Optimising Measurement Performance
Of Infrared Thermal Imaging Cameras
There are many factors to consider when selecting a thermal imaging camera. While emissivity and
wavelength are crucial when measuring the temperature of specific materials or objects, other factors such
as ease of camera set up, software integration capabilities and compactness are equally important, says
Glenn Wedgbrow, Sales Manager at Micro-Epsilon UK.
I
nfrared thermal imaging
element can be treated as zero. Therefore,
have a specific wavelength camera for the
cameras measure the
the heat energy coming from an object
material you need to measure, find one
temperature of an object
only comprises emitted and reflected
that does.
without touching it. It is
radiation. This is why objects such as
therefore possible to perform fast, reliable
polished and shiny metals can only have
temperature measurements of moving
a low emission, or emissivity, as radiation
or rotating objects, or components
from the surrounding environment is
that cannot be touched. Not only are
strongly reflected (and so proportionally
thermal imaging cameras now relatively
high) from these surfaces.
inexpensive, they also offer numerous
features and options, including software
Wavelength
As the graph shows, objects at higher
temperatures emit more infrared energy,
i.e. have a higher emissivity at shorter
wavelengths.
Micro-Epsilon has developed a complete
range of cameras that cater for almost
every conceivable target material. Specific
tools to simplify integration, alarm and
The emissivity of an object, however, will
wavelength cameras for measuring the
limit functions for process control and high
be greater or lower when monitoring
temperature of hot metal surfaces, or the
speed recording for RD&T environments.
the radiated heat energy at different
temperature of glass and glass products
It is now also possible to select thermal
wavelengths. Therefore, developing
(including very thin solar panel glass) and
imagers that operate at specific
cameras that measure temperature at
silicon, as well as cameras that operate at
wavelengths for particular materials, such
specific wavelengths that match the
8-14µm for low temperature matt surfaces,
as metals, ceramics and glass.
high emissivity of specific materials can
are now available – all at affordable prices.
For accurate temperature measurement
using thermal imaging cameras,
significantly increase measurement
accuracy and stability.
The metal processing industry, for
example, has traditionally believed that
users must carefully consider two key
For example, metals have their highest
short wavelength thermal imaging
parameters: emissivity and wavelength.
emissivity at wavelengths of 0.8 to 2.3µm,
cameras were very expensive, i.e. greater
glass 5µm, textiles and most matt surfaces
than £10-15,000 per unit, which made
8-14µm.
the implementation of these in multiple
Emissivity
All bodies above absolute Kelvin (-273°C)
emit infrared radiation in three ways,
via a combination of emitted radiation,
radiation reflected from the surroundings,
and by transmitting the radiation
through itself. How these factors interact
depends on the material of the object to
be measured. However, for non-contact
infrared temperature measurements,
only the emitted radiation element is
important.
The relationship of the emission types
to each other is best described in the
following way. If at any given temperature,
the sum of the radiation of the three
emission types is equal to one, and it
is assumed that solid bodies transmit
negligible radiation, the transmitted
Today, around 80% of thermal imaging
cameras on the market operate over the
wavelength band of 8-14µm, which means
these cameras are only giving accurate and
locations prohibitive. However, the reality
is that specific wavelength cameras for
metals are available from Micro-Epsilon at
prices in the region of £3,000.
stable measurement on objects with high
While this price is similar to current
emissivity in this wavelength band. These
short wave pyrometers (single spot
are generally objects with matt surfaces.
temperature sensors) from other
Metal or shiny surfaces cannot be measured
suppliers, the thermoIMAGER TIM series
accurately using thermal imagers that
from Micro-Epsilon is packed with much
operate at the 8-14µm wavelength band.
more functionality than a pyrometer
When selecting a suitable camera, it is
therefore vital that the wavelength band
and provides temperature measurement
images or video of a larger area.
over which it measures is known and is
In addition, the license-free, fully featured
best suited to the object to be measured.
TIMConnect software is supplied as
The object emissivity values over this
standard with the camera, providing quick
wavelength and the temperature range
and easy set up together with a range of
to be measured must also be known or
software tools and a developer kit.
calculated. If the camera supplier doesn’t