RD4000 Locating System User Manual
Page 33
Taking current readings
Using current measurement to aid identification
Measuring current value on a line helps confirm the identity of the line and provides information about the
condition of cable insulation or pipe coating.
The principle of current measurement
The transmitter applies a signal or current onto a target line.
The current decreases in strength as the distance from the
transmitter increases. This rate of decrease depends on the
type of line and on soil conditions. Regardless of the type of
line and the frequency being used the rate of decrease should
be regular with no sudden drops or changes. Any sudden or
abrupt current change indicates that the line or its condition
has changed.
In congested areas, where there is more than one line, the
receiver may sometimes detect a stronger signal from an
adjacent line to which the signal has coupled or shares
common grounding because it is nearer the surface. Although
current measurement compensates for depth, signal response
will be less as the depth increases.
The line with the highest current measurement, rather than the
line giving the strongest response, is the target line to which
the transmitter signal has been applied.
Measuring current provides useful information about the position of tees and bends. Measuring current after a
tee will indicate the main line that pulls more current along its greater length.
m
%
mA
m
%
mA
100%
60%
40%
mA
mA
mA
RD4000 series
receiver
Target
line
Conventional
locator
response
mA
mA
mA
mA
mA
