Erratic short-circuit detection
地域：
FL
FL Boca Raton
摘要
A fire detection system may include isolation circuit having an isolation switch coupled with a system line of the fire detection system and configured to isolate a first side of the system line from a second side of the system line. The isolation circuit may also include a controller coupled with the isolation switch. The controller may be configured to detect repetitive, intermittent short circuit activity on the system line and control the isolation switch based on this activity.
說(shuō)明書
Typically, fire detection and alarm systems require some type of isolation between different zones (e.g., different floors and/or rooms) of a building. Isolation requirements may allow detection and alarm devices in a first zone to remain enabled and provide continued functionality despite a second zone being disabled due to a short circuit in the second zone. A short circuit may be caused, for example, by wires rubbing during installation or by corrosion. Isolation of different zones may be accomplished by either separately wiring each zone or by adding isolation circuits to a system having all zones on the same wiring. While isolation circuits may provide lower installation costs (e.g., due to less wiring and labor) and may reduce an overall size of a fire detection and alarm system as compared to separately wired zones, isolation circuits may be susceptible to false positives caused by, for example, electrostatic discharge, lightning strikes, or transient signals (e.g., signals from multiple loads or communications on a line).
權(quán)利要求
What is claimed is:1. An isolation circuit comprising:an isolation switch coupled with a system line of a network and configured to isolate a first side of the system line from a second side of the system line; and a controller coupled with the isolation switch and configured to:detect a short circuit on the system line; upon detecting the short circuit, receive a current level signal based on electrical current on the system line and a voltage level signal based on a voltage on the system line; determine whether one or more detection thresholds are satisfied based on at least one of the current level signal and the voltage level signal; control the isolation switch to open or to remain open to isolate the first side from the second side when the one or more detection thresholds are not satisfied; and control the isolation switch to close or to remain closed to un-isolate the first side from the second side when all of the one or more detection thresholds are satisfied. 2. The isolation circuit of claim 1 , further comprising a current monitor coupled between the system line and the controller and configured to sense the electrical current on the system line and to generate the current level signal based on the electrical current. 3. The isolation circuit of claim 2 , further comprising a comparator coupled between the current monitor and the controller and configured to receive the current level signal from the current monitor and to provide a current alert signal to the controller when the current level signal does not satisfy a current threshold. 4. The isolation circuit of claim 3 , wherein the controller is further configured to transition from a sleep mode to an awake mode or remain in the awake mode on receipt of the current alert signal provided from the comparator when the current level signal does not satisfy the current threshold. 5. The isolation circuit of claim 3 , wherein the controller is further configured to determine which of the first side and the second side of the isolation circuit is closest to the short circuit based on the current alert signal provided from the comparator. 6. The isolation circuit of claim 1 , further comprising a timer that, in response to at least one of the voltage level signal being received, is initialized for a predetermined wait period and enabled to time out, said time out defining expiration of the predetermined wait period. 7. The isolation circuit of claim 6 , wherein the controller is further configured to:upon expiration of the predetermined wait period, read a second current level signal based on electrical current level on the system line and a second voltage level signal based on a voltage level on the system line; and determine, based on the second current level signal and the second voltage level signal, whether the one or more detection thresholds are satisfied. 8. The isolation circuit of claim 1 , further comprising a voltage monitor coupled between the system line and the controller, the voltage monitor configured to sense the voltage on the system line and to generate the voltage level signal based on the sensed voltage. 9. The isolation circuit of claim 8 , wherein the voltage monitor comprises:a first voltage monitor to sense a first voltage level at the first side of the system line; and a second voltage monitor to sense a second voltage level at the second side of the system line; wherein the controller is further configured to determine whether the one or more detection thresholds are satisfied further based on one or more of the sensed first voltage level and the sensed second voltage level. 10. The isolation circuit of claim 1 , wherein the network is part of a fire detection system. 11. The isolation circuit of claim 10 , wherein the isolation circuit is embedded in any of: an initiating device, a notification appliance, a fire panel, an annunciator, a fire network repeater, and independent isolator device. 12. The isolation circuit of claim 1 , wherein the isolation switch is a solid-state switch. 13. The isolation circuit of claim 12 , wherein the isolation switch is a transistor. 14. A method of isolating, within an isolator, a first port from a second port, the method comprising the steps of:detecting a condition indicative of a short circuit on a network; adjusting a predetermined duration period based on a number of registered False Positive events; waiting the adjusted predetermined duration period; if, after the predetermined duration period expires, the condition is no longer present, registering a False Positive event; and if, after the predetermined duration period expires, the condition is still present, isolating the first port from the second port; wherein,the first port is in electrical communication with a first portion of the network, and the second port is in electrical communication with a second portion of the network; and wherein, in normal operation the first port is in electrical communication with the second port. 15. The method of claim 14 wherein the isolator is integrated into a device having a non-isolating function. 16. The method of claim 14 wherein the isolator is a standalone device. 17. The method of claim 14 , further comprising the step of resetting the number of registered False Positive events if, after the predetermined duration period expires, the condition is still present. 18. The method of claim 14 , further comprising, after isolating the first port from the second port, determining whether the condition is present, and if the condition is not present:waiting a predetermined delay, after the predetermined delay has expired, determining whether the condition is present, and if the condition is not present, reinstating electrical communication between the first port and the second port. 19. The method of claim 18 further comprising, prior to waiting, the step of adjusting the predetermined delay based on a number of registered repetitive short events. 20. The method of claim 19 further comprising, at predetermined intervals, reducing the number of registered repetitive short events. 21. The method of claim 18 , further comprising, upon reinstating electrical communication between the first port and the second port, registering a repetitive short event. 22. The method of claim 14 , further comprising, at predetermined intervals, reducing the number of registered false positive events. 23. A method of isolating, a first system line segment from a second system line segment, the method comprising the steps of:detecting a short circuit on a system line; waiting a predetermined waiting period; and after expiration of the predetermined waiting period, upon again detecting a short circuit on the system line, electrically isolating the segments from each other, and upon detecting absence of the short circuit, decreasing the predetermined waiting period by a predetermined amount. 24. A method of isolating, a first system line segment from a second system line segment, the method comprising the steps of:detecting a short circuit on a system line; in response to detecting the short circuit, electrically isolating the segments from each other; after a predetermined delay, detecting if the short circuit is no longer present; in response to detecting that the short circuit is no longer present, electrically reconnecting the segments to each other; counting a number of short circuits that have occurred within a predetermined period; and adjusting the predetermined delay based on the number of short circuits.
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