Method and arrangement for measuring changes of capacitive state at a security fence

Claim 1

A method for detecting an alarm or malfunction condition at a security fence by measuring operating capacitance changes thereof, the security fence having a plurality of wire electrodes arranged in parallel, comprising steps of: connecting at least one of the electrodes with an AC voltage so it serves as a transmit electrode and connecting at least one of the remaining electrodes as a receive electrode; identifying for each transmit and receive electrode a standard operating capacitance and storing said standard operating capacitance; measuring a respective current flow in each of the transmit and receive electrodes which is proportional to an operating capacitance of each of the transmit and receive electrodes and determining an operating capacitance for each of the transmit and receive electrodes, the operating capacitances being a function of a capacitance of the respective transmit or receive electrode to ground, a geometric size of the respective transmit or receive electrode, and its geometric spacing relative to the other electrodes; repeatedly measuring the operating capacitance for every transmit electrode and every receive electrode and comparing the respective measured operating capacitance to the respective standard operating capacitance for each such electrode; given a deviation in a respective operating capacitance compared to the respective standard operating capacitance utilizing the respective operating capacitance to calculate actual electrode diameter and determining swelling in relation to electrode swellings of other of said plurality of wire electrodes, utilizing the respective operating capacitance to obtain a variation of said measured operating capacitance with time and determining a rate of change of operating capacitance, and utilizing the respective operating capacitance to determine an absolute change of said variation of said respective operating capacitance with time; and employing results from the determined electrode swelling, determined rate of change, and absolute change to decide whether or not an alarm or malfunction condition exits at said security fence.

Claim 2

A method for detecting an alarm or malfunction condition at a security fence by measuring operating capacitance changes thereof, the security fence having a plurality of wire electrodes arranged in parallel, comprising steps of: connecting at least one of the electrodes with an AC voltage so it serves as a transmit electrode and connecting at least one of the remaining electrodes as a receive electrode; identifying for each transmit and receive electrode a standard operating capacitance and storing said standard operating capacitance; measuring a respective current flow in each of the transmit and receive electrodes which is proportional to an operating capacitance of each of the transmit and receive electrodes and determining an operating capacitance for each of the transmit and receive electrodes, the operating capacitances being a function of a capacitance of the respective transmit or receive electrode to ground, a geometric size of the respective transmit or receive electrode, and its geometric spacing relative to the other electrodes; repeatedly measuring the operating capacitance for every transmit electrode and every receive electrode and comparing the respective measured operating capacitance to the respective standard operating capacitance for each such electrode; given a deviation in a respective operating capacitance compared to the respective standard operating capacitance utilizing the respective operating capacitance to calculate actual electrode diameter and determining swelling in relation to electrode swellings of other of said plurality of wire electrodes, utilizing the respective operating capacitance to obtain a variation of said measured operating capacitance with time and determining a rate of change of operating capacitance, and utilizing the respective operating capacitance to determine an absolute change of said variation of said respective operating capacitance with time; and employing results from the determined electrode swelling, determined rate of change, and absolute change to decide whether or not an alarm or malfunction condition exits at said security fence.