Introduction: radiation thermometer are "non-contact" thermometers
radiation thermometer (infrared thermometer) is a thermometer that can measure the temperature of an object without touching it. Objects emit invisible light called "infrared" depending on their temperature. radiation thermometer detects the intensity of this infrared light and estimates the surface temperature of the object.
They are useful in a variety of situations, including measuring body temperature, cooking, air conditioner vents, and even in factories and space development. However, there are some points to keep in mind when using them correctly, such as the fact that they measure surface temperature and that their appearance changes depending on the material (emissivity).
hello everyone!
You've probably seen those machines at the entrance of a store or in a nurse's office that take your temperature by pointing it at your forehead. Have you ever wondered how they can tell if you have a fever in an instant without even touching you?
Actually, that is a high-tech thermometer called a "radiation thermometer." I am an engineer who normally makes professional temperature sensors used in factories and other places. Today, as your teacher, I will be giving you a special lesson on the secrets of this mysterious thermometer that can measure temperature without touching it!
Everything emits light!
Here's a quick quiz! If you were asked, "What is something that shines?", you would probably think of the sun, a light bulb, or a burning flame.
So, would you believe it if I told you that the smartphone you have, the textbook on your desk, and the glass of cold juice also glow?
You might be thinking, "What? It's not glowing!" That's right, it's invisible to our eyes. But in fact, everything in this world emits "light" that corresponds to its own temperature. One type of light that cannot be seen by the eye is "infrared light," the main focus of this article.
Infrared:invisible lightemitted by everything
Examples of infrared rays in everyday life
Even if you don't touch a bonfire or stove directly, just holding your hand over it makes it feel warm. This is because the infrared rays emitted from the flame reach your hands and transfer the heat.
The sun is warm because infrared rays reach the Earth from space. Surprisingly, not only hot objects like flames but also our bodies, tables, and even ice emit infrared rays, albeit in small amounts.
This phenomenon in which all things emit light (infrared rays) is called radiation.
The "eyes" of radiation thermometer see infrared rays
So how can we determine temperature by measuring infrared rays? The answer is very simple. There is a rule that the higher the temperature of an object, the more infrared rays it emits.
For example, suppose there is a healthy boy A with a body temperature of 36°C, and a boy B with a fever of 38°C. If you compare the amount of infrared rays emitted by these two people, boy B with a fever will emit more infrared rays.
radiation thermometer is a sensor with special "eyes" that detects the "amount" of infrared rays emitted from an object. When you point radiation thermometer at an object, the lens collects the infrared rays emitted from the object. The sensor inside then measures the amount of infrared rays and instantly calculates and display the result in numbers: "Oh, if this amount of infrared rays is being emitted, then the temperature of this object must be XX degrees Celsius!"
It's like it's reading the "heat aura" emitted by objects, which is really cool!
See the diagram: "Collecting" infrared rays and converting them into temperature
Tip: The farther away you are, the larger the "spot" becomes. Get closer to small objects.
A little advanced tip: Does the measurement method change depending on the "color" or "surface"?
If you're a science lover, you might be wondering, "Does the temperature of a black T-shirt measure differently from that of a white T-shirt?"
That's a great question! The answer is no. In the summer sun, black clothes tend to heat up easily, while white clothes don't, because black absorption light well. In fact, objects that absorption light well are also good at emitting light. Conversely, objects that are shiny and reflect light well, like a mirror, are not good at emitting light.
The technical term for this "ease of emitting infrared rays" is emissivity. For example, suppose the same 80°C hot water is poured into a pitch-black cup and a shiny, polished silver cup. When measuring these two with radiation thermometer, the black cup may show a higher temperature than the silver cup.
This is because the black cup emits more infrared rays (has a higher emissivity), so radiation thermometer determines that "Oh, this one looks like it's hotter!"
Even if the temperature is actually the same, it can be easy to make a mistake in judgment based on appearance (ease of emitting infrared rays). That's why radiation thermometer used by professionals have a function that allows you to set emissivity to match the item being measured.
emissivityof different materialsspecifications setting function
Get the basics
Difference from ordinary thermometers (contact type)
Contact thermometers measure the temperature by touching the object with a sensor, while radiation thermometer estimate the temperature "non-contact" by receiving infrared rays emitted from the object.
Advantages: Fast, can measure from a distance, can handle moving objects Caution: Be careful when using on shiny surfaces or through glass
Non-contactmeasurement for fastmoving/high temperature resistantsurface temperature
Tips for measuring correctly (very important)
1. Distance and Spot Size If the spot is larger than the object, the surrounding temperature will be mixed in. For small objects, measure closer to them.
2. Setting emissivity The way infrared rays are emitted varies depending on the material, so it is important to match the settings to the target.
3. Environmental conditions Steam, flames, and glass can cause errors. Please measure from a position where you can see the temperature directly.
Distance/SpotemissivityEnvironmental Conditions
Where is it used?
In a steel factory Safely measure molten metals at temperatures of 1500°C from a distance
At a food factory Clean temperature control without touching pastries or dough
At the airport Quickly check the body surface temperature of people entering the country (using a device called a thermograph)
In a home air conditioner Detects human presence and body temperature control airflow volume and direction for comfort
Let's clear up some common misconceptions
× Can you measure depth even through glass? → No. Most radiation thermometer measure the temperature of the glass surface.
× Can you tell the "temperature inside"? → The basic principle is the surface temperature. It takes time or another method to reach the inside.
× "Glowing = high temperature"? → Visible light is one example. Invisible infrared rays are also emitted depending on the temperature.
Summary: Let's take a look at the invisible world!
There are three main points to note:
1. All objects emit invisible light called "infrared rays" that correspond to their temperature (=radiation).
2. The higher the temperature of an object, the more infrared rays it emits.
3. radiation thermometer measures the amount of infrared radiation and converts it into temperature.
Science becomes more interesting when you value the "why" and "how" of the things around you. In the next article, we'll take a step further and look at how to set emissivity and how thermography works. Stay tuned!
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