by Anthony Johnstone, Director, Access Detection
Being a trainer in the field of pipe and cable locating, Anthony Johnstone has seen a range of locators used in many applications – however, he finds that a lot of the locators purchased by companies are inadequate for the roles that are required of them.
Having the wrong locator can add to the risk of incorrectly locating underground services. This can cause damage and interruption, costs to business, and there is even the potential for loss of life.
So is a single active frequency PEAK-only locator (like a Cat & Genny, C-Scope, Digi Cat or Rycom CAP, to name a few) adequate enough to locate the range of services you may come across accurately? In a word, no. Originally these locators, which were commonly referred to as cable avoidance products or tools, were designed for basic asset location – which they were absolutely fantastic at doing. They are simple to use and do not require a lot of training.
So who should purchase this type of locator? Water authorities and councils who are only required to locate simple services, such as water pipes or isolated utilities in non-congested areas which are easily connected to. Keep in mind that some asset owners require you to be trained to locate their networks, so even opening a pit can cause you to become liable or face hefty fines.
So what type of machine would be best suited to an NBN contractor or a council that has operators who are certified to locate Telstra, or a person looking at moving into locating? Definitely not the above locators. Why? Because single active frequency PEAK-only locators do not have the flexibility required to locate the varied assets, and deal with the many challenges an operator may come across from day-to-day.
An example that comes to mind is the small two pair telephone cable leading from the pit into a house, a common challenge a locating contractor may face. These small two pairs are not normally earthed at the house. So basing this on the theory of locating, a signal will travel along the service you have connected to, then return via the ground back to the transmitter, either through the earth-stake (direct connect) or through the ground to a far end earth (using an induction clamp). As mentioned earlier, because the near end is not earthed, the signal in theory will not have a path to return, so you will normally be unable to locate the service.
A locator overcomes this problem by having higher frequencies (65kHz or above). Higher frequencies allow the signal to jump off a cable more readily (although this can also be a disadvantage). I will not go into the theory of capacitance and inductance, which is a key factor in how you can locate these types of cables, but in short this allows the cable to create an earth return in a very short cable run, allowing you to locate in these situations. It is also a similar situation when using the small traceable rods that an NBN contractor may use to locate conduits leading into the home.
Having more than one transmitter frequency is just one part of purchasing the right locator. Other important functions that a professional locator has is the use of null antennas and current measurement.
Having a null antenna allows you to determine if you have a clean magnetic field (round field) or a distorted field (elongated field). It assists by notifying the operator there is something wrong with your locate, and that your locate position may be incorrect, or worse still, tracing a different service to the one you originally connected to.
Current measurement is another function in your locator which helps determine if you are on a ghost (mutually induced) signal or on your original target signal. Having these extra functions gives the operator the confidence to locate more accurately and, more importantly, notify the person who is excavating in the area if there are any problems.
To the readers who are a bit confused by the different terms that have been discussed in this article, or who are looking at moving into locating for a contract or a career, my first suggestion is join an association that is linked to the industry. The National Utility Locating Contractors Association (NULCA) is a good start. NULCA is the only association dedicated to improving the industry through education, advice and other members benefits. The association is made up of very experienced companies that offer complete locating and mapping solutions.
The second part of becoming a locator is education. Education is the key to reducing the risk in hitting services, which in the end, reduces your costs in insurance and your own downtime. NULCA is one of the very few associations that offer training through registered training organisations that specialise in the pipe and cable locating fields, and all the trainers have had at least ten years infield experience.
Utility locators: key considerations
When purchasing a utility locator, I suggest the following functions as a minimum:
• Peak and null modes
• Multiple frequencies in the low, medium and high frequency ranges
• Current measurement
• Manual or semi-automatic gain control (not automatic gain).
There are of course other specialists modes on more sophisticated units, and the more you spend on a locator, the more functions become available to you, including features like transmitter to receiver communications, current/target direction and fault location.
Companies to look for when purchasing equipment should be long-standing manufacturers who have been in the industry for a long time. Rycom and Radiodetection are just a few who have been manufacturing for over 60 years, and there are many more.
Access Detection also offers theory, and more importantly, practical training on locating equipment, and can also give advice on what type of locator would best suit your needs.
Visit www.accessdetection.com.au for more information.