Communications: electrical – Condition responsive indicating system – Specific condition
Patent
1986-05-15
1987-08-04
Swann, III, Glen R.
Communications: electrical
Condition responsive indicating system
Specific condition
340567, 340573, G08B 1326
Patent
active
046849335
ABSTRACT:
A detection system for a doorway discriminates between persons who are authorized to go through the doorway and those who are not. An oscillator with a resonant L-C circuit includes metallic capacitor plates on opposite sides of the doorway to reduce the oscillator frequency when a person walks through and to provide a transient frequency increase if the person wears or carries a small metal object. A discriminating circuit is connected to the oscillator output to discriminate between persons in the doorway with and without such a metal object.
REFERENCES:
patent: 2355395 (1944-08-01), Rubenstein
patent: 3455835 (1969-05-01), Rudaley
patent: 3493954 (1970-02-01), Bartlett et al.
patent: 3723862 (1973-03-01), Wentzel et al.
patent: 4095214 (1978-06-01), Minasy
patent: 4555696 (1985-11-01), Brown
patent: 4598275 (1986-07-01), Ross et al.
Gray Rita Ann
Swann III Glen R.
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