The Basics of IR Thermometry
IR radiation is part of the electromagnetic spectrum, which includes
radio waves, microwaves, visible light, ultraviolet light, gamma rays, and
X-rays. The IR range is between the visible portion of the spectrum and
radio waves. IR wavelengths are usually expressed in microns, and the spectrum
extends from 0.7 micron to 1000 micron. However, for IR temperature measurement,
only the 0.7-micron to 14-micron band is used.
Noncontact IR thermometers can focus on nearly any portion of the 0.7-micron
to 14-micron band using advanced optic systems and detectors. Because every
object emits an optimum amount of IR energy at a specific point along the
IR band, each process may require unique sensor models with specific optics
and detectors. For example, a sensor with a spectral range centered at 3.43
micron is optimized for measuring the surface temperature of polyethylene
and related materials. A sensor set up for 5 micron is used to measure glass
surfaces. A 1-micron sensor is used for metals and foils. The broader spectral
ranges are used to measure lower temperature surfaces, such as paper, board,
poly, and foil composites.
Target objects reflect, transmit, and emit energy. The intensity of an
object's emitted IR energy is proportional to its temperature. It is this
energy, measured as the target's emissivity, that indicates an object's
temperature. The term emissivity is used to quantify the energy-emitting
characteristics of different objects. IR sensors have adjustable emissivity
settings, generally from 0.1 to 1.0 micron, which allow accurate measurement
of different surface types.
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