| 摘要 |
An electronic sensor (1) which measures the moisture level of a surrounding porous compound, such as soil, by summing the conductances of a plurality of electric paths (12-16) formed by traces of impure water, between a first exposed electrode (4) and a second electrode covered by a hydrophobic dielectric coating. The electrodes are mounted in the same plane (32, 34) parallel planes, or in non-parallel planes structured to reduce reactance between the two electrodes. Beads of water (17-21) form at the points where said traces contact the dielectric-coated-electrode, said beads functioning as point capacitors having said second electrode as a common plate. Both electrodes comprise the reactive element of an astable multivibrator (22) whose frequency varies proportionally to the number of electric paths formed by said traces of impure water. The relatively large reactive component introduced by the series-linked point capacitors tends to mask the variations in conductance between the various paths and contributes to a very linear relationship between the moisture level and the multivibrator frequency over a broad range. The output of the multivibrator is fed to a series of monostables (26-29) to generate signals corresponding to predetermined thresholds of moisture level. |
