Communications: electrical – Systems – Call station
Patent
1975-03-17
1977-03-01
Caldwell, John W.
Communications: electrical
Systems
Call station
340248C, G08B 2100
Patent
active
040104575
ABSTRACT:
A current overload protection device adapted for use in a system sequentially connecting a plurality of selected loads to a common source of excitation, said protection device opening the common circuit during those times when a shorted load is on the circuit. In order to provide indication subsequent to the selection of the shorted load, the device includes a latching relay activating an alarm which will therefore stay on after other properly operating loads are selected. The device comprises a current protecting relay having the coil thereof connected in series with a triac, and a current sensing resistor connected in series with one of the switches of the protection relay forming a circuit across the triac and the coil series. One other switch of the protecting relay, when pulled in, completes the circuit to the latching relay which energizes an alarm. The pull-in action of the protecting relay is controlled by the voltage developed across the current sensing resistor which therefore sets the voltage levels across the triac. The gating of the triac is accomplished by a two-directional diode connected to the protected lead of the circuit.
REFERENCES:
patent: 1699782 (1929-01-01), Erickson
Caldwell John W.
Myer Daniel
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