Soil Resistivity Measurement Procedure (4-Point) - AEMC 4620 User Manual

5.5 Soil Resistivity Measurement Procedure
(4-Point)
Given a sizeable tract of land in which to determine the optimum soil resis-
tivity, some intuition is in order. Assuming that the objective is low resis-
tivity, preference should be given to an area containing moist loam as
opposed to a dry sandy area. Consideration must also be given to the
depth at which resistivity is required.
• Disconnect the shorting link from the X and Xv terminals.
• Arrange the electrodes in a straight line. Be sure that distances
between electrodes are identical.
Example: 10 ft between each electrode for auxiliary ground elec-
trodes that will be driven 10 ft deep (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.
• Press the "Test" button.
• Read the resistance level (R) indicated on the display.
• In the event of difficulties in performing measurements,
consult the previous instructions concerning ground resistance
measurements.
• Apply the following formula in order to determine resistivity ( ρ ):
ρ = 2π x R x A
A = distance between electrodes in cm
ρ = resistivity in Ωcm
R = ohms reading obtained on Model 4620/4630
Example 1: For measurement performed in soil with a high limestone content, the
reading is R = 225Ω, with A = 300cm (3m).
ρ = 2π x 225Ω x 300cm
ρ = 423,900Ωcm
34
Digital Ground Resistance Tester Model 4620 and 4630