An optical smoke detector for pulsed or continuous operation in which optical biasing of a light source and receiving transducer is employed to permit operation of the detector at points of greater sensitivity, stability and linearity than are found at low light levels. The optical biasing may be provided by a light-scattering optical integrator associated with the light source causing controlled impingement of light upon the field of view of the receiving transducer. Adjustment of the relative positions of the light source and transducer and of the disposition of a barrier between those elements as well as the holders of those elements provides further control of the optical biasing. The housing of the detector is provided with smoothly contoured passages for the unimpeded passage of smoke particles to an internal optical detection chamber.
A smoke detector device for signalling a smoke detection in a space in an aircraft such as a cabin, a toilet, or a cargo hold of an aircraft, is mounted in a recessed position in a hole in a wall or ceiling of the aircraft. The device has at least one smoke detector enclosed in a housing (3) that also holds a smoke guide ring forming a funnel collar (7) for guiding smoke from a smoke collecting entrance (9) into a detector inlet opening (11) facing toward the space. The funnel collar (7) has a bottom (10) extending essentially on one level with the smoke inlet opening (11) of the smoke detector. The funnel collar tapers from the smoke collecting entrance (9) of the smoke guide rim to the smoke detector inlet opening (11) to form a smoke trap wherein a smoke stream toward the smoke detector is guided and accelerated. The smoke guide rim itself may function as a mounting for one or more smoke detectors, whereby a separate housing is obviated.
A focused beam of light from a light source is directed into a closed smoke chamber, having inlets for admitting smoke particles, toward a reflector which reflects and refocuses the beam back into the light source, the direct beam and the reflected beam passing through a test zone within the chamber. In the event that smoke particles enter the test zone, the direct and reflected beams strike and bounce off of those particles to produce scattered radiation that will be picked up and detected by a light responsive sensor to generate an alarm signal. By closely controlling, rather than baffling the light, optimum operation is obtained, efficiency is enhanced and false alarms are minimized. Additionally, to prevent any stray light from bouncing off of undesired dirt and dust in the chamber and being received by the light sensor, resulting in a false alarm, surfaces of the chamber are provided with parallel grooves for accumulating that dirt and dust, and the light sensor field of view is focused on an attenuating light trap. Stray light impinging on the grooved surfaces becomes attenuated and absorbed so there will be no reflections, and light entering the light trap is reduced to a negligible level.
The smoke detector uses modulation techniques to differentiate within a smoke detection chamber between ambient energy and energy from a transmitting source. A delayed automatic gain control is provided to reduce the effects of slow change of parameters in the detector itself and to provide greater discrimination between smoke which should cause an alarm and smoke resulting from, for example, tobacco. The smoke detector further provides for increased signal-to-noise ratios thus providing for more accurate and precise measurements.
The invention relates to a detector for scattered light, especially for detecting particles in a carrier medium. Said detector comprises a housing (1) and an inlet (3) and an outlet (5) in the housing (1). The carrier medium flows through the housing between said inlet and outlet and on a flow path (7). The inventive detector also comprises a light source (9) that directs light to a scattered light centre (11) which lies on the flow path (7). The inventive detector further comprises a receiver (13) for a portion of the light which is scattered onto particles in the scattered light centre (15) and a light trap (15) for light which is not scattered in the scattered light centre (11). The aim of the invention is to improve such a detector for scattered light in such a way that compact construction and high responsiveness are guaranteed. The light trap (15) can be embodied in two ways. According to a first embodiment, the light source (9) is arranged outside the flow path (7) and the centre axis (18) of the light cone (20) pertaining to the light source (9) extends at least partially parallel in relation to or on the centre line (58) of the flow path (7). The light trap (15) allocated to the light source (9) is part of the flow channel guiding the flow path (7). According to a second embodiment, the receiver (13) is arranged outside the flow path (7). The axis (14) of the receiver extends at least partially parallel in relation to or on the centre line (58) pertaining to the flow path (7). The light trap (23) allocated to the receiver (13) is part of the flow channel guiding the flow path (7).
A photoelectric smoke detector for providing indications of both alarm and trouble conditions is disclosed having a source of light, a detector apparatus having a light responsive device, said detector apparatus providing an output subject to a first change dependent upon the presence of smoke, the smoke detector further having a housing for mounting the source of light and the light responsive device, the housing having light path means for allowing light from the source of light to fall upon the light responsive device, the output from the detector apparatus being subject to a second change dependent upon trouble conditions, a first level sensor responsive to the first change to provide an alarm indication, and a second level sensor responsive to the second change to provide a trouble indication.
