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• <br /> 1 Electromagnetic Line Locating(EMLL) <br /> Methodology <br /> The EMLL method is used to detect the electromagnetic field resulting from an electric current <br /> flowing on a line. These fields can arise from currents already on the line(passive,or ambient)or <br /> currents applied to aline with a transmitter(active). The most common passive signals are generated <br /> jby live electric lines and re-radiated radio.signals. .Active signals can be introduced by connecting. <br /> the transmitter to the line at accessible locations or by induction. <br /> t, <br /> Instrumentation <br /> The E MLL instruments that we typicallyuse t o locate and confirm positions ofunderground utilities: <br /> include a RadioDetection RD-400 and a Fisher TW-6 "M-Scope." These instruments operate by <br /> generating both ameter reading (unitless) and an audible response when carried over a utility or <br /> metal pipe. The peak instrument response usually occurs when the unit is directly over the object. <br /> Data Analysis <br /> Neither EMLL instrument provides recordable data output that can be used for later computer <br /> processing. Results are generally limited to marking the interpreted position of detected utilities at <br /> several points along the facility and mapping the subsequent alignment. <br /> tLimitations <br /> I <br /> The detection of underground utilities is determined by the composition and construction ofthe line <br /> in question. Utilities detectable with standard line location techniques include any continuously <br /> connected metal pipes,cables/wires or utilities with tracer wires. Unless carrying passive currents, <br /> these utilities must be exposed at the surface or in accessible utility vaults. These generally include <br /> water,electric,natural gas,telephone,and other conduits related to facility operations: Utilities that <br /> are not detectable using standard electromagnetic line location techniques include those made of <br /> non-electricallyconducfivematerials such as PVC,fiberglass,vitrified clay,and pipes with insulated <br /> '. connections. <br /> �. <br /> £ <br /> A-2 <br />