How to use underground cable pipeline?

1. T-Shape Detection

Once the tracking of the pipeline has been completed and markings have been made, the receiver can be used to trace the pipeline again. However, this time it should be traced about one meter away from one side of the detected pipeline, keeping the receiver parallel to the line. At this point, no signal from the main line (or a very weak signal) can be detected, but the response to the branch can be significant.

The most reliable way to locate the branch pipe is to apply the transmitter signal to the end of the branch pipe. This signal will flow from the branch to the main line and then to both sides of the main line. The receiver should be positioned at right angles to the main line, tracking the signal along it. The receiver will show a zero response directly above the T-branch joint, indicating the exact location of the T-branch joint.

2. Parallel Pipeline Detection

Parallel pipelines are common in pipeline detection. In areas with dense pipelines, receivers often pick up interference signals from nearby lines. This can complicate the identification and tracking of target pipelines, affecting positioning and depth accuracy. Therefore, we must adopt methods to minimize the influence of coupling signals from adjacent parallel pipelines.

First, avoid using inductive connections in dense pipeline areas. Instead, use direct connections to apply a transmitter signal to the target pipeline. Additionally, selecting lower transmitter frequencies can help reduce signal coupling. In this case, use peak mode positioning, and the 80% method for depth measurement can help minimize deviation.

Generally, the receiver's response to the target pipeline should be greater than that to nearby pipelines. The target pipeline can be identified and tracked based on the receiver's response. However, if an adjacent pipeline is closer to the surface, the receiver's response may exceed that of the target pipeline. In such cases, we need to measure and compare the current of the signals on both the target pipeline and the adjacent pipeline. The pipeline with the highest current value is the target pipeline to which the transmitter signal is applied.

If there are several parallel lines and the transmitter cannot be connected directly, each line can be probed by applying the line signal. First, use the inductive connection method to search the entire area, identifying the number, general position, and direction of pipelines, and mark them on the ground. Then, place the transmitter flat on the ground, as aligned as possible with the underground pipeline, ensuring that the pipeline is directly beneath the transmitter so that the signal directly below it is zero, while other pipelines can be detected. Continue moving the transmitter and marking the pipeline positions until the first pipeline is traced outside the search area, allowing for accurate positioning of the target pipeline.

3. Deepening Pipeline Detection

If the signal detected by the receiver suddenly becomes weak during the detection process, the target pipeline may have a branch or may be buried deeper. First, use the T-line detection method to check for any branch lines. If there are no branches, the pipeline may have suddenly deepened. In this case, stop immediately and track the position of the pipeline where the signal strength drops rapidly. Adjust the sensitivity to high, center on the signal response drop point, and conduct arc detection within a radius of 2 meters.

4. Dealing with Interference Signals

Signals from adjacent pipelines are a common issue in pipeline detection, potentially leading to inaccurate positioning or depth measurements of the target pipeline, or even the detection of the wrong pipeline. While some degree of induction is often unavoidable, on-site experience can help reduce its impact and improve detection reliability.

Avoid using the inductive connection method to apply the signal, as inductive signals may affect multiple underground pipelines. Identify locations where underground pipelines are complex and relatively close to each other. Begin detecting from simpler pipeline points before moving to complex underground areas. For example, if water pipes, gas pipes, power cables, etc., are present in a building, apply signals from valves or other access points outside the building rather than from inside.

If possible, use lower frequency signals to reduce the response to adjacent pipelines. If the signal returns to the transmitter through another pipe, a double-ended connection can bypass the ground loop issue. When using a single-ended connection method, the ground loop signal may return to the transmitter through other pipelines, sometimes overpowering the target pipeline signal. If access points are available at both ends of the pipeline, using a double-ended connection to connect the transmitter is the most effective way to identify the target pipeline under intensive pipeline conditions.

Connect the transmitter to an access point in the target pipeline, and ground the transmitter to another access point using a long wire. This eliminates the need for grounding to complete the circuit. Ensure the long pipeline is positioned away from the potential direction of the target pipeline.

5. Problems in Power Cable Detection

Before applying the transmitter signal, disassemble the common connector on the cable to trace the target cable. If you wish to track all cables starting from the transfer box, set the transmitter to inductive connection mode, place it beside the transfer box, and align it with the cable to be tracked.

For the transmitter signal to travel sufficient distances, it is necessary to remove the ground connection of the cable. Power cables that form a ring in the ground will weaken the response along the cable path. In this case, increase the search range and return to the point before the response change. The receiver should be able to determine all wire loops except for the minimum in the cable.

Most cable connectors will show a peak pulse signal at the receiver. On-site detection experience and knowledge of the actual situation can help determine whether the peak pulse signal indicates a junction box.

Cables are typically buried directly beneath roads adjacent to metal fences, causing the signal to couple with the metal fence. As the metal fence is close to the antenna at the receiver's base, tracking becomes difficult. Raise the receiver so that the antenna is level with the metal fence to resolve this issue.

Connecting the transmitter signal to a metal pillar of a streetlight can be nearly as effective as using the metal shield of the lighting cable itself, as the shield is usually connected to the metal pillar. For cables coming from wooden poles, concrete poles, or lighting columns, set the transmitter in inductive mode and apply the signal by lining the pole perpendicular to the ground.

6. Some Problems in the Detection of Cast Iron Pipes

This underground pipeline detector can be used to search for steel pipes and cast iron pipes with isolated interfaces. Some cast iron gas pipelines and tap water pipelines have insulated joints. Transmitter signals can be applied to the gas meter or water meter. By using jumpers, the insulating gaskets can be bypassed (a connecting magnet can be placed on both sides of the insulating gasket to ensure a secure connection). Ensure the pipes are well connected and that the two connecting magnets are linked by wires to guarantee a reliable circuit for the cast iron pipes entering the house.