Infrared temperature measurement is not magic, but it sometimes seems that way when it solves an end-user’s problems. Specializing in infrared instruments, Raytek Corp., headquartered in Santa Cruz, Calif., considers educating engineers and others on how infrared technology works an important part of the company’s mission.
Posted on www.raytek.com, a questions and answers section about noncontact infrared sensors helps spread the knowledge. Examples include:
Q. What is an infrared thermometer?
A. An infrared thermometer is a sensor that measures an object’s temperature without physically touching it. Noncontact infrared thermometers use infrared technology to quickly and conveniently measure the object’s surface temperature. They provide fast temperature readings of hot, hazardous or hard-to-reach surfaces without contaminating or damaging the object. Infrared thermometers can provide several readings per second.
Q. Can infrared measure through dust, steam and smoke?
A. Yes. A two-color/ratio infrared thermometer does the job.
Q. Can infrared thermometers measure flame temperatures?
A. Not exactly, but at certain specific wavelengths, it is possible to measure components of the combustion process such as carbon dioxide that are in the flame and thus derive a flame temperature.
Q. Can the object or product being measured be moving?
A. Yes. Measuring moving targets is one of the benefits of using noncontact infrared thermometers.
Q. What is the difference between an optical pyrometer and an infrared sensor?
A. Essentially nothing. Optical pyrometer and infrared sensor mean the same thing. At one point in the history of the technology, there was an instrument that used a disappearing filament, which was referred to as an optical pyrometer. Optical now refers to the fact that sensors use optics to focus on a particular spot.
Q. How does infrared work?
A. Infrared thermometers capture the invisible infrared energy naturally emitted from all objects warmer than absolute zero (0 K). Infrared radiation is part of the electromagnetic spectrum, which includes radio waves, microwaves, visible light, ultraviolet, gamma rays and X-rays. Any object emits energy somewhere within that range. On electromagnetic spectrum, infrared falls between visible light and radio waves. Infrared wavelengths usually are expressed in microns (micron) with the infrared spectrum extending from 0.7 to 1,000 micron. In practice, the 0.7 to 14 micron band is used for infrared temperature measurement.
Q. What is emissivity?
A. Emissivity is the measure of an object’s ability to emit infrared energy. Emitted energy indicates the temperature of the object. Emissivity can have a value from 0 (shiny mirror) to 1.0 (blackbody). Most organic, painted or oxidized surfaces have emissivity values close to 0.95. Many temperature sensors have adjustable emissivity to ensure accuracy when measuring materials such as shiny metals.
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