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"A View on The Future of Thermal Imaging",
the slides from the IR/Info 2004 Keynote talk can be viewed on the web
or downloaded.....
READ MORE

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Online infrared thermography training by distance learning.



Temperature Sensor Types
========================


Big differences exist between different temperature sensor or
temperature measurement device types. Using one perspective, they can
be simply classified into two groups, contact and non-contact. The two
links below take you to descriptive pages on each type with a
breakdown by more specific, detailed types under that simple, first
breakout.

There are also vendors of each sensor type, some vendors sell more
than one type and some sell nearly all types, but not always all
brands. There are differences between brands and the differneces are
most evident among those device types for which there are few if any
recognized standards. Start your search either for a specific
temperature measurement device type or go to the vendor page index and
you can access the vendors of specific types from there.

Both contact and non-contact sensors require some assumptions and
inferences in use to measure temperature. Many, many well-known uses
of these sensors are very straightforward and few, if any, assumptions
are required.

Other uses require some careful analysis to determine the controlling
aspects of influencing factors that can make the apparent temperature
quite different from the indicated temperature.

Tell your new product and application stories at The Temperature
Community website: www.tempsensor.net or feedback to us and we'll
consider adding it here with your byline!

Remember the truism that all sensor have errors in their readings -
all the time. One key secret to high quality measurement results is to
have confidence in the error estimates. Neglecting to make a careful
error analysis can result in error much larger than the assumed
values.

It is worth noting that all competent error analyses start with the
uncertainties assigned to the traceable calibration of the sensor
itself. Without traceable calibration, one is forced to make
assumptions. (You know what the word ass|u|me means, we hope.)

Without traceable measurements, the numerical values of results will
always be questionable and hardly worth the effort, and cost. It most
often pays to get started on the right path to technically sound
measurements by beginning with some understanding of the options
involved in selecting a temperature measurement device and then in
obtaining one that meets the expected conditions and standards, is
calibrated and that the calibration is traceable to either a
fundamental standard (e.g. the triple point of water) or a national
standard. See our calibration and standards pages for more details on
each aspect of sound measurement practice.


Contact Sensors
---------------

Contact temperature sensors measure their own temperature.

One infers the temperature of the object to which the sensor is in
contact by assuming or knowing that the two are in thermal
equilibrium, that is, there is no heat flow between them.


Noncontact Sensors
------------------

Most commercial and scientific noncontact temperature sensors measure
the thermal radiant power of the Infrared or Optical radiation that
they receive from a known or calculated area on its surface, or a
known or calculated volume within it (in those cases where the obect
is semitransparent within the measuring wavelength passbad of the
sensor).

One then infers the temperature of an object from which the radiant
power is assumed to be emitted (some may be reflected rather than
emitted). Sometimes the inference requires a correction for the
spectral emissivity (NB: the two words, spectral & emissivity, are
used together in correcting IR Thermometer readings -the "emissivity",
unspecified, is a big trap which even some of the suppliers of devices
and calibration equipment fall into unwittingly for a variety of
reason about which one can only speculate ) of the object being
measured.

Knowing how and when to apply a spectral emissivity correction is part
of the inference, too, and can introduce significant errors if not
done correctly. See our Trip down the E-missivity Trail to help you
understand that aspect a little better.


Dewpoint Temperature
--------------------


-- Humidity--
-------------

Although this area is in reality just an application of temperature
sensors and other sensors, it grew out of temperature measurements.

Remember the old style humidity indicators that consisted of two
little glass thermometers, the wet and dry bulb thermometers with a
little look up table that told you the humidity, both absolute and
relative? Have a look, it's a very important area in terms of human
comfort, food safety and energy conservation and efficiency in thermal
processes.


Thermal Imaging
---------------

The special world of thermography and thermal images includes the
temperature-measuring kind of thermal imagers called "Radiomatic", by
those in the business, and "Quantitative" by those mostly in R&Dwith
thermal imaging. Then, too, there are those who call it "Thermology"
when it applies to measurements made on the human body and "Medical
Thermography" by still others, some even in the same business.

Users of infrared thermal imaging have many options in cameras both
with and without temperature scales or temperature indication.

It seems really odd to have all these different names kicking about,
when they all refer to the same basic technology. The names seem to
differ only by application area. In reality, they all work because of
the same Law of Physics, called Planck's Law.

That's the same law that describes how IR thermometers, optical
pyrometers, radiation thermometers and infrared intrusion or people
detectors work (note the common trait of multiple names).

The only thing that an IR thermal imager of any denomination really
does is take the output from an infrared detector, or plethera of
detectors, and presents a 2-D scan of the infrared intensity
distribution in the field of view of an optical system. These devices
could be called by one common name. The devices that provide
temperature information, probably more than any other type of device
should be called Infrared Imagers, or Thermal Infrared Imagers or,
simply, Thermal Imagers.

Go to our thermal imaging section by clicking the above underlined
link and learn more than you ever thought you would want to know about
the subject.

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http://www.professionalthermographer.org
Click here to find out about ISPoT!

The Applications page can lead you to many well-known solutions or
examples, possibly similar to the one you are trying to solve. Why
re-invent the wheel?

Two excellent reference by Baker et al. are listed in the References
page and worth reading to get an idea of the complexities that can
arise, how to test and get around them. They are older books and while
the technology of the equipment has changed, especially the
electronics, the measurement fundamentals have not. Heat flow is heat
flow and thermal radiation physics was unified theoretically by Max
Planck more than 100 years ago!

A great many temperature measurement problems are solved through a
good understanding of the heat flow involved in a specific measurement
situation.

Surface temperature problems with contact sensors are often best
solved in many cases through the use of non-contact sensor. They are
in use in many industrial plants worldwide in great numbers. The above
reference texts provide interesting analyses of the likely errors
making contact temperature measurements of surfaces, both stationary
and moving surfaces. We have not seen any recent analyses with as much
detail!

Good luck and best wishes.

If you have some interesting success, let us know and we'll help you
share that with others who visit these pages.

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