLC) and appropriately designed software-programs. The control unit and the software-programs are designed and configured to process the output signal from the radiation sensitive semi-conductors, converting the output signal to a temperature indicating signal, comparing the temperature indicating signals, and to fetch data about the location in the zone of different materials and the ignition temperature of the material in the monitored area, to compare the temperature indicating signal and the ignition temperature of the material in the monitored area and react to the result by issuing an alarm.

The fire detecting system can in a preferred embodiment according to the present invention comprise at least one gas detector. The system resembles that of the fire detecting system. An optical system reproduces different areas of the zone onto the photoactive components which are radiation sensitive semi-conductors organized in a known pattern like an array. The gas detector uses in a first embodiment the blackbody radiation from the background like the walls, floor and the machines as a radiation source. If a gas evolves e.g. due to heated plastic the gas molecules from the plastic will absorb at some wavelengths characteristic of the gas molecules.

The fire detecting system can in yet a further preferred embodiment include in the database, data representing the wavelengths at which at least some gases absorb radiation. The database enables the specification of the heated gas molecules. The database can further comprise detailed information from which plastic said gas molecules originate. If also the temperature at the area of the heated plastic is measured it is possible to determine how close to the ignition point the temperature is. If the wavelengths for e.g. CO are recorded in the database the gas detector can send an alarm that there is a poisonous gas in the zone. Especially for CO it can be important since it does not smell. Other important gases could include the gas dioxin.

The fire detecting system can advantageously comprise an external radiation source. The detection limit will increase so that lower concentrations can be detected.

If there is more than one gas detector and they are situated at two different places they will look across each other and the system can reproduce a three-dimensional picture of the distribution of gases in e.g. a monitored zone, room or area.

In an embodiment of the invention the fire detecting system can comprise a spark detector with a response time faster than or around 8 ms and with a sensitivity lower than or around 1.1 mW/cm². To detect the sparks it is only possible to monitor closed environments where there is no external light. In such an environment where dry materials are transported a spark detector is useful. The woodworking industry where the sawdust or wood chips are sucked in transportation pipes is one example. In all forms of treatment of materials dust is created, which can be ignited by a spark. This is the case in the steel industry and the flour milling industry. Fluids with a low flash point in the form of a spray can easily be ignited by a spark. Such an environment can be found in painting industry, printing industry, petroleum refinery, semi-conductor production, etc. What is most important is that the fire detecting system according to the present invention reacts really fast. Therefore it is preferred to keep electronic analysis simple and fast, to increase the reaction time. This further means that there is not time for detailed investigating whether the fire alarm is due to a false-alarm source. The spark detector may advantageously consist of many radiation sensitive semi-conductors that monitor different areas of the zone or area susceptible to fire. Only machines in the area corresponding to the radiation sensitive semi-conductor that sends an alarm are shut down and extinguishant is only sprinkled in that same area. In this way the damage and production losses are kept low. This can be a huge benefit if there are many false alarms.

In another embodiment of the invention the fire detecting system can comprise a smoke detector. The smoke detector reads the signal from a radiation source. A radiation source is placed at each area that is monitored by a radiation sensitive semi-conductor. If in such area smoke starts to evolve the smoke will scatter and absorb the radiation until there is no light entering the smoke detector. Again the fire detecting system knows where the potential fire source is situated and the fire preventing measures can be localised.

In yet another embodiment of the invention the fire detecting system can comprise a temperature sensor. The temperature sensor can e.g. be a bolometer. The invention also relates to a method for detecting fire using the fire detecting system according to the present invention.

The method comprises the steps of, storing in a database on a control unit ignition temperatures of at least some materials localized in an area susceptible of fire, measuring radiation intensity from at least one point in the area at a first specified wavelength by a first radiation sensitive semiconductor returning a first output signal, measuring radiation intensity from the at least one point in the area at at least one second specified wavelength by at least one second radiation sensitive semi-conductor returning at least one second output signal, converting the returned first output signal from the first radiation sensitive semi-conductor measured at the first wavelength into a first temperature indicating signal, converting the at least second output signal from the at least one second radiation sensitive semi-conductor measured at the at least one second wavelength into at least one second temperature indicating signal, comparing the first temperature indicating signal with the at least one second temperature indicating signal, and determining a first difference value, and if first difference value is less than a first predefined difference value then, comparing the first temperature indicating signal with the database ignition temperature of the material in the monitored area and a second difference value is determined, and if the second difference value is below a second predefined difference value an alarm signal is sent.

By means of these steps it is possible to detect fires at a very early stage and to target the fire extinguishing procedure to the materials and compositions located in a specific zone. When the alert or alarm is send to the fire station the fire fighters are able to take specific precautions as to extinguishing means and what to wear prior to leaving the fire station. Hence the fire fighters will be able to prepare themselves to the fire by using the inventive target directed effective fire extinguishing method above.

In the preferred embodiment the first predefined difference value is chosen to be lower than or around 1O⁰C. This temperature has been established as the lower limit which defines a reasonable discrimination limit for false alarms.

In a modified expedient embodiment, the method according to the present invention is specifically adapted to treat fires involving combustible gases or gas generation qualified.

To this aspect the method comprises the steps of, storing in a database on a control unit absorption wavelengths of a plurality of gas molecules, measuring radiation intensity from at least one zone in the area at at least one absorption wavelength of the at least one monitored gas molecule by a first radiation sensitive semi-conductor returning an absorption output signal, measuring radiation intensity from the at least one zone in the area at at least one non- absorption wavelength of the at least one monitored gas molecule by at least one second radiation sensitive semiconductor returning at least one non-absorption output signal, comparing the at least one absorption output signal with the at least one non-absorption output signal and determining whether there is a difference between at least one absorption output signal and the at least one non-absorption output signal that is due to absorption, and sending an alarm signal if the difference is due to absorption.

The method may advantageously further comprise the step of, converting the temperature corresponding to the first temperature indicating signal to an intensity for at least one absorption wavelength of at least one gas molecule into a first database intensity, measuring the radiation intensity from the at least one area in the zone at at least one absorption wavelength of the at least one monitored gas molecule by at least one second radiation sensitive semi-conductor returning at least one absorption output signal, comparing the at least one absorption output signal with the at least one first database intensity and if the relation between the absorption output signal and the first database intensity for the wavelength characteristic of at least one gas molecule is less than a third predefined relation value, then sending an alarm signal .

Using the method minimizes the risk of explosion and that persons get poisoned by gas formations. Again the fire fighter is able to take considerate precautions and the gas formations may even be realized in such an early stage that no fire occur at all.

This part of the invention may advantageously be used in manufacturing processes in which undesired gasses can evolve during the manufacturing process.

The invention will be explained in greater detail below, describing preferred embodiments with reference to the drawings, in which

fig. 1 shows the blackbody radiation from two bodies at 900⁰C and 1000⁰C, respectively,

fig. 2 shows the transmission of radiation through air,

fig. 3 shows schematically a block diagram of a first embodiment of a fire detecting system according to the present invention, and

fig. 4 shows a detailed circuitry of a part of the hardware of a preferred embodiment of a fire detecting system according to the invention, Fig. 1 illustrates two blackbody radiation curves from two different bodies. Curve 1 and curve 2 show the spectral radiation intensities from two different bodies at 37⁰C and at 100⁰C as a function of wavelengths, respectively. Curve 1 and curve 2 are similar in appearance but curve 1 has its maximum radiation at around 9000nm while curve 2 is a little blue- shifted with a maximum at around 7500nm. The radiation intensity of curve 2 is higher in the whole spectral range than the radiation intensity of curve 1.

The Planck's radiation law describes the radiation intensity from a blackbody as a function of wavelength and temperature:

2hc^z

/ = _/j5 _hc_

in which h is Planck's constant, c is the speed of light, λ is the wavelength, k is Boltzmann's constant and T is the temperature .

From formula (I) follows that the radiation £ from a body with an even higher temperature will show a spectrum with a maximum, which is further blue-shifted, and where the radiation intensity is higher for all wavelengths. The Planck's radiation law relates at a specified wavelength the intensity of the emitted radiation from a material to a certain temperature, thus measuring the intensity at a certain wavelength determines the temperature.

In vacuum, the radiation intensity emitted from a blackbody will be the same as the measured radiation intensity in the whole wavelength range. But in air, the gas molecules in air will absorb radiation at some wavelength ranges, which is shown in fig. 2. There is a first absorption peak 3 or dip in the transmission spectrum at around 1.3μm, a second absorption peak 4 at around 1.9μm, a third absorption peak 5 at around 2.7μm, a fourth absorption peak 6 at around 4.4μm, a fifth absorption peak 7 at around 5.8μm and a sixth absorption peak 8 at around 6.7μm. The fifth 7 and sixth 8 absorption peaks overlap and form a unit absorption band 9. Between these absorption peaks 3,4,5,6,7,8 or dips in the transmissions there are in the IR range for wavelengths up to 15 μm, six ranges where the absorption of air is low. The widest range 10 is between 8μm and 14μm. A second range 11 of low air absorption is identified from 4.8μm to 5μm, a third 12 from 3.2μm to 4.1μm 12, a fourth 13 from 2μm to 2.3μm 13, a fifth 14 from 1.5μm to 1.8μm, and a sixth 15 from 0.750μm to l.lμm. The limit 0.750μm is not due to absorption but due to that the visible range starts. Only in the wavelength ranges 10 to 15 the measured intensity at a certain wavelength determines the temperature.

Fig. 3 shows a block diagram of a preferred embodiment of a fire detecting system 16. At installation a computer (not shown) communicates through the programming interface 17 and electronic connection 18 with control unit 19. The programming interface could in another embodiment be wireless. Data is entered into the computer and transferred through the programming interface 17 and electronic connection 18 to the control unit 19, which stores data for used in the inventive method in a random access memory (RAM) 21. The data include among others the type and distribution of the materials in the monitored zone, in particular the ignition temperatures of said materials, the areas of the zone monitored by the radiation sensitive semi-conductors, the radiation wavelengths each radiation sensitive semi-conductor responds to and a first predefined difference value as well as second predefined difference values identifying the materials of relevance. The meaning of the first predefined difference value and second predefined difference values are explained in further detail below. From the database 20 the control unit 19 fetches data about ignition temperatures of materials in the monitored zone. The ignition temperatures of the materials in the monitored zone and the distribution of the materials in said zone is in the following detailed description commonly denominated "first database data". This is in no way intended to limit the understanding that many more data are included in the database.

If the materials in the monitored zone are changed e.g. by introducing new machines, or an extra pattern, e.g. an array, of radiation sensitive semi-conductors is introduced, these data is entered into the computer and transferred through programming interface 17 and electronic connection 18 to the control unit 19 that stores the new information in the RAM 21.

A sensor unit 22 include three radiation sensitive semiconductors 22a, 22b and 22c respond to radiation by sending electrical analogue output signals through the electrical connections 23a, 23b and 23c to the A/D converter 24, which can if preferred by arranged in the control unit 19. The sizes of the currents of the output signals are measures of the intensity of the radiation at the measured wavelengths. The A/D converter 24 converts the analogue output signals to digital output signals and sends them through electronic connections 27a, 27b and 27c to the control unit 19. The control unit 19 comprises means (not shown) to convert the digital output signals into digital temperature indicating signals. The control unit 19 fetches information about to which wavelengths each radiation sensitive semi-conductors 22a, 22b and 22c respond. The control unit 19 stores the digital temperature indicating signals in the RAM 21. The digital temperature data indicating signals and from which areas each digital temperature indicating signal is measured are in the following description denominated "first measured data". The control unit 19 comprises means to compare the digital temperature indicating signals converted from the digital output signals measured by different radiation sensitive semiconductors at different wavelengths but at the same area. According to Planck's radiation law (I) the temperature should be the same. If the difference of the digital temperature indicating signals from the measurements at the same area is less than the first predefined difference value the radiation is due to blackbody radiation and the measured temperature is deemed to be the temperature of the body. This means that the measured temperature can be compared to e.g. ignition temperature. If the difference is higher than the first predefined difference value the radiation is partly caused by radiation not from a blackbody, or a fault has occurred in the measurements or in the signal treatment. The measurements from that area are not considered until measurements indicate radiation from a blackbody. A notification or error message, alert or an alarm may by triggered according to the factual need and circumstances.

The control unit 19 comprises means to compare the first measured data and the first database data, thereby comparing temperature in an area from the first measured data with the ignition temperature of the material in the area from the first database data. If the difference is not less than the second predefined difference value for the material the situation is not interpreted to be threatening and no action is performed. If the difference between the temperatures is less than the second predefined difference value for the material an alarm signal is sent. The alarm signal is sent through the electronic connection 25 to an alarm diode 26 that can be a light emitting diode. An alarm signal is also sent through the bus 28 to an external fire alarm or to an extinguisher system that will turn off the electricity and the machines situated in the area and e.g. sprinkle extinguishant in the area. Both the electronic connection 25 and the bus 28 can be wireless connections. The address of the fire detecting system 16 is set manually from the outside of the fire detector through the address dipswitch 29 in connection with the control unit 19 through electronic connection 30. A power supply 31 powers the control unit 19 through electrical connection 32.

In one embodiment the function dipswitch 33 is used to manually change the function of the fire detecting system to a gas detecting system or to a smoke detecting system. The function dipswitch is connected with the control unit 19 through electronic connection 34.

If the fire detector is used as a gas detector the procedure resembles the procedure described for the fire detector. The gases can e.g. be part of or used during a production, processing or refining in the industry, be created if something in the production, processing or refining goes wrong, or be created during burning of materials in the monitored room. Measured gas identification data are entered on the computer and transferred through the programming interface 17 and electronic connection 18 to the control unit 19, which stores the data in a RAM 21 situated in the control unit. Also data identifying the areas of the monitored room, which the radiation sensitive semi-conductors monitor, which radiation wavelength each radiation sensitive semi-conductor responds, and the first predefined difference value and a third predefined relation value. The meaning of the third predefined relation value is explained below. From the database the control unit 19 fetches data about the absorption wavelengths of the gases to be monitored in a manner similar to the described above for the fire detecting system.

It is important that some of the radiation sensitive semi- conductors are selected to have response wavelengths at the absorption wavelengths of the gases studied and of interest and others are chosen not to have response wavelengths at the absorption wavelengths of these gases. Walls, floor, ceiling and machines etc., all emit room temperature blackbody radiation. Curve 1 in fig.l illustrates the spectral distribution of the radiation at nearly room temperature. If the machines are hot the machines will of course emit a more intense and more blue shifted blackbody radiation.

When a gas turns up in the monitored room it will be seen as dips in the blackbody radiation spectrum from the objects behind the gas seen from the detector. The wavelengths of the dips are the characteristic wavelength for the absorption peaks of the gas. The relative size of the dips in the blackbody radiation spectrum corresponds to the relative heights of the different absorption peaks and can be used to further confirm the presence of the gas.

The radiation sensitive semi-conductors 22a, 22b and 22c, respond to radiation by sending electrical analogue output signals through the electrical connections 23a, 23b and 23c to the A/D converter 24, in the present embodiment situated in the control unit 19. The sizes of the currents of the output signals are measures of the intensity of the radiation at the measured wavelengths. The A/D converter 24 converts the analogue output signals to digital output signals and sends them through electronic connections 27a, 27b and 27c to the control unit 19.

The control unit 19 fetches information about to which wavelengths each radiation sensitive semi-conductors 22a, 22b and 22c respond. The control unit 19 parts the digital output signals in two categories, where the first category comprises the digital output signals measured by radiation sensitive semi-conductors responding to wavelengths not at the absorption wavelengths of the gases studied and the second category comprises the digital output signals measured by radiation sensitive semi-conductors responding to wavelengths at the absorption wavelengths of the gases studied.

The control unit 19 comprises means to convert the digital output signals of the first category into digital temperature indicating signals. The control unit 19 stores the first category of digital temperature indicating signals and the second category of digital output signals in the RAM 21. The data about the digital temperature indicating signals from the first category and from which areas each digital temperature indicating signal from the first category is measured are in the following description denominated "second measured data". The data about the digital output signals from the second category and from which areas each digital output signal from the second category is measured are in the following description denominated "first measured intensity".

The control unit 19 comprises means to compare the digital temperature indicating signals from the second measured data converted from the digital output signals measured by different radiation sensitive semi-conductors at different wavelengths but at the same area. According to Planck's radiation law (I) the temperature should be the same. If the difference of the digital temperature indicating signals from the first category from the measurements at the same area is less than the first predefined difference value the radiation is due to blackbody radiation and the measured temperature is deemed to be the temperature of the body, in the following denominated "first measured temperature". If the difference is higher than the first predefined difference value the radiation is partly caused by radiation not from a blackbody, or a fault has occurred in the measurements or in the signal treatment. The measurements from that area are not considered until measurements indicate radiation from a blackbody. A notification or error message, alert or an alarm may by triggered according to the factual need and circumstances. The control unit 19 converts the first measured temperature into intensities according to Planck's radiation law (I) for each stored wavelength at which the studied gases absorb. These intensities and corresponding wavelengths are in the following denominated "first database intensities".

The control unit 19 comprises means to compare the first measured intensities and the first database intensities so the radiation intensities at a wavelength from the first measured intensities are compared to the radiation intensities at the same wavelength from the first database intensities and their relation is calculated.

If the relation is less than the third predefined value for the material the situation is not interpreted to be threatening and no action is performed. If the difference between the temperatures is not less than the third predefined value for the material an alarm signal is sent. The alarm signal is sent through the electronic connection 25 to an alarm diode 26 that can be a light emitting diode. An alarm signal is also sent through the bus 28 to an external gas alarm or to e.g. ventilation system that will blow in fresh air or soak the gas out and maybe turn off the electricity and the machines situated in the area if the gas is explosive.

Fig. 4 discloses an example of the configuration of the fire detection system 16 shown in fig. 3 in more detailed, with three radiation sensitive semi-conductors 35a, 35b and 35c. Electrical connections 36a, 36b and 36c forward the electrical output signals from the radiation sensitive semi-conductors to amplifiers 37a, 37b and 37c, respectively. The amplifiers have a negative feedback to avoid oscillation and temperature drift. A circuit 38 with a zener diode 39 keeps the voltage that supplies the amplifiers through electrical connection 40 constant, to give stable amplification. The subcircuit 38 feeds a control unit 41 with a high and a low stable reference potentials through electrical connections 42 and 43, respectively. Electrical connections 44a, 44b and 44c connect three amplifiers with low pass filters 45a, 45b and 45c. Electrical connections 46a, 46b and 46c direct the output signals to the control unit 41. To the control unit is connected an external 8GHz oscillator 47, which functions as the clock for the control unit 41. The power supply (not shown) feeds the control unit through electronic connection 48. A switch function 49, used to switch the detector between the functions fire detector, gas detector and smoke detector is attached by electronic connections 50a, 50b, 50c and 5Od to the control unit at four pins. The switch in one embodiment is done manually by a dipswitch.

A programming interface 51 is used to enable the communication between the control unit and a computer. It consists of a JTAG port 52 that is connected to the control unit 41 through electronic connection 53a, 53b, 53c, 53d and 53e.

Claims

1. A fire detecting system (16) of the kind comprising a first radiation sensitive semi-conductor (22a, 35a) for measuring a first radiation intensity at a first wavelength and emitted from an area susceptible of fire and creating a first output signal representing the first radiation intensity and at least one second radiation sensitive semi-conductor (22b, 22c, 35b, 35c) for measuring at least one second radiation intensity at at least one second wavelength and emitted from the area susceptible of fire and creating a second output signal representing the second radiation intensity, characterised in that the fire detecting system (16) comprises, - that the first radiation sensitive semi-conductor (22a, 35a) and the at least one second radiation sensitive semiconductor (22b, 22c, 35b, 35c) are arranged in a predefined pattern,

- that the fire detecting system (16) has means for converting the first output signal into a first temperature indicating signal and the at least second output signal to at least one second temperature indicating signal,

- processor means for comparing the first temperature indicating signal with the at least second temperature indicating signal, serving as a control for the first temperature indication signal,

- a database (21) including ignitibility data of materials on a susceptible fire target, and - compare means for comparing the temperature indication signals with the database.

2. A fire detecting system (16) according to claim 1, characterised in that the pattern is selected from the group comprising a 2-dimensional array, a 3-dimensional array, concentric circles, polygons or arbitrary order.

3. A fire detecting system (16) according to claim 1, characterised in that the radiation sensitive semiconductors (22a, 22b, 22c, 35a, 35b, 35c) are selected from the group comprising photo diodes, PIN diodes, CMOS circuits, bolometer or CCD chips and combination of these.

4. A fire detecting system (16) according to claim 1, characterised in that the radiation sensitive semi- conductors (22a, 22b, 22c, 35a, 35b, 35c) measure in wavelength range from about 200nm to about 30μm.

5. A fire detecting system (16) according to claim 1, characterised in that the means for converting an output signal into a temperature indicating signal, the processor means and the compare means include a control unit (19,41) and software-programs.

6. A fire detecting system (16) according to any of the preceding claims 1 - 5 characterised in that the fire detecting system (16) further comprises at least one gas detector .

7. A fire detecting system (16) according to claim 6, characterised in that the database (21) includes data representing the wavelengths at which at least some gases absorb radiation.

8. A fire detecting system (16) according to claim 6, characterised in that the fire detecting system (16) has an external radiation source.

9. A fire detecting system (16) according to claim 6, characterised in that the fire detecting system (16) comprises a spark detector with a response time faster than or around 8 ms and with a sensitivity lower than or around 1.1 mW/cm².

10. A fire detecting system (16) according to claim 6, characterised in that the fire detecting system (16) comprises a smoke detector.

11. A fire detecting system (16) according to claim 6, characterised in that the fire detecting system (16) comprises a temperature sensor.

12. A method for detecting fire using the fire detecting system (16) according to any of the preceding claims 1 - 11, characterised in that the method comprises the steps of, storing in a database (20) on a control unit (19,41) ignition temperatures of at least some materials localized in an area susceptible of fire, measuring radiation intensity from at least one area in the zone at a first specified wavelength by a first radiation sensitive semi-conductor (22a, 35a) returning a first output signal, measuring radiation intensity from the at least one area in the zone at at least one second specified wavelength by at least one second radiation sensitive semi-conductor

(22b, 22c, 35b, 35c) returning at least one second output signal, converting the returned first output signal from the first radiation sensitive semi-conductor (22a, 35a) measured at the first wavelength into a first temperature indicating signal, converting the at least second output signal from the at least one second radiation sensitive semi-conductor

(22b, 22c, 35b, 35c) measured at the at least one second wavelength into at least one second temperature indicating signal, comparing the first temperature indicating signal with the at least one second temperature indicating signal, and determining a first difference value, and if first difference value is less than a first predefined difference value then, comparing the first temperature indicating signal with the database ignition temperature of the material in the monitored area and a second difference value is determined, and - if the second difference value is below a second predefined difference value an alarm signal is sent.

13. A method according to claim 12 characterized in that the first predefined difference value is chosen to be lower than or around 1O⁰C.

14. A method for detecting fire according to claim 12 characterized in that the method comprises the steps of,

- storing in a database (20) on a control unit (19,41) absorption wavelengths of a plurality of gas molecules,

- measuring radiation intensity from at least one area in the zone at at least one absorption wavelength of the at least one monitored gas molecule by a first radiation sensitive semi-conductor (22a, 35a) returning an absorption output signal, measuring radiation intensity from the at least one area in the zone at at least one non-absorption wavelength of the at least one monitored gas molecule by at least one second radiation sensitive semi-conductor (22b, 22c, 35b, 35c) returning at least one non-absorption output signal,

- comparing the at least one absorption output signal with the at least one non-absorption output signal and determining whether there is a difference between at least one absorption output signal and the at least one non- absorption output signal that is due to absorption, and — sending an alarm signal if the difference is due to absorption .

15. A method for detecting fire according to any of the preceding claims 12, 13 or 14, characterized in that the method further comprises the step of, converting the temperature corresponding to the first temperature indicating signal to an intensity for at least one absorption wavelength of at least one gas molecule into a first database intensity, measuring the radiation intensity from the at least one area in the zone at at least one absorption wavelength of the at least one monitored gas molecule by at least one second radiation sensitive semi-conductor (22b, 22c, 35b, 35c) returning at least one absorption output signal, comparing the at least one absorption output signal with the at least one first database intensity and if the relation between the absorption output signal and the first database intensity for the wavelength characteristic of at least one gas molecule is less than a third predefined value, then

- sending an alarm signal.