In Meet Je Stad Amersfoort we are working on developing our own soil moisture sensor that measures soil capacity at different depths. See https://meetjestad.net/en/Soil_Moisture for more info.
A first analysis of the first 10 prototype sensors shows some unexpected behaviour in the capacity measurements, see: https://meetjestad.net/en/Soil_Moisture_Data_Analysis
Perhaps anybody recognizes these issues and knows what would be a likely cause?
We anticipated that moisture might affect our measurement and made two sensors which are completely coated (both the PCB and the elctrodes in the tube): 517 and 757. So far these sensors have not shown the unexpected patterns, but they have not been operational for very long, so probably it is too early to draw conclusions.