| 摘要 |
A control system activates motor vehicle windshield wipers when an improved sensing element senses precipitation. The element comprises a thin, substantially planar sheet of electrically insulating material which is impervious to precipitation. First and second electrodes are secured to the sheet and in gapless contact therewith to form a precipitation sensing edge. The element is preferably supported at one end within the center of a trough formed within a holder to present the sensing edge to the atmosphere. The holder facilitates mounting and also protects the element from damage. The first and second electrodes may comprise: thin, substantially planar electrodes coextensive with the sheet; substantially planar electrodes which taper toward the sensing edge; segmented planar electrodes in which alternate segments on opposite sides of the element are removed and present varying percentages of overlap between diagonally adjacent opposite electrodes; and, wires embedded in opposite sides of the edge of an insulating sheet. The electrical resistance between the electrodes is lowered momentarily by drops of water with the lowered resistance being sensed by a control circuit which stretches the momentary period of lowered resistance to a period of time sufficient to operate the windshield wipers through a complete operating cycle.
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