Presence sensing detector and system for detecting a receiver/transmitter device affixed to an article
First Claim
1. A presence sensing system, comprising a detector having a transmitter for transmitting an interrogation signal and a receiver for receiving a presence indicating signal, and a receiver/transmitter device the presence of which is to be detected adapted to receive the interrogation frequency and to transmit said presence indicating signal in response thereto, wherein the detector further comprises a phase lock loop circuit having a first input coupled with the output of the receiver a second input for a reference signal and an output for providing a phase locked signal indicative of phase coherence between the signals on said first and second inputs, a frequency generator having an output coupled with said second input of the phase lock loop, and an alarm coupled with the output of the phase lock loop actuable in response to said phase locked signal.
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Abstract
A presence sensing system comprises a detector having a transmitter for transmitting an interrogation signal to an area to be kept under surveillance and a receiver for receiving a presence indicating signal. A receiver/transmitter device the presence of which is to be detected is adapted to receive the interrogation frequency and to transmit a presence indicating signal in response thereto. A phase locked loop circuit has a first input coupled with the output of the receiver a second input for a reference signal, and an output for providing a phase locked signal which is indicative of phase coherence between the signals on the two inputs. A frequency generator has an output coupled with the second input of the phase lock loop and an alarm is actuable in response to the phase locked signal.
The invention also includes the presence sensing detector described in the above system.
49 Citations
27 Claims
- 1. A presence sensing system, comprising a detector having a transmitter for transmitting an interrogation signal and a receiver for receiving a presence indicating signal, and a receiver/transmitter device the presence of which is to be detected adapted to receive the interrogation frequency and to transmit said presence indicating signal in response thereto, wherein the detector further comprises a phase lock loop circuit having a first input coupled with the output of the receiver a second input for a reference signal and an output for providing a phase locked signal indicative of phase coherence between the signals on said first and second inputs, a frequency generator having an output coupled with said second input of the phase lock loop, and an alarm coupled with the output of the phase lock loop actuable in response to said phase locked signal.
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17. A presence sensing system comprising a presence sensing detector and an active presence indicating transmitter/receiver device provided with means for permitting secure attachment to an article wherein the presence sensing detector comprises an oscillator having an output for providing an interrogation frequency for transmission at said output;
- a gating circuit having first and second inputs and an output, the first input being coupled to the output of the oscillator;
a repetitive pulse generator coupled to the second input of the gating circuit for gating pulses of said frequency for transmission to the output of the gating circuit;
a transmitter coupled with the output of the gating circuit;
a receiver tuned to a presence indicating frequency different from said frequency for transmission and providing an output;
a phase lock loop having an input coupled to the output of the receiver, a second input for a reference signal and an output for providing a phase locked signal indicative of phase coherence between signals on said first and second inputs;
a variable frequency oscillator coupled to said second input of the phase lock loop to form said reference signal which oscillator is controllable in response to the signal from the receiver to lock said phase lock loop; and
an alarm generator actuable in response to said phase locked signal and wherein said active presence indicating transmitter/receiver device comprises a receiver tuned to said frequency for transmission of the presence sensing detector and for providing an output;
synthesizing means having an input coupled with the output of the receiver and an output for providing said presence indicating frequency different from said received frequency and synthesized therefrom; and
a transmitter coupled with the output of the synthesizer for transmitting the presence indicating frequency.
- a gating circuit having first and second inputs and an output, the first input being coupled to the output of the oscillator;
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18. A presence sensing system comprising a presence sensing detector and an active presence indicating transmitter/receiver device provided with means for permitting secure attachment to an article wherein the presence sensing detector comprises a master oscillator having an output for providing a frequency for transmission at said output;
- a gating circuit having first and second inputs and an output, the first input being coupled to the output of the master oscillator;
a repetitive pulse generator coupled to the second input of the gating circuit for gating pulses of said frequency for transmission to the output of the gating circuit;
a transmitter coupled with the output of the gating circuit;
a receiver tuned to a presence indicating frequency different from said frequency for transmission and providing an output;
a phase lock loop having a first input coupled to the output of the receiver a second input for a reference signal and an output for providing a phase locked signal indicative of phase coherence between signals on said first and second inputs and synthesizing means having an input coupled to the output of the master oscillator and an output coupled to the second input of said phase lock loop to provide said reference signal to permit locking of the phase lock loop on receipt of a phase coherent signal; and
an alarm generator actuable in response to said phase locked signal and wherein said active presence indicating transmitter/receiver device comprises a receiver tuned to said frequency for transmission of the presence sensing detector and for providing an output;
synthesizing means having an input coupled with the output of the receiver and an output for providing said presence indicating frequency different from said received frequency and synthesized therefrom; and
a transmitter coupled with the output of the synthesizer for transmitting the presence indicating frequency.
- a gating circuit having first and second inputs and an output, the first input being coupled to the output of the master oscillator;
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19. A detector for a security system comprising generating means for generating a signal for transmission, a transmitter coupled with the generating means for transmitting the transmission signal for receipt by a presence indicating security device, a receiver for receiving a signal from the security device in response to the transmission frequency, and a phase lock loop circuit having first and second inputs and an output, the first input of which is coupled with the output of the receiver;
- a frequency generator having an output coupled with the second input of the phase lock loop the output of the phase lock loop providing on said output a phase locked signal indicative of phase coherence between the inputs on said first and second inputs and an alarm coupled with the output of the phase lock loop actuable in response to said phase locked signal.
- View Dependent Claims (20, 21, 22, 23, 24, 25, 26, 27)
Specification