Electricity: measuring and testing – Magnetic – Displacement
Reexamination Certificate
2000-03-24
2001-06-26
Snow, Walter E. (Department: 2862)
Electricity: measuring and testing
Magnetic
Displacement
C324S207230, C702S150000, C342S463000
Reexamination Certificate
active
06252396
ABSTRACT:
1. TECHNICAL FIELD
The present invention relates generally to a system and method for locating an object positioned in the same or in a different medium as the sensing device. More specifically, one embodiment of the invention is directed to locating a buried object such as a pipe, conduit, or cable but the invention may also be used to monitor movement of an object in air or space that is proximately or closely positioned with respect to the system of the present invention.
2. DESCRIPTION OF THE BACKGROUND
Devices have long been available for detecting buried pipes or other objects. However, presently available devices have significant drawbacks that prevent their reliably locating the underground object in question with a sufficiently high accuracy required for desired operability, e.g., within one or two centimeters. As well, most prior art devices take considerable time to locate the object. They require many discrete tests or continuous searching so that the search time is typically rather long. As well, these devices tend to have little or no value for locating, for instance, the path of movement of proximate objects on the surface or in air with high accuracy as may desired for many various purposes ranging as widely as from robotic control to analyzing the path of a golf swing.
More specifically, prior art devices do not have sufficiently high underground locating accuracy (within 1 or 2 centimeters) for two dimensional X-Y positioning, e.g., positioning relative to surface landmarks. They also lack or do not provide sufficient accuracy (within 1 or 2 centimeters) for three dimensional X-Y-Z positioning, i.e., positioning that provides depth information as well as relationships to surface landmarks. Furthermore, the accuracy of most or all prior art detectors or methods of detection are very sensitive to depth and rapidly lose accuracy and reliability with increasing depth of the buried object. Variable soil conditions significantly affect the operation of presently available detectors to the extent that the same readings are not consistently obtained if ground conditions change. Presently available devices for locating buried objects can be categorized in roughly five classifications that are discussed below.
Records are often used to locate buried pipes. However, records may be inaccurate or unhelpful for many reasons, some of which are discussed here. For instance, records may be permanently lost, or they may be temporarily lost due to improper filing in a large filing system, or they also become torn, faded, or otherwise unreadable in whole or relevant part. References required by records such as landmarks may be lost, survey errors can arise due to improper or inaccurate measurements or recording, unmarked or inaccurately recorded repairs can invalidate records, new local structures can be built, and numerous other changes may occur with time to cause inaccuracies in records.
Presently available electromagnetic and/or magnetic object locators require the object to be within about three feet of the surface. Otherwise, the signals for detection are so greatly attenuated by the earth that they may be unusable or take considerable time to evaluate. The object to be located with such systems must be metallic and must be sufficiently large to produce an adequate signal. Since the detection must occur within about three feet, the approximate relative position of the object must be known or determinable to avoid significant time delays in locating the object. Even after detection is accomplished, it is often difficult or impossible to know whether the detector instrument is directly over the buried object (X-Y position determination inaccuracy) due to signal variations that are related to factors other than proximity of the object such as shape and orientation of the buried object. Three dimensional accuracy that includes the depth or Z coordinate is typically not available with such systems.
Various types of buried markers may be used to improve the accuracy of the detectors. For instance, magnets may be buried alongside of the object to be detected. However, magnets that are strong enough to be detected without excessive false signals tend to be expensive and have a relatively limited lifetime. Other types of markers have been used, such as inductive wire loops and/or capacitive resonant circuits. However, these markers may require accurate positioning or placement to avoid errors in determining when the detector instrument is directly above the object. Furthermore, the marker inaccuracies due to inexact placement, e.g., horizontal loop positioning, will often increase with increasing depth. As well, the depth of the object must not be too great to cause excessive signal attenuation so that signals become too weak for reliable detection.
Soil conditions that affect the above discussed detectors also complicate operation of active and passive acoustic detectors. For instance, dry unconsolidated sand may cause a loss of signal in acoustic detectors because dry, loose soil conditions are not conducive to efficiently conveying the required level acoustic energy for accurate measurements. Variations in the soil such as harder regions or tree roots or rocks may falsely indicate the detection of the desired object. The relatively close proximity of a target, such as a buried pipe, may also present a significant problem for some types of acoustic imaging and acoustic holography.
Ground probing radar has been used in the past with only limited success. Moisture content of the soil must be relatively low for adequate accuracy. As well, homogeneity of the soil should be high. Even if these two requirements are met, a trained professional operator is necessary. Ground probing radar presently does not work well enough to satisfy the requirements of the natural gas industry.
Because of the long-felt need to provide a means for detecting buried objects, numerous inventors have attempted to provide systems for this purpose. The following patents discuss some of the efforts that have been put forth in this area to solve such problems.
U.S. Pat. No. 4,767,237 issued Aug. 30, 1988, to Cosman et al., discloses a marking tape that is positioned underground and above utility lines. The marking tape carries a pair of closely spaced, parallel insulated conductors that extend along the length of the tape and at least one other insulated conductor extending along the length of the tape which is separated from the pair of conductors at a distance that is greater than the distance between the conductors of the pair of conductors. Passive markers having a resonant circuit can be selectively placed along the tape so that the resonant circuit is electromagnetically coupled to the pair of conductors and the other conductor.
U.S. Pat. No. 4,001,822 issued Jan. 4, 1977, to Fred Sterzer, discloses an electronic license tag or plate formed into a unitary structure and including a single antenna system cooperating in a system comprising a harmonic radiator which transmits a pulse coded identification signal in response to an interrogation signal.
U.S. Pat. No. 4,118 662 issued Oct. 3, 1978, to Harold Weber, discloses a method and apparatus for locating concealed or buried structures. The portable device couples, either by direct or indirect connection, high frequency alternating current energy into a more conductive structure that is usually obscured in a less conductive medium.
U.S. Pat. No. 4,673,932 issued Jun. 16, 1987, to Ekchian et al., discloses a computerized transceiver that repeatedly sweeps through a set of frequencies to interrogate a plurality of groups of items in a shelf. Items in each group are tagged with a printed circuit antenna tuned to frequencies assigned to each group.
U.S. Pat. No. 5,099,227 issued Mar. 24, 1992, to Theodore Geiszler, discloses a proximity detection system that combines the advantages of an electric field coupling mechanism with those of an electromagnetic coupling mechanism to overcome the disadvantages of the respective individual coupling mechanisms. Data is tra
Arndt G. Dickey
Carl James R.
Barr Hardie R.
Snow Walter E.
The United States of America as represented by the Administrator
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