Synthetic reference thermal imaging method

• US 6,367,969 B1
• Filed: 05/10/2000
• Issued: 04/09/2002
• Est. Priority Date: 07/21/1999
• Status: Expired due to Fees

• Current Assignee: General Electric Company
• Original Assignee: General Electric Company
• Inventors: Howard, Donald R., Ringermacher, Harry I.
• Primary Examiner(s): Gutierrez, Diego
• Assistant Examiner(s): PRUCHNIC, STANLEY J
• Application Number:
  US09/568,053
• Time in Patent Office: 699 Days
• Field of Search: 374/4-7, 250/341.6, 250/330, 250/332
• US Class Current: 374/7
• CPC Class Codes: G01N 25/72 Investigating presence of flaws

Abstract

In an infrared (IR) transient thermography system a sequence of image frames is acquired from an IR sensitive focal-plane array camera. Each sequentially acquired image frame is made up of an array of pixels and has assigned a frame number that corresponds to elapsed time. A method of analyzing thermal imaging data-frames is presented wherein a synthetically generated temperature-time reference curve is used to determine pixel contrast-versus-time data.

Claims

1. In an infrared (IR) transient thermography system wherein a sequence of image frames is acquired from an IR sensitive camera, each sequentially acquired image frame comprising an array of pixels and having assigned a frame number that corresponds to elapsed time, a method of analyzing thermal imaging data-frames wherein a synthetically generated temperature-time reference curve is used to determine pixel contrast versus time data.

2. The method of claim 1 wherein the synthetically generated temperature-time reference curve is calculated according to the following formula:

3. In an infrared (IR) transient thermography system wherein a sequence of image frames is acquired from an IR sensitive focal-plane array camera, each sequentially acquired image frame comprising an array of pixels and having assigned a frame number that corresponds to elapsed time, a method for determining contrast versus time data for a pixel, comprising the steps of:

(a) acquiring pixel IR intensity versus time data corresponding to a selected analysis pixel in an IR image of an object from a plurality of image frames; and

(b) subtracting from said pixel intensity data a synthetic temperature time reference standard, T_s(t), computed according to the following mathematical relationship;

4. The IR transient thermography method of claim 3 wherein pixel IR intensity versus time data is based at least upon a sequence of IR images and associated frame numbers.

5. The IR transient thermography method of claim 3 further including the step of measuring a surface temperature on the object surface corresponding to said selected analysis pixel.

6. The IR transient thermography method of claim 3 wherein the object is rapidly heated using a flash lamp device.

7. A method for determining a thickness of an object having a surface which can be visualized as an array of pixels, comprising the steps of:

(a) rapidly heating the surface of an object;

(b) recording pixel intensity in a sequence of IR images, each image having an assigned sequential frame number related to time elapsed since heating the object surface in step (a);

(c) determining pixel contrast data based at least upon pixel intensity and a temperature-time reference standard, T_s(t), computed according to the following mathematical relationship;

8. The method of claim 7 further including the step of measuring a temperature on the object surface corresponding to said selected analysis pixel.

9. The method of claim 7 wherein the object is heated using a flash lamp device.

10. An infrared (IR) transient thermography method for determining a thickness of an object, comprising the steps of:

a) using an IR sensitive focal-plane array camera to acquire pixel intensity data from a sequence of IR image frames of the object, each image frame comprising a plurality of pixels and having an assigned sequential frame number related to time elapsed since heating the object surface;

b) calculating a temperature versus time data standard, T_s(t), from a mathematical thermal reference model representative of one-dimensional heat flow into a semi-infinite medium;

c) determining pixel contrast data by subtracting said temperature versus time data standard from acquired pixel intensity data to develop temperature-time contrast data for at least one pixel; and

d) determining actual thickness at a resolution element of the object corresponding to the pixel using said contrast data, said determination based on a heat-flow invariant relationship between an inflection point in the contrast data and a heat-flow characteristic time dependent upon thermal diffusivity of the object.

11. The method of claim 10 wherein the temperature versus time data standard, T_s(t), is calculated according to the following formula:

12. The method of claim 10 wherein the object is rapidly heated using a flash lamp device.