Capacitive probe sensor with reduced effective stray capacitance

摘要

A capacative probe is provided which has reduced effective stray capacitance and is thus able to accurately detect probe contact with a conducting fluid with small fluid volumes. Effective stray capacitance is reduced by dividing stray capacitance sources into two or more sources, by reducing the capacitance value of each of the divided stray capacitance sources to a value which is substantially less than the capacitance difference which occurs as a result of probe contact with the fluid and by connecting at least selected ones of the divided stray capacitance sources in series to further reduce effective stray capacitance. The capacitance value of the stray capacitances are reduced by providing a gap in a conducting tube covering the probe aspirating tube, which gap isolates conductive elements of the probe from the probe tip potential, thus reducing or eliminating the potential across various stray capacitance sources (and thus reducing or eliminating such sources) and also results in reduced plate sizes for such stray capacitance sources. A capacitance across the gap, which may be of a controlled small value, is also in series with selected stray capacitance sources, further reducing the effective stray capacitance of the probe.