Sonel MRU-30, User Manual

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MRU-30
– USER MANUAL
48
12.2.4 Influence of interference current on the result of the earth resistance
measurement for two-clamp method (2C)
The MRU-30 meter may perform a measurement, if the value of the interference current does not
exceed 3 A rms and the frequency complies with the value set in the MENU.
R
E
Additional uncertainty [
Ω]
0.00 to 10.00

0.03 R
E
2
I
Z
10.01 to 99.99

0.0004 R
E
2
I
Z
( I
Z
+10)
If the interference current exceeds 3 A the possibility of measurement is blocked.
12.2.5 Influence of the relation of the resistance measured with clamp for
the multiple earthing branch to the resultant resistance (R
E
3P+C)
R
C
Additional uncertainty
[Ω]
≤ 50 Ω
±(0.003
𝑅
𝐶
𝑅
𝑊
2
)
> 50 Ω
±(0.5
𝑅
𝐶
√𝑅
𝑊
)
R
C
[Ω] is the value of the resistance measured with clamps for the branch displayed by the device,
and R
W
[Ω] is the value of the resultant multiple earth resistance.
12.2.6 Additional uncertainties in accordance with IEC 61557-5 (R
E
3P, R
E
4P)
Influencing factor Symbol Additional uncertainty
Location E
1
0%
Power supply voltage E
2
0% ( not displayed)
Temperature E
3
±0.2digits/°C for R<1 kΩ
±0.07%/°C ±0,digits/°C for R≥1 kΩ
Serial interference voltage E
4
In accordance with formulas in
10.2.1 (V
N
=3 V 50/60 Hz)
Resistance of electrodes and
auxiliary earth electrodes
E
5
In accordance with formula in
10.2.3