Ultraviolet flame detectors testing and calibration
Ultra violet detectors provided in areas where a fire is not likely to generate smoke. An UV detector is continually looking at ultra violet radiation at a factory preset value. When it sees a greater amount of radiation than the preset value a relay is energised and the contacts of this relay can be utilised to perform switching of sounders, beacons, extinguishing equipment and/or shutdown action. The UV detector sensitivity range is normally between 0.185 to 0.245 microns wavelength.
The detector has what is called a cone of vision, typically at 80 degrees with the highest sensitivity along it's axis and a decreasing sensitivity with distance. This cone angle can be reduced with a sleeve attachment to concentrate the view onto specific small items of plant. There are 4 common sources of radiation greater than the factory preset value, which can create false alarms.
1) The sun 2) lightning 3) arc welding 4) flares
Detectors should ideally "look" down on the area to be protected avoiding the horizon, candle lit evenings, (the flares being large candles) adequately shielded from welding and beautiful sunsets.