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Capacitive-type detection device

  • US 4,748,390 A
  • Filed: 09/18/1985
  • Issued: 05/31/1988
  • Est. Priority Date: 09/19/1984
  • Status: Expired due to Fees
First Claim
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1. A detection device mounted on a windshield to detect water adhering to an external surface of the windshield to be wiped by a windshield wiping system, comprising:

  • detection electrode means including a detection electrode and a ground electrode which are mounted adjacent said windshield,oscillation circuit means including a resonance circuit associated with a capacitance between said detection electrode and said ground electrode, said oscillation circuit means changing its oscillation frequency in response to change in said capacitance caused by a presence of water on said external surface of the windshield adjacent said detection electrode means, said water causing said capacitance to vary in accordance with whether it is in the form of drops of water or a film of water, said oscillation circuit means including means for changing the oscillation frequency thereof by a larger amount in response to the presence of drops of water adjacent said detection electrode means and by a lesser amount in response to the presence of a film of water adjacent said detection electrode means, anddetection circuit means for detecting a change of oscillation frequency of said oscillation circuit means and determining whether said change of oscillation frequency in said larger amount indicating the presence of drops of water adjacent said detection electrode means or said lesser amount indicating the presence of a film of water adjacent said detection electrode means, whereby said detection device drives said windshield wiping system in a first mode if said detection circuit means detects said larger amount of change in oscillation frequency and in a second mode if said detection circuit means detects said lesser amount of change in oscillation frequency.

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