Presence detector

• US 3,205,352 A
• Filed: 08/04/1961
• Issued: 09/07/1965
• Est. Priority Date: 08/04/1961
• Status: Expired due to Term

• Current Assignee: John Prucha Martin
• Original Assignee: John Prucha Martin
• Inventors: JOHN PRUCHA MARTIN
• Application Number:
  US04/129,342
• Time in Patent Office: 1,495 Days
• US Class Current: 246/30
• CPC Class Codes: B61L 1/10 actuated by electromagnetic radiation; actuated by particle radiation
• CPC Class Codes: B61L 29/282 magnetic or inductive control by the vehicle
• CPC Class Codes: G08G 1/042 using inductive or magnetic detectors

Claims

1. APPARATUS FOR SENSING THE PRESENCE OF A METALLIC MASS, SAID APPARATUS COMPRISING A FIRST OSCILLATOR INCLUDING AN INDUCTIVE LOOP, SAID LOOP BEING OPERABLE TO VARY IN INDUCTANCE VALUE WHEN A METALLIC MASS ENTERS THE FIELD THEREOF TO VARY THE FREQUENCY OF THE FIRST OSCILLATOR FROM A NORMAL VALUE, A SECOND OSCILLATOR FOR GENERATING A REFERENCE FREQUENCY SUBSTANTIALLY EQUAL TO THE NORMAL FREQUENCY OF THE FIRST OSCILLATOR WITH NO METALLIC MASS IN THE FIELD OF THE LOOP, A BEAT FREQUENCY DETECTOR COUPLED TO BOTH OSCILLATORS AND OPERABLE TO GENERATE A BEAT FREQUENCY SIGNAL WHEN THE FREQUENCY OF THE FIRST OSCILLATOR VARIES FROM THE NORMAL FREQUENCY, RECTIFYING MEANS COUPLED TO THE BEAT FREQUENCY DETECTOR FOR GENERATING A DIRECT VOLTAGE WHEN THE FREQUENCY OF THE FIRST OSCILLATOR VARIES FROM THE NORMAL VALUE, AND AN OUTPUT SWITCHING MEANS COUPLED TO THE RECTIFYING MEANS, SAID SWITCHING MEANS INCLUDING A POSITIVE FEEDBACK PATH TO RENDER THE SWITCHING MEANS PARTIALLY SELF-SUSTANINING.