Obscuration optical detectors

Optical detectors contain a light emitting diode and a receiver. Smoke particles entering the detector either obscure or scatter the light beam causing the output signal from the receiver to vary. This in turn triggers the alarm. 

Since 1970 the subject of amoiphous semiconductors, in particular silicon, has progressed from obscurity to product commercialisation such as flat-panel hquid crystal displays, linear sensor arrays for facsimile machines, inexpensive solar panels, electrophotography, etc. Many other appHcations are at the developmental stage such as nuclear particle detectors, medical imaging, spatial light modulators for optical computing, and switches in neural networks (1,2). 

Figure 4.2.4 Optical smoke detector - obscuration type (Manual of Firemanship. Courtesy The Controller, the Stationery Office)...

Laser detectors operate in a similar way to optical beam detectors. The laser beam is directed across the area to be protected and is deflected or obscured by either the heat, the flame or the smoke rising from a fire, thus changing the intensity of lighf at the receiver. This triggers the alarm. 

Without the installations no reliable or reproducible measurement can be obtained. Then fine droplets with solved solids reach the lenses after few seconds and obscure/blur the detector. Tests with only water are used to investigate if measurements with the installation differ from measurements without the installation, because water droplets evaporate entirely and do not affect the optics. Results show no significant differences in the measurments. Another advantage of the installation is that the optical concentration during the measurement is in the range of the specification of the device all the time. 

The entrance aperture of the telescope is represented by a prime mirror of radius a, with a central obscuration of radius a = sa. A small field stop is visualized as a small detector at the focal point. The optical axis of the telescope is the x-axis. To study diffraction we let a plane wave arrive at an angle a. The plane wave is... 

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