| Ultra low power ndir carbon dioxide sensor fire detector -> Monitor Keywords |
|
|
 
Ultra low power ndir carbon dioxide sensor fire detectorRelated Patent Categories: Radiant Energy, Invisible Radiant Energy Responsive Electric Signalling, Infrared Responsive, With Means To Transmission-test Contained Fluent MaterialUltra low power ndir carbon dioxide sensor fire detector description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070114420, Ultra low power ndir carbon dioxide sensor fire detector. Brief Patent Description - Full Patent Description - Patent Application Claims
FIELD OF THE INVENTION [0001] The present invention is in the field of gas analysis and more particularly relates to an ultra low power Carbon Dioxide (CO.sub.2) sensor designed to be used as a compact, reliable, low cost, fast responding and false alarm resistant fire detector. BACKGROUND OF THE INVENTION [0002] The Non-Dispersive Infrared ("NDIR") technique has long been considered as one of the best methods for gas measurement. In addition to being highly specific, NDIR gas analyzers are also very sensitive, stable, reliable and easy to maintain. The major drawback of the NDIR gas measurement technique has been its relatively expensive implementation and high power consumption. [0003] Ever since the NDIR technique of gas measurement was first introduced and practiced in the mid 1950's, a large number of improved measurement techniques based upon the NDIR principle for gas detection have been proposed and successfully demonstrated. The most notable advances over the years in this field are summarized as follows. [0004] Burch et al. (U.S. Pat. No. 3,793,525) and Blau et al. (U.S. Pat. No. 3,811,776) in 1974 were the first to advance a so-called "Double Beam" technique for NDIR gas measurement by taking advantage of the principle of nonlinear absorption for some strongly absorbing gases such as CO.sub.2 to create a reference channel. Shortly thereafter, this "Double Beam" NDIR gas sensor technique was greatly simplified with the use of two interposed spectral filters (one absorbing and one neutral) to create a sample and a reference detector channel. Subsequent NDIR gas sensors, designed using this technique, have enjoyed good output stability as a function of time. [0005] In U.S. Pat. No. 4,578,762 (1986) Wong advanced the first self-calibrating NDIR CO.sub.2 analyzer using a novel two-wheel chopper and mirror arrangement. Another improved type of such gas analyzer is shown and described in U.S. Pat. No. 4,694,173 (1987) by Wong. This gas analyzer has no moving parts for effecting the interposition of spectral filters or absorbing and non-absorbing cells to create both a sample and reference detector channel as in the NDIR gas analyzers described earlier. [0006] In U.S. Pat. No. 5,163,332 (1992), Wong advanced the so-called "wave-guide" sample chamber for simplifying NDIR gas sensors into ones that are compact, rugged and low-cost while still maintaining their superior performance characteristics. [0007] All of the NDIR gas analyzers described above for the measurement of the concentrations of one or more gases in a mixture perform well functionally and have contributed overwhelmingly to the overall technical advancement in the field of gas analysis during the past two decades. They have been widely accepted in both the medical and industrial communities. Despite their undisputed success over the years, there still remain a number of important applications, primarily in the industrial sector, where these NDIR techniques are still too complex, and hence too costly, to be taken advantage of. One such example is the methane gas detector for the miners. The ideal solution here is a small, very low cost and battery-operated methane gas sensor mountable directly below the headlight on the miner's helmet. In the event the miner encounters a methane gas pocket during excavation in the mine, this particular sensor can detect a dangerous level of the gas much sooner than the current setup in which a relatively bulky methane analyzer is normally located quite a distance behind the working miners. Furthermore, such a helmet-mounted methane gas sensor allows the alarm to be placed inside the helmet and close to the miner's ears thereby avoiding the tragic possibility that the alarm from a more remote methane analyzer might be drowned out by the machine noises in the mine. [0008] Another example is the commonplace household fire detector. A majority of fire detectors in use today in almost all public buildings and private dwellings are in essence smoke detectors as they only detect the smoke resulting from a fire. The most common smoke detectors currently in use belong to two types. The first type is the so-called ionization smoke detector best for detecting invisible smoke particles ranging in size from <1.0 microns to .about.5 microns. The second type is called the photoelectric smoke detector best for detecting visible smoke particles >5 microns in size. For the past two decades, the ionization smoke detectors because of their low cost (<$10 retail) have dominated the fire market and are in use in over 90% of households. In recent years, photoelectric smoke detectors, because of their higher cost (<$30 retail), have fallen significantly behind in sales. Combined ionization and photoelectric smoke detectors, albeit at an even higher cost (.about.$40 retail), have also been available for quite sometime but have not to date received much acceptance by the public. [0009] Despite their low cost, relatively maintenance-free operation and wide acceptance by the buying public, the smoke detectors in widespread use today are not without problems and certainly are far from being ideal. One of the biggest problems with ionization smoke detectors besides being radioactive (Americium-241) is their frequent false-alarm. By the nature of its operational principle, any micron-size particulate matter other than smoke from an actual fire can set off the alarm. Kitchen grease particles generated by a hot stove is one classic example. Overzealous dusting of objects and/or furniture near the detector is another. Frequent false-alarms are not just a harmless nuisance; some people actually disable their smoke detectors by temporarily removing the battery in order to escape such annoying episodes. This latter situation could be outright dangerous especially when these people forget to rearm their smoke detectors. [0010] Another significant drawback for the current ionization smoke detector is its relatively slow speed to alert people of a fire. There are several factors that contribute to this particular drawback. The first fact is the detector trigger threshold for smoke which directly affects its response time to the onset of a fire. No doubt a lower trigger threshold would mean a faster fire detector. However, it also means more frequent annoying false alarms for the user. The second factor is the particular placement of the detector with respect to the spot where fire breaks out. Unlike ordinary gases, smoke is actually a complex sooty molecular cluster that consists mostly of carbon. It is much heavier than air and thus diffuses much slower than the gases we encounter everyday. Therefore, if the detector happens to be at some distance from the location of the fire, it will be awhile before enough smoke gets into the sampling chamber of the smoke detector to trigger the alarm. A third factor is the nature or type of the fire itself. Although smoke usually accompanies fire, the amount produced can vary significantly depending upon the composition of the material that catches fire. For example, oxygenated fuels such as ethyl alcohol and acetone give less smoke than the hydrocarbon from which they are derived. Thus, under free-burning conditions oxygenated fuels such as wood and polymethylmethacrylate give substantially less smoke than hydrocarbon polymers such as polyethylene and polystyrene. As a matter of fact, a small number of pure fuels, namely carbon monoxide, formaldehyde, metaldehyde, formic acid and methyl alcohol, burn with non-luminous flames and do not produce smoke at all. [0011] Since fire is an oxidation process, detection of a sudden increase in ambient CO.sub.2 level, one of the three principal effluent gases of fire, is an effective way of detecting same. For the past 20 years, the use of CO.sub.2 sensor as a standalone fire detector or in combination with smoke detectors has been continually advocated by experts as the most effective fire detector. The reason is two-fold. First, there is a significant advantage of using a CO.sub.2 sensor rather than a smoke detector for fire initiation detection. The mobility of CO.sub.2 as a gas is far greater than that for smoke which is much heavier. Therefore CO.sub.2 diffuses from the fire to the detector in a much shorter time leading to a faster response time for enunciating fire. Second, over the past two decades, compact, low cost and reliable NDIR type CO.sub.2 sensors have become readily available. As a matter of fact, over the same period of time, a large number of deployment schemes, fire fighting techniques and fire control strategies, which use either a standalone NDIR CO.sub.2 sensor or in combination with smoke detectors, have been advanced. The most notable proposals of such are summarized as follows. [0012] In U.S. Pat. No. 5,053,754 (1991), Wong advanced the first NDIR CO.sub.2 sensor used as a standalone fire detector. A fire detection system using at least two NDIR CO.sub.2 sensors positioned at spaced locations in an area for pin-pointing the exact origin of a fire was described in U.S. Pat. No. 5,079,422 (1992) by Wong. Meanwhile a standalone and compact low-cost fire detector which responds quickly to an increase in the concentration of CO.sub.2 gas in the ambient air was advanced in U.S. Pat. No. 5,103,096 (1992) by Wong. In U.S. Pat. No. 5,369,397 (1994), an adaptive fire detector taking advantage of the capability of an NDIR CO.sub.2 sensor for computing the rate of CO.sub.2 increase to shorten the response time for enunciating the onset of a fire was also advanced by Wong. In U.S. Pat. No. 5,592,147 (1997), an NDIR CO.sub.2 sensor used cooperatively in combination with a photoelectric smoke detector for significantly reducing false alarms was put forth by Wong. Also in 1997 and in U.S. Pat. No. 5,691,704, Wong disclosed another NDIR CO.sub.2/photoelectric smoke detector combination fire detector with special software which can be designed into a single semiconductor chip for cost reduction and further false alarm improvement. In U.S. Pat. No. 5,767,776 (1998), Wong disclosed the design of an NDIR CO.sub.2 and smoke detector combination which reduces the maximum average response time to less than 1.5 minutes. Further refinement of this design was described in U.S. Pat. No. 5,798,700 (1998) by Wong, U.S. Pat. No. 5,945,924 (1999) by Marman et al. and U.S. Pat. No. 5,966,077 (1999) by Wong. Finally, a method for dynamically adjusting criteria for detecting fire through smoke concentration using an NDIR CO.sub.2 and smoke detector combination was described by Wong in U.S. Pat. No. 6,107,925 (2000). [0013] Despite the continual and persistent advocacy of many fire experts that an NDIR CO.sub.2 sensor, either as a standalone fire detector or in combination with a smoke detector, is better than present-day smoke detectors in both speed of response and proof against false alarms, it has yet to be exploited as a superior fire detector. The reasons are two-fold. First, even with the drastic cost reduction for present-day NDIR CO.sub.2 sensors, the cost is still far too high when compared with ionization type smoke detectors. Second and by far the most significant is the fact that being an NDIR gas sensor, its active infrared source uses far too much power when operated continuously. Because of this, it is not suitable for use in almost any circumstance, whether it is residential, commercial or industrial. [0014] Accordingly, there is a long felt need for an improved NDIR CO.sub.2 sensor that can be used in a fire detector that is economical and can replace present day ionization fire detectors that have slower response times and suffer from environmental concerns due to their use of radioactive materials. SUMMARY OF THE INVENTION [0015] The present invention is generally directed to a fire detector that uses an NDIR CO.sub.2 sensor that generates a detector signal based upon a 15.mu. absorption band of CO.sub.2 and generates an alarm signal when a signal processor receives the detector signal and a preselected criterion is met. [0016] In a first, separate group of aspects of the present invention, the signal processor relies upon a detection algorithm that is based upon a sudden drop of the detector output signal (e.g., when the drop is >20%) indicative of the onset of a fire. [0017] In a second, separate group of aspects of the present invention, the NDIR CO.sub.2 sensor further generates a reference detector signal based upon a 9.0.mu. neutral band, the signal processor utilizes synchronized signal processing from the detector signal and the signal processor relies upon a detection algorithm that is based upon a synchronized output signal representative of CO.sub.2 concentration. [0018] In a third, separate group of aspects of the present invention, the NDIR CO.sub.2 sensor (which can be used as a standalone smoke detector or combined with a smoke detector) has a waveguide sample chamber (that can be U-shaped) with at least one opening covered with a thin filtering membrane (such as a few thousandths of an inch of polyethylene) that allows CO.sub.2 molecules to diffuse freely into and out of the sample chamber but rejects dust, smoke and water particles from entering the sample chamber, a semiconductor blackbody source (with an infrared source temperature of approximately 350.degree. K) mounted in one end of the chamber and a detector (with a detector temperature of approximately 300.degree. K) equipped with a spectral filter mounted on the other end of the chamber. [0019] In a fourth, separate group of aspects of the present invention, a fire detector uses a CO.sub.2 sensor that generates a detector signal representative of attenuation of radiation observed normally from a source to the detector that has a CO.sub.2 detector, a filter for a 15.mu. absorption band of CO.sub.2 and electronics for receiving the detector signal and generating an alarm signal when a preselected criterion is detected by an algorithm based at least in part upon the detector signal. The CO.sub.2 sensor can also have a second reference detector with a 9.0.mu. neutral band filter with a FWHM=0.5.mu.. [0020] In a fifth, separate group of aspects of the present invention, a method for generating an alarm signal in response to a fire is based upon using a CO.sub.2 sensor to generate a detector signal based upon a 15.mu. absorption band of CO.sub.2 and generating the alarm signal when a preselected criterion indicative of the onset of a fire is met based upon an analysis of the detector signal. The analysis of the detector signal can be performed by using a detection algorithm that relies upon a trending pattern of the detector signal such as recognizing a substantial drop in the detector signal strength when CO.sub.2 subsequently arrive near the sensor as the fire persists. [0021] In a sixth, separate group of aspects of the present invention, a method for generating an alarm signal in response to a fire is based upon using a CO.sub.2 ensor to generate both a detector signal based upon a 15.mu. absorption band of CO.sub.2 and a reference detector signal based upon a 9.0.mu. neutral band with a FWHM of 0.5.mu., generating a synchronized output signal representative of CO.sub.2 concentration based upon the detector signal and the reference detector signal and then generating an alarm signal when a preselected criterion indicative of the onset of a fire is met based upon an analysis of the detector signal which is performed by using a detection algorithm that analyzes the synchronized output signal. Continue reading about Ultra low power ndir carbon dioxide sensor fire detector... Full patent description for Ultra low power ndir carbon dioxide sensor fire detector Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Ultra low power ndir carbon dioxide sensor fire detector patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. Start now! - Receive info on patent apps like Ultra low power ndir carbon dioxide sensor fire detector or other areas of interest. ### Previous Patent Application: Gas sensor array with a light channel in the form of a conical section rotational member Next Patent Application: System to monitor the health of a structure, sensor nodes, program product, and related methods Industry Class: Radiant energy ### FreshPatents.com Support Thank you for viewing the Ultra low power ndir carbon dioxide sensor fire detector patent info. IP-related news and info Results in 0.15444 seconds Other interesting Feshpatents.com categories: Qualcomm , Schering-Plough , Schlumberger , Seagate , Siemens , Texas Instruments , 174 |
 * Protect your Inventions * US Patent Office filing 
PATENT INFO |
|
