Optical Flame Detection
Optical flame detectors are devices which respond to radiant energy. Ultraviolet (UV) radiation and infrared (IR) radiation detectors are the most common. These have proven to provide prompt detection, but have not always been proven reliable as single source detection devices. However, there are several techniques which reduce false alarms and failures. Two commonly used techniques are dual IR and combination UV/IR detection devices. Dual IR and combination UV / IR detection devices reduce false alarms from sources such as welding arcs, flickering sunlight, hot bodies, or flashing lamps
The sensitivity of optical sensors depends upon the cleanliness of the lens. Sensors installed where dust or other materials may accumulate on the lens should be of the self cleaning type or be located where routine maintenance can be readily performed.
Optical flame detectors are best employed in areas where very fast response is required for actuation of protective or emergency shutdown systems. The actual detector placement depends on the area or equipment being monitored (physical dimensions, complexity, production importance, etc.), detector cone of vision, and sensitivity level of the sensor. Installation should closely adhere to the manufacturers recommendations. Optical flame detectors may also be provided with swivel bases to allow for optimum sensor positioning.
Optical flame detectors used as the primary detection device are considered a suitable alternate for standard thermal detection devices. Optical flame detectors find wide acceptance in enclosures where suppression or inerting systems require immediate actuation. To enhance reliability, additional control safeguards are often utilized, such as cross-zone or voting logic.