This is the most common instrument for tracing out buried utilities, both pipes and cables. These instruments originated a little over 100 years ago and still
operate on the same basic principle. The transmitter applies minor AC current to the conductive portion of the utility, and this results in an electromagnetic field
(EMF) being emitted around the length of the conductor. The receiver contains coil antennas that detect the EMF and allows the utility line to be followed out.
Formerly, they have been called “pipe locators”, “cable locators”, or just “locators”. In recent years, the acronym “PCL” has become the more common name. Technically, they are EMF locators because they are the only geophysical instrument that detects EMF and this makes them the most crucial instrument for tracing out utilities.
PCLs can operate in any type of soil, and many of the modern PCLs can operate in any one of four methods: direct connection, clamp induction, standard
induction, and passive. This makes them capable of tracing any pipe or cable with metallic content of some kind, which the vast majority of utility lines possess. With a 10-watt transmitter, the EMF can be detected up to roughly 15 to 20 feet deep.
The biggest difference between individual PCLs is the frequency selection. Overall frequency selection on a PCL is between 512Hz and 480 kHz. However, some have only one frequency available, usually very high. Some have 2 frequencies: a mid range and a high frequency. The most useful instruments may have a dozen or more active frequencies including one or more low frequencies (below 1 kHz), and a few passive frequencies such as Radio Passive and Power Passive. All of these frequencies can be very useful, especially when you are trying to locate a variety of utilities in a variety of situations.
Some technicians carry two PCLs in their truck, one for common locating and one with a very high frequency for scanning an area for unknown utilities.