Forward and back scattering loss compensated smoke detector

• US 5,352,901 A
• Filed: 04/26/1993
• Issued: 10/04/1994
• Est. Priority Date: 04/26/1993
• Status: Expired due to Term

• Current Assignee: Cummins Incorporated
• Original Assignee: Cummins Electronics Company, Inc.
• Inventors: Poorman, Richard N.
• Primary Examiner(s): Nelms, David C.
• Assistant Examiner(s): Lee, John R.
• Application Number:
  US08/052,900
• Time in Patent Office: 526 Days
• Field of Search: 250/574, 250/575, 250/573, 356/343, 356/342, 356/338, 356/336
• US Class Current: 250/574
• CPC Class Codes: G01N 15/0205 by optical means
• CPC Class Codes: G01N 21/532 with measurement of scattering and transmission
• CPC Class Codes: G08B 17/107 for detecting light-scattering due to smoke
• CPC Class Codes: G08B 17/113 Constructional details

Abstract

A forward scattering loss compensated smoke sensor or smoke detector and a back scattering loss compensated smoke detector are disclosed. Both systems include first and second light sources for supplying a light signal into a fluid containing particulates. Both systems also include first and second photodetector devices for detecting directly transmitted, forward scattered and/or back scattered light. A ratiometric value or signal is produced in accordance with direct versus scattered detected light levels. The selection of forward versus back scattering particulate detection devices and methods is driven by the efficiency of the scattering which is a function of light source frequencies and particulate size.

Claims

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

a first light source responsive to signals supplied to a first input to project a first light beam into the fluid;

a second light source responsive to signals supplied to a second input to project a second light beam into the fluid;

a first light detector positioned opposite said first light source to directly receive said first light beam, said first light detector producing a first detector signal corresponding to the intensity of light impinging thereon;

a second light detector positioned opposite said second light source to directly receive said second light beam, said second light detector 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, 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, respectively, in accordance therewith, said control circuit also supplying said power signal to said second input to activate said second light source, said control circuit monitoring and comparing said first and second detector signals to produce a third output signal and a fourth output signal, respectively, 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.

2. The device of claim 1 wherein said said first and said second light detectors are positioned so that forward scattered light from said first or second light beams strikes said second and said first light detectors, respectively.

3. The device of claim 2 including first and second fiber optic means situated between said first and second light sources and said fluid, respectively, to facilitate situating said first and second light sources remotely from said fluid.

4. The device of claim 3 including third and fourth fiber optic means situated between said fluid and said first and second light detectors, respectively, to facilitate situating said first and second light detectors remotely from said fluid.

5. The device of claim 4 wherein each of said first and second light sources includes a light emitting diode for producing light and a focusing means for injecting light emitted by said light emitting diodes into said first and second fiber optic means.

6. The device of claim 5 wherein said first, said second, said third, and said fourth fiber optic means each include a fiber optic connector situated in series with each of said fiber optic means thereby enabling removable connection of said fiber optic means.

7. The device of claim 1 wherein said second light detector is situated to receive back scattered light from said first light source and said first light detector is situated to receive back scattered light from said second light source.

8. The device of claim 7 including first and second fiber optic means situated between said first and second light sources and said fluid, respectively, to facilitate situating said first and second light sources remotely from said fluid.

9. The device of claim 8 including third and fourth fiber optic means situated between said fluid and said first and second light detectors, respectively, to facilitate situating said first and second light detectors remotely from said fluid.

10. The device of claim 9 wherein each of said first and second light sources includes a light emitting diode for producing light and a focusing means for injecting said light emitted by said light emitting diode into said first and second fiber optic means, respectively.

11. The device of claim 10 wherein said first, said second, said third, and said fourth fiber optic means each include a fiber optic connector situated in series with each of said fiber optic means thereby enabling removable connection of said fiber optic means.

12. The device of claim 7 wherein said first light detector and said second light source are situated in close proximity to one another and wherein said second light detector and said first light source are situated in close proximity to one another.

13. The device of claim 1 wherein said first light detector, said second light detector, said first light source and said second light source are situated substantially in a plane perpendicular to the flow of the fluid.

14. The device of claim 1 wherein said ratiometric value is an opacity factor determined by taking the square root of the following value:

the product of said second and said third output signals divided by the product of said first and said fourth output signals.

15. 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.

16. 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.

17. 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.