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US 4,622,541 AGranted
Intrusion detection system
AssigneeNapco Security Systems, Inc.
InventorRoy Stockdale
Life of this patent
Estimating the term…
Abstract
There is disclosed an intrusion detection system employing vibration sensors which are arranged in a series loop consisting of first and second wires and which loop is terminated by a terminating impedance. Coupled to the wires is a processing circuit which supplies a square wave biasing waveform for the loop and a DC voltage determined by the terminating impedance. By detecting the magnitude of the DC level, the processor can determine if the loop has been opened or shorted or if any one of the sensors in the loop has been activated due to an intrusion. Thus the system described employs two wires for supplying both power and sensing of output signals from the loop being monitored.
Claims21
An intrusion detection system, comprising:
- first and second lines with one of said lines being a common,
- a plurality of sensors arranged in parallel between said lines, with each sensor including unidirectional rectifying means for providing a DC operating potential to each sensor upon application to said first line of a potential of a given polarity, with each sensor further including latching means responsive to sensor operation to provide a given impedance across said lines when said sensor is operated due to an intrusion,
- a terminating impedance arranged in parallel with said sensors between said lines,
- driving means coupled between said lines and operative to provide a repetitive waveform characterized in having a first cycle indicative of a first transititon period and a second cycle indicative of a second transition period, whereby said unidirectional rectifying means is responsive to said first cycle to provide said operating potential to said sensors,
- processing means coupled to said first line and operative to provide a first impedance during said first cycle and a second impedance during said second cycle of said repetitive waveform said processing means including detection means operative during said second cycle to detect the voltage on said loop as determined by said second impedance, said line terminating impedance and said given impedance whereby if a sensor is operated due to an intrusion, said processing means detects a low voltage condition during said second cycle, whereby if said line terminating impedance were removed said processing means detects a high voltage condition during said second cycle in accordance with the expected ratio of said line terminating impedance and said given impedance as compared to said second impedance, with said first impedance of said processing means being of a value to prevent the operation of said detection means during said first cycle.
2 more elements
An intrusion detection system, comprising:
- first and second lines,
- at least one sensor arranged between said lines, with said sensor having an input terminal connected to one of said lines, with said input terminal coupled to unidirectional rectifier means and operative upon receipt of a given polarity signal to provide an operating potential for said sensor, and means associated with said sensor to provide upon the detection of an intrusion a low impedance across said lines,
- a line resistor in parallel with said sensor and across said lines,
- a drive source coupled to said input terminal for providing a repetitive waveform, with said waveform having a first cycle indicative of a first polarity period and a second cycle indicative of a second polarity period, whereby said unidirectional biasing means provides said operating potential to said sensor for said first cycle,
- processing means coupled to said input terminal and operative only during said second cycle to detect any change in impedance across said lines during said second cycle, and wherein when said change of impedance is due to an intrusion said sensor provides said low impedance and this condition is detected by said processing means.
2 more elements
An intrusion detection system, comprising:
- first and second lines with one of said lines being a common,
- a plurality of biasable sensors each having an input terminal for receiving an input and at output terminal coupled to said input terminal via a normally closed tamper switch, whereby said first line is connected to said input terminal of said first sensor and the output terminal of said first sensor is connected to the input terminal of said next sensor and so on with a terminating resistor connected to the output terminal of said last sensor to form a loop, with each of said sensors operative to provide a low impedance in shunt with said terminating impedance upon detection of an intrusion to thereby shunt said terminating impedance upon the occurrence of said intrusion with each of said sensors including unidirectional rectifying means coupled to said input terminal and operative to provide a biasing signal for said sensor when energized by a given polarity signal from a repetitive waveform applied as said input,
- driving means coupled to said input terminal of said first sensor and operative to supply said repetitive waveform as said input to said sensors for biasing the same, said repetitive waveform having a first given cycle and a second given cycle each of a different polarity, whereby said sensors are biased during said first given cycle,
- first means operative during said second given cycle and coupled to said line responsive to the operation of one of said sensors providing said shunting impedance as affecting the resistance ratio of said line to indicate an alarm condition and second means operative during said second given cycle coupled to said line and responsive to the opening of said line manifesting the removal of said terminating impedance to thereby provide an indication of an open circuit condition.
1 more element
A biasable sensor circuit for use in detecting an intrusion by placing said sensor circuit in a loop which has impressed upon a line of said loop a repetitive waveform for application to an input terminal of said sensor circuit, said sensor circuit comprising:
- an input terminal coupled to said line and adapted to receive said repetitive waveform,
- a rectifier coupled coupled to said input terminal and operative to rectify said waveform to provide a DC potential,
- means for applying said DC potential to said sensor to bias the same,
- means responsive to the operation of a sensor device to provide an output when said sensor device detects an intrusion, said sensor device taking the form of a seismic sensor including an annular member supported by two contacts through which said bias potential is applied, with said annular member capable of moving off at least one contact to provide an opening of said bias potential indicative of a pulse,
- comparator means coupled to said sensor device and responsive to said pulse to provide said output when said sensor is vibrated,
- a controllable impedance device having one terminal coupled to said line and another terminal coupled to a point of reference potential and operative in a first state to provide low impedance between said terminals and in a second state to provide a high impedance between said terminals, means response to said output to control said device to operate in said first state during said output to thereby load said line with said low impedance,
- latching means responsive to the operation of said device in said first state to provide an indication of said operation,
- an output terminal for applying said repetitive waveform received by said input terminal to any succeeding biasable sensor circuit connected to said loop, and
- means connecting said output terminal to said input terminal through selected portions of said biasable sensor circuit, and to said rectifier and said controllable impedance device.
6 more elements
Dependencies are inferred from the claim text.