how do laser pointed thermometer guns find a reading of the temperature?
In: Technology
Atoms jiggle around because of temperature. This jiggling jiggles the electrons too. When electrons move back and forth, they create light. In fact thats basically what light is, a history of the motion of an electron, propogating outward at the speed of light.
We can relate the frequency/color of light to the temperature associated with the amount of jiggling in the atoms, which is what we call temperature
The temperature of an object is related to the infrared radiation it radiates away. They are just IR-cameras with a chip that can calculate the temperature based on the distribution of IR wavelengths
The laser is just there so you know where the reading is being taken from. Everything emits infrared radiation as long as it’s above absolute zero and if it gets hot enough it starts emitting visible light. The radiation things normally emit based on their temperature is a form of light below what the human eye can see unless it gets intensely hot. The laser thermometer is able to sense this radiation and determine temperature based on how strong and what “color” the light is.
1.Heated objects “glow” infrared light. We cannot see it, but we can feel it.
2.Thermometers can actually see that light and it’s intensity.
3.One of the mechanisms for seeing is filtering – there is a photon detector (simple camera) behind a special filter that lets only infrared light go through it.
All heated bodies emit light out of it, and so does our body. Except, this light is not visible to human eyes. The laser pointer thermometers are like special eyes which can see this kind of light. Depending on the wavelength of this light, the thermometer can determine what is the temperature of the body.
What the lasers do: The lasers pointers are there so you know where you are measuring from and what distance, if you have two laser beams which cross 30cm (1foot) from the device it is really easy to get the user to always take a measurment from 30cm away from the object, becuse at this range the two merge into one. They use lasers because they emit only a single frequency of light so it wont interfere with the reading.
How the reading works: objects emit radiation in proportion to their temperature (to the power 4), hot objects (like the sun) emit more light at higher energies (more blue). cold objects like you emit most of their light in the, low energy, infra red (redder than red) wavelengths. All the thermometer is doing is measuring light from one particular wavelength in the infra red part of the spectrum. It then uses this number and a model called ‘black body radiation’ to estimate the temperature of the surface that emited the light. This model just says how much light will be emitted at each wavelength for a given temperature.
There are lots of problems with this which lead to limitations of how these thermometers can be used, firstly this is just light so if you point it at somthing that is reflecting the sun it’s going to say it’s really hot even if it isn’t, if you point it at somthign which is opaque to visible light but clear to IR light it wont see it at all/ it will say it’s very cold. Also the distance from the object matters a lot, which is why they put the lasers on. But lastly, most things are not perfect ‘black bodies’, this means that they don’t emit light in a neat predictable curve so you will get different measurments for different materials of the same temperature, so these devices are typically calibrated for a particular task eg, skin temperature, or they are just quite inaccurate. Sometimes these differences are small and don’t matter sometimes they matter a lot (imagine measuring the temperatre of an infra red LED!, it’s not hot but it is emitting loads of infra red light. The thermometer is blind to all the other light, so it will just think that the LED is emiting loads of light at every wavelength, because thats what a black body would do!
Depends on the gun. The ones you’re asking about work as others have described.
There is a type that uses the laser itself, and it is pretty accurate, but it’s considerably more expensive, and not as easy to use.
Laser light is extremely homogenous. All of the light is one wavelength, with very little variation. When that light strikes a surface, the movement of atoms in the material due to temperature causes a doppler shift, and by comparing the laser light that was emitted to the light that returns, the computer can see how much the spectrum of the light has broadened, and infer the temperature.
Others did a fine job giving the explanation. The rabbit hole you’re seeking is the search term ‘black body radiation.’ Very key and important problem to solve in the late 1800s for process control in making steel. The solution was literally a quantum leap.
We can tell roughly how hot something is by looking at it. Frozen skin is pale and white. Burnt skin is bright red.
Cameras can see way more detail than us, so they can look at the skin and calculate a much more accurate temperature.
The laser pointer is just to tell the camera where to look.
How accurate are these things? I was refused service at a dentist’s office after they used one of those on my forehead and it read 99.8. There was no reason I should have had a temp and when I got home and used a traditional thermometer it was around 97.5 which is normalish for me. I had been in the sun a few minutes prior to their reading but not long enough to get any color. Thoughts?
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