Smoke detectors in general, are usually threshold devices that frequently experience false alarms. Optical smoke detectors usually depend on the measurement of optical power absorption and scattering across an air gap and are usually threshold devices. Fiber optic sensor technology offers potential improvements for existing smoke detector technology. We have developed a new smoke sensor design based on wavelength selective absorption and scattering that generates a continuous measurement of smoke density. This technique provides first order compensation for water and dirt coatings on the optical surfaces and for optical power and ambient light changes. The sensor has a 2 inch sensing region and utilizes multimode technology with an 850 nanometer LED source. Experimental models of the fiber optic smoke sensors were tested successfully in our laboratory and on the ex-USS SHADWELL. Operational performance advantages of the fiber optic smoke sensor are expected in the areas of monitoring visibility, reducing false alarms, improving reliability, and continuous measurement of smoke density; this will improve fire detection capability and will assist in developing fire fighting strategy. Application of the sensors are planned for the shipboard environment to provide sensor input to new damage control management systems.
The U.S. Navy is presently developing fiber optic sensor technology for machinery monitoring and control and damage control systems. We have developed a redundant, reflective star network of four fiber optic sensors (temperature, pressure, liquid level, and smoke) which can be monitored using either Time Division Multiplexing or Frequency Modulated Continuous Wave techniques. The sensors used are short cavity, low finesse Fabry- Perot sensors; processing utilizes the varying power reflectances from the sensors and is done in a desk top computer. The networks allow for the passive, remote monitoring of an area or of a machine using a single fiber and opto-electronics package. The paper presents the philosophies of the two designs and the results of network testing. Projections are made concerning the maximum number of sensors that are multiplexable using these approaches, and comparisons are drawn between the two methods. The sensors used have been qualified for shipboard application and thus compete directly with electrical equivalents.