900 Series Optical Detector

The optical smoke detector has an internal pulsing LED and a photo-diode at an obtuse angle. In clear air conditions the photo-diode in the monitor receives no light from the LED and produces a corresponding analogue signal. This signal increases when smoke enters the chamber and light is  scattered onto the photodiode. The signal is processed by the electronic circuitry and transmitted to the control equipment in exactly the same way as in the case of the ionisation smoke monitor.