Camille Bauer GOSSEN METRAWATT GEOHM C, Operating Instructions Manual

Page: 54 / 236

18 GMC-I Messtechnik GmbH
5.4.2 Setting a Limit Value – LIMIT Function
If required, an earthing resistance limit value R
E
can be selected by press-
ing the LIMIT key. If measured values in excess of this limit value occur, the
red LIMIT LED lights up.
Activate the limit value menu. Set the limit value.
Setting the Limit Value:
Display the desired numeric value and a decimal point if required with the
help of the
and the keys, and select the value with the corre-
sponding softkey. The cursor moves one place to the right after each
selection has been made. After entries have been made for a maximum of
3 places, and after either
Ω
or k
Ω
has been selected, the entry window is
exited automatically. The cursor can be moved one place to the right or
the entry window can be exited during data entry by pressing the
→
softkey. The selected limit value is automatically saved to memory when
the entry window is exited.
5.5 Measuring Earthing Resistance
5.5.1 Measuring Circuit Setup, Measuring Instructions
3-Wire Connection
Figure 2 Measuring Earthing Resistance with a 3-Wire
Test Setup
Ð
Position the probe at least 20 meters, and the auxiliary earth electrode
at least 40 meters from the earth electrode (see also Figure 2 on page
18).
Ð
Make sure that contact resistance between the probe and the soil is
not too great.
Ð
If a 3-wire test setup is utilized, the earth electrode is connected to
jack “
E ” at the test instrument with a measurement cable, the probe is
connected to jack “ S ” and the auxiliary earth electrode is connected to
jack “ H ”.
Ð
Press the R
E3-P
key in order to select 3-wire connection.
Resistance of the cable from the earth electrode to the instrument has a
direct influence on measuring results.
In order to minimize error caused by measurement cable resistance, a
short cable with a large cross section should be used to connect the earth
electrode to jack “
E ” for measurements performed with a 3-wire setup.
Connector cable resistance can be measured with the 2-wire method (see
chapter 5.7 on page 24).
E
S H
≥
20 m
≥
20 m
S H ES E