Thermography camera configured for leak detection

• US 8,659,664 B2
• Filed: 03/23/2007
• Issued: 02/25/2014
• Est. Priority Date: 03/23/2007
• Status: Active Grant

• Current Assignee: Teledyne FLIR LLC (Teledyne Technologies Incorporated)
• Original Assignee: FLIR Systems, Inc. (Teledyne Technologies Incorporated)
• Inventors: Benson, Robert G., Scanlon, Thomas J., Czerepuszko, Paul A.
• Primary Examiner(s): Lee, Michael
• Application Number:
  US11/726,918
• Publication Number:
  US 20080231719A1
• Time in Patent Office: 2,531 Days
• Field of Search: 348/222.1, 348164-166, 250/330, 250/339.03, 250/338.1, 250/338.4, 250/339.01, 250/332
• US Class Current: 348/164
• CPC Class Codes: G01J 2005/0077 Imaging
• CPC Class Codes: G01J 5/06 Arrangements for eliminating effects of disturbing radiation; Arrangements for compensating changes in sensitivity for adjusting of solid angle of collected radiation G01J5/07; means for wavelength selection G01J5/0801
• CPC Class Codes: G01J 5/061 by controlling the temperature of the apparatus or parts thereof, e.g. using cooling means or thermostats
• CPC Class Codes: G01J 5/0802 Optical filters
• CPC Class Codes: G01J 5/0806 Focusing or collimating elements, e.g. lenses or concave mirrors
• CPC Class Codes: G01N 2021/1793 Remote sensing
• CPC Class Codes: G01N 2021/3531 without instrumental source, i.e. radiometric
• CPC Class Codes: G01N 21/3518 Devices using gas filter correlation techniques; Devices using gas pressure modulation techniques
• CPC Class Codes: H04N 23/54 Mounting of pick-up tubes, electronic image sensors, deviation or focusing coils
• CPC Class Codes: H04N 5/33 Transforming infrared radiation cameras or camera modules for generating image signals from infrared radiation H04N23/20; circuitry of SSIS for transforming infrared radiation into image signals H04N25/20

Abstract

A portable camera system (100) includes a lens (104) for forming a focused image of a survey scene (106) onto a focal plane array (108). The focal plane array (108) comprises a cooled two dimensional array of quantum well infrared photo detectors, (QWIP) having a peak spectral responsivity in the wavelength range of 10.4 to 10.8 μm. The camera includes a cooled band pass optical filter (110) having a peak spectral transmittance approximately centered at a wavelength of 10.57 μm and a full width half maximum spectral transmittance bandwidth of approximately 10.3 to 10.7 μm. The camera system (100) is usable to detect an invisible gas plume in a video image of a survey scene if the gas plume contains sulfur hexafluoride (SF₆), ammonia, (NH₃), Uranyl Fluoride (U₂O₂F₂), or any other gas having an absorption band that that at least partially falls within the wavelength band 10.3 to 10.8 μm.

Claims

1. A camera system configured to render a video image of a scene, the camera system comprising:

a lens element having a field of view for collecting radiation from the scene and forming a focused image of the scene at a focal plane;

a focal plane array, disposed substantially coincident with the focal plane, comprising an active area formed by a two dimensional array of quantum well infrared photo detectors (QWIPs) each having an active surface and each generating a photo current responsivity profile in response to an irradiance at the active surface, wherein the QWIPs are tuned using alternating layers of quantum wells and barriers to have a photo current responsivity profile having a peak response within a wavelength range of 10.4 μ

m to 10.8 μ

m and a full width half maximum spectral bandwidth of less than 0.7 μ

m;

a narrowband optical filter positioned between the focal plane array and the lens element and having a peak transmittance within the wavelength range of 10.4 μ

m to 10.8 μ

m;

a housing for enclosing the focal plane array therein and for supporting the lens element attached to a surface thereof;

a readout, contained within the housing and associated with the focal plane array, for reading a photo current output from each QWIP; and

a signal processor, contained within the housing, for receiving the photo current output from each QWIP from the readout, for converting the photo current output from each QWIP to a digital signal value, and for rendering a video image of the scene in accordance with the digital signal values, wherein the less than 0.7 μ

m spectral bandwidth of the focal plane array is selected to reduce signal noise substantially outside the wavelength range of 10.4 μ

m to 10.8 μ

m associated with the optical band pass filter and/or the focal plane array.

2. The camera system of claim 1, wherein:

the narrowband optical band pass filter has a transmittance of 0.1% or less of the peak transmittance outside the wavelength range of 10.4 μ

m to 10.8 μ

m; and

the less than 0.7 μ

m spectral bandwidth of the focal plane array is selected to reduce dark current associated with the optical band pass filter and/or the focal plane array.

3. The camera system of claim 2 further comprising a refrigeration device contained within the housing and configured to cool the focal plane array and the optical band pass filter to an operating temperature of less than 65°

K.

4. The camera system of claim 1 wherein

the quantum well layers comprise GaAs doped with silicon to generate a desired flow of free electrons in response to the radiation and wherein

the barrier layers AlGaAs.

5. The camera system of claim 2 further comprising a vacuum tight enclosure formed to enclose the focal plane array and the optical band pass filter in a vacuum cavity drawn down to a vacuum pressure to thermally insulate elements contained with the vacuum cavity.

6. The camera system of claim 5 further comprising a video driver and a video display device, each contained within the housing, and wherein the video driver receives the video image from the signal processor and formats the video image for display on the display device.

7. The camera system of claim 6 further comprising a user interface module comprising actuator elements disposed on external surfaces of the housing for converting user actions into input commands suitable for operating the camera system in one or more operating modes.

8. The camera system of claim 7 further comprising a power module that includes a rechargeable battery attached to the housing for operating the camera system as a portable device.

9. A method for detecting a gaseous compound in a survey scene comprising:

collecting radiation from the survey scene with a lens element;

passing the radiation collected from the survey scene through an optical band pass filter configured with a transmittance profile having a peak transmittance and a full width half maximum transmittance spectral bandwidth each falling within a wavelength range of 10.3 μ

m to 10.8 μ

m;

focusing the radiation collected from the survey scene and filtered by the optical band pass filter onto a focal plane comprising an active area formed by a two dimensional array of quantum well infrared photo detectors (QWIPs) each having an active surface and each generating a photo current responsivity profile in response to an irradiance at the active surface, wherein the QWIPs are tuned using alternating layers of quantum wells and barriers to have a photo current responsivity profile having a peak response within a wavelength range of 10.4 μ

m to 10.8 μ

m and a full width half maximum spectral bandwidth of less than 0.7 μ

m;

reading out analog photo current values from each QWIP; and

converting the analog photo current values to corresponding digital signal values; and

rendering a video image corresponding to the digital signal values, wherein the less than 0.7 μ

m spectral bandwidth of the focal plane array is selected to reduce signal noise substantially outside the wavelength range of 10.4 μ

m to 10.8 μ

m associated with the optical band pass filter and/or the focal plane array.

10. The method of claim 9, further comprising cooling the focal plane array to an operating temperature of less than 65°

K.

11. The method of claim 10 further comprising:

formatting the video image for display on a display device; and

,

displaying the video image on a display device.

12. The method of claim 11 wherein the formatting the video image further comprises:

generating video signals for displaying text or graphic information that may be informative to a user; and

,

displaying the video signals simultaneously with the video image.

13. The method of claim 12 further comprising repeating the following at a rate of 15 to 100 cycles per second:

reading out analog photo current values from each QWIP;

converting the analog photo current values to corresponding digital signal values;

rendering a video image corresponding to the digital signal values;

formatting the video image for display on the display device; and

,

displaying the video image on the display device.

14. The method of claim 13 further comprising:

pointing the camera system at a survey scene that may include a gas leak plume comprising a compound having an absorption band that at least partially falls within the wavelength range of 10.4 μ

m to 10.8 μ

m; and

,

observing the display device to determine if there is a gas leak plume visible on the display device.

15. The method of claim 9, wherein:

the passing the radiation collected from the survey scene through an optical band pass filter comprises passing the radiation collected from the survey scene through an optical band pass filter configured with a transmittance profile having a peak transmittance and a full width half maximum transmittance spectral bandwidth each falling within a wavelength range of 10.3 μ

m to 10.7 μ

m; and

the less than 0.7 μ

m spectral bandwidth of the focal plane array is selected to reduce dark current associated with the optical band pass filter and/or the focal plane array.

16. The method of claim 15 further comprising:

pointing the camera system at a survey scene that may include a gas leak plume comprising a compound having an absorption band that at least partially falls within the wavelength range of 10.3 μ

m to 10.7 μ

m; and

,

observing the display device to determine if there is a gas leak plume visible on the display device.

17. The method of claim 13 wherein the displaying the video image includes displaying a black and white grey scale image with different grey scale values corresponding with different analog photo current values.

18. The method of claim 13 wherein the displaying the video image includes displaying a color image with different colors corresponding with different analog photo current values.