Method and system for detecting gases or vapors in a monitored area

• US 6,061,141 A
• Filed: 01/20/1998
• Issued: 05/09/2000
• Est. Priority Date: 01/20/1998
• Status: Expired due to Term

• Current Assignee: Spectronix Ltd. (Emerson Electric Company)
• Original Assignee: Spectronix Ltd. (Emerson Electric Company)
• Inventors: Goldenberg, Ephraim, Spector, Yechiel, Serero, Shaul, Jacobson, Esther, Cohen, David
• Primary Examiner(s): Rosenberger, Richard A.
• Application Number:
  US09/009,421
• Time in Patent Office: 840 Days
• Field of Search: 356/437, 356/409, 356/410, 356/411, 250/343, 250/345
• US Class Current: 356/437
• CPC Class Codes: G01N 21/3504 for analysing gases, e.g. multi-gas analysis

Abstract

A method of detecting the presence of a predetermined vapor of a predetermined concentration in a monitored area, the method including the steps of (a) exposing gas in or from the monitored area to radiation at wavelengths at least covering and surrounding from both sides a main absorption peak of the vapor; (b) simultaneously sensing the radiation after passing through the gas by a signal sensor and a reference sensor, each of the sensors including a radiation sensing element, wherein the signal sensor further includes a first optical filter passing wavelengths covering the main absorption peak, yet substantially blocking wavelengths from both sides of the main absorption peak of the vapor, whereas the reference sensor further includes a second optical filter passing wavelengths surrounding from both sides the main absorption peak, yet substantially blocking wavelengths covering the main absorption peak of the vapor; and (c) comparing signals obtained from the signal and reference sensors for determining a presence or absence of the vapor of the predetermined concentration in the gas.

Claims

1. A method of increasing the sensitivity of detecting the presence of a predetermined first vapour of a predetermined threshold concentration having a first main absorption peak in a monitored area in optional presence of a second vapour having a second, yet close, main absorption peak, the method comprising the steps of:

(a) exposing gas at the monitored area to radiation at wavelengths at least covering and surrounding from both sides said main absorption peaks of the vapours;

(b) simultaneously sensing said radiation after passing via an open path through said gas by three independent sensors including a signal sensor, a reference sensor and an additional sensor identical to said signal or to said reference sensor, each of said three sensors including a radiation sensing element, wherein said signal sensor further includes a first optical filter passing wavelengths covering said first main absorption peak, yet substantially blocking wavelengths from both sides said first main absorption peak and wavelengths covering said second main absorption peak, whereas said reference sensor further includes a second optical filter passing wavelengths surrounding from both sides said first main absorption peak, yet substantially blocking wavelengths covering said first and second main absorption peaks; and

(c) comparing signals obtained from said three sensors for determining a presence or absence of the first vapour of the predetermined concentration in said gas.

2. The method of claim 1, wherein said radiation is effected via a radiation source selected from the group consisting of a flashlamp and a modulated filament lamp.

3. The method of claim 2, wherein said flashlamp is a quarts Xenon flashlamp.

4. The method of claim 1, wherein said second filter is a notch filter.

5. The method of claim 4, wherein said notch filter includes a first substance passing radiation at wavelengths covering and surrounding from both sides said first main absorption peak and a second substance substantially blocking radiation at wavelengths covering said first main absorption peak.

6. The method of claim 1, wherein said first filter includes a first substance passing radiation at wavelengths covering said first main absorption peak and a second substance substantially blocking radiation at wavelengths covering said second main absorption peak.

7. A method of detecting the presence of a predetermined vapour of a predetermined threshold concentration in a monitored area, the method comprising the steps of:

(a) exposing gas at the monitored area to radiation at wavelengths at least covering and surrounding from both sides a main absorption peak of the vapour;

(b) simultaneously sensing said radiation after passing via an open path through said gas by three independent sensors including a signal sensors, a reference sensor and an additional sensor identical to said signal or to said reference sensor, each of said three sensors including a radiation sensing element, wherein said signal sensor further includes a first optical filter passing wavelengths covering said main absorption peak, yet substantially blocking wavelengths from both sides of said main absorption peak of the vapour, whereas said reference sensor further includes a second optical filter passing wavelengths being close from at least one side to said main absorption peak, yet substantially blocking wavelengths covering said main absorption peak of the vapour; and

(c) comparing signals obtained from said three sensors for determining a presence or absence of the vapour of the predetermined concentration in said gas, thereby obviating the need for a beamsplitter.

8. The method of claim 7, wherein said radiation is effected via a radiation source selected from the group consisting of a flashlamp and a modulated filament lamp.

9. The method of claim 8, wherein said flashlamp is a quarts Xenon flashlamp.

10. The method of claim 7, wherein said second filter passes wavelengths surrounding from both sides said main absorption peak, yet substantially blocking wavelengths covering said main absorption peak of the vapour.

11. The method of claim 10, wherein said second filter is a notch filter.

12. The method of claim 11, wherein said notch filter includes a first substance passing radiation at wavelengths covering and surrounding from both sides said main absorption peak and a second substance substantially blocking radiation at wavelengths covering said main absorption peak.

13. The method of claim 7, wherein said three sensors include two units of said reference sensor and a single unit of said signal sensor.

14. The method of claim 7, wherein said three sensors include two units of said signal sensor and a single unit of said reference sensor.

15. The method of claim 7, wherein said three sensors include two signal sensors, one of said signal sensors further includes a third optical filter passing wavelengths covering a second main absorption peak of the vapour, yet substantially blocking wavelengths surrounding from both sides said second main absorption peak of the vapour.

16. The method of claim 7, wherein said comparison is accompanied by a re-zeroing procedure in which zero ratios of signals obtained from said signal and reference sensors are redefined in accordance with non-vapour spectral disturbances.

17. A system for increasing the sensitivity of detecting the presence of a predetermined first vapour of a predetermined threshold concentration having a first main absorption peak in a gas in a monitored area in optional presence of a second vapour having a second, yet close, main absorption peak, the system comprising:

(a) a radiation source for providing radiation at wavelengths at least covering and surrounding from both sides said main absorption peaks of the vapours; and

(b) three independent sensors including;

(i) a signal sensor including a first radiation sensing element and a first optical filter passing wavelengths covering said first main absorption peak, yet substantially blocking wavelengths from both sides of said first main absorption peak and wavelengths covering said second main absorption peak;

(ii) a reference sensor including a second radiation sensing element and a second optical filter passing wavelengths surrounding from both sides said first main absorption peak, yet substantially blocking wavelengths covering said first and second main absorption peaks; and

(iii) an additional sensor being identical to said signal sensor or to said reference sensor;

wherein an open path exists between said radiation source and each of said sensors such that simultaneously sensing said radiation after passing via said open path through the gas by said three independent sensors and comparing signals obtained from said sensors enables determining a presence or absence of the first vapour of the predetermined concentration in the gas.

18. The system of claim 17, wherein said radiation is effected via a radiation source selected from the group consisting of a flashlamp and a modulated filament lamp.

19. The system of claim 18, wherein said flashlamp is a quarts Xenon flashlamp.

20. The system of claim 17, wherein said second filter is a notch filter.

21. The system of claim 20, wherein said notch filter includes a first substance passing radiation at wavelengths covering and surrounding from both sides said first main absorption peak and a second substance substantially blocking radiation at wavelengths covering said first main absorption peak.

22. The system of claim 17, wherein said first filter includes a first substance passing radiation at wavelengths covering said first main absorption peak and a second substance substantially blocking radiation at wavelengths covering said second main absorption peak.

23. A system for detecting the presence of a predetermined vapour of a gas in a predetermined threshold concentration in a monitored area, the system comprising:

(a) a radiation source for providing radiation at wavelengths at least covering and surrounding from both sides a main absorption peak of the vapour; and

(b) three independent sensors including;

(i) a signal sensor including a first radiation sensing element and a first optical filter passing wavelengths covering said main absorption peak, yet substantially blocking wavelengths from both sides of said main absorption peak of the vapour;

(ii) a reference sensor including a second radiation sensing element and a second optical filter passing wavelengths being close from at least one side to said main absorption peak, yet substantially blocking wavelengths covering said main absorption peak of the vapour; and

(iii) an additional sensor being identical to said signal sensor or to said reference sensor;

wherein an open path exists between each of said three independent sensors and said radiation source, such that simultaneously sensing said radiation after passing via said open path through the gas by said three independent sensors and comparing signals obtained from said sensors enables determining a presence or absence of the vapour of the predetermined concentration in the gas, and obviates the need for a beamsplitter.

24. The system of claim 23, wherein said radiation is effected via a radiation source selected from the group consisting of a flashlamp and a modulated filament lamp.

25. The system of claim 24, wherein said flashlamp is a quarts Xenon flashlamp.

26. The system of claim 23, wherein said second filter passes wavelengths surrounding from both sides said main absorption peak, yet substantially blocking wavelengths covering said main absorption peak of the vapour.

27. The system of claim 26, wherein said second filter is a notch filter.

29. The system of claim 23, wherein said three sensors include two units of said reference sensor and a single unit of said signal sensor.

30. The system of claim 23, wherein said three sensors include two units of said signal sensor and a single unit of said reference sensor.

31. The system of claim 23, wherein said three sensors include two signal sensors, one of said signal sensors further includes a third optical filter passing wavelengths covering a second main absorption peak of the vapour, yet substantially blocking wavelengths from both sides of said second main absorption peak of the vapour.

32. The system of claim 23, further comprising a window being substantially transparent to said radiation and positioned in front of said reference sensor.

33. The system of claim 23, further comprising a housing formed with windows being substantially transparent to said radiation and positioned in front of each of said three sensors, said widows being covered with a water repellent material.

28. The system of claim 37, wherein said notch filter includes a first substance passing radiation at wavelengths covering and surrounding from both sides said main absorption peak and a second substance substantially blocking radiation at wavelengths covering said main absorption peak.