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About Temperature Sensors-Your Free Guide to Temperature Sensors on the Web

Radiation Thermometer Types and Construction

There are numerous types of Radiation Thermometers (Pyrometers, if you will) available on the market. In general, they can be broken down into four broad categories:

Spot measuring thermometers

    Ones that are intended to measure the temperature of a spot at some distance. These are the most common types. They can be further subdivided by whether they are intended for portable (hand-held) use or fixed mounting; they can also be classified according to their technical type, i.e whether they collect and measure thermal radiation in a single spectral region, "single waveband devices," sometimes known as "spot radiometers".

    Devices measuring in two wavebands simultaneously are called Two Color Thermometers (pyrometers) or Ratio Thermometers.
    Single waveband radiation thermometers can be classified by the wavebands or center wavelength of the measuring waveband. So, too, they can be given distinctive names by their developer, to help differentiate among brands in some way, e.g "Automatic Optical", "Hot Spot" " Cyclops".
    Then, too, there are specialized variations for well defined uses such as the medical unit used to measure the temperature of humans by inserting a small probe on one end of a unit into the outer part of the ear canal, called (not surprisingly) The IR Ear Thermometer.


Optical pyrometers

The oldest and original hand-held optical temperature sensor which was believed to be the only true, accurate method to measure temperature without contact. Although they have been around for about 100 years and have today nearly vanished from industry and science. They are unique and deserve a mention on their own. In some organizations and publications they are called disappearing filament pyrometers because of the principle upon which their operation is based: the use of the human eye (and later a photocell circuit) to detect a balance in brightness between a lamp filament and the object of measurement in a narrow visible wavelength passband.
Optical pyrometers, with few exceptions measured the brightness or spectral radiance temperature of the target. These devices are usually limited to object temperatures above incandescence, typically above about 700°C.

Line measuring thermometers.

These sensors measure a linear region over a defined angular range. If there's an object of sufficient temperature covered by that angle, then the device produces a linear trace along the line "seen" by the sensor. Some line measuring thermometers are connected to computers in such a way, that if the object moves perpendicular to the measured line, a series of temperature profiles can be connected together to form a sample of the two-dimensional temperature distribution on the object.

Area measuring thermometers (or Quantitative Infrared Thermal Imagers)

If one wants a two dimensional temperature map of a surface, a Quantitative Thermal Imager is often the first choice. These are instrument systems that have been developed from Thermal Imagers. If you don't know about them, check out the James Cameron film "Predator" starring Arnold Schwartzenegger. The Predator's view of our world was created using a real thermal imager.
Thermal Imagers themselves are very sophisticated instruments, but the right models in the hands of a skilled user can find water trapped between sheets of roofing material on a flat roof, or tell if the refractory brick insulation in a high temperature furnace or kiln has gone bad!
Some Thermal Imager models are even claimed to be capable of looking through walls and clothing. Indeed, some units enable fire fighters to see better in thick smoke to locate victims and uncooled hot spots. Many rescues have been attributed to them and most fire-fighting organizations in the USA have been acquiring units designed especially for the kinds of conditions they can encounter.
Another remarkable set of uses have been developed by Law Enforcement in North America. At our last check there were something like 11 or 12 "approved" uses of Thermal Imagers described by the Law Enforcement Thermography Association, a group that trains professionals in the successful use of these devices.

WATCH THIS SPACE for further updates on the uses of these amazing devices-- for two reasons:
1. Because the technology has taken a giant step forward with the development of many competing kinds of focal plane array sensors now entering the market, and,
2. Because the large volume production (high volume means lower unit prices) of some models for uses in automobiles, e.g. night vision devicesare now available on some car models.


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