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How exactly does a (capacitive) humidity sensor work?

Physics Asked on February 26, 2021

How exactly does a humidity sensor work? For example, how can it differentiate between a relative humidity of 30 % and 35 %?

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I know how a capacitance works but for me that principle is way too high level to understand a humidity sensor, I’d say.
How does a sensor know that it is water inside the liquid and not just a random mixture of any kind of liquid that causes that measured value of dielectrica?

One Answer

The capacitor does not know, what changes the dielectric behavior, but in usual circumstances only water vapor comes in the capacitor. Probably it would not work if you expose it to other vapors, but how should this happen? If it shall measure the relative humidity and not the absolute it has to be coupled with a temperature sensor.

Answered by trula on February 26, 2021

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