Detector placement

The following are some general guidelines on the placement of gas detectors. The manufacturers of detectors should be consulted for recommendations on placement of their detectors, since they are more familiar with their performance characteristics and capabilities. At the same time the system designer must do his/her own research to ensure the equipment being installed will deliver the required results. 

In general, single-point detectors, such as the catalytic, infrared, solid-state, and electrochemical types, can be put in locations up to 3,000 feet from the control room.14 Sampling systems are more limited because of the length of the tubing needed to bring the sample to the detector. 

Generally, when considering the placing of detectors, one should consider the sources around the site that are most likely to lead to a release such as  

The second tier of locations for detectors are those areas that could be affected by a release, such as  

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Placement of detectors should consider the need for protection from physical damage, weather effects (snow, icing, wind-driven rain, or dust), or direct water hose spray during an area wash down. Detector placement should also allow safe access to perform required periodic testing and inspection. Typical approaches to flammable gas detection layout are ... 

For interferometric detection, the correlation of the electric fields at the various pairs of detectors is calculated. It can be shown that the mutual coherence function of the electric fields at detector placements rx = (xl7 yx) and r2 = (x2, y2) can be written as [65]... 

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... 

Major issues related to the detector placement process shall include but not be limited to the following (for combustible gases. Clause 3.4.3 of Chapter X may also... 

The feasibility of detection-based defensive strategies also depends on how the detectors are deployed and how they are actually used. Deployment considerations include the number and placement of detectors, whether in open spaces or in HVAC ductwork. In this respect, airport terminals are likely to be more difficult to protect by this strategy than are aircraft, owing to the vastly greater air volume and necessarily greater physical spacing between detectors in terminals. To the extent that more than one type of independent detection or verification system is needed to achieve acceptable POD and PFA, the system costs are multiplied. 

I-1.3.6.3 The compressor building configuration shall be considered in selecting the number, type, and placement of detectors and alarms. 

In common industrial and laboratory continuous analyzers, the requirements on the magnitude of the cell are not as rigorous as with chromatographic, CFA and FIA detectors and thus the construction of the detector can be quite simple. The principal requirements are a sufficiently high and reproducible flow-rate in the vicinity of the ISE membrane, good electrical connection between the ISE and the reference electrode by the flowing liquid and, when a differential circuit is not used, placement of the reference electrode after the ISE to avoid possible interference from solution leaking from the reference electrode. 

Early detection is essential. The placement of detectors inside cabinets can significantly reduce the time to detection. An early warning high sensitivity smoke detector (HSSD) smoke detection system can be used to detect incipient stage fires and allow planned repairs prior to equipment failure. Hence, fire suppression may not be required. 

Additional general guidance on the placement of detectors can be found in FM Data Sheet 5-28, Smoke Detectors and in NFPA 72, National Fire Alarm Code. 

Most flow-through sensors integrating retention and detection involve placement of an inert support in the flow-cell of a non-destructive spectroscopic detector where the analytes or their retention products are retained temporarily for sensing, and then eluted. Rendering these sensors reusable entails including a regeneration step suited to the way retention is performed. 

FIGURE 7.9 Three common electrode placements for an electrochemical detector. (A) The working electrode is integrated into the flow cell wall while the reference and auxiliary electrodes are placed downstream. (B) Both the working and auxiliary electrodes are integrated into the flow cell wall and the reference electrode is placed downstream. (C) The working electrode is integrated into the flow cell wall adjacent to the column effluent. As in example A, the reference and auxiliary electrodes are placed downstream. 

The preceding setup allows both X-ray diffraction (32) and absorption experiments (33, 34). The capillary geometry was used until about 30 years ago for ex situ XRD studies in connection with the placement of Lindemann tubes in powder Debye-Scherrer cameras. At that time, films were used to detect the diffracted X-rays. Today, this cumbersome technique has been almost completely replaced as modern detectors are used. 

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