Capacitance intrusion detection system
US4295132A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Jul 28, 1980 |
| Grant date | Oct 13, 1981 |
| Priority date | — |
| Expiry date | Jul 28, 2000 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG08B29/046
- WIPO fieldControl
- WIPO sectorInstruments
Abstract
A capacitance intrusion detection system for use with a metal object or objects insulated from ground comprises a circuit for cyclically charging and discharging the object at a relatively low frequency, for example, less than 500 Hz, and simultaneously integrating the charge on the object to develop a DC voltage proportional to the capacitance of the object. The integrating network is AC coupled to a bandpass filter which passes signals having frequencies corresponding to changes in capacitance of the object caused by an intruder and these signals are applied to a threshold circuit for activating an alarm when an intrusion occurs. Tamper alarm circuits are provided to detect unauthorized disconnection of any portion of the protected object (decrease capacitance) or the addition of capacitance in an attempt to defeat the system.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.