Position Of The Auxiliary Electrodes In Measurements - AEMC 4620 User Manual

4.3.1 Position of the Auxiliary Electrodes in Measurements

The goal in precisely measuring the resistance to ground is to place the auxiliary
current electrode Z far enough from the ground electrode under test so that the
auxiliary potential electrode Y will be outside of the effective resistance areas of
both the ground electrode and the auxiliary current electrode. The best way to
find out if the auxiliary potential rod Y is outside the effective resistance areas is
to move it between X and Z and to take a reading at each location. If the auxiliary
potential rod Y is in an effective resistance area (or in both if they overlap),
by displacing it, the readings taken will vary noticeably in value. Under these
conditions, no exact value for the resistance to ground may be determined.
On the other hand, if the auxiliary potential rod Y is located outside of the
effective resistance areas as Y is moved back and forth, the reading variation is
minimal. The readings taken should be relatively close to each other, and are the
best values for the resistance to ground of the ground X. The readings should be
plotted to ensure that they lie in a "plateau" region as shown in Figure 10.
Digital Ground Resistance Tester Models 4620 & 4630
X Y' Y Y''
X-Y Distance
X Y Y Y''
X-Y Distance
Z
Reading Variation
Figure 9
Figure 10
Effective Resistance
Areas (Overlapping)
Z
Effective Resistance
Areas (No Overlap)
Reading Variation
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