Hioki FT3151 - Page 105

41
Measurement Precautions and Tips
earthing rod S(P) is positioned closer to the earthing body E or the
auxiliary earthing rod H(C).
Besides, when the electrodes E and H(C) are positioned close to
each other, the earth resistance of the measurement object (Rx)
and the earth resistance of the auxiliary earthing rods (Rc) cannot
be separated, leading to a measurement error.
In the case of an architectural structure that is grounded over a
large area, the resistance range of the earth resistance (Rx) in the
gure (a) becomes very wide.
This means that it is necessary to position the auxiliary earthing
rods S(P) and H(C) at a sufciently large distance from the earthing
body E.
To determine the proper distance, perform measurement at several
points, bringing the auxiliary earthing rod S(P) closer to the auxiliary
earthing rod H(C). Check whether there is an area where the
measured resistance remains approximately constant although
the position of the auxiliary earthing rod S(P) is changed. This
corresponds to the horizontal section in the gure (b).
If such area cannot be found, the measurement distance is not
sufcient. Move the auxiliary earthing rods S(P) and H(C) farther
away from the measurement object.
Ground
surface
Horizontal
section
Resistance area
of electrode E
Resistance area
of electrode H(C)
Measured value
S(P)
H(C)
1
2
3
4
5
6
7
Appx. Ind.