The evaluation team believed that an EM line locator would be best for sweeping. The optimal active frequency and best equipment for the task required further investigation. The criteria were the following:
- Induction capability – the ability to easily energize lines without directly connecting
- Induction frequency – best signal to “light-up” or energize the most underground conductors
- Simplicity – equipment that is easily adoptable by crews at the jobsite
Additionally, the EM locator should be able to trace both good conductors and poor conductors – essentially verifying marks as needed. Good conductors will conduct signal well, making them easier to energize (with the transmitter) and to detect/pick-up (with the receiver). Poor conductors can be challenging to energize and to detect.
It became clear that part of the best technology for finding everything, including unmarked lines, is application of higher frequencies. Similarly, the ability to connect with a low frequency can best verify, isolate, and identify lines at the dig site.
The EM locator had to be simple to learn and easy to use. Locating and sweeping is a small, yet incredibly important part of the job. If crews found the equipment or procedure too difficult and time-consuming, the damage prevention efforts could be diminished.
The evaluation team tested a number of EM locators to assess performance against the objectives. Because ultra-high frequency is critical to success, the team looked further to the manufacturers’ experience and understanding in this area. Pipehorn and its dual-frequency Model 800-HL best met our selection criteria for frequency, induction, and simplicity. The ultra-high 480 kHz frequency for induction and sweeping for difficult conductors, plus a low frequency for connecting and isolating a line, was a good match. This particular locator also came with a handle to hold the transmitter closer to the ground when sweeping without having to bend over.