Flame sensor

• US 6,677,590 B2
• Filed: 09/06/2001
• Issued: 01/13/2004
• Est. Priority Date: 05/14/1999
• Status: Expired due to Fees

• Current Assignee: Kokusai Gijutsu Kaihatsu Kabushiki Kaisha
• Original Assignee: Kokusai Gijutsu Kaihatsu Kabushiki
• Inventors: Hirasawa, Masanori, Nakauchi, Shunsaku
• Primary Examiner(s): Hannaher, Constantine
• Assistant Examiner(s): Gabor, Otilia
• Application Number:
  US09/947,594
• Publication Number:
  US 20030042420A1
• Time in Patent Office: 859 Days
• Field of Search: 250/339.15, 250/339.14, 250/339.05, 250/342, 250/338.1, 250/554, 340/578
• US Class Current: 250/339.15
• CPC Class Codes: G08B 17/12 Actuation by presence of radiation or particles, e.g. of infrared radiation or of ions

Abstract

A flame sensor capable of being easily produced and accurately detecting a flame includes a broadband filter having a transmission band inclusive of a line spectrum of resonance radiation of a carbonic acid gas, a narrowband filter permitting the passage of only the line spectrum of the resonance radiation of the carbonic acid gas and having its band center not coincident with that of the broadband filter, a light reception device, amplifiers, a circuit for computing the difference of mean intensities of spectrums transmitting through the filters and passing through the amplifiers, and a circuit for raising an alarm when the output of the computation circuit exceeds a predetermined value.

Claims

1. A flame sensor comprising:

a narrowband filter which passes only light of a band corresponding to a line spectrum of carbonic acid gas resonance radiation generated by a flame;

a broadband filter which passes light of a band broader than the band corresponding to the line spectrum, and which has a band center different from a band center of the band corresponding to the line spectrum;

a first light reception device which converts light passing through the narrowband filter to an electric signal; and

a second light reception device which converts light passing through the broadband filter to an electric signal.

2. A flame sensor according to claim 1, further comprising:

a judgment device which judges whether or not a difference between a mean intensity of the electric signal of the first light reception device, which is calculated based on bandwidth of the narrowband filter, and a mean intensity of the electric signal of the second light reception device, which is calculated based on bandwidth of the broadband filter, equals to or exceeds a predetermined value.

3. A flame sensor according to claim 2, wherein the difference between the mean intensities is determined by a differential amplifier.

4. A flame sensor according to claim 2, wherein the difference between the mean intensities is calculated by a digital circuit including a CPU.

5. A flame sensor according to claim 2, wherein the predetermined value is varied in accordance with an intensity of the electric signal of the second light reception device.

6. A flame sensor according to claim 1, wherein each of the light reception devices uses one of lead selenide, a thermopile and a pyroelectric-type light reception device.

7. A flame sensor according to claim 1, wherein the presence of a flame can be detected based on an alternating component due to flicker of light from the flame being included in a signal corresponding to the line spectrum of the carbonic acid gas resonance radiation, said signal being obtained on the basis of the two electric signals obtained from said first and second filters.

8. A flame sensor according to claim 1, wherein a dome-shaped diffusive transparent plate is used as a light reception window of the flame sensor.

9. A flame sensor according to claim 1, further comprising:

a preventing member for preventing generating a secondary radiation at the narrowband filter and the broadband filter, the preventing member being provided at a front side of the narrowband filter and the broadband filter.

10. A flame sensor according to claim 9, wherein the preventing member is a silicon plate.

11. A flame sensor comprising:

a first filter having a predetermined band for passing light, and having, within the predetermined band, a band blocking light of a band corresponding to a line spectrum of carbonic acid gas resonance radiation generated by a flame;

a second filter having a band substantially the same as the predetermined band, passing light of a band inclusive of the band corresponding to the line spectrum, and having a band center different from a band center of the band corresponding to the line spectrum;

a first light reception device which converts light passing through the first filter to an electric signal; and

a second light reception device which converts light passing through the second filter to an electric signal.

12. A flame sensor according to claim 11, further comprising:

a judgment device which judges whether or not a difference between a mean intensity of a signal obtained by subtracting the electric signal of the first light reception device from the electric signal of the second light reception device, which is calculated based on bandwidth corresponding to the line spectrum, and a mean intensity of the electric signal of the second light reception device, which is calculated based on bandwidth of the second filter, equals to or exceeds a predetermined value.

13. A flame sensor according to claim 12, wherein the difference between the mean intensities is determined by a differential amplifier.

14. A flame sensor according to claim 12, wherein the difference between the mean intensities is calculated by a digital circuit including a CPU.

15. A flame sensor according to claim 11, wherein each of the light reception devices uses one of lead selenide, a thermopile and a pyroelectric-type light reception device.

16. A flame sensor according to claim 11, wherein the presence of a flame can be detected based on an alternating component due to flicker of light from the flame being included in a signal corresponding to the line spectrum of the carbonic acid gas resonance radiation, said signal being obtained on the basis of the two electric signals obtained from said first and second filters.

17. A flame sensor according to claim 11, wherein a dome-shaped diffusive transparent plate is used as a light reception window of the flame sensor.

18. A flame sensor according to claim 11, further comprising:

a preventing member for preventing generating a secondary radiation at the first filter and the second filter, the preventing member being provided at a front side of the first filter and the second filter.

19. A flame sensor comprising:

a first filter having a predetermined band for passing light, and having, within the predetermined band, a band blocking light of a band corresponding to a line spectrum of carbonic acid gas resonance radiation generated by a flame;

a second filter having a band substantially the same as the predetermined band, passing light of a band inclusive of the band corresponding to the line spectrum, and having a band center different from a band center of the band corresponding to the line spectrum;

a first light reception device which converts light passing through the first filter to an electric signal;

a second light reception device which converts light passing through the second filter to an electric signal; and

a preventing member for preventing generating a secondary radiation at the first filter and the second filter, the preventing member being provided at a front side of the first filter and the second filter.

20. A flame sensor according to claim 19, wherein the preventing member is a silicon plate.

21. A flame sensor according to claim 19, further comprising:

a circuit for calculating a mean intensity of the first light reception device, obtained such that a light energy passing through the first filter is divided by bandwidth of the first filter, and a mean intensity of the second light reception device obtained such that a light energy passing through the second filter is divided by bandwidth of the second filter.