A sonde is a self-contained transmitter used for tracing the paths of pipes, ducts, sewers and drains and in the precise location of blockages or collapses. Sondes are an essential part of the locating process because non-metal assets like sewer pipes, storm drains and conduits are extremely common. While sondes can be standalone devices they are also built into other pieces of equipment. Sondes can be found in CCTV inspection crawlers, push cameras, lateral launch systems and other kinds of inspection equipment. Sondes benefit a variety of industry applications. In water & sewer, they can help pin-point blockages or pipeline defects when used with video inspection systems. In the utility locating industry, sondes are used to locate non-metal underground pipe such as HDPE, PVC, or clay tile. Sondes are also helpful for improving inaccurate or incomplete utility maps.

How does a Sonde Work?

The sonde emits a standard frequency, usually 512 Hz (in the United States). The locator programs the receiver to match the frequency to trace its movement. As the sonde moves through the pipeline this electromagnetic field moves with it. Above ground, the operator uses an EM locator or receiver to detect and mark the transmitter’s location. This makes it possible for the locator to pinpoint the exact location of a utility line. The sonde’s signal is limited, meaning that the operator must have a general understanding of the pipe’s position before locating. The depth accuracy of a sonde’s position can help reduce excavation costs and time. Depending on frequency, a sonde can be detected as deep as 15 ft. When used with video inspection crawlers, these transmitters can determine the location of blockages and pipe defects.

How are Sondes Used?

Standalone sondes are attached to a long cable that allows operators to push them into pipes. The operator first inserts the sonde into a non-metal pipe, via a cable if it’s a standalone instrument or as part of a larger piece of equipment such as an inspection crawler. Inspection cameras with built-in sondes provide operators with real-time video footage that can help identify potential pipe issues and indicate exactly where it is underground. Next, the operator uses a locator to detect the sonde’s signal. The operator marks the pipe’s position on the ground with paint or flags. Then, the operator continues to push the sonde further into the pipe. The operator uses the receiver to relocate the transmitter, and again marks the pipe’s location. This is done until they have traced the length of pipe, and identified the location of connections, bends, or defects.

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