Physical detecting devices

In many cases, it is necessary to complement physical security by the installation of an intruder alarm system in order to achieve the standard of security commensurate to the risk exposure. The scope of protection to be afforded by the alarm system depends on the security risk, but it may embrace fences, windows, doors, roofs, walls, internal areas, yards and external open areas, and vehicles inside and outside buildings. There is a comprehensive range of detection devices, but the choice of detector is critical to ensure that it provides the desired level of protection and is stable in the particular environment. 

PBDS will also be useful in a related area for the examination of catalysts which are opaque not because of high unit absorption but because they are physically large, i.e., entire catalyst pellets. This is made possible by the favourable geometry of the apparatus and detection device. As indicated schematically in Fig. 1, the sample is merely placed at the focus of the IR beam (an off-axis elliptical mirror is used to focus the IR beam about 1 cm from the edge of the mirror) and a laser beam grazes the surface. The "sample space of the spectrometer is thus of indefinite volume and can be made as large as needed to examine massive objects (in the present apparatus, a sphere of about 20 cm diameter could be accomodated). An example is shown in Fig. 8. 

Phthalocyanines were chosen for these experiments because they are electronic semiconductors and because they are quite stable materials — an important consideration in fabricating any practical gas-detecting device. A considerable body of literature exists describing the physical and chemical properties of the phthalocyanines. A review of the work prior to 1965 is contained in the chapter by A. B. P. Lever in Volume 7 of Advances in Inorganic Chemistry and Radiochemistry (2). Electrical properties of phthalocyanines have been receiving increased attention in recent years. The photoconductivity of metal-free phthalocyanine has been studied in detail (3,4). Electrical properties of lead phthalocyanine have been studied extensively, especially by Japanese workers (5, ,7,8i). They have also studied the alteration of the conductivity of this material upon exposure to oxygen ( ,10.). The effects of a series of adsorbed gases (0, , CO, and NO) on the conductivity of iron phthalo-... 

Collection of effluent fractions is followed by their analyses using the detection devices based on a physical property such as refractive index, condictivity, ultra violet or visible absorption. 

Two general type of detection devices are available. These are bulk property detectors and solute property detectors. The bulk property detector measures a change in some overall physical property in the mobile phase as it emerges from the column. Two typical examples are measurement of refractive index and conductance. The solute property detector is sensitive to changes in a physical property of the solute as it emerges from the column in the mobile phase a typical example is the measurement of ultraviolet and / or visible absorption. In general,... 

There are some detection devices in which there is no clear division of probe and transducer. Methods based on physical properties and separation are good examples mass spectrometry and gas or liquid chromatography. Mass spectrometry (MS) is a major analytical technique in which materials to be analyzed are converted into gaseous ions or otherwise... 

Light interacts with solid materials as scattering, absorption, transmission (transmittance), reflectance (both regular and diffuse), and diffraction. The purpose of spectroscopy is to quantify or qualify these interactions by the use of a variety of photon-produdng and photon-detection devices. The physics of these interaction phenomena and devices will be presented in this chapter. 

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