Patent Application
20130148245
The present invention relates generally to serial line isolators, and more specifically, to a method and apparatus for isolating faults in emergency input and notification circuits.
In emergency systems, notification and input devices are powered through the use of input device circuits (IDCs) and notification appliance circuits (NACs). These circuits include several different zones, each containing one or more devices. Input devices include such devices as smoke detectors; and notification devices include such devices as sirens and strobe lights. IDCs and NACs have generally been set up such that the devices are connected to one another in series. Due to this series configuration, a fault in any given zone or device will affect all other zones or devices in the circuit. Regulations require that a fault in one zone does not affect the operation of other zones.
Traditionally, line isolators have been implemented on the notification and input circuits in order to isolate faults in any given zone. These line isolators have been implemented in a series configuration, such that each isolator is connected in series with each zone. If a short circuit fault, such as a wire-to-wire short, is detected in the zone, the line isolators on each end of the zone open, isolating the zone from the rest of the circuit. Power is then supplied on a return path in order to continue to power the devices in the zones which are further down the line from the newly opened isolator.
This past configuration works for isolating a single fault, but does not work to isolate multiple faults in a circuit, or to handle open circuit faults. If a fault occurs in a first zone, and then another fault occurs in a second zone further down the line, there is no way for the system to continue to provide power to any of the intermediate zones. Thus, there is a need to be able to isolate multiple faults in an emergency system without losing operation of any functional zone or device.
An emergency system includes first and second power lines, a plurality of zones, and first and second line isolators for each zone. The first line isolator is connected between the first power line and the respective zone, and disconnects power from the first power line when a short circuit fault is present in the respective zone. The second line isolator is connected between the second power line and the respective zone, and connects power to the respective zone from the second power line when an open circuit fault is present in the respective zone.
The present invention involves a fault isolation system for isolating one or more faults in an emergency system. In particular, the system includes a circuit controller, two power lines, and a plurality of devices divided up into a plurality of zones. The devices within each zone are connected to one another in series. The zones are connected to one another in parallel, and each zone has two dedicated line isolators. The first line isolator is connected between the first power line and a first end of the zone, and remains closed until a short circuit fault is detected in the zone; and the second line isolator is connected between the second power line and a second end of the zone, and remains open until an open circuit fault is detected in the zone. The circuit controller provides power to the two power lines.
Isolators 14a-14n, 16a-16n, and 26a-26b are devices that can be either open or closed. In the closed state, the isolator provides a continuous conduction path; and in the open state, the isolator provides a break in the circuit, cutting off power to any devices down the line. Isolators 14a-14n, 16a-16n, and 26a-26b may be implemented using, among other things, a relay, or solid-state devices such as metal-oxide-semiconductor field-effect transistors (MOSFET's). Isolators 14a-14n, 16a-16n, 26a-26b may control themselves, by opening and closing in response to a loss of power, or may be controlled by circuit controller 12.
During normal system operation, all isolators 14a-14n and 26a-26b are closed, all isolators 16a-16n are open, and circuit controller 12 provides power to both power lines 22 and 24. Isolator 26a is connected between power line 22 and the circuit controller 12; and isolator 26b is connected between power line 24 and circuit controller 12. Isolators 26a and 26b are included in order to allow they system to disconnect power from circuit controller 12 to power lines 22 and 24 in the event of short circuit faults in system. Therefore, during normal system operation, power flows from circuit controller 12, through power line 22, to each of zones 18a-18n. Isolators 16a-16n remain open to prevent zones 18a-18n from receiving power from both power lines 22 and 24.
Isolators 14a-14n, and 26a are configured to handle short circuit faults. Upon occurrence of a short circuit fault in any of zones 18a-18n, isolator 26a will sense a spike in current and a drop in voltage, and in response, will open, cutting off power from circuit controller 12 to power line 22. All isolators 14a-14n will sense the loss of power on power line 22, and in response, will also open. Circuit controller 12 will then close isolator 26a after a short period of time. Once isolator 26a has closed, isolators 14a-14n will check their respective zones 18a-18n to determine if there is a short circuit fault present in the zone. This may be accomplished by each isolator 14a-14n supplying a small current to its respective zone 18a-18n and monitoring the response. If a zone 18a-18n contains a short circuit fault, respective isolator 14a-14n will remain open. Otherwise, if no short circuit fault is present in respective zone 18a-18n, respective isolator 14a-14n will close. Therefore, all zones 18a-18n without short circuit faults will be provided power from power line 22. This procedure can be repeated for any number of short circuit faults in system 10.
For example, if a short circuit fault, such as a wire-to-wire short, occurs between devices 20b and 20c of zone 18c, isolator 26a will immediately open after sensing a spike in current on power line 22. All isolators 14a-14n will then open in response to the loss of power on power line 22 after isolator 26a has opened. After isolators 14a-14n open, isolator 26a will close, and remain closed if the short circuit fault is no longer detected on power line 22. Isolators 14a-14n will then use power from power line 22 to apply a small current to each of their respective zones to determine if there is a short circuit fault present. Isolator 14c will detect the short circuit fault and will remain open. All other isolators 14a-14n will detect no short circuit fault and will close. Power will then be provided from circuit controller 12, through power line 22, to each zone 18a-18n with no short circuit fault present. Zone 18c will be isolated from the rest of the system, and will receive no power from either power line 22 or power line 24.
A second short circuit fault may then be handled in any of the other zones 18a-18n. If a second short circuit fault occurs in zone 18a, isolator 26a will again open due to a spike in current on power line 22. Isolators 14a-14n will open in response to the loss of power on power line 22 due to isolator 26a opening. Isolators 14a-14n will check their respective zones 18a-18n for short circuit faults by applying a small current to the zone. Isolators 14a and 14c will both remain open due to detection of a short circuit fault in their respective zones. All other isolators 14a-14n will close, providing power from power line 22 to each zone 18a-18n with no short circuit fault. Therefore, zone 18b will continue to receive power from power line 22 even though zones 18a and 18c contain short circuit faults.
Isolators 16a-16n are configured to handle open circuit faults in any of zones 18a-18n. If an open circuit fault occurs in any of zones 18a-18n, respective isolator 16a-16n will detect the loss of power from the zone and will transition to a closed state. Any devices 20a-20n that lose power from power line 22 due to the open circuit fault will then receive power from power line 24 and continue to function properly. For example, if there is an open circuit fault between device 20b and 20c of zone 18b, devices 20c-20n will stop receiving power from power line 22 through isolator 14b. Isolator 14b remains closed and power continues to be supplied to devices 20a and 20b from power line 22. Isolator 16b will detect the loss of power in zone 18b due to the open circuit and will transition to a closed state. Devices 20c-20n will then receive power from power line 24 and resume functioning properly.
In this way, the present invention describes a method and apparatus for isolating multiple faults in emergency input and notification circuits. Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.
