How does infrared thermometer work? What is emissivity? | Black & Grey Bodies | Yong Tuition 201006

Based on Planck's formula for thermal radiation of a black body, the intensity of the radiation can be derived in a form of a quartic equation, known as the Stefan-Boltzmann equation.
Any infrared thermometer you can buy in the market is designed based on the formula in Physics. Nevertheless, a real object may be noticeably different from an ideal black body in its efficiency in emitting its thermal energy. A parameter, called emissivity, is introduce to take this fact into account. By definition, the emissivity is a ratio of the gray body radiation intensity to that of a black body. You can google emissivity lists, such as from thermoworks.com/emissivity-table.
In practice, a simple IR thermometer whose default emissivity is fixed will give temperatures lower than the actual temperature is the emissivity of the object is less than unit, say 0.8 or 0.6. To overcome this apparent discrepancy, you may choose an IR thermometer with adjustable emissivity function.
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[@13lack_Rose]

thank you for adding captions 🙏🏻

[@yongtuition]

I just have finished it.

[@pravinbutte1466]

Nicely explained Sir

[@ramsaha7940]

Great presentation, thank you

[@jesmarykj]

Very nicely explained 👏🏻👏🏻👏🏻. Thank you!

[@linggiman]

Thank you for the education.. Admire you a lot

[@ratankanade7395]

Great informative video 💯

[@motoservo]

I get the basics of black body radiation and the Plank curve. But how does an IR thermometer see a wall that's 20 meters away when the air is the same temperature?

[@yongtuition]

Good question. As you noticed that an object is immersed in air, the diplayed temperature on an IR thermometer is close to the interface temperature where air has almost the same temperature as the object surface.

[@helgecatoaamodt50]

Ver clear presentation- By the way what is emissivity of CO2 ? molecyle ?

[@yongtuition]

Good question. In gas form, someone had used 0.2-0.3, but other argued to be 0.8, for the emissivity of CO2. In general, emissivity is defined a relative ratio to that of a blackbody. In my opinion, the emissvity should be proportional to the gas density.

[@ramsaha7940]

Blue light has a higher frequency & carries more energy than red light, however, IR image Red color portion more heater than blue color why? please reply, thank you

[@yongtuition]

IR ray is invisible. The colors, known as "false colors", in an IR image are merely used to visualize the image. In other words, you can use any color to represent the IR intensity detected.

[@sagesage695]

Thank you so much sir ,but I have a question what's the role of black body in the detection of temperature by the infrared thermometer?

[@yongtuition]

It acts as a standard or reference, namely it has the maximum emissivity.

[@tony3785]

I've also read that amore plausible source of the increase in Earth's Temperature is the excess UVB radiation penetrating the Stratosphere due to a depleted O3 . Using Planks law E=hf, The IR radiation at 15 microns has only an E= 0.04 ev/photon while UVB at 300 nanometers has an E=4 ev/photon. That 50 times more energy than the IR from CO2 ! Also read that the Effusive volcanos emit tons of Halogens (Chlorine, bromine etc ) into the atmosphere. (1 atom Chlorine destroys 100,000 molecules of O3) I'd love to hear your comments on that also..

[@brendawilliams8062]

Very nice. Thankyou

[@mustafanashwan5932]

Hello, is Stephen Boltzmann and Wien's law of displacement used in this device on humans?

[@yongtuition]

Only the Stefan-Boltzmann law is used as the total radiation intensity is detected.

[@mustafanashwan5932]

@@yongtuition Well because I read in several sources that the temperature is measured by calculating the wavelength of infrared rays and substituting it with Wiens' law to extract the temperature through the law temperature×wave length=0.0029 is that true?

[@yongtuition]

@@mustafanashwan5932 To apply the Wein's displacement law, you need to use a spectrometer, or FTI.R, which is too expensive >$800,000. The product I used is less than $100.,

[@Fr3shBoiKim]

Say for instance you measure something at 1.0 emissivity, and got a temperature reading of 250 degree F. But later you found out the actual emissivity of the object was 0.75. How do you re-calculate the temperature only knowing the information from the first reading?

[@yongtuition]

1.0*sigma* (T_1)^4 = 0.75*sigma*(T_true)^4 where T_1 is (250°F − 32) × 5/9 + 273.15 = 394.261K, sigma is the StefanBoltzmann constant.

[@ramsaha7940]

@@yongtuition Finally, we get T actual=423.66 K=309.19F right?, thank you

[@yongtuition]

@@ramsaha7940 I think so, but you can doubly chech the result.

[@qwas7901]

Great video

[@trivikramaraju]

good sir

[@pyepaing5360]

Thank you very much

[@maxmustermann5353]

Nice video, but how does the sensor determines the temperature? If it would by detecting the amount of infrared radiation, it would also decrease with distance. How is it possible to measure the same temperature with different distances?

[@yongtuition]

By definition, radiation intensity is the detected power per unit area of the radiator. So, it can be done by selecting a larger area while the distance increases. For a large object, such as clouds, the intensity is almost independent of the distance because it can be treated as a plane source rather than a point source.

[@maxmustermann5353]

@@yongtuition Thank you so much! Now I finally got it. In hindsight it's so obvious. You helped me a lot :-) Thanks. I would like to build a low cost, relatively high resolution, thermal camera. I want to use a mirror telescope to measure a small area and scan a large area with it, to generate a large picture. Now I at least understand how the principle behind the measurement works. 👍

[@ramsaha7940]

Why do we set emissivity 1.0 when we measure Reflected Ambient Temperature (Trefl) with Aluminium foil? Please feedback me, thank you

[@yongtuition]

Ideally, you would choose a measured emissivity for a IR source instead of 1.0.

[@ramsaha7940]

@@yongtuition Thank you so much, have a great holiday

[@mahsaamini8555]

Just great great great

[@yongtuition]

Thank you. I am glad you can understand the principle now.

[@bekind7211]

Does this thermometer works on zeroth law

[@yongtuition]

No. it merely detects the radiation intensity of an object.