The four key features of an EMF Locator:
- Manual Gain
- Separate Peak and Null
- A range of Frequencies
- Be able to read Current
These features are required to enable us to provide a reliable electronic location.
The four steps to a reliable location:
- Connect. Direct or clamp
- Confirm. Sweep, determine signal point and identify target by current
- Trace. Minimise gain adjustments and check Peak/Null
- Sanity Check. Trace to known end
AS-5488 Quality Levels:
- QL-A Verified Potholed +/- 50mm
- QL-B Reliable electronic location. 300mm Horizontal, 500mm Vertical
- QL-C Identify buried assets by surface features but not able to achieve QL-B
- QL-D Identify asset in the vicinity by plans but not able to achieve QL-B
- Gain must be manual, not automatic.
- Set to 50-60%
- When gain changes it is telling you something.
- Change of direction or depth.
- A split or tee in the target.
Peak / Null:
- Allows us to determine if we have a round signal or a distorted signal.
- Tells us if we can give an accurate depth.
- If Peak and Null do not align we have a distorted signal and should not give a depth.
- Allows us to determine true location of the target. Half the distance between the Peak and Null and transfer outside the Peak.
- ALWAYS check Peak and Null before placing a mark.
Signal Trace Frequencies:
- Low Frequency – Typically 8 kHz and lower - Low frequencies are best for Direct Connection.
- Medium Frequency – Typically 33kHz - Medium frequencies are best for Induction Method of Connection.
- High Frequency – Typically 65kHz and higher - High frequencies are best for Induction and the Inductive Clamping method of Connection.
- We read it in milli amps mA
- It is used to determine the target. Highest mA.
- Used to identify branch line or tees.
- We want to achieve Maximum current for best signal flow.
To increase CURRENT:
- Reduce resistance - e.g. water on earth stake, use bigger earth stake, connect bigger target (largest cable size)
- Increase voltage - Increase transmitter output
Active Methods of Locating:
- Why? Because we apply the signal using the transmitter
- They are:
- Direct Connect
Passive Methods of Locating:
- We use only the receiver
- We detect naturally occurring noise.
- We can only determine conductive assets
- We can not identify them.
Caution! Power Passive does not necessarily identify power cables.
Work to a process:
- Where is the job site
- Obtain DBYD (essential) and any other plans or anecdotal information
- Clarify work area with client
- Walk and inspect work area looking for signs of buried assets.
- Check all plans and prioritise them
- Locate everything you can to QL-B
- Identify that which is QL-D
- Complete active and passive sweeps
- Complete site report and go over with client
Plans are not 100% accurate:
- Never take plans as the truth. They are a guide.
- Always compare what the plan says to what you see and let your locator discover the truth.
- Open every pit.