UV Spectral-Sensitive Photoelectric Sensors Proposal

NOVEMBER 1, 2011


A fire starts in a room, the faster it can be located and extinguished, the less the damage there will be. Smoke detectors are devices that detect smoke, typically as an indicator of fire. Commercial, industrial, and mass residential devices issue a signal to a fire alarm system, while household detectors, known as smoke alarms, generally issue a local audible and/or visual alarm from the detector itself. Some advanced system turn on extinguishing systems to help prevent the spread of fire and help remove the fire altogether.


The most common and currently used systems contain either a semiconductor photo-detector or an ionization chamber. However these systems detect the smoke for a fire and not the fire itself. In some case, smoke is not always present in a fire, or by the time smoke has reached a detector, a large portion of the area has already set alight. A different type of detector is required for these cases, one that can detect the actual fire itself and not the byproduct.


Spectral-sensitive photoelectric sensors have a select set of wavelengths that they can detect. Some detect visible light (violet, blue, green, yellow, orange, red), some detect larger wavelengths (infrared, microwave, radio), and others detect smaller wavelengths (ultra-violet, x-ray, gamma ray). Fire emits a large spectrum of wavelengths; from infrared (300um), through the visible light spectrum, to ultraviolet (10nm). In most areas, visible light is always present; therefore infrared (IR) and ultraviolet (UV) wavelengths are the best to associate fire with. A large source of light that is present in most areas is sunlight, out of 1 kilowatt per square meter at sea level; 527 watts is IR radiation, 445 watts is visible light, and 32 watts is UV radiation. Therefore, an ultraviolet sensor is the best detector as it will be less affected by outside sources when detecting the presence of a flame.


Ultraviolet detectors make use of the photoelectric effect of metal and the gas multiplication effect. The photoelectric effect deals with electrons being emitted from matter as a result energy absorption from electromagnetic radiation of such as visible or ultraviolet light. The gas multiplication effect involves using electrons that collide with gas molecules to create ionization. These sensors can be set for a range (wide or narrow) of UV wavelengths and are completely unresponsive to visible light, unlike semiconductor detectors which require optical filters. The UV detector will emit a pulse to a circuit when detecting a flame which can be seen as a binary output.


The following are examples UV Spectral-sensitive photoelectric sensors:
  • Flame detectors for gas/oil lighters and matches
  • Fire alarms
  • Combustion monitors for burners
  • Inspection of UV leakage
  • Detection of corona discharge
  • UV switches