eli5 How do contactless clinical thermometers work, when it’s cold outside?


eli5 How do contactless clinical thermometers work, when it’s cold outside?

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Why would it not work the same way as when it is warm outside? They should work fine for the temperate range they are designed for.

They work by messing with the amount of infrared radiation emitted from an object and it depends on the temperature of the object. The ambient air temperature does not change the amount of infrared radiation emitted.

The temperature of the electronics in the thermometer does have an effect on their electrical parameters. So you need to design them to compensate for the temperature effect of the electronics. So the device will have a working temperature range. Battery voltage drop with temperature so I would not be surprised if that is the limiting factor.

Is the temperature of the electronic, not the air and it takes some time for it to cool down when you take it outside. So even if it is not designed to operate at cold temperatures it will work until its temperature has dropped.

You know how when something gets very hot (like an electric stove), it glows red or even yellow hot? Well, it turns out everything that has a temperature above absolute zero is actually “glowing” hot. Our eyes can only see a small range of colors, so most thing glow at colors outside of those we can see. But you can use special cameras or infrared detectors which can pick up the glow put off by humans at around 98.6F (or 37C).

Contactless thermometers use sensors to detect the infrared glow our bodies put off. If your temperature is higher than normal (a fever), you will glow slightly brighter, and a slightly different color. These thermometers can pick these differences up.