It is difficult to identify flame from different burners.Because the frequency of flame of adjacent burner is very close to the main flame sometimes, frequency signal should be analyzed in order to improve the recognition ability.Besides providing gain adjustment mode, the flame detector also has the function of frequency band selection.There are 8 frequency bands, and different frequencies can be selected to meet the needs of flame recognition.The final recognition effect can be obtained by combining the frequency band selection with the gain setting.The frequency band selection also has an automatic frequency band. When the frequency and intensity of the frequency band are both higher than the set threshold value, the signal processor automatically adjusts the frequency band according to the different frequency signals, and it is judged as "fire".On the contrary, it is judged as "no fire".This is very reliable in most cases.However, sometimes due to the occasional disturbance or "black dragon" during the flame combustion process, the intensity or frequency of the flame will be below the threshold for a short time. At this time, if the "no fire" signal is sent, the possibility of misoperation of the fire protection system will be increased.In order to avoid sending fire extinguishment signal by mistake and improve the reliability of flame detector, the delay time of general flame detector is increased by 1 ~ 5s.However, it is difficult to determine the length of delay, because a short delay will inevitably cause misoperation, and a long delay will reduce the sensitivity of protective action, or even cause rejection.The intelligent flame detection device specially designs a delay circuit with inverse time characteristics, so that the length of non-fire delay depends on the change rate of intensity and frequency before extinguishing.When the intensity and frequency of the flame drop below the threshold at a high rate, the delay time should be longer.Because there is enough energy in the furnace to support combustion, it will not be able to actually extinguish the fire.When the intensity and frequency of the flame slowly fall to the threshold value, it indicates that the support energy of the flame is small and the delay time is shorter to prevent rejection."No fire" - "fire" delay is inversely proportional to the rising speed of intensity and frequency;"Fire" - "no fire" delay is inversely proportional to the rate of decline in intensity and frequency.Thus the reliability and accuracy of flame detection are improved.