1. Field
The present disclosure relates to optical sensors, including solar blind sensors and sensors useful for fire detection.
2. Background
Property management, whether for government buildings, institutions, business buildings and residence, is implemented for protecting and preserving the buildings, stored properties and occupants. A multisensor system is usually employed by property managers to minimize adverse impact due to climate, pollution, theft, vandalism, insects, mold and fire. Fire, because of the speed and totality of its destructive forces, constitutes one of the more serious threats, and thus fire detection is one of the most important issues in today's building design.
The most commonly used fire detector in fire safety sector is the smoke detector. Conventional smoke detectors often have a high false alarm rate, with some estimates of ratios of false to actual alarms in excess of 10 to 1. Smoke detectors also suffer from their slow response for a large monitoring area due to the fact that the detector will not be activated until the smoke generated from the fire source reaches the detector. Smoke detectors are unsuitable as a fire detection device in car parks, since the products of combustion produced by exhaust fumes from a vehicle will cause a smoke detector to activate and produce a false alarm.
In another type of fire detector, a quartz tube filled with an inert gas conducts electricity when a photon of wavelength between 185 and 260 nm of a flame temporarily makes the gas conductive. The tube amplifies this conduction by a cascade effect and outputs a current pulse. Disadvantages of this technology include that the detection system is 1) bulky; 2) expensive (a pulse counter is needed for signal readout); 3) hard to maintain (high-voltage operation usually causes a lifetime in the order of only 10,000 hours); and 4) prone to crosstalk interference because the discharge tube itself emits ultraviolet radiation in operation. It is also difficult to use and does not allow the use of two or more flame detectors of this kind at the same time in close proximity since they may optically interfere with each other.