A Brief History of <CD> - Current Direction

By: Gus Salles

gsalles@eastcomassoc.om

I first became aware of Current Direction (<CD>) in 1992, when Radiodetection introduced the RD432PDL/RD433HCTx kit. It had been under development for a while, part of research being carried out by Radiodetection in conjunction with AT&T for locating & identifying long haul armored fiber optic cables, being installed at a frantic pace all over the world at the time. It was a novel advancement for critical locates.

<CD> then was limited to 256/512Hz,/256Hz great for congested environments, but very low frequencies for regular locating, and only applicable by directly connecting the Transmitter (Tx) to the target line. Furthermore, the target line had to be a very good conductor which limited its practical use to telecoms and transmission pipeline companies.

For many years, this great feature remained inaccessible, or unusable, to locating technicians doing “run of the mill” locates: water lines, electric lines, signaling cables, site lighting, gas distribution.

Then, in late 2015, Radiodetection introduced the RD8100 line of locators, with “High Frequency <CD>” at 4kHz/8kHz which made Current Direction a “feature for the locating masses”. It can be used in many more applications than before, and it works with both Direct Connection leads and a Signal Clamp. I have resorted to <CD> in many field demonstrations and training sessions to identify a specific line from within two or more signals of similar characteristics. It works great!

Simply put, when <CD> is chosen, the Tx assigns a “direction of flow” to the locate signal as it if were a simple electrical circuit. Signal flows out of the Tx, along the red lead, into the target line to be located, then out along the target line, and it flows back to the ground stake and black lead to close the loop. Basic electricity.

The receiver in the <CD> mode will “detect” the direction in which the locate signal flows, and show it to the user with a simple arrow on the receiver’s display pointing either flowing away from the Tx, or flowing back to it. Then, knowing where your Tx is in relation to you, you can tell if you are above your target (signal flowing away from Tx) or on something else (signal flowing back to Tx).