Optical flame fire detector FD 8040 is designed to provide early warning of a fire condition responding to open flame. The fire detector reacts within the light spectrum of the flame and has maximum sensitivity of the infrared range. The opearation principle is based on the reception of flame emissions with their typical flicker frequency within the whole spectrum range. The infrared sensor signal - amplified, filtered and shaped is being sent to the time delay circuit. If the flame impact has decreased during the time delay , the fire detector dos not activate.