Because utility locator frequencies jump from one utility to another, it is common to find signals on more than one utility. Shallower utilities such as telephone and cable TV can have a stronger locate signal indicating that it is the target utility.

The RD8000, RD7000, RD4000 and some other pipe and cable locators include a current measurement feature. The RD8000 and RD7000 automatically display the depth or current anytime the locator is aligned with the pipe or cable and above it. It the depth is displayed, hold the antenna mode button until the depth changes to current. The current measurement value is the amount of signal from the transmitter on the utility at that point. Any current that may be flowing through the cable from other sources does not affect this measurement. The utility that you apply signal to with the transmitter will have the highest current measurement. The strength of the current measurement signal varies depending on the conditions, but the important part is the strength of the current measurement signal is higher than the others. Accurate current measurement depends on accurate depth measurement.

Cable and Pipe Identification with Current Direction

The forward arrow displays when the receiver senses signal from the same utility that the locator transmitter is applying signal to. All other utilities will show the backwards arrow. After long distances the signal may need to be reset by locating the center of the target utility and pressing the menu key.

The Radiodetection RD8000 PDL offers a unique feature that identifies utilities. A Tx10 transmitter connected directly or with the "Low Frequency / Current Direction" is necessary.

Cable and Pipe Depth Verification

Interference form other pipes, cables and utilities can cause errors in depth measurement. To check the accuracy of depth measurements, check the depth at ground level, the raise the pipe and cable locator up by a known height. If the change in the depth readings equals the height that you raised the pipe locator, then the locator depth readings are accurate.

Pipe and cable depths are to the center of the cable or pipe.

The depth accuracy specification for the RD8000 and RD7000 pipe and cable locator is within 2.5% of the depth when not affected by other pipe or cable signals.

With the RD7000 or RD8000 utility locators the depth accuracy is easier to verify. Switch to continuous current measurement by hold to antenna selection button, if needed, then slowly raise and lower the locator receiver. A consistent reading of current indicates that the depth is unaffected by errors.

Which Locator Frequency Should I Use?

Use the lowest frequency that works.

The signal from a utility locator transmitter transfers by conductivity and inductance.

Signals traveling by conductance are like DC or 60 hz AC circuits, when the switch is closed connecting the circuit the current flows. When the switch is opened discounting the wires the current stops. The amount of current from the locator transmitter that flows by conductivity depends on the resistance. High resistance can be caused by dry soil, rusty connections and others. The signal traveling by conductance will find the easiest path (path with the least resistance.)

Signals traveling by inductance work like a radio transmitter and radio receiver.

Low frequencies have very little signal traveling by inductance, so the signal remains on the utility that the transmitter is connected to.

Locator Accuracy Verification with Peak and Null Antennas

The RD8000, RD7000, RD4000, RD400 and some other pipe and cable locators have both peak (horizontal) and null (vertical) antennas. The peak antennas display a maximum signal above the utility. The null antennas display a minimum signal when above the pipe or cable and a maximum on each side of the pipe or cable. When there is no interference from nearby utilities, the peak and null locate signals are both shown in the correct position, directly above the underground pipe or cable.

However, nearby pipes, cables or other utilities can cause distortion of the locator signal around the target utility. The distortion causes the position of both the peak and null to shift in the same direction. The position of the null signal moves more than the peak signal causing the position of the null signal to be in different position than the peak. When the peak and null are in a different place, both measurements are being affected and have errors.

The peak signal is affected less than the null signal by interference, if the peak and null signals are different, the peak signal will be closer.

Reducing the signal on other utilities improves the locater signal accuracy.

RJM Company

Brian Moss

brianmoss@rjmcompany.com

Office: 360-828-5732, 800-620-4773

Cell: 360-903-0558

Fax: 208-988-6447

9808 NE 134th Ave, Vancouver WA 98682

Representatives for Radiodetection in Oregon, Washington, Idaho and Montana, Utah, Wyoming. For other areas please contact Radiodetection at 877-247-3797 x 181 to find the dealer near you. cable fault locators, sondes, plastic pipe locators, water leak detectors, metal detectors, RD2000, CAT underground cable locator, RD7000 pipe and cable, RD8000 cable locators.