AEMC 4620 User Manual page 33

In Figure 13, The X and Z electrodes are sufficiently spaced so that the areas of
effective resistance do not overlap. If we plot the resistance, measured we find
that the measurements level off when Y is placed at 62% of the distance from X
to Z, and that the readings on either side of the initial Y setting are most likely to
be within the established tolerance band. This tolerance band is defined by the
user and expressed as a percent of the initial reading: ±2%, ±5%, ±10%, etc.
Digital Ground Resistance Tester Models 4620 & 4630
Ground Auxiliary
Electrode Potential
Under Test Electrode
X
Distance from Y to Ground Electrode
Ground
Electrode
Under Test
X
62% of D
Resistance of
Auxiliary Current
Electrode
Resistance of Earth Electrode
Distance from Y to Ground Electrode
Auxiliary
Current
Electrode
Y Z
Figure 12
Auxiliary
Potential
Electrode
Y
D
38% of D
Figure 13
Overlapping Effective
Resistance Areas
Auxiliary
Current
Electrode
Z
Effective
Resistance
Areas Do
Not Overlap
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