Smoke detectors particularly ducted smoke detectors
AssigneeSiemens Aktiengesellschaft
InventorMartin Terence Cole
Life of this patent
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Abstract
The present invention relates to the detection of particles suspended in fluid particularly smoke detectors suitable for mounting on ducting for the early detection of smoke created by unwanted pyrolysis or combustion of materials in a protected area or fire zone to which the duct is connected. The present invention provides alternately illuminating a detection zone with one of either a first or a second illumination. The improvement embodied in the current invention is the ability to retain sensitivity to a wide range of particle sizes and also to discriminate between different kinds of smoke or dust according to particle size, whilst also achieving relatively long service life, small size, light weight and low cost.
Claims25
A particle detector including:
- a body having an inlet through which sample(s) of fluid, including air, is provided, and an output for indicating an alarm condition;
- and
- a particle detection unit including a source of light with at least a first light source having a first wavelength, and a particle size discrimination unit;
- the alarm condition being provided by determining over a predetermined period of time a change in the concentration of selected particles sizes(s) and/or particle size range(s);
- and
- the alarm condition being an alarm condition indicative of an accelerant being used if it is determined that, prior to a rapid increase in particles smaller than said first wavelength, there was a small period or no period of pyrolysis characterized by a slow increase in particles larger than said first wavelength.
A method of detecting an alarm condition for a pyrolysis, smoldering and/or smoke event, the method comprising the steps of:
- providing a sample of fluid,
- impinging upon the fluid sample, light emanating at a first wavelength from a source of light,
- determining, using the emanating light, particle size(s) and/or particle size range(s),
- determining over a predetermined period of time whether the number or concentration of selected particle size(s) and/or particle size range(s) has changed,
- providing an alarm if the determination made over a predetermined period of time falls within selected criteria, and
- the alarm provided in the providing step being an alarm condition indicative of an accelerant being used if it is determined that, prior to a rapid increase in particles smaller than said first wavelength, there was a small period or no period of pyrolysis characterized by a slow increase in particles larger than the first wavelength.
Dependencies are inferred from the claim text.