Proximity detecting apparatus

• US 4,621,258 A
• Filed: 08/22/1983
• Issued: 11/04/1986
• Est. Priority Date: 08/22/1983
• Status: Expired due to Fees

• Current Assignee: Campman, James P.
• Original Assignee: Campman, James P.
• Inventors: Campman, James P.
• Primary Examiner(s): Rowland, James L.
• Assistant Examiner(s): Hofsass, Jeffery A.
• Application Number:
  US06/524,940
• Time in Patent Office: 1,170 Days
• Field of Search: 340/562, 340/567, 340/561, 340/552, 340/553, 307/116, 361/179
• US Class Current: 340/567
• CPC Class Codes: G08B 13/26 by proximity of an intruder causing variation in capacitance or inductance of a circuit

Abstract

Apparatus and method for detecting changes in capacitance of an antenna due to intrusion into the antenna field by a body of different dielectric constant, in the presence of induced AC voltages on the antenna from electromagnetic radiation. The apparatus includes four operational amplifiers connected in a circuit for processing the production of voltage pulses. The first amplifier operates to rectify the AC voltages from the antenna to a DC fluctuating voltage, which voltages are averaged to produce a constant voltage above ground potential so long as there is no intrusion of the field. During this period no signal voltage is transmitted to the second amplifier. Intrusion will result in a decreased voltage level which causes the second amplifier output to swing from quiescent level to a lower level whereupon a negative going square wave voltage pulse appears at the output of the second amplifier and, through a capacitor, is applied to the inverting input of the third amplifier having its noninverting input terminal grounded. Normally, the third amplifier has zero output voltage and a negative going square wave voltage pulse from the second amplifier will produce a positive going square wave voltage pulse from the third amplifier, which feeds through a combined diode and R/C circuit and accumulator which has its output connected to the non-inverting input terminal of the fourth amplifier whose output is a positive going square wave voltage pulse applied to a transistor for triggering an alarm after a predetermined number of pulses have been accumulated.

Claims

1. Apparatus for detecting an intrusion of an ambient electromagnetic field of an antenna, in the presence of radiation about said antenna that produce voltages on the antenna for providing an indication of the intrusion of said electromagnetic field;

an antenna capable of receiving said electromagnetic radiation and having a voltage generated therein by said radiation and wherein there is a change in level of voltage so generated which will be above or below the level where there is no intrusion,

a first amplifier for receiving said alternating current voltages at said levels and for producing a direct current voltage fluctuation at the same frequency as said alternating current voltage, but at a level elevated from that of the alternating current voltage;

filtering means for receiving said direct current fluctuations and for producing a constant direct current voltage at a level responsive to each change in level of the fluctuating direct current voltage;

a second amplifier receiving changes in level of said constant voltage to produce a negative or positive going square wave voltage pulse, constant in amplitude;

a third amplifier responsive only to the negative going square wave voltage pulses to produce a positive going square wave voltage pulse;

a fourth amplifier for receiving the output from said third amplifier having means there between whereby response of said fourth amplifier can be selectively made responsive to a single square wave voltage pulse or to a square wave voltage pulse produced after the occurrence of a plurality of square wave voltage pulses; and

means receiving the output of said fourth amplifier for triggering an indication of said intrusion.

2. Apparatus according to claim 1, wherein the antenna is a pair of uniformly spaced conductors separated one from the other by a dielectric material that also encompasses both said conductors, one of said conductors serving as the antenna connected to the input terminal of said first amplifier and the other of said conductors connected to ground.

3. Apparatus according to claim 1, wherein the means coupling said fourth and third amplifiers comprise,

means connected to the output of said third amplifier for measuring out the number of pulses required to cause a response of said fourth amplifier, and

means for shunting said measuring means to cause a response of said fourth amplifier to each and every single square wave voltage pulse.