SECURITY ALARM Russian patent published in 1998 - IPC

FIELD: detection of intruders which carry magnetic objects and cause ground vibrations. SUBSTANCE: device has serial circuit of charge amplifier, first band-pass filter, first threshold gate, which output is connected to one input of comparator. Start and end of multiple-turn circuit are connected to inputs of differential amplifier, which output is connected to serial circuit of second band-pass filter and second threshold gate which is connected to another input of comparator. In addition device has combined cable detector which has several conductors which are covered by external conductor which is covered with isolating cord which is covered with working layer which is made from material which generates electric charge by application of mechanical force. Latter layer is covered with shielding conductor which is covered with zero potential line. Shielding electrode is connected to zero potential line. External conductor is connected to input of charge amplifier. EFFECT: increased sensitivity, increased stability to noise. 2 dwg