Abstract
Aim: Optical point smoke detectors have a number of significant drawbacks. The foremost are: dependence on the sensitivity of average smoke particle size, of different smoke variety, detection of the smoke emission path, dispersed by given particles, and reaction lead time, determined by the speed of convective air flow and design characteristics of the smoke detector chamber. These drawbacks are absent in linear optical smoke detectors, where the reaction to a fire is determined by the control of flow intensity of transmitted rays (non-dispersed) from smoke emissions. The purpose of this research is to improve the optical design of laser smoke detectors by exploiting traditional fire detection methods (intensity level of rays dispersed by smoke particles), and techniques used by linear smoke detectors.
Project and methods: The project aim is realized with the aid of mathematical techniques and experimental modeling of energy transfer processes, by recording light beam expansion in an optically disparate environment, using aerosol smoke.
Results: two-channel laser smoke detector model was produced and tested for effectives. The main focus of tests was on the sensor’s sensitivity threshold. Tests were conducted in a flow through smoke chamber, with transverse dimensions of 500-500 mm². The optical smoke density in the channel was controlled by a smoke control block. Sawdust was applied to create smoke. The lowest average unit value of optical smoke density during tests revealed a stable deviation for measured signals in both channels of the sensor. During an absence of smoke the value was identified as 0.11 dB/m. The optical smoke density measurements in the testing chamber, for dispersed ray emissions of the test model, revealed a reading of 0.065 dB/m.
Conclusions: Sensitivity research results for the enhanced laser smoke detector confirmed the potential for improving reliability, by increasing the proportion of detected emissions dispersed at small angles. The special structure of the detector light beam allows for the creation of an effective algorithm used for processing of registered signals, thus improving the sensor’s resistance to noise interference.
Keywords: optical point smoke detector, linear smoke detector, laser source, smoke, sensitivity, emission
Type of article: original scientific article