THERMAL IMAGING

What is thermal imaging? Thermal Imaging is the means by which

humans enable themselves to see in the infrared portion of the spectrum of light.

Type of infra-red imaging science. Also known as ‘Thermography’ or ‘Infra-red

Thermography’.

Basics of Light

Energy is inversely proportional to wavelength.

Violet has the most energy and red has the least.

Infra-red region

Divided into three regions:-I. Near-Infrared Region:

Closest to visible light. Wavelengths ranging from 0.7 to 1.3 microns.

II. Mid-Infrared Region: Wavelengths ranging from 1.3 to 3 microns.

for example: remote control

III. Far-Infrared Region: Largest component of the infra-red spectrum Wavelengths ranging from 3 to over 30 microns. Also called as thermal infra-red region.

Physics of emissivity

Incident Energy = Emitted Energy + Transmitted Energy + Reflected Energy

100%= Emitted % + Reflected % +Transmitted %

Incident light

Reflected

Absorbed

Transmitted

Active & Passive Thermography

AT PTOpen FlameAir streamCurrentMan-made lightSunlight

Induction heatingPressureMicrowavesMan-made light

Construction & Working

Construction and Working

Conversion to Electricity

Electriccurrent

Electriccurrent

EMR

Amplifiedcurrent

Conversion toEMR

EMR

AmplificationAmplifiedcurrent

1.)

2.)

3.)

1.)

2.)

3.)

1.)

2.)

Photo-Cathodes A negatively charged electrode used for

light detection. Coated with a photo-sensitive material When struck by light, the absorbed energy

results in electron emission (Photo-electric Effect)

Ex : Compounds of Ga, As, Cs, Sb, Na.

Photo-electric effect The photoelectric effect is the emission, or

ejection, of electrons from the surface of, generally, a metal in response to incident light.

Photo Multiplier tubes Extremely sensitive detectors of light that multiply

the current produced by incident light.

Temperature Calibration

Advantages

It shows a visual picture so temperatures over a large area can be compared.

It is capable of catching moving targets in real time It can be used to measure or observe in areas.

inaccessible or hazardous for other methods . It can be used to find defects in shafts, pipes, and other

metal or plastic parts . It can be used to see better in dark areas .

Limitations

Due to the low volume of thermal cameras, quality cameras often have a high price range .

Images can be difficult to interpret accurately when based upon certain objects, specifically objects with erratic temperatures, although this problem is reduced in active thermal imaging.

Accurate temperature measurements are hindered by differing emissivities and reflections from other surface.

Most cameras have ±2% accuracy or worse and are not as accurate as contact methods.

Only able to directly detect surface temperatures.

Maritime & Navigation

Volcanology &Geological surveys

Law enforcement Night vision

Research

Medical Imaging

Maintenance &Monitoring

Applications

Future applications

The latest trend in imaging systems is the combining of imaging cameras to the power of the personal computer (PC).

The electronics are contained on a card which can plug directly into the computer and take advantage of the high resolution display, processing capability and mass storage. The camera connects directly to a port on the computer.

The cost overhead associated with separate displays, separate memory and enclosures is thus avoided.

References

1. Infra-red Spectroscopy: Fundamentals and Applications- Barbara Stuart, John Wiley and Sons Ltd., Wiley Publications

2. Hand book of Analytical Instruments- R.S. Khandpur, Tata McGraw Hill Publishing Company Ltd.

3. Biomedical Instrumentation- R.S. Khandpur, Tata McGraw Hill Publishing Company Ltd.

4. Practical application of IR techniques – Ricardo Vanzetti.

5. Thermal Imaging techniques – P.E Glaser

Thank you