There are many situations where is it desirable to locate buried utilities such as pipes and cables. For example, before starting any new construction involving excavation, it is important to locate existing underground utilities such as underground power-lines, gas lines, phone lines, fiber optic cable conduits, CATV cables, sprinkler control wiring, water pipes, sewer pipes, etc., collectively and individually referred to hereinafter as “utilities” or “objects.” As used herein the term “buried” refers not only to objects below the surface of the ground, but in addition, to objects located inside walls, between floors in multi-story buildings or cast into concrete slabs, etc. If a backhoe or other excavation equipment hits a high voltage line or a gas line, serious injury and property damage may result. Severing water mains and sewer lines leads to messy cleanups. The destruction of power and data lines may seriously disrupt the comfort and convenience of residents and cost businesses huge financial losses.
Buried objects may be located, for example, by sensing an alternating current (AC) electromagnetic signal emitted by the same. Some cables such as power-lines are already energized and emit their own long cylindrical electromagnetic field. Location of other conductive lines may be facilitated by energizing the line sought with an outside electrical source having a frequency typically in the region of approximately 50 Hz to 500 kHz. Location of buried long conductors is often referred to in the art as “line tracing,” a term that is so used herein.
A “sonde” (also referenced in the art as a “transmitter,” “beacon” or “duct probe”, for example) is a term used herein to denominate a signal transmitter apparatus that typically includes a coil of wire wrapped around a ferromagnetic core. The coil is energized with a standard electrical source at a desired frequency, typically in the frequency region of approximately 50 Hz to 500 kHz. The sonde may be attached to a push cable or line or it may be self-contained so that it may be flushed through a pipe with water. A sonde typically generates a dipole electromagnetic field, which is more complex than the long cylindrical pattern produced by an energized line. However, a sonde may be localized to a single point. A typical low frequency sonde does not strongly couple to other objects and thereby avoids the production of complex interfering field patterns that may occur during the tracing. The term “buried objects” is used herein in a general sense and includes, for example, sondes and buried locatable markers such as marker balls.
When locating buried objects before excavation, it is also very desirable to determine the depth of the buried objects. This may be done by measuring the difference in field strength at two locations. Although various methods of determining depth of buried conductors are well-established in the art, it is also well-known that existing methods may produce variable and therefore unreliable results leading to potentially dangerous errors in depth estimation when operating in the presence of complex or distorted electromagnetic fields.
Portable locators that heretofore have been developed offer limited functionality insufficient for quickly and accurately locating buried utilities. Accordingly, there is still a clearlyfelt need in the art for improved compact man-portable locator systems with user interface (UI) features permitting the locator operator to quickly and accurately manage the simultaneous detection and localization of a plurality of buried and/or inaccessible targets.