Signal processing circuit for intrusion alarm system

Claim 1

AN INTRUSION DETECTION SYSTEM ADAPTED TO RESPONDTO SIGNALS PRODUCED BY MOVEMENT OF AN INTRUDER IN A PROTECTED AREA AND TO DISCRIMINATE AGAINST SPURIOUS RANDOM SIGNALS, COMPRISING GATING MEANS HAVING FIRST AND SECOND INPUTS AND HAVING FIRST AND SECOND OPERATING STATES, MEANS FOR APPLYING INTRUDER AND SPURIOUS SIGNALS TO SAID FIRST INPUT, SAID GATING MEANS IN SAID FIRST OPERATING STATE BLOCKING SAID INPUT SIGNALS AND IN SAID SECOND OPERATING STATE PASSING SAID INPUT SIGNALS, A SAMPLING OSCILLATOR CONNECTED TO THE SECOND INPUT OF SAID GATING MEANS AND ADAPTED SUCCESSIVELY TO SWITCH SAID GATING MEANS BETWEEN SAID FIRST AND SECOND OPERATING STATES AT THE FREQUENCY OF SAID OSCILLATOR, MEANS FOR SELECTIVELY CHANGING THE FREQUENCY OF SAID OSCILLATOR, SIGNAL STORAGE MEANS CONNECTED TO THE OUTPUT OF SAID GATING MEANS COMPRISING A RESISTOR-CAPACITOR NETWORK HAVING A PREDETERMINED DISCHARGE RATE, SAID NETWORK BEING CHARGED BY EACH SIGNAL PASSED BY SAID GATING MEANS THAT EXCEEDS A PREDEETERMINED LEVEL, AND MEANS RESPONSIVE TO THE CHARGE ON SAID NETWORK IN EXCESS OF A PREDETERMINED MAGNITUDE FOR INDICATING THAT CONDITION.