Amprobe Multitest-2000 Continuity-Tester - Manual (Page 159)

AMPROBE
MULTITEST2000
The measuring method allows the operator to
define the specific resistance up to the depth
corresponding approximately to the distance
“a” between the rods. If you increase the
distance “a” you can reach deeper ground
layers and check the ground homogeneity.
After several
ρ measurements, at growing
distances “a”, you can trace a profile like the
following ones, after which the most suitable
rod is chosen:
Curve1: as
ρ decreases only in depth, it’s
possible to use only a rod in depth.
Curve2: as
ρ decreases only until the depth
A, it’s not useful to increase the depth of the
rod beyond A.
Curve3: even at an increased depth,
ρ does
not decrease, therefore a ring rod must be
used.
APPROXIMATE EVALUATION OF THE CONTRIBUTION OF INTENTIONAL RODS (64-
12 2.4.1)
The resistance of a rod Rd can be calculated with the following formulas (
ρ = medium
resistivity of the ground).
a) Resistance of a vertical rod
Rd =
ρ / L
L= length of the element touching the ground
1
2
3
Earth rods distances "a" (m)
Resistivity
(Ω
m)