US 4,206,443 AGranted

Protective load disconnect unit for remote load control systems

AssigneeWestinghouse Electric Corp.

InventorJames S. Britton

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Abstract

A protective load disconnect unit is remotely controlled at a single control input terminal from a master controller and monitoring unit. A power switching circuit is actuated to switch a load to be controlled from on to off by a control signal from the master unit. The input terminal is maintained electrically isolated from the switching circuit. A load status response circuit senses the on-off conditions of the power switching circuit. A variable impedance circuit included in the load status response circuit is isolated from the power switching circuit and is connected to the input terminal. The on and off conditions of the power switching circuit changes the variable impedance circuit so that an electrical condition at the input terminal is varied to indicate the load status while the control signal concurrently actuates the switching circuit.

Claims10

Dependent claims

A protective load sensing and disconnect arrangement for a remote load control system comprising:

a pair of power terminals for connecting a load to be controlled to a power line source of electric power energization;
a single control terminal for receiving a control signal;
power switching means including a switch connected between said power terminals, said power switching means further including actuating circuit means for producing closed and open states of said switch to selectively energize and deenergize said load to be controlled, and said power switching means further including first isolated control means having a pair of inputs connected in series with said single control terminal and electrically isolated from a pair of outputs thereof, said pair of outputs being connected with said actuating circuit means so that said first isolated control means is selectively activated by said control signal to cause said actuating circuit means to effect an open switch state and deenergize said load to be controlled;
load status response means connected to one of said power terminals and including second isolated control means having a pair of inputs responsive to the energization and deenergization of said load to be controlled and electrically isolated from a pair of outputs thereof, said second isolated control means being selectively activated and deactivated in response to the energization and deenergization, respectively, of said load to be controlled, said load status response means further including variable impedance means connected and responsive to said pair of outputs of said second isolated control means so that lower and higher impedance values are produced therein in response to the activation and deactivation of said second isolated control means;
and
said variable impedance means further being operatively connected with said single control terminal so as to vary an electrical condition at said single control terminal when said control signal is received thereat for initiating and maintaining the deenergization of said load to be controlled wherein the variations of said electrical condition correspond to the changes between energization and deenergization of said load to be controlled.

3 more elements

A remote load control system comprising:

a master controller and monitoring unit including an output terminal and a control signal source for producing a control signal to said output terminal in response to a load turn-off command, said master controller and monitoring unit further including a status monitoring circuit connected with said output terminal;
single conductor means connected to said output terminal;
a load sensing and disconnect unit including a control input terminal connected to said single conductor means, input and output power terminals, a power switching means having an output including a pair of switch contacts connected between said input and output power terminals and operative between normally closed and open switch states, said power switching means having an input electrically isolated from said control input terminal and responsive to said control signal applied from said single conductor means so as to operate said switch contacts between said normally closed and open switch states, load status response means including an input and an output electrically isolated from each other, said input being connected to said output power terminal and said output including a variable electrical means being variable in response to energized and deenergized conditions at said input to said load status response means, said variable electrical means being connected with said control input terminal so as to vary an electrical condition thereat so that said status monitoring circuit in the master unit is rendered operative to indicate the load energizing and deenergizing condition of said output power terminal.

Dependencies are inferred from the claim text.