Short circuit detector and isolator
AssigneePittway Corporation, a Delaware Corporation
InventorLee Tice
Life of this patent
Estimating the term…
Abstract
An isolation circuit, which draws essentially zero current in a normal or stand-by state, uses a normally closed relay in combination with a storage element. A capacitor can be used as the storage element to energize the relay, using previously stored energy, in the event that a communication line to which the isolator is coupled exhibits a short circuit or low voltage condition. In this instance, the prestored energy on the capacitor activates the relay for a predetermined period of time, thereby open circuiting the communication line. When voltage is reapplied to one side of the isolator circuit, the relay is continuously energized and maintained in its open circuit condition until the low voltage or short circuit has been remedied.
Claims18
An isolation circuit for responding to and isolating a short circuit or a high loading condition in an electrical transmission system in which a voltage difference above a predetermined value is periodically or usually maintained across at least two conductors comprising:
- a normally-closed, non-latching, relay having an energy input as well as first and second switch ports, said switch ports of said relay being couplable in series with one of the conductors;
- the said relay maintaining a very low impedance when the line voltage temporarily goes to a low value until it switches to an open state;
- an energy storage element coupled to said energy input of said relay, said energy storage element being capable of storing a predetermined quantity of energy in the presence of the voltage difference;
- and
- switching circuitry coupled to said switch ports, to said energy input of said relay and to said energy storage element, and being couplable to at least one of the conductors, said circuitry being capable of changing state in the presence of the short circuit or high loading condition where the line voltage will not go above a predetermined level, thereby discharging said stored energy of said energy storage element into said energy input and opening said relay, thereby isolating the short circuit or high loaded section.
A circuit for responding to and isolating a short circuit in an electrical transmission system in which a voltage difference is usually maintained, at least intermittently, across at least two lines, comprising:
- a normally-closed, non-latching, relay having first and second terminals, and having a control coil with first and second ends, wherein said relay exhibits an open circuit between said terminals when said coil is energized, said terminals being couplable in series with one of the lines;
- an energy storage element coupled to said first end of said coil, said energy storage element being capable of storing a predetermined quantity of energy;
- and
- switching circuitry coupled to said ends of said coil and to said terminals of said relay, wherein said circuitry is capable of responding to the presence of a short circuit, thereupon discharging said energy storage element, and energizing said coil to isolate the short circuit.
A method of responding to and isolating a low voltage condition in an electrical transmission system in which an intermittent voltage difference is maintainable across at least two lines, comprising:
- storing a quantity of energy;
- detecting the low voltage condition;
- determining if the detected condition has been present for a predetermined period of time and in response thereto, using the stored quantity of energy to create an open circuit in one of the lines for a period of time, thereby isolating the condition;
- and
- restoring the voltage difference across at least a portion of lines and using that voltage differences to maintain the open circuit.
An isolation circuit for responding to and isolating a low voltage condition or a short circuit in an electrical transmission system in which a voltage difference can usually be maintained across at least two conductors comprising:
- a normally-closed relay having an energy input as well as first and second switch ports, said switch ports of said relay being couplable in series with one of the conductors;
- an energy storage element coupled to said energy input of said relay, said energy storage element being capable of storing a predetermined quantity of energy in the presence of the voltage difference;
- and
- switching circuitry coupled to said switch ports, to said energy input of said relay and to said energy storage element, and being couplable to at least one of the conductors, said circuitry being capable of changing state in the presence of one of a low voltage condition or short circuit, thereby discharging said stored energy of said energy storage element into said energy input and opening said relay, thereby isolating the short circuit.
Dependencies are inferred from the claim text.