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These days, the most prestigious on the street are the security personnel in public places and the staff in various communities. No matter how big you usually are, and no matter which planet you come from, we must obediently meet them when we meet them, either raising our hands or reaching out and taking a shot.

Temperature site 1

Temperature site 2 (the temperature gun is shown in the picture, thank you)

Although we have been tested quite a few times these days, for many friends, this thing is relatively rare in previous life. Because of its unfamiliarity, it led to problems lingering in the brain.

Why does the temperature gun know the temperature by “hitting a shot” on your head; it can’t accurately measure the temperature; and the most concerned among relatives, will it affect your health if you hit it more?

As long as you understand the principle of the temperature measuring gun, these problems will be solved one by one. Although the principle is complicated, don’t worry. After reading the explanation of my aunt, I can understand that my grandmother and grandpa can understand it clearly.

Will the temperature measurement gun be too much to hurt your health?

The measured temperature gunWill it hurt your health if you hit too much? -This question is classic.

Temperature gun, scientific name is “infrared thermometer” or “infrared radiation thermometer”. Many people are shocked when they hear the words “infrared” and “radiation”.

Speaking of which, it has always been a hassle to popularize equipment that has always included “infrared” and “radiation”. You should know that in the “relative group”, no one believes that you say “any object radiates”; let alone no one talks to you about the dose. They only know that as long as there is “radiation”, they should “believe it.”

Unfortunately, although the thermometer is crowned with “radiation” and “infrared” on its name, it will not exert any influence on your body.

Because it is a receiver, not a transmitter.

In general, the principle of the infrared thermometer is: passively absorb the infrared radiation energy of the target to obtain the temperature value of the object.

It means that your body is diffusing radiant energy outwards all the time, and the role of the thermometer is to receive the radiant energy from a certain area of ​​your body. If you really say that this process is harmful, then you should be worried that the radiation is also a temperature measuring gun, in case one day you can measure a 1000 ℃ forehead by yourself.

So although this thing looks like a gun, it can only be passively beaten.

Okay, explain this question, maybe some friends want to answer it-does this mean that the working process of the thermometer is like a thermometer, and you can directly feel the “temperature signal” emitted by you. How about it? -This statement is actually not correct.

Infrared thermometers can only receive electromagnetic waves in various bands, not direct temperature conduction. And the most important one, the conversion process from “electromagnetic wave information” to “temperature information”, it is necessary to mention the real point to be said today-the law of black body radiation.

The Law of Blackbody Radiation

When you try to search the principle of any technology product on the Chinese media platform,Find some copy-paste monsters that pretend to be popular science, that is, some textbook-style books that read theories and paste formulas.

Auntie likes to call this irresponsible science popular science “lazy science.” Specifically, this time, the “principle of temperature measuring guns” is that they will almost only move out of the paragraph based on the law of black body radiation:

Every object in nature that is above absolute zero (-273.15 ℃) is constantly radiating energy. The amount of radiant energy of an object and its distribution by wavelength are very similar to its surface temperature Close relationship, the higher the temperature of the object, the stronger the infrared radiation ability.

Admittedly, this sentence is the basis of everything, but I believe that if we do not disassemble the sentences and explain the theory of black body radiation, few people can sink their heart to understand what this sentence means.

Hey, it’s actually quite simple.

What is this black body radiation law used for? To put it plainly, physicists want to understand the conversion relationship between “electromagnetic wave information” and “temperature (energy) information”.

So they conceived the “black body” thing.

At this time we continue to send my aunt’s old friend Karby to the scene. It is assumed that “Black Carby” is a standard “black body”, and its characteristics are: all incident electromagnetic waves are absorbed, neither reflected nor transmitted.

Kibby’s body is that the food he eats is never spit out, and all of it is digested without waste.

So, the digested things finally become the heat in the Kabi body, which is the heat radiation (we can understand it as the temperature)

So the process from “electromagnetic radiation” (light) to “thermal radiation” (heat) is called blackbody radiation.

Okay, now that you know this principle, a new question is coming-how do we know how much “hot” the “light” absorbed by the black body turns into?

This problem has been studied since Newton discovered the phenomenon of triangular prism light dispersion in the 17th century. Scientists have been studying it for hundreds of years. Finally, in 1900, Max Planck announced at the German Physical Society. The “Formula of Blackbody Radiation Law”.

The formula of black body radiation law

The concept of “quantum mechanics”, a derivative of which was introduced to prove this formula, has by the way become one of the two basic pillars of modern physics.

How hard it is for humans to get this formula, just look at how many face values ​​it uses in exchange:

So, in order to keep the value of this depletion not to be disappointed, let’s understand this formula now. Don’t look complicated to write, it is actually a paper tiger. What it reveals is nothing more than the relationship between light and temperature— < / p>

Look if you draw it as a picture, is it better to understand it? (No)

How to understand this graph? The trends of these lines reflect the intensity of heat radiation at different wavelengths at a fixed temperature (unit K / international standard temperature unit).

For example 6000K (5727 ° C) inside, this is the temperature of the sun-so based on the black body radiationThe law formula allows us to calculate the heat radiation energy (intensity / I) of different wavelengths of sunlight (such as red, green, blue, a certain infrared, a certain ultraviolet …).

Similarly, if we know the intensity of the heat radiation and the wavelength of light, we can also calculate the “temperature” it represents.

Okay, I know that many students still want to say “still ca n’t understand”, it ’s okay. Now I can wake up to see the sleeping students. Let ’s continue to reduce the difficulty of understanding. The following is the focus. .

As long as we understand, the intensity of blackbody radiation at high temperatures is higher than that of blackbody radiation at low temperatures in any wavelength range.

It is reflected in the figure that the red high temperature curve at 1500 ° C has higher intensity than the yellow curve at 1200 ° C at each wavelength:

The infrared thermometer is designed based on this characteristic.

Based on this theory, there are three main design directions for infrared thermometers depending on the measurement accuracy required for engineering applications.

First, the monochromatic temperature measurement method: use the ratio of the monochromatic radiation intensity at a single wavelength to determine the temperature;

Second, the two-color temperature measurement method: measure the intensity change of the measured object’s radiation intensity ratio at two wavelengths to determine, this method is less affected by the outside world and the error is smaller than the former;

Whether you can understand the previous two kinds depends on personal fortune, let’s talk about the third one in detail ——

Third, the full radiation temperature measurement method.

The name of the full-radiometry method sounds the best, but it is actually the least accurate of the three methods, but the advantage lies in the simple structure and low cost.

The reason lies in its “wonderful miracle” design idea-total radiation temperature measurement method, which determines the radiation temperature of an object by measuring the total intensity of thermal radiation at the full wavelength of the radiating object.

How do we understand this concept? It ’s like comparing a full-band radiation intensity map at a temperature to a meter mountain. Now let KabiThe whole Mishan was eaten. Let’s measure how much heat radiation energy it converts after eating, and finally derive the temperature value at that time.

The whole radiation temperature measurement method

Infrared thermometers that give you body temperature at the gate of the community are basically designed with this idea in mind.

So after the idea is clear, we only need to put one such Kabi in a temperature measurement gun and measure the amount of heat radiation it releases after absorbing radiation, and then we can convert the temperature corresponding to the measured object.

The thing that can convert the received “infrared electromagnetic wave radiation” into “thermal radiation” (blackbody radiation process), and then convert “thermal radiation” into electrical signals (thermoelectric conversion process) is: pyroelectric infrared sensor (Abbreviation: PIR)

List briefly how this thing works:

By the way, this stuff is really not expensive: