Forward and back scattering loss compensated smoke detector

A device for detecting particulate levels in a fluid, said device comprising:

• a first light source means responsive to signals supplied to a first input to project a first light beam into the fluid;
• a second light source means responsive to signals supplied to a second input to project a second light beam into the fluid;
• a first light detector means positioned opposite said first light source means to directly receive said first light beam, said first light detector means producing a first detector signal corresponding to the intensity of light impinging thereon;
• a second light detector means positioned opposite said second light source means to directly receive said second light beam, said second light detector means producing a second detector signal corresponding to the intensity of light impinging thereon;
• and
• a control circuit that supplies a power signal to said first input to activate said first light source means, said control circuit monitoring and comparing said first detector signal and said second detector signal to produce and store a first output signal and a second output signal in accordance therewith, said control circuit also supplying said power signal to said second input to activate said second light source means, said control circuit monitoring and comparing said first and said second detector signals to produce a third output signal and a fourth output signal in accordance therewith, and wherein said first, second, third and fourth output signals are combined to produce a ratiometric value indicative of particulate levels in the fluid.

A smoke particulate detection device for measuring particulate emissions in an exhaust stream comprising:

• first light source means for producing a first light signal in response to a first activation signal;
• second light source means for producing a second light signal in response to a second activation signal;
• first focusing means for optically concentrating said first light signal into a first concentrated light beam;
• second focusing means for optically concentrating said first light signal into a second narrow light beam;
• first fiber optic means for providing an optical conduit over which said first narrow light beam is conveyed from said first focusing means to a first location adjacent the exhaust stream;
• second fiber optic means for providing an optical conduit over which said second concentrated light beam is conveyed from said second light source to a second location adjacent the exhaust stream;
• first beam expanding means for spreading said first concentrated light beam into a first expanded light beam and conveying said first expanded light beam into said exhaust stream along a first path;
• second beam expanding means for spreading said second concentrated light beam into a second expanded light beam and conveying said second expanded light beam into said exhaust stream along a second path;
• third focusing means situated in the path of said first expanded light beam for focusing a portion of said first expanded light beam into a first direct light signal;
• fourth focusing means situated in the path of said second expanded light beam for focusing a portion of said second expanded light beam into a second direct light signal;
• first photodetector means for producing a first electrical signal corresponding to the intensity of light impinging on said first photodetector;
• second photodetector means for producing a second electrical signal corresponding to the intensity of light impinging on said second photodetector;
• third fiber optic means situated adjacent said third focusing means for providing an optical conduit over which said first direct light signal is guided to said first photodetector means;
• fourth fiber optic means situated adjacent said fourth focusing means for providing an optical conduit over which said second direct light signal is guided to said second photodetector means;
• and
• circuit means for supplying said first activation signal to said first light source means and comparing the output from said first and second photodetector devices to produce a first ratiometric value representative of particulate levels in the exhaust stream, said circuit means also supplying said second activation signal to said second light source means and comparing the output from said first and second photodetector devices while said first light source means is inactive to produce a second ratiometric value representative of particulate levels in the exhaust stream, and wherein said first and second ratiometric values are combined to produce a value indicative of particulate levels in the exhaust stream.

A method for detecting particulate levels in a fluid comprising the steps of:

• providing a first light emitter and a first light detector situated so that a first light beam produced by said first light emitter passes through said fluid before striking said first light detector;
• providing a second light emitter and a second light detector situated so that a second light beam produced by said second light emitter passes through said fluid before striking said second light detector;
• locating said first light emitter and said second light emitter so that said first light beam and said second light beam are substantially planar;
• exciting said first light emitter to produce said first light beam and measuring the response produced by said first and said second light detectors as a first detected signal and a second detected signal;
• exciting said second light emitter to produce said second light beam and measuring the response produced by said first and said second light detectors as a third detected signal and a fourth detected signal;
• and
• combining said first, second, third and fourth detected signals to produce a value representative of the opacity of the fluid.