×

Article presence sensor

  • US 4,004,234 A
  • Filed: 06/23/1975
  • Issued: 01/18/1977
  • Est. Priority Date: 06/23/1975
  • Status: Expired due to Term
First Claim
Patent Images

1. Apparatus for sensing the presence of an article which comprises, in combination:

  • a source of alternating current;

    a high impedance resistor of at least 100 megohms value having one side thereof connected to said source of alternating current;

    a metallic sensing element connected to the other side of said resistor;

    a voltage follower circuit, connected to the same side of said resistor as said sensing element, for amplifying any signal generated as a result of an article being present before said sensing element;

    electronic circuit means, connected to the output of said voltage follower circuit, for furnishing an output signal quantity representative of the total range of the signal from said voltage follower circuit;

    said electronic circuit means includingfirst electronic means for sampling and holding the positive going peak of any electrical signal from said voltage follower;

    second electronic means for sampling and holding the negative going peak of any electrical signal from said voltage follower; and

    electronic difference means, connected to the output of both said first and second electronic means for sampling and holding, for generating an output signal quantity indicative of the peak to peak output value of said voltage follower;

    electronic minimum level detection means connected to said electronic circuit means for detecting and holding the minimum value presented by said electronic circuit means during a pre-selected time period; and

    electronic comparison means, connected to said minimum level detection means and to said electronic circuit means, for generating an output signal indicative of the presence of an article in response to said output signal from said electronic circuit means exceeding said minimum value by a pre-selected amount.

View all claims
  • 1 Assignment
Timeline View
Assignment View
    ×
    ×