Electricity: measuring and testing – Fault detecting in electric circuits and of electric components – For fault location
Reexamination Certificate
2000-08-31
2001-11-27
Metjahic, Safet (Department: 2858)
Electricity: measuring and testing
Fault detecting in electric circuits and of electric components
For fault location
C324S533000
Reexamination Certificate
active
06323654
ABSTRACT:
TECHNICAL FIELD
This invention relates to remote changing of the characteristics of a signal produced by a signal generator. This invention has particular application to locating or identifying one or more electrical conductors such as household wiring, commercial wiring, and industrial wiring installations. Examples of such wiring are TV coax and antenna wires, all types of electrical wires, telephone and data wires, environmental control wires, etc. No instrumentation is needed at the remote end of the wiring under test to effect the change in signal characteristic.
BACKGROUND OF THE INVENTION
Many devices exist that inject a signal onto a length of wire or pair of wires for the purpose of physically locating other parts of the length thereof. These devices are commonly called ‘tone generators’, even though these devices themselves only produce an electrical signal and a receiver functions to produce the actual audible tone. U.S. Pat. No. 5,457,441, for example, discloses a receiver of the inductive pick-up type which produces a tone when it picks up a signal. A receiver can be incorporated as part of a standard telephone test set or other common test equipment. Such a process is used when the location of one end of a cable or wire is known and the location of the other end is not known or is closely bundled with other cables or wires and can not be specifically identified.
To illustrate, consider the simple situation of a pair of wires isolated at one end and grouped with a few other pairs at the other end. The ‘tone generator’ is connected to the isolated end of the pair of wires and the receiver is placed near the group of wires at the other end. The receiver is positioned closely adjacent to each wire sequentially, and when the tone output of the receiver is loudest, one might reasonably conclude that the receiver is closest to the wire in question.
While this process often works well, it fails when the wires are in sufficient proximity for the injected signal to couple across to one or more of them. In that case, the tone output of the receiver is often equally loud when placed near many of the wires and identification is not possible. In the not so simple case where the known end of the wires is already bundled in a large quantity of wires, and this bundle along with other bundles are routed in close proximity for a long length, the process almost always fails, allowing a tone to be produced from the signal on many of the wires. While this failed process has often reduced the count of possible solutions, it sometimes does not.
The next process usually followed by the person interested in finding the wires is to individually test the wires by placing a short on the known end and measuring for that short on the possible unknown ends. This process requires that the person make several trips from one end of the wiring to the other. These trips can involve flights of stairs, or even be between buildings. This is clearly an inefficient process.
There exist expensive and complex devices that allow for the remote changing of the injected signal but require special instrumentation at the remote end. See, for example, the arrangement disclosed in U.S. Pat. No. 4,862,491. There are also remotely controllable signal generators that are used for the testing of telephone lines that require specific instrumentation at the remote end to affect that change in the signal generator. See, for example, U.S. Pat. No. 5,307,398. These existing methods and devices require specific and expensive pieces of test equipment that may be justified for use by test technicians, but are not generally in the possession of ordinary households. Yet, there exists in ordinary households the need to identify wires in the course of owner-performed home improvements or repair.
This invention provides a solution to the problem of positive identification of wires without regard to the characteristics of the wire type or the intended use of the wires, and with no additional instrumentation being required at the remote end. When appropriately implemented in a signal generator or detector employed in other types of equipment, such as multimeters or time domain reflectometers (TDR's), there is minimal or no additional cost to that signal generator or detector. This allows for the low cost inclusion of this wire location/identification capability in an existing piece of test equipment suitable for home or professional use.
DISCLOSURE OF INVENTION
This invention provides a method for changing the characteristics of the signal generated by a ‘tone generator’ when a detector coupled to that ‘tone generator’ detects a significant change in the impedance of the wire or pair of wires it is connected to. By using impedance change as the ‘trigger’ for the signal characteristic change, the user does not need any instrumentation at the remote end to effect the change. This impedance change can be accomplished by merely shorting and then opening the ends of the wire pair suspected to be the wire pair of interest. The resultant change in the ‘tone generator’ signal characteristics is non-transient; that is, the change remains in effect until such time that another change in the detector output causes another change in the signal characteristic.
An exemplary embodiment of this invention contains a versatile signal generator, an open/short detector, and a simple flip flop. These circuits are coupled such that whenever the detector output changes from short to open, it flips the state of the flip flop. The output of the flip flop controls one of the characteristics of the signal generator such as its frequency. Thus, in actual use, when the user first shorts and then opens a pair of wires connected to the device, the tone heard in the receiver will change and hold its changed frequency.
It is not necessary that the two conductors connected to the generator be of the same type or length, just that there be two conductors. When a single wire is involved, the other conductor could, for example, be earth ground, a water pipe, or any other common conductor available at both ends of the wire in question.
While this invention can be used in a stand-alone signal generator/detector whose sole purpose is to generate this tone signal and respond to indications from its detector, the preferred approach is to employ the invention in a more versatile device such as a multimeter or TDR that contains among other elements a versatile signal generator, a detector, and a control circuit that directs the operation of the device. In such a preferred embodiment, this invention can be implemented totally in the software of the control circuit at minimal or even no additional cost.
Note that many types of detection mechanisms can be used when practicing this invention, such as a multimeter to detect resistance or voltage, or a TDR to measure length or termination type (Open, Shorted, Terminated). Many types of signal generators and characteristics (frequency, duty cycle, tone pattern) can also be used. It is suggested that ‘volume’ not be utilized as a changeable characteristic since it is the inability of the process to distinguish relative signal strengths that causes the identification problem with respect to prior art devices in the first place.
Other features, advantages, and objects of the present invention will become apparent with reference to the following description and accompanying drawings.
REFERENCES:
patent: 3781665 (1973-12-01), Gale
patent: 4862491 (1989-08-01), La Salle et al.
patent: 5122800 (1992-06-01), Philipp
patent: 5268644 (1993-12-01), Klassen et al.
patent: 5444695 (1995-08-01), Copley et al.
patent: 5726578 (1998-03-01), Hook
Gin Gary
Needle David L.
Shepard Stan F.
Jovial Test Equipment
Lampe Thomas R.
Metjahic Safet
Nguyen Vincent Q
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