After some extensive testing, here's my overall input.
The sensors (as stated) do vary a bit in terms of the 3V output. They usually range anywhere between 2.75-2.9. I have not seen any of them get to exactly 3V.
My application for these is in agriculture (outdoor gardens).
Since these sensors are FDR (I'm assuming), then you really need to be careful with the installation. If any of the green stick is exposed to air, your results will be off (read very low). My suggestion is to dig a small hole in the ground, bury the sensor (including the black part), and pack in the dirt. Then I highly suggest watering your soil, and THEN taking a measurement. You should see around 50% in mineral soil (composted soil in raised beds for gardening).
I'm currently using the following formula for VWC (assuming 50% is the correct estimation... I am definitely looking for some help here with these sensors).
float VWC;
// Calculate VWC
if (sensorVoltage < 1.1) {
VWC = (10 * sensorVoltage) - 1;
}
else if (sensorVoltage < 1.3) {
VWC = (25 * sensorVoltage) - 17.5;
}
else if (sensorVoltage < 1.82) {
VWC = (48.08 * sensorVoltage) - 47.5;
}
else if (sensorVoltage < 2.2) {
VWC = (26.32 * sensorVoltage) - 7.89;
}
else {
VWC = (62.5 * sensorVoltage) - 87.5;
}
if (VWC <= 0.0) {
VWC = 0.0;
} else if (VWC > 100.0) {
VWC = 100.0;
}I actually disagree with the 43% VWC calculation mentioned on this forum, but please help me understand why 43% instead of 50%. I saw 50% on the following white paper as well
http://edis.ifas.ufl.edu/ae266.
In regards to soil specific calibration, I have not gone through the 24 hour calibration of my soil. With that being said, I think I am seeing around 90% accuracy with these sensors uncalibrated for my needs if I follow the installation steps carefully.
I've considered calibrating my soil and using that as a baseline for other gardeners, but please help me understand if that would be feasible. Overall, for the money these sensors work very well. It would be nice to not have to calibrate the sensors, but I think that would probably dramatically increase cost. Ok... any input is greatly appreciated!
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