SeekTech
Informational Locating
The normal shape of a field around a long conductor such as a pipe or cable is circular (cylindrical in three dimensions). When over the center of a circular field, the operator can observe the following indicators:
•Maximum Signal Strength
•Maximum Proximity Signal (Line Trace Mode)
•Centered Tracing line with minimized distortion
•Guidance arrows centered, agreeing with Tracing line
•Minimum Measured Depth
•Sound pitch and volume will increase until they maximize over the target utility.
Figure 66: Over a Circular Field
particular line or pipe is visual inspection, such as by potholing.
Compound or complex fields will produce different indications on the
•Disagreement between guidance arrows, Tracing Line and Distortion Indicator
•Inconsistent or unrealistic Measured Depth signal
•Fluctuating random indications (also caused by very weak signal)
•Inconsistent Proximity Signal compared to guidance arrows (Active or Passive Line Trace modes)
•Signal strength maximizing off to one side of the conductor.
Figure 67: Over a Distorted Field
The experienced operator learns to “see” the ground situation by knowing how the different pieces of information provided by the
By comparing the Guidance Arrows, the Tracing Line, Signal Strength, Signal Angle, Measured Depth, and Proximity Signal, an operator can see which way the field is being distorted. Comparing the field information with an educated view of the ground, noticing where transformers, meters, junction boxes, manholes, and other indicators are located can help in understanding what is causing field distortion. It is important to remember, especially in complex situations, that the only guarantee of the location of a
Generally, distortion is likely to be worse at higher frequencies, compared to lower frequencies. This is due to the tendency of higher frequency signals to “jump” to adjacent conductors. Large iron and steel objects such as vault and manhole covers, trench plates, structural supports, rebar and vehicles can significantly distort even the lowest frequencies. In general, passive locating is more subject to distortion than active locating, especially in regards to depth measurements. Power transformers, buried and overhead power lines are a common source of strong distortion. It may be impossible to get an accurate locate close to a large power transformer.
Notes on Accuracy
Measured Depth, Proximity, and Signal Strength measurements rely on a strong signal being received by the
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