METHOD FOR DETECTING AN INTRUSION IN PROTECTED AREA AND DEVICE FOR IMPLEMENTING THE SAME

摘要

The present invention essentially relates to a method which comprises measuring an extremely low frequency electromagnetic field, wherein said field is excited by the intrusion of an object in a protected area. The voltage is then separated and an alarm signal is generated upon any change in the latter, said change resulting from a disturbance in the field during the unauthorised intrusion of an object having electrical loads. The device of the present invention comprises an electromagnetic-field sensitive member in the form of a functional amplifier (2), wherein said amplifier is surrounded by a deep negative connection and comprises open inverting as well as grounded non-inverting inputs. The input resistance at the inverting input of the functional amplifier (2) is higher than 10<12> Ohms. Low-frequency and high-frequency filters (4, 9) are serially connected to the output of the functional filter (2), while the output of the high-frequency filter (9) is connected to the input of a comparator (14) having its output connected to the input of a cascade (20) for generating an alarm signal.