Isolation circuitry
First Claim
1. Isolation circuitry for automatically disconnecting a load from a source upon detecting a short and for automatically reconnecting the load to the source after the short circuit clears, said circuitry comprising,a first node connected to a second node via a first transmission path,a third node connected to a fourth node via a second transmission path maintained at a different voltage than said first transmission path,a switch between said nodes on said first transmission path,a sensing circuit connected between said first and second transmission paths that includes a current generator that induces a fault indicating current into a load between said first and second transmission paths and monitors the fault indicating current for an increase over a threshold when the load impedance falls below a lower limit indicating a short circuit, said sensing circuit providing a control signal to said switch to open if a short circuit is detected and to close if a short circuit is not detected, andwherein said current generator of said sensing circuit includes short responsive capacitance in the current generator that charges up in the absence of a short circuit impedance between said first and second transmission paths and discharges in the presence of said fault indicating current and a control element that provides said control signal depending upon the charge condition of said capacitance.
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Accused Products
Abstract
Isolation circuitry for automatically disconnecting a load from a source upon detecting a short and for automatically reconnecting the load to the source after the short circuit clears. The isolation circuitry includes a first node connected to a second node via a first transmission path, and a third node connected to a fourth node via a second transmission path maintained at a different voltage than the first transmission path. There is a switch between the nodes on the first transmission path, and a sensing circuit that is connected between the first and second transmission paths. The sensing circuit includes a current generator that induces a fault indicating current into a load between the first and second transmission paths and monitors the fault indicating current for an increase over a threshold defined by an operating voltage setting circuit when the load impedance falls below a lower limit indicating a short circuit. The sensing circuit provides a control signal to open the switch if a short circuit is detected and to close the switch if a short circuit is not detected.
55 Citations
18 Claims
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1. Isolation circuitry for automatically disconnecting a load from a source upon detecting a short and for automatically reconnecting the load to the source after the short circuit clears, said circuitry comprising,
a first node connected to a second node via a first transmission path, a third node connected to a fourth node via a second transmission path maintained at a different voltage than said first transmission path, a switch between said nodes on said first transmission path, a sensing circuit connected between said first and second transmission paths that includes a current generator that induces a fault indicating current into a load between said first and second transmission paths and monitors the fault indicating current for an increase over a threshold when the load impedance falls below a lower limit indicating a short circuit, said sensing circuit providing a control signal to said switch to open if a short circuit is detected and to close if a short circuit is not detected, and wherein said current generator of said sensing circuit includes short responsive capacitance in the current generator that charges up in the absence of a short circuit impedance between said first and second transmission paths and discharges in the presence of said fault indicating current and a control element that provides said control signal depending upon the charge condition of said capacitance.
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12. Isolation circuitry for automatically disconnecting a load from a source upon detecting a short and for automatically reconnecting the load to the source after the short circuit clears, said circuitry comprising,
a first node connected to a second node via a first transmission path, a third node connected to a fourth node via a second transmission path maintained at a different voltage than said first transmission path, a switch between said nodes on said first transmission path, a sensing circuit connected between said first and second transmission paths that detects the presence or absence of a short circuit between said first and second transmission paths, said sensing circuit providing a control signal to said switch to open if a short circuit is detected and to close if a short circuit is not detected, a light emitting diode connected to said sensing circuit to indicate if a short circuit is detected, and wherein said sensing circuit includes short responsive capacitance in the sensing circuit that charges up in the absence of a short circuit impedance between said first and second transmission paths and discharges in the presence of a short circuit impedance between said first and second transmission paths and a control element that provides said control signal depending upon the charge condition of said capacitance, said light emitting diode being connected to charge said capacitance.
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14. A loop system comprising
a plurality of isolation circuitries, each comprising a first node connected to a second node via a first transmission path, a third node connected to a fourth node via a second transmission path maintained at a different voltage than said first transmission path, a switch between said nodes on said first transmission path, and a sensing circuit connected between said first and second transmission paths that includes a current generator that induces a fault indicating current into a load between said first and second transmission paths and monitors the fault indicating current for an increase over a threshold when the load impedance falls below a lower limit indicating a short circuit, said sensing circuit providing a control signal to said switch to open if a short circuit is detected and to close if a short circuit is not detected, said isolation circuitries being connected in a loop, a plurality of loop devices connected between said transmission paths along said loop, a loop controller connected to said transmission paths to provide power to and communicate with said loop devices on said loop, and wherein each said fault generator of said sensing circuit includes short responsive capacitance that charges up in the absence of a short circuit impedance between said first and second transmission paths and discharges in the presence of said fault indicating current and a control element that provides said control signal depending upon the charge condition of said capacitance.
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15. A loop system comprising
a plurality of isolation circuitries, each comprising a first node connected to a second node via a first transmission path, a third node connected to a fourth node via a second transmission path maintained at a different voltage than said first transmission path, a switch between said nodes on said first transmission path, and a sensing circuit connected between said first and second transmission paths that includes a current generator that induces a fault indicating current into a load between said first and second transmission paths and monitors the fault indicating current for an increase over a threshold when the load impedance falls below a lower limit indicating a short circuit, said sensing circuit providing a control signal to said switch to open if a short circuit is detected and to close if a short circuit is not detected, said isolation circuitries being connected in a loop, a plurality of loop devices connected between said transmission paths along said loop, and a loop controller connected to said transmission paths to provide power to and communicate with said loop devices on said loop, and wherein said system is a fire protection system and said loop devices include smoke, fire, or temperature detectors.
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17. A method of automatically disconnecting a load from a source upon detecting a short and for automatically reconnecting the load to the source after the short circuit clears, said method comprising
providing isolation circuitry including first and second transmission paths connected between said source and said load and maintained at different voltage levels, a switch between a node connected to said source and a node connected to said load on said first transmission path, and a sensing circuit that is connected between said first and second transmission paths and includes a current generator, inducing a fault indicating current by said current generator into a load between said first and second transmission paths, monitoring said fault indicating current for an increase over a threshold when the load impedance falls below a lower limit indicating a short circuit, providing a control signal from said sensing circuit to said switch to open if a short circuit is detected and to close if a short circuit is not detected, opening or closing said switch in response to said control signal, wherein said current generator of said sensing circuit includes short responsive capacitance and a control element, and wherein said detecting includes charging up said capacitance in the absence of a short circuit impedance between said first and second transmission paths and discharging said capacitance in the presence of said fault indicating current, and wherein said control signal is provided by said control element depending upon the charge condition of said capacitance.
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18. A method of automatically disconnecting a load from a source upon detecting a short and for automatically reconnecting the load to the source after the short circuit clears, said method comprising
providing isolation circuitry including first and second transmission paths connected between said source and said load and maintained at different voltage levels, a switch between a node connected to said source and a node connected to said load on said first transmission path, and a sensing circuit that is connected between said first and second transmission paths and includes a current generator, inducing a fault indicating current by said current generator into a load between said first and second transmission paths, monitoring said fault indicating current for an increase over a threshold when the load impedance falls below a lower limit indicating a short circuit, providing a control signal from said sensing circuit to said switch to open if a short circuit is detected and to close if a short circuit is not detected, and opening or closing said switch in response to said control signal, wherein said providing includes providing a plurality of said isolation circuitries in a loop including a loop controller and a plurality of loop devices that are connected between said transmission paths along said loop and are powered by and communicate with said loop controller, and wherein said switches in said isolation circuitries after being open, close in sequence beginning with the circuitries electrically closest to said loop controller.
Specification