Detection False Alarms

Keywords wireless sensor network detection theory Kalman filtering target intrusion detection false alarm. 

At PicArsn (Ref 19), the fast neutron activation approach for detection of expls in suitcases was extended to the activation of both nitrogen and oxygen using two 7-ray detector stations in sequence. After 14 MeV neutron irradiation, the baggage is first monitored for 6.1 MeV 7-rays from the l60(n,p),6N reaction (7.5 sec half-life), followed by measurement of the 10 min 13N. Because expls are also rich in oxygen and have characteristic ratios of N/O, it was felt that this approach would increase the probability of detection with a corresponding decrease in the false alarm rate... 

PFA POD PROACT PROTECT probability of false alarms probability of detection Protective and Response Options for Airport Counter-Terrorism Program for Response Options and Technology Enhancements for Chemical/Biological Terrorism... 

A staggering number of papers are published each year in the literature on various candidate chemical/biological detection systems. Researchers and manufacturers make diverse claims of detection limits, sensitivity, false-alarm rates, and robustness for these systems. The committee believes that in many cases, researchers emphasize the strengths of their particular detection systems while minimizing or ignoring their flaws. This practice makes it virtually impossible to evaluate the likely performance of a detection system in real-world air transportation environments. 

For the detection of slow-acting biological agents (which may not produce symptoms for several days), the system response time would depend on the frequency of sampling and analysis. The frequency of sampling and analysis would be determined by factors such as the cost of the assay, the frequency with which critical reagents need to be replaced, the robustness of the detector, and so on. The minimum response time would be determined by the time required to collect a sample, prepare it for analysis, conduct the assay, and report the results. In the event of an alarm from a detector with a significant false-alarm rate, additional time would be required to determine its validity and to decide on an appropriate response. 

All detection systems feature a trade-off between the probability of detection (POD) of the target substance and the probability of false (positive) alarms (PFA). POD refers to the probability that the instrument will detect a threat material that is present PFA refers to the probability that the instrument will alarm when a threat material is not present at a given threshold level. The overall concentration of the target substance affects this trade-off higher concentrations are easier to detect, resulting in performance closer to the optimum operating point (perfect detection with zero false alarms). In addition, where data are accumulated over time, one can increase POD and decrease PFA by increasing the accumulation time. 

This is a simple example for the capability of KAMINA to be used as a sensitive fire warning device. Unlike conventional devices for that purpose, which work on the basis of optical aerosol particle detection, the gas analytical KAMINA will not give false alarms caused by dust or soot particles. 

Multi-sensor fire detectors provide faster detection with fewer false alarms. These sensors are capable of monitoring the environment for multiple purposes, e.g. carbon monoxide concentration, concentration of flammable gases and indoor air quality, too. 

When properly applied, ultraviolet detectors can serve as excellent fire detectors in munitions manufacturing. Detection times as fast as 10 milliseconds can be achieved while effectively resisting false alarms. 

The infrared (IR) detector is an extremely fast device that is capable of detection times as short as five milliseconds. In the past, infrared detectors have been unsuitable for general applications because of the large number of false alarm sources found in the work place. However, when properly applied in controlled surroundings, they can provide reliable and effective protection. 

False Alarm Reduction In Industrial Flame Detection Roger A. Wendt, Armteck Industries, Manchester, New Hampshire... 

Heat detectors normally have a higher reliability factor than other types of fire detectors. This tends to lead to fewer false alarms. Overall they are slower to activate than other detecting devices. They should be considered for installation only where speed of activation is not considered critical or as a backup fire detection device to other fire detection devices. They have an advantage of suitability for outdoor applications but the disadvantage of not sensing smoke particles or visible flame from a fire. 

Flame detectors alarm at the presence of light from flames usually in the ultraviolet or infared range. The detectors are set to detect the typical light flicker of a flame. They may be equipped with a time delay features to eliminate false alarms from transient flickering light sources. 

Where instantaneous reaction is not imperative, susceptibility to false alarms can be reduced by requiring the fire signal to be present for a predetermined period of time. However, the time delay reduces the advantages of high speed early detection. In most applications, the tradeoffs between false alarms and the damage incurred in the first few seconds of a fire have been inconsequential. 

The use of two separate electrical or mechanical zones of detectors, both of which must be actuated before the confirmation of a fire or gas detection. For example, the detectors in one zone could all be placed on the north side of a protected area, and positioned to view the protected area looking south, while the detectors in the second zone would be located on the south side and positioned to view the northern area. Requiring both zones to be actuated reduces the probability of a false alarm activated by a false alarm source such as welding operations, from either the north or the south outside the protected area. However this method is not effective if the zone facing away from the source, sees the radiation. Another method of cross zoning is to have one set of detectors cover the area to be protected and another set located to face away from the protected area to intercept external sources of nuisance UV. If welding or lighting should occur outside the protected area, activation of the alarm for the protected area would be inhibited by second... 

Using the field model described in section 1, detection probabilities are to be computed for each grid point to find the breach probability. The optimal decision rule that maximizes the detection probability subject to a maximum allowable false alarm rate a is given by the Neyman-Pearson formulation [20]. Two hypotheses that represent the presence and absence of a target are set up. The Neyman-Pearson (NP) detector computes the likelihood ratio of the respective probability density functions, and compares it against a threshold which is designed such that a specified false alarm constraint is satisfied. 

The system parameter values depend on the particular application. When a house or a factory is to be monitored for intrusion detection, the cost of false alarms is relatively low. On the other hand, the financial and personnel cost of a false alarm is significantly higher when the perimeter security of a nuclear reactor is to be provided by deploying a SWSN to monitor unauthorized access. The cost of a false alarm might involve the transportation of special forces and/or personnel of related government agencies to the site, as well as the evacuation of residents in the surrounding area. 

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