Electromagnetic locating (EML) is a technique where a unique signal is put onto a metallic / conductive utility. This does not have to be a cable, it can also be a metal pipe. The signal can then be followed from the surface using an EML receiver, so that we can determine the position of a utility. The accuracy of an EML survey is very high, because a single utility is exposed to the signal. Meaning, when that signal is followed you will know exactly which utility you are tracking. When the utility is traced and the position is known, the location is surveyed using extremely high accuracy GPS, 06-GPS and TS (Total Station) equipment. This allows precise mapping of these findings.
In the case of a big and complex cable cluster there is the possibility that the electromagnetic signal jumps onto a nearby cable. This phenomenon is called ‘crosstalk’ and influences the accuracy of the survey negatively. By combining EML surveys with GPR surveying and trench digging we can easily correct and overcome this influence.
Locating non-metallic utilities
Non-metallic utilities such as optical fiber, PVC/concrete, sewers and drains cannot be located using EML. Instead, we use GPR or manual digging and soil probing. There is also a method that enables EML detection of non-metallic utilities. We can insert a probe that sends a signal or insert a conduit rod, on which we put our signal, and track this signal the same way as with a metallic utility. This method is used when, for example, we have to locate a HDD pipe filled with optical fiber cables or when mapping municipal sewer pressure lines. Through a diverse set of innovation programmes we have developed several systems in order to work with pressure lines (gas and sewage). Through this we have also developed a pressure lock, which we can place on a gas pipe, so that we can put a conduit rod through it without a chance of any gas leaking out.
You can also read our article: “GPR – “soil scan” or utility investigation? In this article we discuss the benefits of combining different detection techniques.
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