A purchaser of a locator should look at several factors before purchasing an EMF locator;

1. Equipment type 2. Servicing of that equipment 3. Training and more importantly the level of equipment the operator requires. For example, it is no use buying a locator with all the bells and whistles if the operator only uses it once or twice a month, or is doing the very basics of operation.

I would categorise EMF locators into three categories;

1. Cable avoidance products 2. General locators 3. Specialised locators.

Cable avoidance products

These types of instruments usually offer very basic functions, have usually only one active frequency (uses the transmitter), may have various passive modes (able to locate power and telco cables without the transmitter), and offer a peak only response (have a tone and/or display that rises over the top of the cable). Some older style units, sometimes referred to as split boxes, may have a null only response (have a tone and/or signal either side of the cable and minimum signal or no signal on top of the cable).

The benefits of this type of locator are that it offers a simple and easy to use instrument that a novice could easily operate in the field. It is important that even though these instruments are easy to use the operator still needs to understand the basic theory on how a locator picks up a cable or pipe, and more importantly, needs to know the limitations of these instruments. Therefore, training is an important part of the purchase.

When purchasing a basic instrument, the operator needs only a few features. This type of product should have minimal buttons or switches and have a clear, easy to read, display. The receiver should offer a very manual approach. For example, manual gain that gives the operator a little bit more flexibility when operating near congested areas or where cables may cross over. Generally these units use a frequency around the 33 kilohertz (kHz) area, a frequency that is very good in 80 to 90 per cent of locations and is less likely to jump across in congested areas. Most of these receivers have digital depth readout with a depth button.

Passive modes can give the operator some flexibility in first locating a service before hooking up, but should not be relied upon for locating services due to the inconsistencies in signal strength using this type of detection method. I have, on many occasions, scanned an area on a live power cable using the passive modes and because there was no load (current flow) on the cable, the locator missed the service. This is why you should always locate using the transmitter where possible.

The transmitters in this category usually have a 0.5 watt to 1 watt transmitter output, which would be more than enough in general locations for a distance of several hundred metres and a depth of around 1 to 2 metres on average signal connections. Although having more power can help by throwing out a stronger signal in difficult hook ups, the quality of signal relates to several factors.

There are many units in this category available from companies like Radiodetection (CAT), Rycom (CAP), C Scope and Metro-tech. The most popular of these instruments are used by water authorities, excavation companies, and councils who require a general locator for locating their own services. Pricing in this category is usually between $A1,600 to $A4,000.

General locators Moving into this category gives the operator more flexibility and more controls available for difficult locations. Some of the features in this category are peak and null, which can give the ability to decipher if there is a field distortion of the signal in the area, and current measurement (measures the current output of the transmitter; good in areas where you feel you might have cross over or ghosting of your target cable). The general locator usually has depth and passive modes as standard and a broad range of frequencies, which assist the operator and give clearer information for location work.

As well as the above features, the locator being considered to purchase should have at least two active frequencies with up to a maximum of five. These frequencies should be in various ranges; low frequency 512 Hz to 1 kHz, medium frequencies 8 to 51 kHz and high frequencies 65 to 82 kHz. Some units do have higher frequencies but this can create a lot of signal coupling or ghosting. Each frequency has its strengths and weakness, but it gives the operator more flexibility to be able to use these in various situations. Having hundreds of frequencies on the one unit is not really advantageous unless using other manufacturers' transmitters and only one receiver.

The system should still be relatively easy to use but additional training is essential to get the most benefits from this category of locator.

The transmitters in this category usually have a 2 watt to 10 watt transmitter output, which is more than enough for general locations and location work. Unless you are travelling long distances with your locations, 2 to 3 watts is more than adequate. The only exception is if you use the transmitter for induction searching (applying a signal to a cable without connecting to the service by being over the top of it), then having over 2 watts and a good performing transmitter is always better; but remember higher frequencies are usually restricted to 1 watt due to laws governing output in the higher frequency range.

Some of these systems offer cable fault finding by an optional or standard A-frame system. This system uses the A-frame to find faults to ground on power and telco cables.

There are many units in this category available from companies; Radiodetection RD7000, RD8000, Rycom 8800 series, Metrotech 9800 series, Fuji 3M and Subsite 950t.

Special note: some newer technology that uses multi array antennas on the receiver uses a simple line on the screen that shows the direction of the cable. If you turn the locator sideways, it will also rotate the line to match up. It has great advantages such as making locating quick and simple with instant depth and easy to read display. However, some locators do not allow the operator the same type of flexibility as a traditional peak and null system and use an automatic gain system which doesn’t allow the user any type of adjustment. Some of these units are from companies like Goldak, Rigid and Sewerin.

Specialised locators

A specialised locator offers special features unique to that machine. They are classed as specialised because they offer the operator a benefit or feature in certain types of works. Units that fit this category are the RD8000PDL and the Metrotech i5000. Other products are the PCM from Radiodetection: this unit is used to locate faults on cathodic protected gas and petroleum pipelines.

The i5000 offers on board GPS, which helps an operator locate the general area that a cable may be positioned. The RD8000 also offers this feature by utilising an external GPS system from manufacturers like Trimble, who offer complete packages for surveying needs. These external systems are usually far more superior in accuracy but this comes at a higher price.

The other feature that the RD8000 has is current direction (CD) This systems emulates a DC type current (current flow in the one direction) using the lower frequencies, it displays a directional arrow on the target line and alerts the operator if he has strayed onto other services by the change in direction of the arrow. This is a feature that is unique to this type of instrument and Radiodetection currently have a patent withstanding.

Transmitters in this category usually have a 10 watt output; some have up to a 1,000 watt output, for example pipe current mapping. Prices for these units vary from around $A8,000 upwards.

I am not covering GPR as it is not an EMF-based technology. The major manufacturers in this area are IDS, MALA, and GSSI. Servicing of equipment

It is important for any prospective customer that they also look at after sales service. This is as important as the actual instrument purchase itself. Make sure the company that you are dealing with has a full service centre. If you are local to the area where the company is based, visit their service centre.

Technology is fantastic when it is operating, but when things go wrong make sure the system is easily repairable and does not require expensive board replacements, which appear to be a common issue with the more sophisticated units. Can the company service the instrument here or does it have to go overseas for repair? How quick is their turnaround? Do they have a loan/rent system available if your locator is in repair for weeks?

These are all important factors when purchasing and, as all operators will know, not having your prized locator for weeks could cost you a fortune; something to consider when making your initial purchase.

Training

Training is crucial to get the best benefits of your new instrument; even the most experienced operators should get thorough training in the particular instruments they purchase. Even the most experienced operators can learn something new and having a knowledgeable salesperson to get the most from your new instrument is extremely beneficial. For the less experienced operator a training course should be part of the purchase price.

NULCA’s extensive training program will assist a lot with educating new and old operators and has huge benefits for government departments, including councils, but the manufacturer or supplier of the locating equipment should thoroughly understand and be able to educate the end user of the benefits of their particular instrument.

I have only scratched the surface so remember do your homework and talk to the prospective suppliers. The NULCA website is a starting point for information.