AEMC 4500 - Page 36

34 Digital Ground Resistance Tester Model 4500
• DisconnecttheshortingstripfromtheXandXvterminals.
• Arrangetheelectrodesinastraightline.Besurethatdistances
between electrodes are identical: e.g. 3 meters between each
electrode(SeeFigure18).
• Thedistancebetweenpolesisproportionaltotheaveragedepth
of the soil sample you wish to make.
• Theelectrodesshouldbeplacedatadepthofapproximately6"
(0.15m),sothatthedepthisapproximately1/20thofthedistance
between electrodes.
• UseleadstoconnecttheX,Xv,Y,andZelectrodestotherespec-
tive terminals on the Digital Ground Resistance Tester.
• Itispreferabletoplacetheselectorinarangepositionwhich
variesinverselyinrelationtothedistanceidentiedas“A”;in
other words, the farther apart the four electrodes, the lower the
test current should be.
• Pressthe“TEST”button.
• Readtheresistancelevel(R)indicatedonthedisplay.
• Intheeventofdifcultiesinperformingmeasurements,consult
the previous instructions concerning ground resistance measure-
ments.
• Applythefollowingformulainordertodetermineresistivity(ρ):
ρ=2πx225Ωx3m
ρ=4350Ωm
Example: After inspection, the area to be investigated has been narrowed
downtoaplotofgroundapproximately75squarefeet(22.5m
2
).Assume
thatyouneedtodeterminetheresistivityatadepthof15ft.(450cm).The
distance “A” between the electrodes must then be equivalent to the depth
atwhichaverageresistivityistobedetermined(15ft,or450cm).Using
themoresimpliedWennerformula(ρ=2πAR),theelectrodedepthmust
thenbe1/20thoftheelectrodespacingor8-7/8"(22.5cm).
Lay out the electrodes in a grid pattern (Figure 20) and connect to the
Model 4500 as shown in Figure 19. Proceed as follows:
• RemovetheshortingstripbetweenXandXv
• Connectallfourauxiliaryrods