Electricity: measuring and testing – Of geophysical surface or subsurface in situ – For small object detection or location
Reexamination Certificate
2001-10-31
2003-03-04
Patidar, Jay (Department: 2862)
Electricity: measuring and testing
Of geophysical surface or subsurface in situ
For small object detection or location
Reexamination Certificate
active
06529006
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method and apparatus for determining the horizontal and/or vertical location of a buried or otherwise hidden conductive body such as a pipe, wire, cable, storage tank, or drum.
The invention also relates to a method and apparatus for identifying a buried conductive body, even when located in close proximity with other buried conductive bodies.
According to the invention, location and identification of a conductive body is achieved by impressing a known electromagnetic waveform upon the conductive body, detecting radiation emitted by the conductive body in response to the impressed waveform, locating the source of the emitted waveform by evaluating the amplitudes of signals received by at least one sensor,-and evaluating the waveforms of the received signals for deviations from the impressed waveform in order to determine the pattern of distortion caused by the conductive body and thereby identify the conductive body.
2. Description of Related Art
There are several situations where improved apparatus and methods of locating and identifying buried conductive bodies are needed.
One such situation involves location of underground utilities that may be present at a construction site. Before construction or excavation of a parcel of land, it is often necessary for the owners of buried utility systems in the area to mark out on the ground surface the exact location of their buried facilities. This prevents the construction or excavation from accidentally disrupting utility service, and reduces the chance that serious injury or property damage could occur as a result of unintentional contact between the digging equipment and buried facilities such as gas lines and electrical cables.
Another situation in which improved location and identification of buried conductive bodies is needed is the situation where a parcel of land may include underground storage tanks or drums containing hazardous waste. In that situation, location and identification of the tanks or drums is required for the purpose of assessing environmental risks or as part of a clean-up effort.
Most of the related prior art is directed to location rather than identification of buried conductive bodies. Location of buried conductive bodies is generally accomplished by electromagnetic detection systems and methods, although ground penetrating radar and seismic or acoustic detection methods have also been proposed. Identification of the buried conductive bodies, on the other hand, is carried out by combining the results of the electromagnetic detection with a review of records and plats. In order to ensure that all active services or buried facilities of interest have been detected and marked, the locator personnel must compare information obtained from the electromagnetic detection to that contained on the records. In this manner, the locator can determine if all active services or other buried facilities of interest have been located.
Conventional electromagnetic detection systems and methods generally fall into one of two categories. The first category includes active detection systems and methods in which a signal generator is used to place a signal directly on the structure. The second category includes passive detection systems and methods, in which a signal naturally present on the structure is used. The systems of both categories include a receiver designed to detect and evaluate the electromagnetic field radiated from the object and infer its location.
Systems and methods for locating buried conductors based on electromagnetic detection, i.e., on an analysis of radiation emitted by the conductors (either in response to currents normally carried by the conductors in the case of underground utility lines, or in response to an applied signal) are disclosed in U.S. Pat. Nos. 6,215,888 (Eslambolchi et al.); 6,211,807 (Wilkison); 6,140,819 (Peterman et al.); 5,754,049 (Howell); 5,640,092 (Motazed et al.); 5,471,143 (Doany); 5,418,447 (Beha et al.); 5,365,163 (Satterwhite et al.); 5,361,029 (Rider et al.); 5,093,622 (Balkman); 4,843,324 (Humphreys et al.); 4,818,944 (Rippingale); 4,639,674 (Rippingale); 4,542,344 (Darilek et al.); 4,438,389 (De Sa); 4,427,942 (Sole); 4,520,317 (Peterman); 4,506,210 (Chase); 4,387,340 (Peterman); 4,295,095 (Thomas et al.); and 3,418,572 (Humphreys)
As evidenced by the length of this list of patents, which is by no means an exclusive listing, the problem of locating buried conductors has been of substantial concern for a number of years, and continues to be so today. Despite all of the attention given the problem, however, the failure of existing active and passive systems and methods to locate and/or identify buried utility services or other hidden conductors continues to result in significant property damage and injuries, as well as economic losses and consequential damages due to unintended utility service disruption.
Among the problems which limit the effectiveness of existing active systems is the problem of “signal bleed,” in which a signal placed on the conductive body migrates to other conductive bodies, thus rendering the conductive body of interest undetectable, or at the very least indistinguishable from the interfering conductive bodies. This problem is particularly acute in the case of utility services, which tend to be located in densely packed conduits or corridors.
When a signal is coupled to a conductive body, it will form a circuit via the path of least resistance. In many cases the path of least resistance will be through a conductive body other than the conductive body of interest. Complicating the situation in the case of utility services is the fact that many utility systems share common grounding points, making isolation of individual services almost impossible. This is a very common occurrence in today's congested utility corridors, which makes locating the more deeply buried services quite difficult. Lowering the frequency of the injected signal can reduce the amount of inductive signal bleed, but at the cost of higher power consumption, and does little to solve the problem when there are common grounding points. Low frequency signals, i.e., signals having frequencies of less than approximately 8 kHz, are also difficult to induce onto buried services, and do not travel far on poorly conductive services such as those made from iron.
Passive detection systems and methods suffer from serious shortcomings as well. First, the amount of naturally occurring signals present on a given service may be insufficient to provide for a reliable detection, and second, there is no way to differentiate one service from the next. This makes passive detection techniques unsuitable for the bulk of service detection needs, particularly when dangerous services such as gas and electric utilities are involved, and of course passive detection cannot be used to detect buried conductive bodies such as storage tanks that do not carry detectable electric signals.
In general, the prior systems and methods described in the above-listed patents are best suited to location of isolated conductive bodies that can be identified by other methods, such as by a review of records or plats. The basic concept of these systems and methods is to use multiple sensors to sense the amplitude of signals ostensibly radiated by a conductive body of interest, and to use basic geometric principles to resolve the position of the radiating conductive body based on differences in amplitude between the sensed signals.
Of all of the patents listed above, only one of these patents, U.S. Pat. No. 5,754,049 (Howell), even attempts to both identify and locate conductive bodies, as in the present invention. This patent discloses a system and method which, like that of the present invention, relies on analysis of the effect of the conductive bodies on impressed signals, rather than just detection of signal amplitudes. In particular, this patent discloses use of a radio transmitter to apply signals of two or more different sine waves of discrete
Bacon & Thomas
Patidar Jay
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