Detector coverage

For best system performance and reliability, always use redundant detector coverage. 

Three-dimensional detector coverage, as shown in Figure 8-5, can be obtained by a triangular grid (isometric) pattern of point or open path detectors, with a maximum separation less than the gas cloud diameter that can... 

FGS philosophy documents Performance criteria selection Assessment of detector technology Detector placement study Detector coverage assessment Cause—effect diagram Assessment of FGS functional safety FGS specifications Testing and maintenance supports... 

Detector coverage The probability of the device actually seeing the hazard. 

Fig. 1.18. Whole brain perfusion study on a Siemens SOMATOM Definition AS+ Using a detector configuration of 128x0.6mm and a detector coverage of 38.4mm, whole brain perfusion studies can be carried out by using a special spiral shuttle mode that uses a sinosoi-dal motion of the patient table to cover the whole brain for a period of 30 s...

Fig. 1.19. Wider and wider detectors can also be used for interventional applications. Previously interventional CT was a 2D application due to the still limited detector coverage of up...

Light sources can either be broadband, such as a Globar, a Nemst glower, an incandescent wire or mercury arc lamp or they can be tunable, such as a laser or optical parametric oscillator (OPO). In the fomier case, a monocln-omator is needed to achieve spectral resolution. In the case of a tunable light source, the spectral resolution is detemiined by the linewidth of the source itself In either case, the spectral coverage of the light source imposes limits on the vibrational frequencies that can be measured. Of course, limitations on the dispersing element and detector also affect the overall spectral response of the spectrometer. 

Sohd-state multi-element detector arrays in the focal planes of simple grating monochromators can simultaneously monitor several absorption features. These devices were first used for uv—vis spectroscopy. Infrared coverage is limited (see Table 3), but research continues to extend the response to longer wavelengths. Less expensive nir array detectors have been appHed to on-line process instmmentation (125) (see Photodetectors). 

Microwave movement detectors utilize the principle of the Doppler effect on high-frequency low-power radio waves. These units are moderate in cost and suitable for large-volume coverage. Microwaves, however, penetrate certain materials easily, such as plasterboard, and careful siting is required to avoid false alarms. 

Ultrasonic movement detectors utilize the principle of the Doppler effect on high-frequency sound waves. Ultrasonic movement detectors do not penetrate solid objects, but have smaller volume of coverage than microwave movement detectors. These units may also be affected by moving hot or cold air pockets in a room. 

Figure 3. Optical and infrared detector zoology . The wavelength region is stated on the first row, with corresponding wavelength (in /rm) shown on the second row. The type of detector material and associated manufacturers are shown in the boxes below, which also depict the wavelength coverage possible with each kind of detector material.

A sphere has a larger mass than a typical bar (L = 5D) resonating at the same frequency, and because it is equally sensitive for all directions and polarizations it has a cross-section (for the same material) that is about 75 times larger. A single sphere is also capable of determining the source direction and polarization. A spherical detector is the only detector for GWs with isotropic sky coverage and the capability of finding the location of the source. Both laser interferometers and bar detectors are unable to do this with just one detector six bar detectors would be needed to build an omni-directional observatory. 

In a typical application, UV detectors are used in general or spot coverage locations. General coverage detectors are usually mounted in the comers and along the walls of a hazardous area. 

Spot coverage detectors are normally mounted as close as possible to the point of potential ignition. Examples are the extruder/cutter in a high explosives machining operation or the compression point in a shell loading machine. Spot detectors assure the fastest possible detection time by physically being mounted the closest to the point of ignition. 

Where overall large area coverage is necessary or desired, such as the monitoring of facility borders, pump alleys, entire onshore units or offshore modules, "line of sight" IR beam detectors are used, otherwise "point source", catalytic detectors are provided. The point source locations should be at least on either side of the leak point, which at least one of the detectors downstream ventilation pattern. 

We employ the Neyman-Pearson detector to find the sensing coverage area of the surveillance wireless sensor networks. In order to find the breach path, we apply Dijkstra s shortest path algorithm by us-... 

Fig. 31 (A) Principle of a sandwich immunoassay using FDA particulate labels. The analyte is first immobilized by the capture antibody preadsorbed on the solid phase (a) and then exposed to antibody-coated microparticle labels (b). Every microparticle contains 108 FDA molecules. High signal amplification is achieved after solubilisation, release, and conversion of the precursor FDA into fluorescein molecules by the addition of DMSO and NaOH (c). (B) Calibration curves of IgG-FDA microcrystal labels with increasing surface coverage of detector antibody (a-d) compared with direct FITC-labeled detector antibody (e). The fluorescence signals increase with increasing IgG concentration. FDA microcrystals with a high IgG surface coverage (c,d) perform better than those with lower surface coverage (a,b). (Reprinted with permission from [189]. Copyright 2002 American Chemical Society)...

At 11 09 A.M., a high-LEL detector in the catalyst preparation area sounded on the DCS. The lead outside operator was contacted by radio communications to investigate the problem. He said he was just leaving the Reactor No. 1 area and would go right to the catalyst preparation area. The thunderstorm had passed overhead and the rain was diminishing. At about 11 10 A.M., a whooshing noise (assumed to be the fireball) was heard by many and the heat detector for the automatic water-spray sprinkler coverage in this area alarmed in the control room. The lead outside operator did not respond when called on the radio. 

Leaks on flammahle or toxic material systems. Give special consideration to whether the LEL detectors are correctly located and whether they offer complete coverage. 

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