The utility locating industry, sondes are radio transmitters that are used to locate non-metal underground utilities. Sonde locating works best when you have an easy access point, as these transmitters are inserted into pipes to identify their location. Sondes are an essential part of the locating process because non-metal assets like sewer pipes, storm drains and conduits are extremely common. When used with video inspection crawlers, these transmitters can determine the location of blockages and pipe defects. Sondes are also helpful for improving inaccurate or incomplete utility maps.
How Do Sondes Work?
The transmitter emits an electromagnetic (EM) field at a standard frequency, usually 33 Hz (in the United Kingdom). 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.
The sonde’s signal is limited, meaning that the operator must have a general understanding of the pipe’s position before locating. Due to its limited signal the depth accuracy of sondes is not perfect, but it helps locators get a rough estimate of pipe depth and length.
