Sonel MRU-30, User Manual

Page: 19 / 56

MRU-30
– USER MANUAL
17
Note:
Earth resistance measurements are usually good if the interference voltage is
< 24 V. The meter can measure in the presence of interference voltage up to
100 V. Over 40 V it is indicated as hazardous. Do not connect the meter to a volt-
age exceeding 100 V.

Pay attention to the quality of the connection to the electrode object of test with the test
leads
– the contact area must be cleaned of paint, rust, corrosion etc.

If the resistance of the auxiliary electrodes is too high, then the measurement of the R
E
earth
electrode will be distorted by additional uncertainty. A particularly high measurement
uncertainty is generated if we measure a low value of the earth resistance with electrodes of
a loose contact with the soil (such a situation occurs often if the earth electrode is properly
made and the upper layer of the ground is dry and characterized by a low conductivity). Then
the relation between the electrode resistance and the resistance of the measured earthing is
very high, and so is the case of the measurement uncertainty which depends on it. What may
be done then is to perform, in accordance with the formulae specified in point 12.2,
calculations, which will permit to evaluate the influence of the measurement conditions. It is
also possible to improve the contact of the electrode with the ground, for example by means
of moistening of the place when the electrode is driven, its driving into the ground in another
place or using a 80 cm electrode. Check also the test leads and make sure the insulation is
not damaged and the contacts: test lead
– banana plug – electrode are not corroded or
loosened. In most cases the achieved resolution of the measurement is sufficient, but it is
necessary to be conscious of the uncertainty the measurement is burdened with.
Additional information displayed by the meter
R
E
>9999
Ω
Measurement range exceeded.
V
N
>100V , >100V and a continuous
tone

, ‘
NOISE!’
and
The voltage on the measurement terminals is > 100 V.
The measurement cannot proceed.
V
N
xxV , >40V and a continuous tone

, ‘
NOISE!’
and
Where xx is the value of the interfering voltage. The volt-
age on the measurement terminals is > 40 V. The meas-
urement cannot proceed.
V
N
xxV , >24V ,
‘ NOISE!’
and
Where xx is the value of the interfering voltage. The volt-
age on the measurement terminals is > 24 V, but < 40 V.
The measurement cannot proceed.
‘ NOISE!’
The value of the interfering voltage is < 24 V, but has a
high value. Results may be affected by additional uncer-
tainty.
and ER along with % value
The uncertainty caused by resistance of the electrodes is >
30%. (Uncertainties calculated on the basis of the meas-
ured values.)
and
R
H
or R
S
along with
Ω value
The resistance of H and S electrodes, or one of them ex-
ceeds 19.9 k
Ω. The measurement is subject to error.
Flashing symbols:
, , ,
Flashing symbols E, Es, H, S, indicate a test lead is dis-
connected from the measurement terminals.