Infrared Temperature Sensors
Infrared (IR) radiation is part of the electromagnetic spectrum,
which includes radio waves, microwaves, visible light, and
ultraviolet light, as well as gamma rays and X-rays.
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The IR range falls between the visible portion of the spectrum
and radio waves. IR wavelengths are usually expressed in
microns, with the lR spectrum extending from 0.7 to 1000
microns. Only the 0.7-14 micron band is used for IR
Using advanced optic systems and detectors, noncontact IR
thermometers can focus on nearly any portion or portions
of the0.7-14 micron band. Because every object (with the
exception of a blackbody) 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
For example, a sensor with a narrow spectral range centered
at 3.43 microns is optimized for measuring the surface
temperature of polyethylene and related materials. A sensor
set up for 5 microns 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.
An object reflects,
transmits, and emits
energy, as shown
in the diagram.
The intensity of an object's emitted IR energy increases or
decreases in proportion to its temperature. It is the emitted
energy, measured as the target's emissivity, that indicates
an object's temperature.
Emissivity is a term used to quantify the energy-emitting
characteristics of different materials and surfaces. IR sensors
have adjustable emissivity settings, usually from 0.1 to 1.0,
which allow accurate temperature measurements of several
The emitted energy comes from an object and reaches the
IR sensor through its optical system, which focuses the
energy onto one or more photosensitive detectors. The
detector then converts the IR energy into an electrical
signal, which is in turn converted into a temperature value
based on the sensor's calibration equation and the target's
emissivity. This temperature value can be displayed on the
sensor, or, in the case of the smart sensor, converted to
a digital output and displayed on a computer terminal.
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