METHANE GAS DETECTION SYSTEM USING INFRARED

• US 3,662,171 A
• Filed: 09/21/1970
• Issued: 05/09/1972
• Est. Priority Date: 09/21/1970
• Status: Expired due to Term

• Current Assignee: Singer PLC (Hayleys Plc)
• Original Assignee: Andrew J. Brengman, Maxwell R. Krasno
• Inventors: Brengman, Andrew J., Krasno, Maxwell R.
• Primary Examiner(s): Borchelt, Archie R.
• Application Number:
  US05/073,787
• Time in Patent Office: 596 Days
• Field of Search: 250/43.5R,83.3H
• US Class Current: 250/342
• CPC Class Codes: G01M 3/002 by using thermal means
• CPC Class Codes: G01M 3/38 by using light G01M3/02 takes precedence
• CPC Class Codes: G01N 21/3504 for analysing gases, e.g. multi-gas analysis

Abstract

A gas detection system utilizing infrared absorption properties of the gas in a very narrow, predetermined wavelength band located in an atmospheric spectrum window. An airborne surveillance system employs the earth as a temperature source and compensates for temperature changes by utilization of reference and analysis frequency bands while employing a large field of view.

Claims

2. The method of claim 1 further defined by forming said detector to have a response that is maximum at the center thereof and which decreases toward the detector edges.

3. The method of claim 3 further defined by filtering the output of said detector to remove high frequency components therefrom.

4. The method of claim 1 further defined by measuring the temperature of said detector and at least periodically compensating the detector output for temperature variations thereof.

5. THe method of claim 1 further defined by flying an airplane containing said infrared detector at an altitude in the range of 300 to 500 feet and limiting the field of view of said detector to a solid angle of the order of 4 to 5*.

6. The method of claim 1 further defined by said analysis band being limited substantially to the range of 7.67 to 7.78 micrometers wavelength.

7. A system for detection of methane gas in the atmosphere that may result from gas leaks in a high pressure pipeline comprising an airborne infrared detector;

means directing said detector toward the earth as a source of infrared radiation at a distance therefrom to thus produce electrical signals having amplitudes proportional to detected radiation;

first and second filter means respectively passing a first analysis band of infrared radiation wavelengths and a second reference band of infrared radiation wavelengths, said analysis band comprising wavelengths in the range of substantially 7.67 to 8.16 micrometers wavelength in which methane has a high absorption and there is very little absorption by water vapor, said reference band comprising wavelengths in the range of substantially 8.16 to 8.58 micrometers wavelength in which there is very little absorption by methane or water vapor;

means rapidly moving said filter means to alternately dispose said first filter means and said second filter means in front of said detector whereby said detector produces output signals alternately responsive to detected infrared radiation in said analysis and reference bands;

comparator means receiving the output of said detector and providing an alternating current comparison of the output signals thereof; and

means indicating the results of said comparison.

8. A system for detection of a predetermined gas in the atmosphere that is not normally present therein in appreciable quantities comprising an infrared detector;

means directing said detector toward a source of infrared radiation at a distance therefrom to thus produce electrical signals having amplitudes proportional to detected radiation;

first and second filter means respectively passing a first analysis band of infrared radiation wavelengths and a second reference band of infrared radiation wavelengths, said analysis band comprising a range of wavelengths in which said predetermined gas has a high absorption and there is very little absorption by water vapor, said reference band comprising a range of wavelengths of which there is very little absorption by said gas or water vapor;

means rapidly moving said filter means to alternately dispose said first filter means and said second filter means in front of said detector whereby said detector produces output signals alternately responsive to detected infrared radiation in said analysis and reference bands;

temperature sensing means disposed adjacent said detector and producing electrical signals proportional to the detector temperature, an additional second filter means having a reflective surface on the side opposite thereof from said detector and moved with said first and second filter means across said detector to produce a temperature output signal from said detector comparator means receiving the output of said detector and providing an alternating current comparison thereof;

means compensating said comparator means by said detector temperature signal and temperature sensing means output; and

means indicating the results of said comparison.

9. The system of claim 7 further defined by a filter position signal generator operating in synchronism with said filter movement and producing a switching signal indicating which filter is in front of said detector, a pair of amplifier channels connected to inputs of said comparator means, and switching means connected to said detector and controlled by said switching signal to apply analysis band detector signals to a firsT channel and reference band detection signals to a second channel.

10. The system of claim 9 further defined by a periodically operating nulling circuit connected to an amplifier in said first channel for periodically changing the gain thereof to compensate for drift in the system.

11. The system of claim 7 further defined by said detector being adapted for mounting upon an airplane with a field of view toward the ground of the order of 4 to 5* of solid angle, temperature sensing means disposed adjacent said detector and producing electrical signals proportional to detector temperature, an additional second filter means having a reflective surface on the opposite side thereof from said detector and moved with said first and second filter means across said detector to produce temperature output signals from said detector, a temperature function comparator storing the function of difference with temperature of detector response to earth source in said analysis band and said reference band, means applying to said temperature function comparator the output said temperature sensing means and the detector output from said second filter and other reflective second filter, controllable amplifying means connected to the output of said detector, and gain control means connected to said temperature function comparator and said amplifying means for controlling the amplification of detector signals in the analysis band to maintain a null indication in the absence of said predetermined gas in the field of view of said detector.