Communications – electrical: acoustic wave systems and devices – Distance or direction finding – By combining or comparing signals
Patent
1980-12-19
1991-09-10
Pihulic, Daniel T.
Communications, electrical: acoustic wave systems and devices
Distance or direction finding
By combining or comparing signals
367135, 367136, 340566, G01S 380
Patent
active
050479954
ABSTRACT:
A detector system having a channel for comparing the peak amplitude of at least one of two electrical signals, produced at the output of two spaced geophones, against an amplitude threshold, to produce an indication of a moving object when this threshold is exceeded. To reduce the number of false indications, the system includes a parallel channel for measuring the phase difference between the two signals, and a processing circuit responsive to both channels, to ensure that indication is allowed only when the measured phase difference changes sense. The parallel channel includes four flip-flops each to measure the phase difference and the outputs of these flip-flops are added together, to produce a phase dependent signal for controlling the processing circuit. Further discrimination is provided by timing the phase transition, a time gate being used to inhibit indication when the phase transition does not occur within prescribed time limits. The processing circuit also includes a memory circuit for comparing successive phase transitions. This memory circuit resolves transitions following in close succession and inhibits when intermediate phase transition of opposite sense occur, thus allowing resolution of close moving objects. The sense of the phase transition is used for indication of direction of transit.
REFERENCES:
patent: 3205438 (1965-09-01), Buck
patent: 3348195 (1967-10-01), Spandock
patent: 3824532 (1974-07-01), Vandierendonck
patent: 4005384 (1977-01-01), Pryor, Jr. et al.
patent: 4279027 (1981-07-01), Van Sloun
Pihulic Daniel T.
The Secretary of State for Defence in Her Britannic Majesty's Go
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