Communications: electrical – Condition responsive indicating system – Specific condition
Patent
1983-08-22
1986-11-04
Rowland, James L.
Communications: electrical
Condition responsive indicating system
Specific condition
340562, 340552, G08B 1326
Patent
active
046212582
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.
REFERENCES:
patent: 4155078 (1979-05-01), Bowling et al.
patent: 4345167 (1982-08-01), Calvin
Hofsass Jeffery A.
Rowland James L.
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