Electricity: measuring and testing – Fault detecting in electric circuits and of electric components – Combined with a flashlight
Reexamination Certificate
2002-03-15
2004-02-03
Deb, Anjan K. (Department: 2858)
Electricity: measuring and testing
Fault detecting in electric circuits and of electric components
Combined with a flashlight
C324S550000
Reexamination Certificate
active
06686744
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to electrical circuits that include an electrical fuse, and more particularly, to an apparatus for evaluating the electrical fuse and for measuring the current that is drawn across the fuse in the electrical circuit.
2. Background Information
An electrical fuse is a device that is placed within an electrical circuit to disconnect the circuit if the current being drawn across the fuse exceeds a predetermined amount. A fuse is typically comprised of two leads that are connected by a thin conductive element, or filament. As the current that is drawn across the filament increases, the temperature of the element also rises. When the temperature increases beyond a predetermined threshold, the filament is “blown,” thereby breaking the path between the two leads. Once a fuse is “blown,” the circuit remains disconnected and inoperable until the fuse is removed and replaced.
Electrical fuses are commonly utilized in electrical circuits for a wide variety of applications to protect devices or appliances that draw electrical power within the circuit. If the current drawn across the fuse exceeds its rated amount, the fuse disconnects the circuit so that the corresponding device or appliance that is connected in the circuit no longer draws power. This protects the device or appliance from being overloaded, which could cause damage to either the device or the power source. The fuse is selected to have a rating below the maximum threshold for the device or appliance.
There are many reasons why a fuse may blow to disconnect an electrical circuit. As one example, a circuit may include one or more devices that have a varying load or resistance, which in turn creates variances in the amount of current flowing through the circuit. If too many devices are added to the circuit and draw too much current at one time (e.g., simultaneously operating headlamps, stereo, air conditioning, windshield wipers, and electric windows in a car), a fuse may blow to protect the devices from an overload. As another example, a fuse may also blow if the ambient temperature is too high, which adds to the heat experienced by the filament within the fuse. If a circuit is operating near peak capacity, an extreme ambient temperature may cause the filament to overheat and blow. In still another example, a fuse may blow upon experiencing a surge in the power supply (e.g., lightning) to protect the devices operating within the circuit.
In some instances, a fuse may blow even when the circuit and the power supply are operating correctly and within predetermined tolerances. Because fuses are designed to be inexpensive and disposable, it is often possible that a fuse may be defective. It is also possible that the filament within the fuse may break due to vibration or from other environmental conditions. Therefore, a blown fuse is not always an indicator of a problem within the circuit, and may be corrected simply by replacing the fuse.
Fuses are typically designed to indicate when the filament is broken and the fuse is “blown.” Many fuses are designed with a clear or translucent area covering the filament, which enables a technician to determine if the filament has ruptured after removing the fuse from a socket within the circuit. If an application requires hundreds of fuses, however, it is preferable to use fuses that provide an indication of whether they are in operation without having to disconnect the circuits. For such applications, fuses are available that include a light emitting diode (LED) that activates once the fuse is blown. In this manner, for example, a technician can immediately assess the condition of several hundred fuses in an equipment rack without having to interfere with the operation of the circuits.
When a technician detects that a fuse is blown (either by removing the fuse from a socket or noting that an LED is lit on a fuse board), the circuit should be tested to determine whether the problem was caused by a defective fuse or by other elements within the circuit. Depending upon the size and shape of the fuse and the fuse socket, the circuit can be tested by placing leads to an ammeter against the electrical contacts within the fuse socket. This will temporarily re-connect the circuit to enable a technician to measure the current flowing through the circuit. If the current is less than the rated value for the fuse, then it will be known that the fuse is defective. If the current has risen above the rated value for the fuse, then there may be problems with either the power supply or the load on the circuit, which should be corrected before the fuse is replaced.
In many applications, the sockets in fuse panels are too small or narrow to enable a technician to connect leads of an ammeter to the electrical contacts in the socket. As an example, the fuses that are used within a Central Office in a telecommunications facility are grouped together on a fuse panel that regulates many circuits in an equipment rack (fourteen on a board and approximately three hundred in a rack). To test these circuits, a technician must disconnect the entire fuse panel, thereby disabling several hundred circuits. If a circuit board in a telecommunications facility is disabled, hundreds of calls may be disconnected, resulting in a telephone service interruption. If fuses are blown for different reasons within a Central Office on a regular basis, the disabling of the corresponding circuit boards can result in a significant service failure.
In view of the foregoing, it can be appreciated that a substantial need exists for a method and apparatus that enables a technician to test a circuit without disabling an entire fuse panel, when the fuse sockets in the fuse panel are too small to receive leads to an ammeter.
SUMMARY OF THE INVENTION
The present invention relates to an apparatus for use in measuring current drawn across a fuse socket in an electrical circuit. An exemplary embodiment of an apparatus according to the present invention is a fuse adapter that includes an outer shell that is specifically molded to fit within a corresponding fuse socket. The shell includes two contacts that electrically contact leads when inserted within the socket. The contacts also protrude through the inner surface of the fuse adapter. First and second electrically conductive paths, or wires, are connected to each contact on the inner surface of the adapter and extend outward from the base of the adapter to contact with leads of an ammeter to test the current across the fuse socket.
In another exemplary embodiment, a fuse specifically designed for use in a particular fuse socket is modified by removing the filament and other materials within its inner surface, with the contacts that protrude through the inner surface of the fuse remaining. First and second electrically conductive paths are connected to each contact on the inner surface of the adapter and extend outward from the base of the adapter, to contact with leads of an ammeter when testing the current across the fuse socket.
It is an object of the present invention to provide an adapter for measuring current drawn across a fuse in a circuit when the shape of the fuse socket for receiving the fuse prevents direct contact between ammeter leads and conductive leads within the fuse socket. The adapter includes an adapter shell that is shaped to fit within a fuse socket. First and second electrical leads protrude from an outer surface of the shell, which are positioned to contact with first and second leads on an inner surface of the fuse socket, respectively. First and second wires are electrically connected to the respective first and second electrical leads and extend from the adapter shell to enable an electrical connection to leads of an ammeter.
Another object of the present invention is to provide an adapter for connecting leads of an ammeter to a fuse socket. An adapter shell is shaped to fit within a fuse socket. A first and second conductive means are included for contacting with first and second leads on a
BellSouth Intellectual Property Corporation
Deb Anjan K.
Shaw Pittman LLP
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