General purpose self-tuning capacitance sensor [for oil recycling and soil moisture measurement application]

Moisture measurement is of interest in many different engineering applications. There is a commercial need for a moisture measurement system in the oil recycling industry where oil is often contaminated with water, and in agriculture where soil moisture is an important parameter in the growth cycle of crops. The aim of this study has been to develop a versatile self-toning instrument to measure capacitance by means of multiple-feedback synchronous detection. The advantage of self-tuning is that the multiple feedback loops are held with the correct phase shifts required for synchronous detection regardless of component or environmental variations.