Hioki FT3151 - Earth Resistance Measurement

32
Measuring Earth Resistance Precisely
(Precise Measurement, 3-Pole Measurement Method)
Earth resistance measurement
Select the range selector to the suitable
resistance range from ×1
Ω
, ×10
Ω
,
and ×100
Ω
, and have the needle of
the galvanometer points to the center
of the mark ▼ by turning the dial knob
while pressing the MEASURE button.
Read the indication on the resistance
dial and multiply it with the setting of the
range selector. The result is the earth
resistance.
In general, perform measurement using ×100
Ω
range rst, and then select
the lower range as necessary.
Setting the Poles selector 2 will cause an incorrect measured value.
As shown in “3.3 Measuring Range and Tolerances” (p. 48), each
inuence creates error. The total value of intrinsic uncertainty and inuence
quantity will be ±17.8% f.s. This indicates that the error will be ±17.8% f.s.
at a maximum (±1.78
Ω
for ×1
Ω
range) depending on conditions. If an
earth resistance of 1.78
Ω
or less is measured with the range ×1
Ω
set, the
galvanometer may be balanced with the resistance dial pointing to in the
right side of zero (the negative side) owing to such an error. In this case,
the earthing resistance is considered to be 1.78
Ω
or less. However, the
needle of galvanometer does not move correspondingly to the resistance
dial adjustment pointing to in the right side of zero, the measurement is
invalid.