Flame Detector for Your Application
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MSA’s Guide to Selecting the Right Flame Detector for Your Application INNOVATION IN employing scientific disciplines (IR) bands. Figure 2 schematically such as physical chemistry, shows a typical hydrocarbon fire FLAME DETECTION physics, electro-optics, emission spectrum where UV and electromagnetic physics, IR spectral bands are "highlighted" ndustries involved in electromagnetic spectral analysis to show the spectral ranges that Imanufacturing, processing, and thermodynamics. This Guide are usually selected for existing storing or transportation of describes an innovative approach flame detectors. flammable material are constantly to flame spectral analysis that has in need of reliable and fast led to the development of a The flame radiation spectral response fire detection systems. unique multipurpose Infrared-type pattern, being unique, allows It is evident that the smaller the (IR) flame detector. several spectral ranges to be fire, when detected, the easier it employed in the various detection is to extinguish. In this respect, BACKGROUND FOR devices. Flame detectors usually fire detection systems, especially utilize optical sensors working at optical flame detectors, are the FIRE DETECTION specific spectral ranges (usually most powerful apparatus in fire narrow band) that record the fire scenario can be analyzed fighting due to their ability to incoming radiation at the selected by several approaches, remotely detect a small fire from A wavelengths. The signals recorded a long distance. depending on the monitored by the sensor are then analyzed parameters such as fuel according to a predetermined It may seem simple and straight consumption, oxygen/air technique that includes one or forward to design a sensitive consumption, heat evolving or more of the following: optical flame detector by utilizing chemical reactions taking place in Ultraviolet (UV), Infrared (IR) or a the vaporized fuel zone. Figure 1 1. Flickering frequency combination of UV/IR sensors. describes the anatomy of a analysis However, these detectors often hydrocarbon fire where the 2. Threshold energy signal operate in industrial environments vaporized fuel is dispersed in the comparison which contain many radiation surrounding atmosphere where it 3. Mathematical correlation sources that could impair detector immediately reacts with oxygen between several signals performance and even cause and the flame chemical chain 4. Comparison techniques false alarms. Moreover, many reaction takes place to give off (Ration, AND gate, OR gate applications require flame gaseous products such as CO2, techniques) detectors to withstand harsh H2O, HC - (unburned environmental conditions and still hydrocarbon molecules), C 5. Correlation to memorized maintain their entire envelope of (Soot), CO. Fire detection spectral analysis performance. technologies throughout the years Detection devices using several of have relied on these factors for the above-mentioned techniques Most applications for optical flame the developing detection devices. detectors are "High Risk - High promise to be most reliable with Value", that require detectors to OPTICAL FLAME respect to detection sensitivity be designed, qualified and versus immunity to false alarms. manufactured according to DETECTION sophisticated and advanced Four major families of optical methods to ensure the installed he energy radiated from a fire detectors have emerged in the product is reliable. Tserves as a major factor in it's last 20 years. detection analysis. 30% - 40% of 1. UV Detectors These requirements have this energy is dissipated in the 2. IR Detectors accelerated the technology race form of electromagnetic radiation to research and develop new at various spectral ranges, such as 3. UV/IR Detectors approaches to fire detection Ultraviolet (UV), visible, infrared 4. IR/IR Detectors Guide to Selecting the Right Flame Detector for Your Application AnatomyAnatomy ofof aa FirFiree Figure 1. Guide to Selecting the Right Flame Detector for Your Application Each of these detector families The occurrence of random UV mathematical techniques are uses one or several of the radiation from sources such as employed. The most accepted are parameter analyses listed lightning, arc welding, radiation flickering analysis and narrow previously, and employ the most and solar radiation (which are not band IR threshold signals advanced optical sensors at the absorbed by the atmosphere due processed in the IR 4.1um-4.6um specific spectral wavelengths. to holes in the ozone layer and wavelengths. These IR detectors However, each family of detectors solar bursts) cause false alarms are still subject to false alarms is recommended for use only in in UV detectors. caused by blackbody radiation specific applications. These (heaters, incandescent lamps, applications are usually IR FLAME halogen lamps plus others). determined by evaluating to what DETECTION extent false alarms caused by In order to minimize or eliminate false alarms, dual wavelength environmental stimulus could nfrared radiation is present in technology has been adopted for create major problems. most flames (as can be seen I optical flame detection. UV FLAME from Fig 2). The flame temperature, its mass of hot This dual wavelength technology DETECTION gases (fire products), emit a has two major branches: specific spectral pattern that can he UV spectral band, because be easily reorganized by 1. UV/IR Spectral Bands Tof shortwave characteristics, employing IR sensor technology. 2. IR/IR Spectral Bands is absorbed in the surrounding atmosphere by air, smoke, dust, However, the flames are not the In recent years dual spectral gases and various organic only source of IR radiation and detection was considered the materials. Hence UV radiation any hot surface such as ovens, most advanced method to cope dispersed in the atmosphere, lamps, incandescent halogen with false alarms. especially at wavelengths shorter lamps, furnaces, solar radiation, than 300 nm (the solar blind emit IR radiation which coincides UV/IR FLAME spectral band), is being absorbed with the flame IR radiation DETECTION by the surrounding atmosphere wavelengths. and will not create false alarms on he dual spectrum UV/IR these flame detectors. UV DUAL WAVELENGTH Ttechnology employs a solar detectors based on this technology DETECTION blind UV sensor, with a high signal are detecting flames at high speed to noise ratio and a narrow band (3-4 milliseconds) due to the UV n order to discern the flames' IR sensor. The UV sensor itself is high energy radiation emitted by I"spectral signature" from other a good fire detector but is easily fires and explosions at the instant IR source spectral signatures, activated by alarm stimuli such as of their ignition. various parameter analysis and welding, lightning, Xrays and solar Figure 2. Guide to Selecting the Right Flame Detector for Your Application spikes. To prevent false alarms channel, thus impairing its ability caused by these sources, the IR to detect a fire. • Flickering analysis sensing channel was added. The • Radiation intensity IR spectral channel has a spectral Further discrimination relating to above a certain threshold the percentage of time each signal signature characteristic to fire in The ratio between both signals is present using "windows" where • addition to the fire's UV flame received at the 2 sensors detector spectral signature and the UV signals are counted together serve as a reliable continuously, enable elimination of Since most of these dual IR detector for most mid-range strong signals not emitted by detectors use the 4.3um sensor as applications. Even this advanced actual fires. Comparable their main channel for fire technology has limitations, since techniques using "AND-gate" recognition (where the CO2 each type of fire has its own methods, process the UV and IR emission peak exists), they suffer specific ratio of UV to IR output. signals received by both sensors from atmospheric attenuation, in the detector, thus ensuring the especially on long range detection For example, a hydrogen flame accuracy of these detectors. applications. generates a high amount of UV radiation with very little IR, while a IR/IR FLAME ADVANCED coal fire generates little UV DETECTION radiation and a high amount of IR TECHNIQUES FOR radiation. Since the dual UV/IR nother dual wavelength FLAME SPECTRAL detector combines both signals to Atechnology combines two ANALYSIS an “AND-gate", there could be a narrow spectral ranges in the near fire that will not be detected. To IR spectral band. Since the ach of the previously ensure the reliability of the fire hydrocarbon flames emit energy of described detection methods signal, a discriminating circuit E a continuous nature in the near IR has drawbacks. It is evident that compares the UV radiation (0.9um - 3.0um) and a unique classic fire analysis methods are threshold signal, the IR threshold peak at the 4.3um -4.5um (caused insufficient for some applications. signal, and their ratio, as well as by the hot CO fire product) these The development of electro-optic their flickering mode. 2 features are the "heart" of most technology enables advanced dual IR detectors. Common dual The fire alarm is confirmed only techniques for performing deeper IR flame detectors employ two when all parameters satisfy the and more comprehensive spectral narrow bands 0.9um and 4.3um, detection mathematical algorithm. analysis. for fire signal analysis. In industrial environments the The spectrum of flame radiation sources for false alarms