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Patent Issued for Fuse and Breaker Alarm Device and Method Using a Finite State Machine

2012 AUG 22 (VerticalNews) -- By a News Reporter-Staff News Editor at Telecommunications Weekly -- According to news reporting originating from Alexandria, Virginia, by VerticalNews journalists, a patent by the inventors Coffey, Joseph C. (Burnsville, MN); Blichfeldt, Brad (Savage, MN), filed on December 14, 2009, was cleared and issued on August 7, 2012.

The assignee for this patent, patent number 8237578, is ADC Telecommunications, Inc. (Eden Prairie, MN).

Reporters obtained the following quote from the background information supplied by the inventors: "Direct current (DC) electrical circuits generally provide a source of current to downstream devices operating at a specific voltage. The current that is provided to the downstream devices generally falls within an acceptable range which corresponds to the expected load resistance of the devices. Due to variations in the activity or possible failure of one or more of the downstream devices, the load resistance may vary. Variations in the load, or variations in a voltage or current source attached to the load, causing an unexpectedly high current level can cause device failure if the current drawn by the circuit exceeds a threshold amount.

"Alarm circuits are commonly used to protect load devices from electrical currents above the rated threshold of the particular load. Circuit protection devices and alarm triggering mechanisms are commonly used in such alarm circuits. The circuit protection devices, such as fuses or circuit breakers, are generally located at an 'upstream' location in series with the load, such that an interruption caused by the circuit protection device disrupts the current path through the load circuit. The alarm triggers generate an alarm signal when the circuit protection device interrupts the circuit to indicate the occurrence of such an interruption.

"FIGS. 1A-1C illustrate operation of a prior art alarm circuit using a secondary alarming fuse which can be used in a direct current circuit. FIG. 1A shows normal operation of the alarm circuit in which current passes through the primary circuit protection device, shown as the main fuse 10. FIG. 1B shows the current path when the main fuse 10 blows, and indicates that the current shifts to pass through the secondary fuse placed in parallel with the main fuse 10, shown as GMT fuse 12. Because the GMT fuse 12 is selected to have a lower current rating than the main fuse 10, it also soon blows, enabling the alarm signal 14 as shown in FIG. 1C. This configuration has a cost disadvantage, because each time the primary fuse 10 blows, both it and the secondary alarming fuse must be replaced, adding to the maintenance cost of the circuit. Further, additional user-accessible space is required for two fuses. The secondary fuse also creates a potential electrical hazard because the full input voltage is present at the output terminals of the circuit. Also, unprotected GMT fuses potentially eject the metallic fuse portion of the blown fuse from the fuse holder when blown, creating a fire or injury hazard.

"FIGS. 2A-2B illustrate operation of a prior art alarm circuit using a monitoring circuit. FIG. 2A shows normal operation of the alarm circuit, in which a monitoring circuit 16 connects in parallel to the main fuse 10. The current passes through the main fuse 10 and load 20. FIG. 2B shows operation of the alarm circuit after the main fuse 10 blows. The current passes through the monitoring circuit 16 and load 20. Therefore, even when the main fuse 10 blows, a current path exists through the monitoring circuit 16 and a voltage appears at the output terminals. Therefore, it can be difficult for monitoring personnel to detect the location or existence of the fault.

"FIG. 2C illustrates operation of an alarm circuit where two power feeds are connected to a load equipped with OR-ing diodes for power redundancy. In such a configuration, when a main fuse 10 blows, leakage current flows though the OR-ing diode which in turn prevents the monitoring circuit from detecting the status of the main fuse. As a result, no fuse alarm signal is generated and the load is no longer protected with dual power feeds. In addition, the leakage current creates a potential across the power input terminals of the load preventing on-board voltage sensors from detecting a fault condition. This can result in a catastrophic system failure because there is no warning of a fault condition.

"Therefore, improvements are desirable."

In addition to obtaining background information on this patent, VerticalNews editors also obtained the inventors' summary information for this patent: "The embodiments of the present disclosure provide an alarm circuit using a programmable circuit. The alarm circuit has a circuit protection device connected in series at an input voltage of a load, and the programmable circuit is connected in parallel to the circuit protection device. The programmable circuit includes a plurality of functional states and controls an alarm signal. At least one of the functional states corresponds to activation of the alarm signal. Activation of the alarm signal corresponds to an interrupt condition in the circuit protection device.

"In another aspect, a method of monitoring a circuit protection device is disclosed. The method includes connecting a programmable circuit in parallel to the circuit protection device. The programmable circuit is programmed to include a plurality of functional states, and at least one functional state corresponds to activation of the alarm signal. The method also includes detecting the absence of a circuit protection device. The method further includes detecting the presence of the circuit protection device. The method also includes detecting a failure in the circuit protection device. The method includes, upon detection of a failure in the circuit protection device, entering the at least one functional state, thereby enabling an alarm signal.

"The programmable circuit can be clocked or unclocked, and can control an indicator and a pull down circuit. The indicator visually displays the status of the circuit protection device. The pull down circuit ensures that there is less than 1 VDC of voltage difference across the load of the general DC circuit when the circuit protection device has interrupted the circuit. The programmable circuit can be implemented in a circuit panel, such as a power distribution panel."

For more information, see this patent: Coffey, Joseph C.; Blichfeldt, Brad. Fuse and Breaker Alarm Device and Method Using a Finite State Machine. U.S. Patent Number 8237578, filed December 14, 2009, and issued August 7, 2012. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&p=57&u=%2Fnetahtml%2FPTO%2Fsearch-bool.html&r=2827&f=G&l=50&co1=AND&d=PTXT&s1=20120807.PD.&OS=ISD/20120807&RS=ISD/20120807

Keywords for this news article include: ADC Telecommunications Inc..