About 50 years ago, when underground utility locators were first introduced, they didn’t need to find much, except buried server, gas and water lines. Nowadays however, locating underground services has become much more complex, as optic and telecommunications cables have joined the underground utility lines club. But regardless of this fact, today’s service locators still rely on the same technology, and work in a similar concept – sending an electric signal underground and picking it back up through a transmitter once the signal comes across a cable or pipe.
However, a modern underground services locator has much better reach, and can pierce through virtually anything. Moreover, it can estimate the depth of the utility line, and differentiate it from other nearby utilities. That being said, a reliable and professional underground services locator can precisely pinpoint a fiber optic cable, gas line, power line, sewer and water line, and CATV cable. When you combine their ability to differentiate different types of lines with their precise depth and location of the utility, you get the ideal way to prevent damage while conducting work in or around a work site.
There are several types of signals and locating techniques. A passive signal is a signal that naturally occurs around an underground utility. Some examples of passive signals include current flowing along an electric supply cable, radio frequency currents from VLF radio transmissions that penetrate the ground and flow along underground utilities, and earth return current from power systems that utilise cable sheaths or metal pipes as convenient conductors.
A passive sweep is a technique that is used to look for abandoned, inaccessible or unknown utilities. This is done by traversing a survey grid in power mode, and utilities are found with the receiver blade being put in line with the direction of movement. When a utility is found present, it’s pinpointed and marked. The sweep continues until all the utilities have been pinpointed and marked, and the entire survey grid has been traversed in both directions. Then, the entire process is repeated in radio mode in order to find utilities that radiate VLF signals.
An active signal is a signal which is intentionally generated by the transmitter of the service locator. The signal can either be applied to the utility through induction or a direct connection. This allows utilities to be traced, identified and their depth to be determined with the receiver. A direct connection involves plugging a cable into the transmitter and connecting it directly to the target line. This can either be done with a transmitter clamp or connection clips.