Image Processing Reference
from the others in the bank. Thermal imaging enables transformers and many other
machines and components to be examined quickly and safely for thermal anomalies
that are an indication of malfunction or imminent failure.
Small electrical circuits also lend themselves to the same kind of noncontact
thermography as in the above example, since the electrical characteristics of a
circuit can be changed by physical contact or even close proximity of a temperature
probe (especially in high-speed circuits like those used in communications).
Figure 2.22 shows visible and MWIR images of a high-speed electronic circuit
board with overheating integrated circuits. The circuit performance is unaffected
by the thermal imaging equipment, so the temperature measurements are a true
indication of the thermal performance characteristics in operation.
Imaging Invisible Gases
Certain gases have strong resonances with infrared light at specific wavelengths.
For example, hydrocarbon gases like methane and propane contain carbon-
hydrogen or C-H bonds. The carbon and hydrogen atoms will move toward and
away from each other like masses on a spring. The “spring constant” of the
bond determines the resonant frequency which corresponds to the frequency of
lightwaves with a wavelength of 3.3 micrometers. A midwave IR camera that is
restricted to see only light right around 3.3 micrometers can image hydrocarbon
gases in the air, gases that are normally quite invisible to the human eye. The
wavelength restriction is accomplished with a bandpass filter that is placed inside
the camera. Figure 2.23 shows an example of a propane leak out of a tank. To the
eye, the leak is quite invisible. Within the narrow waveband of the camera, the cold
gas absorbs light emitted by my skin behind it and looks like black smoke.
Figure2.22 Visible (left) and MWIR (3-5 mm) (right) images of a high-speed circuit board.