Optical gas imaging (OGI) cameras rely on changes in infrared (IR) radiation as it passes through a gas. The technique is still relatively new and no official standard yet exists to characterize how effective any particular IR camera is at detecting leaks, or to say how small a leak a given camera can find. But by recording IR transmission as a function of wavelength (considering that all gases have a unique absorption spectrum), engineers at FLIR (Wilsonville, OR) have developed a noise-equivalent concentration length (NECL) method that quantifies, in real time and at the location of a leak, the concentration of gas over a given path length that is undetectable above the intrinsic noise of the camera.
The NECL method requires three pieces of equipment: a high-uniformity blackbody radiator that can produce a stable 30°C background temperature, a gas cell filled with a calibration gas, and a sensor to record cell wall temperature. Next, a camera under test records at least 150 images over 10 seconds. Excluding camera noise, a Matlab program computes NECL as a function of the temperature difference between the cell, the gas, and the blackbody radiator, the concentration of gas in the cell, and the absorption properties of the gas. Different cameras can be evaluated for their performance with certain gases and gas concentrations, improving camera selection for thermal OGI in the oil and gas industry. Reference: https://goo.gl/JzZm6p.
