The working principle of a flame detector is based on the physical characteristics of the flame to detect the presence or absence of the flame. Here is a detailed introduction for you:

The working principle of a flame detector is based on the physical characteristics of the flame to detect the presence or absence of the flame. Here is a detailed introduction for you:

Detecting radiation energy: During flame combustion, ultraviolet, visible, and infrared rays are released. Flames produced by the combustion of different fuels emit varying levels of light intensity and spectral range. For example, in coal powder flames, in addition to non luminous three atom gases such as CO2 and water vapor, there are also some hot and glowing coke particles and charcoal particles that emit strong infrared, visible light, and some ultraviolet radiation; In oil flames used for heating and ignition, in addition to a portion of CO2 and water vapor, there are also a large number of luminescent carbon black particles that can emit strong visible light, infrared, and ultraviolet radiation; When combustible gases are used as the main fuel for combustion, they emit strong ultraviolet radiation in the initial combustion zone of the flame.

UV detection: For fuels such as combustible gases that emit strong UV radiation in the initial combustion zone of flames, UV sensitive detection components such as UV photodiodes, UV detectors, UV sensors, etc. can be used. These components can convert ultraviolet radiation into electrical signals. For example, a potassium phosphide (GaP) sensor is a photoresistor that is particularly sensitive to ultraviolet radiation. The flickering ultraviolet radiation generated during fuel combustion induces it, converts it into an electrical signal, and outputs an analog signal after being amplified.

Visible light detection: using visible light emitted by flames for detection. Some flame detectors determine the presence of flames by detecting the intensity and characteristics of visible light. For example, when using inferior coal powder or co fired coal, the black dragon zone of the flame becomes longer, and the visible light detector can detect the high-frequency component of flame flicker, because visible light still has a certain performance in the black dragon zone and initial combustion zone, which can more accurately reflect the flame situation.

Infrared detection: suitable for detecting coal powder flames or oil flames, etc. For example, lead sulfide (PbS) sensor is a photoresistor that is particularly sensitive to infrared radiation. The scintillation infrared radiation generated by fuel combustion induces it, converts it into an electrical signal, and outputs an analog signal through amplifier processing. Its spectral sensitivity range can effectively collect most of the infrared radiation and also cover some of the red light in visible light, ensuring the authenticity of the collected flame signal.

Utilizing the pulsating characteristics of flames: All flames exhibit pulsating changes, except for the radiation of steady-state electromagnetic waves, and the flicker frequency varies among different fuels and burners. For example, flame monitoring of single burner industrial boilers can utilize the characteristics of flame pulsation changes, using infrared solid detectors with low-pass filters (10-20Hz) (usually lead sulfide); The maximum difference in radiation intensity between coal powder with fire and without fire occurs at a flicker frequency of about 300Hz, while the difference between oil with fire and without fire occurs at a higher frequency (above 100Hz) for better detection. A flame detector uses the flicker frequency of a flame and the radiation intensity of light to comprehensively determine the presence and strength of a flame. Generally speaking, the flame flicker frequency is higher in the initial combustion zone and then decreases gradually towards the burnout zone; The closer the detector is to the initial combustion zone of the flame, the stronger the high-frequency components (100-400Hz) detected; The narrower the angle of view of the detector probe, the more realistic the flame signal detected.