Magnetic Locators find underground objects with ferrous metal content, using the earth’s magnetic field. They do not emit a signal, but rather, they measure magnetic field distortion that surrounds a buried metal target.
Typical Locate: Magnetic Field Detection
Detecting the magnetic field of an iron marker
- Magnetic field stronger at sensor A than B
- Creates a signal strength that is larger than zero
- Audio tone frequency increases as signal strength increases
Object Shape and Orientation Affects Findings
Signals from vertical and horizontal Targets
- With locator directly over a vertical target, signal strength peaks
- Audio signal, digital readout, and bar graph indications also peak over each end of a horizontal target
Strongly Magnetized Markers
Near-surface markers provide a weaker indication to either side
- From point A to B: signals increase slightly and then decrease
- Beyond B: signals increase rapidly, peak directly over marker, decrease at point C
- From C to D: signals increase and decrease again
Cast Iron Pipe Weld Joints
Cast-iron pipes produce the strongest magnetic signals at joints
- Sensitivity setting at maximum
- Vertical hold 1 to 1.5 ft. above surface, walk without tilting or turning
- Mark locations of maximum signal strength
Locating a Steel Drum
Orientation is key for accuracy
- Signal pattern varies depending on vertical or horizontal orientation
- Depth of target also affects signal pattern
- 55 gallon drum can be located at depths from 5 to 12 feet