Manual

Gossen Metrawatt GmbH 71
15.11 Earthing Resistance Measurement, Battery Powered, “Battery Mode” – Measurement of Soil Resistivity 
E
(PROFITEST MPRO & PROFITEST MXTRA only)
General
The determination of soil resistivity is necessary for the planning of
earthing systems. Reliable values need to be ascertained which
take even the worst possible conditions into account (see „Geo-
logic Evaluation“ on page 71).
Soil resistivity is decisive with regard to the magnitude of an earth
electrode’s dissipation resistance. Soil resistivity can be measured
with the test instrument using the method according to Wenner.
Four earth spikes of greatest possible length are driven into the
ground in a straight line at distance d from one another, and are
connected to the earth tester (see figure above).
The earth spikes usually have a length of 30 to 50 cm. Longer
earth spikes can be used for soil which demonstrates poor con-
ductivity (sandy soil etc.). The depth to which the earth spikes are
driven into the ground may not exceed one twentieth of distance
d.
Note
Erroneous measurement may result if piping, cables or
other underground metal conduits run parallel to the
measuring setup.
Soil resistivity is calculated as follows:

E
=2  d  R
Where:
 = 3.1416
d = distance in m between two earth spikes
R = ascertained resistance value in (this value corresponds to R
E
as
determined with the 4-wire method)
Connection
➭ Position the spikes
for the probe and the
auxiliary electrode at equal distances (see figure above).
➭ Make sure that no excessively high contact resistances occur
between the probe and the ground.
➭ Attach the PRO-RE adapter (Z501S) to the test plug.
➭ Connect the probes, the auxiliary electrode and the electrode
via the 4 mm banana plug sockets at the PRO-RE adapter.
In doing so, observe labeling on the banana plug sockets.
Select Measuring Function
Select Operating Mode
The selected operating mode is displayed inversely:
white battery icon against black background.
Set Parameters
❏ Measuring range: AUTO, 50 k, 20 k, 2 k, 200 , 20 
❏ Connection:

E
(Rho)
❏ Transformer ratio: irrelevant in this case
❏ Distance d for measurement of

E
: adjustable from 0.1 to 999
Start Measurement
Geologic Evaluation
Except in extreme cases, the ground is measured down to a
depth which is roughly equal to probe distance d.
And thus it’s possible to arrive at conclusions regarding the
ground’s stratification by varying probe distance. Layers which
are highly conductive (water table) into which earth electrodes
should be installed, can thus be discovered within a region which
is otherwise not very conductive.
Soil resistivity is subject to considerable fluctuation which may be
due to various causes such as porosity, moisture penetration,
concentration of dissolved salts in the ground water and climatic
fluctuation.
Characteristic values for 
E
relative to season (soil temperature
and the soil’s negative temperature coefficient) can be approxi-
mated quite closely by means of a sinusoidal curve.
ES ESH
dd d
Measurement of Soil Resistivity
R
E
+
E
(%)
10
20
30
-10
-20
-30
Jan. MarchMay July Sept. Nov.
Soil Resistivity E Relative to Season Without the Effects
of Precipitation (earth electrode depth < 1.5 m)