Infrared Thermometers

Written by Nicholas Kamuda
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Infrared thermometers are non-contact temperature measurement devices that are widely used in professional and domestic applications and feature many characteristics--including an unmatchable ease-of-use--that make them highly desired in a number of fields. As the technology behind infrared thermometers continues to grow in power and shrink in cost, IR thermometers may become even more widespread, perhaps even becoming common household tools.

The Development of Infrared Thermometers

Infrared thermometers are a direct outgrowth of postwar research in utilizing light outside of the visible spectrum. The English astronomer Herschel discovered infrared radiation in 1800, though products that use IR radiation weren't commercially developed until the second half of the twentieth century. This period saw the growth of IR thermometers, night-vision goggles, and other Infrared detection systems.

Like night-vision goggles, infrared thermometers translate infrared data into a more useful format. Night-vision goggles trace infrared information into recognizable shapes, displaying different strength levels of IR radiation into different colors. IR thermometers calculate the surface temperature of an object based on the total radiation energy radiated from the object's surface..

IR sensors can produce accurate temperature data from almost any distance (usually within a few hundred feet is best), but the closer the operator is to the target, the more reliable that data generally is. This is because the target area of almost all infrared sensors increases in size as the distance between the sensor and the target increases. The proportional relationship between the distance to the target and the size of the sensor's measured target area is called the distance-to-spot ratio (i.e., the D:S ratio).

Features of Different IR Thermometers

The D:S ratio of IR thermometers typically varies with the quality of the device. In general, compact, domestic-use infrared thermometers have a lower D:S than professional models. For example, pocket thermometers, which are useful for everything from automotive maintenance to food preparation, usually have a D:S of approximately 3:1, indicating that at three feet away, the target area will be one foot in diameter. In contrast, some professional models may have D:S ratios of over 150:1.

Other characteristics of infrared thermometers that are important to consider are features such as adjustable emissivity, response time, laser targeting, and minimum and maximum temperatures. Emissivity is the ability of an object to radiate infrared radiation or thermal enery--many glossy or reflective objects have different emissivity ratings than organic objects. Though some IR thermometers have adjustable emissivity control, others may not, which can lead to inaccurate measurements for some objects.

Laser pointing or targeting capability also is a feature that varies among the different models of IR thermometers. In general, laser targeting is typically found in more expensive professional models, though still useful in many consumer models. High-end professional models may also feature a multiple laser targeting system that brackets the entire measured target area with projected dots.

Fixed-Mount Infrared Thermometers

Besides handheld infrared thermometers, fixed-mount systems are also common. Fixed-mount systems are often incorporated into manufacturing machinery as a method of monitoring the temperature of the product or of raw materials without physically interfering with the process. In some cases, they are connected to computerized cooling systems and function as highly accurate digital thermostats.

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