PATOL - Infra-red fire detection - Principles of operation

Infra-red emissions occur for all materials. The wave length spectrum and intensity of this IR depends on the material’s temperature, and for solid bodies such as coal is determined by the Laws of Physics formulated by Planck, Stefan, Boltzmann & Wien.
Planck’s Law defines the spectrum and level of IR emissions at any given temperature,as shown as in chart 1 on the left.
Wein's displacement principle corelates the wavelength of peak emission to temperature.
The Stefan-Boltzmann Law is that IR Power emitted is proportional to the fourth power of the Absolute Temperature (Deg.K).
It is with an understanding of these laws that the Patol infrared detection equipment has been designed. For example the Patol 5000 Series optical filter system both linearises the Stefan Fourth Power hyperbolic curve and rejects shorter wavelengths, including solar emissions and those in the visible light band. Refer to chart 2

The sensor monitors materials moving through its field of view, and responds to abnormal increases in infra-red emissions. The monitored IR levels are dependant on the materials temperature and wavelength filters (chart 2), together with the size of the IR radiator / target.
The Series 5000 sensor is designed to detect both small glowing “coals” of 25mm dia. and larger areas of material at abnormal pre-ignition temperatures as may occur when a burning coal is buried below the surface of the material.
The system has four settable levels of 10 to 40 micro-watt sensitivity to accommodate various applications and installation differences. In practice small “embers” will impart energy to surrounding material which increases response. e.g. a 30mm “coal” at the edge of visibility (500 to 600 deg C) will produce a level 3 trigger.
The sensors have multiple detectors configured using a multi-facet / focal axis technique such that a large number of focal points are spread across the field of view (monitored path). This arrangement achieves a much more uniform spread of sensitivity than single lens/detector systems and as detector-focal points combinations duplicate across the monitored field a voting (double-knock) feature can be selected as an option.