| Predictive
Maintenance using Thermal Imaging |
INTRODUCTION Thermal
imaging (Infrared thermography) is a technique that produces a visible graph or
thermographic image of thermal energy radiated from objects. The human eye can
only see the narrow middle band of visible light that encompasses all the colours
of light in the rainbow. Thermography utilizes a portion of the infrared band
of the electromagnetic spectrum between approximately 1 and 14 microns. Thermal
infrared images translate the energy transmitted in the infrared wavelength into
data that can be processed into a visible light spectrum video display. Thermal
infrared imagers are detector and lens combinations that give a visual representation
of infrared energy emitted by all objects. In other words thermal imagers let
you "see" heat. Depending
upon the sophistication used, thermography is capable of providing very detailed
images of situations invisible to the naked eye. Thermal imaging thus finds its
applications in different fields.
ELECTROMAGNETIC
RADIATION
Electromagnetic radiation is emission of energy from a source, which could be
a solid, liquid or gas. This radiation is given off in the form of alternating
electric, magnetic waves produced by the acceleration and deceleration of charged
electric particles. Although the electromagnetic spectrum is comprised of many
different types of electromagnetic radiation there are similarities that must
be recognized. As mentioned all electromagnetic radiation is produced by the movement
of electric particles. A second point is that all electromagnetic radiation, unhindered
by gases, travels at the speed of light. As the intensity of the radiation increases,
the wavelength becomes shorter and the frequency becomes higher. On the other
hand as the intensity decreases, the wavelength becomes longer and the frequency
lower. The main difference between the various classes of electromagnetic radiation
is the wavelength and frequency, as well as the way it is produced and the "equipment"
used to detect it. The chart below depicts the many classifications of electromagnetic
radiation and their relation to one another.
ELECTROMAGNETIC SPECTRUM The
amount of energy in light wave is related to its wavelength. Of visible light
violet has the most energy red has least. Just next to visible light spectrum
is infrared spectrum Infrared
light can be split into 3 different categories: NEAR
Infrared: closest to visible light wavelength range from 0.7-1.3 microns
MID
Infrared: has wavelengths ranging from1.3-3 microns, both near IR and mid IR are
used by variety of electronic devices, including remote controls.
THERMAL Infrared:
occupying in the largest part of infrared spectrum, this has wavelengths ranging
from 3microns -over 3microns. The
key difference between thermal IR and other two is that thermal IR is emitted
by an object instead of reflected of it. Infrared rays are emitted because of
what's happening at the atomic level. ATOMS
Atoms are constantly in motion. They continuously vibrate, move and rotate. Even
the atoms that make up the chairs that we sit in are moving around. Solids are
actually in motion! Atoms can be in different states of excitation. In other words,
they can have different energies. If we apply a lot of energy to an atom, it can
leave what is called the ground-state energy level and move to an excited level.
The level of excitation depends on the amount of energy applied to the atom via
heat, light or electricity. An
atom consists of a nucleus (containing the protons and neutrons) and an electron
cloud. Think of the electrons in this cloud as circling the nucleus in many different
orbits. Although more modern views of the atom do not depict discrete orbits for
the electrons, it can be useful to think of these orbits as the different energy
levels of the atom. In other words, if we apply some heat to an atom, we might
expect that some of the electrons in the lower energy orbitals would transition
to higher energy orbitals, moving farther from the nucleus
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