General Machine Products RD7000 Traceable Rod Detection - Manual (Page 24)

18 RD7000 Operation Manual
5.3 Current readings
5.3.1 Identification using current
measurements
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.
mA mA
0.6 1.0
m m
25 25
mA mA
90 30
% %
mA
mA
mA
Figure 5.3: Current readings
Figures 5.4 – 5.6: Taking
current readings
5.3.2 About current measurements
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 bends and intersections. Measuring current
after a tee will indicate the main line that pulls more
current along its greater length.