MI 3290 Earth Analyser
Tests and Measurements
92
11.3.3 Schlumberger method Measurement
Place the two earth probes (ES and S) at a distance
d
from one another and place the
second two earth probes (E and H) at a distance
a
from ES and S probes. All probes must
be placed on a straight line and to a depth of
b
, considering the condition
b << a,d
. Distance
d
must be between 0.1 m and 49.9 m and the distance
a
must be
a>2*d
. Connect the cables
to the probes, then to terminals H, S, ES, and E.
E a r t h
H
S
ES
E
MI 3290 Earth Analyser
a
G
V
A
S - probe
ES - probe
E - probe
H - probe
d
a
b
Figure 11.46: Schlumberger method example
Schlumberger method with unequal distances between test probes:
b << a, d
a > 2 ∗ d
𝜌
𝑠𝑐ℎ𝑙𝑢𝑚𝑏𝑒𝑟𝑔𝑒𝑟
=
𝜋 ⋅ 𝑎 ⋅ (𝑎 + 𝑑) ⋅ 𝑅
𝑒
𝑑
= [𝛺𝑚]
where:
R
e
..................................... Measured earth resistance in 4-pole method
a
....................................... Distance between earth probes (E, ES) and (H, S)
d
....................................... Distance between earth probes (S, ES)
b
....................................... Depth of earth probes
π ....................................... Number π is a mathematical constant (3.14159)
