capsensehumiditysensingsensor
I’m trying to figure out how the following soil moisture sensor works.
It’s obviously a capacitive sensor where the capacitance changes when the soil moisture varies.
However, as you can see, the sensor is ENCLOSED, so how does the capacitor get contact with the soil moisture to sense it?
A likely mechanism for the operation of the sensor is by creating a Galvanic Cell battery out of the probe electrodes, with the moisture in the soil acting as the electrolyte / "salt-bridge".
From the Wikipedia page referenced above:
The "sensor probe" would consist of two dissimilar metals such as Zinc and Copper, which @JimDearden correctly surmises in his answer.
However, the actual current flow due to Galvanic redox reactions is what would create the energy to deflect the needle of the sensor, rather than conductivity of the moist soil alone. The moisture here works merely as an electrolytic medium for the electrochemical reaction.
This sensor would fail if used in distilled or otherwise very pure water, or moisture containing no dissolved salts / electrolytes.
It's giving you units of "wetness", from 0 meaning "bone dry", and 950 meaning "sopping wet".
It's for an Arduino. It doesn't give you anything as technical as real units - just a rough scale between wet and dry. It's entirely up to you how you interpret that value.
It's about as accurate as sticking your finger in the soil to feel how wet it is.
You could divide the sampled value by 10 and use it as a percentage of sogginess.
Best Answer
It could be also TDR sensor (Time Domain Reflectometer) if it very pricy. But also capacitive moisture sensors have the cap on it. Would you expect to bury the whole electronics into the soil? Of course not, the self capacitance is somehow deducted with the calibration.