Detectors basic requirements

Required locations of gas detectors (sensors) are often specified by the authority having jurisdiction. For example, API RP 14C recommends certain locations for combustible detectors. These recommendations have been legislated into requirements in U.S. Federal waters by the Minerals Management Service. RP 14C should be referred to for specific details, but, basically, combustible gas detectors are required offshore in all inadequately ventilated, classified, enclosed areas. The installation of sensors in nonenclosed areas is seldom either required or necessary. Ignitible or high toxic levels of gas seldom accumulate and remain for significant periods of time in such locations. 

The basic requirements for the CBMS II are to reliably detect and identify with sufficient sensitivity and selectivity both CWA and BWA in point detection and reconnaissance missions, in order to be deployable in wheeled reconnaissance vehicles and be operable by nontechnical personnel wearing, at the extreme, MOPP IV protective gear. Contrary to the usual practice for a military detector system, the CBMS II does not have its own requirements document. Instead, the requirements and specifications for the CBMS II are based on the detector requirements of the host platforms in which it will be deployed. These requirements are described in terms of performance, as opposed to the usual practice of being enumerated in volumes of detailed specifications. As is usual for a complex multiyear program, the requirements changed over the course of the CBMS II program as the requirements for the host platforms evolved. 

According to Campbell [1] there are four basic requirements for the detector, which constitutes the critical part of the luminometer ... 

Chandler and McNair (Hercules Inc.) [278] discussed the requirements for the basic parts of a high pressure liquid chromatographic system. These include a solvent reservoir, pump, injection system, column detector and recorder. They listed some of the different models available and described their major features. The developments in HPLC apparatus have also been reviewed by Martin and Guiochon [279] and the basic requirements also described by Bombaugh (Chromatec Inc.) [280]. The pumps and injectors available have been reviewed [281]. Some detectors currently used in HPLC have also been reviewed [282]. 

The relationship between the probe current and image visibility can be understood by analyzing the basic requirements that an image will not be obscured by background noise. Background noise in an SEM system is generated by fluctuation of the electron beam current and signal amplification in the detector, and cannot be totally eliminated. 

A new detector unit has been designed to add an internal check of radiation detection sensitivity by including a Th source in the detector LiF foil assembly. This provides continuous alpha-particle emission to test the ability of the foil detector to sense the neutron alpha-particle interaction in the LiF foil. An internal clock circuit forces the SCR to trigger if the detector amplifier fails for longer than 1 min. The unit produces a radiation alarm with any detected pulse rate from the LiF foil >4 pulse/s. Mechanical and electrical compatibility of the new detector design with the existing detection system has been a basic requirement not only to maintain the existing radiation sensitivity but also to minimize installation costs. 

A compact ion attachment mass spectrometer was designed that is simple and small and fulfills all the basic requirements for lAMS the system can be used to obtain only molecular ions by detecting any chemical species in real time [93]. This custom-made apparatus (Fig. 6.11) consists of a Li+ ion attachment ion source into which a stream of gas from a capillary leak inlet is directed, an electrostatic lens system (ELS), and a quadrupole mass spectrometer and detector, all of which are installed in a vacuum-separated envelope. The system employs a single tuibomo-lecular pirmp on the vacuum envelope instead of a differential pumping system. 

The basic requirements of detectors for liquid chromatography and especially HPLC are fast response, low distortion of the concentration profile of the sample (low washing out of the concentration peaks) and high ratio of analytical to background signal. These properties are achieved both by proper geometry of the cell and electrode system and application of a suitable measuring technique. 

The basic requirements of the SNOM technique are to have either a light source or a detector, generically described here as a probe, with dimensions smaller than A/2 and then to hold this within a few nanometers of the sample surface, in the near field of the probe. Typically, the probe is some form of aperture in an opaque material through which light is either transmitted to or collected from the sample. 

A photon source used in photoelectron (PE) spectroscopy must fulfil at least two basic requirements. First, the incident radiation must be monochromatic the second requirement is high photon intensity. In order to achieve sufficient electron flux at the detector a source with a typical intensity of lO -lO photons s is needed. The most commonly used source in the XPS technique is the X-ray tube, while in valence shell PE spectroscopy resonance lamps are applied. 

A flow scheme for the basic form of ion chromatography is shown in Fig. 7.3, which illustrates the requirements for simple anion analysis. The instrumentation used in IC does not differ significantly from that used in HPLC and the reader is referred to Chapter 8 for details of the types of pump and sample injection system employed. A brief account is given here, however, of the nature of the separator and suppressor columns and of the detectors used in ion chromatography. 

Figure 4-8. Basic components of a simple mass spectrometer. A mixture of molecules is vaporized in an ionized state in the sample chambers.These molecules are then accelerated down the flight tube by an electrical potential applied to accelerator grid A. An adjustable electromagnet, E, applies a magnetic field that deflects the flight of the individual ions until they strike the detector, D.The greater the mass of the ion, the higher the magnetic field required to focus it onto the detector.

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