Capacitive intrusion detector circuitry utilizing reference oscillator drift
US4169260A · kind A · utility
Assignee
Inventor
Key dates
| Filing date | Apr 11, 1978 |
| Grant date | Sep 25, 1979 |
| Priority date | — |
| Expiry date | Apr 11, 1998 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG08B13/26
- WIPO fieldControl
- WIPO sectorInstruments
Abstract
Protected objects are connected together to form an antenna. Preferably, the cabinet for the detector circuitry is also included in the antenna. The antenna is excited by a voltage controlled oscillator (VCO). The capacitive reactance of the antenna changes when an intrusion occurs. This causes the frequency of the VCO signal to undergo an instantaneous change. A phase comparator compares the phase of the VCO signal with the phase of a reference oscillator signal. An instantaneous change in the frequency of the VCO signal due to a change in the capactive reactance of the antenna when an intrusion occurs is reflected by a shift in phase between the VCO signal and the reference oscillator signal. This causes the phase comparator signal to change. A deriving means, preferably including a dual differentiator circuit, which derives the rate of the rate of change of the phase comparator signal, and a differential comparator, which is triggered by the dual differentiator circuit in the event of an intrusion, activates a signaling circuit so as to produce an alarm when an intrusion occurs. Since the antenna is connected to the VCO and there is no bidirectional coupling between the VCO and …
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.