Electricity: measuring and testing – Fault detecting in electric circuits and of electric components – Instruments and devices for fault testing
Reexamination Certificate
1999-04-01
2001-07-10
Metjahic, Safet (Department: 2858)
Electricity: measuring and testing
Fault detecting in electric circuits and of electric components
Instruments and devices for fault testing
C324S133000
Reexamination Certificate
active
06259257
ABSTRACT:
BACKGROUND
The present invention relates generally to test equipment, and more particularly, to nonintrusive power and continuity testing tools for use with AC circuits and wiring.
Continuity testing tools are available to test AC lines for continuity. For example, one noncontact tool available at Home Depot, for example, is manufactured by GB Instruments and is marketed under the trade name “Circuit Alert”. This tool has an enlarged pencil-like housing and contains an LED and annunciator that, when the tool is turned on, and approaches a “hot” AC contact, such as the “hot” socket of an electrical plug outlet, for example, the LED lights up and the annunciator sounds an alert that is proportional to the distance from the contact or socket. However, the Circuit alert tool cannot be used to detect continuity of a wire within an electrical cord plugged into the electrical plug outlet or in an unplugged appliance or tool, for example.
What is needed is a tool that has the ability to detect continuity of any type of conductor that carries electric current, whether it is exposed or not, and whether it is powered or not. Furthermore, such a tool should be safe that does not jeopardize a user when in the proximity of potentially dangerous electrical circuits. Therefore, it is an objective of the present invention to provide for nonintrusive power and continuity testing tools for use with AC circuits and wiring.
SUMMARY OF THE INVENTION
The present invention provides for nonintrusive power and continuity testing tools that may be used with AC circuits and wiring to detect continuity and the presence of 120 volt AC power, for example. The tools each comprise a housing with a conductive probe extending therefrom. The housing contains a switching/amplifying device, such as a transistor. A contact is exposed at the surface of the housing that is coupled to a switching terminal of the switching/amplifying device that is used to operate the tool.
In a first embodiment, a coupling wire is disposed in the interior of the housing that is wrapped around an internal portion of the probe so that the probe and coupling wire are twisted together to provide electromagnetic coupling therebetween. The probe and the coupling wire are electrically isolated from direct contact with each other. A power source is coupled through the switching/amplifying device and a serially coupled indicator. The coupling wire is coupled to the power source, and consequently, the probe is electromagnetically coupled to the power source via the coupling wire. The probe may be used to directly contact “hot” AC terminals. Physical touching of the contact by a user activates the tool. Because the probe is electromagnetically coupled to circuitry in the housing and is not directly coupled thereto, there is no danger to a user or to the circuitry of the tool.
In a second embodiment, the probe is directly coupled to the power source and the coupling wire is not present within the housing. The balance of the circuitry within the housing is substantially the same as the first embodiment. An external twisted wire pair coupling device is used with the second embodiment of the tool that in essence replaces the internal twisted configuration used in the first embodiment. The external coupling device has two wires that are electrically isolated from each other and are twisted around each other to provide electromagnetic coupling therebetween. One of the wires of the external coupling device is used to contact “hot” AC wires, and the like. The probe of the tool contacts the other of the wires of the external coupling device to implement continuity testing. Because the two conductors of the external coupling device are electromagnetically coupled together and are not directly coupled together, there is no danger to a user or to the circuitry of the tool when the probe contacts the second wire of the external coupling device.
One important aspect of the present invention is that the user is part of the operative circuit when the tool is in use. In particular, the user physically contacts the contact to operate the tool, and thus the user is part of the electrical circuit. While it is not entirely understood, when the user is part of the operational circuit, the tool is entirely functional under substantially all circumstances. However, when the user does not physically contact the switch, the tool does not work. It is believed that this aspect of the present invention is not used in any prior art device of this type.
In addition, under certain circumstances, the use of a conductive gel, paste, or putty may be used to enhance operation of the tool and in certain circumstances may be required for use. For example, it has been found that the use of a dab of a certain toothpaste on the outer surface of an electrical cord readily allows detection of the “hot” wire within the cord. However, when the conductive gel, paste, or putty is not used on the cord, the tool does not work.
REFERENCES:
patent: 3919631 (1975-11-01), Brown
patent: 4006409 (1977-02-01), Adams
patent: 4205264 (1980-05-01), Gold
patent: 4233560 (1980-11-01), Blenman
Float Kenneth W.
Metjahic Safet
Nguyen Vincent Q.
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