Method and apparatus for detecting flame

• US 4,983,853 A
• Filed: 05/05/1989
• Issued: 01/08/1991
• Est. Priority Date: 05/05/1989
• Status: Expired due to Term

• Current Assignee: John D. Spencer
• Original Assignee: Saskatchewan Power Corporation (Crown Holding Company)
• Inventors: Spencer, John D., Davall, Peter W. N.
• Primary Examiner(s): Willis, Davis L.
• Assistant Examiner(s): Messinger, Michael
• Application Number:
  US07/348,685
• Time in Patent Office: 613 Days
• Field of Search: 250/554, 250/339, 250/342, 250/226, 340/578, 356/315, 431/79, 431/75
• US Class Current: 250/554
• CPC Class Codes: F23N 2223/02 Multiplex transmission
• CPC Class Codes: F23N 2223/08 Microprocessor; Microcomputer
• CPC Class Codes: F23N 2223/10 Correlation
• CPC Class Codes: F23N 5/082 using electronic means
• CPC Class Codes: G08B 17/12 Actuation by presence of radiation or particles, e.g. of infrared radiation or of ions

Abstract

A method of detecting flame within a region where flame is expected. Radiation emissions from the region are measured within selected portions of the visible and infra-red frequency bands. Spectral characteristics of the two measurements, including their auto spectra, coherency and transfer function, are derived. The derived spectral characteristics are compared with prestored spectral signatures representative of the spectral characteristics of radiation emitted from the region within the selected portions of the visible and infra-red frequency bands while known flame conditions prevail within the region--thereby estimating the deviation of the derived spectral characteristics from the prestored spectral signatures. The deviations aforesaid are compared with predetermined threshold alarm values to assess the presence or absence of flame.

Claims

1. A method of detecting flame within a region, comprising the steps of:

(a) measuring radiation emitted from said region within a selected portion of a visible frequency band;

(b) concurrently measuring radiation emitted from said region within a selected portion of an infra-red frequency band;

(c) deriving the coherency between said measurements;

(d) comparing said coherency with a prestored coherency signature representative of the coherency between measurements of radiation emitted from said region within said selected portions of said visible and infra-red frequency bands while known flame conditions prevail within said region, thereby estimating the deviation of said derived coherency from said prestored coherency signature; and

,

(e) comparing said deviation with a first predetermined threshold alarm value.

2. A method as defined in claim 1, further comprising:

(a) deriving the auto spectrum of said visible frequency band measurements;

(b) comparing said visible measurement auto spectrum with a prestored auto spectrum signature representative of the auto spectrum between measurements of radiation emitted from said region within said selected portion of said visible frequency band while known flame conditions prevail within said region, thereby estimating the deviation of said derived visible measurement auto spectrum from said prestored visible auto spectrum signature; and

,

(c) comparing said deviation with a second predetermined threshold alarm value.

3. A method as defined in claim 2, further comprising:

(a) deriving the auto spectrum of said infra-red frequency band measurements;

(b) comparing said infra-red measurement auto spectrum with a prestored auto spectrum signature representative of the auto spectrum between measurements of radiation emitted from said region within said selected portion of said infra-red frequency band while known flame conditions prevail within said region, thereby estimating the deviation of said derived infra-red measurement auto spectrum from said prestored infrared auto spectrum signature; and

,

(c) comparing said deviation with a third predetermined threshold alarm value.

4. A method as defined in claim 3, further comprising:

(a) deriving the transfer function of said visible and infra-red frequency band measurements;

(b) comparing said transfer function with a prestored transfer function signature representative of the transfer function between measurements of radiation emitted from said region within said selected portions of said visible and infra-red frequency bands while known flame conditions prevail within said region, thereby estimating the deviation of said derived transfer function from said prestored transfer function signature; and

,

(c) comparing said deviation with a fourth predetermined threshold alarm value.

5. A method as defined in claim 1, further comprising repeating said measurements for other portions of said visible and infra-red frequency bands.

6. A method as defined in claim 2, further comprising repeating said measurements for other portions of said visible and infra-red frequency bands.

7. A method as defined in claim 3, further comprising repeating said measurements for other portions of said visible and infra-red frequency bands.

8. A method as defined in claim 4, further comprising repeating said measurements for other portions of said visible and infra-red frequency bands.

9. A method as defined in claim 5, wherein said coherency comparing step comprises applying a weighted least squares fit to said derived coherency and said prestored coherency signature.

10. A method as defined in claim 6, wherein said visible auto spectrum comparing step comprises applying a weighted least squares fit to said derived visible auto spectrum and said prestored visible auto spectrum signature.

11. A method as defined in claim 7, wherein said infra-red auto spectrum comparing step comprises applying a weighted least squares fit to said derived infra-red auto spectrum and said prestored infra-red auto spectrum signature.

12. A method as defined in claim 8, wherein said transfer function comparing step comprises applying a weighted least squares fit to said derived transfer function and said prestored transfer function signature.

13. A method as defined in claim 5, wherein said coherency comparing step comprises applying a stochastic fit to said derived coherency and said prestored coherency signature.

14. A method as defined in claim 6, wherein said visible auto spectrum comparing step comprises applying a stochastic fit to said derived visible auto spectrum and said prestored visible auto spectrum signature.

15. A method as defined in claim 7, wherein said infra-red auto spectrum comparing step comprises applying a stochastic fit to said derived infra-red auto spectrum and said prestored infra-red auto spectrum signature.

16. A method as defined in claim 8, wherein said transfer function comparing step comprises applying a stochastic fit to said derived transfer function and said prestored transfer function signature.

17. A method as defined in claim 5, wherein said coherency comparing step comprises applying a bounded limits fit to said derived coherency and said prestored coherency signature.

18. A method as defined in claim 6, wherein said visible auto spectrum comparing step comprises applying a bounded limits fit to said derived visible auto spectrum and said prestored visible auto spectrum signature.

19. A method as defined in claim 7, wherein said infra-red auto spectrum comparing step comprises applying a bounded limits fit to said derived infra-red auto spectrum and said prestored infra-red auto spectrum signature.

20. A method as defined in claim 5, wherein said coherency comparing step comprises applying a Gaussian fit to said derived coherency and said prestored coherency signature.

21. A method as defined in claim 6, wherein said visible auto spectrum comparing step comprises applying a Gaussian fit to said derived visible auto spectrum and said prestored visible auto spectrum signature.

22. A method as defined in claim 7, wherein said infra-red auto spectrum comparing step comprises applying a Gaussian fit to said derived infra-red auto spectrum and said prestored infra-red auto spectrum signature.

23. A method as defined in claim 8, wherein said transfer function comparing step comprises applying a Gaussian fit to said derived transfer function and said prestored transfer function signature.

24. A method as defined in claim 5, further comprising:

(a) weighting said coherency deviation estimates;

(b) summing said weighted estimates;

(c) averaging said summed, weighted estimates; and

,

(d) normalizing said averaged, summed, weighted estimates.

25. A method as defined in claim 6, further comprising:

(a) weighting said visible auto spectrum deviation estimates;

(b) summing said weighted estimates;

(c) averaging said summed, weighted estimates; and

,

(d) normalizing said averaged, summed, weighted estimates.

26. A method as defined in claim 7, further comprising:

(a) weighting said infra-red auto spectrum deviation estimates;

(b) summing said weighted estimates;

(c) averaging said summed, weighted estimates; and

,

(d) normalizing said averaged, summed, weighted estimates.

27. A method as defined in claim 8, further comprising:

(a) weighting said transfer function deviation estimates;

(b) summing said weighted estimates;

(c) averaging said summed, weighted estimates; and

,

(d) normalizing said averaged, summed, weighted estimates.

28. A method as defined in claim 1, further comprising repeating said coherency comparing step with prestored coherency signatures representative of selected flame conditions.

29. A method as defined in claim 2, further comprising repeating said visible auto spectrum comparing step with prestored coherency signatures representative of selected flame conditions.

30. A method as defined in claim 3, further comprising repeating said infra-red auto spectrum comparing step with prestored infra-red auto spectrum signatures representative of selected flame conditions.

31. A method as defined in claim 4, further comprising repeating said transfer function comparing step with prestored transfer function signatures representative of selected flame conditions.

32. A method of detecting flame within a region, comprising the steps of:

(a) deriving "m" data signals x₁ (t), where i=1, 2, . . . m, each of said data signals characterizing radiation emitted from said region within a corresponding portion of the visible frequency band;

(b) sampling each of said data signals "N" times in each of "k" block periods, where "k" is an integer, each block having duration "T" seconds, to derive a plurality of "c" signal samples characterized by x_ik (c);

(c) deriving the discrete auto-power spectrum density estimate S_iik [L] for x_i (t) as;

space="preserve" listing-type="equation">S.sub.iik [L]=X.sub.ik [L] *·

X.sub.ik [L]

where;

X_ik [L]is the complex discrete Fourier transform of sampled signal x_i (t) for the k_th sample block;

"L" =0, 1, . . . N/2-1 is the L_th harmonic component at frequency (L/T) Hertz; and

, "*" denotes the complex conjugate;

(d) comparing said auto-power spectrum density estimate with a prestored auto-power spectrum density signature representative of the auto-power spectrum density between measurements of radiation emitted from said region within said corresponding portions of said visible frequency band while known flame conditions prevail within said region, thereby estimating the deviation of said derived auto-power spectrum density from said prestored auto-power spectrum density signature; and

,

(e) comparing said deviation with a first predetermined threshold alarm value.

33. A method as defined in claim 32, further comprising:

(a) while deriving said data signals x_i (t), concurrently deriving "m" data signals xj(t), where j=1, 2, . . . m, each of said data signals xj(t) characterizing radiation emitted from said region within a corresponding portion of the infra-red frequency band;

(b) sampling each of said data signals xj(t) "N" times in each of "k" block periods, where "k" is an integer, each block having duration "T" seconds, to derive a plurality of "c" signal samples characterized by x_ak (c), where a=1, 2, ... m;

(c) deriving the discrete auto-power spectrum density estimate S_jjk [L] for x_j (t) as;

space="preserve" listing-type="equation">S.sub.jjk [L]=X.sub.jk [L] *·

X.sub.jk [L]

where;

X_jk [L]is the complex discrete Fourier transform of sampled signal x_j (t) for the k_th sample block;

(e) comparing said auto-power spectrum density estimate S_jjk [L] with a prestored auto-power spectrum density signature representative of the auto-power spectrum density between measurements of radiation emitted from said region within said corresponding portions of said infra-red frequency band while known flame conditions prevail within said region, thereby estimating the deviation of said derived auto-power spectrum density S_jjk [L] from said prestored auto-power speotrum density signature; and

,

(e) comparing said deviation with a second predetermined threshold alarm value.

34. A method as defined in claim 33, further comprising:

(a) deriving the discrete modulus squared transfer function estimate H_jik [L] for x_i (t) and x_j (t) as;

space="preserve" listing-type="equation">H.sub.jik [L]=(S.sub.jik [L])*·

S.sub.jik [L])/(S.sub.jk [L]·

S.sub.ik [L])

(b) comparing said discrete modulus squared transfer function estimate with a prestored discrete modulus squared transfer function signature representative of the discrete modulus squared transfer function between measurements of radiation emitted from said region within said corresponding portions of said visible and infra-red frequency bands while known flame conditions prevail within said region, thereby estimating the deviation of said derived discrete modulus squared transfer function from said prestored discrete modulus squared transfer function signature; and

,

(c) comparing said deviation with a third predetermined threshold alarm value.

35. A method as defined in claim 34, further comprising:

(a) deriving the discrete modulus squared coherency function estimate C_jik [L] for x_i (t) and x_j (t) as;

space="preserve" listing-type="equation">C.sub.jik [L]=((S.sub.jik [L])*·

S.sub.jik [L])/(S.sub.jk [L]·

S.sub.ik [L])

(b) comparing said discrete modulus squared coherency function estimate with a prestored discrete modulus squared coherency function signature representative of the discrete modulus squared coherency function between measurements of radiation emitted from said region within said corresponding portions of said visible and infra-red frequency bands while known flame conditions prevail within said region, thereby estimating the deviation of said derived discrete modulus squared coherency function from said prestored discrete modulus squared coherency function signature; and

,

(c) comparing said deviation with a fourth predetermined threshold alarm value.

36. A method as defined in claim 35, further comprising repeating said data signal derivation steps within a plurality of portions of said visible and infra-red frequency bands and then repeating said comparison steps for each of said derived data signals.

37. A method as defined in claim 36, wherein said prestored signatures "z" comprise the average "Z_ave ", minimum "Z_min ", and maximum "Z_max ", values of spectral estimates derived for said known flame conditions, said method further comprising deriving the probability "p(x)" that each of said derived estimates "x" is a measure of the corresponding prestored signature "z", as follows:

(a) if Z_min <

Z_ave ;

deriving e=(x-Z_ave)² ;

deriving e_max =(Z_min -Z_ave)² ;

deriving p(x)=1.0-e/e_max ;

or,

(b) if Z_ave <

x<

Z_max ;

deriving e=(x-Z_ave)² ;

deriving e_max =(Z_max -Z_ave)² ;

deriving p(x)=1.0-e/e_max ;

or,

(c) if (x<

Z_min) or (x>

Z_max);

setting p(x)=0.0.

38. A method as defined in claim 36, wherein said prestored signatures "z" comprise the average "Z_ave ", minimum "Z_min ", and maximum "Z_max ", values of spectral estimates derived for said known flame conditions, said method further comprising deriving the normalized probability "(p[j]/p_max)" that each of said derived estimates "x" is a measure of the corresponding prestored signature "z", where:

space="preserve" listing-type="equation">p[i]=prob{Z, Z.sub.min +i·

δ

<

Z<

Z.sub.min +(i+1)·

δ

};

j=int ((x-Z_min)/δ

)

δ

=(Z_max -Z_min)/n;

Σ

p[i]=1.0; and

,

p_max =max{p[i],i=0 .. n}.

39. A method as defined in claim 36, wherein said prestored signatures "Z" comprise the average "Z_ave ", minimum "Z_min ", and maximum "Z_max ", values of spectral estimates derived for said known flame conditions, said method further comprising deriving the probability "p(x)" that each of said derived estimates "x" is a measure of the corresponding prestored signature "z", as follows:

(a) if Z_minn <

X<

Z_ave ;

deriving e=|X-Z_ave |;

deriving e_max =|Z_min -Z_ave |;

deriving p(x)=1.0-ƒ

(e/e_max);

or,

(b) if Z_ave <

X<

Z_max ;

deriving e=|x-Z_ave |;

deriving e_max =Z_max -Z_ave |;

deriving p(x) =1.0-ƒ

(e/e_max);

or,

(c) if (x<

Z_min) or (x≦

Z_max)l ;

setting p(x)=0.0;

where the function ƒ

(·

) is defined for all values in the range 0, . . . , 1 and is normalized such that;

ƒ

(0)=0;

ƒ

(1)=1; and

,

0≦

ƒ

(·

)≦

1.0.

40. A method as defined in claim 39, wherein said function ƒ

(·

) is a uniform weighting function [ƒ

(x)=1.0 (0<

x<

1.0)].

41. A method as defined in claim 39, wherein said function ƒ

(·

) is a triangular weighting function [ƒ

(x)=x;

(0<

x<

1.0)].

42. A method as defined in claim 39, wherein said function ƒ

(·

) is a cubic weighting function [ƒ

(x)=x³ ].

43. A method as defined in claim 36, wherein said prestored signatures "z" comprise the average "Z_ave ", standard deviation "Z_dev " values of spectral estimates derived for said known flame conditions, said method further comprising deriving the probability "p(x)" that each of said derived estimates "x" is a measure of the corresponding prestored signature "z", as follows:

space="preserve" listing-type="equation">p(x)=exp((x-Zave).sup.2 /Zdev.sup.2).

44. A method as defined in claim 37, further comprising weighting, summing and normalizing said probabilities to obtain an overall fit probability "p_fit ", where:

p_fit =Σ

w[i]·

p(x[i]), for all estimates x[i]; and

, Σ

w[i]=1.0.

45. A method as defined in claim 38, further comprising weighting, summing and normalizing said probabilities to obtain an overall fit probability "p_fit ", where:

p_fit =Σ

w[i]·

p(x[i]), for all estimates x[i]; and

, Σ

w[i]=1.0.

46. A method as defined in claim 39, further comprising weighting, summing and normalizing said probabilities to obtain an overall fit probability "p_fit ", where:

p_fit =Σ

w[i]·

p(x[i]), for all estimates x[i]; and

, Σ

w[i]=1.0.

47. A method as defined in claim 43, further comprising weighting, summing and normalizing said probabilities to obtain an overall fit probability "p_fit ", where:

p_fit =Σ

w[i]·

p(x[i]), for all estimates x[i]; and

, Σ

w[i]=1.0.

48. A method as defined in claim 44, wherein said deviation comparison step comprises deriving said deviation "d[i]" as:

space="preserve" listing-type="equation">d[i]=min{|x[i]ave-Z[i]ave|/Z[i]dev}

where;

Z[j], J=0,1,1. . . m, is a predetermined flame "off" signature;

X is a predetermined flame "on" signature;

[i]_ave denotes the average signature value; and

[i]_dev denotes the signature standard deviation.

50. A method as defined in claim 48, wherein:

(a) said signature weighting function 2[i]=(d[i]/d_max)² ; and

,

(b) d_max =Σ

d[i] for all spectral functions x[i].

49. A method as defined in calim 48, wherein:

(a) said signature weighting function w[i]=(d[i]/d_max); and

,

(b) d_max =Σ

d[i] for all spectral functions x[i].