Line Tracing
The art of locating is based upon detecting electrical current on a target conductor, usually a pipe, cable or tracer wire, underground. A transmitter is used to apply an electrical current to the target line and a receiver is used above ground to detect the electromagnetic fields generated by this current. In almost all cases, more current flowing through the target conductor, will provide a stronger signal that is easier to locate accurately. Electrical current can only flow if a circuit is present. A locating circuit is a closed loop between a transmitter and a conductor. The loop is created when current flows from the transmitter, through the conductor (utility), and then back to the transmitter. The better the circuit (less resistance), the more efficiently the current can flow, and the stronger the locatable signal. In this article we will explore what makes a good locating circuit for locating underground utilities and how to increase current flow to make locating easier and more accurate.
Direct Connect
Energizing a target line by direct connection requires metal-to-metal contact.
1. Use the clip’s built-in scraper to remove paint, dirt, or debris from the connection point to ensure good metal-to-metal contact.
2. Attach one of the transmitter’s lead clips to the target line.
3. Push the grounding stake into the ground as far as possible and attach the transmitter’s other lead clip to it. With the transmitter’s lead clips attached to the target line and the grounding stake, a circuit is created for the signal to travel. The circuit allows current to flow, energizing the target line. Note: A weak ground connection can cause a poor tracing circuit. Refer to the Improving the Tracing Circuit section for more information on grounding.
4. Begin tracing the line.
Tracing the Target Line
To trace the target line using Active Line Trace Mode, follow these steps:
1. Set the transmitter to Direct Connect Mode, Inductive Clamp Mode, or Inductive Mode. Note: SeekTech transmitters automatically switch to Inductive Clamp Mode when a SeekTech clamp is plugged in.
2. Set the transmitter’s frequency and press the Frequency Key on the SR‑24 to set the receiver to the same frequency. Note: Make sure you have selected an Active Line Trace frequency and not a Sonde frequency . Refer to the Setting the Frequency section for instructions on how to set the frequency.
3. Make sure the SR‑24 is detecting the transmitter’s signal. Position the receiver approximately 1 m [3 ft] from one of the transmitter’s leads and observe the Signal Strength reading. If the locating circuit is good, the Signal Strength reading will be strong and steady, with minimal fluctuation.
4. Center the Tracing Line to get an initial location of the utility. Orient the Tracing Line and the SR‑24 to correctly utilize the Guidance Arrows.
5. In the absence of signal distortion, balance the Guidance Arrows, orient the Guidance Line, and maximize the Proximity Number and Signal Strength to pinpoint the location of the target line. Be aware that minor disagreements between the various location indicators are normal and represent small differences between the measured signal and the theoretical, ideal signal. Large discrepancies may indicate a problem with the signal and must be resolved before the location of the target line may confidently be determined.
Confirming Accuracy
To confirm the accuracy of a locate, check that all of the following are true:
• The Guidance Arrows and Guidance Line are aligned with the Tracing Line.
• The Tracing Line shows little or no distortion.
• The Proximity Number and Signal Strength maximize when the Tracing Line crosses the map center.
• The measured depth increases appropriately and the Tracing Line remains aligned when the Depth Verification Test is performed.
SR-20 OPERATING INSTRUCTIONAL VIDEOS:
https://www.youtube.com/watch?v=j_vXcSPVrRY
https://www.youtube.com/watch?v=10m8xvXODzE