Introduction:
In the world of construction, particularly when dealing with underground utilities, the accuracy of electromagnetic (EM) locating signals is paramount.
Misidentification or poor precision can lead to disastrous outcomes, including damage to underground utilities and safety hazards.
Therefore, it's crucial to perform regular checks and tests on your EM locating equipment to ensure accurate and reliable results.
How to check if your Electromagnetic locator signal is round?
The five checks to a round signal, for Utility Locators are:
- Peak VS Null
- Digital Depth
- Triangulation
- Peak
- Null
See below for details on steps to check your em signal.
1. Peak VS Null
Understanding the Match
The peak and null signals of your EM locator should coincide if the signal is round and free of interference. A mismatch might indicate interference from a more conductive material or another signal.
Pro Tip: The Two-Thirds Plus One Rule
When the peak and null signals don't align, apply the Two-Thirds plus One Rule. Locate the true position halfway between the peak and null marks, leaning towards the peak side. This adjustment should be within the AS5488 locator tolerances for QLB.
2. Digital Depth
Measuring Technique
Lift the EM locator approximately 30cm from the ground. The digital depth reading should correspondingly increase by 30cm.
Pro Tip: Transmitter Distance
Ensure that the transmitter is at least 20 meters away when inducting onto a cable or pipe. The depth measurements should be accurate within a range of +3-5%, under suitable conditions.
3. Triangulation
Balancing the Signal
Hold the receiver at a 45-degree angle and move it to either side of the peak. Adjust until the readings on both sides are balanced. This method is effective if the field shape is round.
4. Peak
Ensuring Equal Readings
Match readings on each side of the peak signal. Pull the receiver equidistantly on either side of the peak's center. The readings should match at equal and opposite distances.
5. Null
Verifying the Null Mode
Raise the receiver straight up while in null mode. A correct null reading should persist if the signal is round.
Quality Level B (QLB) Compliance
Following these checks, any markings that align with these tests can be considered accurate as per Quality Level B under AS5488 standards.
Proactive Verification with QLA Potholing
For added assurance, especially in construction projects involving underground utilities, employ Quality Level A (QLA) Potholing.
Preferably, use non-destructive digging (NDD) methods to minimize risk and ensure accuracy, such as using hydro vacuum or air vacuum services.
Conclusion
Regularly testing and verifying your EM locating signals using these methods is essential. It not only ensures compliance with industry standards like AS5488 but also significantly enhances safety and precision in construction projects involving underground utilities. Always prioritize accuracy and caution to prevent costly and hazardous mistakes.