Thermography (Thermal Imaging)
About thermography or thermal imaging
Thermography, or thermal imaging,
involves scanning an infrared radiation detector across an object. The
information gathered is then processed and an output in the form of
the temperature distribution across the object is produced.
Temperature measurement over the range from -20°C up to +1500°C is
possible.
The radiation detector uses the same principles of operation as a
radiation pyrometer in inferring the temperature of the point that the
instrument is focused on from a measurement of the incoming infrared
radiation. However, instead of providing a measurement of the
temperature of a single point at the focal point of the instrument,
the detector is scanned across a body or scene, and thus provides
information about temperature distributions.
Because of the scanning mode of operation of the instrument, radiation
detectors with a very fast response are required, and only
photoconductive or photovoltaic sensors are suitable. These are
sensitive to the portion of the infrared spectrum between the
wavelengths of 2 µm and 14 µm.
Simpler versions of thermal imaging instruments consist of hand-held
viewers which are pointed at the object of interest. The output from
an array of infrared detectors is directed on to a matrix of red
light-emitting diodes assembled behind a glass screen, and the output
display thus consists of different intensities of red on a black
background, with the different intensities corresponding to different
temperatures. Measurement resolution is high, with temperature
differences as small as 0.1°C being detectable. Such instruments are
used in a wide variety of applications such as monitoring product
flows through pipework, detecting insulation faults, and detecting hot
spots in furnace linings, electrical transformers, machines, bearings,
etc. The number of applications is extended still further if the
instrument is carried in a helicopter, where uses include scanning
electrical transmission lines for faults, searching for lost or
injured people and detecting the source and spread pattern of forest
fires.
More complex thermal imaging systems
comprise a tripod-mounted detector connected to a desktop computer and
display system. Multi-color displays are commonly used in such
systems, where up to 16 different colors represent different bands of
temperature across the measured range. The heat distribution across
the measured body or scene is thus displayed graphically as a
contoured set of colored bands representing the different temperature
levels. Such color–thermography systems find many applications such as
inspecting electronic circuit boards and monitoring production
processes. There are also medical applications in body scanning.
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Temperature Measurements
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