Fire detectors are the foundation of virtually all fire protection systems. However, this does not mean all detectors are the same. On the contrary, the requirements for reliably detecting fires vary as greatly as the application areas themselves: Fire detectors analyse the surrounding air to identify elements of fire, such as smoke, heat or carbon monoxide.

This task may be relatively easy or very hard depending, for example, on the presence or absence of deceptive phenomena like exhaust gases and kitchen fumes. Therefore, Siemen’s portfolio includes automatic detectors covering the whole spectrum from simple to highly complex signal analysis, for guaranteed fault-free detection under all circumstances. From data centres to industrial production facilities – we offer appropriate detector equipment for all environments, thanks to our intelligent detector technology (DA) and advanced signal analysis (ASAtechnology) that exactly matches the conditions on site.

Sensor design of an ASA Detector

Judging only by its name, Advanced Signal Analysis, it can be concluded that ASA stands for fire detection algorithms i.e. signal processing only. However, accurate measurement signals from the sensors are prerequisites for a reliable danger evaluation.

A dual-scattering ASA detector consists of the following sensing components:

  1. Two infrared semiconductor light sources positioned relative to the receiver (3) so that a forward scattering angle of approximately 60° degrees and a backward scattering angle of approximately 120° are obtained
  2. In Figure 1, the red cone of light emerging from the two sources (1) are shown
  3. Receiver for infrared light, with a spatial characteristic indicated in green, which intersects with the light cones from the two sources (2) and forms the so-called scattering volume
  4. Labyrinth or light trap, which suppresses the biasing of the receiver element due to the light not scattered by smoke (e.g. external infrared radiation or reflected light from the two sources). The labyrinth must be open enough in order to allow for smoke penetration into the measurement volume and ensure a uniform directional response. This is one of the key detection components.
  5. Two temperature sensors measure the temperature of the ambient air. They are positioned 180° apart from each other allowing for equalized response to temperature changes measured in all directions, allowing at the same time for a lowprofile detector.
  6. CO sensor (a separate product variant) measures the instantaneous concentration of carbon monoxide in the ambient air, with a sub-ppm resolution. Together with, in terms of mass production the precise absolute calibration of better than 10%, it allows detection of low levels of CO, increasing the sensitivity of the detector to fire without increasing the rate of false alarms.

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