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Ground Resistance Testers Models 6422 & 6424
3.3.4 Current Measurement (Model 6424)
Quantities of
influence
Limits of the range
of use
Variation of the measurement
Typical
Maximum
Temperature
(14 to 122) °F
(-10 to 50) °C
± 250 ppm R
± 500 ppm R
Relative humidity
(10 to 90) % RH
± 0 % R
± 1 % R
Frequency
DC to 440 Hz
-
-3 dB
Peak factor
1.4 to 3 (up to 30 A)
± 0 % R
± 1 %
3.4 UNCERTAINTY
The instruments comply with standard IEC-61557 part 5, which requires that the
operating uncertainty (B) be less than 30 %.
In ground measurement:
with
A = intrinsic uncertainty
E
1
= influence of the reference position ± 90 °
E
2
= influence of the supply voltage within the limits indicated by the
manufacturer
E
3
= influence of the temperature between 32 and 95 °F (0 and 35 °C)
E
4
= influence of the interference voltage in series mode (3 V at 16.6; 50; 60 and
400 Hz)
E
5
= influence of the resistance of the rods from 0 to 100 x R
A
but ≤ 50 kΩ
E
7
= influence of the network frequency from 99 to 101 % of the nominal
frequency
E
8
= influence of the network voltage from (85 to 110) % of the nominal voltage
The uncertainty of operation of the instrument is ≤ 15 % + 1 Ω
