What Frequency will I use Jim?

Successful Locating Depends on Knowing Which Frequency to Use

Electromagnetic locating is possibly the most widely used method for the location of underground utilities. This technology has been around for near on 60 years and over this time it has developed into a reliable and cost effective method for locating buried pipes and cables.

Understanding Frequency Selection

The advancement of locating equipment has provided the locating professional with more available options including strength of signal current reading, a range of frequencies and variable power output.

By itself a RF (radio frequency) receiver can detect power lines and other conductors radiating their own electromagnetic field, however with the introduction of a transmitter/receiver combination and an induction clamp, a specific signal can be applied to the target line that is more detectable from the surface with the receiver.

Professional locating operators will use a combination of passive, inductive or direct connect method to perform an effective locate, however an operator must have a knowledge of the signal properties and the ability to select the optimal frequency.

What is Frequency?

An electromagnetic field is created by placing an alternating current onto a metallic conductor. This alternating current rises and falls a certain number of times per second, which in turn causes a magnetic field to build and collapse around the conductor at a predictable rate. This rate is known as the frequency. Frequency is expressed in units of hertz (Hz), which means the number of wave cycles per second (the number of times per second, or cycles per second, that the magnetic field builds and collapses), or kilohertz (kHz), which means thousands of cycles per second.

Frequency Affects the Locator’s Ability to Trace a Line

Choosing the frequency that will give the locator the clearest signal depends on many variables. Different frequencies can and will have different effects on your locate. Different frequencies behave differently depending on the line conductivity, earthing variations, soil moisture content or differing ground types.

The properties of each utility line and even the soil surrounding the line can be conducive or resistant to the flow of electrical current. A highly conductive line will provide a strong flow of electrical current. A highly resistant line will provide a poor flow of electrical current. A frequency selection for one particular job may not be optimal for another. The selection that worked best one day may not work at all on another. Locate professionals may have a favourite frequency that they commonly use, but it may not always produce the desired result.

The “Golden Rule” for frequency selection says, “Use the lowest frequency that will produce a traceable signal over the distance that is needed to cover.” By understanding the range of frequencies available and how they interact with surroundings, the professional locator can better choose which frequency is needed. Understanding how high and low frequencies act in a given situation will help the locate professional achieve consistently better results.

Locating Unlimited delivers a range of professional courses designed to assist in Utility Damage Prevention. Courses range from Utility Plan Reading and Basic Locator Training all the way through to Advanced Locator Training and GPR Training. Contact Jeff on 0419 44 66 27 now for further information