What is Electromagnetic Locating?

Electromagnetic (EM) locating is a technique used to detect and map underground utility lines by identifying electromagnetic fields. This method is essential for contractors and surveyors who need a precise understanding of subsurface structures.

Active vs. Passive EM Locating

Active EM Locating:

• Transmitting Signals: In active EM locating, a specific frequency is actively sent through the underground utility. This is achieved by connecting a transmitter to the utility’s conductive material.
• Direct Connection: The transmitter can be attached directly to utility lines via a grounding wire or another appropriate structure above the ground.
• Signal Detection: The EM locator then reads the transmitted active signals, making it suitable for detecting live utility lines with great accuracy.

Passive EM Locating:

• Ambient Signal Detection: Unlike the active method, passive EM locating relies on sensing existing electromagnetic signals already present in the environment.
• No Direct Connection Required: It doesn’t require transmitting any frequencies or making any direct connections to utility lines.
• Uses Natural Frequencies: This method picks up naturally occurring signals from AC power or radio transmissions, often used for mapping unknown utility paths.

Applications and Advantages

• Open-Field Surveys: Passive EM locating is advantageous in open-field metal surveys. It leverages electromagnetic induction (EMI) to detect buried objects without the need for additional signal generation.
• Data Interpretation: The EMI device features coils that transmit a primary magnetic field and sense secondary fields, which aids in forming a contour map showing conductivity variations in the soil.
• Choosing the Right Method: Selecting between active and passive locating depends on the specific needs of a project, the types of utilities present, and the level of precision required.

In summary, electromagnetic locating is a versatile tool for subsurface exploration, with active and passive methods offering unique strengths tailored to different surveying scenarios.