DETECTION OF PARTICLE CHARACTERISTICS

• US 20110255087A1
• Filed: 09/04/2009
• Published: 10/20/2011
• Est. Priority Date: 09/05/2008
• Status: Active Grant

• Current Assignee: Garrett Thermal Systems Ltd. (Honeywell International Inc.)
• Original Assignee: Xtralis Technologies Ltd (Honeywell International Inc.)
• Inventors: Vayeda, Nitin, Alexander, Brian, Ajay, Kemal
• Granted Patent: US 9,128,047 B2
• Time in Patent Office: Days
• US Class Current: 356/338
• CPC Class Codes: G01F 1/667 Arrangements of transducers for ultrasonic flowmeters; Circuits for operating ultrasonic flowmeters
• CPC Class Codes: G01N 15/06 Investigating concentration of particle suspensions by weighing G01N5/00; investigating sedimentation of particle suspensions G01N15/04; investigating individual particles G01N15/10
• CPC Class Codes: G01N 15/075 by optical means
• CPC Class Codes: G01N 15/1434 Optical arrangements
• CPC Class Codes: G01N 2021/4733 Discriminating different types of scatterers
• CPC Class Codes: G01N 21/53 within a flowing fluid, e.g. smoke
• CPC Class Codes: G01N 2201/061 Sources
• CPC Class Codes: G01N 2201/062 LED's
• CPC Class Codes: G08B 17/10 Actuation by presence of smoke or gases , e.g. automatic alarm devices for analysing flowing fluid materials by the use of optical means
• CPC Class Codes: G08B 17/107 for detecting light-scattering due to smoke
• CPC Class Codes: G08B 17/113 Constructional details
• CPC Class Codes: G08B 29/26 by updating and storing reference thresholds

Abstract

A method of detecting particles in an air flow is described. The method includes receiving a signal indicative of light intensity scattered from the air flow at a plurality of wavelengths and processing the signal indicative of the intensity of received light at each of the wavelengths and a corresponding wavelength dependent parameter to generate an output signal indicative of at least one characteristic of particles in the air flow. A particle detection system is also described.

Claims

1. A method of detecting particles in an airflow including:

receiving a signal indicative of light intensity scattered from the air flow at a plurality of wavelengths;

processing the signal indicative of the intensity of received light at each of the wavelengths and a corresponding wavelength dependent parameter to generate an output signal indicative of at least one characteristic of particles in the air flow.

2. The method of claim 1 wherein the step of processing includes:

fitting at least one function to the signals indicative of the intensity of received light and corresponding wavelength dependent parameters; and

determining an output signal indicative of at least one characteristic of particles in the air flow on the basis of the at least one function.

3. The method of claim 2 including fitting a plurality of functions to the signals indicative of the intensity of received light and their corresponding wavelength dependent parameters.

5. The method of claim 3 wherein the, or one of the, functions is a polynomial.

6. The method of claim 3 wherein the output signal is determined on the basis of a gradient at, at least one point on at least one of said functions.

7. The method of claim 5 in which a plurality of linear functions are fitted to two or more signals and their corresponding wavelength dependent parameters.

8. The method of claim 7 wherein the output signal is determined on the basis of the gradient of a plurality of said linear functions.

9. The method of claim 7 wherein the two or more signals used to fit a linear function are represent scattered light at adjacent wavelengths.

10. The method of claim 7 wherein the two or more signals used to fit each linear function include a signal corresponding to a common wavelength.

11. The method of claim 1 wherein the step of processing the signal indicative of the intensity of received light at each of the wavelengths and a corresponding wavelength dependent parameter includes, applying a statistical method to the signal indicative of the intensity of received light at each of the wavelengths and a corresponding wavelength dependent parameter to generate an output signal indicative of a characteristic of particles in the air flow.

12. The method as claimed in claim 1 wherein the wavelength dependent parameter is selected from:

wavelength, energy or frequency;

or

a parameter based on wavelength, energy or frequency.

13. The method of claim 2 includes comparing the at least one function to one or more predetermined signatures corresponding to one or more characteristics of particles in the air flow.

14. The method of detecting particles as claimed in claim 1 wherein the step processing the signal indicative of the intensity of received light at each of the wavelengths and a corresponding wavelength dependent parameter to generate an output signal indicative of a characteristic of particles in the air sample includes:

comparing the signal indicative of the intensity of received light at a plurality of wavelengths to one or more predetermined signatures corresponding to one or more characteristics of particles in the airflow.

15. The method of detecting particles as claimed in claim 1 wherein at least three wavelengths are used.

16. The method of detecting particles as claimed in claim 1 wherein four wavelengths are used.

17. The method as claimed in claim 13 wherein one or more of the predetermined signatures can relate to any one or more of the following characteristics of particles in the airflow:

particle size, particle size distribution, particle colour, particle composition, particle type, particle shape, fire type, fire progression stage, particles produced by a certain combustion material.

18. The method as claimed in claim 15 wherein a predetermined signature can correspond to the following particle types:

smoke particles, dust particles, lint particles, other nuisance particles, macroscopic foreign bodies, particles in a predetermined size range, particles produced by combustion of a certain material.

19. The method as claimed in claim 1 which includes normalising either or both of, the signals indicative of the intensity of received light, or their corresponding wavelength dependent parameters.

20. The method as claimed in claim 1 which further includes repeating said method one or more times to track at least one characteristic of the particles in the air flow characterised by the output signal output over time.

21. The method as claimed in claim 20 wherein the method further includes comparing at least one tracked characteristic over time to a time based signature.

22. The method as claimed in claim 21 which further includes, identifying a condition based on said comparison.

23. The method as claimed in claim 21 in which the condition is selected from:

a fire, a change in a fire, progression of a fire stage, dust producing event, a transient nuisance condition, detector fault, encroachment of a foreign body into the detection chamber, the combustion of a certain material.

24. The method as claimed in claim 1 which includes pre-processing the signal indicative of the intensity of received light at a wavelength to remove the effect of background light.

25. The method as claimed in claim 1 which further includes determining a concentration of particles in a size range on the basis of the output signal.

26. A particle detection system including:

a detection chamber adapted to receive an air sample;

means for illuminating the air sample at a plurality of wavelengths;

means for receiving light scattered from the air sample at the plurality of wavelengths and to output a signal indicative of the intensity of received light at each of the wavelengths; and

processing means for processing the signal indicative of the intensity of received light at each of the wavelengths and a corresponding wavelength dependent parameter to generate an output signal indicative of at least one characteristic of particles in the air sample using a method as claimed in any one of the preceding claims.

4. (canceled)

27. A particle detection system for including:

a detection chamber adapted to receive an air sample;

first particle detection means including a first light source for illuminating a first volume of the air sample at least a first wavelength, and a first light receiver having a field of view intersecting with the first volume for receiving light scattered from the detection chamber and outputting a first signal indicative of the scattered received light;

second particle detection means including a second light source for illuminating a second volume of the air sample at least a second wavelength, and a second light receiver having a field of view intersecting with the second volume for receiving light scattered from the detection chamber and outputting a second signal indicative of the scattered received light;

light source activation means adapted to selectively activate the first light source in a first time period and the second light source in a second time period; and

processing means adapted to receive a first signal from the first light receiver and a second signal from the second light receiver corresponding to the first time period and process the received signals to generate a first output corresponding to the first time period corrected for background light; and

to receive a first signal from the first light receiver and a second signal from the second light receiver corresponding to the second time period and process the received signals to generate a second output corresponding to the second time period that is corrected for background light.

28. The particle detection system as claimed in claim 27 wherein the detection chamber includes at least one wall within the field of view of each of the first and second light receivers and wherein the first and second light receivers are positioned such that substantially the same portion of said chamber wall lies within the field of view of each of the first and second light receivers.

29. The particle detection system as claimed in claim 27 wherein the first and second light receivers are positioned with respect to their corresponding first and second light sources such that the field of view of the first light receiver and the second volume do not intersect, and the field of view of the second light receiver and the first volume do not intersect.

30. The particle detection system as claimed in claim 27 wherein the first and second wavelengths are different wavelengths.

31. The particle detection system as claimed in claim 27 wherein the first output corresponding to the first time period is corrected for background light by a process including subtracting the second signal indicative of the scattered received light corresponding to the first time period from the first signal indicative of the scattered received light corresponding to the first time period.

32. The particle detection system as claimed in claim 27 wherein the second output corresponding to the second time period is corrected for background light by a process including subtracting the first signal indicative of the scattered received light corresponding to the second time period from the second signal indicative of the scattered received light corresponding to the second time period.

33. The particle detection system as claimed in claim 27 wherein the first and second wavelengths are the same wavelengths.

35. The ultrasonic flow sensor as claimed in claim 33 wherein a cross sectional shape of the input port is different to a cross sectional shape of the flow sensing chamber.

34. An ultrasonic flow sensor including an input port for receiving an air sample said input port having a first cross-sectional area, and an output port through which an air sample leaves the flow sensor, a flow sensing chamber extending between the input port and the outlet port, wherein the cross sectional area of the flow sensing chamber is substantially equal to that of the input port.