Communications: electrical – Condition responsive indicating system – Specific condition
Patent
1987-02-24
1988-04-05
Swann, III, Glen R.
Communications: electrical
Condition responsive indicating system
Specific condition
340571, 340572, 340687, G08B 2100
Patent
active
047361956
ABSTRACT:
In the method of the invention, a signal is injected into the power cord of an appliance and a reference voltage is set in response corresponding to a reference impedance at the point of signal injection. The reference impedance is present with the appliance connected to the power source. The reference voltage is continuously compared against a present voltage corresponding to present impedance at the point of signal injection. An alarm sounds if the present voltage changes to exceed the reference voltage, indicating a higher impedance because the appliance has been disconnected. In one embodiment, the apparatus includes an impedance bridge having an adjustable reference arm for producing a reference voltage corresponding to the impedance of the cord and appliance and a sensing arm for producing the present voltage. In a second embodiment, the apparatus injects an adjustable current into the power cord and appliance for a predetermined time to provide a present voltage. The present voltage is then compared against a reference voltage. The third embodiment is designed for mounting within the chassis of an appliance. The current is injected into the power cord and power source for a predetermined time to produce the present voltage for comparison against a reference voltage.
REFERENCES:
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patent: 4658242 (1987-04-01), Zeder
patent: 4680574 (1987-07-01), Ruffner
McMurtry Christopher J.
Poss John W.
Rathbun Lowell A.
Associates West, Inc.
Swann III Glen R.
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