Detection of moving objects

Claim 1

In a system for detecting moving ground vehicles of the type including a seismic detector capable of detecting seismic vibrations generated by moving vehicles and of providing in response a corresponding electrical signal; first detector means connected to the seismic detector, responsive to the electrical signal, for providing a first information signal, to distinguish electrical signals having peak amplitudes above and below a first amplitude threshold, namely a threshold of such set value as to distinguish electrical signals corresponding to seismic vibrations of peak amplitude characteristic of moving ground vehicles, from electrical signals corresponding to other seismic vibrations; and indicator means connected to the first detector means, responsive to the information signal therefrom, for indicating the presence of a detected moving vehicle; the improvement comprising a second detector means connected to the seismic detector, parallel to the first detector means, responsive to the electrical signal, for providing a further information signal, to distinguish electrical signals having peak amplitudes above and below a second amplitude threshold, namely a threshold of such set value as to distinguish electrical signals corresponding to seismic vibrations of peak amplitude characteristic of moving ground vehicles of a particular kind from electrical signals corresponding to seismic vibrations of peak amplitude characteristic of other sources including moving vehicles not of this particular kind; said indicator means also being responsive to said further information signal, and being capable of providing in response an indication of the kind of moving vehicle detected, said system further including a duration channel connected to the seismic detector for discriminating against electrical signals of less than and longer than a given time interval, the duration channel including, connected in series in the following order: a first signal comparator, a monostable, an integrator, and an amplifier; the amplifier being connected to the first signal comparator to provide a first reference signal, the duration channel also including a second signal comparator connected to the amplifier, and a voltage source connected to the second signal comparator to provide a second reference signal for defining the time interval.